Decorin (DCN) Downregulation Activates Breast Stromal Fibroblasts and Promotes Their Pro-Carcinogenic Effects through the IL-6/STAT3/AUF1 Signaling

Decorin (DCN), a member of the small leucine-rich proteoglycan gene family, is secreted from stromal fibroblasts with non-cell-autonomous anti-breast-cancer effects. Therefore, in the present study, we sought to elucidate the function of decorin in breast stromal fibroblasts (BSFs). We first showed DCN downregulation in active cancer-associated fibroblasts (CAFs) compared to their adjacent tumor counterpart fibroblasts at both the mRNA and protein levels. Interestingly, breast cancer cells and the recombinant IL-6 protein, both known to activate fibroblasts in vitro, downregulated DCN in BSFs. Moreover, specific DCN knockdown in breast fibroblasts modulated the expression/secretion of several CAF biomarkers and cancer-promoting proteins (α-SMA, FAP- α, SDF-1 and IL-6) and enhanced the invasion/proliferation abilities of these cells through activation of the STAT3/AUF1 signaling. Furthermore, DCN-deficient fibroblasts promoted the epithelial-to-mesenchymal transition and stemness processes in BC cells in a paracrine manner, which increased their resistance to cisplatin. These DCN-deficient fibroblasts also enhanced angiogenesis and orthotopic tumor growth in mice in a paracrine manner. On the other hand, ectopic expression of DCN in CAFs suppressed their active features and their paracrine pro-carcinogenic effects. Together, the present findings indicate that endogenous DCN suppresses the pro-carcinogenic and pro-metastatic effects of breast stromal fibroblasts.

Ovarian tumor cell-derived JAGGED2 promotes omental metastasis through stimulating the Notch signaling pathway in the mesothelial cells

The primary site of metastasis for epithelial ovarian cancer (EOC) is the peritoneum, and it occurs through a multistep process that begins with adhesive contacts between cancer cells and mesothelial cells. Despite evidence that Notch signaling has a role in ovarian cancer, it is unclear how exactly it contributes to ovarian cancer omental metastasis, as well as the cellular dynamics and intrinsic pathways that drive this tropism. Here we show that tumor cells produced the Notch ligand Jagged2 is a clinically and functionally critical mediator of ovarian cancer omental metastasis by activating the Notch signaling in single-layered omental mesothelial cells. In turn, Jagged2 promotes tumor growth and therapeutic resistance by stimulating IL-6 release from mesothelial cells. Additionally, Jagged2 is a potent downstream mediator of the omental metastasis cytokine TGF-β that is released during omental destruction. Importantly, therapeutic inhibition of Jagged2-mediated omental metastasis was significantly improved by directly disrupting the Notch pathway in omental mesothelial cells. These findings highlight the key role of Jagged2 to the functional interplay between the TGF-β and the Notch signaling pathways during the metastatic process of ovarian cancer cells to the omentum and identify the Notch signaling molecule as a precision therapeutic target for ovarian cancer metastasis.

Long noncoding RNA DLEU2 and ROR1 pathway induces epithelial-to-mesenchymal transition and cancer stem cells in breast cancer

Breast cancer (BC) patient who receives chemotherapy for an extended length of time may experience profound repercussions in terms of metastases and clinical outcomes due to the involvement of the epithelial-to-mesenchymal transition (EMT) mechanism and enriched cancer stem cells (CSCs). BC cells that express high levels of lncRNA deleted in lymphocytic leukemia-2 (lncRNA DLEU2) and type I tyrosine kinase-like orphan receptor ROR1 (ROR1) may play roles in the enhanced ability of the activation EMT and CSC induction. Here we find that lncRNA DLEU2 and ROR1 are specifically upregulated in tumor tissues compared to their normal counterparts in TCGA, PubMed GEO datasets, and samples from archived breast cancer tumor tissues. Following chemotherapy, lncRNA DLEU2 and ROR1 were enhanced in BC tumor cells, coupled with the expression of CSCs, EMT-related genes, and BMI1. Mechanistically, ROR1 and lncRNA DLEU2 overexpression led to enhanced tumor cell proliferation, inhibition of apoptosis, cell-cycle dysregulation, chemoresistance, as well as BC cell's abilities to invade, migrate, develop spheroids. These findings imply that the role of lncRNA DLEU2 and ROR1 in BC therapeutic failure is largely attributed to EMT, which is intricately linked to enriched CSCs. In conclusion, our findings indicate that a lncRNA DLEU2 and ROR1-based regulatory loop governs EMT and CSC self-renewal, implying that targeting this regulatory pathway may improve patients' responses to chemotherapy and survival.

Ionizing radiation normalizes the features of active breast cancer stromal fibroblasts and suppresses their paracrine pro-carcinogenic effects

BACKGROUND

Radiotherapy is an important therapeutic strategy for breast cancer patients through reducing the chances of recurrence and metastasis, which are fueled by cancer-associated fibroblasts (CAFs). Thereby, we addressed here the effect of various doses of X-rays on breast CAFs and their adjacent counterparts.

METHODS

We have used WST1 and annexin V-associated with flow cytometry to test the cytotoxic effects of X-rays. Immunoblotting and ELISA was used to assess the expression/secretion of various proteins. Immunohistochemistry was utilized to determine the level of β-galactosidase and Ki-67. Sphere formation assay was used to test the ability of breast cancer cells to form tumorspheres. Orthotopic tumor xenografts were also used to evaluate the effect of X-ray-treated breast stromal fibroblasts on breast cancer tumor growth in vivo.

RESULTS

Breast stromal fibroblasts showed high resistance to X-rays. While the low dose (5 Gy) inhibited cell proliferation and the active features of CAFs, the higher doses (16 and 50 Gy) promoted senescence. However, this was not accompanied by the senescence-associated secretory phenotype (SASP), but rather a reduction in the synthesis/secretion of various cancer-associated cytokines. Additionally, X-rays suppressed the features of active breast stromal fibroblasts, and their paracrine pro-carcinogenic effects. The ablative dose (16 Gy) inhibited the capacity of active stromal fibroblasts to promote the pro-metastatic processes epithelial-to-mesenchymal transition, the formation of cancer stem cells, as well as the growth of humanized orthotopic breast tumor xenografts.

CONCLUSION

Together, these findings indicate that X-rays can normalize the features of active breast stromal fibroblasts through promoting senescence without SASP.

KEAP1/NRF2 Mutations in Stem Cells Define an Aggressive Subset of Head and Neck Cancer Patients Who Have a Poor Prognosis, Lung Metastasis, and Therapeutic Failure

Mutations in Keap1/Nrf2 in head and neck cancer result in abnormal cell growth. Progenitor cells, bulk tumor cells, and head and neck cancer stem cells (HN-CSCs) may all harbor these mutations. Nevertheless, whether Keap1/Nrf2 mutations in HN-CSCs have an impact on clinical outcomes is unknown. Cancerous HN-CSCs and benign stem cells were obtained from freshly resected head and neck cancer patients (n = 50) via flow cytometry cell sorting and tested for Keap1/Nrf2 mutations. The existence of Keap1/Nrf2 mutations in HN-CSCs, as well as their correlations with tumor mutations, pathologic tumor stage, tumor histologic grades, lung metastasis, treatment outcomes, and the patient's age and conditions, are assessed at the last follow-up visit. Thirteen tumors were found to have Keap1/Nrf2 mutations in their HN-CSCs. More than half of the lung metastases and disease progression occurred in HN-CSCs with mutations. Patients whose tumors carried Keap1/Nrf2 mutations in their HN-CSCs had significantly shorter progression-free survival, overall survival, and time of treatment failure than their non-HN-CSC counterparts. These associations were partly driven by HN-CSCs, in which Keap1/Nrf2 mutations were overrepresented in fast progressors and associated with an increased risk of disease progression. Our findings suggest that molecular genotyping of HN-CSCs may facilitate personalized treatment strategies and assist in identifying patients who are likely to benefit from chemotherapy.

Activated breast stromal fibroblasts exhibit myoepithelial and mammary stem cells features

BACKGROUND

Active breast cancer-associated fibroblasts (CAFs) promote tumor growth and spread, and like tumor cells they are also heterogeneous with various molecular sub-types and different pro-tumorigenic capacities.

METHODS

We have used immunoblotting as well as quantitative RT-PCR to assess the expression of various epithelial/mesenchymal as well as stemness markers in breast stromal fibroblasts. Immunofluorescence was utilized to assess the level of different myoepithelial and luminal markers at the cellular level. Flow cytometry allowed to determine the proportion of CD44- and ALDH1-positive breast fibroblasts, while sphere formation assay was used to test the ability of these cells to form mammospheres.

RESULTS

We have shown here that IL-6-dependent activation of breast and skin fibroblasts promotes mesenchymal-to-epithelial transition and stemness in a STAT3- and p16-dependent manner. Interestingly, most primary CAFs isolated from breast cancer patients exhibited such transition and expressed lower levels of the mesenchymal markers N-cadherin and vimentin as compared to their adjacent normal fibroblasts (TCFs) isolated from the same patients. We have also shown that some CAFs and IL-6-activated fibroblasts express high levels of the myoepithelial markers cytokeratin 14 and CD10. Interestingly, 12 CAFs isolated from breast tumors showed higher proportions of CD24^low/CD44^high and ALDH^high cells, compared to their corresponding TCF cells. These CD44^high cells have higher abilities to form mammospheres and to enhance cell proliferation of breast cancer cells in a paracrine manner relative to their corresponding CD44^low cells.

CONCLUSION

Together, the present findings show novel characteristics of active breast stromal fibroblasts, which exhibit additional myoepithelial/progenitor features.

The curcumin analogue PAC has potent anti-anaplastic thyroid cancer effects

Anaplastic thyroid carcinoma (ATC) is the rarest type of thyroid cancer, but is the common cause of death from these tumors. The aggressive behavior of ATC makes it resistant to the conventional therapeutic approaches. Thus, the present study was designed to evaluate the anti-ATC efficacy of the piperidone analogue of curcumin (PAC). We have shown that PAC induces apoptosis in thyroid cancer cells in a time-dependent fashion through the mitochondrial pathway. Immunoblotting analysis revealed that PAC suppressed the epithelial-to-mesenchymal transition (EMT) process in ATC cells by upregulating the epithelial marker E-cadherin and reducing the level of the mesenchymal markers N-cadherin, Snail, and Twist1. This anti-EMT effect was confirmed by showing PAC-dependent inhibition of the proliferation and migration abilities of ATC cells. Furthermore, PAC inhibited the AKT/mTOR pathway in ATC cells. Indeed, PAC downregulated mTOR and its downstream effectors p70S6K and 4E-BP1 more efficiently than the well-known mTOR inhibitor rapamycin. In addition to the promising in vitro anticancer efficacy, PAC significantly suppressed the growth of humanized thyroid tumor xenografts in mice. Together, these findings indicate that PAC could be considered as promising therapeutic agent for anaplastic thyroid carcinomas.

Osteoprotegerin (OPG) Upregulation Activates Breast Stromal Fibroblasts and Enhances Their Pro-Carcinogenic Effects through the STAT3/IL-6 Signaling

Breast carcinomas are composed of cancer cells surrounded by various types of non-cancer cells such as fibroblasts. While active cancer-associated fibroblasts (CAFs) support tumor initiation and progression, quiescent breast stromal fibroblasts (BSFs) inhibit these effects through various cytokines such as osteoprotegerin (OPG). We showed here that OPG is upregulated in CAFs as compared to their adjacent normal tumor counterpart fibroblasts. Interestingly, breast cancer cells can upregulate OPG in BSFs in an IL-6-dependent manner through the IL-6/STAT3 pathway. When upregulated by ectopic expression, OPG activated BSFs through the NF-κB/STAT3/AUF1 signaling pathway and promoted their paracrine pro-carcinogenic effects in an IL-6-dependent manner. In addition, this increase in the OPG level enhanced the potential of BSFs to promote the growth of humanized orthotopic tumors in mice. However, specific OPG knock-down suppressed active CAFs and their paracrine pro-carcinogenic effects. Similar effects were observed when CAF cells were exposed to the pure recombinant OPG (rOPG) protein. Together, these findings show the importance of OPG in the activation of stromal fibroblasts and the possible use of rOPG or inhibitors of the endogenous protein to target CAFs as precision cancer therapeutics.

High AUF1 level in stromal fibroblasts promotes carcinogenesis and chemoresistance and predicts unfavorable prognosis among locally advanced breast cancer patients

Background

Locally advanced breast cancer (LABC), the most aggressive form of the disease, is a serious threat for women's health worldwide. The AU-rich RNA-binding factor 1 (AUF1) promotes the formation of chemo-resistant breast cancer stem cells. Thereby, we investigated the power of AUF1 expression, in both cancer cells and their stromal fibroblasts, as predictive biomarker for LABC patients’ clinical outcome following neoadjuvant treatment.

Methods

We have used immunohistochemistry to assess the level of AUF1 on formalin-fixed paraffin-embedded tissues. Immunoblotting was utilized to show the effect of AUF1 ectopic expression in breast stromal fibroblasts on the expression of various genes both in vitro and in orthotopic tumor xenografts. Cytotoxicity was evaluated using the WST1 assay, while a label-free real-time setting using the xCELLigence RTCA technology was utilized to assess the proliferative, migratory and invasive abilities of cells.

Results

We have shown that high AUF1 immunostaining (≥ 10%) in both cancer cells and their adjacent cancer-associated fibroblasts (CAFs) was significantly associated with higher tumor grade. Kaplan–Meier univariate analysis revealed a strong correlation between high AUF1 level in CAFs and poor patient’s survival. This correlation was highly significant in patients with triple negative breast cancer, who showed poor disease-free survival (DFS) and overall survival (OS). High expression of AUF1 in CAFs was also associated with poor OS of ER+/Her2− patients. Similarly, AUF1-positive malignant cells tended to be associated with shorter DFS and OS of ER+/Her2+ patients. Interestingly, neoadjuvant therapy downregulated AUF1 to a level lower than 10% in malignant cells in a significant number of patients, which improved both DFS and OS. In addition, ectopic expression of AUF1 in breast fibroblasts activated these cells and enhanced their capacity to promote, in an IL-6-dependent manner, the epithelial-to-mesenchymal transition and stemness processes. Furthermore, these AUF1-expressing cells enhanced the chemoresistance of breast cancer cells and their growth in orthotopic tumor xenografts.

Conclusions

The present findings show that the CAF-activating factor AUF1 has prognostic/predictive value for breast cancer patients and could represent a great therapeutic target in order to improve the precision of cancer treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-022-01543-x.

High DNMT1 Expression in Stromal Fibroblasts Promotes Angiogenesis and Unfavorable Outcome in Locally Advanced Breast Cancer Patients

Background

Active breast cancer-associated fibroblasts (CAFs) play a leading role in breast carcinogenesis through promoting angiogenesis and resistance to therapy. Consequently, these active stromal cells have significant influence on patient outcome. Therefore, we explored here the role of the DNA methyltransferase 1 (DNMT1) protein in CAF-dependent promotion of angiogenesis as well as the prognostic power of DNMT1 level in both cancer cells and their adjacent CAFs in locally advanced breast cancer patients.

Methods

We applied immunohistochemistry to evaluate the level of DNMT1 in breast cancer tissues and their adjacent normal counterparts. Quantitative RT-PCR and immunoblotting were performed to investigate the role of DNMT1 in regulating the expression of pro-angiogenic genes in active CAFs and also their response to the DNMT1 inhibitors decitabine (DAC) as well as eugenol.

Results

We have shown that DNMT1 controls the pro-angiogenic potential of CAFs both in vitro and in vivo through positive regulation of the expression/secretion of 2 important pro-angiogenic factors VEGF-A and IL-8 as well as their upstream effectors mTOR and HIF-1α. To confirm this, we have shown that these DNMT1-related pro-angiogenic effects were suppressed by 2 DNMT1 inhibitors decitabine and eugenol. Interestingly, in a cohort of 100 tumors from locally advanced breast cancer patients (LABC), we have shown that high expression of DNMT1 in tumor cells and their adjacent stromal fibroblasts is correlated with poor survival of these patients.

Conclusion

DNMT1 upregulation in breast stromal fibroblasts promotes angiogenesis via IL-8/VEGF-A upregulation, and correlates well with poor survival of LABC patients.

Osteoprotegerin (OPG) mediates the anti-carcinogenic effects of normal breast fibroblasts and targets cancer stem cells through inhibition of the β-catenin pathway

Normal breast fibroblasts (NBFs) support and maintain the architecture of the organ, and can also suppress tumorigenesis. However, the mechanisms involved are not fully understood. We have shown here that NBFs suppress breast carcinogenesis through secretion of osteoprotegerin (OPG), a soluble decoy receptor for the Receptor Activator of NF-κB ligand (RANKL). Indeed, NBFs and human recombinant OPG (rOPG), suppressed breast cancer cells proliferation and motility through inhibition of the epithelial-to-mesenchymal transition (EMT) process both in vitro and in vivo. Additionally, rOPG inhibited the IL-6/STAT3 and NF-κB pathways as well as the OPG gene, which turned out to be STAT3-regulated. This was confirmed using denosumab, a RANKL-targeted antibody, which also inhibited NF-κB, down-regulated OPG and repressed EMT in breast cancer cells grown in 2D and 3D. Importantly, both rOPG and denosumab targeted cancer stem cells (CSCs). This was mediated through inhibition of the CSC-related pathway β-catenin. Moreover, rOPG reduced tumor growth and inhibited breast CSC biomarkers in orthotopic humanized breast tumors. Therefore, normal mammary fibroblasts can suppress carcinogenesis through OPG, which constitutes great potential as preventive and/or therapeutic molecule for breast carcinomas.

Tocilizumab suppresses the pro-carcinogenic effects of breast cancer- associated fibroblasts through inhibition of the STAT3/AUF1 pathway

Active breast cancer-associated fibroblasts (CAFs), the most influential cells in breast tumor microenvironment (TME), express/secrete high levels of the proinvasive/metastatic interleukin-6 (IL-6). Therefore, we have tested here the effect of the IL-6 receptor (IL-6R) inhibitor tocilizumab (Actemra) on different active breast CAFs. We have shown that tocilizumab potently and persistently suppresses the expression of various CAF biomarkers, namely α-SMA, SDF-1 as well as the STAT3 pathway and its downstream target AUF1. Tocilizumab also inhibited the proliferation, migration, and invasion abilities of active breast CAF cells. Additionally, tocilizumab repressed the ability of CAF cells in promoting epithelial-to-mesenchymal transition, and enhancing the migratory/invasive and proliferative capacities of breast cancer cells in vitro. Importantly, these findings were confirmed in orthotopic humanized breast tumors in mice. Furthermore, tocilizumab suppressed the expression of the pro-angiogenic factor VEGF-A and its transactivator HIF-1α in CAF cells, and consequently inhibited the angiogenic-promoting effect of active CAFs both in vitro and in orthotopic tumor xenografts. These results indicate that inhibition of the IL-6/STAT3/AUF1 pathway by tocilizumab can normalize active breast CAFs and suppress their paracrine pro-carcinogenic effects, which paves the way towards development of specific CAF-targeting therapy, badly needed for more efficient breast cancer treatments.

Eugenol modulates genomic methylation and inactivates breast cancer-associated fibroblasts through E2F1-dependent downregulation of DNMT1/DNMT3A

Active cancer-associated fibroblasts (CAFs) are major components of the tumor microenvironment, which promote carcinogenesis and modulate response to therapy. Therefore, targeting these cells or reducing their paracrine pro-carcinogenic effects could be of great therapeutic value. To this end, we sought to investigate the effect of eugenol, a natural phenolic molecule, on active breast CAFs. We have shown that decitabine (5-Aza-2'-deoxycytidine, DAC) and eugenol inhibit the expression of the DNA methyltransferase genes DNMT1 and DNMT3A at both the protein and mRNA levels in breast CAF cells. While the effect of eugenol was persistent, DAC had only a transient inhibitory effect on the mRNA level of both DNMT genes. Furthermore, eugenol and DAC suppressed the invasive/migratory and proliferative potential of CAF cells as well as their paracrine pro-carcinogenic effects both in vitro and in humanized orthotopic tumor xenografts. Interestingly, these inhibitory effects of decitabine and eugenol were mediated through E2F1 downregulation. Indeed, ectopic expression of E2F1 upregulated both genes and attenuated the effects of eugenol. Additionally, we provide clear evidence that eugenol, like DAC, strongly modulates the methylation pattern in active CAF cells, through methylating several oncogenes and demethylating various important tumor suppressor genes, which affected their mRNA expression levels. Importantly, the E2F1 promoter was also hypermethylated and the gene downregulated in response to eugenol. Together, these findings show that the active features of breast CAF cells can be normalized through eugenol-dependent targeting of DNMT1/DNMT3A and the consequent modulation in gene methylation.

Cucurbitacin I (JSI-124)-dependent inhibition of STAT3 permanently suppresses the pro-carcinogenic effects of active breast cancer-associated fibroblasts

Active cancer-associated fibroblasts (CAFs), which constitute the most preponderant cell type in breast tumors, contribute actively to all aspects of cancer progression, stimulate recurrence, and restrain drug sensitivity. In the present study, we tested the effect of the selective JAK/STAT3 inhibitor cucurbitacin I (JSI-124) on active breast CAFs. We have shown that JSI-124 at non-cytotoxic concentration (20 nM) can inhibit the IL-6/STAT3/NF-κB positive feedback loop in breast myofibroblasts, which enabled persistent inactivation of these cells. Interestingly, JSI-124 treatment suppressed the paracrine promotion of the epithelial-to-mesenchymal transition (EMT) process and the pro-migratory/-invasive and -proliferative effects of CAFs on breast cancer cells in vitro. Similarly, JSI-124 inhibited the capacity of CAF cells in promoting tumor growth, EMT, stemness as well as angiogenesis in orthotopic humanized breast cancer tumors. Together, these findings indicate that JSI-124-dependent inhibition of STAT3 could be of great therapeutic value for the treatment of breast cancer through targeting cancer cells as well as their growth supportive stromal fibroblasts and blood vessels. This could pave the path to developing a precise CAF-targeted anticancer therapy.

Tocilizumab inhibits IL-8 and the proangiogenic potential of triple negative breast cancer cells

Triple-negative breast cancer (TNBC) is the most aggressive subtype of the disease with lack of recognized molecular targets for therapy. TNBC cells are known to secrete high levels of the proinflammatory cytokines interleukin-6 (IL-6) and IL-8, which promote angiogenesis and favor the growth and spread of the disease. In the present study, we have shown that the humanized anti-IL-6 receptor tocilizumab (Actemra) is also a potent inhibitor of IL-8 in TNBC cells. Similar effect was also obtained by specific IL-6 inhibition either by small interfering RNA or by neutralizing antibody. Likewise, neutralizing IL-8 with specific antibody downregulated IL-8 and inhibited the IL-6/signal transducer and activator of transcription 3 and nuclear factor-κB pathways. Interestingly, simultaneous co-inhibition of IL-6 and IL-8 did not increase the effects of the single inhibitors. Additionally, we present clear evidence that tocilizumab has potent antiangiogenic effect. Indeed, tocilizumab abolished the ability of TNBC cells to induce the differentiation of endothelial cells into network-like tubular structures in vitro and impaired neovascularization in humanized breast orthotopic tumor xenografts. This was associated with tocilizumab-dependent downregulation of the main proangiogenic factor vascular endothelial growth factor A and its coactivator hypoxia-inducible factor 1 both in vitro and in vivo. Therefore, tocilizumab could be of great therapeutic value for TNBC patients through targeting angiogenesis.

Tocilizumab potentiates cisplatin cytotoxicity and targets cancer stem cells in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a very aggressive subtype with high recurrence rate and no molecular targets for therapies. This subtype is characterized by high expression/secretion of the proinvasive/metastatic interleukin-6 (IL-6) cytokine. In the present study, we have shown that tocilizumab inhibits the IL-6/STAT3 signaling and suppresses the cancer/inflammatory epigenetic IL-6/STAT3/NF-κB positive feedback loop. Furthermore, tocilizumab inhibited the proliferative and the migratory/invasiveness capacities as well as the epithelial-to-mesenchymal transition (EMT) process in TNBC cells. Importantly, tocilizumab suppressed the stemness-related characteristics of TNBC cells, through the inhibition of the Wnt/β-catenin breast cancer stem cell-related pathway. Additionally, we have shown that tocilizumab suppresses the paracrine activation of normal breast stromal fibroblasts to myofibroblats. Moreover, tocilizumab sensitized TNBC cells to the cytotoxic effect of cisplatin in vitro. Furthermore, pharmacological inhibition of IL-6 by tocilizumab had great inhibitory effect on tumor growth and the EMT process in humanized orthotopic breast tumors in mice. In addition, tocilizumab potentiated the proapoptotic effect of cisplatin in humanized breast tumors. Together, these findings indicate that tocilizumab can suppress the prometastatic capacity of TNBC cells and enhances the cytotoxic effect of cisplatin against these cells. Therefore, tocilizumab could be of great therapeutic value for these hard-to-treat TNBC patients.

AUF1 promotes stemness in human mammary epithelial cells through stabilization of the EMT transcription factors TWIST1 and SNAIL1

The AU-rich element RNA-binding protein 1 (AUF1) is an RNA-binding protein, which can both stabilize and destabilize the transcripts of several cancer-related genes. Since epithelial-to-mesenchymal transition (EMT) and the acquisition of cancer stem cell traits are important for cancer onset and progression, we sought to determine the role of AUF1 in these two important processes. We have shown that AUF1 induces EMT and stemness in breast epithelial cells via stabilization of the SNAIL1 and TWIST1 mRNAs, and their consequent upregulation. Indeed, AUF1 binds the transcripts of these two genes at their 3′UTR and reduces their turnover. Ectopic expression of AUF1 also promoted stemness in mammary epithelial cells, and thereby increased the proportion of cancer stem cells. Importantly, breast cancer cells that ectopically express AUF1 were more efficient in forming orthotopic tumor xenografts in nude mice than their corresponding controls with limiting cell inocula. On the other hand, AUF1 downregulation with specific siRNA inhibited EMT and reduced the stemness features in breast cancer cells. Moreover, AUF1 knockdown sensitized breast cancer cells to the killing effect of cisplatin. Together, these findings provide clear evidence that AUF1 is an important inducer of the EMT process through stabilization of SNAIL1 and TWIST1 and the consequent promotion of breast cancer stem cells. Thereby, AUF1 targeted molecules could constitute efficient therapeutics for breast cancer patients.

Clinical and functional significance of tumor/stromal ATR expression in breast cancer patients

Background

Most breast cancer-associated fibroblasts (CAFs) are active and important cancer-promoting cells, with significant impact on patient prognosis. Therefore, we investigated here the role of the protein kinase ATR in breast stromal fibroblasts in the prognosis of locally advanced breast cancer patients.

Methods

We have used immunohistochemistry to assess the level of ATR in breast cancer tissues and their adjacent normal tissues. Immunoblotting as well as quantitative RT-PCR were utilized to show the role of breast cancer cells and IL-6 as well as AUF-1 in downregulating ATR in breast stromal fibroblasts. Engineered human breast tissue model was also used to show that ATR-deficient breast stromal fibroblasts enhance the growth of breast cancer cells.

Results

We have shown that the protein kinase ATR is downregulated in cancer cells and their neighboring CAFs in breast cancer tissues as compared to their respective adjacent normal tissues. The implication of cancer cells in ATR knockdown in CAFs has been proven in vitro by showing that breast cancer cells downregulate ATR in breast fibroblasts in an IL-6/STAT3-dependent manner and via AUF-1. In another cohort of 103 tumors from locally advanced breast cancer patients, we have shown that absence or reduced ATR expression in tumoral cells and their adjacent stromal fibroblasts is correlated with poor overall survival as well as disease-free survival. Furthermore, ATR expression in CAFs was inversely correlated with tumor recurrence and progression.

Conclusion

ATR downregulation in breast CAFs is frequent, procarcinogenic, and correlated with poor patient survival.

A validated RP-HPLC method for the determination of piperidone analogue of curcumin

Curcumin (Diferuloylmethane) is a natural product extracted from the root of Curcuma longa. 5-Bis (4-hydroxy-3-methoxybenzylidene)-N-methyl-4-piperidone, the piperidone analogue of curcumin (PAC), was one of the analogues that, demonstrated potential anticancer effects against breast and colon cancers compared with native curcumin. A simple, accurate, and rapid isocratic reverse phase high performance liquid chromatography (HPLC) analytical method utilizing UV detection was developed and validated for the determination of PAC utilizing C₁₈ column with run time was 7 min. Chromatogram showed a peak of PAC at retention time of 5.8±0.92 min. The method was validated for linearity, accuracy, precision, limit of detection, limit of quantitation and robustness. Linear relationship (r > 0.99) was observed between AUP of PAC and the corresponding concentrations over 100-10000μg/mL. The LOQ of this assay was 3.9ng/mL with a corresponding relative standard deviation of 4.8 and 4.0%. The LOD was 13.1ng/mL at a signal-to-noise ratio of >3.

Sequential combination of cisplatin with eugenol targets ovarian cancer stem cells through the Notch-Hes1 signalling pathway

Background

Ovarian carcinomas are the deadliest gynecological malignancies owing to their high rate of recurrence and high resistance to platinum-based chemotherapy. Recent studies have shown platinum-dependent enrichment of ovarian tumors with side population as well as cancer stem cells, which are highly resistant to the treatment. To overcome this treatment-limiting factor, we sought to combine cisplatin with eugenol, a natural substance known to have anti-cancer effects.

Methods

The efficiency of combining cisplatin with eugenol was first tested in vitro on two ovarian cancer cell lines SKOV3 and OV2774 using the WST1 and the flow cytometry techniques. The effect of this combination on ovarian cancer stem cells was determined by the tumorsphere formation assay, while the implication of the Notch pathway was evaluated post-ectopic expression of the Hes1 gene. The resulting changes in the expression of several markers was assessed by immunoblotting, immunofluorescence as well as quantitative RT-PCR. Cell sorting was also used to isolate specific ovarian cancer sub-population of cells. Furthermore, tumor-bearing mouse models were utilized to prove the potential therapeutic value of the cisplatin/eugenol combination treatment in vivo.

Results

We have shown that adding eugenol to cisplatin-treated ovarian cancer cells synergistically inhibited their growth and survival through induction of apoptosis. Importantly, this sequential inhibition strongly reduced the proportion of side population cells and suppressed cisplatin-dependent enrichment in ovarian cancer stem cells. Additionally, while increase in the level of Hes1 promoted stemness and enhanced resistance to cisplatin, cisplatin/eugenol cotreatment inhibited the Notch-Hes1 pathway and strongly downregulated the drug resistance ABC transporter genes. These findings were confirmed in vivo by showing that cisplatin/eugenol cotherapy inhibited tumor growth in animals, reduced the proportion and self-renewal capacities of cancer stem cells and significantly improved disease-free survival of tumor-bearing animals compared with either therapy alone.

Conclusions

These results indicate that cisplatin/eugenol sequential combination could be of great therapeutic value for ovarian cancer patients through targeting the Notch-Hes1 pathway and the consequent elimination of the resistant cancer stem cells.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1360-3) contains supplementary material, which is available to authorized users.

AUF1 positively controls angiogenesis through mRNA stabilization-dependent up-regulation of HIF-1α and VEGF-A in human osteosarcoma

Osteosarcoma is the most common malignant bone tumor in children, adolescents, and young adults. This pleiomorphic tumor depends on new blood vessel development, also known as angiogenesis, for tumor growth and metastasis. Therefore, it’s of utmost importance to identify the key genes and pathways that regulate this pro-metastatic process in order to develop more efficient therapies. Here, we have shown that the RNA-binding protein AUF1 positively regulates the expression of the pro-angiogenic factor VEGF-A and its positive regulator HIF-1alpha through direct binding and stabilization of their mRNAs. This effect is mediated through the seeding sequence of the AUF1 protein in the VEGF-A and HIF-1alpha 3’UTR sequences. As a consequence, the expression of the 3 genes was highly correlative in various osteosarcoma cell lines, and AUF1 enhanced the pro-angiogenic capabilities of osteosarcoma cells both in vitro and in vivo. Indeed, while inhibition of AUF1 using specific siRNA suppressed the pro-angiogenic effects of osteosarcoma cells, ectopic expression of AUF1 enhanced the pro-angiogenic effect in a VEGF-A-dependent manner. Therefore, in the era of targeted therapy, anti-angiogenic therapies targeting AUF1 could provide effective methods for treating osteosarcoma.

ATR suppresses the pro-tumorigenic functions of breast stromal fibroblasts

The ATR protein kinase is a master regulator of the cellular responses to DNA damage and replication stresses. Despite these crucial physiological roles, the implication of ATR in human carcinogenesis remains elusive. We have shown here that the ATR level is reduced in most cancer-associated fibroblasts (CAFs) as compared to their adjacent normal counterparts. Importantly, specific ATR knockdown activated breast fibroblasts, and enhanced their paracrine pro-carcinogenic effects via strong increase in the expression/secretion of SDF-1 and IL-6. Furthermore, ATR-deficient fibroblasts enhanced tumor growth and aggressiveness in orthotopic breast tumor xenografts. On the other hand, ectopic expression of ATR suppressed the expression/secretion of several cancer-promoting proteins such as IL-6, TGF-β1 and SDF-1, and inhibited the migration and invasion capacities of breast myofibroblast cells. Furthermore, ATR up-regulation in active breast fibroblasts reduced their paracrine pro-migratory/-invasive effects on breast cancer cells. Interestingly, the cancer promoting effects of ATR-deficient cells were repressed by ectopic expression of the ATR effector p53. These results indicate that ATR is a major target of cancer cells in breast fibroblasts wherein this protein kinase represses both autocrine and paracrine pro-carcinogenic effects. This indicates that the ATR status in these cells could be of great prognostic/diagnostic values.

Let-7b inhibits cancer-promoting effects of breast cancer-associated fibroblasts through IL-8 repression

Cancer-associated fibroblasts (CAFs) are major players in the development and spread of breast carcinomas through non-cell-autonomous signaling. These paracrine effects are under the control of several genes and microRNAs. We present here clear evidence that let-7b, a tumor suppressor microRNA, plays key roles in the persistent activation of breast stromal fibroblasts and their functional interplay with cancer cells. We have first shown that let-7b is down-regulated in CAFs as compared to their corresponding normal adjacent fibroblasts, and transient specific let-7b inhibition permanently activated breast fibroblasts through induction of the IL-6-related positive feedback loop. More importantly, let-7b-deficient cells promoted the epithelial-to-mesenchymal transition process in breast cancer cells in an IL-8-dependent manner, and also enhanced orthotopic tumor growth in vivo. On the other hand, overexpression of let-7b by mimic permanently suppressed breast myofibroblasts through blocking the positive feedback loop, which inhibited their paracrine pro-carcinogenic effects. Furthermore, we have shown that let-7b negatively controls IL-8, which showed higher expression in the majority of CAF cells as compared to their adjacent normal counterparts, indicating that IL-8 plays a major role in the carcinoma/stroma cross-talk. These findings support targeting active stromal fibroblasts through restoration of let-7b/IL-8 expression as a therapeutic option for breast carcinomas.

The inflammatory/cancer-related IL-6/STAT3/NF-κB positive feedback loop includes AUF1 and maintains the active state of breast myofibroblasts

The IL-6/STAT3/NF-κB positive feedback loop links inflammation to cancer and maintains cells at a transformed state. Similarly, cancer-associated myofibroblats remains active even in absence of cancer cells. However, the molecular basis of this sustained active state remains elusive. We have shown here that breast cancer cells and IL-6 persistently activate breast stromal fibroblasts through the stimulation of the positive IL-6/STAT3/NF-κB feedback loop. Transient neutralization of IL-6 in culture inhibited this signaling circuit and reverted myofibrobalsts to a normalized state, suggesting the implication of the IL-6 autocrine feedback loop as well. Importantly, the IL-6/STAT3/NF-κB pro-inflammatory circuit was also active in cancer-associated fibroblasts isolated from breast cancer patients. Transient inhibition of STAT3 by specific siRNA in active fibroblasts persistently reduced the level of the RNA binding protein AUF1, blocked the loop and normalized these cells. Moreover, we present clear evidence that AUF1 is also part of this positive feedback loop. Interestingly, treatment of breast myofibroblasts with caffeine, which has been previously shown to persistently inhibit active breast stromal fibroblasts, blocked the positive feedback loop through potent and sustained inhibition of STAT3, AKT, lin28B and AUF1. These results indicate that the IL-6/STAT3/NF-κB positive feedback loop includes AUF1 and is responsible for the sustained active status of cancer-associated fibroblasts. We have also shown that normalizing myofibroblasts, which could be of great therapeutic value, is possible through the inhibition of this procarcinogenic circuit.

The DNA methyl-transferase protein DNMT1 enhances tumor-promoting properties of breast stromal fibroblasts

The activation of breast stromal fibroblasts is a crucial step toward tumor growth and spread. Therefore, it is extremely important to understand the molecular basis of this activation and determine the molecules and the mechanisms responsible for its sustainability. In the present report we have shown that the DNA methyl-transferase protein DNMT1 is critical for the activation of breast stromal fibroblasts as well as the persistence of their active status. Indeed, we have first revealed DNMT1 up-regulation in most cancer-associated fibroblasts relative to their corresponding adjacent normal fibroblasts. This effect resulted from HuR-dependent stabilization of the DNMT1 mRNA. Furthermore, ectopic expression of DNMT1 activated primary normal breast fibroblasts and promoted their pro-carcinogenic effects, both in vitro and in orthotopic tumor xenografts. By contrast, specific DNMT1 knockdown normalized breast myofibroblasts and repressed their cancer-promoting properties. These effects were sustained through inhibition of the IL-6/STAT3/NF-κB epigenetic cancer/inflammation positive feedback loop. Furthermore, we have shown that DNMT1-related activation of breast fibroblasts is mediated through upregulation of the RNA binding protein AUF1, which is also part of the loop. The present data demonstrate the critical function of DNMT1 in breast cancer-related sustained activation of breast stromal fibroblasts.

Eugenol potentiates cisplatin anti-cancer activity through inhibition of ALDH-positive breast cancer stem cells and the NF-κB signaling pathway

Triple-negative breast tumors are very aggressive and contain relatively high proportion of cancer stem cells, and are resistant to chemotherapeutic drugs including cisplatin. To overcome these limitations, we combined eugenol, a natural polyphenolic molecule, with cisplatin to normalize cisplatin mediated toxicity and potential drug resistance. Interestingly, the combination treatment provided significantly greater cytotoxic and pro-apoptotic effects as compared to treatment with eugenol or cisplatin alone on several triple-negative breast cancer cells both in vitro and in vivo. Furthermore, adding eugenol to cisplatin potentiated the inhibition of breast cancer stem cells by inhibiting ALDH enzyme activity and ALDH-positive tumor initiating cells. We provide also clear evidence that eugenol potentiates cisplatin inhibition of the NF-κB signaling pathway. Indeed, the binding of NF-κB to its cognate binding sites present in the promoters of IL-6 and IL-8 was dramatically reduced, which led to potent down-regulation of the IL-6 and IL-8 cytokines upon combination treatment relative to the single agents. Similar effects were observed on proliferation, inhibition of epithelial-to-mesenchymal transition and stemness markers in tumor xenografts. These results provide strong preclinical justification for combining cisplatin with eugenol as therapeutic approach for triple-negative breast cancers through targeting the resistant ALDH-positive cells and inhibiting the NF-κB pathway.

Abstract 5937: Obesity-induced destabilization of p16INK4A promotes the procarcinogenic effects of breast stromal adipocytes through miR-141/miR-146b-5p-dependent inhibition of leptin

Obesity, a disease linked to increased number of adipocytes in various tissues, is increasingly recognized as a risk factor for the development of breast cancer. However, the molecular basis of adipocyte-related breast carcinogenesis remains elusive. In this study, we established and characterized normal stromal adipocytes from post-plastic surgery of breast tissues from obese and lean women. We have shown that adipocytes from obese women express low level of the tumor suppressor p16 protein, have higher secretion of various adipokines and higher invasion and migration capabilities as compared to adipocytes from lean women. In addition, down-regulation of p16INK4A by shRNA in adipocytes from lean women increased the expression/secretion levels of various adipokines including leptin, activated breast adipocytes and enhanced their migration/invasion abilities. Consequently, media conditioned with p16-deficient adipocytes or adipocytes from obese women promote epithelial-to-mesenchymal-transition in normal breast luminal cells in a leptin-dependent manner and induced tumor growth in vivo. Indeed, p16INK4A suppresses Leptin at the mRNA level through miR-141 and miR-146b-5p, which inhibits Leptin expression through a specific sequence at the Leptin 3’UTR. These results show the existence of active adipocytes in the mammary gland of obese women in absence of breast cancer cells and provide the first indication that p16INK4A through targeting miR-141 and miR-146b-5p suppresses Leptin and its procarcinogenic effects. This indicates that p16 pathway has non-cell-autonomous tumor suppressor function in breast stromal adipocytes.

Note: This abstract was not presented at the meeting.

Citation Format: Huda H. Alkhalaf, Abdelilah Aboussekhra. Obesity-induced destabilization of p16INK4A promotes the procarcinogenic effects of breast stromal adipocytes through miR-141/miR-146b-5p-dependent inhibition of leptin [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 5937. doi:10.1158/1538-7445.AM2017-5937

p16INK4A enhances the transcriptional and the apoptotic functions of p53 through DNA-dependent interaction

p16^INK4A and p53 are two important tumor suppressor proteins that play essential roles during cell proliferation and aging through regulating the expression of several genes. Here, we report that p16^INK4A and p53 co-regulate a plethora of transcripts. Furthermore, both proteins colocalize in the nucleus of human primary skin fibroblasts and breast luminal cells, and form a heteromer whose level increases in response to genotoxic stress as well as aging of human fibroblasts and various mouse organs. CDK4 is also present in this heteromeric complex, which is formed only in the presence of DNA both in vitro using pure recombinant proteins and in vivo. We have also shown that p16^INK4A enhances the binding efficiency of p53 to its cognate sequence presents in the CDKN1A promoter in vitro, and both proteins are present at the promoters of CDKN1A and BAX in vivo. Importantly, the fourth ankyrin repeat of p16^INK4A and the C-terminal domain of p53 were necessary for the physical association between these two proteins. The physiologic importance of this association was revealed by the inability of cancer-associated p16^INK4A mutants to interact with p53 and to transactivate the expression of its major targets CDKN1A and BAX in the p16-defective U2OS cells expressing either wild-type or mutated p16^INK4A . Furthermore, the association between p16^INK4A and p53 was capital for their nuclear colocalization, the X-ray-dependent induction of p21 and Bax proteins as well as the induction of apoptosis in various types of cells. Together, these results show DNA-dependent physical interaction between p16^INK4A and p53.

miR-146b-5p mediates p16-dependent repression of IL-6 and suppresses paracrine procarcinogenic effects of breast stromal fibroblasts

Increasing evidence support the critical roles of active stromal fibroblasts in breast cancer development and spread. However, the mediators and the mechanisms of regulation are still not well defined. We have shown here that the tumor suppressor p16^INK4A protein inhibits the pro-carcinogenic effects of breast stromal fibroblasts through repressing the expression/secretion of IL-6. Indeed, p16^INK4A suppresses IL-6 at the mRNA and protein levels. This effect is mediated trough miR-146b-5p, which inhibits IL-6 expression through a specific sequence at the IL-6 3′UTR. In addition, we present clear evidence that miR-146b-5p inhibition is sufficient to transactivate breast stromal fibroblasts, which promote epithelial-to-mesenchymal-transition in breast cancer cells in a paracrine manner. By contrast, ectopic expression of miR-146b-5p in active fibroblasts abrogated their pro-carcinogenic effects. The physiological importance of miR-146b-5p inhibition was revealed by showing that the levels of pre-miR-146b-5p as well as its mature form are reduced in cancer-associated fibroblasts as compared with their normal adjacent counterparts from cancer-free tissues isolated from the same patients. Interestingly, treatment of active breast stromal fibroblasts with curcumin increased the level of the p16^INK4A coding CDKN2A mRNA and miR-146b-5p and suppressed IL-6, which confirms the repressive effect of these two tumor suppressor molecules on IL-6, and shows the possible “normalization” of cancer-related active fibroblasts. These results show that miR-146b-5p has non-cell-autonomous tumor suppressor function through inhibition of IL-6, suggesting that targeting this microRNA in breast stromal fibroblasts could be of great therapeutic value.

CHEK2 represses breast stromal fibroblasts and their paracrine tumor-promoting effects through suppressing SDF-1 and IL-6

Background

Active fibroblasts, the predominant and the most active cells of breast cancer stroma, are responsible for tumor growth and spread. However, the molecular mediators and pathways responsible for stromal fibroblast activation, and their paracrine pro-carcinogenic effects are still not well defined. The CHEK2 tumor suppressor gene codes for a protein kinase, which plays important roles in the cellular response to various genotoxic stresses.

Methods

Immunoblotting, quantitative RT-PCR and Immunofluorescence were used to assess the expression of CHEK2 in different primary breast fibroblasts and in tissues. The effect of CHEK2 on the expression and secretion of SDF-1 and IL-6 was evaluated by immunoblotting and ELISA. The WST-1 colorimetric assay was used to assess cell proliferation, while the BD BioCoat Matrigel invasion chambers were utilized to determine the effects of CHEK2 on the migratory and the invasiveness capacities of breast stromal fibroblasts as well as breast cancer cells.

Results

We have shown that CHEK2 is down-regulated in most cancer-associated fibroblasts (CAFs) as compared to their corresponding tumor counterpart fibroblasts (TCFs) at both the mRNA and protein levels. Interestingly, CHEK2 down-regulation using specific siRNA increased the expression/secretion of both cancer-promoting cytokines SDF-1 and IL-6, and transdifferentiated stromal fibroblasts to myofibroblasts. These cells were able to enhance the proliferation of non-cancerous epithelial cells, and also boosted the migration/invasion abilities of breast cancer cells in a paracrine manner. The later effect was SDF-1/IL-6-dependent. Importantly, ectopic expression of CHEK2 in active CAFs converted these cells to a normal state, with lower migration/invasion capacities and reduced paracrine pro-carcinogenic effects.

Conclusion

These results indicate that CHEK2 possesses non-cell-autonomous tumor suppressor functions, and present the Chk2 protein as an important mediator in the functional interplay between breast carcinomas and their stromal fibroblasts.

PAC down-regulates estrogen receptor alpha and suppresses epithelial-to-mesenchymal transition in breast cancer cells

Background

Triple-negative breast cancer (TNBC) is an aggressive histological subtype with limited treatment options and very poor prognosis following progression after standard chemotherapeutic regimens. Therefore, novel molecules and therapeutic options are urgently needed for this category of patients. Recently, we have identified PAC as a curcumin analogue with potent anti-cancer features.

Methods

HPLC was used to evaluate the stability of PAC and curcumin in PBS and also in circulating blood. Cytotoxicity/apoptosis was assessed in different breast cancer cell lines using propidium iodide/annexinV associated with flow cytometry. Furthermore, immunoblotting analysis determined the effects of PAC on different oncogenic proteins and pathways. Additionally, the real time xCELLigence RTCA technology was applied to investigate the effect of PAC on the cellular proliferation, migration and invasion capacities.

Results

PAC is more stable than curcumin in PBS and in circulating blood. Furthermore, we have shown differential sensitivity of estrogen receptor-alfa positive (ERα⁺) and estrogen receptor alfa negative (ERα⁻) breast cancer cells to PAC, which down-regulated ERα in both cell types. This led to complete disappearance of ERα in ERα⁻ cells, which express very low level of this receptor. Interestingly, specific down-regulation of ERα in receptor positive cells increased the apoptotic response of these cells to PAC, confirming that ERα inhibits PAC-dependent induction of apoptosis, which could be mediated through ERα down-regulation. Additionally, PAC inhibited the proliferation and suppressed the epithelial-to-mesenchymal transition process in breast cancer cells, with higher efficiency on the TNBC subtype. This effect was also observed in vivo on tumor xenografts. Additionally, PAC suppressed the expression/secretion of 2 important cytokines IL-6 and MCP-1, and consequently inhibited the paracrine procarcinogenic effects of breast cancer cells on breast stromal fibroblasts.

Conclusion

These results indicate that PAC could be considered as important candidate for future therapeutic options against the devastating TNBC subtype.

Abstract 2907: Eugenol potentiates the effect of cisplatin on cancer stem-like cells through targeting the NF-κB pathway

Triple-negative subtype of breast cancer (TNBC) contains exclusively tumorigenic and often endowed with self-renewing and resistance to cytotoxic chemotherapy, such as, paclitaxel resulting in relative increases in CSCs phenotype. Signaling through NF-kB may be essential for the CSCs self-renewal and could present potential target for novel treatment in breast cancer patients. We explored the possible involvement of NF-kB pathway that contribute to the functions and maintenance of breast CSCs and targeting this pathway by cisplatin combining with a natural product eugenol both in vitro and in vivo, using estrogen dependent (MCF-7) and independent (MDA-MB-231, MDA-MB-468 and BT-20) cell lines and xenografted both subcutaneous and orthotopic (fat pad) sites in nude mice. Chromatin immunoprecipitation (ChIP) assay was utilized to assess the NF-kB associated DNA binding capacity in promoter region. Surprisingly, neither cisplatin nor eugenol was capable of complete diminishing the CSCs populations. Cisplatin alone administration partially diminished apoptosis, mammospheres formation, aldehyde dehydrogenase 1 (ALDH1) activity, invasion and growth on nude mice. We observed cisplatin-induced activation of NF-kB associated with survival and regrowth of mamospheres. For effective elimination of CSCs phenotype by cisplatin, we cotreated cells with eugenol. Combination of eugenol and cisplatin significantly eradicated cisplatin induced NF-kB DNA binding capability assed by EMSA and ChIP assays, which was associated with abrogated apoptosis, mammospheres formation, ALDH1 activity and invasion. In vivo, combination therapy reduced the tumor size in synergistic manner. This was possibly due to induction of apoptosis, inhibition of proliferation, angiogenesis and downregulation of cisplatin-induced expression of proteins of NF-kB target genes. Although treatment of mammospheres by cisplatin partially induced the CSCs population through interleukin (IL)-6 pathway, however, only coadministration of eugenol and cisplatin reduced the numbers of CSCs to virtually undeletable levels in vitro and in vivo. Our data suggest that eugenol may be well suited to increase targeting of breast CSCs by cisplatin.

Citation Format: Syed S. Islam, Al-Sharif Ibtehaj, Sultan Ahlam, Abdelilah Aboussekhra. Eugenol potentiates the effect of cisplatin on cancer stem-like cells through targeting the NF-κB pathway. [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 2907.

Abstract 757: p16INK4A negatively regulates Leptin through miR-141 and miR-146b-5p in breast stromal adipocytes

Obesity, a disease linked to increased number of adipocytes in various tissues, is increasingly recognized as a risk factor for the development of breast cancer. Obesity has been reported to be associated with the occurrence of larger, more advanced tumors and aggressive cancer pathological features, including lymph node metastasis, advanced tumor stage, and high grade. Accumulating recent evidence highlights the tumor-surrounding adipose tissue as a key component of breast cancer progression. However, the molecular basis of adipocyte-related breast carcinogenesis remains elusive. To shed light on this important phenomenon, we investigated the autocrine and paracrine roles of the tumor suppressor p16 INK4A protein in adipocytes. We have found that down-regulation of p16INK4A by specific shRNA in breast adipocytes enhanced their migration/invasion abilities and increased the expression/secretion levels of various adipokines including leptin. In addition, we have shown that p16INK4A protein inhibits the pro-carcinogenic effects of breast stromal adipocytes in vitro and in tumor xenografts through repressing the expression/secretion of Leptin. Indeed, p16INK4A suppresses Leptin at the mRNA level. This effect is mediated trough miR-141 and miR-146b-5p, which inhibits Leptin expression through a specific sequence at the Leptin 3’UTR. In addition, we present clear evidence that down-regulation of p16INK4A is sufficient to trans-activate breast stromal adipocytes, which promote epithelial-to-mesenchymal-transition in normal breast luminal cells in a leptin-dependent manner.

These results provide the first indication that p16INK4A and miR-141 and miR-146b-5p represses Leptin and its procarcinogenic effects in breast stromal adipocytes. This indicates that p16 pathway has non-cell-autonomous tumor suppressor function.

Citation Format: Huda H. Alkhalaf, Abdelilah Aboussekhra. p16INK4A negatively regulates Leptin through miR-141 and miR-146b-5p in breast stromal adipocytes. [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 757.

Overexpression of sonic hedgehog in the triple negative breast cancer: clinicopathological characteristics of high burden breast cancer patients from Bangladesh

Dysregulation of Hedgehog (Hh) signaling pathway has been documented in mammary gland development and breast cancer (BC) progression. Despite the remarkable progress in therapeutic interventions, BC related mortality in Bangladesh increased in the last decade. Triple negative breast cancer (TNBC) still presents a critical therapeutic challenge. Thus effective targeted therapy is urgently needed. In this study, we report the clinicopathological characteristics and prognosis of BC patients from Bangladesh. Routine immunohistochemical analysis and high throughput RNA-Seq data from the TCGA library were used to analyze the expression pattern and association of high and low level of Shh expression in a collection of BC patients with a long-term follow-up. High levels of Shh were observed in a subset of BC tumors with poor prognostic pathological features. Higher level of Shh expression correlated with a significantly poorer overall survival of patients compared with patients whose tumors expressed a low level of Shh. These data support the contention that Shh could be a novel biomarker for breast cancer that is involved in mediating the aggressive phenotype of BC. We propose that BC patients exhibiting a higher level of Shh expression, representing a subset of BC patients, would be amenable to Shh targeted therapy.

Abstract P4-04-26: Down-regulation of p16INK4a inhibits miR-146b-5p and modulates IL-6 in breast stromal fibroblasts

Breast cancer is a major health problem that threatens millions of women’s lives each year worldwide. Cancer-associated fibroblasts (CAFs), which constitute the major component of the tumor stroma, have been reported to actively contribute to tumor cells proliferation and invasion. Recently, we have shown down-regulation of the tumor suppressor p16INK4a protein in breast cancer-associated fibroblasts. Moreover, p16INK4a deficiency led to the activation of the stromal fibroblasts, which express/secrete elevated levels of IL-6, a major player in breast carcinogenesis. We have shown here that p16INK4a negatively regulates the IL-6 expression and secretion in breast stromal fibroblasts. Furthermore, we have shown that IL-6 is playing a major role in mediating the paracrine pro-carcinogenic effect of p16-deficient fibroblasts. We have also shown that p16INK4a inhibits the IL-6 expression in a miRNA-146b-5p-dependent manner. Importantly, we present clear evidence that miR-146b-5p inhibition activates breast stromal fibroblast. Indeed, miR-146b-5p inhibition increased the migration/invasion abilities of breast stromal fibroblasts, and the paracrine effect of these cells on the migration/invasion of breast cancer cells. Furthermore, miR-146b-5p-deficient stromal fibroblasts triggered epithelial to mesenchymal transition in breast cancer cells in a paracrine manner. In addition, we have shown that miR-146b-5p is down-regulated in CAFs as compared to their adjacent counterpart fibroblasts. These results indicate that p16INK4a negatively regulates IL-6 through the activation of miR-146b-5p, which plays a major role in repressing breast stromal fibroblasts and inhibiting their pro-carcinogenic effects. This indicates that miR-146b-5p has cell-non-autonomous tumor suppressor function. Therefore, this miRNA could be of great therapeutic value.

Citation Format: Mysoon M Al-Ansari, Abdelilah Aboussekhra. Down-regulation of p16INK4a inhibits miR-146b-5p and modulates IL-6 in breast stromal fibroblasts [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-04-26.

p16(INK4A) inhibits the pro-metastatic potentials of osteosarcoma cells through targeting the ERK pathway and TGF-β1

Extracellular signal-regulated kinase (ERK) is a downstream component of the evolutionarily conserved mitogen-activated protein kinase-signaling pathway, which controls the expression of a plethora of genes implicated in various physiological processes. This pathway is often hyper-activated by mutations or abnormal extracellular signaling in different types of human cancer, including the most common primary malignant bone tumor osteosarcomas. p16(INK4A) is an important tumor suppressor gene frequently lost in osteosarcomas, and is associated with the progression of these malignancies. We have shown, here, that the ERK1/2 protein kinase is also activated by p16(INK4A) down-regulation in osteosarcoma cells and normal human as well as mouse cells. This inhibitory effect is associated with the suppression of the upstream kinase MEK1/2, and is mediated via the repression of miR-21-5p and the consequent up-regulation of the MEK/ERK antagonist SPRY2 in osteosarcoma cells. Furthermore, we have shown that p16(INK4) inhibits the migration/invasion abilities of these cells through miR-21-5p-dependent inhibition of ERK1/2. In addition, we present clear evidence that p16(INK4) represses the paracrine pro-migratory effect of osteosarcoma cells on stromal fibroblasts through the inhibition of the TGF-β1 expression/secretion. This effect is also ERK1/2-dependent, indicating that in addition to their cell-autonomous actions, p16(INK4) and ERK1/2 have also non-cell-autonomous cancer-related functions. Together, these results indicate that the tumor suppressor p16(INK4) protein represses the carcinogenic process of osteosarcoma cells not only as a cell cycle regulator, but also as a negative regulator of pro-carcinogenic/-metastatic pathways. This indicates that targeting the ERK pathway is of utmost therapeutic value.

PAC exhibits potent anti-colon cancer properties through targeting cyclin D1 and suppressing epithelial-to-mesenchymal transition

Colorectal cancer (CRC) is a major cause of cancer morbidity and mortality worldwide. Although response rates and overall survival have been improved in recent years, resistance to multiple drug combinations is inevitable. Therefore, the development of more efficient drugs, with fewer side effects is urgently needed. To this end, we have investigated in the present report the effect of PAC, a novel cucumin analogue, on CRC cells both in vitro and in vivo. We have shown that PAC induces apoptosis, mainly via the internal mitochondrial route, and inhibits cell proliferation through delaying the cell cycle at G2/M phase. Interestingly, the pro-apoptotic effect was mediated through STAT3-dependent down-regulation of cyclin D1 and its downstream target survivin. Indeed, change in the expression level of cyclin D1 modulated the expression of survivin and the response of CRC cells to PAC. Furthermore, using the ChIP assay, we have shown PAC-dependent reduction in the binding of STAT3 to the cyclin D1 promoter in vivo. Additionally, PAC suppressed the epithelial-to-mesenchymal process through down-regulating the mesenchymal markers (N-cadherin, vimentin and Twist1) and inhibiting the invasion/migration abilities of the CRC cells via repressing the pro-migration/invasion protein kinases AKT and ERK1/2. In addition, PAC inhibited tumor growth and repressed the JAK2/STAT3, AKT/mTOR and MEK/ERK pathways as well as their common downstream effectors cyclin D1 and survivin in humanized CRC xenografts. Collectively, these results indicate that PAC has potent anti-CRC effects, and therefore could constitute an effective alternative chemotherapeutic agent, which may consolidate the adjuvant treatment of colon cancer.

The molecular significance of methylated BRCA1 promoter in white blood cells of cancer-free females

BACKGROUND

BRCA1 promoter methylation has been detected in DNA from peripheral blood cells of both breast cancer patients and cancer-free females. However, the pathological significance of this epigenetic change in white blood cells (WBC) remains an open question. In this study, we hypothesized that if constitutional BRCA1 methylation reflects an elevated risk for developing breast cancer (BC), WBC that harbor methylated BRCA1 in both cancer-free females and BC patients should exhibit similar molecular changes.

METHODS

BRCA1 promoter methylation was examined by methylation-specific PCR in WBC from 155 breast cancer patients and 143 cancer-free females. The Human Breast Cancer EpiTect Methyl II Signature PCR Array and The Human Breast Cancer RT2 Profiler™ PCR Array were used to study the methylation status and the expression profile of several breast cancer-related genes, respectively. In addition, we used label-free MS-based technique to study protein expression in plasma.

RESULTS

We have shown that 14.2% of BC patients and 9.1% of cancer-free females (carriers) harbored methylated BRCA1 promoter in their WBC. Interestingly, 66.7% of patients harbored methylated BRCA1 promoter in both WBC and tumors. Importantly, we have shown the presence of epigenetic changes in 9 other BC-related genes in WBC of both patients and carriers. Additionally, BRCA1 and 15 other important cancer -related genes were found to be differentially expressed in WBC from patients and carriers as compared to controls. Furthermore, we have shown that the carriers exhibited a unique plasma protein pattern different from those of BC patients and controls, with 10 proteins similarly differentially expressed in patients and carriers as compared to controls.

CONCLUSIONS

The present results suggest the presence of a strong link between aberrant methylation of the BRCA1 promoter in WBC and breast cancer -related molecular changes, which indicate the potential predisposition of the carriers for developing breast cancer. This informs the potential use of the aberrant methylation of BRCA1 promoter in WBC as a powerful non-invasive molecular marker for detecting predisposed individuals at a very early age.

Obesity is a significant risk factor for breast cancer in Arab women

Background

Breast cancer (BC) is the most common malignancy and the leading cause of cancer-related death amongst women worldwide. The risk factors of this disease are numerous, and their prevalence varies between racial and ethnic groups as well as geographical regions. Therefore, we sought to delineate the association of socio-demographic, reproductive and life-style related risk factors with breast cancer in the Arab population.

Methods

Unmatched case-control study was conducted in the kingdom of Saudi Arabia using 534 cases of histologically confirmed breast cancer and 638 controls. Controls were randomly selected from primary health care visits and were free of breast cancer. Unconditional logistic regression analysis was performed to estimate odds ratios (ORs) and to examine the predictive effect of each factor on risk for BC. All study participants were interviewed by trained interviewers at hospital (cases) or at primary health care centers (controls).

Results

A total of 1172 women were eligible for this study, of which 281 (24.0%) were aged ≤35 years, 22.9% illiterate, 43.6% employed, 89.5% married, and 38.1% were obese. Grade III tumors constituted 38.4% of cases. Tumor stage I was 7.5%; II, 50.7%; II, 30.9%; IV, 11.1%. We have shown strong association between breast cancer among Arab females and obesity (OR =2.29, 95% CI 1.68-3.13), positive family history of breast cancer (OR =2.31, 95% CI 1.60 – 3.32), the use of hormonal replacement therapy (OR =2.25, 95% CI 1.65 – 3.08), post-menopause (OR =1.72, 95% CI 1.25 – 2.38), lack of education (OR =9.09, 95% CI 5.88 – 14.29), and never breastfeed (OR =1.89, 95% CI 1.19 – 2.94).

Conclusion

These results indicate the presence of classical risk factors established in the western countries, and also some specific ones, which may result from genetic and/or environmental factors. Thereby, these findings will be of great value to establish adequate evidence-based awareness and preventative measures in the Arab world.

MicroRNA-141 and microRNA-146b-5p inhibit the prometastatic mesenchymal characteristics through the RNA-binding protein AUF1 targeting the transcription factor ZEB1 and the protein kinase AKT

miR-141 and miR-146b-5p are two important tumor suppressor microRNAs, which control several cancer-related genes and processes. In the present report, we have shown that these microRNAs bind specific sites at the 3'-untranslated region (UTR) of the mRNA-binding protein AUF1, leading to its down-regulation. This inverse correlation between the levels of these microRNAs and AUF1 has been identified in various osteosarcoma cell lines. Additionally, we present clear evidence that AUF1 promotes mesenchymal features in osteosarcoma cells and that miR-141 and miR-146b-5p suppress this prometastatic process through AUF1 repression. Indeed, both microRNAs suppressed the invasion/migration and proliferation abilities of osteosarcoma cells through inhibiting the AKT protein kinase in an AUF1-dependent manner. We have also shown that AUF1 binds to and stabilizes the mRNA of the AKT activator phosphoinositide-dependent kinase-1 (PDK1). Furthermore, miR-141 and miR-146b-5p positively regulate the epithelial markers (E-cadherin and Epcam) and repress the mesenchymal markers (N-cadherin, Vimentin, Twist2, and ZEB1). These effects were mediated via the repression of the epithelial-to-mesenchymal inducer ZEB1 through targeting AUF1, which binds the 3'-UTR of the ZEB1 mRNA and reduces its turnover. These results indicate that at least some tumor suppressor functions of miR-141 and miR-146b-5p are mediated through the repression of the oncogenic potentials of AUF1. Therefore, these 3'-UTR-directed post-transcriptional gene expression regulators constitute promising new targets for diagnostic and/or therapeutic interventions.

The cytokine IL-6 reactivates breast stromal fibroblasts through transcription factor STAT3-dependent up-regulation of the RNA-binding protein AUF1

The development and spread of mammary carcinomas require synergetic interplay between tumor cells and their microenvironment through paracrine secretions, which are still not well defined. We have shown here that interleukin-6 (IL-6), either recombinant or secreted from highly invasive breast cancer cells, down-regulates the tumor suppressor proteins p16(INK4A), p21(WAF1), and p53 and activates breast stromal fibroblasts in a paracrine manner. The formation of myofibroblasts requires p16(INK4A) down-regulation and the activation of the JAK2/STAT3 pathway. Indeed, the transcription factor STAT3 positively controls the expression of the three major myofibroblast markers, SDF-1, α-smooth muscle actin (α-SMA), and TGF-β1, and mediates IL-6-related down-regulation of p16(INK4A), p21(WAF1), and p53 as well as the activation of stromal fibroblasts. Importantly, these effects were mediated through STAT3-dependent up-regulation of the mRNA-binding protein AUF1, whose promoter contains three canonical STAT3 binding sites. AUF1 binds the SDF-1, α-SMA, TGF-β1, and IL-6 mRNAs and reduces their turnover. Consequently, specific AUF1 down-regulation inhibits IL-6-dependent activation of breast stromal fibroblasts, whereas AUF1 ectopic expression of p37(AUF1) activated these cells and enhanced their paracrine induction of epithelial-to-mesenchymal transition in breast cancer cells, which shows a non-cell-autonomous oncogenic function of AUF1. Together, these results demonstrate a major role of IL-6 in activating breast stromal fibroblasts through STAT3-dependent AUF1 induction.

Breast stromal fibroblasts from histologically normal surgical margins are pro-carcinogenic

There is evidence that normal breast stromal fibroblasts (NBFs) suppress tumour growth, while cancer-associated fibroblasts (CAFs) promote tumourigenesis through functional interactions with tumour cells. Little is known about the biology and the carcinogenic potential of stromal fibroblasts present in histologically normal surgical margins (TCFs). Therefore, we first undertook gene expression analysis on five CAF/TCF pairs from breast cancer patients and three NBF samples (derived from mammoplasties). This comparative analysis revealed variation in gene expression between these three categories of cells, with a TCF-specific gene expression profile. This variability was higher in TCFs than in their paired CAFs and also NBFs. Cytokine arrays show that TCFs have a specific secretory cytokine profile. In addition, stromal fibroblasts from surgical margins expressed high levels of α-SMA and SDF-1 and exhibited higher migratory/invasiveness abilities. Indirect co-culture showed that TCF cells enhance the proliferation of non-cancerous mammary epithelial cells and the epithelial-to-mesenchymal transition of breast cancer cells. Moreover, TCF and CAF cells increased the level of PCNA, MMP-2 and the phosphorylated/activated form of Akt in normal breast luminal fibroblasts in a paracrine manner. Furthermore, TCFs were able to promote the formation and growth of humanized orthotopic breast tumours in nude mice. Interestingly, these TCF phenotypes and the extent of their effects were intermediate between those of NBFs and CAFs. Together, these results indicate that stromal fibroblasts located in non-cancerous tissues exhibit a tumour-promoting phenotype, indicating that their presence post-surgery may play important roles in cancer recurrence.

Caffeine mediates sustained inactivation of breast cancer-associated myofibroblasts via up-regulation of tumor suppressor genes

Background

Active cancer-associated fibroblasts (CAFs) or myofibroblasts play important roles not only in the development and progression of breast carcinomas, but also in their prognosis and treatment. Therefore, targeting these cells through suppressing their supportive procarcinogenic paracrine effects is mandatory for improving the current therapies that are mainly targeting tumor cells. To this end, we investigated the effect of the natural and pharmacologically safe molecule, caffeine, on CAF cells and their various procarcinogenic effects.

Methodology/Principal Findings

We have shown here that caffeine up-regulates the tumor suppressor proteins p16, p21, p53 and Cav-1, and reduces the expression/secretion of various cytokines (IL-6, TGF-β, SDF-1 and MMP-2), and down-regulates α-SMA. Furthermore, caffeine suppressed the migratory/invasiveness abilities of CAF cells through PTEN-dependent Akt/Erk1/2 inactivation. Moreover, caffeine reduced the paracrine pro-invasion/−migration effects of CAF cells on breast cancer cells. These results indicate that caffeine can inactivate breast stromal myofibroblasts. This has been confirmed by showing that caffeine also suppresses the paracrine pro-angiogenic effect of CAF cells through down-regulating HIF-1αand its downstream effector VEGF-A. Interestingly, these effects were sustained in absence of caffeine.

Conclusion/Significance

The present findings provide a proof of principle that breast cancer myofibroblasts can be inactivated, and thereby caffeine may provide a safe and effective prevention against breast tumor growth/recurrence through inhibition of the procarcinogenic effects of active stromal fibroblasts.

Eugenol triggers apoptosis in breast cancer cells through E2F1/survivin down-regulation

Background

Breast cancer is a major health problem that threatens the lives of millions of women worldwide each year. Most of the chemotherapeutic agents that are currently used to treat this complex disease are highly toxic with long-term side effects. Therefore, novel generation of anti-cancer drugs with higher efficiency and specificity are urgently needed.

Methods

Breast cancer cell lines were treated with eugenol and cytotoxicity was measured using the WST-1 reagent, while propidium iodide/annexinV associated with flow cytometry was utilized in order to determine the induced cell death pathway. The effect of eugenol on apoptotic and pro-carcinogenic proteins, both in vitro and in tumor xenografts was assessed by immunoblotting. While RT-PCR was used to determine eugenol effect on the E2F1 and survivin mRNA levels. In addition, we tested the effect of eugenol on cell proliferation using the real-time cell electronic sensing system.

Results

Eugenol at low dose (2 μM) has specific toxicity against different breast cancer cells. This killing effect was mediated mainly through inducing the internal apoptotic pathway and strong down-regulation of E2F1 and its downstream antiapoptosis target survivin, independently of the status of p53 and ERα. Eugenol inhibited also several other breast cancer related oncogenes, such as NF-κB and cyclin D1. Moreover, eugenol up-regulated the versatile cyclin-dependent kinase inhibitor p21^WAF1 protein, and inhibited the proliferation of breast cancer cells in a p53-independent manner. Importantly, these anti-proliferative and pro-apoptotic effects were also observed in vivo in xenografted human breast tumors.

Conclusion

Eugenol exhibits anti-breast cancer properties both in vitro and in vivo, indicating that it could be used to consolidate the adjuvant treatment of breast cancer through targeting the E2F1/survivin pathway, especially for the less responsive triple-negative subtype of the disease.

The cyclin-dependent kinase inhibitor p16INK4a physically interacts with transcription factor Sp1 and cyclin-dependent kinase 4 to transactivate microRNA-141 and microRNA-146b-5p spontaneously and in response to ultraviolet light-induced DNA damage

p16(INK4a) is a tumor suppressor protein involved in several stress-related cellular responses, including apoptosis. Recent lines of evidence indicate that p16(INK4a) is also a modulator of gene expression. However, the molecular mechanisms underlying this novel function are still obscure. Here, we present clear evidence that p16(INK4a) modulates the levels of various microRNAs, with marked positive effect on miR-141 and miR-146b-5p. This effect is mediated through the formation of the p16-CDK4-Sp1 heterocomplex, which binds to Sp1 consensus-binding motifs present in the promoters of miR-141 and miR-146b-5p, and it enables their transcription. In addition, we have shown that p16(INK4a) interacts with Sp1 through the fourth ankyrin repeat, which is crucial for Sp1 binding to the miR-141 and miR-146b-5p promoters and their transcriptional activation. The physiological importance of this association was revealed by the inability of cancer-related p16(INK4a) mutants to interact with Sp1. Moreover, we have shown p16-CDK4-Sp1-dependent up-regulation of miR-141 and miR-146b-5p following UV light-induced DNA damage and the role of these two microRNAs in mediating p16-related induction of apoptosis in response to this genotoxic stress. Together, these results indicate that p16(INK4a) associates with CDK4 not only to inhibit the cell cycle but also to enable the transcription of two important onco-microRNAs, which act as downstream effectors.

Prevalence of PIK3CA mutations and the SNP rs17849079 in Arab breast cancer patients

Carcinomas initiate and progress due to genetic and epigenetic alterations in epithelial cells. However, recently, these alterations have also been reported in stromal fibroblasts. The gain-of-function mutations in the PI3K p110 catalytic subunit (PIK3CA) have been identified in many cancers with a current global incidence of 26% (18-40%) in breast carcinomas. We analyzed the mutational frequency of PIK3CA of three hotspots (exons 1, 9, and 20) in 81 primary invasive breast cancers (BC) and 25 cultured breast cancer-associated fibroblast (CAF) samples by Sanger sequencing in Arab breast cancer patients. Associations between the incidence of any PIK3CA mutation and several clinicopathologic characteristics were assessed using chi-square tests for categorical or t test for continuous variables. Furthermore, survival curves were estimated using the Kaplan-Meier method with the log rank test to evaluate the significance of their differences. We identified a total of 21 PIK3CA missense mutations with a frequency of 25.9%. The majority of the mutations, 17 out of 21 (81%), were in exon 20 (p.His1047Arg, p.His1047Lys, p.Thr1025Ala, p.Gly1049Arg, p.Asp1056Asn) while the remainder, 4 out of 21 (19%) were in exon 9 (p.Glu545Lys). PIK3CA mutations were significantly associated with lower grade and hormone receptor positivity. Although there was a favorable trend in overall survival for patients whose tumor harbored PIK3CA mutations, the difference was not statistically significant (P = 0.10). However, we did not detect any somatic mutations in CAFs. Furthermore, we have shown a high prevalence (8.2-fold) of a silent variant (SNP, rs17849079) in the Arab breast cancer population compared with disease-free individuals.

p16(INK4A) positively regulates p21(WAF1) expression by suppressing AUF1-dependent mRNA decay

Background

p16^INK4a and p21^WAF1 are two independent cyclin-dependent kinase inhibitors encoded by the CDKN2A and CDKN1A genes, respectively. p16^INK4a and p21^WAF1 are similarly involved in various anti-cancer processes, including the regulation of the critical G1 to S phase transition of the cell cycle, senescence and apoptosis. Therefore, we sought to elucidate the molecular mechanisms underlying the link between these two important tumor suppressor proteins.

Methodology/Principal Findings

We have shown here that the p16^INK4a protein positively controls the expression of p21^WAF1 in both human and mouse cells. p16^INK4a stabilizes the CDKN1A mRNA through negative regulation of the mRNA decay-promoting AUF1 protein. Immunoprecipitation of AUF1-associated RNAs followed by quantitative RT-PCR indicated that endogenous AUF1 binds to the CDKN1A mRNA in a p16^INK4A-dependent manner. Furthermore, while AUF1 down-regulation increased the expression level of the CDKN1A mRNA, the concurrent knockdown of AUF1 and CDKN2A, using specific silencing RNAs, restored the normal expression of the gene. Moreover, we used EGFP reporter fused to the CDKN2A AU-rich element (ARE) to demonstrate that p16^INK4A regulation of the CDKN1A mRNA is AUF1- and ARE-dependent. Furthermore, ectopic expression of p16^INK4A in p16^INK4A-deficient breast epithelial MCF-10A cells significantly increased the level of p21^WAF1, with no effect on cell proliferation. In addition, we have shown direct correlation between p16^INK4a and p21^WAF1 levels in various cancer cell lines.

Conclusion/Significance

These findings show that p16^INK4a stabilizes the CDKN1A mRNA in an AUF1-dependent manner, and further confirm the presence of a direct link between the 2 important cancer-related pathways, pRB/p16^INK4A and p14^ARF/p53/p21^WAF1.

ATR controls the UV-related upregulation of the CDKN1A mRNA in a Cdk1/HuR-dependent manner

Ultraviolet (UV) light is a carcinogenic agent that upregulates the expression of several genes involved in various cellular processes, including cell cycle checkpoints and apoptosis. The universal cyclin-dependent kinase inhibitor p21(WAF1/Cip1) plays major roles in these processes, and the level of its corresponding message increases several times in response to UV-induced DNA damage. This upregulation is mainly posttranscriptional owing to HuR-dependent mRNA stabilization. Since the protein kinase Atr plays major roles during the cellular response to UV damage, we sought to investigate its possible implication in the stabilization of the p21(WAF1/Cip1) coding mRNA. We have shown that the UV-dependent accumulation of the CDKN1A mRNA is indeed under the control of the Atr protein kinase. Upon UV damage, Atr allows nuclear-cytoplasmic shuttling of the HuR protein, which binds the CDKN1A mRNA and reduces its turnover. This ATR-dependent effect is mediated through UV-related phosphorylation/inactivation of the Cdk1 protein kinase by Atr, which leads to the dissociation of HuR from Cdk1. Indeed, inhibition or shRNA specific knockdown of CDK1 in ATR-deficient cells enhanced the cytoplasmic level of HuR and restored the CDKN1A mRNA upregulation in response to UV damage. These results show that ATR stabilizes the CDKN1A message in response to UV damage through Cdk1-related cytoplasmic accumulation of HuR.