Sameer Phalke1, Slim Mzoughi1,2, Marco Bezzi1,2, Nancy Jennifer1, Wei Chuen Mok1, Diana Low11,3, Aye Aye Thike4, Vladimir Kuznetsov3, Puay Hoon Tan4, Mathijs Voorhoeve5,2 and Ernesto Guccione1,2.
1- Institute of Molecular and Cell Biology (IMCB), Singapore
2- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
3- BioInformatics Institute (BII), Singapore
4- Singapore General Hospital, Department of Pathology, Outram Road Singapore
5- Cancer and Stem Cell Biology Program, Duke NUS, 8 College Road, Singapore
Published online in Nucl. Acids Res. on 16 September 2012.
p21 is a potent cyclin-dependent kinase inhibitor that plays a role in promoting G1-cell cycle arrest and cellular senescence. Consistent with this role, p21 is a downstream target of several tumor suppressors and oncogenes and it is down-regulated in the majority of tumors, including breast cancer. Here, we report that PRMT6, a type I Protein Arginine methyltransferase (PRMT) known to act as a transcriptional cofactor, directly represses the p21 promoter. PRMT6 Knock Down (KD) results in a p21 derepression in breast cancer cells which is p53-independent, and leads to cell cycle arrest, cellular senescence and reduced growth both in soft agar assays and in SCID mice for all the cancer lines examined. We finally show that bypassing the p21-mediated arrest rescues PRMT6 KD cells from senescence and it restores their ability to grow on soft agar. We conclude that PRMT6 acts as an oncogene in breast cancer cells, promoting growth and preventing senescence, making it an attractive target for cancer therapy.
Figure Legend: PRMT6 directly represses the p21 promoter. qPCR analysis of cyclin inhibitors (A) p16 and (B) p21 in PRMT6 depleted (sh-1 and sh-2) or control (sh-c) MCF7 and MDA-MB-231 cells. (C) Immunoblot analysis of p21 protein levels in PRMT6 depleted (sh-1 and sh-2) or control (sh-c) MCF7 and MDA-MB-231 cells. (D) Chromatin immunoprecipitation in MCF7 cells using the antibody indicated on each panel. Data are shown as the % of input DNA for PRMT6 and as % of input DNA normalized to total H3 (% input/H3) for the histone PTMs. The p21 promoter in MCF7 cells is enriched for inactive- (H3R2me2a and H3K27me3) and depleted for active- (H3K4me3 and H3acetyl) chromatin marks in control cells as compared with PRMT6 depleted ones (sh-2, grey lines). Experiment was repeated four times, and a representative plot is shown.
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