ID1, inhibitor of differentiation/DNA binding, is an effector of the p53-dependent DNA damage response pathway.

ID1, inhibitor of differentiation/DNA binding, plays an important role in cell proliferation, differentiation, and tumorigenesis. It has been shown that ID1 is de-regulated in multiple cancers and up-regulation of ID1 is correlated with high grades and poor prognosis of human cancers. In contrast, the p53 tumor suppressor was found to be mutated or inactivated in most human cancers and loss of p53 results in early onset of multiple cancers. Although the biological functions of the ID1 oncogene and the p53 tumor suppressor have been intensively investigated, little is known about the upstream regulators of ID1 and the cross-talk between ID1 and p53. Here, we showed that ID1 is down-regulated in cells treated with various DNA damage agents in a p53-dependent manner. Interestingly, we found that DEC1, which was recently identified as a p53 target and mediates p53-dependent cell cycle arrest and senescence, is capable of inhibiting ID1 expression. Conversely, we found that knockdown of DEC1 attenuates DNA damage-induced ID1 repression. In addition, we identified several potential DEC1 responsive elements in the proximal promoter region of the ID1 gene. Moreover, we showed that overexpression of ID1 or ID1', an isoform of ID1, promotes cell proliferation potentially through inhibition of p21 expression. Finally, we found that the extent of DNA damage-induced premature senescence was substantially decreased by overexpression of ID1 or ID1'. Taken together, our study suggests that p53 trans-repressional activity can be mediated by its own target DEC1 and ID1 is an effector of the p53-dependent DNA damage response pathway.