Downregulation of SIAH2, an ubiquitin E3 ligase, is associated with resistance to endocrine therapy in breast cancer

Pterostilbene alleviates abdominal aortic aneurysm via inhibiting macrophage pyroptosis by activating the miR-146a-5p/TRAF6 axis

Pterostilbene (PTE), a natural stilbene found in blueberries and several varieties of grapes, has several pharmacological activities, including anti-inflammatory and antioxidative activities. However, its role in abdominal aortic aneurysm (AAA), which is a severe inflammatory vascular disease, remains incompletely understood. In this study, we investigated the protective effects of natural stilbene PTE on AAA formation and the underlying mechanism. Two AAA mouse models (Ang II-induced model and PPE-induced model) were used to examine the effect of PTE on AAA formation. We showed that PTE administration attenuated AAA formation in mice. Furthermore, we found that PTE significantly inhibited inflammatory responses in mouse aortas, as PTE suppressed macrophage pyroptosis and prevented macrophage infiltration in aortas, resulting in reduced expression of pro-inflammatory cytokines in aortas. We also observed similar results in LPS + ATP-treated Raw 264.7 cells (a macrophage cell line) and primary peritoneal macrophages in vitro. We showed that pretreatment with PTE restrained inflammatory responses in macrophages by inhibiting macrophage pyroptosis. Mechanistically, miR-146a-5p and TRAF6 interventions in vivo and in vitro were used to investigate the role of the miR-146a-5p/TRAF6 axis in the beneficial effect of PTE on macrophage pyroptosis and AAA. We found that PTE inhibited macrophage pyroptosis by miR-146a-5p-mediated suppression of downstream TRAF6 expression. Moreover, miR-146a-5p knockout or TRAF6 overexpression abrogated the protective effect of PTE on macrophage pyroptosis and AAA formation. These findings suggest that miR-146a-5p/TRAF6 axis activation by PTE protects against macrophage pyroptosis and AAA formation. PTE might be a promising agent for preventing inflammatory vascular diseases, including AAA.

Favoring the hierarchical constraint in penalized survival models for randomized trials in precision medicine

BACKGROUND

The research of biomarker-treatment interactions is commonly investigated in randomized clinical trials (RCT) for improving medicine precision. The hierarchical interaction constraint states that an interaction should only be in a model if its main effects are also in the model. However, this constraint is not guaranteed in the standard penalized statistical approaches. We aimed to find a compromise for high-dimensional data between the need for sparse model selection and the need for the hierarchical constraint.

RESULTS

To favor the property of the hierarchical interaction constraint, we proposed to create groups composed of the biomarker main effect and its interaction with treatment and to perform the bi-level selection on these groups. We proposed two weighting approaches (Single Wald (SW) and likelihood ratio test (LRT)) for the adaptive lasso method. The selection performance of these two approaches is compared to alternative lasso extensions (adaptive lasso with ridge-based weights, composite Minimax Concave Penalty, group exponential lasso and Sparse Group Lasso) through a simulation study. A RCT (NSABP B-31) randomizing 1574 patients (431 events) with early breast cancer aiming to evaluate the effect of adjuvant trastuzumab on distant-recurrence free survival with expression data from 462 genes measured in the tumour will serve for illustration. The simulation study illustrates that the adaptive lasso LRT and SW, and the group exponential lasso favored the hierarchical interaction constraint. Overall, in the alternative scenarios, they had the best balance of false discovery and false negative rates for the main effects of the selected interactions. For NSABP B-31, 12 gene-treatment interactions were identified more than 20% by the different methods. Among them, the adaptive lasso (SW) approach offered the best trade-off between a high number of selected gene-treatment interactions and a high proportion of selection of both the gene-treatment interaction and its main effect.

CONCLUSIONS

Adaptive lasso with Single Wald and likelihood ratio test weighting and the group exponential lasso approaches outperformed their competitors in favoring the hierarchical constraint of the biomarker-treatment interaction. However, the performance of the methods tends to decrease in the presence of prognostic biomarkers.

"The ubiquitin ligase SIAH2 is a female-specific regulator of circadian rhythms and metabolism"

Circadian clocks enable organisms to predict and align their behaviors and physiologies to constant daily day-night environmental cycle. Because the ubiquitin ligase Siah2 has been identified as a potential regulator of circadian clock function in cultured cells, we have used SIAH2-deficient mice to examine its function in vivo. Our experiments demonstrate a striking and unexpected sexually dimorphic effect of SIAH2-deficiency on the regulation of rhythmically expressed genes in the liver. The absence of SIAH2 in females, but not in males, altered the expression of core circadian clock genes and drastically remodeled the rhythmic transcriptome in the liver by increasing the number of day-time expressed genes, and flipping the rhythmic expression from nighttime expressed genes to the daytime. These effects are not readily explained by effects on known sexually dimorphic pathways in females. Moreover, loss of SIAH2 in females, not males, preferentially altered the expression of transcription factors and genes involved in regulating lipid and lipoprotein metabolism. Consequently, SIAH2-deficient females, but not males, displayed disrupted daily lipid and lipoprotein patterns, increased adiposity and impaired metabolic homeostasis. Overall, these data suggest that SIAH2 may be a key component of a female-specific circadian transcriptional output circuit that directs the circadian timing of gene expression to regulate physiological rhythms, at least in the liver. In turn, our findings imply that sex-specific transcriptional mechanisms may closely interact with the circadian clock to tailor overt rhythms for sex-specific needs.

The emerging roles of E3 ubiquitin ligases in ovarian cancer chemoresistance

Epithelial cancer of the ovary exhibits the highest mortality rate of all gynecological malignancies in women today, since the disease is often diagnosed in advanced stages. While the treatment of cancer with specific chemical agents or drugs is the favored treatment regimen, chemotherapy resistance greatly impedes successful ovarian cancer chemotherapy. Thus, chemoresistance becomes one of the most critical clinical issues confronted when treating patients with ovarian cancer. Convincing evidence hints that dysregulation of E3 ubiquitin ligases is a key factor in the development and maintenance of ovarian cancer chemoresistance. This review outlines recent advancement in our understanding of the emerging roles of E3 ubiquitin ligases in ovarian cancer chemoresistance. We also highlight currently available inhibitors targeting E3 ligase activities and discuss their potential for clinical applications in treating chemoresistant ovarian cancer patients.

The role of Siah2 in tumorigenesis and cancer therapy

Seven in absentia homolog 2 (Siah2), an RING E3 ubiquitin ligases, has been characterized to play the vital role in tumorigenesis and cancer progression. Numerous studies have determined that Siah2 promotes tumorigenesis in a variety of human malignancies such as prostate, lung, gastric, and liver cancers. However, several studies revealed that Siah2 exhibited tumor suppressor function by promoting the proteasome-mediated degradation of several oncoproteins, suggesting that Siah2 could exert its biological function according to different stages of tumor development. Moreover, Siah2 is subject to complex regulation, especially the phosphorylation of Siah2 by a variety of protein kinases to regulate its stability and activity. In this review, we describe the structure and regulation of Siah2 in human cancer. Moreover, we highlight the critical role of Siah2 in tumorigenesis. Furthermore, we note that the potential clinical applications of targeting Siah2 in cancer therapy.

Novel Insights Into E3 Ubiquitin Ligase in Cancer Chemoresistance

Drug resistance can obstruct successful cancer chemotherapy. The ubiquitin-proteasome pathway has emerged as a crucial player that controls steady-state protein levels regulating multiple biological processes, such as cell cycle, cellular proliferation, apoptosis, and DNA damage response, which are involved in oncogenesis, cancer development, prognosis, and drug resistance. E3 ligases perform the final step in the ubiquitination cascade, and determine which protein becomes ubiquitylated by specifically binding the substrate protein. They are promising drug targets thanks to their ability to regulate protein stability and functions. Although patient survival has increased in recent years with the availability of novel agents, chemoresistance remains a major problem in cancer management. E3 ligases attract increasing attention with advances in chemoresistance knowledge. To explore the role of E3 ligase in cancer chemotherapy resistance and the underlying mechanism, we summarize the growing number of E3 ligases and their substrate proteins, which have emerged as crucial players in cancer chemoresistance and targeted therapies.

Dual mTOR Kinase Inhibitor MLN0128 Sensitizes HR+/HER2+ Breast Cancer Patient-Derived Xenografts to Trastuzumab or Fulvestrant

Purpose: Therapeutic strategies against hormonal receptor-positive (HR⁺)/HER2⁺ breast cancers with poor response to trastuzumab need to be optimized.Experimental Design: Two HR⁺/HER2⁺ patient-derived xenograft (PDX) models named as COH-SC1 and COH-SC31 were established to explore targeted therapies for HER2⁺ breast cancers. RNA sequencing and RPPA (reverse phase protein array) analyses were conducted to decipher molecular features of the two PDXs and define the therapeutic strategy of interest, validated by in vivo drug efficacy examination and in vitro cell proliferation analysis.Results: Estrogen acted as a growth driver of trastuzumab-resistant COH-SC31 tumors but an accelerator in the trastuzumab-sensitive COH-SC1 model. In vivo trastuzumab efficacy examination further confirmed the consistent responses between PDXs and the corresponding tumors. Integrative omics analysis revealed that mammalian target of rapamycin (mTOR) and ERα signaling predominantly regulate tumor growth of the two HR⁺/HER2⁺ PDXs. Combination of the dual mTOR complex inhibitor MLN0128 and anti-HER2 trastuzumab strongly suppressed tumor growth of COH-SC1 PDX accompanied by increasing ER-positive cell population in vivo Instead, MLN0128 in combination with antiestrogen fulvestrant significantly halted the growth of HR⁺/HER2⁺ cancer cells in vitro and trastuzumab-resistant COH-SC31 as well as trastuzumab-sensitive COH-SC1 tumors in vivoConclusions: Compared with the standard trastuzumab treatment, this study demonstrates alternative therapeutic strategies against HR⁺/HER2⁺ tumors through establishment of two PDXs coupled with integrative omics analyses and in vivo drug efficacy examination. This work presents a prototype of future "co-clinical" trials to tailor personalized medicine in clinical practice. Clin Cancer Res; 24(2); 395-406. ©2017 AACR.

HERC4 Is Overexpressed in Hepatocellular Carcinoma and Contributes to the Proliferation and Migration of Hepatocellular Carcinoma Cells

Recently, more and more evidences unveiled that ubiquitin-proteasome system (UPS) makes an important contribution to the occurrence and development of cancer. HERC4 is one identified Ubiqutin ligase E3, a member of UPS. Although some studies showed that HERC4 abnormally expresses in many cancer cells, till now, nothing has been reported about the function of HERC4 in the development of hepatoma carcinoma. To this end, in this study, we studied the function of HERC4 for the first time in hepatoma carcinoma cells. We detected the expression of HERC4 in tumor and normal tissues, and in hepatoma carcinoma cell lines by using qRT-PCR, Western blot, immunohistochemistry, and immunofluorescence. The data showed that tumor tissues expressed higher HERC4 than normal ones. HERC4 was expressed, although to a different extent, in hepatoma carcinoma cell lines. Colony formation assay, CCK-8 assay, EdU assay, wound healing assay, and FACS indicated that HERC4 plays a role in cell proliferative and migration ability. HERC4 overexpression increases the proliferative and migration ability and reduces apoptosis of hepatoma carcinoma cells; in contrast, knockdown of HERC4 decreases the proliferative and migration ability and increases the apoptosis rate of hepatoma carcinoma cells. Taken together, our findings showed that HERC4 has an effect on the occurrence and development of hepatoma carcinoma by promoting hepatoma carcinoma cell proliferation and migration, and by reducing cell apoptosis, further providing another therapeutic target for the intervention of related diseases.

The substrate binding domains of human SIAH E3 ubiquitin ligases are now crystal clear

BACKGROUND

Seven in absentia homologs (SIAHs) comprise a family of highly conserved E3 ubiquitin ligases that play an important role in regulating signalling pathways in tumorigenesis, including the DNA damage repair and hypoxia response pathways. SIAH1 and SIAH2 have been found to function as a tumour repressor and a proto-oncogene, respectively, despite the high sequence identity of their substrate binding domains (SBDs). Ubiquitin-specific protease USP19 is a deubiquitinase that forms a complex with SIAHs and counteracts the ligase function. Much effort has been made to find selective inhibitors of the SIAHs E3 ligases. Menadione was reported to inhibit SIAH2 specifically.

METHODS

We used X-ray crystallography, peptide array, bioinformatic analysis, and biophysical techniques to characterize the structure and interaction of SIAHs with deubiquitinases and literature reported compounds.

RESULTS

We solved the crystal structures of SIAH1 in complex with a USP19 peptide and of the apo form SIAH2. Phylogenetic analysis revealed the SIAH/USP19 complex is conserved in evolution. We demonstrated that menadione destabilizes both SIAH1 and SIAH2 non-specifically through covalent modification.

CONCLUSIONS

The SBDs of SIAH E3 ligases are structurally similar with a subtle stability difference. USP19 is the only deubiquitinase that directly binds to SIAHs through the substrate binding pocket. Menadione is not a specific inhibitor for SIAH2.

GENERAL SIGNIFICANCE

The crystallographic models provide structural insights into the substrate binding of the SIAH family E3 ubiquitin ligases that are critically involved in regulating cancer-related pathways. Our results suggest caution should be taken when using menadione as a specific SIAH2 inhibitor.

SIAH ubiquitin ligases regulate breast cancer cell migration and invasion independent of the oxygen status

Seven-in-absentia homolog (SIAH) proteins are evolutionary conserved RING type E3 ubiquitin ligases responsible for the degradation of key molecules regulating DNA damage response, hypoxic adaptation, apoptosis, angiogenesis, and cell proliferation. Many studies suggest a tumorigenic role for SIAH2. In breast cancer patients SIAH2 expression levels correlate with cancer aggressiveness and overall patient survival. In addition, SIAH inhibition reduced metastasis in melanoma. The role of SIAH1 in breast cancer is still ambiguous; both tumorigenic and tumor suppressive functions have been reported. Other studies categorized SIAH ligases as either pro- or antimigratory, while the significance for metastasis is largely unknown. Here, we re-evaluated the effects of SIAH1 and SIAH2 depletion in breast cancer cell lines, focusing on migration and invasion. We successfully knocked down SIAH1 and SIAH2 in several breast cancer cell lines. In luminal type MCF7 cells, this led to stabilization of the SIAH substrate Prolyl Hydroxylase Domain protein 3 (PHD3) and reduced Hypoxia-Inducible Factor 1α (HIF1α) protein levels. Both the knockdown of SIAH1 or SIAH2 led to increased apoptosis and reduced proliferation, with comparable effects. These results point to a tumor promoting role for SIAH1 in breast cancer similar to SIAH2. In addition, depletion of SIAH1 or SIAH2 also led to decreased cell migration and invasion in breast cancer cells. SIAH knockdown also controlled microtubule dynamics by markedly decreasing the protein levels of stathmin, most likely via p27(Kip1). Collectively, these results suggest that both SIAH ligases promote a migratory cancer cell phenotype and could contribute to metastasis in breast cancer.

Annexin-A1 and caldesmon are associated with resistance to tamoxifen in estrogen receptor positive recurrent breast cancer

Tamoxifen therapy resistance constitutes a major cause of death in patients with recurrent estrogen receptor (ER) positive breast cancer. Through high resolution mass spectrometry (MS), we previously generated a 4-protein predictive signature for tamoxifen therapy outcome in recurrent breast cancer. ANXA1 and CALD1, which were not included in the classifier, were however the most differentially expressed proteins. We first evaluated the clinical relevance of these markers in our MS cohort, followed by immunohistochemical (IHC) staining on an independent set of tumors incorporated in a tissue microarray (TMA) and regression analysis in relation to time to progression (TTP), clinical benefit and objective response. In order to assess which mechanisms ANXA1 and CALD1 might been involved in, we performed Ingenuity pathway analysis (IPA) on ANXA1 and CALD1 correlated proteins in our MS cohort. ANXA1 (Hazard ratio [HR] = 1.83; 95% confidence interval [CI]: 1.22-2.75; P = 0.003) and CALD1 (HR = 1.57; 95% CI: 1.04-2.36; P = 0.039) based patient stratification showed significant association to TTP, while IHC staining on TMA showed that both ANXA1 (HR = 1.82; 95% CI: 1.12-3.00; P = 0.016) and CALD1 (HR = 2.29; 95% CI: 1.40-3.75; P = 0.001) expression was associated with shorter TTP independently of traditional predictive factors. Pearson correlation analysis showed that the majority of proteins correlated to ANXA1 also correlated with CALD1. IPA indicated that ANXA1 and CALD1 were associated with ER-downregulation and NFκB signaling. We hereby report that ANXA1 and CALD1 proteins are independent markers for tamoxifen therapy outcome and are associated to fast tumor progression.

Assessment of subnetwork detection methods for breast cancer

Subnetwork detection is often used with differential expression analysis to identify modules or pathways associated with a disease or condition. Many computational methods are available for subnetwork analysis. Here, we compare the results of eight methods: simulated annealing–based jActiveModules, greedy search–based jActiveModules, DEGAS, BioNet, NetBox, ClustEx, OptDis, and NetWalker. These methods represent distinctly different computational strategies and are among the most widely used. Each of these methods was used to analyze gene expression data consisting of paired tumor and normal samples from 50 breast cancer patients. While the number of genes/proteins and protein interactions detected by the eight methods vary widely, a core set of 60 genes and 50 interactions was found to be shared by the subnetworks identified by five or more of the methods. Within the core set, 12 genes were found to be known breast cancer genes.

Seven In Absentia Homolog 2 (SIAH2) downregulation is associated with tamoxifen resistance in MCF-7 breast cancer cells

BACKGROUND

A significant percentage of estrogen receptor (ER)-positive breast cancers are resistant to tamoxifen therapy. Seven in Absentia Homolog 2 (SIAH2), an E3 ubiquitin protein ligase, has been shown to be associated with resistance to antiestrogens. We sought to assess its role in the resistance of a breast cancer cell line, MCF-7, to the ER antagonist, tamoxifen.

MATERIALS AND METHODS

A bioinformatic approach was used for the analysis of SIAH2 expression in breast cancer. MCF-7 and MDA-MB-231, which are ER-positive and -negative breast cancer cell lines, respectively, were used for in vitro studies. SIAH2 and ER-α were selectively knocked down in these cell lines with small-interfering RNAs. Knockdowns were confirmed with Western blot analysis and quantitative real-time polymerase chain reaction. Cells with SIAH2 knockdown were treated with tamoxifen and compared with controls.

RESULTS

Knockdown of SIAH2 followed by treatment with tamoxifen resulted in a significant decrease in the sensitivity of treated ER-positive cells. Of note, knockdown of SIAH2 resulted in downregulation of ER-α, whereas knockdown of ER-α had minimal effect on SIAH2. Consistent with this result, the bioinformatic analysis of clinical data revealed that SIAH2 expression is significantly correlated with ER positivity in human breast cancers, and low SIAH2 expression is associated with a poorer response to tamoxifen.

CONCLUSIONS

SIAH2 appears to be an important modulator of tamoxifen sensitivity in ER-positive MCF-7 cells, mediated, at least in part, through regulation of ER-α expression. Low expression of SIAH2 may be one of the mechanisms that contribute to tamoxifen resistance in human breast cancer.

A common variant in the SIAH2 locus is associated with estrogen receptor-positive breast cancer in the Chinese Han population

Background

Genome-wide association studies (GWAS) have identified many loci associated with breast cancer risk. These studies have primarily been conducted in populations of European descent.

Objective

To determine whether previously reported susceptibility loci in other ethnic groups are also risk factors for breast cancer in a Chinese population.

Method

We genotyped 21 previously reported single nucleotide polymorphisms (SNPs) within a female Chinese cohort of 1203 breast cancer cases and 2525 healthy controls using the Sequenom iPlex platform. Fourteen SNPs passed the quality control test. These SNPs were subjected to statistical analysis for the entire cohort and were further analyzed for estrogen receptor (ER) status. The associations of the SNPs with disease susceptibility were assessed using logistic regression, adjusting for age. The Bonferroni correction was used to conservatively account for multiple testing, and the threshold for statistical significance was P<3.57×10⁻³ (0.05/14).

Result

Although none of the SNPs showed an overall association with breast cancer, an analysis of the ER status of the breast cancer patients revealed that the SIAH2 locus (rs6788895; P = 5.73×10⁻⁴, odds ratio [OR] = 0.81) is associated with ER-positive breast cancer.

Conclusion

A common variant in the SIAH2 locus is associated with ER-positive breast cancer in the Chinese Han population. The replication of published GWAS results in other ethnic groups provides important information regarding the genetic etiology of breast cancer.

LMTK3 is implicated in endocrine resistance via multiple signaling pathways

Resistance to endocrine therapy in breast cancer is common. With the aim of discovering new molecular targets for breast cancer therapy, we have recently identified LMTK3 as a regulator of the estrogen receptor-alpha (ERα) and wished to understand its role in endocrine resistance. We find that inhibition of LMTK3 in a xenograft tamoxifen (Tam)-resistant (BT474) breast cancer mouse model results in re-sensitization to Tam as demonstrated by a reduction in tumor volume. A whole genome microarray analysis, using a BT474 cell line, reveals genes significantly modulated (positively or negatively) after LMTK3 silencing, including some that are known to be implicated in Tam resistance, notably c-MYC, HSPB8 and SIAH2. We show that LMTK3 is able to increase the levels of HSPB8 at a transcriptional and translational level thereby protecting MCF7 cells from Tam-induced cell death, by reducing autophagy. Finally, high LMTK3 levels at baseline in tumors are predictive for endocrine resistance; therapy does not lead to alteration in levels, whereas in patient's plasma samples, acquired LMTK3 gene amplification (copy number variation) was associated with relapse while receiving Tam. In aggregate, these data support a role for LMTK3 in both innate (intrinsic) and acquired (adaptive) endocrine resistance in breast cancer.

Seven in absentia homolog 2 (Siah2) protein is a regulator of NF-E2-related factor 2 (Nrf2)

Under pathological conditions such as ischemia-reperfusion, Nrf2 acts as a key regulator of cellular oxidative response. Provided that Nrf2 is sensitive to hypoxia during ischemia, Nrf2 may affect reactive oxygen species metabolism during reoxygenation. In this study, hypoxia suppressed Nrf2 protein, and its hypoxic suppression was not recovered with knockdown of the Nrf2 repressor Keap1. Moreover, an Nrf2 mutant lacking the Keap1 binding domain was suppressed under hypoxia, suggesting that Keap1 does not contribute to hypoxic Nrf2 suppression. HIF-1α and Siah2 are both key regulators of hypoxic responses. Hypoxia induced the Siah2 protein. Although inhibition or knockdown of Siah2 prevented the suppression of Nrf2, knockdown of HIF-1α did not. Moreover, Siah2 interacted with Nrf2 through a binding motif, suggesting that Siah2 contributes to the suppression of Nrf2. Some cytosolic kinases also play important roles in Nrf2 regulation. In this study, PKC phosphorylates serine residues of Nrf2 during hypoxia. Knockdown of Siah2 rescued hypoxic decreases in an Nrf2 mutant that mimicked phosphorylation at serine 40 or lacked this phosphorylation site, suggesting that Siah2 contributes to the degradation of Nrf2 irrespective of its phosphorylation status. Moreover, knockdown of Siah2 attenuated ubiquitination of the Nrf2 mutant, suggesting that association of Siah2 with Nrf2 causes proteasome-mediated degradation of Nrf2.

Expression and clinical significance of SIAH in laryngeal squamous cell carcinoma

SIAH is widely expressed in lot of kinds of tumors. It plays a significant role in human cancer, but its clinicopathologic and prognostic significance in laryngeal squamous cell carcinoma (LSCC) has not yet been elucidated. The SIAH expression was examined at mRNA and protein levels by real-time quantitative polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemistry in LSCC tissues and adjacent normal larynx tissues. Statistical analyses were applied to test the associations between SIAH expression, clinicopathologic factors, and prognosis. Western blots and RT-PCR showed that the expression level of SIAH was lower in LSCC tissues than in adjacent normal larynx tissues. By immunohistochemical analysis, reduced expression of SIAH was found in 71.67 % LSCCs. After multivariate analysis, along with pathologic differentiation, the protein expression level of SIAH was an independent and significant predictive factor (P = 0.04). Furthermore, patients with SIAH-low tumors had a shorter disease-free survival and overall survival (P = 0.002 and P = 0.045, respectively). Our study suggests that SIAH protein expression is a valuable biomarker for LSCC. Low expression of SIAH is associated with poor disease-free survival and overall survival in LSCC patients.

SIAH ubiquitin ligases target the nonreceptor tyrosine kinase ACK1 for ubiquitinylation and proteasomal degradation

Activated Cdc42-associated kinase 1 (ACK1) is a nonreceptor tyrosine kinase linked to cellular transformation. The aberrant regulation of ACK1 promotes tumor progression and metastasis. Therefore, ACK1 is regarded as a valid target in cancer therapy. Seven in absentia homolog (SIAH) ubiquitin ligases facilitate substrate ubiquitinylation that targets proteins to the proteasomal degradation pathway. Here we report that ACK1 and SIAH1 from Homo sapiens interact in a yeast two-hybrid screen. Protein-protein interaction studies and protein degradation analyses using deletion and point mutants of ACK1 verify that SIAH1 and the related SIAH2 interact with ACK1. The association between SIAHs and ACK1 depends on the integrity of a highly conserved SIAH-binding motif located in the far C-terminus of ACK1. Furthermore, we demonstrate that the interaction of ACK1 with SIAH1 and the induction of proteasomal degradation of ACK1 by SIAH1 are independent of ACK1's kinase activity. Chemical inhibitors blocking proteasomal activity corroborate that SIAH1 and SIAH2 destabilize the ACK1 protein by inducing its proteasomal turnover. This mechanism apparently differs from the lysosomal pathway targeting ACK1 after stimulation with the epidermal growth factor. Our data also show that ACK1, but not ACK1 mutants lacking the SIAH binding motif, has a discernable negative effect on SIAH levels. Additionally, knockdown approaches targeting the SIAH2 mRNA uncover specifically that the induction of SIAH2 expression, by hormonally-induced estrogen receptor (ER) activation, decreases the levels of ACK1 in luminal human breast cancer cells. Collectively, our data provide novel insights into the molecular mechanisms modulating ACK1 and they position SIAH ubiquitin ligases as negative regulators of ACK1 in transformed cells.

Mutual regulation between SIAH2 and DYRK2 controls hypoxic and genotoxic signaling pathways

The ubiquitin E3 ligase SIAH2 is an important regulator of the hypoxic response as it leads to the ubiquitin/proteasomal degradation of prolyl hydroxylases such as PHD3, which in turn increases the stability of hypoxia-inducible factor (HIF)-1α. In the present study, we identify the serine/threonine kinase DYRK2 as SIAH2 interaction partner that phosphorylates SIAH2 at five residues (Ser16, Thr26, Ser28, Ser68, and Thr119). Phosphomimetic and phospho-mutant forms of SIAH2 exhibit different subcellular localizations and consequently change in PHD3 degrading activity. Accordingly, phosphorylated SIAH2 is more active than the wild-type E3 ligase and shows an increased ability to trigger the HIF-1α-mediated transcriptional response and angiogenesis. We also found that SIAH2 knockdown increases DYRK2 stability, whereas SIAH2 expression facilitates DYRK2 polyubiquitination and degradation. Hypoxic conditions cause a SIAH2-dependent DYRK2 polyubiquitination and degradation which ultimately also results in an impaired SIAH2 phosphorylation. Similarly, DYRK2-mediated phosphorylation of p53 at Ser46 is impaired under hypoxic conditions, suggesting a molecular mechanism underlying chemotherapy resistance in solid tumors.

A genome-wide association study identifies a genetic variant in the SIAH2 locus associated with hormonal receptor-positive breast cancer in Japanese

In Japan, breast cancer is the most common cancer among women and the second leading cause of cancer death among women worldwide. To identify genetic variants associated with the disease susceptibility, we performed a genome-wide association study (GWAS) using a total of 1086 Japanese female patients with hormonal receptor-positive (HRP) breast cancer and 1816 female controls. We selected 33 single-nucleotide polymorphisms (SNPs) with suggestive associations in GWAS (P-value of <1 × 10(-4)) as well as 4 SNPs that were previously implicated their association with breast cancer for further replication by an independent set of 1653 cases and 2797 controls. We identified significant association of the disease with a SNP rs6788895 (P(combined) of 9.43 × 10(-8) with odds ratio (OR) of 1.22) in the SIAH2 (intron of seven in absentia homolog 2) gene on chromosome 3q25.1 where the involvement in estrogen-dependent diseases was suggested. In addition, rs3750817 in intron 2 of the fibroblast growth factor receptor 2 gene, which was reported to be associated with breast cancer susceptibility, was significantly replicated with P(combined) of 8.47 × 10(-8) with OR=1.22. Our results suggest a novel susceptibility locus on chromosome 3q25.1 for a HRP breast cancer.

Vascular normalization by loss of Siah2 results in increased chemotherapeutic efficacy

Tumor hypoxia is associated with resistance to antiangiogenic therapy and poor prognosis. The Siah E3 ubiquitin ligases regulate the hypoxic response pathway by modulating the turnover of the master proangiogenic transcription factor hypoxia-inducible factor-1α (Hif-1α). In this study, we show that genetic deficiency in the Siah family member Siah2 results in vascular normalization and delayed tumor growth in an established transgenic model of aggressive breast cancer. Tumors arising in a Siah2(-/-) genetic background showed increased perfusion and pericyte-associated vasculature, similar to that occurring with antiangiogenic therapy. In support of the role of Siah2 in regulating levels of Hif-1α, expression of angiogenic factors was decreased in Siah2(-/-) tumors. Blood vessel normalization in Siah2(-/-) tumors resulted in an increased response to chemotherapy and prolonged survival. Together, our findings offer a preclinical proof of concept that targeting Siah2 is sufficient to attenuate Hif-1α-mediated angiogenesis and hypoxia signaling, thereby improving responses to chemotherapy.

A role for estrogen receptor phosphorylation in the resistance to tamoxifen

About two thirds of all human breast cancer cases are estrogen receptor positive. The drug of first choice for these patients is tamoxifen. However, about half of the recurrences after removal of the primary tumor are or become resistant to this drug. While many mechanisms have been identified for tamoxifen resistance in the lab, at present only a few have been translated to the clinic. This paper highlights the role in tamoxifen resistance of phosphorylation by different kinases on different sites of the estrogen receptor. We will discuss the molecular pathways and kinases that are involved in phosphorylation of ERα and how these affect tamoxifen resistance. Finally, we will elaborate on the clinical translation of these observations and the possibility to predict tamoxifen responses in patient tumor samples before treatment onset. The findings made originally on the bench may translate into a better and personalized treatment of breast cancer patients using an old and safe anticancer drug: tamoxifen.

The expression of the ubiquitin ligase SIAH2 (seven in absentia homolog 2) is mediated through gene copy number in breast cancer and is associated with a basal-like phenotype and p53 expression

Introduction

The seven in absentia homolog 2 (SIAH2) protein plays a significant role in the hypoxic response by regulating the abundance of hypoxia-inducible factor-α; however, its role in breast carcinoma is unclear. We investigated the frequency and expression pattern of SIAH2 in two independent cohorts of sporadic breast cancers.

Methods

Immunohistochemical evaluation of SIAH2protein expression was conducted in normal breast tissues and in tissue microarrays comprising ductal carcinoma in situ (DCIS) and a cohort of invasive breast carcinomas. Correlation analysis was performed between SIAH2 and clinicopathological variables and intrinsic breast cancer subgroups and validated in a cohort of 293 invasive ductal carcinomas. Promoter methylation, gene copy number and mRNA expression of SIAH2 were determined in a panel of basal-like tumors and cell lines.

Results

There was a significant increase in nuclear SIAH2 expression from normal breast tissues through to DCIS and progression to invasive cancers. A significant inverse correlation was apparent between SIAH2 and estrogen receptor and progesterone receptor and a positive association with tumor grade, HER2, p53 and an intrinsic basal-like subtype. Logistic regression analysis confirmed the significant positive association between SIAH2 expression and the basal-like phenotype. No SIAH2 promoter methylation was identified, yet there was a significant correlation between SIAH2 mRNA and gene copy number. SIAH2-positive tumors were associated with a shorter relapse-free survival in univariate but not multivariate analysis.

Conclusions

SIAH2 expression is upregulated in basal-like breast cancers via copy number changes and/or transcriptional activation by p53 and is likely to be partly responsible for the enhanced hypoxic drive through abrogation of the prolyl hydroxylases.

Protein microarrays for genome-wide posttranslational modification analysis

Protein microarray technology has emerged as a powerful tool for comparing binding interactions, expression level, substrate specificities, and posttranslational modifications (PTMs) of different proteins in a parallel and high-throughput manner. The ability to immobilize proteins to a solid surface and register the specific address of each protein has bridged major limitations for investigating the proteome in biological samples, namely, the wide dynamic range of protein concentrations and the perturbation of the physical and chemical properties of proteins by their modification. Recent advances introduced the use of functional mammalian cell extracts to assay PTMs under different cellular conditions. This assay offers a new approach for performing large-scale complex biochemical analysis of protein modifications. Here, we review studies of PTM profiling using protein microarrays and discuss the limitations and potential applications of the system. We believe that the information generated from such proteomic studies may be of significant value in our elucidation of the molecular mechanisms that govern human physiology.

Siah1 proteins enhance radiosensitivity of human breast cancer cells

Background

Siah proteins play an important role in cancer progression. We evaluated the effect of Siah1, its splice variants Siah1L and the Siah1 mutant with the RING finger deleted (Siah1ΔR) on radiosensitization of human breast cancer cells.

Methods

The status of Siah1 and Siah1L was analysed in five breast cancer cell lines. To establish stable cells, SKBR3 cells were transfected with Siah1, Siah-1L and Siah1ΔR. Siah1 function was suppressed by siRNA in MCF-7 cells. The impact of Siah1 overexpression and silencing on apoptosis, proliferation, survival, invasion ability and DNA repair was assessed in SKBR3 and MCF-7 cells, also in regards to radiation.

Results

Siah1 and Siah1L mRNA expression was absent in four of five breast cancer cells lines analysed. Overexpression of Siah1 and Siah1L enhanced radiation-induced apoptosis in stable transfected SKBR3 cells, while Siah1ΔR failed to show this effect. In addition, Siah1 and Siah1L significantly reduced cell clonogenic survival and proliferation. Siah1L sensitization enhancement ratio values were over 1.5 and 4.0 for clonogenic survival and proliferation, respectively, pointing to a highly cooperative and potentially synergistic fashion with radiation. Siah1 or Siah1L significantly reduced invasion ability of SKBR3 and suppressed Tcf/Lef factor activity. Importantly, Siah1 siRNA demonstrated opposite effects in MCF-7 cells. Siah1 and Siah1L overexpression resulted in inhibition of DNA repair as inferred by increased levels of DNA double-strand breaks in irradiated SKBR3 cells.

Conclusion

Our results reveal for the first time how overexpression of Siah1L and Siah1 can determine radiosensitivity of breast cancer cells. These findings suggest that development of drugs augmenting Siah1 and Siah1L activity could be a novel approach in improving tumor cell kill.

Decreased expression of EZH2 is associated with upregulation of ER and favorable outcome to tamoxifen in advanced breast cancer

The purpose of this study is to investigate EZH2 in a large series of breast cancer patients for its prognostic and predictive value, and to evaluate its functional role in treatment response in vitro. EZH2 levels were measured using quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) in primary breast cancer specimens and related to clinicopathologic factors and disease outcome. EZH2 expression was downregulated with siRNAs in MCF7, to assess expression alterations of putative EZH2 downstream genes and to determine cell numbers after treatment with the anti-estrogen ICI 164384. In 688 lymph node-negative patients who did not receive adjuvant systemic therapy, EZH2 was not significantly correlated with metastasis-free survival (MFS). In 278 patients with advanced disease treated with first-line tamoxifen monotherapy, the tertile with highest EZH2 levels was associated with the lowest clinical benefit (OR = 0.48; P = 0.02) and with a shorter progression-free survival (PFS) in both univariate (HR = 1.80; P < 0.001) and multivariate analysis, including traditional factors (HR = 1.61; P = 0.004). In vitro, EZH2 silencing in MCF7 caused a 38% decrease in cell numbers (P < 0.001) whereas ICI 164384 treatment resulted in a 25% decrease (P < 0.001) compared to controls. Combining EZH2 silencing with ICI treatment reduced cell numbers with 67% (P < 0.001) compared to control conditions. EZH2 downregulation was associated with an almost two-fold upregulation of the estrogen receptor alpha (ER) (P = 0.001). In conclusion, EZH2 has no prognostic value in breast cancer. High levels of EZH2 are associated with poor outcome to tamoxifen therapy in advanced breast cancer. Downregulated EZH2 leads to upregulation of the ER and better response to anti-estrogens.

Siah proteins: novel drug targets in the Ras and hypoxia pathways

The Siah (seven in absentia homolog) family of RING-domain proteins are components of ubiquitin ligase complexes, targeting proteins for proteasomal degradation. Siah family members have been reported to function in Ras, estrogen, DNA-damage, and hypoxia response pathways. Although earlier reports implicated Siah proteins as tumor suppressors, recent studies in mouse models have shown that Siah inhibition impairs tumor growth and metastasis. Given their central role in oncogenic and angiogenic pathways, Siah proteins are attractive novel therapeutic targets in cancer.