Abstract 572: Interference with Sin3 PAH-2 domain function induces epigenetic reprogramming, differentiation and growth inhibition in breast cancer cells

Abstract

Abstract Our recent work in understanding silenced retinoic acid response genes in breast cancer led us to explore the role of transcription repressor complexes in gene silencing in breast cancer. To this end we constructed a set of tagged vectors that contain a specific MAD1 motif called SID (mSin3A interaction domain), which binds with high affinity to block the function of the Sin3. Sin3A/B serve as multisubunit co-repressor scaffold protein that regulate gene transcription by recruiting histone deacetylase and histone demethylase activities to sequence-specific transcriptional repressors which are aberrant in breast cancer. The PAH2 domain of Sin3A/B binds with high affinity to a small number of transcription factors, and offers a more specific epigenetic target which contributes to the development of breast cancer. PAH-2 domain a specific component of a transcriptional repressor complex that plays an important role in modulating a small number of transcription factors containing the Sin3 PAH-2 interaction domain (SID). Here we demonstrated that in both human and mouse breast cancer cells, the targeted disruption of Sin3 function by introduction with their partners by the expression of SID transcript or peptide decoy interfered with PAH2 binding to SID-containing partner proteins as measured by co-immunoprecipitation and mammalian two-hybrid assays, reverteds the silencing of several genes involved in cell growth and differentiation. We observed that the SID decoy induced clear signs of differentiation in both human and mouse breast cancer cellsIn particular, the which include theSID decoys led to acinar morphogenesis in 3D cultures, increased adherence to collagen type-IV and laminin, reduced invasive phenotype and impaired tumor growth in vivo (>75%). This was associated with epigenetic reprogramming characterized by a marked increase in H3K4 2/3 methylation and a modest increase in H3 acetylation in the promoter region, promoter DNA demethylation and re-expression of the important breast cancer-associated silenced genes encoding E-cadherin, and, estrogen receptor α (ERα) and retinoic acid receptor β (RARβ)and impairment in tumor growth in vivo. There was increased expression of E-cadherin, CRBP1 and p27 known RAR response genes. The re-expression of ERα and RARβ in the “triple negative” MDA-MB-231 breast cancer cell line is functional since there was significant growth inhibition by tamoxifen after stimulation with 17b-estradiol and RAR activation by atRA and AM580. Therefore, the development of small molecules that mimic the 13 amino acid SID peptide and block interactions between PAH2 and SID-containing proteins This offers a new novel approach for treating this type of breast cancer and may also provide wider therapeutic implicationstriple negative breast cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 572.