Metastasis-associated Protein 1 Knockdown Research Articles

SiMTA1-Loaded Exosomes Enhanced Chemotherapeutic Effect of Gemcitabine in Luminal-b Type Breast Cancer by Inhibition of EMT/HIF-α and Autophagy Pathways.

Advanced breast cancer holds a poor prognosis for chemotherapy and endocrine therapy resistance. Autophagy is one of the main causes of tumor drug-therapy failure, and increasing evidence shows that EMT also is responsible for that. Metastasis-associated protein1 (MTA1) is up regulated in lots of tumors, which leads to tumor progression and drug resistance. However, the role of MTA1 in chemotherapeutic resistance in luminal-b breast cancer is still unclear. In this paper, our research shows that higher expression of MTA1 accompanies with worse prognosis in luminal-b breast cancer. Knockdown of MTA1 enhances the sensitivity of MCF-7 to gemcitabine and weakens the metastasis ability of MCF-7 in vitro and in vivo. Further, we find that knockdown of MTA1 strengthens the gemcitabine-mediated tumor growth inhibition effect in vivo, through reversion of the EMT process and inhibition of the autophagy process. Furthermore, our research builds the siMTA1-loaded exosomes, which increases the gemcitabine-mediated tumor growth inhibition effect in vivo.

MTA1 promotes tumorigenesis and development of esophageal squamous cell carcinoma via activating the MEK/ERK/p90RSK signaling pathway.

Metastasis-associated protein 1 (MTA1) is upregulated in multiple malignancies and promotes cancer proliferation and metastasis, but whether and how MTA1 promotes esophageal squamous cell carcinoma (ESCC) tumorigenesis remain unanswered. Here, we established an ESCC model in MTA1 transgenic mice induced by the chemical carcinogen 4-nitroquinoline 1-oxide (4-NQO) and found that MTA1 promotes ESCC tumorigenesis in mice. MTA1 overexpression was observed in ESCC cells and clinical ESCC samples. Overexpressed MTA1 increased colony formation and the invasiveness and migration of ESCC cells, whereas knock down of MTA1 in ESCC cells significantly decreased colony formation, invasion and migration in vitro and inhibited the growth of xenograft tumors in vivo. RNA sequencing (RNA-seq) analysis combined with western blot assays revealed that MTA1 promotes carcinogenesis by enhancing MEK/ERK/p90RSK signaling. The phosphorylation of MEK, ERK and their downstream target p90RSK was significantly decreased after MTA1 knockdown in ESCC cells and was increased in MTA1-overexpressing cells. Moreover, colony formation, invasion and migration potential were dramatically suppressed when cells overexpressing MTA1 were treated with MEK (PD0325901) or ERK (SCH772948) inhibitors. In conclusion, MTA1 plays a pivotal oncogenic role in ESCC tumorigenesis and development through activating the MEK/ERK/p90RSK pathway.

Metastasis-associated protein 1, modulated by miR-30c, promotes endometrial cancer progression through AKT/mTOR/4E-BP1 pathway

ObjectiveThough metastasis-associated protein 1 (MTA1) is widely overexpressed in human cancers and is associated with advanced clinicopathological characteristics and survival in related diseases, the association between MTA1 and endometrial cancer (EC) is little known and needs to be studied. MethodsWestern blot and immunohistochemistry were used to analyze protein expression level of cells and tissues, while real-time PCR was used for RNA detection. Bioinformatics tool analysis revealed the relationship between MTA1 and clinicopathological characteristics and survival. CCK-8 assay, colony-formation assay, cell scratch assay, and Transwell assay were performed to determine cell proliferation, migration and invasion abilities, respectively. ResultsThe expression level of MTA1 was significantly higher in human EC tissues than in normal endometrium. MTA1 expression was correlated positively with lymph nodes metastasis and poor survival rate in EC. Experimentally overexpressed MTA1 could promote cell proliferation, migration and invasion abilities of EC cell lines Ishikawa, HEC-1B, and RL-952, while reduction of MTA1 inhibited these cell biological behaviors. Moreover, MTA1 could also reverse the negative effect of miR-30c, a direct modulator of MTA1, on EC cells. Our research also revealed that overexpression of MTA1 contributed to EC tumor growth, while knockdown of MTA1 resulted in tumor growth inhibition. Additionally, the phosphorylation levels of mTOR (S2448) and 4E-BP1 (T37/46) changed significantly along with AKT (T308) under regulation of MTA1, both in vivo and vitro. ConclusionOur results showed that MTA1, as a downstream target of miR-30c, might promote EC progression via AKT/mTOR/4E-BP1 pathway, which indicated the potential therapy target of MTA1 in EC.

Upregulation of MTA1 expression by human papillomavirus infection promotes CDDP resistance in cervical cancer cells via modulation of NF-κB/APOBEC3B cascade.

Compelling evidence establishes the etiological role of viral proteins E6 and E7 of high-risk human papillomaviruses (HPV) in cervical carcinogenesis, but their contribution in chemoresistance that leads to advanced metastatic lesions remains poorly defined. Since metastasis-associated protein 1 (MTA1) upregulation and augmentation of APOBEC3B expression are both strongly associated with cervical cancer (CCa) development, and both molecules have been shown to be functionally associated with NF-κB pathway, we therefore sought to investigate the potential mechanistic link between MTA1, APOBEC3B and NF-κB during the pathogenesis of cisplatin (CDDP) resistance in HPV-positive CCa cells. MTA1 expression was assessed in HPV-transfected CCa cells using quantitative RT-PCR and immunoblotting. Effects of MTA1 deregulation on CDDP chemosensitivity in CCa cells were determined by measuring cell viability, apoptosis and in vivo oncogenic capacity. Finally, we studied the transcriptional regulation of the antiviral DNA cytosine deaminase APOBEC3B by MTA1 using multiple approaches including DNA deaminase activity assay, luciferase reporter assay, chromatin immunoprecipitation, co-immunoprecipitation and transient/stable transfection, at the molecular and functional levels. Expression levels of MTA1 were significantly induced in HPV-positive CCa cells. Transduction experiments showed that the E6 oncoprotein alone was sufficient to cause MTA1 upregulation. Moreover, MTA1 knockdown potentiated CDDP sensitivity in highly metastatic CCa cells. Mechanistically, MTA1 acted as an indirect upstream modulator of APOBEC3B transcription during the pathogenesis of CDDP chemoresistance. HPV-mediated stimulation of APOBEC3B expression was accompanied by the enhanced recruitment of Iκκ α/β and p65 to the NF-κB consensus sites in the APOBEC3B promoter, and this recruitment was substantially abrogated by MTA1 siRNA treatment. These findings reveal an obligatory coregulatory role of MTA1 in the indirect regulation of APOBEC3B expression via classical NF-κB pathway, and also suggest that inhibition of MTA1/NF-κB/APOBEC3B cascade may be repositioned to suppress cancer mutagenesis, dampen tumor evolution, and decrease the probability of adverse outcomes from CDDP resistance in CCa.

MTA1 drives malignant progression and bone metastasis in prostate cancer.

Prostate cancer often metastasizes to the bone, leading to morbidity and mortality. While metastasis‐associated protein 1 (MTA1) is highly overexpressed in metastatic tumors and bone metastatic lesions, its exact role in the development of metastasis is unknown. Here, we report the role of MTA1 in prostate cancer progression and bone metastasis in vitro and in vivo. We found that MTA1 silencing diminished formation of bone metastases and impaired tumor growth in intracardiac and subcutaneous prostate cancer xenografts, respectively. This was attributed to reduced colony formation, invasion, and migration capabilities of MTA1 knockdown cells. Mechanistic studies revealed that MTA1 silencing led to a significant decrease in the expression of cathepsin B (CTSB), a cysteine protease critical for bone metastasis, with an expected increase in the levels of E‐cadherin in both cells and xenograft tumors. Moreover, meta‐analysis of clinical samples indicated a positive correlation between MTA1 and CTSB. Together, these results demonstrate the critical role of MTA1 as an upstream regulator of CTSB‐mediated events associated with cell invasiveness and raise the possibility that targeting MTA1/CTSB signaling in the tumor may prevent the development of bone metastasis in prostate cancer.

Abstract 3607: Metastasis-associated protein 1 negatively regulates expression of androgen receptor in ER-positive breast cancer cells

Abstract Androgen receptor (AR) is expressed in more than 80% of ER-positive breast cancer and its expression is correlated with better prognosis in ER-positive breast cancer. However, little is known about the regulation of AR expression in breast cancer. We have previously reported that metastasis-associated protein 1 (MTA1), a cancer-promoting gene that is overexpressed in breast cancer, increases the expression of ERα in breast cancer. Here, we investigated the role of MTA1 on AR expression in three different ER-positive breast cancer cell lines. First, small interfering RNA-mediated knockdown of MTA1 increased protein and mRNA expression of AR in MCF7, T47D, and ZR75-1. Overexpression of MTA1 down-regulated expression of AR in these cell lines. Activity of the reporter-encoding AR promoter (-2408 bp ~ +1126 bp) was decreased in the presence of MTA1 in a dose-dependent manner. Analysis of the chromatin immunoprecipitation sequencing data (http://encodeproject.org/ENCODE) revealed that MTA1 may bind to 1 kilo base downstream of AR transcription start site. Together, our results demonstrated that MTA1 negatively regulates expression of AR in breast cancer cells. These results suggest that the negative regulation of AR may be associated with the cancer promoting effects of MTA1, which may provide a therapeutic opportunity against ER-positive breast cancer. Citation Format: SeungSu Kim. Metastasis-associated protein 1 negatively regulates expression of androgen receptor in ER-positive breast cancer cells [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 3607. doi:10.1158/1538-7445.AM2017-3607

MTA1 promotes epithelial to mesenchymal transition and metastasis in non-small-cell lung cancer.

The present study assessed the role of metastasis-associated protein 1 (MTA1) in epithelial to mesenchymal transition (EMT) and metastasis in non-small-cell lung cancer (NSCLC) cells using a normal lung epithelium cell line, three NSCLC cell lines, a mouse NSCLC model, and 56 clinical NSCLC samples. We observed that MTA1 overexpression decreased cellular adhesion, promoted migration and invasion, and changed cytoskeletal polarity. MTA1 knockdown had the opposite effects. MTA1 overexpression decreased E-cadherin, Claudin-1, and ZO-1 levels and increased Vimentin expression in vitro and in vivo, through activation of AKT/GSK3β/β-catenin signaling. However, treatment with the AKT inhibitor MK2206 did not completely rescue effects associated with MTA1 expression changes, indicating that pathways other than the AKT/GSK3β/β-catenin pathway could be involved in MTA1-induced EMT. Compared with normal lung tissues, MTA1 expression was elevated in NSCLC patient tissues and was correlated with American Joint Committee on Cancer stage, T stage, lymphatic metastasis, and patient overall survival. Additionally, MTA1 expression was positively associated with p-AKT and cytoplasmic β-catenin levels. These findings indicate MTA1 promotes NSCLC cell EMT and metastasis via AKT/GSK3β/β-catenin signaling, which suggests MTA1 may be an effective anti-NSCLC therapeutic target.

Abstract 2924: Metastasis-associated protein 1 induces tamoxifen resistance in MCF7 breast cancer cells

Abstract Tamoxifen is most commonly used to treat estrogen receptor-alpha positive breast cancer, but its therapeutic benefit is limited by the development of drug resistance. Metastasis associated protein 1 (MTA1) is a cancer progression-related gene and has been reported to be overexpressed in a variety of human cancers including breast cancer. Here, we showed that transient overexpression of MTA1 in MCF7 breast cancer cells results in tamoxifen resistance, whereas si-RNA mediated knockdown of MTA1 was more susceptible to tamoxifen-induced growth inhibition. Moreover, stable overexpression of MTA1 in MCF7 cells promoted cell proliferation and reduced tamoxifen sensitivity. To explore the mechanisms of MTA1-mediate tamoxifen resistance, we used microarray analysis to profile the gene expression patterns of MTA1 overexpress MCF7 stable cells after tamoxifen treatment. From microarray data analysis, 538 genes were selected as associated with MTA1-mediated tamoxifen resistance (P < 0.05, LPE test; cutoff ≥ 1.5-fold). The Database for Annotation, Visualization and Integrated Discovery (DAVID) analysis revealed that the predominant biological processes associated with these genes are M phase, negative regulation of cell proliferation, mitosis and M phase of mitotic cell cycle. Further, we found that cell-cycle regulator Cyclin D1 and cyclin B1 protein levels were increased in MTA1 overexpression MCF7 stable cells. Analyses of publicly available patient data sets indicated that MTA1 levels are higher in patients after endocrine therapy failure (recurrence), compared to those of responders (non-recurrence). These results suggest that MTA1 may contributed tamoxifen resistance through the regulation of cell cycle components. Citation Format: Min-Ho Lee, Dahae Koh, Mi-Ock Lee. Metastasis-associated protein 1 induces tamoxifen resistance in MCF7 breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2924.

Metastasis-associated protein 1 (MTA1) signaling in rheumatoid synovium: Regulation of inflammatory response and cytokine-mediated production of prostaglandin E2 (PGE2)

Abnormal perpetual inflammatory response and sequential cytokine-induced prostaglandin E2 (PGE2) play important roles in the pathogenesis of rheumatoid arthritis (RA). The underlying regulatory mechanism, however, remain largely unknown. Here, we discovered that expression level of Metastasis associated protein 1 (MTA1), an important chromatin modifier that plays a critical role in transcriptional regulation by modifying DNA accessibility for cofactors, was upregulated in human rheumatoid synovial tissues. Furthermore, a knockdown of MTA1 by siRNA in the human fibroblast-like synovial cell line MH7A was found to impair the 4-hydroxynonenal (4-HNE)-induced transcriptional expression levels of certain proinflammatory cytokines including IL-1β, TNF-α and IL-6. Moreover, endogenous MTA1 was required for the cytokines-induced PGE2 synthesis by rheumatoid synoviocytes. Collectively, the coordinated existence of MTA1 inside distinct cascade loops points to its indispensable role in the modulation of the integrated cytokine network along the pathogenesis of RA. Further exploration of the functional details of this master transcriptional regulator should be an attractive strategy to identify novel therapeutic target for RA and warrants execution.

Overexpression of eukaryotic translation initiation factor 5A2 (EIF5A2) correlates with cell aggressiveness and poor survival in gastric cancer.

Eukaryotic translation initiation factor 5A2 (EIF5A2) plays an important role in tumor progression and prognosis evaluation. However, little information is available about its potential role in gastric cancer. This study aimed to investigate the function of EIF5A2 in tumor progression and its potential mechanisms. EIF5A2 expression was measured in human gastric cancer cell lines, the immortalized gastric mucosal epithelial cell line (GES-1) and human gastric cancer tissues and knocked down by RNA interference or upregulated by EIF5A2 plasmid transfection. Cell proliferation, migration and invasion were assessed in vitro. The downstream targets of EIF5A2 were examined by western blotting. EIF5A2 and its potential target metastasis-associated protein 1 (MTA1) expression were examined in 160 pairs of human gastric cancer and adjacent non-tumor specimens using immunohistochemistry (IHC) staining, and its correlation with clinicopathological features and survival was investigated. Knockdown of EIF5A2 or MTA1 caused an apparent suppression of HGC27 cell proliferation, migration and invasion. After knockdown of EIF5A2 in HGC27 cells, E-cadherin levels were upregulated and vimentin, cyclin D1, cyclin D3, C-MYC and MTA1 levels were downregulated. Upregulation of EIF5A2 in MKN45 cells resulted in the converse. IHC results showed a positive correlation between EIF5A2 and MTA1 expression in gastric cancers (P<0.001). Both EIF5A2 and MTA1 overexpression were correlated with pT stage (P=0.018 and P=0.042), pN stage (P=0.037 and P=0.020) and lymphovascular invasion (P=0.016 and P=0.044). EIF5A2 or MTA1 overexpression was significantly associated with poor overall survival and disease-free survival (All P<0.05). Multivariate analyses identified EIF5A2 as an independent predictor for both overall survival (P=0.012) and disease-free survival (P=0.008) in gastric cancer patients. Our findings indicate that EIF5A2 upregulation plays an important oncogenic role in gastric cancer. EIF5A2 may represent a new predictor for poor survival and is a potential therapeutic target for gastric cancer.

Resveratrol regulates PTEN/Akt pathway through inhibition of MTA1/HDAC unit of the NuRD complex in prostate cancer

Metastasis associated protein 1 (MTA1) is a component of the nucleosome remodeling and deacetylating (NuRD) complex which mediates gene silencing and is overexpressed in several cancers. We reported earlier that resveratrol, a dietary stilbene found in grapes, can down-regulate MTA1. In the present study, we show that PTEN is inactivated by MTA1 in prostate cancer cells. Further, we show that resveratrol promotes acetylation and reactivation of PTEN via inhibition of the MTA1/HDAC complex, resulting in inhibition of the Akt pathway. In addition, we show that MTA1 knockdown is sufficient to augment acetylation of PTEN indicating a crucial role of MTA1 itself in the regulation of PTEN acetylation contributing to its lipid phosphatase activity. Acetylated PTEN preferentially accumulates in the nucleus where it binds to MTA1. We also show that MTA1 interacts exclusively with PTEN acetylated on Lys125 and Lys128, resulting in diminished p-Akt levels. Finally, using orthotopic prostate cancer xenografts, we demonstrate that both resveratrol treatment and MTA1 knockdown enhance PTEN levels leading to a decreased p-Akt expression and proliferation index. Taken together, our results indicate that MTA1/HDAC unit is a negative regulator of PTEN which facilitates survival pathways and progression of prostate cancer and that resveratrol can reverse this process through its MTA1 inhibitory function.

The subcellular distribution and function of MTA1 in cancer differentiation.

The functions and mechanisms of metastasis-associated protein 1 (MTA1) in cancer progression are still unclear due to a lagged recognition of the subcellular localization. In the present study, using multiple molecular technologies we confirmed for the first time that MTA1 localizes to the nucleus, cytoplasm and nuclear envelope. MTA1 is primarily localized in the nucleus of normal adult tissues but in the cytoplasm of embryonic tissues. While in colon cancer, both distributions have been described. Further investigation revealed that MTA1 localizes on the nuclear envelope in a translocated promoter region (TPR)-dependent manner, while in the cytoplasm, MTA1 shows an obvious localization on microtubules. Both nuclear and cytoplasmic MTA1 are associated with cancer progression. However, these functions may be associated with different mechanisms because only nuclear MTA1 has been associated with cancer differentiation. Overexpression of MTA1 in HCT116 cells inhibited differentiation and promoted proliferation, whereas MTA1 knockdown resulted in cell differentiation and death. Theses results not only suggest that nuclear MTA1 is a good marker for cancer differentiation diagnosis and a potential target for the treatment of cancers but also reveal the necessity to differentially examine the functions of nuclear and cytoplasmic MTA1.

Involvement of a chromatin modifier in response to mono-(2-ethylhexyl) phthalate (MEHP)-induced Sertoli cell injury: Probably an indirect action via the regulation of NFκB/FasL circuitry

The Fas/FasL signaling pathway, controlled by nuclear factor-κB (NFκB) at the transcriptional level, is critical for triggering germ cell apoptosis in response to mono-(2-ethylhexyl) phthalate (MEHP)-induced Sertoli cell (SC) injury, but the exact regulation mechanism remain unknown. Here, we discovered that expression level of Metastasis associated protein 1 (MTA1), a component of the Mi-2/nucleosome remodeling and deacetylase complex, was upregulated in SCs during the early recovery after MEHP exposure. This expression change was in line with the dynamic changes in germ cell apoptosis in response to MEHP treatment. Furthermore, a knockdown of MTA1 by RNAi in SCs was found to impair the MEHP-induced early activation of NFκB pathway and abolish the recruitment of NFκB onto FasL promoter, which consequently diminished the MEHP-triggered FasL induction. Considering that Fas/FasL is a well characterized apoptosis initiating signaling during SCs injury, our results point to a potential “switch on” effect of MTA1, which may govern the activation of NFκB/FasL cascade in MEHP-insulted SCs. Overall, the MTA1/NFκB/FasL circuit may serve as an important defensive/repairing mechanism to help to control the germ cell quality after SCs injury.

Repression of NR4A1 by a chromatin modifier promotes docetaxel resistance in PC-3 human prostate cancer cells

Epigenetic silencing mechanisms play an important role in chemoresistance of human cancer. Here we report the upregulated expression of metastasis-associated protein 1 (MTA1), a component of the nucleosome remodeling deacetylation (NuRD) complex, in chemoresistant prostate cancer (PCa). MTA1 knockdown in PC-3 cells inhibited cell proliferation and enhanced docetaxel (DTX)-induced cell death. Conversely, overexpression of MTA1 promotes DTX chemoresistance in PC-3 cells. MTA1 acted as a potent corepressor of the nuclear receptor NR4A1 transcription by interacting with histone deacetylase 2 (HDAC2). These findings suggest that MTA1 may serve as a novel DTX-resistance promoter in PC-3 cells.

Overexpression of EIF5A2 promotes colorectal carcinoma cell aggressiveness by upregulating MTA1 through C-myc to induce epithelial–mesenchymaltransition

Background and AimsThe authors have previously isolated a putative oncogene, eukaryotic initiation factor 5A2 (EIF5A2) from 3q26. In this study, EIF5A2 was characterised for its role in colorectal carcinoma (CRC)...

Metastasis-Associated Protein 1 and Its Short Form Variant Stimulates Wnt1 Transcription through Promoting Its Derepression from Six3 Corepressor

Although Wnt1 downstream signaling components have been well studied and activated in human cancer, the pathways that regulate Wnt1 itself have not been explored in depth. Here, we provide gain-of-function, loss-of function, and molecular evidence supporting functional interactions between metastasis-associated protein 1 short-form (MTA1s), metastasis-associated protein 1 (MTA1), and Wnt1 signaling components during mammary gland development and tumorigenesis. Using multiple model systems involving overexpression or knockdown of MTA1s or MTA1, we discovered that MTA1s and MTA1 hyperactivate the Wnt1 pathway due to increased expression of Wnt1 transcription. MTA1s and MTA1 physically interact with Six3 chromatin, a protein product of which is a direct histone deacetylase inhibitor-dependent repressor of Wnt1 transcription. Deletion of the MTA1s and MTA1 allele in murine embryonic fibroblasts resulted in the upregulation of Six3 and downregulation of Wnt signaling. In addition, mammary glands from the MTA1s/MTA1(-/-) mice exhibited increased recruitment of Six3 corepressor complex to the Wnt1 promoter and inhibition of Wnt1 pathway in mammary glands. These findings identify MTA1s and MTA1 as important upstream modifiers of the Wnt1 transcription, and consequently its functions, by directly inhibiting the transcription of Six3, allowing derepression of Wnt1 transcription.

Resveratrol enhances p53 acetylation and apoptosis in prostate cancer by inhibiting MTA1/NuRD complex

Dietary compounds and epigenetic influences are well recognized factors in cancer progression. Resveratrol (Res), a dietary compound from grapes, has anticancer properties; however, its epigenetic effects are understudied. Metastasis-associated protein 1 (MTA1) is a part of the nucleosome remodeling deacetylation (NuRD) corepressor complex that mediates posttranslational modifications of histones and nonhistone proteins resulting in transcriptional repression. MTA1 overexpression in prostate cancer (PCa) correlates with tumor aggressiveness and metastasis. In this study, we have identified a novel MTA1-mediated mechanism, by which Res restores p53-signaling pathways in PCa cells. We show, for the first time, that Res causes down-regulation of MTA1 protein, leading to destabilization of MTA1/NuRD thus allowing acetylation/activation of p53. We demonstrated that MTA1 decrease by Res was concomitant with accumulation of Ac-p53. MTA1 knockdown further sensitized PCa cells to Res-dependent p53 acetylation and recruitment to the p21 and Bax promoters. Furthermore, MTA1 silencing maximized the levels of Res-induced apoptosis and pro-apoptotic Bax accumulation. HDAC inhibitor SAHA, like MTA1 silencing, increased Res-dependent p53 acetylation and showed cooperative effect on apoptosis. Our results indicate a novel epigenetic mechanism that contributes to Res anticancer activities: the inhibition of MTA1/NuRD complexes due to MTA1 decrease, which suppresses its deacetylation function and allows p53 acetylation and subsequent activation of pro-apoptotic genes. Our study identifies MTA1 as a new molecular target of Res that may have important clinical applications for PCa chemoprevention and therapy, and points to the combination of Res with HDAC inhibitors as an innovative therapeutic strategy for the treatment of PCa.

Hepatitis B virus X protein induces the expression of MTA1 and HDAC1, which enhances hypoxia signaling in hepatocellular carcinoma cells

Expression level of metastasis-associated protein 1 (MTA1) is closely related to tumor growth and metastasis in various cancers. Although increased expression level of MTA1 was observed in hepatocellular carcinoma (HCC), role of MTA1 complex containing histone deacetylase (HDAC) in hepatitis B virus (HBV)-associated hepatocarcinogenesis has not been studied. Here, we demonstrated that HBx strongly induced the expression of MTA1 and HDAC1 genes at transcription level. MTA1 and HDAC1/2 physically associated with hypoxia-inducible factor-1 alpha (HIF-1 alpha) in vivo in the presence of HBx, which was abolished by knockdown of MTA1 by short interfering RNA (siRNA). HBx induced deacetylation of the oxygen-dependent degradation domain of HIF-1 alpha, which was accompanied with dissociation of prolyl hydroxylases and von Hippel-Lindau tumor suppressor from HIF-1 alpha. These results indicate that HBx-induced deacetylation is important for proteasomal degradation of HIF-1 alpha. Further, we observed that protein levels of MTA1 and HDAC1 were increased in the liver of HBx-transgenic mice. Also, there was a higher expression of HDAC1 in HCC than in the adjacent non-tumorous cirrhotic nodules in 10 out of 12 human HBV-associated HCC specimens. Together, our data indicate a positive cross talk between HBx and the MTA1/HDAC complex in stabilizing HIF-1 alpha, which may play a critical role in angiogenesis and metastasis of HBV-associated HCC.

Heat shock factor 1 represses estrogen-dependent transcription through association with MTA1

Heat shock factor 1 (HSF1), the transcriptional activator of the heat shock genes, is increasingly implicated in cancer. We have shown that HSF1 binds to the corepressor metastasis-associated protein 1 (MTA1) in vitro and in human breast carcinoma samples. HSF1-MTA1 complex formation was strongly induced by the transforming ligand heregulin and complexes incorporated a number of additional proteins including histone deacetylases (HDAC1 and 2) and Mi2alpha, all components of the NuRD corepressor complex. These complexes were induced to assemble on the chromatin of MCF7 breast carcinoma cells and associated with the promoters of estrogen-responsive genes. Such HSF1 complexes participate in repression of estrogen-dependent transcription in breast carcinoma cells treated with heregulin and this effect was inhibited by MTA1 knockdown. Repression of estrogen-dependent transcription may contribute to the role of HSF1 in cancer.

Metastasis-associated protein 1 (MTA1) is an essential downstream effector of the c-MYC oncoprotein

The c-myc oncogene is among the most commonly overexpressed genes in human cancer. c-myc encodes a basic helix-loop-helix/leucine zipper (bHLH/LZ) transcription factor (c-MYC) that activates a cascade of downstream targets that ultimately mediate cellular transformation. Although a large number of genes are regulated by c-MYC, only a few have been functionally linked to c-MYC-mediated transformation. By expression profiling, the metastasis-associated protein 1 (MTA1) gene was identified here as a target of the c-MYC oncoprotein in primary human cells, a result confirmed in human cancer cells. MTA1 itself has been previously implicated in cellular transformation, in part through its ability to regulate the epithelial-to-mesenchymal transition and metastasis. MTA1 is a component of the Mi-2/nucleosome remodeling and deacetylating (NURD) complex that contains both histone deacetylase and nucleosome remodeling activity. The data reported here demonstrate that endogenous c-MYC binds to the genomic MTA1 locus and recruits transcriptional coactivators. Most importantly, short hairpin RNA (shRNA)-mediated knockdown of MTA1 blocks the ability of c-MYC to transform mammalian cells. These data implicate MTA1 and the Mi-2/NURD complex as one of the first downstream targets of c-MYC function that are essential for the transformation potential of c-MYC.