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The SMRT coregulator enhances growth of estrogen receptor-?-positive breast cancer cells by promotion of cell cycle progression and inhibition of apoptosis.

ABSTRACT: The SMRT coregulator functions as a dual coactivator and corepressor for estrogen receptor-? (ER?) in a gene-specific manner, and in several studies its elevated expression correlates with poor outcome for breast cancer patients. A specific role of SMRT in breast cancer progression has not been elucidated, but SMRT knock-down limits estradiol-dependent growth of MCF-7 breast cancer cells. In this study, small-interfering RNA (siRNA) and short-hairpin RNA (shRNA) approaches were used to determine the effects of SMRT depletion on growth of ER?-positive MCF-7 and ZR-75-1 breast cancer cells, as well as the ER?-negative MDA-MB-231 breast cancer line. Depletion of SMRT inhibited growth of ER?-positive cells grown in monolayer but had no effect on growth of the ER?-negative cells. Reduced SMRT levels also negatively impacted the anchorage-independent growth of MCF-7 cells as assessed by soft agar colony formation assays. The observed growth inhibitions were due to a loss of estradiol-induced progression through the G1/S transition of the cell cycle and increased apoptosis in SMRT-depleted compared with control cells. Gene expression analyses indicated that SMRT inhibits apoptosis by a coordinated regulation of genes involved in apoptosis. Functioning as a dual coactivator for anti-apoptotic genes and corepressor for pro-apoptotic genes, SMRT can limit apoptosis. Together these data indicate that SMRT promotes breast cancer progression through multiple pathways leading to increased proliferation and decreased apoptosis.

SUBMITTER: Blackmore JK

PROVIDER: S-EPMC4138560 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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The SMRT coregulator enhances growth of estrogen receptor-α-positive breast cancer cells by promotion of cell cycle progression and inhibition of apoptosis.

Blackmore Julia K JK Karmakar Sudipan S Gu Guowei G Chaubal Vaishali V Wang Liguo L Li Wei W Smith Carolyn L CL

Endocrinology 20140627 9

The SMRT coregulator functions as a dual coactivator and corepressor for estrogen receptor-α (ERα) in a gene-specific manner, and in several studies its elevated expression correlates with poor outcome for breast cancer patients. A specific role of SMRT in breast cancer progression has not been elucidated, but SMRT knock-down limits estradiol-dependent growth of MCF-7 breast cancer cells. In this study, small-interfering RNA (siRNA) and short-hairpin RNA (shRNA) approaches were used to determine ...[more]

PMID: 24971610

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Project description:BACKGROUND:CDK4/6 inhibitors in combination with endocrine therapy (AE/AI/SERDs) are approved for the treatment of ER+ advanced breast cancer (BCa). However, not all patients benefit from CDK4/6 inhibitors therapy. We previously reported a novel therapeutic agent, ERX-11, that binds to the estrogen receptor (ER) and modulates ER-coregulator interactions. Here, we tested if the combination of ERX-11 with agents approved for ER+ BCa would be more potent. METHODS:We tested the effect of combination therapy using BCa cell line models, including those that have acquired resistance to tamoxifen, letrozole, or CDK4/6 inhibitors or have been engineered to express mutant forms of the ER. In vitro activity was tested using Cell Titer-Glo, MTT, and apoptosis assays. Mechanistic studies were conducted using western blot, reporter gene assays, RT-qPCR, and mass spectrometry approaches. Xenograft, patient-derived explants (PDEs), and xenograft-derived explants (XDE) were used for preclinical evaluation and toxicity. RESULTS:ERX-11 inhibited the proliferation of therapy-resistant BCa cells in a dose-dependent manner, including ribociclib resistance. The combination of ERX-11 and CDK4/6 inhibitor was synergistic in decreasing the proliferation of both endocrine therapy-sensitive and endocrine therapy-resistant BCa cells, in vitro, in xenograft models in vivo, xenograft-derived explants ex vivo, and in primary patient-derived explants ex vivo. Importantly, the combination caused xenograft tumor regression in vivo. Unbiased global mass spectrometry studies demonstrated profound decreases in proliferation markers with combination therapy and indicated global proteomic changes in E2F1, ER, and ER coregulators. Mechanistically, the combination of ERX-11 and CDK4/6 inhibitor decreased the interaction between ER and its coregulators, as evidenced by immunoprecipitation followed by mass spectrometry studies. Biochemical studies confirmed that the combination therapy significantly altered the expression of proteins involved in E2F1 and ER signaling, and this is primarily driven by a transcriptional shift, as noted in gene expression studies. CONCLUSIONS:Our results suggest that ERX-11 inhibited the proliferation of BCa cells resistant to both endocrine therapy and CDK4/6 inhibitors in a dose-dependent manner and that the combination of ERX-11 with a CDK4/6 inhibitor may represent a viable therapeutic approach.

Project description:PurposeIn early stage, ERα-positive breast cancer, concurrent use of endocrine therapy and chemotherapy has not been shown to be superior to sequential use. We hypothesized that genetic biomarkers can aid in selecting patients who would benefit from chemo-endocrine therapy. Our previous studies revealed that ZNF423 is a transcription factor for BRCA1 and an intronic single nucleotide polymorphism (SNP) in ZNF423, rs9940645, determines tamoxifen response. Here, we identified mitosis-related genes that are regulated by ZNF423 which led us to investigate taxane response in a rs9940645 SNP- and tamoxifen-dependent fashion.MethodsThe Cancer Genome Atlas (TCGA) breast cancer dataset was used to identify genes correlated with ZNF423. Quantitative reverse transcription PCR, chromatin immunoprecipitation, and luciferase reporter assays were used to validate the gene regulation. We used CRISPR/Cas9 to engineer paired ZR-75-1 cells which differ only in ZNF423 rs9940645 SNP genotype to test SNP-dependent phenotypes including cell cycle and cell viability. We validated our findings in an additional two breast cancer cell lines, Hs578T-ERα and HCC1500.ResultsMitosis-related genes VRK1 and PBK, which encode histone H3 kinases, were experimentally validated to be regulated by ZNF423. ZNF423 knockdown decreased VRK1 and PBK expression and activity. Additionally, ZNF423 knockdown enhanced docetaxel-induced G2/M arrest and cytotoxicity through VRK1 or PBK regulation. Lastly, cells carrying the rs9940645 variant genotype had increased G2/M arrest and decreased cell viability when treated with docetaxel in combination with estradiol and 4-OH-TAM.ConclusionsWe identified ZNF423 regulated genes involved in the G2/M phase of the cell cycle. 4-OH-TAM sensitized ERα-positive breast cancer cells to docetaxel in a ZNF423 SNP-dependent manner. Our findings suggest that patients with rs9940645 variant genotype may benefit from concurrent tamoxifen and docetaxel. This would impact a substantial proportion of patients because this SNP has a minor allele frequency of 0.47.

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The SMRT coregulator enhances growth of estrogen receptor-?-positive breast cancer cells by promotion of cell cycle progression and inhibition of apoptosis.

Publications

The SMRT coregulator enhances growth of estrogen receptor-α-positive breast cancer cells by promotion of cell cycle progression and inhibition of apoptosis.

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