Phosphatase magnesium-dependent 1 δ (PPM1D), serine/threonine protein phosphatase and novel pharmacological target in cancer

Aberrations in DNA damage response genes are recognized mediators of tumorigenesis and resistance to chemo- and radiotherapy. While protein phosphatase magnesium-dependent 1 δ (PPM1D), located on the long arm of chromosome 17 at 17q22-23, is a key regulator of cellular responses to DNA damage, amplification, overexpression, or mutation of this gene is important in a wide range of pathologic processes. In this review, we describe the physiologic function of PPM1D, as well as its role in diverse processes, including fertility, development, stemness, immunity, tumorigenesis, and treatment responsiveness. We highlight both the advances and limitations of current approaches to targeting malignant processes mediated by pathogenic alterations in PPM1D with the goal of providing rationale for continued research and development of clinically viable treatment approaches for PPM1D-associated diseases.

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.

Evaluation of p53 and Its Target Gene Expression as Potential Biomarkers of Cholangiocarcinoma in Thai Patients

BACKGROUND

Cholangiocarcinoma (CCA), a common cancer in northeastern Thailand, is a severe disease with poor prognosis and short survival time following diagnosis. DNA damage in CCA is believed to be caused by liver fluke infection in combination with exposure to carcinogens. p53, a tumor suppressor, is the most mutated gene in human cancers including liver fluke-associated CCA. Hence, expression patterns of p53 and its target genes may be useful for diagnosis and/or prognosis of CCA patients.

METHODS

Differential mRNA expression of p53 and its target genes, namely, FUCA1, ICAM2 MDM2, p21, PAI-1, S100A9, and WIP1 in CCA tissue samples (n = 30) relative to matched adjacent non-tumor tissues was determined by quantitative RT-PCR and compared to clinicopathological features. Level of p53 protein was determined by immunohistochemistry and correlated with the expression of its target genes.

RESULTS

Immunohistochemistry showed elevation of p53 protein level in 77% of the cases, while RT-PCR showed downregulation of p53 mRNA and its seven target genes in 23% and 47-97% of the samples. PAI-1 was down-regulated in almost all CCA samples, thus highlighting it as a potential diagnostic marker for CCA. However, no significant clinical associations were found except for down-regulation of WIP1 that was significantly correlated with non-papillary type tissue (p-value = 0.001) and with high p53 protein level (p-value = 0.007).

CONCLUSION

Our results demonstrated statistically significant association between down-regulation of WIP1 with non-papillary type and with high p53 protein level, and PAI-1 was down-regulated in almost all CCA. Therefore, expression level of WIP1 and PAI-1 may be useful for predicting p53 functional status and as a potential diagnostic marker of CCA, respectively.

Potentiality of Protein phosphatase Mg2+ /Mn2+ dependent 1D as a biomarker for predicting prognosis in acute myeloid leukemia patients

Objective

The present study aimed to investigate the correlation of protein phosphatase Mg²⁺/Mn²⁺ dependent 1D (PPM1D) with the risk stratification, treatment response, and survival profile in acute myeloid leukemia (AML) patients.

Methods

Totally 221 de novo AML patients and 50 healthy donors were enrolled. The bone marrow samples were collected before treatment from AML patients and acquired after enrollment from healthy donors. And bone marrow mononuclear cells were separated for detecting the mRNA/protein expressions of PPM1D by reverse transcription‐quantitative polymerase chain reaction and Western blot. Complete remission (CR) was assessed after induction treatment, and event‐free survival (EFS) and overall survival (OS) were calculated in AML patients.

Results

PPM1D mRNA (P < .001)/protein (P < .001) relative expressions were increased in AML patients compared with healthy donors, and receiver operating characteristic curve presented that PPM1D mRNA (AUC: 0.728, 95% CI: 0.651‐0.806)/protein (AUC: 0.782, 95% CI: 0.707‐0.857) relative expressions could differentiate AML patients from healthy donors. In AML patients, PPM1D mRNA (P < .001)/protein (P < .001) high relative expressions were correlated with poor‐risk stratification. As for its association with prognosis, PPM1D mRNA (P < .001)/protein (P = .010) relative expressions were elevated in CR patients compared with non‐CR patients. Patients with PPM1D mRNA (P < .001 for EFS; P = .004 for OS)/protein (P < .001 for EFS; P = .006 for OS) high relative expressions exhibited reduced EFS and OS compared with those with low expressions.

Conclusion

PPM1D high expression correlates with poor‐risk stratification and might serve as a potential biomarker for worse prognosis in AML patients, suggesting its potential to guide AML management.

Wip1 cooperates with KPNA2 to modulate the cell proliferation and migration of colorectal cancer via a p53-dependent manner

Due to the increasing incidence and mortality, the early diagnosis, specific targeted therapies, and prognosis for colorectal cancer (CRC) attract more and more attention. Wild-type p53-induced phosphatase 1 (Wip1) and karyopherin α2 (KPNA2) have been regarded as oncogenes in many cancers, including CRC. Wip1 dephosphorylates p53 to inactivate it. TP53 activator and Wip1 inhibitor downregulate KPNA2 expression. Therefore, we speculate that Wip1 may co-operate with KPNA2 to modulate CRC progression in a p53-dependent manner. Here, Wip1 and KPNA2 messenger RNA expression and protein levels are significantly increased in CRC tissues and cell lines and are positively correlated with each other. Wip1 silence increases p53 phosphorylation while decreases KPNA2 protein. Wip1 knockdown remarkably suppresses CRC cell proliferation and migration while KPNA2 overexpression exerts an opposing effect. KPNA2 overexpression could partially rescue Wip1 silence-inhibited CRC cell proliferation and migration. Finally, Wip1 interacts with KPNA2 to modulate the activation of AKT/GSK-3β signaling and metastasis-related factors. In summary, Wip1 could co-operate with KPNA2 to modulate CRC cell proliferation and migration, possibly via a p53-dependent manner, through downstream AKT/GSK-3β pathway. We provided a novel mechanism of Wip1 interacting with KPNA2, therefore modulating CRC cell proliferation and migration.

Wip1 gene silencing enhances the chemosensitivity of human colon cancer cells

Colon cancer is one of the most common cancers in the world. Multidrug resistance is one of the main reasons for failure of therapy in patients with advanced colon cancer. In previous studies, multiple methods were investigated to reverse the multidrug resistance of colon cancer cells. However, to date, no clinical method has been identified to be satisfactory. Therefore, successful reversal of drug resistance in colon cancer cells still requires new therapeutic strategies or pharmaceuticals. Wild-type p53-induced phosphatase (Wip1), a member of the 2C type serine/threonine protein phosphatase family, is closely associated with the p53 gene, which is the most important tumor-suppressor gene. Wip1 was reported to be associated with the chemosensitivity of breast cancer cells. However, the correlation between the expression of Wip1 gene and the chemosensitivity of colon cancer cells has not been reported yet. In the present study, Wip1-811 small interfering RNA (siRNA) targeting Wip1 was investigated to reverse the multidrug resistance of colon cancer cells. The siRNA duplexes were transfected into RKO colon cancer cells. The messenger RNA (mRNA) expression of Wip1 was measured by reverse transcription-quantitative polymerase chain reaction. The protein level of Wip1 was detected by western blotting. The cell viability was measured by MTS assay. The cell apoptosis and cell cycle were analyzed by flow cytometry. Intracellular adriamycin cumulative concentration was determined using flow cytometry. Wip1-811 siRNA efficiently inhibited the expression of Wip1 at the mRNA and protein levels, and enhanced the sensitivity of RKO colon cancer cells towards chemotherapy, which was accompanied by increased cell apoptosis, following the inhibition of Wip1 gene expression. These results indicate that Wip1 gene silencing could enhance the chemosensitivity of colon cancer cells, which may provide a new potential approach for the reversal of multidrug resistance in colon cancer cells.

Clinical significance of Wip1 overexpression and its association with the p38MAPK/p53/p16 pathway in NSCLC

Wip1 is deregulated in numerous human malignancies. However, its roles in non-small cell lung cancer (NSCLC) remain unclear. In the current study, the expression of Wip1 was investigated in NSCLC and its clinical significance was detected. Immunohistochemical staining was used to measure the expression of (wild-type p53 induced phosphatase 1) Wip1, p38 mitogen-activated protein kinase (MAPK), p53, p16 protein in a group of 60 NSCLC and 20 normal lung tissues. In addition, western blotting was performed to detect the Wip1 protein in fresh tissues. The correlations between clinical characteristics and Wip1 expression were analyzed using SPSS, version 16.0 software. The expression of Wip1 was positive in 63.3% (38/60) of NSCLC tissues, and in none of the normal lung tissues (0/20; P<0.01). In addition, Wip1 overexpression was significantly associated with tumor length and differentiation (P=0.008 and 0.03, respectively). The expression of Wip1 was negatively correlated with that of p38MAPK, p53 and p16 (r=−0.284, −0.352 and −0.348, respectively). The results of the current study demonstrated that Wip1 was frequently overexpressed in NSCLC, which may serve an essential role in the p38MAPK/p53/p16 signaling pathway.

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.

Hedgehog Signaling in the Maintenance of Cancer Stem Cells

Cancer stem cells (CSCs) represent a rare population of cells with the capacity to self-renew and give rise to heterogeneous cell lineages within a tumour. Whilst the mechanisms underlying the regulation of CSCs are poorly defined, key developmental signaling pathways required for normal stem and progenitor functions have been strongly implicated. Hedgehog (Hh) signaling is an evolutionarily-conserved pathway essential for self-renewal and cell fate determination. Aberrant Hh signaling is associated with the development and progression of various types of cancer and is implicated in multiple aspects of tumourigenesis, including the maintenance of CSCs. Here, we discuss the mounting evidence suggestive of Hh-driven CSCs in the context of haematological malignancies and solid tumours and the novel strategies that hold the potential to block many aspects of the transformation attributed to the CSC phenotype, including chemotherapeutic resistance, relapse and metastasis.

Down-regulated MYH11 expression correlates with poor prognosis in stage II and III colorectal cancer

The MYH11 gene may be related to cell migration and adhesion, intracellular transport, and signal transduction. However, its relationship with prognosis is still uncertain. The aim of this study was to investigate correlations between MYH11 gene expression and prognosis in 58 patients with stage II and III colorectal cancer. Quantitative real-time polymerase chain reaction was performed in fresh CRC tissues to examine mRNA expression, and immunohistochemistry was performed with paraffin-embedded specimens for protein expression. On univariate analysis, MYH11 expression at both mRNA and protein levels, perineural invasion and lymphovascular invasion were related to disease-free survival (p<0.05; log-rank test). Cancers with lower MYH11 expression were more likely to have a poor prognosis. Otherwise, MYH11 expression was unrelated to patient clinicopathological features. On multivariate analysis, low MYH11 expression proved to be an independent adverse prognosticator (p<0.05). These findings show that MYH11 can contribute to predicting prognosis in stage II and III colorectal cancers.

DNA damage checkpoint recovery and cancer development

Cell cycle checkpoints were initially presumed to function as a regulator of cell cycle machinery in response to different genotoxic stresses, and later found to play an important role in the process of tumorigenesis by acting as a guard against DNA over-replication. As a counterpart of checkpoint activation, the checkpoint recovery machinery is working in opposition, aiming to reverse the checkpoint activation and resume the normal cell cycle. The DNA damage response (DDR) and oncogene induced senescence (OIS) are frequently found in precancerous lesions, and believed to constitute a barrier to tumorigenesis, however, the DDR and OIS have been observed to be diminished in advanced cancers of most tissue origins. These findings suggest that when progressing from pre-neoplastic lesions to cancer, DNA damage checkpoint barriers are overridden. How the DDR checkpoint is bypassed in this process remains largely unknown. Activated cytokine and growth factor-signaling pathways were very recently shown to suppress the DDR and to promote uncontrolled cell proliferation in the context of oncovirus infection. In recent decades, data from cell line and tumor models showed that a group of checkpoint recovery proteins function in promoting tumor progression; data from patient samples also showed overexpression of checkpoint recovery proteins in human cancer tissues and a correlation with patients׳ poor prognosis. In this review, the known cell cycle checkpoint recovery proteins and their roles in DNA damage checkpoint recovery are reviewed, as well as their implications in cancer development. This review also provides insight into the mechanism by which the DDR suppresses oncogene-driven tumorigenesis and tumor progression.

WIP1 regulates the proliferation and invasion of nasopharyngeal carcinoma in vitro

Wild-type p53-induced phosphatase (WIP1) is overexpressed and functionally altered in multiple human malignancies. The present study investigated its abnormal expression and dysfunctions in nasopharyngeal carcinoma (NPC) in vitro. Here, analysis of WIP1 mRNA and protein in human NPC tissues revealed that both WIP1 messenger RNA (mRNA) and protein were elevated and were correlated with NPC clinical stage and metastasis in patients. In vitro experiments further showed that WIP1 inhibition led to a decrease in the proliferative ability of NPC CNE-2 and 5-8F cells accompanied by cell cycle arrest and increased apoptosis. In addition, WIP1 knockdown inhibited the invasiveness of CNE-2 and 5-8F cells and was associated with the down-regulation of the expression of matrix metallopeptidase 9 (MMP-9) mRNA and protein. Taken together, our data demonstrate that WIP1 regulates the proliferation and invasiveness of NPC cells in vitro, and this may be correlated with its modulation of MMP-9 expression, cell cycle progression and apoptosis. WIP1 functioned as a potential therapeutic target in NPC management.