The Over-expression of the β2 Catalytic Subunit of the Proteasome Decreases Homologous Recombination and Impairs DNA Double-Strand Break Repair in Human Cells

Anita Collavoli,Laura Comelli,Tiziana Cervelli,Alvaro Galli

doi:10.1155/2011/757960

Abstract

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 β2 subunit of the proteasome in HeLa cells and determined the effect on intrachromosomal HR. Results showed that the overexpression of β2 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 β2 subunit increases the sensitivity to the camptothecin that induces DNA double-strand break (DSB). This suggests that the β2 subunit has an active role in HR and DSB repair but does not alter the intracellular level of the Rad51p.

Highlights

Homologous recombination (HR) is essential in maintenance genome stability in all organisms [1,2,3]
Most proteins implicated in the DNA double-strand break (DSB) repair by homologous recombination (HR) were identified using the yeast Saccharomyces cerevisiae as genetic model [31]
There is no direct evidence that spontaneous HR is due to DNA DSBs, several studies report that spontaneous DSBs may occur in mammalian cells [33, 34]

Summary

Introduction

Homologous recombination (HR) is essential in maintenance genome stability in all organisms [1,2,3]. Most information about the genetic control and mechanisms of HR comes from studies on the yeast Saccharomyces cerevisiae, where deletion of RAD52, RAD51, and RAD54 genes profoundly impairs HR [4, 5]. As HR is crucial for the maintenance of genome integrity, it must be tightly regulated to avoid dangerous and potentially lethal events. Mutations in the tumor suppressor genes BRCA1 or BRCA2, which have a regulatory function in HR, may lead to cancer. Defects in the BLM gene encoding for a DNA helicase, which regulates the outcome of HR, may lead to cancer prone disease [2]. The primary role of HR is to repair double-strand breaks (DSBs) that can be induced by a variety of DNA-damaging agents including UV and γ-radiation [6,7,8]

Methods

Results

Conclusion