JBC Papers in Press . Published on May 5 , 2010 as Manuscript R110 . 119743 The latest version is at http://www.jbc.org/cgi/doi/10.1074/jbc.R110.119743

Abstract

Rsf-1 (HBXAP) has been reported as an amplified gene in human cancer, including the highly aggressive ovarian serous carcinoma. Rsf-1 protein interacts with SNF2H to form an ISWI chromatin remodeling complex, RSF. In this study, we investigated the functional role of Rsf-1 by observing phenotypes after expressing it in non-transformed cells. Acute expression of Rsf-1 resulted in DNA damage as evidenced by DNA strand breaks, nuclear γH2AX foci and activation of the ATM-CHK2-p53-p21 pathway, leading to growth arrest and apoptosis. Deletion mutation and gene knockdown assays revealed that formation of a functional RSF complex with SNF2H was required for Rsf-1 to trigger DNA damage response (DDR). Gene knockout of TP53 alleles, TP53 mutation, or treatment with an ATM inhibitor abolished upregulation of p53 and p21 and prevented Rsf-1-induced growth arrest. Chronic induction of Rsf-1 expression resulted in chromosomal aberration and clonal selection for cells with c-Myc amplification and CDKN2A/B deletion. Co-culture assays indicated Rsf-1-induced DDR as a selecting barrier that favored outgrowth of cell clones with TP53 mutation. The above findings suggest that increased Rsf-1 expression and thus excessive RSF activity, which occurs in tumors harboring Rsf-1 amplification, can induce chromosomal instability likely through DDR.

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