Expression of a Homeostatic Regulator, Wip1 (Wild-type p53-induced Phosphatase), Is Temporally Induced by c-Jun and p53 in Response to UV Irradiation

Abstract

Wild-type p53-induced phosphatase (Wip1) is induced by p53 in response to stress, which results in the dephosphorylation of proteins (i.e. p38 MAPK, p53, and uracil DNA glycosylase) involved in DNA repair and cell cycle checkpoint pathways. p38 MAPK-p53 signaling is a unique way to induce Wip1 in response to stress. Here, we show that c-Jun directly binds to and activates the Wip1 promoter in response to UV irradiation. The binding of p53 to the promoter occurs earlier than that of c-Jun. In experiments, mutation of the p53 response element (p53RE) or c-Jun consensus sites reduced promoter activity in both non-stressed and stressed A549 cells. Overexpression of p53 significantly decreased Wip1 expression in HCT116 p53 As a master cell regulator, p53 activates genes involved in DNA repair, cell cycle control, and apoptosis to mediate cellular responses to agents that cause stress and DNA damage (1, 2). Wild-type p53-induced phosphatase 1 (Wip1) 2 is a recently identified member of the protein phosphatase type 2C and p53 target gene families (3, 4). Once induced by p53, Wip1 directly dephosphorylates checkpoint kinase 1 (Chk1), checkpoint kinase 2 (Chk2), p38 MAPK, uracil DNA glycosylase, ataxia-telangiectasia-mutated (ATM) kinase, mdm2, and p53, so that cells can return to normal after DNA repair (5-9). The Wip1 gene is frequently amplified or overexpressed in human cancers, including ϳ11% to 16% of breast cancers, 40% of ovarian clear cell adenocarcinomas, 40% of neuroblastomas, and 36% of pancreatic cancers, which rarely contain the p53 mutation (10 -14). Overexpressed Wip1 promotes tumor growth by switching off major checkpoint kinases and p53; facilitates cell proliferation; and transforms primary fibroblasts together with Ras, Myc, and Neu (15). Wip1 can promote unrestricted entry into the cell cycle in response to DNA damage via dephosphorylation of ATM/ATR and p38 MAPK through a mechanism similar to that used by protein phosphatase 5 and protein phosphatase 1 (16 -18). Wip1-null mouse embryonic fibroblast (MEF) cells exhibit increased expression of p53, p21, p16, and p19; severe proliferation defects; and vulnerability to replicative senescence (19,20). Although the exact mechanism by which Wip1 controls the cell cycle is unknown, Wip1 likely plays a conserved role in the progression of the normal cell cycle in eukaryotic cells.The search for a Wip1-specific chemical inhibitor has been undertaken by Belova et al. and Rayter et al. (21,22). A major factor influencing the use of Wip1 as a therapeutic target is that loss of Wip1 promotes apoptosis in response to external stresses. Wip1 Ϫ/Ϫ MEF cells exhibit increased caspase-3 and PARP cleavage and sustained activation of p38 MAPK and c-Jun N-terminal kinase (JNK), whereas wild-type MEF cells exhibit strong G 2 /M arrest upon etoposide treatment (23). Thus, p53 activation is necessary; however, the p53 downstream target, Wip1, should not be activated in cancer therapies.Mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase...

Oncogenic Wip1 Phosphatase Is Inhibited by miR-16 in the DNA Damage Signaling Pathway

“…A cyclic AMP response element (CRE) and a p53 response element are located in the 5' untranslated region (UTR) of the WIP1 gene. CREB binding to the CRE contributes to the regulation of basal expression of Wip1 and directs transcription initiation at upstream sites, while the p53 response element is required for the p53-dependent induction of transcription(24;40). Our results showed that the level of Wip1 transcripts was immediately induced at the very early stage of the DNA damage response, but Wip1 protein levels increased at a much slower pace.…”

Downregulation of Wip1 phosphatase modulates the cellular threshold of DNA damage signaling in mitosis

“…Since transcription of Wip1 is controlled by p38/MAPK-p53 and JNK/c-Jun stress-responsive pathways, we hypothesized that the moderate difference in expression of Wip1 in G 1 and G 2 phases may be masked in cells synchronized with thymidine. 23,37 To substantiate our findings obtained by biochemical analysis of mixed cell populations, we set up an automated microscopic analysis of multiple individual cells. Total intensity of the DAPI signal was proportional to the DNA content and, as expected, was 2-fold higher in G 2 cells compared with G 1 cells.…”

Akt confers cisplatin chemoresistance in human gynecological carcinoma cells by modulating PPM1D stability

“…It was first identified as a phosphatase induced by ultraviolet (UV) and ionizing radiation (IR) in a p53-dependent manner [9][10][11]. PPM1D expression has also been shown to be regulated by several other transcription factors including estrogen receptor a (ERa) [12], cyclic AMP response element binding protein (CREB) [11], E2F1 [13], NF-kB [14], and c-Jun [15]. PPM1D has been shown to preferentially target phosphoproteins containing SQ/TQ or TXY motifs for dephosphorylation [10,[16][17][18].…”