Mice Deficient for the Wild-Type p53-Induced Phosphatase Gene (Wip1) Exhibit Defects in Reproductive Organs, Immune Function, and Cell Cycle Control

Abstract

The Wip1 gene is a serine/threonine phosphatase that is induced in a p53-dependent manner by DNAdamaging agents. We show here that Wip1 message is expressed in moderate levels in all organs, but is present at very high levels in the testes, particularly in the postmeiotic round spermatid compartment of the seminiferous tubules. We have confirmed that Wip1 mRNA is induced by ionizing radiation in mouse tissues in a p53-dependent manner. To further determine the normal biological function of Wip1 in mammalian organisms, we have generated Wip1-deficient mice. Wip1 null mice are viable but show a variety of postnatal abnormalities, including variable male runting, male reproductive organ atrophy, reduced male fertility, and reduced male longevity. Mice lacking Wip1 show increased susceptibility to pathogens and diminished T-and B-cell function. Fibroblasts derived from Wip1 null embryos have decreased proliferation rates and appear to be compromised in entering mitosis. The data are consistent with an important role for Wip1 in spermatogenesis, lymphoid cell function, and cell cycle regulation.The p53 tumor suppressor protein plays a critical role in integration of signals that regulate cell growth and death in response to a variety of stressors (11,12,26). Loss or mutation of the gene encoding the p53 protein predisposes a cell to neoplastic transformation (8,21,23). Mutation of the p53 gene has been observed in half of all human cancers, and loss of p53 signaling may play a role in over 80% of all tumors (8,12,13).In response to a variety of cell stresses, including DNA damage, aberrantly activated oncogenes, and hypoxia, p53 is phosphorylated on multiple serine and threonine residues, becomes stabilized, and accumulates in the nucleus (11,12,26). The activated p53 protein is a transcription factor that can upregulate as well as downregulate a battery of genes which participate in the biological response to the cell stress. This response can be in the form of cell cycle arrest, apoptosis, differentiation, or senescence. Any of these responses are likely to prevent the outgrowth of a nascent cancer cell.Among the many p53 transcriptional targets that have recently been identified is the wild-type p53-induced phosphatase (Wip1) (5). The Wip1 gene exhibits a close similarity to type 2C phosphatases (2, 5). The type 2C phosphatases are distinguished from the PP1, PP2A, and PP2B phosphatases by their insensitivity to phosphatase inhibitors such as okadaic acid and requirement for divalent cations (Mg 2ϩ or Mn 2ϩ ) (3, 15). The type 2C phosphatases have been identified in a wide range of organisms and have often been associated with stress response, sexual differentiation, and cell cycle control (3, 15).The Wip1 gene was originally identified in a screen for p53 target genes (5). Wip1 was shown to be upregulated in a p53-dependent manner by ionizing radiation (IR) and by UV radiation (UV) (5, 25). Following IR, Wip1 mRNA was rapidly induced and the protein was localized to the nucleus. The first specific target of the W...

A chemical inhibitor of PPM1D that selectively kills cells overexpressing PPM1D

“…Additional functions for PPM1D include the regulation of the base excision pathway of DNA repair (Lu et al, 2004), progesterone receptor function (Proia et al, 2006), the homoeostatic regulation of the checkpoint kinases CHK1 and CHK2 (Lu et al, 2005;Fujimoto et al, 2006;Nannenga et al, 2006;OlivaTrastoy et al, 2006;Yoda et al, 2006;Yu et al, 2006) and the activation of ataxia-telangiectasia mutated (Shreeram et al, 2006), all of which may also contribute to the oncogenic effects of PPM1D overexpression. Mice deficient in Ppm1d are viable, with only minor defects in immune function and spermatogenesis (Choi et al, 2002). However, these animals are resistant to mammary tumours induced by mouse mammary tumor virus-driven cHras1 or cNeu as well as to spontaneous tumour formation (Bulavin et al, 2004;Nannenga et al, 2006).…”

Regulation of the antioncogenic Chk2 kinase by the oncogenic Wip1 phosphatase

“…In this respect, it is of interest to note that fibroblasts from Wip1-null embryos exhibit a decreased proliferation rate. 36 It has been reported that Wip1 contributes to suppression of UVirradiation-induced apoptosis by dephosphorylating and inactivating p38. 24 However, g-irradiation-induced apoptosis of MCF7 cells transfected with Wip1 siRNAs was unaffected in the absence or presence of the specific inhibitor of p38, SB203580 (data not shown).…”

The Wip1 phosphatase (PPM1D) antagonizes activation of the Chk2 tumour suppressor kinase

“…The mammalian PPM1D gene coding for the nuclear PP2C delta isoform (or Wip1) was originally identified by its p53-dependent transcriptional induction in response to ionizing IR (Fiscella et al, 1997) and was thus of particular interest for further study. Mice deficient for Wip1 exhibit defects in reproductive organ and immune function, and Wip1 À/À MEF cells have decreased proliferation rates owing to the activation of the p16 (Ink4a) and p19 (ARF) pathways (Choi et al, 2002;Bulavin et al, 2004). In response to genotoxic stress, Wip1 was recently shown to downregulate several checkpoint pathways.…”