Identification of Ku70/Ku80 as ADD1/SREBP1c interacting proteins

In vertebrates, multisubunit cofactors regulate gene expression through interacting with cell‐type‐ and gene‐specific DNA‐binding proteins in a chromatin‐selective manner. ADD1/SREBP1c regulates fatty acid metabolism and insulin‐dependent gene expression through binding to SRE and E‐box motif with dual DNA binding specificity. Although its transcriptional and post‐translational regulation has been extensively studied, its regulation by interacting proteins is not well understood. To identify cellular proteins that associate with nuclear form of ADD1/SREBP1c, we employed the GST pull‐down system with Hela cell nuclei extract. In this study, we demonstrated that Ku proteins interact specifically with ADD1/SREBP1c protein. GST pull‐down combined with peptide sequencing analysis revealed that Ku80 binds to ADD1/SREBP1c in vitro. Additionally, western blot analysis showed that Ku70, a heterodimerizing partner of Ku80, also associates with ADD1/SREBP1c. Furthermore, co‐transfection of Ku70/Ku80 with ADD1/SREBP1c enhanced the transcriptional activity of ADD1/SREBP1c. Taken together, these results suggest that the Ku proteins might be involved in the lipogenic and/or adipogenic gene expression through interacting with ADD1/SREBP1c.