YTHDF1 enhances stemness and chemoresistance in triple-negative breast cancer cells by upregulating SIAH2

Triple-negative breast cancer (TNBC) is the most lethal and aggressive subtype of breast cancer, and chemoresistance is the major determinant of TNBC treatment failure. This study explores the molecular mechanism of TNBC chemoresistance. The Cancer Genome Atlas, breast cancer integrative platform, and GEPIA databases were used to analyze the expression and correlation of YTHDF1 and seven in absentia homology 2 (SIAH2) in breast cancer. Knockdown of YTHDF1 and SIAH2, or overexpression of SIAH2 in vitro and in vivo, was conducted to evaluate the impact of changes in YTHDF1 and SIAH2 expression on TNBC cell proliferation, apoptosis, stemness, drug resistance, and Hippo pathway gene expression. YTHDF1 and SIAH2 were highly expressed in breast cancer patients and TNBC cells. Knockdown of YTHDF1 and SIAH2 significantly inhibited proliferation and stemness and promoted apoptosis and chemosensitivity of TNBC cells. Mechanistically, the knockdown of YTHDF1 inhibited the expression of SIAH2, thereby downregulating the Hippo pathway, which inhibited proliferation and stemness and promoted apoptosis and chemosensitivity of TNBC cells. The current findings revealed the regulatory mechanism of YTHDF1 in TNBC and clarified the role of the YTHDF1/SIAH2 axis in TNBC drug resistance and stemness. This could provide new insights into the vital role of targeting YTHDF1/SIAH2 to suppress drug resistance and stemness in TNBC cells.

CBX2-mediated suppression of SIAH2 triggers WNK1 accumulations to promote glycolysis in hepatocellular carcinoma

Previous studies have highlighted the poor prognosis of liver cancer, and treatment effects are overall limited. We aimed to confirm the biological roles of SIAH2 in liver cancer and provide potential therapeutic targets. Differential analysis was conducted based on public datasets and found that SIAH2 expressed lowly in HCC samples relative to normal tissues, which was demonstrated in tumor samples via immunohistochemistry (IHC). Besides, SIAH2 overexpression could significantly suppress HCC proliferation. SIAH2 deficiency induced cell proliferation, migration and self-renewal abilities in vitro and in vivo. Mechanistically, SIAH2 could interact with WNK1, and trigger the ubiquitination and degradation of WNK1 proteins. In addition, low SIAH2 depended on elevated WNK1 proteins to drive HCC malignant features, including proliferation, migration and stemness. Meanwhile, we further found that CBX2 could regulate SIAH2 expressions. CBX2 cooperated with EZH2 to mediate the H3K27me3 enrichment on the promoter region of SIAH2 to suppress its transcriptional levels. High CBX2/EZH2 levels in HCC correlated with poor prognosis of patients. Gene set enrichment analysis (GSEA) further implicated that WNK1 correlates tightly with glycolytic process in HCC samples. WNK1 overexpression was found to notably enhance glycolytic activity, whereas WNK1 deficiency could significantly suppress the HCC glycolysis activity. Lastly, the subcutaneous tumor model further demonstrated that targeting WNK1 was effective to inhibit the in vivo tumor growth of SIAH2^low HCC. Collectively, down-regulated SIAH2 expressions induced by CBX2/EZH2 could drive progression and glycolysis via accumulating WNK1 proteins, indicating that CBX2/SIAH2/WNK1 axis is a potential prognostic biomarker and therapeutic vulnerability for human HCC.

Methods to Evaluate the Effects of HAT/KAT Inhibition on SIAH2-Driven Reactive Oxygen Species Generation in Helicobacter pylori-Infected Gastric Epithelial Cells

Helicobacter pylori infection is one of the leading factors that promotes, among other diseases, gastric cancer (GC). Infection of gastric epithelial cells (GECs) by H. pylori enhances the expression as well as acetylation of the E3 ubiquitin ligase SIAH2 which promotes GC progression. The histone acetyltransferase (HAT) activity of p300 catalyzes SIAH2 acetylation following H. pylori infection. Since reactive oxygen species (ROS) generation in H. pylori-infected GECs accelerates GC progression, acetylation-mediated SIAH2 regulation might be a crucial modifier of ROS generation in the infected GECs. Here, we describe a compendium of methods to evaluate the effects of HAT/lysine acetyl transferase (KAT) inhibitors (HAT/KATi) on SIAH2-mediated ROS regulation in H. pylori-infected GECs.

Proteasome Inhibitors Silence Oncogenes in Multiple Myeloma through Localized Histone Deacetylase 3 (HDAC3) Stabilization and Chromatin Condensation

Proteasome inhibitors have become the standard of care for multiple myeloma (MM). Blocking protein degradation particularly perturbs the homeostasis of short-lived polypeptides such as transcription factors and epigenetic regulators. To determine how proteasome inhibitors directly impact gene regulation, we performed an integrative genomics study in MM cells. We discovered that proteasome inhibitors reduce the turnover of DNA-associated proteins and repress genes necessary for proliferation through epigenetic silencing. Specifically, proteasome inhibition results in the localized accumulation of histone deacetylase 3 (HDAC3) at defined genomic sites, which reduces H3K27 acetylation and increases chromatin condensation. The loss of active chromatin at super-enhancers critical for MM, including the super-enhancer controlling the proto-oncogene c-MYC, reduces metabolic activity and cancer cell growth. Epigenetic silencing is attenuated by HDAC3 depletion, suggesting a tumor-suppressive element of this deacetylase in the context of proteasome inhibition. In the absence of treatment, HDAC3 is continuously removed from DNA by the ubiquitin ligase SIAH2. Overexpression of SIAH2 increases H3K27 acetylation at c-MYC-controlled genes, increases metabolic output, and accelerates cancer cell proliferation. Our studies indicate a novel therapeutic function of proteasome inhibitors in MM by reshaping the epigenetic landscape in an HDAC3-dependent manner. As a result, blocking the proteasome effectively antagonizes c-MYC and the genes controlled by this proto-oncogene.

Expression of the preadipocyte marker ZFP423 is dysregulated between well-differentiated and dedifferentiated liposarcoma

Background

Well-differentiated and dedifferentiated liposarcomas are rare soft tissue tumors originating in adipose tissue that share genetic abnormalities but have significantly different metastatic potential. Dedifferentiated liposarcoma (DDLPS) is highly aggressive and has an overall 5-year survival rate of 30% as compared to 90% for well-differentiated liposarcoma (WDLPS). This discrepancy may be connected to their potential to form adipocytes, where WDLPS is adipogenic but DDLPS is adipogenic-impaired. Normal adipogenesis requires Zinc Finger Protein 423 (ZFP423), a transcriptional coregulator of Perixosome Proliferator Activated Receptor gamma (PPARG2) mRNA expression that defines committed preadipocytes. Expression of ZFP423 in preadipocytes is promoted by Seven-In-Absentia Homolog 2 (SIAH2)-mediated degradation of Zinc Finger Protein 521 (ZFP521). This study investigated the potential role of ZFP423, SIAH2 and ZFP521 in the adipogenic potential of WDLPS and DDLPS.

Methods

Human WDLPS and DDLPS fresh and paraffin-embedded tissues were used to assess the gene and protein expression of proadipogenic regulators. In parallel, normal adipose tissue stromal cells along with WDLPS and DDLPS cell lines were cultured, genetically modified, and induced to undergo adipogenesis in vitro.

Results

Impaired adipogenic potential in DDLPS was associated with reduced ZFP423 protein levels in parallel with reduced PPARG2 expression, potentially involving regulation of ZFP521. SIAH2 protein levels did not define a clear distinction related to adipogenesis in these liposarcomas. However, in primary tumor specimens, SIAH2 mRNA was consistently upregulated in DDLPS compared to WDLPS when assayed by fluorescence in situ hybridization or real-time PCR.

Conclusions

These data provide novel insights into ZFP423 expression in adipogenic regulation between WDLPS and DDLPS adipocytic tumor development. The data also introduces SIAH2 mRNA levels as a possible molecular marker to distinguish between WDLPS and DDLPS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09379-6.

Regulation of the SIAH2-HIF-1 Axis by Protein Kinases and Its Implication in Cancer Therapy

The cellular response to hypoxia is a key biological process that facilitates adaptation of cells to oxygen deprivation (hypoxia). This process is critical for cancer cells to adapt to the hypoxic tumor microenvironment resulting from rapid tumor growth. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor and a master regulator of the cellular response to hypoxia. The activity of HIF-1 is dictated primarily by its alpha subunit (HIF-1α), whose level and/or activity are largely regulated by an oxygen-dependent and ubiquitin/proteasome-mediated process. Prolyl hydroxylases (PHDs) and the E3 ubiquitin ligase Von Hippel-Lindau factor (VHL) catalyze hydroxylation and subsequent ubiquitin-dependent degradation of HIF-1α by the proteasome. Seven in Absentia Homolog 2 (SIAH2), a RING finger-containing E3 ubiquitin ligase, stabilizes HIF-1α by targeting PHDs for ubiquitin-mediated degradation by the proteasome. This SIAH2-HIF-1 signaling axis is important for maintaining the level of HIF-1α under both normoxic and hypoxic conditions. A number of protein kinases have been shown to phosphorylate SIAH2, thereby regulating its stability, activity, or substrate binding. In this review, we will discuss the regulation of the SIAH2-HIF-1 axis via phosphorylation of SIAH2 by these kinases and the potential implication of this regulation in cancer biology and cancer therapy.

The Ubiquitin Ligase SIAH2 Negatively Regulates Glucocorticoid Receptor Activity and Abundance

Glucocorticoids are clinically essential drugs used routinely to control inflammation. However, a host of metabolic side effects manifests upon usage beyond a few days. In the present study, we tested the hypothesis that seven-in-absentia mammalian homolog-2 (SIAH2), a ubiquitin ligase that regulates adipogenesis, is important for controlling adipocyte size, inflammation, and the ability of adipose tissue to expand in response to a glucocorticoid challenge. Using mice with global deletion of SIAH2 exposed or not to corticosterone, we found that adipocytes are larger in response to glucocorticoids in the absence of SIAH2. In addition, SIAH2 regulates glucocorticoid receptor (GR) transcriptional activity and total GR protein abundance. Moreover, these studies reveal that there is an increased expression of genes involved in fibrosis and inflammatory signaling pathways found in white adipose tissue in response to glucocorticoids in the absence of SIAH2. In summary, this is the first study to identify a role for SIAH2 to regulate transcriptional activity and abundance of the GR, which leads to alterations in adipose tissue size and gene expression during in vivo exposure to glucocorticoids.

miR-146b-5p regulates bone marrow mesenchymal stem cell differentiation by SIAH2/PPARγ in aplastic anemia children and benzene-induced aplastic anemia mouse model

This study aimed to reveal the mechanism of miR-146b-5p in the differentiation of bone marrow mesenchymal stem cells (BMSCs) derived from children with aplastic anemia (AA). Here, we found that miR-146b-5p was highly expressed in BMSCs from children with AA, and the BMSCs surface markers expressions in BMSCs derived from children with AA and the healthy controls exerted no significant differences. Besides, the overexpression of miR-146b-5p in normal human-derived BMSCs promoted the adipogenic differentiation of BMSCs. Furthermore, miR-146b-5p negatively regulated SIAH2 luciferase activity, and the interference with miR-146b-5p reduced the stability of PPARγ protein and inhibited SIAH2-mediated ubiquitination of PPARγ protein. Besides, the interference with miR-146b-5p was beneficial for ameliorating AA in a mouse model of AA. Overall, our results found that miR-146b-5p was highly expressed in BMSCs from children with AA, and our further studies indicated that miR-146b-5p improved AA via promoting SIAH2-mediated ubiquitination of PPARγ protein.

Targeting GRP78-dependent AR-V7 protein degradation overcomes castration-resistance in prostate cancer therapy

Rationale: Androgen receptor splice variant 7 (AR-V7) is a leading cause of the development of castration-resistant prostate cancer (CRPC). However, the regulation and function of AR-V7 at levels of post-translational modifications in prostate cancer therapy remain poorly understood. Here, we conducted a library screen of natural products to identify potential small molecules responsible for AR-V7 protein degradation in human prostate cancer cell lines.

Methods: A natural product library was used to screen the inhibitor of AR-V7. Co-IP and biomass spectrum assays were used to identify the AR-V7-interacting proteins, whereas western blot, confocal microscopy, RNA interfering, and gene transfection were used to validate these interactions. Cell viability, EDU staining, and colony formation assays were employed to detect cell growth and proliferation. Flowcytometry assays were used to detect the distribution of cell cycle. Mouse xenograft models were used to study the anti-CRPC effects in vivo.

Results: This screen identified rutaecarpine, one of the major components of the Chinese medicine Evodia rutaecarpa, as a novel chemical that selectively induces AR-V7 protein degradation via K48-linked ubiquitination. Mechanically, this effect relies on rutaecarpine inducing the formation of a GRP78-AR-V7 protein complex, which further recruits the E3 ligase SIAH2 to directly promote the ubiquitination of AR-V7. Consequently, the genetic and pharmacological activation of the GRP78-dependent AR-V7 protein degradation restores the sensitivity of castration-resistant prostate cancer to anti-androgen therapy in cell culture and animal models.

Conclusions: These findings not only provide a new approach for overcoming castration-resistance in prostate cancer therapy, but also increase our understanding about the interplay between molecular chaperones and ubiquitin ligase in shaping protein stability.

Regulation of tumor suppressor EAF2 polyubiquitination by ELL1 and SIAH2 in prostate cancer cells

RNA Polymerase II Elongation Factor (ELL)-associated factor 2 (EAF2) is a tumor suppressor frequently down-regulated in human prostate cancer. We previously reported that its binding partner ELL1 can enhance EAF2 protein stability and activity. Here we show that EAF2 can be polyubiquitinated and its degradation blocked by proteasome inhibitor. Co-immunoprecipitation detected EAF2 binding to SIAH2, an E3 ligase, and SIAH2 overexpression enhanced polyubiquitination of EAF2. Co-transfection of EAF2 binding partner ELL1 blocked EAF2 ubiquitination, providing a mechanism for EAF2 stabilization. Finally, EAF2K81R mutant, which exhibits reduced polyubiquitination and increased stability, was more potent than wild-type EAF2 in apoptosis induction. These findings suggest that SIAH2 is an E3 ligase for EAF2 polyubiquitination and ELL1 can enhance EAF2 level and function by blocking its polyubiquitination.

Polo-like kinase 3, hypoxic responses, and tumorigenesis

The cellular hypoxic response contributes to cell transformation and tumor progression. Hypoxia-inducible factor 1 (HIF-1) is a key transcription factor that mediates transcription of genes whose products are essential for cellular adaptation to hypoxia. The activity of HIF-1 is largely regulated by the abundance of its alpha subunit (HIF-1α), which is primarily regulated by an oxygen-dependent and ubiquitin/proteasome-mediated degradation process. The HIF-1α protein level is also regulated by protein kinases through phosphorylation. Polo-like kinase 3 (Plk3) is a serine/threonine protein kinase with a tumor suppressive function. Plk3 phosphorylates and destabilizes HIF-1α. Plk3 also phosphorylates and stabilizes PTEN, a known regulator of HIF-1α stability via the PI3K pathway. Our latest study showed that the Plk3 protein is suppressed by hypoxia or nickel treatment via the ubiquitin/proteasome system. We discovered that Seven in Absentia Homologue 2 (SIAH2) is the E3 ubiquitin ligase of Plk3 and that Plk3 in turn destabilizes SIAH2. Given the role of SIAH2 in promoting stability of HIF-1α, our work reveals a novel mutual regulatory mechanism between Plk3 and SIAH2, which may function to fine-tune the cellular hypoxic response. Here we discuss the role of Plk3 in the hypoxic response and tumorigenesis in light of these latest findings.

Mutual regulation between Polo-like kinase 3 and SIAH2 E3 ubiquitin ligase defines a regulatory network that fine-tunes the cellular response to hypoxia and nickel

Elevated cellular response to hypoxia, which contributes to cell transformation and tumor progression, is a prominent feature of malignant cells in solid tumors. Polo-like kinase 3 (Plk3) is a serine/threonine protein kinase known to inhibit the cellular response to hypoxia and tumorigenesis. Nickel compounds are well-established human carcinogens that induce tumorigenesis partly through their hypoxia-mimicking effects. Despite previous research efforts, the role of Plk3 in the hypoxic response induced by hypoxia or nickel is not completely understood. Here, we show that NiCl₂ (Ni(II)) or hypoxia reduces the protein level and shortens the half-life of cytoplasmic Plk3 in a ubiquitin-proteasome-dependent manner. We identify SIAH2, a RING finger E3 ubiquitin ligase associated with the cellular hypoxic response, to be the ubiquitin E3 ligase that mediates the degradation of Plk3. We show that SIAH2 binds to Plk3 and mediates its ubiquitination primarily through its polo-box domain. We report that USP28, a deubiquitinase known to be inhibitable by Ni(II) or hypoxia, may also contribute to the suppression of the Plk3 protein by Ni(II). We also show that Plk3 in turn suppresses the SIAH2 protein level in a kinase activity-dependent manner. Our study revealed an interesting mutual regulation between Plk3 and SIAH2 and uncovered a regulatory network that functions to fine-tune the cellular hypoxic response. We propose that suppression of Plk3 expression contributes to carcinogenesis and tumor progression induced by nickel compounds.

MiR-30 Family Potentially Targeting PI3K-SIAH2 Predicted Interaction Network Represents a Novel Putative Theranostic Panel in Non-small Cell Lung Cancer

Non-small cell lung cancer (NSCLC) comprises about 84% of all lung cancers. Many treatment options are available but the survival rate is still very low due to drug resistance. It has been found that phosphoinositide-3-kinase (PI3K) affects sensitivity to tyrosine kinase inhibitors (TKIs), including gefitinib and erlotinib. Expression level of seven in absentia homolog 2 (SIAH2), an E3 ubiquitin-protein ligase, is upregulated in NSCLC and correlated with tumor grade. However, the relationship between PI3K and SIAH2 remains unclear and therefore it is not known whether they can act as treatment co-targets and theranostic dual markers for overcoming TKI resistance. It is worthy to note that PI3K and SIAH2 are potentially regulated by a common group of microRNAs in miR-30 family. Our bioinformatics analyses showed upregulated SIAH2 expression in NSCLC based on mass spectrometry data, explored its indirect interaction with PI3K and predicted their targeting microRNAs in common. We have also explored the potential role of miR-30 family in the modulation of PI3K-SIAH2 interaction in NSCLC.

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.

The expression and function of E3 ligase SIAH2 in acute T lymphoblastic leukemia

INTRODUCTION

The seven in absentia homolog 2 (SIAH2) protein plays a significant role in human cancer by regulating hypoxia-inducible factor-a (HIF-1α); however, its role in T-cell acute lymphoblastic leukemia (T-ALL) is less clear.

METHODS

Immunofluorescence evaluation of SIAH2 protein expression and location were conducted in Jurkat cell (a T-ALL cell line) as well as in bone marrow mononuclear cells (BMMNCs) from T-ALL and idiopathic thrombocytopenic purpura (ITP) patients. The expression of SIAH2 mRNA was also examined by quantitative real-time PCR (qRT-PCR) in these cells. Lentivirus-packed shRNA targeting on SIAH2 (Lv-shSIAH2) was used to knock down SIAH2 expression in Jurkat cells. Cell proliferation, apoptosis, invasion and protein levels were then determined by CCK-8 assay, annexin V-PI assay, transwell and Western blotting, respectively.

RESULTS

The mRNA expression of SIAH2 in BMMNCs from primary T-ALL patients was significantly higher than cells from ITP patients (P=0.0312); There were significant positive associations between SIAH2 expression and the extramedullary infiltration (EMI) (P=0.0003), especially with the mediastinal lymph node metastasis (P=0.0168) and the pleural effusion (P=0.014). However, SIAH2 expression in T-ALL BMMNCs was not correlated with age, gender, white cell count or the clinical risk classification. SIAH2 knockdown by shRNA led to increased apoptosis and decreased proliferation, migration and invasion of Jurkat cells. Moreover, Prolyl Hydroxylase (PHD), P27 and Caspase3 were upregulated and HIF-1α, VEGF, VEGF Receptor 2, MMP-13, CyclinE1, C-myc and BCL2 were downregulated in SIAH2 knockdown Jurkat cells.

CONCLUSIONS

Our results suggest that SIAH2 regulates multi processes in T-ALL and may be an attractive therapeutic target.

miR-335 Targets SIAH2 and Confers Sensitivity to Anti-Cancer Drugs by Increasing the Expression of HDAC3

We previously reported the role of histone deacetylase 3 (HDAC3) in response to anti-cancer drugs. The decreased expression of HDAC3 in anti-cancer drug-resistant cancer cell line is responsible for the resistance to anti-cancer drugs. In this study, we investigated molecular mechanisms associated with regulation of HDAC3 expression. MG132, an inhibitor of proteasomal degradation, induced the expression of HDAC3 in various anti-cancer drug-resistant cancer cell lines. Ubiquitination of HDAC3 was observed in various anti-cancer drug-resistant cancer cell lines. HDAC3 showed an interaction with SIAH2, an ubiquitin E3 ligase, that has increased expression in various anti-cancer drug-resistant cancer cell lines. miRNA array analysis showed the decreased expression of miR-335 in these cells. Targetscan analysis predicted the binding of miR-335 to the 3'-UTR of SIAH2. miR-335-mediated increased sensitivity to anti-cancer drugs was associated with its effect on HDAC3 and SIAH2 expression. miR-335 exerted apoptotic effects and inhibited ubiquitination of HDAC3 in anti-cancer drug-resistant cancer cell lines. miR-335 negatively regulated the invasion, migration, and growth rate of cancer cells. The mouse xenograft model showed that miR-335 negatively regulated the tumorigenic potential of cancer cells. The down-regulation of SIAH2 conferred sensitivity to anti-cancer drugs. The results of the study indicated that the miR-335/SIAH2/HDAC3 axis regulates the response to anti-cancer drugs.

Significance of expression of RIN1 and SIAH2 proteins in gastric carcinoma

AIM: To examine the expression of Ras and Rab interactor 1 (RIN1) and seven in absentia homologue 2 (SIAH2) proteins in gastric carcinoma and to analyze their relationship with clinicopathological factors.

METHODS: The expression of RIN1 and SIAH2 was detected by immunohistochemistry in 80 gastric carcinoma and 40 normal gastric tissues.

RESULTS: The positive rates of RIN1 and SIAH2 protein expression were significantly higher in gastric carcinoma than in normal gastric tissues (61.2% vs 32.5%, 60.0% vs 27.5%, P < 0.05 for both). In gastric carcinoma, RIN1 expression was related to tumor size, clinical stage, histopathological grade, lymph node metastasis and depth of invasion (P < 0.05 for all), but not to patients' age or gender (P > 0.05 for both); SIAH2 expression was related to clinical stage, histopathological grade, lymph node metastasis and depth of invasion (P < 0.05 for all), but not to tumor size (P > 0.05). There was a positive correlation between the expression of RIN1 and SIAH2 in gastric carcinoma (r = 0.607, P < 0.01).

CONCLUSION: The overexpression of RIN1 and SIAH2 might play an important role in the progression, invasion and metastasis of gastric carcinoma, and they may be used as early diagnostic markers and therapeutic targets for gastric carcinoma.

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.