Abstract PR06: CARM1 methylates BAF155 and perturbs chromatin remodeling machinery to enhance tumor progression

Abstract

Abstract CARM1 belongs to the type I protein arginine (R) methyltransferase (PRMT) family and asymmetrically di-methylates proteins on arginines. Because CARM1 is highly expressed in high grade breast tumors and was shown to transactivate cancer-relevant transcription factors including ERα, NF-κB, p53 and E2F1, it has been strongly implicated in tumorigenesis. To fully characterize functions of CARM1 in breast cancer, we knocked-out CARM1 from several breast cancer cell lines using Zinc-Finger Nuclease technology. Western blot using an asymmetric di-methylated R antibody revealed striking differences between CARM1 KO and parental MCF7 cell lysates, indicating that CARM1 methylates a significant number of substrates in breast cancer cells. BAF155, a core subunit of SWI/SNF chromatin remodeling complex, was identified as a CARM1 substrate by mass spectrometry. Further biochemical analyses validated that BAF155 was methylated by CARM1 in vivo and in vitro and methylation was mapped to a single site, R1064. We next generated BAF155R1064K knock-in MCF7 and MDA-mb-231 cells and showed that methylation of BAF155 is essential for breast cancer cell growth, colony formation and migration. Further, we developed an antibody that selectively recognized methylated form of BAF155 (me-BAF155) and observed strong nuclear me-BAF155 staining in invasive ductal carcinoma but not in the normal breast tissue. Importantly, me-BAF155 immunostaining positively correlates with tumor stage and metastasis. To understand the molecular mechanism by which BAF155 methylation affects tumorigenesis, we performed ChIP-seq using ChIP-validated BAF155 antibody in the BAF155WT or BAF155R1064K knock-in MCF7 cells. Interestingly, C-Myc pathway genes were only identified in WT but not mutant BAF155 regulated categories. Individual ChIP assays validated differential binding of BAF155WT or BAF155R1064K to specific target genes and importantly, the mRNA levels of these genes were affected correspondingly. This result suggests that BAF155 methylation affects gene expression by altering genomic association of BAF155, and perhaps the SWI/SNF complex, to chromatin regions. Collectively, our study revealed novel mechanisms by which CARM1 perturbs the chromatin remodeling machinery to enhance tumor progression. This work is supported by DOD ERA of HOPE Scholar Award and Shaw Scientist Award to W.X. This abstract is also presented as Poster A37. Citation Format: Lu Wang, Zibo Zhao, Mark Meyer, Wesley J. Pike, Wei Xu. CARM1 methylates BAF155 and perturbs chromatin remodeling machinery to enhance tumor progression. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr PR06.