Acute loss of DP1, but not DP2, induces p53 mRNA and augments p21Waf1/Cip1 and senescence

The transcription factors DP1 and DP2 have been implicated in crucial gene regulation as heterodimer partners of E2F; however, the functional differences between DP1 and DP2 remain poorly understood. To gain insight into DPs in human somatic cells, we first suppressed endogenous DP1 and DP2 using RNA interference and examined the effect of their loss on gene expression changes in HeLa cervical cancer cells. A DNA microarray and gene pathway analysis revealed that the suppression of well‐known E2F/DP‐regulated pathways, including the G1 to S phase transition of the cell cycle and DNA replication, was manifested in accordance with the acute loss of DP1 and DP2. On the other hand, the acute loss of DP1 and DP2 increased the p21Waf1/Cip1 mRNA level compared with the control RNA treatment. We further showed that the inactivation of DP1, but not DP2, resulted in mRNA induction for p53, an upstream regulator of p21Waf1/Cip1. Furthermore, in A549 lung cancer cells as well as HeLa cells, the mRNA and protein levels of p53 and p21Waf1/Cip1 were stabilized specifically upon DP1 depletion, whereas p53‐regulated apoptotic factor BAX mRNA was unchanged. Finally, the impairment of DP1, but not DP2, increased senescence in HeLa, A549 and WI‐38 diploid fibroblasts but not in p53 null Saos‐2 osteosarcoma cells. Taken together, these results suggest that DP1, but not DP2, is uniquely involved in the regulation of the p53 and p21Waf1/Cip1 pathway, thereby augmenting senescence in human somatic cells. Copyright © 2011 John Wiley & Sons, Ltd.