Functional proteomics of transforming growth factor-β1-stimulated Mv1Lu epithelial cells: Rad51 as a target of TGFβ1-dependent regulation of DNA repair

Transforming growth factor-β (TGFβ) conveys regulatory signals through multiple intracellular pathways, subsequently affecting various cellular functions. To identify new targets for TGFβ, we studied the changes in the proteome of Mv1Lu lung epithelial cells in response to TGFβ1 treatment. Thirty-eight non-abundant protein spots, affected by TGFβ1, were selected, and proteins were identified by peptide mass-fingerprinting (PMF). Among them, proteins involved in regulation of immune response, apoptosis, regulation of TGFβ signalling, metabolism and DNA repair were identified. Twenty-eight of the 38 proteins are new targets for TGFβ1, thus suggesting novel ways of integration of TGFβ signalling in intracellular regulatory processes. We show that TGFβ1-dependent decrease in expression of one of the new targets, Rad51, correlates with a decrease in DNA repair efficiency. This was evaluated by formation of nuclear Rad51-containing DNA repair complexes in response to DNA damage, by single cell gel electrophoresis and by cell survival assay. The TGFβ1-dependent inhibition of DNA repair was reversed by ectopic overexpression of Rad51. Therefore, TGFβ can promote DNA instability through down-regulation of Rad51 and inhibition of DNA repair.