Chimeric galectin-3 and collagens: Biomarkers and potential therapeutic targets in fibroproliferative diseases

Fibrosis, stiffening and scarring of an organ/tissue due to genetic abnormalities, environmental factors, infection, and/or injury, is responsible for > 40% of all deaths in the industrialized world, and to date, there is no cure for it despite extensive research and numerous clinical trials. Several biomarkers have been identified, but no effective therapeutic targets are available. Human galectin-3 is a chimeric gene product formed by the fusion of the internal domain of the collagen alpha gene [N-terminal domain (ND)] at the 5'-end of galectin-1 [C-terminal domain (CRD)] that appeared during evolution together with vertebrates. Due to the overlapping structural similarities between collagen and galectin-3 and their shared susceptibility to cleavage by matrix metalloproteases to generate circulating collagen-like peptides, this review will discuss present knowledge on the role of collagen and galectin-3 as biomarkers of fibrosis. We will also highlight the need for transformative approaches targeting both the ND and CRD domains of galectin-3, since glycoconjugate binding by the CRD is triggered by ND-mediated oligomerization and the therapies targeted only at the CRD have so far achieved limited success.

MYH9 binds to dNTPs via deoxyribose moiety and plays an important role in DNA synthesis

The accepted notion of dNTP transport following cytoplasmic biosynthesis is ‘facilitated diffusion’; however, whether this alone is sufficient for moving dNTPs for DNA synthesis remains an open question. The data presented here show that the MYH9 gene encoded heavy chain of non-muscle myosin IIA binds dNTPs potentially serving as a ‘reservoir’. Pull-down assays showed that MYH9 present in the cytoplasmic, mitochondrial and nuclear compartments bind to DNA and this interaction is inhibited by dNTPs and 2-deoxyribose-5-phosphate (dRP) suggesting that MYH9-DNA binding is mediated via pentose sugar recognition. Direct dNTP-MYH9 binding was demonstrated by ELISA and a novel PCR-based method, which showed that all dNTPs bind to MYH9 with varying efficiencies. Cellular thermal shift assays showed that MYH9 thermal stability is enhanced by dNTPs. MYH9 siRNA transfection or treatment with myosin II selective inhibitors ML7 or blebbistatin decreased cell proliferation compared to controls. EdU labeling and cell cycle analysis by flow cytometry confirmed MYH9 siRNA and myosin II inhibitors decreased progression to S-phase with accumulation of cells in G0/G1 phase. Taken together, our data suggest a novel role for MYH9 in dNTP binding and DNA synthesis.

RAD6B Loss Disrupts Expression of Melanoma Phenotype in Part by Inhibiting WNT/β-Catenin Signaling

Canonical Wnt signaling is critical for melanocyte lineage commitment and melanoma development. RAD6B, a ubiquitin-conjugating enzyme critical for translesion DNA synthesis, potentiates β-catenin stability/activity by inducing proteasome-insensitive polyubiquitination. RAD6B expression is induced by β-catenin, triggering a positive feedback loop between the two proteins. RAD6B function in melanoma development/progression was investigated by targeting RAD6B using CrispR/Cas9 or an RAD6-selective small-molecule inhibitor #9 (SMI#9). SMI#9 treatment inhibited melanoma cell proliferation but not normal melanocytes. RAD6B knockout or inhibition in metastatic melanoma cells downregulated β-catenin, β-catenin-regulated microphthalmia-associated transcription factor (MITF), sex-determining region Y-box 10, vimentin proteins, and MITF-regulated melan A. RAD6B knockout or inhibition decreased migration/invasion, tumor growth, and lung metastasis. RNA-sequencing and stem cell pathway real-time RT-PCR analysis revealed profound reductions in WNT1 expressions in RAD6B knockout M14 cells compared with control. Expression levels of β-catenin-regulated genes VIM, MITF-M, melan A, and TYRP1 (a tyrosinase family member critical for melanin biosynthesis) were reduced in RAD6B knockout cells. Pathway analysis identified gene networks regulating stem cell pluripotency, Wnt signaling, melanocyte development, pigmentation signaling, and protein ubiquitination, besides DNA damage response signaling, as being impacted by RAD6B gene disruption. These data reveal an important and early role for RAD6B in melanoma development besides its bonafide translesion DNA synthesis function, and suggest that targeting RAD6B may provide a novel strategy to treat melanomas with dysregulated canonical Wnt signaling.

Natural agents inhibit colon cancer cell proliferation and alter microbial diversity in mice

The current study was undertaken to investigate the effect of differentially formulated polyphenolic compound Essential Turmeric Oil-Curcumin (ETO-Cur), and Tocotrienol-rich fraction (TRF) of vitamin E isomers on colorectal cancer (CRC) cells that produce aggressive tumors. Combinations of ETO-Cur and TRF were used to determine the combinatorial effects of ETO-Cur and TRF-mediated inhibition of growth of CRC cells in vitro and HCT-116 cells xenograft in SCID mice. 16S rRNA gene sequence profiling was performed to determine the outcome of gut microbial communities in mice feces between control and ETO-Cur-TRF groups. Bacterial identifications were validated by performing SYBR-based Real Time (RT) PCR. For metagenomics analysis to characterize the microbial communities, multiple software/tools were used, including Quantitative Insights into Microbial Ecology (QIIME) processing tool. We found ETO-Cur and TRF to synergize and that the combination of ETO-Cur-TRF significantly inhibited growth of HCT-116 xenografts in SCID mice. This was associated with a marked alteration in microbial communities and increased microbial OTU (operation taxonomic unit) number. The relative abundance of taxa was increased and the level of microbial diversity after 34 days of combinatorial treatment was found to be 44% higher over the control. Shifting of microbial family composition was observed in ETO-Cur-TRF treated mice as evidenced by marked reductions in Bacteroidaceae, Ruminococcaceae, Clostridiales, Firmicutes and Parabacteroids families, compared to controls. Interestingly, during the inhibition of tumor growth in ETO-Cur treated mice, probiotic Lactobacillaceae and Bifidobacteriaceae were increased by 20-fold and 6-fold, respectively. The relative abundance of anti-inflammatory Clostridium XIVa was also increased in ETO-Cur-TRF treated mice when compared with the control. Our data suggest that ETO-Cur-TRF show synergistic effects in inhibiting colorectal cancer cell proliferation in vitro and in mouse xenografts in vivo, and might induce changes in microbial diversity in mice.

Gercumin synergizes the action of 5-fluorouracil and oxaliplatin against chemoresistant human cancer colon cells

Advanced colon cancer is extremely difficult to cure, underscoring the need to develop novel therapeutic agents. Prenylated curcumins that are semisynthetic curcumin derivatives with significant anti-cancer potential have been studied herein to assess their therapeutic potential for colon cancer and tested to this aim in vitro for their growth inhibitory properties against 5-fluorouracil + oxaliplatin resistant human colon cancer CR-HT29 and HCT-116 cells. The resulting most active product, gercumin (mono-O-geranylcurcumin), has been further tested for its synergistic effects with FOLFOX (a combination of 5-fluorouracil and oxaliplatin) on the same cell lines. Activity of this combination on colonosphere formation was also investigated. Gercumin was able to suppress the growth of cancer cells with a potency similar to that of curcumin. A synergistic effect of this compound and FOLFOX was also observed. doses tested for synergy in the colonosphere assays did not show greater suppression of colonosphere formation than independent treatment with either reagent alone. Only one of the combinations was shown to be more effective at suppressing colonosphere formation [gercumin 5  μM + FOLFOX (2x)]. Thus, the growth inhibitory effects of curcumin against human cancer cells can be modulated and enhanced by the introduction of hydrophobic chains, normally found in several natural compounds, like the geranyl one. Such compounds are also able to synergize with known chemotherapeutics.

RAD6B is a major mediator of triple negative breast cancer cisplatin resistance: Regulation of translesion synthesis/Fanconi anemia crosstalk and BRCA1 independence

Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype with few therapy options besides chemotherapy. Although platinum-based drugs have shown initial activity in BRCA1-mutated TNBCs, chemoresistance remains a challenge. Here we show that RAD6B (UBE2B), a principal mediator of translesion synthesis (TLS), is overexpressed in BRCA1 wild-type and mutant TNBCs, and RAD6B overexpression correlates with poor survival. Pretreatment with a RAD6-selective inhibitor, SMI#9, enhanced cisplatin chemosensitivity of BRCA1 wild-type and mutant TNBCs. SMI#9 attenuated cisplatin-induced PCNA monoubiquitination (TLS marker), FANCD2 (Fanconi anemia (FA) activation marker), and TLS polymerase POL η. SMI#9-induced decreases in γH2AX levels were associated with concomitant inhibition of H2AX monoubiquitination, suggesting a key role for RAD6 in modulating cisplatin-induced γH2AX via H2AX monoubiquitination. Concordantly, SMI#9 inhibited γH2AX, POL η and FANCD2 foci formation. RAD51 foci formation was unaffected by SMI#9, however, its recruitment to double-strand breaks was inhibited. Using the DR-GFP-based assay, we showed that RAD6B silencing or SMI#9 treatment impairs homologous recombination (HR) in HR-proficient cells. DNA fiber assays confirmed that restart of cisplatin-stalled replicating forks is inhibited by SMI#9 in both BRCA1 wild-type and mutant TNBC cells. Consistent with the in vitro data, SMI#9 and cisplatin combination treatment inhibited BRCA1 wild-type and mutant TNBC growth as compared to controls. These RAD6B activities are unaffected by BRCA1 status of TNBCs suggesting that the RAD6B function in TLS/FA crosstalk could occur in HR-dependent and independent modes. Collectively, these data implicate RAD6 as an important therapeutic target for TNBCs irrespective of their BRCA1 status.

Galectin-3 and cancer stemness

Over the last few decades galectin-3, a carbohydrate binding protein, with affinity for N-acetyllactosamine residues, has been unique due to the regulatory roles it performs in processes associated with tumor progression and metastasis such as cell proliferation, homotypic/heterotypic aggregation, dynamic cellular transformation, migration and invasion, survival and apoptosis. Structure-function association of galectin-3 reveals that it consists of a short amino terminal motif, which regulates its nuclear-cytoplasmic shuttling; a collagen α-like domain, susceptible to cleavage by matrix metalloproteases and prostate specific antigen; accountable for its oligomerization and lattice formation, and a carbohydrate-recognition/binding domain containing the anti-death motif of the Bcl2 protein family. This structural complexity permits galectin-3 to associate with numerous molecules utilizing protein-protein and/or protein-carbohydrate interactions in the extra-cellular as well as intracellular milieu and regulate diverse signaling pathways, a number of which appear directed towards epithelial-mesenchymal transition and cancer stemness. Self-renewal, differentiation, long-term culturing and drug-resistance potential characterize cancer stem cells (CSCs), a small cell subpopulation within the tumor that is thought to be accountable for heterogeneity, recurrence and metastasis of tumors. Despite the fact that association of galectin-3 to the tumor stemness phenomenon is still in its infancy, there is sufficient direct evidence of its regulatory roles in CSC-associated phenotypes and signaling pathways. In this review, we have highlighted the available data on galectin-3 regulated functions pertinent to cancer stemness and explored the opportunities of its exploitation as a CSC marker and a therapeutic target.

Gut microbiome profiling and colorectal cancer in African Americans and Caucasian Americans

AIM

To determine whether and to what extent the gut microbiome is involved in regulating racial disparity in colorectal cancer (CRC).

METHODS

All patients were recruited and experiments were performed in accordance with the relevant guidelines and regulations by the Institutional Review Boards (IRB), committees of the John D. Dingell VAMC and Wayne State University guidelines. African American (AA) and Caucasian American (CA) patients were scheduled for an outpatient screening for colonoscopy, and no active malignancy volunteer patients were doubly consented, initially by the gastroenterologist and later by the study coordinator, for participation in the study. The gut microbial communities in colonic effluents from AAs and CAs were examined using 16sRNA profiling, and bacterial identifications were validated by performing SYBR-based Real Time PCR. For metagenomic analysis to characterize the microbial communities, multiple software/tools were used, including Metastats and R statistical software.

RESULTS

It is generally accepted that the incidence and mortality of CRC is higher in AAs than in CAs. However, the reason for this disparity is not well understood. We hypothesize that the gut microbiome plays a role in regulating this disparity. Indeed, we found significant differences in species richness and diversity between AAs and CAs. Bacteroidetes was more abundant in AAs than in CAs. In particular, the pro-inflammatory bacteria Fusobacterium nucleatum and Enterobacter species were significantly higher in AAs, whereas probiotic Akkermansia muciniphila and Bifidobacterium were higher in CAs. The polyphyletic Clostridia class showed a divergent pattern, with Clostridium XI elevated in AAs, and Clostridium IV, known for its beneficial function, higher in CAs. Lastly, the AA group had decreased microbial diversity overall in comparison to the CA group. In summary, there were significant differences in pro-inflammatory bacteria and microbial diversity between AA and CA, which may help explain the CRC disparity between groups.

CONCLUSION

Our current investigation, for the first time, demonstrates microbial dysbiosis between AAs and CAs, which could contribute to the racial disparity of CRC.

Nano-delivery of RAD6/Translesion Synthesis Inhibitor SMI#9 for Triple-negative Breast Cancer Therapy

The triple-negative breast cancer (TNBC) subtype, regardless of their BRCA1 status, has the poorest outcome compared with other breast cancer subtypes, and currently there are no approved targeted therapies for TNBC. We have previously demonstrated the importance of RAD6-mediated translesion synthesis pathway in TNBC development/progression and chemoresistance, and the potential therapeutic benefit of targeting RAD6 with a RAD6-selective small-molecule inhibitor, SMI#9. To overcome SMI#9 solubility limitations, we recently developed a gold nanoparticle (GNP)-based platform for conjugation and intracellular release of SMI#9, and demonstrated its in vitro cytotoxic activity toward TNBC cells. Here, we characterized the in vivo pharmacokinetic and therapeutic properties of PEGylated GNP-conjugated SMI#9 in BRCA1 wild-type and BRCA1-mutant TNBC xenograft models, and investigated the impact of RAD6 inhibition on TNBC metabolism by ¹H-NMR spectroscopy. GNP conjugation allowed the released SMI#9 to achieve higher systemic exposure and longer retention as compared with the unconjugated drug. Systemically administered SMI#9-GNP inhibited the TNBC growth as effectively as intratumorally injected unconjugated SMI#9. Inductively coupled mass spectrometry analysis showed highest GNP concentrations in tumors and liver of SMI#9-GNP and blank-GNP-treated mice; however, tumor growth inhibition occurred only in the SMI#9-GNP-treated group. SMI#9-GNP was tolerated without overt signs of toxicity. SMI#9-induced sensitization was associated with perturbation of a common set of glycolytic pathways in BRCA1 wild-type and BRCA1-mutant TNBC cells. These data reveal novel SMI#9 sensitive markers of metabolic vulnerability for TNBC management and suggest that nanotherapy-mediated RAD6 inhibition offers a promising strategy for TNBC treatment.

A novel mechanism of lncRNA and miRNA interaction: CCAT2 regulates miR-145 expression by suppressing its maturation process in colon cancer cells

Background

Although both long and micro RNAs are emerging as important functional components in colorectal cancer (CRC) progression and metastasis, the mechanism of their interaction remains poorly understood. CCAT2 (Colon cancer-associated transcript-2), a long noncoding RNA (lncRNA), has been reported to be over-expressed in CRC and is found to promote tumor growth. miRNAs, a class of naturally occurring short RNAs negatively control the expression of target genes by cleaving mRNA or through translation repression. Recently, we reported that miR-145 and miR-21 cooperate to regulate colon cancer stem cell (CSC) proliferation and differentiation. Considering that CCAT2 is mainly located in the nucleus and miRNA maturation process begins in the nucleus, we hypothesize that CCAT2 selectively blocks miR-145 maturation process, resulting in decreased mature miR-145 affecting colon CSC proliferation and differentiation.

Methods

The levels of CCAT2 were manipulated by transfection of CCAT2 expression plasmid or knockdown by siRNA or by CRISPR/Cas9. Quantitative RT-PCR was performed to examine the expression of CCAT2 and pri-, pre- and mature miR-145/21. Fluorescence in situ hybridization (FISH) was used to visualize CCAT2 in the cells. In vitro processing of pri-miRNA-145 was performed using T7 RNA polymerase and recombinant human Dicer.

Results

We have observed that modulated expression of CCAT2 regulates the expression of miR-145 in colon cancer HCT-116 and HT-29 cells. Knockout of CCAT2 increases miR-145 and negatively regulates miR-21 in HCT-116 cells, impairs proliferation and differentiation. In contrast, stable up-regulation of CCAT2 decreases mature miR-145 and increases the expression of several CSC markers in colon cancer cells. We have also observed that CCAT2 is enriched in the nucleus and correlates with the expression of pre-miR-145 but not pre-miR-21 in HCT-116 cells. These results indicate CCAT2 selectively blocks miR-145 maturation by inhibiting pre-miR-145 export to cytoplasm. Further, we revealed that CCAT2 blocks cleavage of pre-miR-145 by Dicer in vitro.

Conclusions

Our results identify CCAT2 as a negative regulator of miRNA-145 biogenesis, and expose a novel mechanism of lncRNA-miRNA crosstalk.

Electronic supplementary material

The online version of this article (10.1186/s12943-017-0725-5) contains supplementary material, which is available to authorized users.

Cancer Self-Defense: An Immune Stealth

The hurdles in realizing successful cancer immunotherapy stem from the fact that cancer patients are either refractory to immune response and/or develop resistance. Here, we propose that these phenomena are due, in part, to the deployment/secretion of a "decoy flare," for example, anomalous cancer-associated antigens by the tumor cells. The cancer secretome, which resembles the parent cell make-up, is composed of soluble macromolecules (proteins, glycans, lipids, DNAs, RNAs, etc.) and insoluble vesicles (exosomes), thus hindering cancer detection/recognition by immunotherapeutic agents, resulting in a "cancer-stealth" effect. Immunotherapy, or any treatment that relies on antigens' expression/function, could be improved by the understanding of the properties of the cancer secretome, as its clinical evaluation may change the therapeutic landscape. Cancer Res; 77(20); 5441-4. ©2017 AACR.

Abstract 1149: Targeting Rad6B suppresses melanomagenesis

Active β-catenin signaling in melanoma is associated with aggressive disease. We have previously shown that Rad6B, an ubiquitin conjugating enzyme, is a positive regulator of β-catenin stability and transcriptional activity, and is itself a transcriptional target of β-catenin. This stabilization is mediated by Rad6B-induced K63-linked polyubiquitination of β-catenin that renders it insensitive to 26S proteasomal degradation. Immunohistochemical analysis of human cutaneous melanoma samples showed the first detectable expression of Rad6B in melanocyte hyperplasia and continued Rad6B and β-catenin overexpression in primary and metastatic melanomas. These data implicate a critical role for Rad6B in melanocyte transformation and a continuing role in melanoma progression. To analyze the role of Rad6B in melanomagenesis, we targeted Rad6B expression/activity in human M14 metastatic melanoma cells by using a Rad6-selective small molecule inhibitor SMI#9 and the CrispR/Cas9 gene editing system. Immunoblot analysis showed that compared to controls, M14 cells treated with SMI#9 showed decreased levels of β-catenin, and β-catenin driven transcriptional targets Rad6, vimentin, Mitf-M, and Melan A. Although Snail levels were not altered, SMI#9 treated cells showed increase in phosphorylated Snail. Immunocytochemical staining verified the western blot data and showed cytoplasmic relocalization of PCNA and Snail in SMI#9 treated cells which is consistent with increase in phosphorylated Snail. Concordant with the decrease in vimentin and unphosphorylated Snail levels, Rad6B-inhibited cells display poor capacity to migrate as compared to controls. Whereas Rad6B knockout cells were severely growth impaired, Rad6B edited clones showing partial expression (potentially from only one allele) similarly showed decreased levels of β-catenin, vimentin, and Mitf-M. Similar to Rad6B-inhibited cells, Rad6B edited cells were migration- and invasion-impaired. Whereas control cells produced robust tumors and overt lung metastases, the Rad6B gene edited cells were poorly tumorigenic. Rad6B gene edited clones showed complete loss of Melan A. Since Mitf-M is a transcriptional regulator of Melan A and a key player in melanocyte lineage specification, our data suggest that targeting Rad6B could potentially inhibit melanomagenesis by reprogramming melanoma cells. Supported by NIH CA178117 and 3Balls Racing.

Citation Format: Ashapurna Sarma, Sarah Petit, Fangchao Liu, Pratima Nangia-Makker, Guangzhao Mao, Malathy Shekhar. Targeting Rad6B suppresses melanomagenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1149. doi:10.1158/1538-7445.AM2017-1149

Pharmacological targeting of RAD6 enzyme-mediated translesion synthesis overcomes resistance to platinum-based drugs

Platinum drug-induced cross-link repair requires the concerted activities of translesion synthesis (TLS), Fanconi anemia (FA), and homologous recombination repair pathways. The E2 ubiquitin-conjugating enzyme RAD6 is essential for TLS. Here, we show that RAD6 plays a universal role in platinum-based drug tolerance. Using a novel RAD6-selective small-molecule inhibitor (SMI#9) targeting the RAD6 catalytic site, we demonstrate that SMI#9 potentiates the sensitivities of cancer cells with innate or acquired cisplatin or oxaliplatin resistance. 5-Iododeoxyuridine/5-chlorodeoxyuridine pulse-labeling experiments showed that RAD6 is necessary for overcoming cisplatin-induced replication fork stalling, as replication-restart was impaired in both SMI#9-pretreated and RAD6B-silenced cells. Consistent with the role of RAD6/TLS in late-S phase, SMI#9-induced DNA replication inhibition occurred preferentially in mid/late-S phase. The compromised DNA repair and chemosensitization induced by SMI#9 or RAD6B depletion were associated with decreased platinum drug-induced proliferating cell nuclear antigen (PCNA) and FANCD2 monoubiquitinations (surrogate markers of TLS and FA pathway activation, respectively) and with attenuated FANCD2, RAD6, γH2AX, and POL η foci formation and cisplatin-adduct removal. SMI#9 pretreatment synergistically increased cisplatin inhibition of MDA-MB-231 triple-negative breast cancer cell proliferation and tumor growth. Using an isogenic HCT116 colon cancer model of oxaliplatin resistance, we further show that γH2AX and monoubiquitinated PCNA and FANCD2 are constitutively up-regulated in oxaliplatin-resistant HCT116 (HCT116-OxR) cells and that γH2AX, PCNA, and FANCD2 monoubiquitinations are induced by oxaliplatin in parental HCT116 cells. SMI#9 pretreatment sensitized HCT116-OxR cells to oxaliplatin. These data deepen insights into the vital role of RAD6/TLS in platinum drug tolerance and reveal clinical benefits of targeting RAD6 with SMI#9 for managing chemoresistant cancers.

Bile acid: a potential inducer of colon cancer stem cells

Background

Although the unconjugated secondary bile acids, specifically deoxycholic acid (DCA) and lithocholic acid (LCA), are considered to be risk factors for colorectal cancer, the precise mechanism(s) by which they regulate carcinogenesis is poorly understood. We hypothesize that the cytotoxic bile acids may promote stemness in colonic epithelial cells leading to generation of cancer stem cells (CSCs) that play a role in the development and progression of colon cancer.

Methods

Normal human colonic epithelial cells (HCoEpiC) were used to study bile acid DCA/LCA-mediated induction of CSCs. The expression of CSC markers was measured by real-time qPCR. Flow cytometry was used to isolate CSCs. T-cell factor/lymphoid-enhancing factor (TCF/LEF) luciferase assay was employed to examine the transcriptional activity of β-catenin. Downregulation of muscarinic 3 receptor (M3R) was achieved through transfection of corresponding siRNA.

Results

We found DCA/LCA to induce CSCs in normal human colonic epithelial cells, as evidenced by the increased proportion of CSCs, elevated levels of several CSC markers, as well as a number of epithelial–mesenchymal transition markers together with increased colonosphere formation, drug exclusion, ABCB1 and ABCG2 expression, and induction of M3R, p-EGFR, matrix metallopeptidases, and c-Myc. Inhibition of M3R signaling greatly suppressed DCA/LCA induction of the CSC marker ALDHA1 and also c-Myc mRNA expression as well as transcriptional activation of TCF/LEF.

Conclusions

Our results suggest that bile acids, specifically DCA and LCA, induce cancer stemness in colonic epithelial cells by modulating M3R and Wnt/β-catenin signaling and thus could be considered promoters of colon cancer.

Racial disparity in colorectal cancer: Gut microbiome and cancer stem cells

Over the past two decades there has been remarkable progress in cancer diagnosis, treatment and screening. The basic mechanisms leading to pathogenesis of various types of cancers are also understood better and some patients, if diagnosed at a particular stage go on to lead a normal pre-diagnosis life. Despite these achievements, racial disparity in some cancers remains a mystery. The higher incidence, aggressiveness and mortality of breast, prostate and colorectal cancers (CRCs) in African-Americans as compared to Caucasian-Americans are now well documented. The polyp-carcinoma sequence in CRC and easy access to colonic epithelia or colonic epithelial cells through colonoscopy/colonic effluent provides the opportunity to study colonic stem cells early in course of natural history of the disease. With the advent of metagenomic sequencing, uncultivable organisms can now be identified in stool and their numbers correlated with the effects on colonic epithelia. It would be expected that these techniques would revolutionize our understanding of the racial disparity in CRC and pave a way for the same in other cancers as well. Unfortunately, this has not happened. Our understanding of the underlying factors responsible in African-Americans for higher incidence and mortality from colorectal carcinoma remains minimal. In this review, we aim to summarize the available data on role of microbiome and cancer stem cells in racial disparity in CRC. This will provide a platform for further research on this topic.

Abstract 986: Long noncoding RNA CCAT2 cooperates with miR-145 and miR-21 to regulate colon cancer stem cells

Colon cancer-associated transcript-2 (CCAT2), a long noncoding RNA (lncRNA), has been reported to be over-expressed in colorectal cancer to promote tumor growth and metastasis and also reduces sensitivity to chemotherapy, a property related to cancer stem cells (CSCs). MicroRNAs, small endogenous noncoding RNAs, negatively control the expression of target genes by cleaving mRNA or through translation repression. We have recently reported cooperation of miR-21 and miR-145 to regulate colon CSCs proliferation and differentiation. Down-regulation of miR-21 enhances CSC enriched chemo-resistant colon cancer cells’ susceptibility to chemo- therapeutic regimens. Although both CCAT2 and miR-21 increase WNT signaling activity and reduce chemosensitivity to 5-FU, a critical evidence on how CCAT2 regulates stemness leading to chemo-resistance is lacking. The primary goal of this investigation was to examine whether CCAT2 associates with miR-145 and miR-21 and whether this association plays a role in regulating stemness of colon cancer cells. We have observed that CCAT2 transcript level is dependent on p53 expression and activity, as evidenced by a marked increase in CCAT2 expression in p53 wild type harboring HCT-116 colon cancer cells compared with p53 null HCT-116 and p53 mutant HT-29 cells. We further revealed that knockdown of CCAT2 increased the expression of miR-145 and negatively regulates miR-21 in HCT-116 cells and impairs proliferation and differentiation of these cells. On the other hand, upregulation of CCAT2 induces proliferation of HCT-116 cells and also increases the expression of CSC markers CD44 and CD166. We have also observed that miR-145 and miR-21 cooperation plays a role in regulating colon cancer stem cells by down-regulating Sox2 and increased activity of Wnt/β-catenin pathway. Our current results suggest that lncRNA CCAT2 cooperates with miR-145 and miR-21 to regulate colon cancer stem cells, which provides a potential therapeutic target for chemoresistance in colorectal cancer.

Citation Format: Yingjie Yu, Pratima Nangia-Makker, Lulu Farhana, Adhip P. N. Majumdar. Long noncoding RNA CCAT2 cooperates with miR-145 and miR-21 to regulate colon cancer stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 986.

Role of cancer stem cells in racial disparity in colorectal cancer

Although African‐Americans (AAs) have a higher incidence of colorectal cancer (CRC) than White people, the underlying biochemical mechanisms for this increase are poorly understood. The current investigation was undertaken to examine whether differences in self‐renewing cancer stem/stem‐like cells (CSCs) in the colonic mucosa, whose stemness is regulated by certain microRNAs (miRs), could partly be responsible for the racial disparity in CRC. The study contains 53 AAs and 47 White people. We found the number of adenomas and the proportion of CD44⁺CD166⁻  CSC phenotype in the colon to be significantly higher in AAs than White people. MicroRNAs profile in CSC‐enriched colonic mucosal cells, expressed as ratio of high‐risk (≥3 adenomas) to low‐risk (no adenoma) CRC patients revealed an 8‐fold increase in miR‐1207‐5p in AAs, compared to a 1.2‐fold increase of the same in White people. This increase in AA was associated with a marked rise in lncRNA PVT1 (plasmacytoma variant translocation 1), a host gene of miR‐1207‐5p. Forced expression of miR‐1207‐5p in normal human colonic epithelial cells HCoEpiC and CCD841 produced an increase in stemness, as evidenced by morphologically elongated epithelial mesenchymal transition( EMT) phenotype and significant increases in CSC markers (CD44, CD166, and CD133) as well as TGF‐β, CTNNB1, MMP2, Slug, Snail, and Vimentin, and reduction in Twist and N‐Cadherin. Our findings suggest that an increase in CSCs, specifically the CD44⁺CD166⁻ phenotype in the colon could be a predisposing factor for the increased incidence of CRC among AAs. MicroRNA 1207‐5p appears to play a crucial role in regulating stemness in colonic epithelial cells in AAs.

Role of cancer stem cells in age-related rise in colorectal cancer

Colorectal cancer (CRC) that comprises about 50% of estimated gastrointestinal cancers remains a high mortality malignancy. It is estimated that CRC will result in 9% of all cancer related deaths. CRC is the third leading malignancy affecting both males and females equally; with 9% of the estimated new cancer cases and 9% cancer related deaths. Sporadic CRC, whose incidence increases markedly with advancing age, occurs in 80%-85% patients diagnosed with CRC. Little is known about the precise biochemical mechanisms responsible for the rise in CRC with aging. However, many probable reasons for this increase have been suggested; among others they include altered carcinogen metabolism and the cumulative effects of long-term exposure to cancer-causing agents. Herein, we propose a role for self-renewing, cancer stem cells (CSCs) in regulating these cellular events. In this editorial, we have briefly described the recent work on the evolution of CSCs in gastro-intestinal track especially in the colon, and how they are involved in the age-related rise in CRC. Focus of this editorial is to provide a description of (1) CSC; (2) epigenetic and genetic mechanisms giving rise to CSCs; (3) markers of CSC; (4) characteristics; and (5) age-related increase in CSC in the colonic crypt.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead

Low-dose exposures to common environmental chemicals that are deemed safe individually may be combining to instigate carcinogenesis, thereby contributing to the incidence of cancer. This risk may be overlooked by current regulatory practices and needs to be vigorously investigated.

Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals. In total, 85 examples of chemicals were reviewed for actions on key pathways/mechanisms related to carcinogenesis. Only 15% (13/85) were found to have evidence of a dose-response threshold, whereas 59% (50/85) exerted low-dose effects. No dose-response information was found for the remaining 26% (22/85). Our analysis suggests that the cumulative effects of individual (non-carcinogenic) chemicals acting on different pathways, and a variety of related systems, organs, tissues and cells could plausibly conspire to produce carcinogenic synergies. Additional basic research on carcinogenesis and research focused on low-dose effects of chemical mixtures needs to be rigorously pursued before the merits of this hypothesis can be further advanced. However, the structure of the World Health Organization International Programme on Chemical Safety ‘Mode of Action’ framework should be revisited as it has inherent weaknesses that are not fully aligned with our current understanding of cancer biology.

The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis

The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.

miR-21 and miR-145 cooperation in regulation of colon cancer stem cells

Background

Acquired drug resistance is one of the major reasons for failing cancer therapies. Although the reasons are not fully understood, they may be related to the presence of cancer stem cells (CSCs). We have reported that chemo-resistant (CR) colon cancer cells, highly enriched in CSCs, exhibit a marked up-regulation of miR-21 and that down-regulation of this miR renders the CR cells more susceptible to therapeutic regimens. However, the underlying molecular mechanism is poorly understood. The aim of this investigation is to unravel this mechanism.

Methods

The levels of miR-145 and miR-21 were manipulated by transfection of mature, antago-miRs or pCMV/miR-145 expression plasmid. Quantitative RT-PCR or/and Western blots were performed to examine the expression of CD44, β-catenin, Sox-2, PDCD4, CK-20 and k-Ras. Colonosphere formation and SCID mice xenograft studies were performed to evaluate the tumorigenic properties of CSC-enriched colon CR cells.

Results

We investigated the role that microRNAs (miRs), specifically miR-21 and miR-145 play in regulating colon CSCs. We found the expression of miR-21 to be greatly increased and miR-145 decreased in CR colon cancer cells that are highly enriched in CSC, indicating a role for these miRNAs in regulating CSCs. In support of this, we found that whereas forced expression of miR-145 in colon cancer cells greatly inhibits CSCs and tumor growth, up-regulation of miR-21 causes an opposite phenomenon. In addition, administration of mature miR-145 or antagomir-21 (anti-sense miR-21) greatly suppresses the growth of colon cancer cell xenografts in SCID mice. This was associated with decreased expression of CD44, β-catenin, Sox-2 and induction of CK-20 indicating that administration of miR-145 or antagomir-21 decreases CSC proliferation and induces differentiation. In vitro studies further demonstrate that miR-21 negatively regulates miR-145 and vice versa. k-Ras appears to play critical role in regulation of this process, as evidenced by the fact that the absence of k-Ras in CR colon cancer cells increases miR-145 expression, suppresses miR-21, and interrupts the negative cooperation between miR-21 and miR-145.

Conclusions

Our current observations suggest that miR-21, miR-145, and their networks play critical roles in regulating CSCs growth and/or differentiation in the colon cancer and progression of chemo-resistance.

Omega-3 fatty acid is a potential preventive agent for recurrent colon cancer

Increasing evidence supports the contention that many malignancies, including sporadic colorectal cancer, are driven by the self-renewing, chemotherapy-resistant cancer stem/stem-like cells (CSC/CSLC), underscoring the need for improved preventive and therapeutic strategies targeting CSCs/CSLCs. Omega-3 polyunsaturated fatty acids (ω-3 PUFA), have been reported to inhibit the growth of primary tumors, but their potential as a preventive agent for recurring cancers is unexplored. The primary objectives of this investigation are (i) to examine whether eicosapentaenoic acid (EPA; one of the ω-3 PUFA) synergizes with FuOx (5-FU+Oxaliplatin), the backbone of colon cancer chemotherapy, and (ii) whether EPA by itself or in combination with conventional chemotherapy prevents the recurrence of colon cancer via eliminating/suppressing CSCs/CSLCs. FuOx-resistant (chemoresistant; CR) colon cancer cells, highly enriched in CSCs, were used for this study. Although EPA alone was effective, combination of EPA and FuOx was more potent in (i) inhibiting cell growth, colonosphere formation, and sphere-forming frequency, (ii) increasing sphere disintegration, (iii) suppressing the growth of SCID mice xenografts of CR colon cancer cells, and (iv) decreasing proinflammatory metabolites in mice. In addition, EPA + FuOx caused a reduction in CSC/CSLC population. The growth reduction by this regimen is the result of increased apoptosis as evidenced by PARP cleavage. Furthermore, increased pPTEN, decreased pAkt, normalization of β-catenin expression, localization, and transcriptional activity by EPA suggests a role for the PTEN-Akt axis and Wnt signaling in regulating this process. Our data suggest that EPA by itself or in combination with FuOx could be an effective preventive strategy for recurring colorectal cancer.

Lactose-functionalized dendrimers arbitrate the interaction of galectin-3/MUC1 mediated cancer cellular aggregation

By using lactose-functionalized poly(amidoamine) dendrimers as a tunable multivalent platform, we studied cancer cell aggregation in three different cell lines (A549, DU-145, and HT-1080) with galectin-3. We found that small lactose-functionalized G(2)-dendrimer 1 inhibited galectin-3-induced aggregation of the cancer cells. In contrast, dendrimer 4 (a larger, generation 6 dendrimer with 100 carbohydrate end groups) caused cancer cells to aggregate through a galectin-3 pathway. This study indicates that inhibition of cellular aggregation occurred because 1 provided competitive binding sites for galectin-3 (compared to its putative cancer cell ligand, TF-antigen on MUC1). Dendrimer 4, in contrast, provided an excess of ligands for galectin-3 binding; this caused crosslinking and aggregation of cells to be increased.

Galectin-3 in angiogenesis and metastasis

Galectin-3 is a member of the family of β-galactoside-binding lectins characterized by evolutionarily conserved sequences defined by structural similarities in their carbohydrate-recognition domains. Galectin-3 is a unique, chimeric protein consisting of three distinct structural motifs: (i) a short NH2 terminal domain containing a serine phosphorylation site; (ii) a repetitive proline-rich collagen-α-like sequence cleavable by matrix metalloproteases; and (iii) a globular COOH-terminal domain containing a carbohydrate-binding motif and an NWGR anti-death motif. It is ubiquitously expressed and has diverse biological functions depending on its subcellular localization. Galectin-3 is mainly found in the cytoplasm, also seen in the nucleus and can be secreted by non-classical, secretory pathways. In general, secreted galectin-3 mediates cell migration, cell adhesion and cell-cell interactions through the binding with high affinity to galactose-containing glycoproteins on the cell surface. Cytoplasmic galectin-3 exhibits anti-apoptotic activity and regulates several signal transduction pathways, whereas nuclear galectin-3 has been associated with pre-mRNA splicing and gene expression. Its unique chimeric structure enables it to interact with a plethora of ligands and modulate diverse functions such as cell growth, adhesion, migration, invasion, angiogenesis, immune function, apoptosis and endocytosis emphasizing its significance in the process of tumor progression. In this review, we have focused on the role of galectin-3 in tumor metastasis with special emphasis on angiogenesis.

Multivalent scaffolds induce galectin-3 aggregation into nanoparticles

Galectin-3 meditates cell surface glycoprotein clustering, cross linking, and lattice formation. In cancer biology, galectin-3 has been reported to play a role in aggregation processes that lead to tumor embolization and survival. Here, we show that lactose-functionalized dendrimers interact with galectin-3 in a multivalent fashion to form aggregates. The glycodendrimer–galectin aggregates were characterized by dynamic light scattering and fluorescence microscopy methodologies and were found to be discrete particles that increased in size as the dendrimer generation was increased. These results show that nucleated aggregation of galectin-3 can be regulated by the nucleating polymer and provide insights that improve the general understanding of the binding and function of sugar-binding proteins.

Nuclear transport of galectin-3 and its therapeutic implications

Galectin-3, a member of β-galactoside-binding gene family is a multi-functional protein, which regulates pleiotropic biological functions such as cell growth, cell adhesion, cell-cell interactions, apoptosis, angiogenesis and mRNA processing. Its unique structure enables it to interact with a plethora of ligands in a carbohydrate dependent or independent manner. Galectin-3 is mainly a cytosolic protein, but can easily traverse the intracellular and plasma membranes to translocate into the nucleus, mitochondria or get externalized. Depending on the cell type, specific experimental conditions in vitro, cancer type and stage, galectin-3 has been reported to be exclusively cytoplasmic, predominantly nuclear or distributed between the two compartments. In this review we have summarized the dynamics of galectin-3 shuttling between the nucleus and the cytoplasm, the nuclear transport mechanisms of galectin-3, how its specific interactions with the members of β-catenin signaling pathways affect tumor progression, and its implications as a therapeutic target.

Comedo-DCIS is a precursor lesion for basal-like breast carcinoma: identification of a novel p63/Her2/neu expressing subgroup

Basal breast cancer comprises ~15% of invasive ductal breast cancers, and presents as high-grade lesions with aggressive clinical behavior. Basal breast carcinomas express p63 and cytokeratin 5 (CK5) antigens characteristic of the myoepithelial lineage, and typically lack Her2/neu and hormone receptor expression. However, there is limited data about the precursor lesions from which they emerge. Here we wished to determine whether comedo-ductal carcinoma in situ (comedo- DCIS), a high-risk in situ breast lesion, serve as precursors for basal-like breast cancer. To determine this link, p63, CK5, Her2/neu, epidermal growth factor receptor (EGFR), estrogen receptor (ER) and progesterone receptor (PgR) expression were analyzed by immunohistochemistry in 17 clinical comedo- and 12 noncomedo-DCIS cases, and in tumors derived from unfractionated and CK5-overexpressing subpopulation (MCF10DCIS.com-CK5(high)) of MCF10DCIS.com cells, a model representative of clinical comedo-DCIS. p63 and Her2/neu coexpression was analyzed by immunofluorescence double labeling. A novel p63/CK5/Her2/neu expressing subpopulation of cells that are ER-/PgR-/EGFR- were identified in the myoepithelial and luminal areas of clinical comedo-DCIS and tumors derived from unfractionated MCF10DCIS.com and MCF10DCIS.com-CK5(high) cells. These data suggest that p63 and Her2/neu expressors may share a common precursor intermediate. P63, but not Her2/neu, expression was significantly associated (P = 0.038) with microinvasion/recurrence of clinical comedo-DCIS, and simultaneous expression of p63 and Her2/neu was marginally associated (P = 0.067) with comedo-DCIS. These data suggest that p63/Her2/neu expressing precursor intermediate in comedo-DCIS may provide a cellular basis for emergence of p63+/Her2/neu- or p63+/Her2/neu+ basal-like breast cancer, and that p63/Her2/neu coexpression may serve as biomarkers for identification of this subgroup of basal-like breast cancers.

Galectin-3: A possible complementary marker to the PSA blood test

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Background: The prostate-specific antigen (PSA) is a test widely used to detect, monitor, and predict the biology of prostate cancer (PCa). Galectin-3 (Gal-3) is a carbohydrate-binding protein and is present in the seminal fluid. It is a tumor-associated protein, which plays a role in metastasis, apoptosis, and tumor growth. We recently reported that PSA cleaves Gal-3. Cleavage status of Gal-3 in the prostate tissue might be associated with the tumor formation and progression of PCa. Therefore, we compared Gal-3 levels in the blood of non-cancer urology patients and metastatic PCa patients. Methods: Non-cancer and metastatic PCa patients were recruited from the genitourinary oncology clinics. Sixteen men (8 PCa patients and 8 controls) were recruited during their clinic visit from May to August 2012. The metastatic PCa patients could be either castrate-sensitive or castrate-resistant. The control patients could not have any history of invasive cancer. A blood sample was collected from each study patient. Levels of Gal-3 were analyzed by Western blot and ELISA. The study design was a small, prospective, single institution pre-pilot study. The primary statistical endpoint was the mean level of serum galectin-3. Within each of the two groups of patients, it was desired to estimate the mean Gal-3 level to within 0.50 standard deviations (SD’s) of the true mean, with 80% confidence. This study design required N=8 men per group. Results: The cancer-free control patients had lower levels of serum Gal-3 than did any of the 8 PCa patients (see Table). These results suggest that serum Gal-3 levels in metastatic PCa patients and cancer-free controls are quite different. The serum PSA distributions of these 2 patient groups overlap slightly, hence PSA did not distinguish them quite as well as did Gal-3. Conclusions: This is the first report to show serum Gal-3concentrations were uniformly higher in patients with metastatic PCa as compared to non-cancer control patients. [Table: see text]

Galectin-3: a possible complementary marker to the PSA blood test

The prostate-specific antigen (PSA) test has served as a blood marker of prostate cancer (PCa), and for monitoring recurrence/metastasis in patients after therapeutic intervention. However, the applicability/reliability of the PSA test was recently questioned as it is not without challenges, in particular in men who have PCa without an elevated PSA (false negative), or in men who are disease-free with elevated levels of PSA (false positive). Galectin-3 is a tumor-associated protein; present in the seminal fluid and is a substrate for the PSA enzyme e.g., a chymotrypsin-like serine protease. We hypothesized that the cleavage status and level of galectin-3 in the prostate tissue and sera are associated with PCa. Thus, we compared galectin-3 levels obtained from sera of non-cancer urology patients to those of metastatic PCa patients. The data were confirmed by analyzing PCa tissue arrays. Here, we report that galectin-3 levels in the sera of patients with metastatic PCa were uniformly higher as compared to the non-cancer patient controls. The data suggest that galectin-3 serum level may be a useful serum complementary marker to the PSA blood test to be used for initial and follow-up PSA complimentary diagnostic/prognostic tool for recurrence in PCa patients.

Ocimum gratissimum retards breast cancer growth and progression and is a natural inhibitor of matrix metalloproteases

Ocimum genus (a.k.a holy basil or tulsi) is a dietary herb used for its multiple beneficial pharmacologic properties including anti-cancer activity. Here we show that crude extract of Ocimum gratissimum (OG) and its hydrophobic and hydrophilic fractions (HB and HL) differentially inhibit breast cancer cell chemotaxis and chemoinvasion in vitro and retard tumor growth and temporal progression of MCF10ADCIS.com xenografts, a model of human breast comedo-ductal carcinoma in situ (comedo-DCIS). OG-induced inhibition of tumor growth was associated with decreases in basement membrane disintegration, angiogenesis and MMP-2 and MMP-9 activities as confirmed by in situ gelatin zymography and cleavage of galectin-3. There was also decrease in MMP-2 and MMP-9 activities in the conditioned media of OG-treated MCF10AT1 and MCF10AT1-EIII8 premalignant human breast cancer cells as compared with control. The MMP-2 and MMP-9 inhibitory activities of OG were verified in vitro using gelatin, a synthetic fluorogenic peptide and recombinant galectin-3 as MMP substrates. Mice fed on OG-supplemented drinking water showed no adverse effects compared with control. These data suggest that OG is non-toxic and that the anti-cancer therapeutic activity of OG may in part be contributed by its MMP inhibitory activity.

Novel inhibitors of Rad6 ubiquitin conjugating enzyme: design, synthesis, identification, and functional characterization

Protein ubiquitination is important for cell signaling, DNA repair, and proteasomal degradation, and it is not surprising that alterations in ubiquitination occur frequently in cancer. Ubiquitin-conjugating enzymes (E2) mediate ubiquitination by selective interactions with ubiquitin-activating (E1) and ubiquitin ligase (E3) enzymes, and thus selective E2 small molecule inhibitor (SMI) will provide specificity unattainable with proteasome inhibitors. Here we describe synthesis and functional characterization of the first SMIs of human E2 Rad6B, a fundamental component of translesion synthesis DNA repair. A pharmacophore model for consensus E2 ubiquitin-binding sites was generated for virtual screening to identify E2 inhibitor candidates. Twelve triazine (TZ) analogs screened in silico by molecular docking to the Rad6B X-ray structure were verified by their effect on Rad6B ubiquitination of histone H2A. TZs #8 and 9 docked to the Rad6B catalytic site with highest complementarity. TZs #1, 2, 8, and 9 inhibited Rad6B-ubiquitin thioester formation and subsequent ubiquitin transfer to histone H2A. SMI #9 inhibition of Rad6 was selective as BCA2 ubiquitination by E2 UbcH5 was unaffected by SMI #9. SMI #9 more potently inhibited proliferation, colony formation, and migration than SMI #8, and induced MDA-MB-231 breast cancer cell G2-M arrest and apoptosis. Ubiquitination assays using Rad6 immunoprecipitated from SMI #8- or 9-treated cells confirmed inhibition of endogenous Rad6 activity. Consistent with our previous data showing Rad6B-mediated polyubiquitination stabilizes β-catenin, MDA-MB-231 treatment with SMIs #8 or 9 decreased β-catenin protein levels. Together these results describe identification of the first Rad6 SMIs.

Autocrine motility factor promotes HER2 cleavage and signaling in breast cancer cells

Trastuzumab (Herceptin) is an effective targeted therapy in HER2-overexpressing human breast carcinoma. However, many HER2-positive patients initially or eventually become resistant to this treatment, so elucidating mechanisms of trastuzumab resistance that emerge in breast carcinoma cells is clinically important. Here, we show that autocrine motility factor (AMF) binds to HER2 and induces cleavage to the ectodomain-deleted and constitutively active form p95HER2. Mechanistic investigations indicated that interaction of AMF with HER2 triggers HER2 phosphorylation and metalloprotease-mediated ectodomain shedding, activating phosphoinositide-3-kinase (PI3K) and mitogen-activated protein kinase signaling and ablating the ability of trastuzumab to inhibit breast carcinoma cell growth. Furthermore, we found that HER2 expression and AMF secretion were inversely related in breast carcinoma cells. On the basis of this evidence that AMF may contribute to HER2-mediated breast cancer progression, our findings suggest that AMF-HER2 interaction might be a novel target for therapeutic management of patients with breast cancer, whose disease is resistant to trastuzumab.

Abstract 2017: Galectin-3 SNP rs10148371 in the anti-death motif NWGR is related to the colon cancer incidence in African Americans

Survival after cancer diagnosis is poorer for African Americans than for Caucasians. While some of this survival difference is driven by differences in the stage at diagnosis, even within the stage this trend is evident. For example, 5-year relative survival for colorectal cancer diagnosed as regional stage is 68.5% for Caucasians and only 60.6% for African Americans. Little is known about racial differences in response to chemotherapy and the subsequent impact on survival. A number of recent reports have focused on single nucleotide polymorphisms (SNPs) with the notion that such genetic event(s) can/may contribute to cancer development or progression. We have identified a SNP, rs10148371, which results in the substitution of R183K in the NWGR anti-death motif of the galectin-3 gene. Galectin-3, belonging to the family of carbohydrate-binding galectins is a multi-function tumor associated protein, which regulates cell growth, cell proliferation, cell adhesion, angiogenesis and apoptosis. It contains the NWGR motif characteristic of BH1 domain of Bcl-2 family responsible for protecting cells from apoptosis. To understand the significance of this SNP, we generated point mutation G548 to A in galectin-3 cDNA leading to R183K substitution. The resulting cDNA was stably transfected into low galectin-3 expressing colon carcinoma cells SW480 and RKO. Selected clones were analyzed for cell survival and apoptotic potential against cisplatin, 5 fluoro-uracil and oxaliplatin. The clones containing mutated galectin-3 showed a higher susceptibility to apoptosis compared to the wild type galectin-3. The WT clones showed an up-regulation of β-catenin and its downstream target proteins, which was not seen in the mutant clones. Ability/inability of mutated galectin-3 in the nuclear translocation of β-catenin is being studied. The racial distribution of the SNP rs10148371 in the normal population of the African Americans is 22%, while in Caucasians and Asians disease free population it can be found in less than 1%. To analyze the significance of this SNP in relation to breast and colorectal cancer, we performed genotype analysis with breast cancer (N=124) or colorectal cancer (N=129) patients. Stratified analyses revealed that the Lys variant was marginally significantly inversely associated with advanced tumor stage (p=0.08) and younger (<50 years for breast cancer and <60 years for colorectal) onset (p=0.05). However, survival did not show that this variant was associated with the risk of overall deaths (hazard ratio 0.79 (95% confidence interval: 0.40-1.56)). Next, we analyzed if the variations in genotype distribution can be related to sex in colorectal cancer. We saw a significant increase in the percent of Lysine harboring males with colorectal cancer. The Chi-Square probability was 0.0509. Albeit not a dramatic difference but certainly suggestive, which will require further study.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2017. doi:1538-7445.AM2012-2017

Abstract 322: Functional significance of tyrosine phosphorylation of galectin-3 in prostate cancer progression

Galectin-3 is a carbohydrate binding chimeric lectin, which interacts with intracellular glycoproteins, cell surface molecules and extracellular matrix proteins based on its intra and extracellular distribution. Galectin-3 is one of the most studied galectins in the family and affects various biological phenomena such as cell growth, adhesion, angiogenesis, apoptosis, motility and metastasis. This protein is widely expressed in various tumor cells and its expression is correlated with tumorigenesis, tumor progression and metastasis. The functions of galectin-3 are dependent on its binding partners, its localization and can change as a result of post-translational modifications such as cleavage and phosphorylation. Recently, we demonstrated that gal-3 can be phosphorylated by c-Abl at Tyr 79, 107 and 118; Tyr107 is the major phosphorylation site. It was also shown that galectin-3 can be cleaved by prostate specific antigen, chymotrypsin-like serine protease, after Tyr 107 and this cleavage destroys galectin-3 multivalency while preserving its carbohydrate-binding activity. In solution, galectin-3 largely occurs as a monomer. It can also form homodimer by self-association through its CRDs in the absence of its binding ligands. However, in the presence of its carbohydrate binding ligands, galectin-3 can polymerize up to pentamers through its N-terminal domain. Oligomerization is a unique feature of secreted galectin-3, which allows its function by forming ordered galectin-glycan structures, also called lattices, on the cell surface or through direct engagement of specific cell surface glycoconjugates by traditional ligand-receptor interactions. We suggest that phosphorylation on Tyr 107 may block the cleavage of galectin-3 by PSA. Our experiments confirm this hypothesis and we suggest a model describing the role of galectin-3 in prostate cells with increased activity of c-Abl and Arg kinase. We demonstrate that PSA resistant intact galectin-3 may exert biological activities through ligand cross-linking to boost the tumorigenesis and progression of prostate cancer, while the protein cleaved after Tyr 107 cannot. The effect of cleaved galectin-3 on angiogenesis, chemotaxis and cell motility was significantly lower compare to full-length galectin-3. We posit that post-translational modifications of galectin-3 in the cells are but one component of a constellation of factors contributing to cancer disease prevalence and severity. In conclusion, the data show that galectin-3 phosphorylated on Tyr 107 can be associated with metastasis, cell growth, and tumorigenicity of prostate cancer cells and thus might used as a marker for prognosis of prostate cancer and a therapeutic target for the treatment of prostate cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 322. doi:1538-7445.AM2012-322

Abstract 212: gp78/AMFR is involved in ubiquitination of PGI/AMF

Phosphoglucose isomerase/autocrine motility factor (PGI/AMF) is a multifunctional protein that intracellularly catalyzes the interconversion of glucose 6-phosphate and fructose 6-phosphate in both glycolytic and gluconeogenesis pathways and extracellularly acts as a cytokine associated with aggressive tumor phenotype. Secreted PGI/AMF promotes cancer cell invasion and metastasis by stimulating cell motility via an autocrine manner following binding to its seven-transmembrane glycoprotein receptor gp78/AMFR. Gp78/AMFR also demonstrates an additional function in the endoplasmic reticulum (ER) as ubiquitin ligase (E3). Thus, gp78/AMFR represents a potential link between ubiquitination, ER-associated degradation (ERAD) and metastasis. We questioned if gp78/AMFR is involved in the ubiquitination of PGI/AMF, and whether the ubiquitinated PGI/AMF can be related to cancer progression and metastasis. In this study, we found that indeed PGI/AMF can be ubiquitinated and gp78/AMFR is involved in this process. PGI/AMF was predominantly ubiquitinated via K29-linked ubiquitin chains. Monoubiquitinated PGI/AMF increases the secretion of PGI/AMF and this is the first report to show that monoubiquitinated PGI/AMF is secreted out of the cells. As secretion of PGI/AMF plays a significant role in tumor cell migration and invasion during metastasis, these studies assist in understanding the regulation of PGI/AMF and the mechanisms of its secretion, which may provide a new therapeutic target for tumor metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 212. doi:1538-7445.AM2012-212

Tyrosine-phosphorylated galectin-3 protein is resistant to prostate-specific antigen (PSA) cleavage

Galectin-3 is a chimeric carbohydrate-binding protein, which interacts with cell surface carbohydrate-containing molecules and extracellular matrix glycoproteins and has been implicated in various biological processes such as cell growth, angiogenesis, motility, and metastasis. It is expressed in a wide range of tumor cells and is associated with tumor progression. The functions of galectin-3 are dependent on its localization and post-translational modifications such as cleavage and phosphorylation. Recently, we showed that galectin-3 Tyr-107 is phosphorylated by c-Abl; concomitantly, it was also shown that galectin-3 can be cleaved at this site by prostate-specific antigen (PSA), a chymotrypsin-like serine protease, after Tyr-107, resulting in loss of galectin-3 multivalency while preserving its carbohydrate binding activity. Galectin-3 is largely a monomer in solution but may form a homodimer by self-association through its carbohydrate recognition domain, whereas, in the presence of a ligand, galectin-3 polymerizes up to pentamers utilizing its N-terminal domain. Oligomerization is a unique feature of secreted galectin-3, which allows its function by forming ordered galectin-glycan structures, i.e. lattices, on the cell surface or through direct engagement of specific cell surface glycoconjugates by traditional ligand-receptor binding. We questioned whether Tyr-107 phosphorylation by c-Abl affects galectin-3 cleavage by PSA. The data suggest a role for galectin-3 in prostate cells associated with increased activity of c-Abl kinase and loss of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) activity. In addition, the ratio of phosphorylated/dephosphorylated galectin-3 might be used as a complementary value to that of PSA for prognosis of prostate cancer and a novel therapeutic target for the treatment of prostate cancer.

Rad6B acts downstream of Wnt signaling to stabilize β-catenin: Implications for a novel Wnt/β-catenin target

BACKGROUND

Aberrant Wnt/β-catenin signaling is associated with breast cancer even though genetic mutations in Wnt signaling components are rare. We have previously demonstrated that Rad6B, an ubiquitin conjugating enzyme, stabilizes β-catenin via polyubiqutin modifications that render β-catenin insensitive to proteasomal degradation. Rad6B is a transcriptional target of β-catenin, creating a positive feedback loop between Rad6B expression and β-catenin activation.

METHODS

To isolate subpopulations expressing high or low Rad6B levels, we transfected MDA-MB-231 or WS-15 human breast cancer cells with ZsGreen fluorescent reporter vector in which the expression of ZsGreen was placed under the control of Rad6B promoter. ZsGreenhigh and ZsGreenlow subpopulations, reflective of high and low Rad6B promoter activity, respectively, were isolated by FACS. To determine the relevance of Wnt signaling in Rad6B-mediated β-catenin stabilization/activation, the ZsGreenhigh cells were transfected with signaling-defective Wnt coreceptor LRP6Δ173. Rad6B expression and promoter activity were determined by RT-PCR, Western blot and Rad6B promoter-mediated luciferase assays. β-catenin levels and transcriptional activity were determined by Western blot and TOP/FOP Flash reporter assays. Tumor formation and morphologies of ZsGreenlow, ZsGreenhigh, and ZsGreenhigh/LRP6Δ173 cells compared to unsorted vector controls were evaluated in nude mice. Expression of Wnt signaling related genes was profiled using the Wnt signaling pathway RT2 Profiler PCR arrays.

RESULTS

ZsGreenhigh subpopulations showed high Rad6B expression and Rad6B promoter activity as compared to ZsGreenlow cells. ZsGreenhigh (high Rad6B expressors) also showed elevated β-catenin levels and TOP/Flash activity. Inhibiting Wnt signaling in the high Rad6B expressors decreased ZsGreen fluorescence, Rad6B gene expression, β-catenin levels and TOP/Flash activity. Tumors derived from high Rad6B expressors were predominantly composed of cells with epithelial mesenchymal transition (EMT) phenotype as compared to control tumors that were composed of both cuboidal and EMT-type cells. Tumors derived from low Rad6B expressors lacked EMT phenotype. Inhibition of LRP6 function in the high Rad6B expressors abrogated the EMT phenotype. Gene expression profiling showed upregulation of several Wnt signaling pathway regulators in high Rad6B expressors that were downregulated by interference of Wnt signaling with mutant LRP6 or by Rad6B silencing.

CONCLUSIONS

These data reveal a functional link between the canonical Wnt pathway and Rad6B in β-catenin activation and breast cancer progression.

Abstract 5588: Szygium aromaticum (clove): A novel natural breast cancer inhibitor

The dried flower buds of clove (Syzygium aromaticum syn Eugenia aromaticum or caryophyllata) belonging to family Myrtaceae are used as a spice worldwide. Clove has been reported to exhibit antimicrobial, anti-viral, anesthetic, insecticidal, anti-convulsant, anti-oxidative and free radical scavenging activities. Eugenol, an active component of essential oil isolated from clove has anti-mutagenic, anti-genotoxic and anti-inflammatory properties. It also restricts DMBA induced skin carcinogenesis in mice. Aqueous extract of clove was effective in reducing the incidence of hyperplasia, dysplasia, and carcinoma in situ in benzo[a]pyrene induced lung carcinoma in mice. However, there are no reports on the effects of clove on human cancers.

In this study we have analyzed the inhibitory effects of the aqueous extract of clove (CAE) on breast cancer using in vitro studies like cell growth, cell migration, three-dimensional capillary tube formation / morphogenesis and apoptosis; and in vivo studies like breast tumor growth in nude mice. Our results indicate that CAE inhibited the growth and proliferation of breast cancer cell lines MDA-MB-231, MCF10ADCIS.com, and MCF10AEIII 8 cells in a dose dependent manner. In addition, it also reduced cell migration towards Matrigel. CAE also inhibited the enzymatic activity of the Matrix Metalloproteinase-2 (MMP-2), which was analyzed by using two substrates, namely galectin-3 and a fluorescence-quenched substrate MOCAcPLGLA2pr(Dnp)AR-NH2. Cell cycle analysis of MCF10ADCIS.com cells using flow cytometry after propidium iodide (PI) staining indicated an arrest mainly in S-phase. We also observed an inhibition of DNA synthesis in CAE-treated MCF10ADCIS.com cells by bromodeoxyuridine (BrdU) incorporation. Expressions of apoptosis-related proteins, poly(ADP-ribose)polymerase (PARP), caspase-3 and caspase-8 remained unchanged after CAE treatment, but CDK2, CDK4, cyclin A and cyclin D2 were down-regulated in treated cells indicating that CAE might affect tumor growth by inducing cell cycle arrest but not apoptosis. There was a 50% reduction in tumor volume in nude mice injected with MCF10ADCIS.com cells that received CAE extract in their drinking water compared to the control mice. The expression of proliferation, apoptosis, angiogenesis and tumor progression markers (PCNA, TUNEL, p63, CD31, smooth muscle actin, collagen IV, MMP-2 are being investigated in the xenografts. The results suggest that CAE may be explored further as a novel inhibitor of breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5588. doi:10.1158/1538-7445.AM2011-5588

Abstract 1495: Tyrosine phosphorylation of galectin-3 regulated its cleavage by PSA

Galectin-3, one of 15 animal lectins, is an intracellular and extracellular lectin which interacts with intracellular glycoproteins, cell surface molecules and extracellular matrix proteins. Recent research revealed that galectin-3 (gal-3) is involved in various biological phenomena including cell growth, adhesion, angiogenesis, apoptosis, motility and metastasis. This protein is widely expressed in various tumor cells and its expression is correlated with tumorigenesis, tumor progression and metastasis. The functions of gal-3 are dependent on its binding partners, its localization and can change as a result of post-translational modifications such as cleavage and phosphorylation. Recently we demonstrated that gal-3 can be phosphorylated by c-Abl at Tyr 79, 107 and 118; Tyr107 is the major phosphorylation site. In a recent report Saraswati et al revealed that gal-3 can be cleaved by prostate specific antigen after Tyr107. Our research confirms their data and demonstrates that phosphorylation of Tyr107 blocks this cleavage. This cleavage removes the collagen like sequence from carbohydrate binding domain of gal-3 and reduces the ability of gal-3 to create oligomers, thus blocking its ability to create lattice and promote cancer behavior of the cells. These results indicate an important role of post-translational modifications of galectin-3 in prostate cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1495. doi:10.1158/1538-7445.AM2011-1495

Calpain activation through galectin-3 inhibition sensitizes prostate cancer cells to cisplatin treatment

Prostate cancer will develop chemoresistance following a period of chemotherapy. This is due, in part, to the acquisition of antiapoptotic properties by the cancer cells and, therefore, development of novel strategies for treatment is of critical need. Here, we attempt to clarify the role of the antiapoptotic molecule galectin-3 in prostate cancer cells using siRNA and antagonist approaches. The data showed that Gal-3 inhibition by siRNA or its antagonist GCS-100/modified citrus pectin (MCP) increased cisplatin-induced apoptosis of PC3 cells. Recent studies have indicated that cisplatin-induced apoptosis may be mediated by calpain, a calcium-dependent protease, as its activation leads to cleavage of androgen receptor into an androgen-independent isoform in prostate cancer cells. Thus, we examined whether calpain activation is associated with the Gal-3 function of regulating apoptosis. Here, we report that Gal-3 inhibition by siRNA or GCS-100/MCP enhances calpain activation, whereas Gal-3 overexpression inhibits it. Inhibition of calpain using its inhibitor and/or siRNA attenuated the proapoptotic effect of Gal-3 inhibition, suggesting that calpain activation may be a novel mechanism for the proapoptotic effect of Gal-3 inhibition. Thus, a paradigm shift for treating prostate cancer is suggested whereby a combination of a non-toxic anti-Gal-3 drug together with a toxic chemotherapeutic agent could serve as a novel therapeutic modality for chemoresistant prostate cancers.

Cleavage of galectin-3 by matrix metalloproteases induces angiogenesis in breast cancer

Galectin-3 cleavage is related to progression of human breast and prostate cancer and is partly responsible for tumor growth, angiogenesis and apoptosis resistance in mouse models. A functional polymorphism in galectin-3 gene, determining its susceptibility to cleavage by matrix metalloproteinases (MMPs)-2/-9 is related to racial disparity in breast cancer incidence in Asian and Caucasian women. The purpose of our study is to evaluate (i) if cleavage of galectin-3 could be related to angiogenesis during the progression of human breast cancer, (ii) the role of cleaved galectin-3 in induction of angiogenesis and (iii) determination of the galectin-3 domain responsible for induction of angiogenic response. Galectin-3 null breast cancer cells BT-459 were transfected with either cleavable full-length galectin-3 or its fragmented peptides. Chemotaxis, chemoinvasion, heterotypic aggregation, epithelial-endothelial cell interactions and angiogenesis were compared to noncleavable galectin-3. BT-549-H(64) cells harboring cleavable galectin-3 exhibited increased chemotaxis, invasion and interactions with endothelial cells resulting in angiogenesis and 3D morphogenesis compared to BT-549-P(64) cells harboring noncleavable galectin-3. BT-549-H(64) cells induced increased migration and phosphorylation of focal adhesion kinase in migrating endothelial cells. Endothelial cells cocultured with BT-549 cells transfected with galectin-3 peptides indicate that amino acids 1-62 and 33-250 stimulate migration and morphogenesis of endothelial cells. Immunohistochemical analysis of blood vessel density and galectin-3 cleavage in a breast cancer progression tissue array support the in vitro findings. We conclude that the cleavage of the N terminus of galectin-3 followed by its release in the tumor microenvironment in part leads to breast cancer angiogenesis and progression.

Galectin-3: A novel substrate for c-Abl kinase

Galectin-3, a beta-galactoside-binding lectin, is found in cellular and extracellular location of the cell and has pleiotropic biological functions such as cell growth, cell adhesion and cell-cell interaction. It may exhibit anti- or pro-apoptotic activity depending on its localization and post-translational modifications. Two important post-translational modifications of galectin-3 have been reported: its cleavage and phosphorylation. Cleavage of galectin-3 was reported to be involved with angiogenic potential and apoptotic resistance. Phosphorylation of galectin-3 regulates its sugar-binding ability. In this report we have identified novel tyrosine phosphorylation sites in galectin-3 as well as the kinase responsible for its phosphorylation. Our results demonstrate that tyrosines at positions 79, 107 and 118 can be phosphorylated in vitro and in vivo by c-Abl kinase. Tyrosine 107 is the main target of c-Abl. Expression of galectin-3 Y107F mutant in galectin-3 null SK-Br-3 cells leads to morphological changes and increased motility compared to wild type galectin-3. Further investigation is needed to better understand the functional significance of the novel tyrosine phosphorylated sites of galectin-3.

Abstract 1888: Ocimum gratissimum: a novel natural inhibitor of Matrix Metalloproteases

Ocimum sp. (a.k.a. holy basil or tulsi), exhibits chemo-preventive, anti-carcinogenic, free radical scavenging, radio-protective and numerous other pharmacological properties, and has therefore, been one of the most popular herbs used in Asian and European countries for the treatment of various ailments since ancient times. Extract of Ocimum gratissimum (OG) inhibits proliferation, migration, anchorage-independent growth, three-dimensional growth and morphogenesis, and induction of COX-2 protein in breast cancer cells. In addition, OG extracts also reduced tumor size and neoangiogenesis in a MCF10A DCIS.com xenograft model of human DCIS, suggesting that OG leaf extract may be of value as a breast cancer preventive and therapeutic agent. In an effort to identify the biological target of OG activity, we observed that the aqueous extract of OG inhibited the cleavage of galectin-3 in in vitro conditions. Galectin-3 is a carbohydrate-binding tumor-associated protein containing a collagen-alpha like domain, which is cleavable by Matrix-metalloproteases-2 and −9. We questioned whether the inhibition of galectin-3 cleavage by OG is due to the inhibition of enzymatic activity of MMPs, or the interactions between the MMPs and galectin-3. MCF10AT1, MCF10A and MCF10AEIII8 cells were incubated with various concentrations of the extract and the conditioned media were analyzed for galectin-3 cleavage as well as the gelatinolytic activity by gelatin zymography. The results showed an inhibition of galectin-3 cleavage in the treated cells, but no differences in the MMP activities between the treated and the untreated cells were observed in the zymogram. Next, we performed the gelatin zymography on the recombinant MMP-2 and −9 and incubated the gel with the extract. An inhibition of the gelatinolytic activity was observed in the treated gel. A dose dependent decrease in the MMP-2 and −9 activity was also observed when a fluorogenic peptide, MOCAcPLGLA2pr(Dnp)AR-NH2 was used as a substrate. Furthermore, an inhibition of in vivo activities of MMP-2 and MMP-9 was observed using in situ zymography of fresh frozen MCF10ADCIS.com xenografts in nude mice fed on OG extract compared to the water fed mice. A reduced cleavage of galectin-3 in xenografts harvested from the OG fed mice also indicates a reduced MMP activity. Fractionation of the crude extract indicates that the inhibitory activity is specific to the methanol soluble fraction of OG. Further purification of this fraction by is in progress.

The results suggest that OG inhibits the enzymatic activity of MMP-2 and −9 and can be developed as a novel non-toxic therapeutic agent preventing the invasion and progression of cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1888.

Abstract 1000: Rad6B induced β-catenin stabilization requires intact Wnt signaling

Aberrant activation of Wnt signaling results from stabilization and transcriptional activation of β-catenin and is often associated with carcinogenesis. Clinical evidence suggests that β-catenin accumulation occurs in breast cancer although activating mutations are rare. We have previously shown that Rad6B positively regulates β-catenin stability and transcriptional activity in breast cancer cells by inducing stable polyubiquitin modifications. Here we show that Rad6B physically interacts with β-catenin within the β-catenin amino acid segment containing the first armadillo repeat, which is also a binding site for casein kinase 1 (CK1). β-catenin phosphorylation by GSK3β and subsequent ubiquitination and proteasomal degradation is dependent upon CK1-mediated initiating phosphorylation of β-catenin at Ser45. In vitro kinase assays showed that Rad6B inhibits Ser45 phosphorylation by CK1, and Ser45 phosphorylated β-catenin is decreased in Rad6B overexpressing breast cancer cells. In vitro and in vivo mapping, and site-directed mutation analysis identified K394 of β-catenin as the predominant site for ubiquitination by Rad6B. MCF-7 breast cancer cells engineered to express myc-tagged K394R-β-catenin showed decreased steady-state levels and β-catenin transcriptional activity as compared to cells expressing wild type β-catenin. We also determined whether Rad6B-mediated β-catenin stabilization occurs independently of the canonical Wnt signaling pathway. MDA-MB-231 breast cancer cells overexpressing endogenous Rad6B were isolated on the basis of Rad6B promoter activity, and the consequences of Wnt disruption on β-catenin levels, transcriptional activity and Rad6B expression were determined by expressing a dominant negative mutant of Wnt coreceptor, LRP6. Disruption of Wnt signaling inhibited Rad6B expression and β-catenin accumulation. Both Wnt signaling disruption and Rad6B silencing separately enhanced localization of β-catenin on the cell membranes and decreased intracellular β-catenin accumulation. In summary, our data suggest that the Rad6B overexpression frequently observed in breast carcinomas contribute to β-catenin stabilization and transcriptional activation by inhibiting the CK1-mediated initiating phosphorylation and by ubiquitinating K394. However, the Rad6B induced β-catenin stabilization requires intact Wnt signaling. Supported by DOD W81XWH07-1-0562.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1000.

Abstract 4983: Galectin-3 regulates p21 expression through negatively regulating its degradation

Galectin-3 (Gal-3), a carbohydrate-binding protein, has been demonstrated to be involved in multiple biological events such as cell adhesion, cell migration, cell proliferation, apoptosis and so on. p21, originally described as a inhibitor of cyclin-dependent kinases (CDK), has been shown to have anti-apoptotic activity as well as regulation of cell proliferation. Since both of these two proteins play important roles in cancer and some of their functions overlap, we assumed that there may be some relationship between Gal-3 and p21. Here, we first reported that Gal-3 positively regulates p21 expression in cancer cells, and this effect works at protein degradation level. Over-expression of Gal-3 in Gal-3 null human prostate cancer cell line LNCap and breast cancer cell line BT549 inhibited p21 degradation. Moreover, Gal-3 knockdown in Gal-3 expressing prostate cancer cell line DU145 potentiated p21 degradation, suggesting that Gal-3 negatively regulates p21 degradation in cancer cells. Furthermore, our data showed that Gal-3 negatively regulated proteasomal turnover of p21 in an ubiquitin-dependent way. In this study, we also showed for the first time the direct interaction between Gal-3 and p21. This study suggested that p21 may serve as the downstream molecule of Gal-3 signal transduction pathway to mediate some of Gal-3 functions, and it helps to understand further the mechanisms for Gal-3 functions.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4983.

Regulation of prostate cancer progression by galectin-3

Galectin-3, a beta-galactoside-binding protein, has been implicated in a variety of biological functions including cell proliferation, apoptosis, angiogenesis, tumor progression, and metastasis. The present study was undertaken to understand the role of galectin-3 in the progression of prostate cancer. Immunohistochemical analysis of galectin-3 expression revealed that galectin-3 was cleaved during the progression of prostate cancer. Galectin-3 knockdown by small interfering RNA (siRNA) was associated with reduced cell migration, invasion, cell proliferation, anchorage-independent colony formation, and tumor growth in the prostates of nude mice. Galectin-3 knockdown in human prostate cancer PC3 cells led to cell-cycle arrest at G(1) phase, up-regulation of nuclear p21, and hypophosphorylation of the retinoblastoma tumor suppressor protein (pRb), with no effect on cyclin D1, cyclin E, cyclin-dependent kinases (CDK2 and CDK4), and p27 protein expression levels. The data obtained here implicate galectin-3 in prostate cancer progression and suggest that galectin-3 may serve as both a diagnostic marker and therapeutic target for future disease treatments.

Racial disparity in breast cancer and functional germ line mutation in galectin-3 (rs4644): a pilot study

For reasons largely unknown, Caucasian women are at a significantly higher risk of developing breast cancer than Asian women. Over a decade ago, mutations in BRCA1/2 were identified as genetic risk factors; however, the discovery of additional breast cancer genes and genes contributing to racial disparities are lacking. We report a functional germline mutation (polymorphism) in the galectin-3 gene at position 191 (rs4644) substituting proline with histidine (P64H), which results in susceptibility to matrix metalloproteinase cleavage and acquisition of resistance to drug-induced apoptosis. This substitution correlates with incidence of breast cancer and racial disparity. Genotype analysis of 338 Caucasian (194 disease free and 144 breast cancer patients) and 140 Asian (79 disease free and 61 breast cancer patients) women showed that the allele homozygous for H64 exists in disease free Caucasian and Asian women at a frequency of 12% and 5%, respectively, versus 37% and 82% in breast cancer patients. The data indicate that H/H allele is associated with increased breast cancer risk in both races. The data implicate galectin-3 H(64) in breast cancer and explain, in part, the noted racial disparity, thus providing a novel target for diagnosis and treatment.

Comedo-ductal carcinoma in situ: A paradoxical role for programmed cell death

Comedo-DCIS is a histologic subtype of preinvasive breast neoplasia that is characterized by prominent apoptotic cell death and has greater malignant potential than other DCIS subtypes. We investigated the mechanisms of apoptosis in comedo-DCIS and its role in conversion of comedo-DCIS to invasive cancer. Clinical comedo-DCIS excisions and the MCF10DCIS.com human breast cancer model which produces lesions resembling comedo-DCIS were analyzed. Apoptotic luminal and myoepithelial cells were identified by TUNEL and reactivity to cleaved PARP antibody and cell death assessed by Western blotting, Mitocapture and immunohistochemical assays. MCF10DCIS.com cells undergo spontaneous apoptosis in vitro, both in monolayers and multicellular spheroids; it is associated with increased mitochondrial membrane permeability, increase in Bax/Bcl-2 ratio and occurs via caspase-9-dependent p53-independent pathway. This suggests that apoptosis is stromal-independent and that the cells are programmed to undergo apoptosis. Immunostaining with cleaved PARP antibody showed that myoepithelial apoptosis occurs before lesions progress to comedo-DCIS in both clinical comedo-DCIS and in vivo MCF10DCIS.com lesions. Intense staining for MMP-2, MMP-3, MMP-9 and MMP-11 was observed in the stroma and epithelia of solid DCIS lesions prior to conversion to comedo-DCIS in clinical and MCF10DCIS.com lesions. Gelatin zymography showed higher MMP-2 levels in lysates and conditioned media of MCF10DCIS. com cells undergoing apoptosis. These data suggest that signals arising from the outside (microenvironmental) and inside (internal genetic alterations) of the duct act in concert to trigger apoptosis of myoepithelial and luminal epithelial cells. Our findings implicate spontaneous apoptosis in both the etiology and progression of comedo-DCIS. It is possible that spontaneous apoptosis facilitates elimination of cells thus permitting expansion and malignant transformation of cancer cells that are resistant to spontaneous apoptosis.

Galectin-3 cleavage: a novel surrogate marker for matrix metalloproteinase activity in growing breast cancers

Failed therapies directed against matrix metalloproteinases (MMP) in cancer patients may be attributed, in part, to lack of diagnostic tools to differentiate between pro-MMPs and active MMPs, which indicate whether a treatment is efficacious or not. Because galectin-3 is cleavable in vitro by MMPs, we have developed differential antibodies recognizing its cleaved and noncleaved forms and tested their clinical utilization as a surrogate diagnostic marker for the presence of active MMPs in growing breast cancers. Wild-type and cleavage-resistant galectin-3 were constructed and expressed in galectin-3-null human breast carcinoma cells (BT-549). Tumorigenic and angiogenic potential of the clones was studied by injections into nude mice. MMP-2, MMP-9, full-length, and cleaved galectin-3 were localized in the xenografts by immunohistochemical analysis of paraffin-embedded sections using specific antibodies. Activities of MMP-2/9 were corroborated by in situ zymography on frozen tissue sections. Galectin-3 cleavage was shown in vivo by differential antibody staining and colocalized with predicted active MMPs both in mouse xenografts and human breast cancer specimens. In situ zymography validated these results. In addition, BT-549 cells harboring noncleavable galectin-3 showed reduced tumor growth and angiogenesis compared with the wild-type. We conclude that galectin-3 cleavage is an active process during tumor progression and could be used as a simple, rapid, and reliable surrogate marker for the activities of MMPs in growing breast cancers.

Galectin-3 in apoptosis, a novel therapeutic target

During the past decade, extensive progress has been made toward understanding the molecular basis for the regulation of apoptosis. In mammalian cells undergoing apoptosis, two distinct mechanisms or pathways are operated and are triggered by cell death stimuli from intra- or extra-cellular environments, namely the intrinsic or extrinsic pathways, resulting in mitochondrial membrane depolarization. Several lines of evidence from our laboratories and others have indicated that galectin-3 plays an important role in these pathways by binding to various ligands. Here the authors provide a brief discussion on the role of endogenous or extra-cellular galectin-3 in the regulation of apoptosis and how it could be used as a therapeutic target using natural plant products as its functional inhibitors.