Functional Interaction of p53 and BLM DNA Helicase in Apoptosis

Abstract

The Bloom syndrome (BS) protein, BLM, is a member of the RecQ DNA helicase family that also includes the Werner syndrome protein, WRN. Inherited mutations in these proteins are associated with cancer predisposition of these patients. We recently discovered that cells from Werner syndrome patients displayed a deficiency in p53-mediated apoptosis and WRN binds to p53. Here, we report that analogous to WRN, BLM also binds to p53 in vivo and in vitro, and the C-terminal domain of p53 is responsible for the interaction. p53-mediated apoptosis is defective in BS fibroblasts and can be rescued by expression of the normal BLM gene. Moreover, lymphoblastoid cell lines (LCLs) derived from BS donors are resistant to both ␥-radiation and doxorubicin-induced cell killing, and sensitivity can be restored by the stable expression of normal BLM. In contrast, BS cells have a normal Fas-mediated apoptosis, and in response to DNA damage normal accumulation of p53, normal induction of p53 responsive genes, and normal G 1 -S and G 2 -M cell cycle arrest. BLM localizes to nuclear foci referred to as PML nuclear bodies (NBs). Cells from Li-Fraumeni syndrome patients carrying p53 germline mutations and LCLs lacking a functional p53 have a decreased accumulation of BLM in NBs, whereas isogenic lines with functional p53 exhibit normal accumulation. Certain BLM mutants (C1055S or ⌬133-237) that have a reduced ability to localize to the NBs when expressed in normal cells can impair the localization of wild type BLM to NBs and block p53-mediated apoptosis, suggesting a dominantnegative effect. Taken together, our results indicate both a novel mechanism of p53 function by which p53 mediates nuclear trafficking of BLM to NBs and the cooperation of p53 and BLM to induce apoptosis.

Multiple Genetic Pathways Involving the Caenorhabditis elegans Bloom's Syndrome Genes him-6, rad-51, and top-3 Are Needed To Maintain Genome Stability in the Germ Line

“…We observed only partial checkpoint defects in him-6 C. elegans worms. Similarly, irradiation-induced apoptosis and G 2 /M cell cycle arrest is only partially compromised in human BS Ϫ/Ϫ cells (1,59). It was recently shown that HIM-6 physically interacts with the C. elegans ATR homolog, whose inactivation by RNAi leads to defective checkpoint processes in response to ionizing radiation (8), as well as to HU (A. Gartner, unpublished observation).…”

DNA Repair and Tumorigenesis: Lessons from Hereditary Cancer Syndromes

“…86 BS cells also appear defective in p53-dependent apoptosis following artificial overexpression of p53. 87 However, such a connection to damage-induced apoptosis may not be significant under normal circumstances since BS cells remain exquisitely sensitive to alkylating agents. 82 WRN is another RecQ family helicase that has been linked to the rare genetic disease Werner's syndrome (WS).…”

Regulation and mechanisms of mammalian double-strand break repair

“…Nevertheless, in vitro studies demonstrate that P53 binds both ss and dsDNA (Oberosler et al, 1993;Bakalkin et al, 1994), possesses a 3 0 -5 0 exonuclease activity and promotes DNA reannealing (Oberosler et al, 1993;Mummenbrauer et al, 1996). Furthermore, P53 also binds to mismatches and three-stranded DNA substrates (Lee et al, 1995;Dudenhoffer et al, 1998), and to Holliday junctions, thereby facilitating their resolution (Lee S et al, 1997); complexes with and inhibits RAD51 (Sturzbecher et al, 1996;Buchhop et al, 1997); interacts with BRCA2 (Marmorstein et al, 1998); complexes with BLM and WRN (Blander et al, 1999;Spillare et al, 1999;Wang XW et al, 2001); and regulates the BLM and WRN helicase activities on Holliday junctions in vitro (Blander et al, 1999;Spillare et al, 1999;Wang XW et al, 2001;Yang et al, 2002b). Ectopic overexpression of wild-type P53 suppresses HRR on extrachromosomal and chromosomal DNA substrates .…”