p53-Independent expression of wild-type p53-induced phosphatase 1 (Wip1) in methylmethane sulfonate-treated cancer cell lines and human tumors

MiR-145-5p Inhibits the Invasion of Prostate Cancer and Induces Apoptosis by Inhibiting WIP1

Prostate cancer (PCa) is a common malignant tumor of the male genitourinary system that seriously affects the quality of life of patients. Studying the pathogenesis and therapeutic targets of PCa is important. In this study, we investigated the role of miR-145-5p in PCa and its potential molecular mechanisms. The expression levels of miR-145-5p in PCa tissues and adjacent control tissues were detected by real-time quantitative polymerase chain reaction. The effects of miR-145-5p overexpression on PCa were studied using cell proliferation, migration, and invasion experiments. Furthermore, WIP1 was the target gene of miR-145-5p through the bioinformatics website and dual-luciferase reporter gene experiment. Further studies found that WIP1 downregulation could inhibit the proliferation, invasion, and cloning of PCa cells. Overexpression of WIP1 reversed the anticancer effects of miR-145. The anticancer effect of miR-145 was achieved by inhibiting the PI3K/AKT signaling pathway and upregulating ChK2 and p-p38MAPK. Taken together, these results confirmed that miR-145-5p inhibited the growth and metastasis of PCa cells by inhibiting the expression of proto-oncogene WIP1, thereby playing a role in tumor suppression in PCa and may become a potential therapeutic target for the treatment of PCa.

A miR-210-3p regulon that controls the Warburg effect by modulating HIF-1α and p53 activity in triple-negative breast cancer

Reprogrammed energy metabolism, especially the Warburg effect (aerobic glycolysis), is an emerging hallmark of cancer. Different from other breast cancer subtypes, triple-negative breast cancer (TNBC) exhibits high metabolic remodeling, increased aggressiveness and lack of targeted therapies. MicroRNAs (miRNA) are essential to TNBC malignant phenotypes. However, little is known about the contribution of miRNA to aerobic glycolysis in TNBC. Through an integrated analysis and functional verification, we reported that several miRNAs significantly correlates to the Warburg effect in TNBC, including miR-210-3p, miR-105-5p, and miR-767-5p. Ectopic expression of miR-210-3p enhanced glucose uptake, lactate production, extracellular acidification rate, colony formation ability, and reduced serum starvation-induced cell apoptosis. Moreover, GPD1L and CYGB were identified as two functional mediators of miR-210-3p in TNBC. Mechanistically, miR-210-3p targeted GPD1L to maintain HIF-1α stabilization and suppressed p53 activity via CYGB. Ultimately, miR-210-3p facilitated aerobic glycolysis through modulating the downstream glycolytic genes of HIF-1α and p53. Taken together, our results decipher miRNAs that regulate aerobic glycolysis and uncover that miR-210-3p specifically contributes to the Warburg effect in TNBC.

The role of PPM1D in cancer and advances in studies of its inhibitors

A greater understanding of factors causing cancer initiation, progression and evolution is of paramount importance. Among them, the serine/threonine phosphatase PPM1D, also referred to as wild-type p53-induced phosphatase 1 (Wip1) or protein phosphatase 2C delta (PP2Cδ), is emerging as an important oncoprotein due to its negative regulation on a number of crucial cancer suppressor pathways. Initially identified as a p53-regulated gene, PPM1D has been afterwards found amplified and more recently mutated in many human cancers such as breast cancer. The latest progress in this field further reveals that selective inhibition of PPM1D to delay tumor onset or reduce tumor burden represents a promising anti-cancer strategy. Here, we review the advances in the studies of the PPM1D activity and its relevance to various cancers, and recent progress in development of PPM1D inhibitors and discuss their potential application in cancer therapy. Consecutive research on PPM1D and its relationship with cancer is essential, as it ultimately contributes to the etiology and treatment of cancer.

The emerging roles of phosphatases in Hedgehog pathway

Hedgehog signaling is evolutionarily conserved and plays a pivotal role in cell fate determination, embryonic development, and tissue renewal. As aberrant Hedgehog signaling is tightly associated with a broad range of human diseases, its activities must be precisely controlled. It has been known that several core components of Hedgehog pathway undergo reversible phosphorylations mediated by protein kinases and phosphatases, which acts as an effective regulatory mechanism to modulate Hedgehog signal activities. In contrast to kinases that have been extensively studied in these phosphorylation events, phosphatases were thought to function in an unspecific manner, thus obtained much less emphasis in the past. However, in recent years, increasing evidence has implicated that phosphatases play crucial and specific roles in the context of developmental signaling, including Hedgehog signaling. In this review, we present a summary of current progress on phosphatase studies in Hedgehog pathway, emphasizing the multiple employments of protein serine/threonine phosphatases during the transduction of morphogenic Hedgehog signal in both Drosophila and vertebrate systems, all of which provide insights into the importance of phosphatases in the specific regulation of Hedgehog signaling.

Knockdown of Wip1 Enhances Sensitivity to Radiation in HeLa Cells Through Activation of p38 MAPK

The objectives of the study were to investigate the functional role and potential mechanism of wild-type p53-induced phosphatase (Wip1) in cervical cancer cell line HeLa cells, along with the effect of knockdown of Wip1 in combination with γ-irradiation on the HeLa cells. Expression of Wip1 was silenced or overexpressed. After transfection, cell viability was determined. Moreover, γ-irradiation and SB203580 were performed to explore the effect of colony formation and cell apoptosis. Likewise, protein expression levels of p38, p-p38, p53, and p-p53 were assessed in the presence or not of SB203580 and overexpression of Wip1. Both the mRNA and protein levels of Wip1 were significantly decreased by transfection with Wip1-specific small interfering RNA (siRNA) but were significantly increased by transfection with pcDNA3.1-Wip1. Knockdown of Wip1 significantly decreased cell growth and colony formation ability and increased apoptotic rate. Additionally, better results were obtained by knockdown of Wip1 in combination with γ-irradiation. The protein expression levels of p-p38 (p < 0.05), p53 (p < 0.01), and p-p53 (p < 0.05) were all significantly increased by knockdown of Wip1. However, application of SB203580 reversed the effects. Our study confirms the important roles of Wip1 in cervical cancer. Knockdown of Wip1 enhances sensitivity to radiation in HeLa cells by inhibiting cell proliferation and inducing apoptosis through activation of p38 MAPK.

Association between overexpression of Wip1 and prognosis of patients with non-small cell lung cancer

Wild-type p53-induced phosphatase 1 (Wip1), also termed PPM1D, is a member of the protein phosphatase 2C family, which is characterized by distinctive oncogenic properties. Overexpression of Wip1 is observed in certain types of human tumors that are associated with significantly poor prognosis. The present study aimed to detect the expression of Wip1 in non-small cell lung cancer (NSCLC) and to analyze its prognostic value in such patients. The protein expression level of Wip1 was compared between NSCLC and normal lung tissue specimens using by immunohistochemistry, and it was found that Wip1 was highly expressed in NSCLCs but was absent or weakly expressed in normal lung tissues. Detailed clinical and demographic information of patients were retrospectively collected pre- and postoperatively, and Kaplan-Meier survival and Cox's regression analyses were performed to evaluate the prognosis of patients. Survival analysis revealed that the overall survival rate for patients in the Wip1-positive expression group was significantly lower than that of the Wip1-negative group, and Cox multivariate analysis indicated that positive Wip1 expression, pN classification and pathological stage were significant prognostic predictors. The results of the current study suggest that Wip1 may be associated with pathological diagnosis and prognostic evaluation of NSCLC.

Effects of thonningianin A in natural foods on apoptosis and cell cycle arrest of HepG-2 human hepatocellular carcinoma cells

The anti-cancer activities of Thonningianin A on the HepG-2 human hepatocellular carcinoma cell line were evaluated by MTT assay, flow cytometry, quantitative real-time PCR and western blotting. Results showed that Thonningianin A effectively inhibited the proliferation of HepG-2 cells by inducing apoptosis, as evidenced by increase in the sub-G1 cell population, DNA fragmentation, and increase in the content of reactive oxygen species. Activation of caspase-9 and the subsequent activation of caspase-3 indicated that Thonningianin A-induced apoptosis is caspase-dependent. Thonningianin A also disrupted the mitochondrial membrane potential (Δψm) and down-regulated the Bcl-xL mRNA expression in HepG-2 cells. Thonningianin A induced cell cycle arrest by changing the cyclin D1 and CDK4 mRNA expression levels. Moreover, western blotting showed that Thonningianin A significantly down-regulated the NF-kappa-B cell survival pathway, along with up-regulation of the expression level of phosphorylated P38 and down-regulation of the expression level of phosphorylated ERK. The anti-cancer activity of Thonningianin A was confirmed by the characteristic patterns of DNA fragmentation and cell cycle arrest, suggesting that Th A is an effective antitumor ingredient in natural plant foods, and is worthy of further study.

Spontaneous γH2AX Foci in Human Solid Tumor-Derived Cell Lines in Relation to p21WAF1 and WIP1 Expression

Phosphorylation of H2AX on Ser139 (γH2AX) after exposure to ionizing radiation produces nuclear foci that are detectable by immunofluorescence microscopy. These so-called γH2AX foci have been adopted as quantitative markers for DNA double-strand breaks. High numbers of spontaneous γH2AX foci have also been reported for some human solid tumor-derived cell lines, but the molecular mechanism(s) for this response remains elusive. Here we show that cancer cells (e.g., HCT116; MCF7) that constitutively express detectable levels of p21^WAF1 (p21) exhibit low numbers of γH2AX foci (<3/nucleus), whereas p21 knockout cells (HCT116p21−/−) and constitutively low p21-expressing cells (e.g., MDA-MB-231) exhibit high numbers of foci (e.g., >50/nucleus), and that these foci are not associated with apoptosis. The majority (>95%) of cells within HCT116p21−/− and MDA-MB-231 cultures contain high levels of phosphorylated p53, which is localized in the nucleus. We further show an inverse relationship between γH2AX foci and nuclear accumulation of WIP1, an oncogenic phosphatase. Our studies suggest that: (i) p21 deficiency might provide a selective pressure for the emergence of apoptosis-resistant progeny exhibiting genomic instability, manifested as spontaneous γH2AX foci coupled with phosphorylation and nuclear accumulation of p53; and (ii) p21 might contribute to positive regulation of WIP1, resulting in dephosphorylation of γH2AX.

Wip1 suppresses apoptotic cell death through direct dephosphorylation of BAX in response to γ-radiation

Wild-type p53-induced phosphatase 1 (Wip1) is a p53-inducible serine/threonine phosphatase that switches off DNA damage checkpoint responses by the dephosphorylation of certain proteins (i.e. p38 mitogen-activated protein kinase, p53, checkpoint kinase 1, checkpoint kinase 2, and uracil DNA glycosylase) involved in DNA repair and the cell cycle checkpoint. Emerging data indicate that Wip1 is amplified or overexpressed in various human tumors, and its detection implies a poor prognosis. In this study, we show that Wip1 interacts with and dephosphorylates BAX to suppress BAX-mediated apoptosis in response to γ-irradiation in prostate cancer cells. Radiation-resistant LNCaP cells showed dramatic increases in Wip1 levels and impaired BAX movement to the mitochondria after γ-irradiation, and these effects were reverted by a Wip1 inhibitor. These results show that Wip1 directly interacts with and dephosphorylates BAX. Dephosphorylation occurs at threonines 172, 174 and 186, and BAX proteins with mutations at these sites fail to translocate efficiently to the mitochondria following cellular γ-irradiation. Overexpression of Wip1 and BAX, but not phosphatase-dead Wip1, in BAX-deficient cells strongly reduces apoptosis. Our results suggest that BAX dephosphorylation of Wip1 phosphatase is an important regulator of resistance to anticancer therapy. This study is the first to report the downregulation of BAX activity by a protein phosphatase.

Deficient DNA damage signaling leads to chemoresistance to cisplatin in oral cancer

Activation of the cellular DNA damage response (DDR) is an important determinant of cell sensitivity to cisplatin and other chemotherapeutic drugs that eliminate tumor cells through induction of DNA damage. It is therefore important to investigate whether alterations of the DNA damage-signaling pathway confer chemoresistance in cancer cells and whether pharmacologic manipulation of the DDR pathway can resensitize these cells to cancer therapy. In a panel of oral/laryngeal squamous cell carcinoma (SCC) cell lines, we observed deficiencies in DNA damage signaling in correlation with cisplatin resistance, but not with DNA repair. These deficiencies are consistent with reduced expression of components of the ataxia telangiectasia mutated (ATM)-dependent signaling pathway and, in particular, strong upregulation of Wip1, a negative regulator of the ATM pathway. Wip1 knockdown or inhibition enhanced DNA damage signaling and resensitized oral SCC cells to cisplatin. In contrast to the previously reported involvement of Wip1 in cancer, Wip1 upregulation and function in these SCC cells is independent of p53. Finally, using xenograft tumor models, we showed that Wip1 upregulation promotes tumorigenesis and its inhibition improves the tumor response to cisplatin. Thus, this study reveals that chemoresistance in oral SCCs is partially attributed to deficiencies in DNA damage signaling, and Wip1 is an effective drug target for enhanced cancer therapy.