Mammalian Pleiotropic Regulator PLRG-1 was initially identified as a component of the spliceosome and belongs to a highly conserved family of seven WD40 domain containing proteins in eukaryotes (Ajuh et al., 2000; Ajuh et al., 2001). Founding members of this WD40-repeat protein family, PRL1 and PRL2, were first identified by T-DNA tagging in Arabidopsis thaliana (Nemeth et al., 1998). Whereas in plants the PRL genes are uniquely duplicated, in yeast, C. elegans and mammals there are only single orthologues of the Pleiotropic Regulator family which play important roles in the control of cellular homeostasis by forming at least in mammals, a complex with Pso4 and the cell division and cycle 5 homolog (CDC5L), that regulates both pre-mRNA splicing. To characterize the role of PLRG-1 in vivo, in the present study, I shown that inactivation of PLRG-1 results in embryonic lethality 1.5 days postfertilization in mice, indicating a fundamental role for PLRG-1 in early cell cycle events. Studies on heart- and neuron-specific PLRG-1 knockout mice revealed that massive apoptosis was responsible for their premature death. Moreover, PLRG-1-deficient mouse embryonic fibroblasts (MEFs) fail to enter S-phase upon serum stimulation and show increased apoptosis resulting from enhanced p53 phosphorylation and stabilization. Interestingly, p53-phosphatase WIP1 was seen to interact with CDC5L in wild-type, but not in PLRG-1-deficient MEFs due to cytosolic translocation of CDC5L. p53 downregulation rescues lethality in PLRG-1-deficient MEFs, showing that apoptosis resulting from PLRG-1-deficiency is p53 dependent Taken together, it is shown that the Pso4-CDC5LPLRG-1 complex controls cell proliferation and apoptosis by novel integration of pre-mRNA splicing and DNA repair via a p53-phosphorylation-dependent pathway, thus providing the first evidence for Pso4-complex regulation of p53
