A novel role for the Bcl-2 protein family: specific suppression of the RAD51 recombination pathway.

The oncogenic role of Bcl-2 is generally attributed to its protective effect against apoptosis. Here, we show a novel role for Bcl-2: the specific inhibition of the conservative RAD51 recombination pathway. Bcl-2 or Bcl-X(L) overexpression inhibits UV-C-, gamma-ray- or mutant p53-induced homologous recombination (HR). Moreover, Bcl-2 recombination inhibition is independent of the role of p53 in G1 arrest. At an acute double-strand break in the recombination substrate, Bcl-2 specifically inhibits RAD51-dependent gene conversion without affecting non-conservative recombination. Bcl-2 consistently thwarts recombination stimulated by RAD51 overexpression and alters Rad51 protein by post-translation modification. Moreover, a mutant (G145A)Bcl-2, which is defective in Bax interaction and in apoptosis repression, also inhibits recombination, showing that the death and recombination repression functions of Bcl-2 are separable. Inhibition of error-free repair pathways by Bcl-2 results in elevated frequencies of mutagenesis. The Bcl-2 gene therefore combines two separable cancer-prone phenotypes: apoptosis repression and a genetic instability/mutator phenotype. This dual phenotype could represent a mammalian version of the bacterial SOS repair system.