The p53-Induced Oncogenic Phosphatase PPM1D Interacts with Uracil DNA Glycosylase and Suppresses Base Excision Repair

Abstract

The wild-type p53-induced phosphatase PPM1D (or Wip1) is a serine/threonine phosphatase that is transcriptionally upregulated by p53 following ultraviolet and ionizing radiation. PPM1D is an oncogene in transformation assays and is amplified or overexpressed in several human tumor types. Here, we demonstrate that PPM1D interacts with the nuclear isoform of uracil DNA glycosylase, UNG2, and suppresses base excision repair (BER). Point mutations that inactivate PPM1D phosphatase activity abrogate BER suppression, indicating that dephosphorylation by PPM1D is important for BER inhibition. We have identified UNG2 phosphorylation sites at threonines 6 and 126 that exhibit enhanced phosphorylation following UV irradiation. The UV-induced phosphorylated forms of UNG2 are more active than nonphosphorylated forms in mediating uracil-associated DNA cleavage. PPM1D dephosphorylation of UNG2 at phosphothreonine 6 is associated with reduced UNG2 activity. Thus, PPM1D may inhibit BER by dephosphorylating UNG2 to facilitate its inactivation after completion of DNA repair.

Regulation of the antioncogenic Chk2 kinase by the oncogenic Wip1 phosphatase

“…26 More recently, it has been shown that Wip1 associates with the nuclear isoform of uracil DNA glycosylase, UNG2, and that Wip1 suppresses DNA damage-induced base excision repair (BER) activity by dephosphorylating and inactivating UNG2. 30 In this study, we show that Wip1 interacts with Chk2 both physically and functionally in the nuclei. Wip1 dephosphorylates Thr68 in activated Chk2 both in vitro and in vitro, and inactivates Chk2 kinase activity toward Cdc25C.…”

“…Interestingly, it has been recently reported that Wip1 dephosphorylates the nuclear form of uracil DNA glycosylase (UNG2) and Chk1, thereby suppressing BER and intra-S and G2/M checkpoint regulation, respectively. 30,40 In the case of UNG2 and p38, phosphorylation sites on these molecules, which can be targets for Wip1-mediated dephosphorylation, reveal consensus sequences 'phospho-T-X-phospho-Tyr (Y) (or phospho-T-X-Y, X: optional a.a.)'. 41 In this respect, it is important to note that our in vitro evidence as well as previous report 40 indicate the presence of additional target sequences for Wip1, which are 'phospho-S-Q' or 'phospho-T-Q', well-known fingerprints of ATM kinase (see Table 1).…”

A unified view of base excision repair: Lesion-dependent protein complexes regulated by post-translational modification

“…In each case, this modification has been observed to increase catalytic activity and hence may regulate BER initiation [97,98]. On the other hand, TDG, MPG and NEIL2 are modified and regulated by acetylation (Table III).…”

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

“…Wip1 also dephosphorylates p38 and UNG2 at pT180GY and pT6LY sites, respectively (Takekawa et al, 2000;Lu et al, 2004). In the case of the p38 MAP kinase, the TGY motif is part of the activation loop of the kinase and is diphosphorylated on Thr and Tyr residues when p38 is activated.…”

“…Third, Wip1 directly inhibits Chk1 by dephosphorylating the ATR-targeted phosphoSer345 (Lu et al, 2005). In addition, Wip1 directly dephosphorylates and inhibits a uracil N-glycosylase (Ung2) implicated in the base excision repair of DNA (Lu et al, 2004). The overexpression of Wip1 is likely to be oncogenic given its antagonism of key proteins involved in maintaining genomic stability.…”