Wip1, a novel human protein phosphatase that is induced in response to ionizing radiation in a p53-dependent manner

Abstract

Exposure of mammalian cells to ionizing radiation (IR) induces a complex array of cellular responses including cell cycle arrest and͞or apoptosis. IR-induced G 1 arrest has been shown to depend on the presence of the tumor suppressor p53, which acts as a transcriptional activator of several genes. p53 also plays a role in the induction of apoptosis in response to DNA damage, and this pathway can be activated by both transcription-dependent and -independent mechanisms. Here we report the identification of a novel transcript whose expression is induced in response to IR in a p53-dependent manner, and that shows homology to the type 2C protein phosphatases. We have named this novel gene, wip1. In vitro, recombinant Wip1 displayed characteristics of a type 2C phosphatase, including Mg 2؉ dependence and relative insensitivity to okadaic acid. Studies performed in several cell lines revealed that wip1 accumulation following IR correlates with the presence of wild-type p53. The accumulation of wip1 mRNA following IR was rapid and transient, and the protein was localized to the nucleus. Similar to waf1, ectopic expression of wip1 in human cells suppressed colony formation. These results suggest that Wip1 might contribute to growth inhibitory pathways activated in response to DNA damage in a p53-dependent manner.

Protein serine/threonine phosphatase-1 dephosphorylates p53 at Ser-15 and Ser-37 to modulate its transcriptional and apoptotic activities

“…At the p53 N-terminus, there are 10 serine/threonine residues (Ser-6, -9, -15, -20, -33, -37, -46, and , PP2A (Scheidtmann et al, 1991), PP5 (Zuo et al, 1998), Wip1 and Cdc14 (Fiscella et al, 1997;Li et al, 2000), can dephosphorylate p53, there is no definitive assignment of the concrete phosphatase responsible for dephosphorylating the specific serine/threonine sites until recently. Long et al The inducibility of the Tet-on system.…”

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

“…Plasmids, siRNA, antibodies and extract preparation pGEX-Wip1 expressing a GST-Wip1 fusion protein under an inducible promoter in E. coli, and pCMV-Wip1 constitutively expressing a Wip1-flag protein in mammalian cells were kindly provided by Dr Appella (Fiscella et al, 1997). pGEX-PP2Ca was kindly provided by Dr Solomon (Yale University) and pGEX-Cdc25C by Dr Piwnica-Worms (Schwarz et al, 2003).…”

“…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).…”

The role of the MKK6/p38 MAPK pathway in Wip1-dependent regulation of ErbB2-driven mammary gland tumorigenesis

“…We propose that Wip1 phosphatase operates within the MKK6/p38 MAPK signaling pathway to promote ErbB2-driven mammary gland tumorigenesis. Keywords: Wip1 phosphatase; p38 MAPK; MKK6; breast cancer; ErbB2; proliferation; MMTV The protein phosphatase wild-type p53 induced phosphatase 1 (Wip1) was identified using differential display methodology and its expression was found to be regulated in a p53-dependent manner (Fiscella et al, 1997). Wip1 mRNA is rapidly induced by ionizing radiation in wild-type but not in p53-deficient cells confirming its regulation by p53 after genotoxic stress (hence the name, wild-type p53 induced phosphatase 1) (Fiscella et al, 1997).…”

“…Keywords: Wip1 phosphatase; p38 MAPK; MKK6; breast cancer; ErbB2; proliferation; MMTV The protein phosphatase wild-type p53 induced phosphatase 1 (Wip1) was identified using differential display methodology and its expression was found to be regulated in a p53-dependent manner (Fiscella et al, 1997). Wip1 mRNA is rapidly induced by ionizing radiation in wild-type but not in p53-deficient cells confirming its regulation by p53 after genotoxic stress (hence the name, wild-type p53 induced phosphatase 1) (Fiscella et al, 1997). Further analysis of transcriptional regulation, however, revealed that Wip1 could also be activated through p38 mitogen-activated protein kinases (MAPK) raising the possibility of Wip1 regulation independent of p53 (Takekawa et al, 2000).…”