over-expression of the catalytic subunit of the proteasome decreases recombination and impairs DNA double-strand break repair in human cells

By a human cDNA library screening, we have previously identified two sequences coding two different catalytic subunits of the proteasome which increase homologous recombination (HR) when overexpressed in the yeast Saccharomyces cerevisiae. Here, we investigated the effect of proteasome on spontaneous HR and DNA repair in human cells. To determine if the proteasome has a role in the occurrence of spontaneous HR in human cells, we overexpressed the 2 subunit of the proteasome in HeLa cells and determined the effect on intrachromosomal HR. Results showed that the overexpression of 2 subunit decreased HR in human cells without altering the cell proteasome activity and the Rad51p level. Moreover, exposure to MG132 that inhibits the proteasome activity reduced HR in human cells. We also found that the expression of the 2 subunit increases the sensitivity to the camptothecin that induces DNA double-strand break (DSB). This suggests that the 2 subunit has an active role in HR and DSB repair but does not alter the intracellular level of the Rad51p. Copyright 2011 Anita Collavoli et al.