Mice deficient for the wild-type p53-induced phosphatase gene (Wip1) exhibit defects in reproductive organs, immune function, and cell cycle control

Targeting WIP1 phosphatase promotes partial remission in experimental collapsing glomerulopathy

Collapsing focal segmental glomerulosclerosis (FSGS), also known as collapsing glomerulopathy (CG), is the most aggressive variant of FSGS and is characterized by a rapid progression to kidney failure. Understanding CG pathogenesis represents a key step for the development of targeted therapies. Previous work implicated the telomerase protein component TERT in CG pathogenesis, as transgenic TERT expression in adult mice resulted in a CG resembling that seen in human primary CG and HIV-associated nephropathy (HIVAN). Here, we used the telomerase-induced mouse model of CG (i-TERTci mice) to identify mechanisms to inhibit CG pathogenesis. Inactivation of WIP1 phosphatase, a p53 target acting in a negative feedback loop, blocked disease initiation in i-TERTci mice. Repression of disease initiation upon WIP1 deficiency was associated with senescence enhancement and required transforming growth factor-β functions. The efficacy of a pharmacologic treatment to reduce disease severity in both i-TERTci mice and in a mouse model of HIVAN (Tg26 mice) was then assessed. Pharmacologic inhibition of WIP1 enzymatic activity in either the telomerase mice with CG or in the Tg26 mice promoted partial remission of proteinuria and ameliorated kidney histopathologic features. Histological as well as high-throughput sequencing methods further showed that selective inhibition of WIP1 does not promote kidney fibrosis or inflammation. Thus, our findings suggest that targeting WIP1 may be an effective therapeutic strategy for patients with CG.

PPM1D modulates hematopoietic cell fitness and response to DNA damage and is a therapeutic target in myeloid malignancy

PPM1D encodes a phosphatase that is recurrently activated across cancer, most notably in therapy-related myeloid neoplasms. However, the function of PPM1D in hematopoiesis and its contribution to tumor cell growth remain incompletely understood. Using conditional mouse models, we uncover a central role for Ppm1d in hematopoiesis and validate its potential as a therapeutic target. We find that Ppm1d regulates the competitive fitness and self-renewal of hematopoietic stem cells (HSCs) with and without exogenous genotoxic stresses. We also show that although Ppm1d activation confers cellular resistance to cytotoxic therapy, it does so to a lesser degree than p53 loss, informing the clonal competition phenotypes often observed in human studies. Notably, loss of Ppm1d sensitizes leukemias to cytotoxic therapies in vitro and in vivo, even in the absence of a Ppm1d mutation. Vulnerability to PPM1D inhibition is observed across many cancer types and dependent on p53 activity. Importantly, organism-wide loss of Ppm1d in adult mice is well tolerated, supporting the tolerability of pharmacologically targeting PPM1D. Our data link PPM1D gain-of-function mutations to the clonal expansion of HSCs, inform human genetic observations, and support the therapeutic targeting of PPM1D in cancer.

Clonal haematopoiesis - a novel entity that modifies pathological processes in elderly

Progress in the development of new sequencing techniques with wider accessibility and higher sensitivity of the protocol of deciphering genome particularities led to the discovery of a new phenomenon - clonal haematopoiesis. It is characterized by the presence in the bloodstream of elderly people a minor clonal population of cells with mutations in certain genes, but without any sign of disease related to the hematopoietic system. Here we will review this recent advancement in the field of clonal haematopoiesis and how it may affect the disease's development in old age.

Wip1 inhibits neutrophil extracellular traps to promote abscess formation in mice by directly dephosphorylating Coronin-1a

Neutrophil extracellular traps (NETs) participate in the rapid inhibition and clearance of pathogens during infection; however, the molecular regulation of NET formation remains poorly understood. In the current study, we found that inhibition of the wild-type p53-induced phosphatase 1 (Wip1) significantly suppressed the activity of Staphylococcus aureus (S. aureus) and accelerated abscess healing in S. aureus-induced abscess model mice by enhancing NET formation. A Wip1 inhibitor significantly enhanced NET formation in mouse and human neutrophils in vitro. High-resolution mass spectrometry and biochemical assays demonstrated that Coro1a is a substrate of Wip1. Further experiments also revealed that Wip1 preferentially and directly interacts with phosphorylated Coro1a than compared to unphosphorylated inactivated Coro1a. The phosphorylated Ser426 site of Coro1a and the 28-90 aa domain of Wip1 are essential for the direct interaction of Coro1a and Wip1 and for Wip1 dephosphorylation of p-Coro1a Ser426. Wip1 deletion or inhibition in neutrophils significantly upregulated the phosphorylation of Coro1a-Ser426, which activated phospholipase C and subsequently the calcium pathway, the latter of which promoted NET formation after infection or lipopolysaccharide stimulation. This study revealed Coro1a to be a novel substrate of Wip1 and showed that Wip1 is a negative regulator of NET formation during infection. These results support the potential application of Wip1 inhibitors to treat bacterial infections.

A Study on the Role of Wip1 in Renal Fibrosis by Modulating Macrophage Phenotype

BACKGROUND

Renal fibrosis is the result of chronic kidney diseases, the exploration of the pathogenesis of renal fibrosis and the development of effective treatment methods have become major challenges.

AIMS

To investigate the effect of wild-type p53-induced phosphatase 1 (Wip1) on macrophage phenotype regulation and the role played in renal fibrosis.

METHODS

RAW264.7 macrophages were stimulated by lipopolysaccharide (LPS) plus interferon-γ (IFN-γ) or interleukin 4 (IL-4) to differentiate into M1 or M2 macrophages. Lentivirus vectors were transduced into RAW264.7 macrophages to construct the cell lines that overexpressed or silenced Wip1, respectively. Furthermore, E-cadherin, Vimentin, and α-SMA levels of primary renal tubular epithelial cells (RTECs) were measured after co-culture with macrophages overexpressed or silenced by Wip1.

RESULTS

Macrophages stimulated by LPS plus IFN-γ differentiated into M1 macrophages with high expression of iNOS and TNF-α, while those stimulated by IL-4 differentiated into M2 macrophages with high expression of Arg-1 and CD206. Increased expression of iNOS and TNF-α was observed in macrophages transduced with Wip1 RNA interference, while an increased expression of Arg-1 and CD206 was observed in macrophages transduced with Wip1 overexpressed vector, indicating that RAW264.7 macrophages could be transformed into M2 macrophages after Wip1 overexpression, and transformed into M1 macrophages by down-regulating Wip1. In addition, the E-cadherin mRNA level decreased and Vimentin and α-SMA increased in RTECs co-cultured with Wip1 overexpressed macrophages compared to the control group.

CONCLUSION

Wip1 may participate in the pathophysiological process of renal tubulointerstitial fibrosis by transforming macrophages into the M2 phenotype.

Exploring the immunological role and prognostic potential of PPM1M in pan-cancer

BACKGROUND

PPM1M is a member of the metal-dependent protein phosphatase family, and its role in the immunization process has not been studied in depth. In this study, we investigated the role of PPM1M in pan-cancer.

METHODS

Samples of cancer and normal tissues were obtained from the cancer genome atlas and genotype-tissue expression. Kaplan-Meier survival curves and Cox regression were used to analyze the effect of PPM1M on prognosis. Functional and pathway enrichment analyses were performed using the R package "clusterProfiler" to explore the role of PPM1M. The Sanger Box database was used to analyze the relationship between PPM1M and tumor immune checkpoint, tumor mutational burden, and microsatellite instability. The Tumor Immune Estimation Resource 2 database and CIBERSORT method were used to analyze the relationship between PPM1M and tumor-infiltrating immune cells. Finally, the cBioPortal database was used to analyze the genomic variation in PPM1M.

RESULTS

Among the variety of tumors, the expression of PPM1M was higher in normal tissues than in cancerous tissues. The expression of PPM1M is closely associated with patient prognosis, tumor immune checkpoint, tumor mutational burden, and microsatellite instability. PPM1M is closely associated with the infiltration of immune cells into the tumor microenvironment. In addition, PPM1M is involved in the regulation of several immune-related pathways.

CONCLUSION

In pan-cancer, PPM1M affects patient prognosis and may be a potential immunological biomarker. Furthermore, PPM1M may be a potential therapeutic target in tumor immunology.

Low WIP1 Expression Accelerates Ovarian Aging by Promoting Follicular Atresia and Primordial Follicle Activation

Our previous study demonstrated that ovarian wild-type P53-induced phosphatase 1 (WIP1) expression decreased with age. We hypothesized that WIP1 activity was related to ovarian aging. The role of WIP1 in regulating ovarian aging and its mechanisms remain to be elucidated. Adult female mice with or without WIP1 inhibitor (GSK2830371) treatment were divided into three groups (Veh, GSK-7.5, GSK-15) to evaluate the effect of WIP1 on ovarian endocrine and reproductive function and the ovarian reserve. In vitro follicle culture and primary granulosa cell culture were applied to explore the mechanisms of WIP1 in regulating follicular development. This study revealed that WIP1 expression in atretic follicle granulosa cells is significantly lower than that in healthy follicles. Inhibiting WIP1 phosphatase activity in mice induced irregular estrous cycles, caused fertility declines, and decreased the ovarian reserve through triggering excessive follicular atresia and primordial follicle activation. Primordial follicle depletion was accelerated via PI3K-AKT-rpS6 signaling pathway activation. In vitro follicle culture experiments revealed that inhibiting WIP1 activity impaired follicular development and oocyte quality. In vitro granulosa cell experiments further indicated that downregulating WIP1 expression promoted granulosa cell death via WIP1-p53-BAX signaling pathway-mediated apoptosis. These findings suggest that appropriate WIP1 expression is essential for healthy follicular development, and decreased WIP1 expression accelerates ovarian aging by promoting follicular atresia and primordial follicle activation.

PPM1D suppresses p53-dependent transactivation and cell death by inhibiting the Integrated Stress Response

The p53 transcription factor is a master regulator of cellular stress responses inhibited by repressors such as MDM2 and the phosphatase PPM1D. Activation of p53 with pharmacological inhibitors of its repressors is being tested in clinical trials for cancer therapy, but efficacy has been limited by poor induction of tumor cell death. We demonstrate that dual inhibition of MDM2 and PPM1D induces apoptosis in multiple cancer cell types via amplification of the p53 transcriptional program through the eIF2α-ATF4 pathway. PPM1D inhibition induces phosphorylation of eIF2α, ATF4 accumulation, and ATF4-dependent enhancement of p53-dependent transactivation upon MDM2 inhibition. Dual inhibition of p53 repressors depletes heme and induces HRI-dependent eIF2α phosphorylation. Pharmacological induction of eIF2α phosphorylation synergizes with MDM2 inhibition to induce cell death and halt tumor growth in mice. These results demonstrate that PPM1D inhibits both the p53 network and the integrated stress response controlled by eIF2α-ATF4, with clear therapeutic implications.

The role of serine/threonine phosphatases in human development: Evidence from congenital disorders

Reversible protein phosphorylation is a fundamental regulation mechanism in eukaryotic cell and organismal physiology, and in human health and disease. Until recently, and unlike protein kinases, mutations in serine/threonine protein phosphatases (PSP) had not been commonly associated with disorders of human development. Here, we have summarized the current knowledge on congenital diseases caused by mutations, inherited or de novo, in one of 38 human PSP genes, encoding a monomeric phosphatase or a catalytic subunit of a multimeric phosphatase. In addition, we highlight similar pathogenic mutations in genes encoding a specific regulatory subunit of a multimeric PSP. Overall, we describe 19 affected genes, and find that most pathogenic variants are loss-of-function, with just a few examples of gain-of-function alterations. Moreover, despite their widespread tissue expression, the large majority of congenital PSP disorders are characterised by brain-specific abnormalities, suggesting a generalized, major role for PSPs in brain development and function. However, even if the pathogenic mechanisms are relatively well understood for a small number of PSP disorders, this knowledge is still incomplete for most of them, and the further identification of downstream targets and effectors of the affected PSPs is eagerly awaited through studies in appropriate in vitro and in vivo disease models. Such lacking studies could elucidate the exact mechanisms through which these diseases act, and possibly open up new therapeutic avenues.

Co-targeting WIP1 and PARP induces synthetic lethality in hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is one of the most fatal cancers. Due to limited strategies for effective treatments, patients with advanced HCC have a very poor prognosis. This study aims to identify new insights in HCC to develop novel strategies for HCC management.

Methods

The role of WIP1 (wild type p53 induced protein phosphatase1) in HCC was analyzed in HCC cells, xenograft model, DEN (Diethylnitrosamine) induced mice liver cancer model with WIP1 knockout mice, and TCGA database. DNA damage was evaluated by Gene Set Enrichment Analysis, western blotting, comet assay, and Immunofluorescence.

Results

High expression of WIP1 is associated with the poor prognosis of patients with HCC. Genetically and chemically suppression of WIP1 drastically reduced HCC cell proliferation. Besides, WIP1 knockout retarded DEN induced mice hepato-carcinogenesis. Mechanically, WIP1 inhibition induced DNA damage by increasing H2AX phosphorylation (γH2AX). Therefore, suppression of WIP1 and PARP induced synthetic lethality in HCC in vitro and in vivo by augmenting DNA damage.

Conclusion

WIP1 plays an oncogenic effect in HCC development, and targeting WIP1-dependent DNA damage repair alone or in combination with PARP inhibition might be a reasonable strategy for HCC management.

Increased WIP1 Expression With Aging Suppresses the Capacity of Oocytes to Respond to and Repair DNA Damage

If fertilization does not occur for a prolonged time after ovulation, oocytes undergo a time-dependent deterioration in quality in vivo and in vitro, referred to as postovulatory aging. The DNA damage response is thought to decline with aging, but little is known about how mammalian oocytes respond to the DNA damage during in vitro postovulatory aging. Here we show that increased WIP1 during in vitro postovulatory aging suppresses the capacity of oocytes to respond to and repair DNA damage. During in vitro aging, oocytes progressively lost their capacity to respond to DNA double-strand breaks, which corresponded with an increase in WIP1 expression. Increased WIP1 impaired the amplification of γ-H2AX signaling, which reduced the DNA repair capacity. WIP1 inhibition restored the DNA repair capacity, which prevented deterioration in oocyte quality and improved the fertilization and developmental competence of aged oocytes. Importantly, WIP1 was also found to be high in maternally aged oocytes, and WIP1 inhibition enhanced the DNA repair capacity of maternally aged oocytes. Therefore, our results demonstrate that increased WIP1 is responsible for the age-related decline in DNA repair capacity in oocytes, and WIP1 inhibition could restore DNA repair capacity in aged oocytes.

Wip1 regulates the immunomodulatory effects of murine mesenchymal stem cells in type 1 diabetes mellitus via targeting IFN-α/BST2

Mesenchymal stem cells (MSCs) show significant therapeutic effects in type 1 diabetes mellitus (T1DM) as regulating the inflammatory processes. However, little is known about the detailed process of MSCs immunosuppression in T1DM. In this study, we investigated the effects of wild-type p53-induce phosphatase 1 (Wip1) on regulating MSCs immunosuppressive capacities in T1DM mice. We found that Wip1 knockout (Wip1-/-) MSCs had lower therapeutic effects in T1DM mice, and displayed weaker immunosuppressive capability. In vivo distribution analysis results indicated thatWip1-/-MSCs could home to the damaged pancreas and increase the expression of tumor necrosis factor-α (TNF-α), interleukin-17a (IL-17a), interferon-α(IFN-α), IFN-β, and IFN-γ, while decrease the expression of IL-4 and IL-10. Moreover, we confirmedWip1-/-MSCs exhibited weaker immunosuppressive capacity, as evidenced by enhanced expression of bone marrow stromal cell antigen 2(BST2) and IFN-α. In conclusion, these results revealed Wip1 affects MSCs immunomodulation by regulating the expression of IFN-α/BST2. Our study uncovered that Wip1 is required to regulate the therapeutic effects of MSCs on T1DM treatment, indicating a novel role of Wip1 in MSCs immunoregulation properties.

Wild-Type p53-Induced Phosphatase 1 Plays a Positive Role in Hematopoiesis in the Mouse Embryonic Head

The first adult repopulating hematopoietic stem cells (HSCs) are found in the aorta-gonad-mesonephros (AGM) region, which are produced from hemogenic endothelial cells. Embryonic head is the other site for HSC development. Wild-type p53-induced phosphatase 1 (Wip1) is a type-2Cδ family serine/threonine phosphatase involved in various cellular processes such as lymphoid development and differentiation of adult HSCs. Most recently, we have shown that Wip1 modulates the pre-HSC maturation in the AGM region. However, it is not clear whether Wip1 regulates hematopoiesis in the embryonic head. Here we reported that disruption of Wip1 resulted in a decrease of hematopoietic progenitor cell number in the embryonic head. In vivo transplantation assays showed a reduction of HSC function after Wip1 ablation. We established that Wip1 deletion reduced the frequency and cell number of microglia in the embryonic head. Further observations revealed that Wip1 absence enhanced the gene expression of microglia-derived pro-inflammatory factors. Thus, it is likely that Wip1 functions as a positive regulator in HSC development by regulating the function of microglia in the embryonic head.

Inhibition of the DNA damage response phosphatase PPM1D reprograms neutrophils to enhance anti-tumor immune responses

PPM1D/Wip1 is a negative regulator of the tumor suppressor p53 and is overexpressed in several human solid tumors. Recent reports associate gain-of-function mutations of PPM1D in immune cells with worse outcomes for several human cancers. Here we show that mice with genetic knockout of Ppm1d or with conditional knockout of Ppm1d in the hematopoietic system, in myeloid cells, or in neutrophils all display significantly reduced growth of syngeneic melanoma or lung carcinoma tumors. Ppm1d knockout neutrophils infiltrate tumors extensively. Chemical inhibition of Wip1 in human or mouse neutrophils increases anti-tumor phenotypes, p53-dependent expression of co-stimulatory ligands, and proliferation of co-cultured cytotoxic T cells. These results suggest that inhibition of Wip1 in neutrophils enhances immune anti-tumor responses.

The inhibition of WIP1 phosphatase accelerates the depletion of primordial follicles

RESEARCH QUESTION

What role does wild-type p53-induced phosphatase 1 (WIP1) play in the regulation of primordial follicle development?

DESIGN

WIP1 expression was detected in the ovaries of mice of different ages by western blotting and immunohistochemical staining. Three-day-old neonatal mouse ovaries were cultured in vitro with or without the WIP1 inhibitor GSK2830371 (10 μM) for 4 days. Ovarian morphology, follicle growth and follicle classification were analysed and the PI3K-AKT-mTOR signal pathway and the WIP1-p53-related mitochondrial apoptosis pathway evaluated.

RESULTS

WIP1 expression was downregulated with age. Primordial follicles were significantly decreased in the GSK2830371-treated group, without a significant increase in growing follicles. The ratio of growing follicles to primordial follicles was not significantly different between the control and GSK2830371 groups, and no significant variation was observed in the PI3K-AKT-mTOR signal pathway. The inhibition of WIP1 phosphatase accelerated primordial follicle atresia by activating the p53-BAX-caspase-3 pathway.

CONCLUSIONS

These findings reveal that WIP1 participates in regulating primordial follicle development and that inhibiting WIP1 phosphatase leads to massive primordial follicle loss via interaction with the p53-BAX-caspase-3 pathway. This might also provide valuable information for understanding decreased ovarian reserve during ovarian ageing.

Protein phosphatases in TLR signaling

Toll-like receptors (TLRs) are critical sensors for the detection of potentially harmful microbes. They are instrumental in initiating innate and adaptive immune responses against pathogenic organisms. However, exaggerated activation of TLR receptor signaling can also be responsible for the onset of autoimmune and inflammatory diseases. While positive regulators of TLR signaling, such as protein serine/threonine kinases, have been studied intensively, only little is known about phosphatases, which counterbalance and limit TLR signaling. In this review, we summarize protein phosphorylation events and their roles in the TLR pathway and highlight the involvement of protein phosphatases as negative regulators at specific steps along the TLR-initiated signaling cascade. Then, we focus on individual phosphatase families, specify the function of individual enzymes in TLR signaling in more detail and give perspectives for future research. A better understanding of phosphatase-mediated regulation of TLR signaling could provide novel access points to mitigate excessive immune activation and to modulate innate immune signaling.

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.

Development of Specific Inhibitors for Oncogenic Phosphatase PPM1D by Using Ion-Responsive DNA Aptamer Library

(1) Background: Ser/Thr protein phosphatase PPM1D is an oncogenic protein. In normal cells, however, PPM1D plays essential roles in spermatogenesis and immune response. Hence, it is necessary to develop novel PPM1D inhibitors without side effects on normal cells. Stimuli-responsive molecules are suitable for the spatiotemporal regulation of inhibitory activity. (2) Methods: In this study, we designed an ion-responsive DNA aptamer library based on G-quadruplex DNA that can change its conformation and function in response to monovalent cations. (3) Results: Using this library, we identified the PPM1D specific inhibitor M1D-Q5F aptamer. The M1D-Q5F aptamer showed anti-cancer activity against breast cancer MCF7 cells. Interestingly, the induction of the structural change resulting in the formation of G-quadruplex upon stimulation by monovalent cations led to the enhancement of the inhibitory activity and binding affinity of M1D-Q5F. (4) Conclusions: These data suggest that the M1D-Q5F aptamer may act as a novel stimuli-responsive anti-cancer agent.

The biological function and the regulatory roles of wild-type p53-induced phosphatase 1 in immune system

Wild-type p53-induced phosphatase 1 (WIP1) belongs to the protein phosphatase 2C (PP2C) family and is a mammalian serine/threonine specific protein phosphatase to dephosphorylate numerous signaling molecules. Mammalian WIP1 regulates a wide array of targeting molecules and plays key regulatory roles in many cell processes such as DNA damage and repair, cell proliferation, differentiation, apoptosis, and senescence. WIP1 promotes the formation and development of tumors as an oncogene and a negative regulator of p53. It is also involved in the regulation of aging, neurological diseases and immune diseases. Recent studies demonstrated the critical roles of WIP1 in the differentiation and function of immune cells including T cells, neutrophils and macrophages. In the present manuscript, we briefly summarized the expression patterns, biological function and the target molecules and signal pathways of WIP1 and mainly discussed the latest advances on the regulatory effects of WIP1 in the immune system. WIP1 may be a potential target molecule to treat cancers and immune diseases such as allergic asthma.

Metal-dependent Ser/Thr protein phosphatase PPM family: Evolution, structures, diseases and inhibitors

Protein phosphatases and kinases control multiple cellular events including proliferation, differentiation, and stress responses through regulating reversible protein phosphorylation, the most important post-translational modification. Members of metal-dependent protein phosphatase (PPM) family, also known as PP2C phosphatases, are Ser/Thr phosphatases that bind manganese/magnesium ions (Mn²⁺/Mg²⁺) in their active center and function as single subunit enzymes. In mammals, there are 20 isoforms of PPM phosphatases: PPM1A, PPM1B, PPM1D, PPM1E, PPM1F, PPM1G, PPM1H, PPM1J, PPM1K, PPM1L, PPM1M, PPM1N, ILKAP, PDP1, PDP2, PHLPP1, PHLPP2, PP2D1, PPTC7, and TAB1, whereas there are only 8 in yeast. Phylogenetic analysis of the DNA sequences of vertebrate PPM isoforms revealed that they can be divided into 12 different classes: PPM1A/PPM1B/PPM1N, PPM1D, PPM1E/PPM1F, PPM1G, PPM1H/PPM1J/PPM1M, PPM1K, PPM1L, ILKAP, PDP1/PDP2, PP2D1/PHLPP1/PHLPP2, TAB1, and PPTC7. PPM-family members have a conserved catalytic core region, which contains the metal-chelating residues. The different isoforms also have isoform specific regions within their catalytic core domain and terminal domains, and these regions may be involved in substrate recognition and/or functional regulation of the phosphatases. The twenty mammalian PPM phosphatases are involved in regulating diverse cellular functions, such as cell cycle control, cell differentiation, immune responses, and cell metabolism. Mutation, overexpression, or deletion of the PPM phosphatase gene results in abnormal cellular responses, which lead to various human diseases. This review focuses on the structures and biological functions of the PPM-phosphatase family and their associated diseases. The development of specific inhibitors against the PPM phosphatase family as a therapeutic strategy will also be discussed.

Modeling and measurement of signaling outcomes affecting decision making in noisy intracellular networks using machine learning methods

Characterization of decision-making in cells in response to received signals is of importance for understanding how cell fate is determined. The problem becomes multi-faceted and complex when we consider cellular heterogeneity and dynamics of biochemical processes. In this paper, we present a unified set of decision-theoretic, machine learning and statistical signal processing methods and metrics to model the precision of signaling decisions, in the presence of uncertainty, using single cell data. First, we introduce erroneous decisions that may result from signaling processes and identify false alarms and miss events associated with such decisions. Then, we present an optimal decision strategy which minimizes the total decision error probability. Additionally, we demonstrate how graphing receiver operating characteristic curves conveniently reveals the trade-off between false alarm and miss probabilities associated with different cell responses. Furthermore, we extend the introduced framework to incorporate the dynamics of biochemical processes and reactions in a cell, using multi-time point measurements and multi-dimensional outcome analysis and decision-making algorithms. The introduced multivariate signaling outcome modeling framework can be used to analyze several molecular species measured at the same or different time instants. We also show how the developed binary outcome analysis and decision-making approach can be extended to more than two possible outcomes. As an example and to show how the introduced methods can be used in practice, we apply them to single cell data of PTEN, an important intracellular regulatory molecule in a p53 system, in wild-type and abnormal cells. The unified signaling outcome modeling framework presented here can be applied to various organisms ranging from viruses, bacteria, yeast and lower metazoans to more complex organisms such as mammalian cells. Ultimately, this signaling outcome modeling approach can be utilized to better understand the transition from physiological to pathological conditions such as inflammation, various cancers and autoimmune diseases.

Identification of a phosphorylation site on Ulk1 required for genotoxic stress-induced alternative autophagy

Alternative autophagy is an autophagy-related protein 5 (Atg5)-independent type of macroautophagy. Unc51-like kinase 1 (Ulk1) is an essential initiator not only for Atg5-dependent canonical autophagy but also for alternative autophagy. However, the mechanism as to how Ulk1 differentially regulates both types of autophagy has remained unclear. In this study, we identify a phosphorylation site of Ulk1 at Ser⁷⁴⁶, which is phosphorylated during genotoxic stress-induced alternative autophagy. Phospho-Ulk1⁷⁴⁶ localizes exclusively on the Golgi and is required for alternative autophagy, but not canonical autophagy. We also identify receptor-interacting protein kinase 3 (RIPK3) as the kinase responsible for genotoxic stress-induced Ulk1⁷⁴⁶ phosphorylation, because RIPK3 interacts with and phosphorylates Ulk1 at Ser⁷⁴⁶, and loss of RIPK3 abolishes Ulk1⁷⁴⁶ phosphorylation. These findings indicate that RIPK3-dependent Ulk1⁷⁴⁶ phosphorylation on the Golgi plays a pivotal role in genotoxic stress-induced alternative autophagy.

Unlike canonical macroautophagy, alternative autophagy does not require the factors Atg5 and Atg7, but does require Ulk1. Here the authors show that phosphorylation of Ulk1 at Ser⁷⁴⁶ by RIPK3 is required for alternative autophagy initiation at the Golgi in response to genotoxic stress.

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.

Wild-type p53-induced phosphatase 1 (WIP1) regulates the proliferation of swine Sertoli cells through P53

Wild-type p53-induced phosphatase 1 (WIP1) plays an oncogenic function by increasing cell proliferation in various cancer types. Deficiency in WIP1 expression leads to male infertility, possibly by impairing the blood-testis barrier and spermatogenesis. However, how WIP1 functions in the Sertoli cells to affect male reproduction remains unclear. Thus, in the present study we used a swine Sertoli cell line to investigate whether WIP1 regulated the proliferation of Sertoli cells to participate in male reproduction. The WIP1 inhibitor GSK2830371, WIP1-short interference (si) RNAs and an upstream microRNA (miR-16) were used to inhibit the expression of WIP1, after which the proliferation of swine Sertoli cells, P53 expression and the levels of P53 phosphorylation were determined. Inhibiting WIP1 expression suppressed swine Sertoli cell proliferation, increased P53 expression and increased levels of P53 phosphorylation. In addition, overexpression of miR-16 in swine Sertoli cells resulted in a decrease in WIP1 expression and increases in both P53 expression and P53 phosphorylation. Together, these findings suggest that WIP1 positively regulates the proliferation of swine Sertoli cells by inhibiting P53 phosphorylation, and the miR-16 is likely also involved by targeting WIP1.

Inhibition of lipid droplet formation by Ser/Thr protein phosphatase PPM1D inhibitor, SL-176

Obesity is a worldwide public health problem, which is associated with various severe diseases including diabetes, hypertension, atherosclerosis, and cancer. Recent studies have revealed that combination treatment of several different compounds using low doses is effective to reduce side effects. Thus, there is a need to develop an efficient inhibitor for reducing lipid droplets with a divergent target/pathway. Ser/Thr protein phosphatase PPM1D is involved in cellular metabolic processes and is a promising target for anti-obesity treatment. We have previously developed a potent and specific PPM1D inhibitor, SL-176. In this study, we demonstrated that significant reduction of lipid droplet formation in adipocytes by the PPM1D specific inhibitor, SL-176. Using Oil-red O staining and fluorescent imaging of lipid droplet, we found that treatment of SL-176 significantly suppressed lipid droplet formation of 3T3-L1 cells both in amount and in size. SL-176 also repressed mRNA and protein expression of PPARγ and C/EBPα, adipogenic markers, at nontoxic conditions. Thus, SL-176 is a unique and potent inhibitor of lipid droplet formation that acts via PPM1D, a novel target toward inhibiting adipocyte differentiation.

Integrative Proteomic and Phosphoproteomic Profiling of Testis from Wip1 Phosphatase-Knockout Mice: Insights into Mechanisms of Reduced Fertility

Mice lacking wild-type p53-induced phosphatase 1 (Wip1) display male reproductive defects including smaller testes, subfertility and spermatogenesis defects at the round- and elongating-spermatid stages. However, the molecular mechanisms underlying these abnormalities remain unclear. Here we examined the proteome and phosphoproteome of testes from Wip1-knockout mice using a quantitative proteomic approach. From a total of 6872 proteins and 4280 phosphorylation sites identified, 58 proteins and 159 phosphorylation sites were found to be differentially regulated compared with wild type mice. Pathway enrichment analyses revealed that these regulated proteins and phosphosites were mainly involved in adherens/tight junctions, apoptosis, inflammatory response, spermatogenesis, sperm motility, and cytoskeletal assembly and depolymerization. Wip1-knockout mice showed decreased expression of junction-associated proteins (occludin, ZO-1, and N-cadherin) and impaired integrity of the blood-testis barrier. In addition, Wip1 deficiency was associated with elevated levels of cytokines and germ cell apoptosis in the testis. These results suggest that proinflammatory cytokines may impair the blood-testis barrier dynamics by decreasing the expression of junction-associated proteins, which could lead to subfertility and spermatogenesis defects. Collectively, these findings help to explain the low reproductive function caused by Wip1 deletion and provide novel insights into our understanding of causes of male infertility.

Targeting 17q23 amplicon to overcome the resistance to anti-HER2 therapy in HER2+ breast cancer

Chromosome 17q23 amplification occurs in ~11% of human breast cancers. Enriched in HER2+ breast cancers, the 17q23 amplification is significantly correlated with poor clinical outcomes. In addition to the previously identified oncogene WIP1, we uncover an oncogenic microRNA gene, MIR21, in a majority of the WIP1-containing 17q23 amplicons. The 17q23 amplification results in aberrant expression of WIP1 and miR-21, which not only promotes breast tumorigenesis, but also leads to resistance to anti-HER2 therapies. Inhibiting WIP1 and miR-21 selectively inhibits the proliferation, survival and tumorigenic potential of the HER2+ breast cancer cells harboring 17q23 amplification. To overcome the resistance of trastuzumab-based therapies in vivo, we develop pH-sensitive nanoparticles for specific co-delivery of the WIP1 and miR-21 inhibitors into HER2+ breast tumors, leading to a profound reduction of tumor growth. These results demonstrate the great potential of the combined treatment of WIP1 and miR-21 inhibitors for the trastuzumab-resistant HER2+ breast cancers.

The 17q23 amplicon containing the WIP1 oncogene is frequently amplified in HER2+ breast cancer. Here they find MIR21 to be present in WIP1-containing amplicons, and report nanoparticle based co-delivery of WIP1 and miR-21 inhibitors to be effective in trastuzumab-resistant HER2+ breast cancer.

Protein phosphatase 5 and the tumor suppressor p53 down-regulate each other's activities in mice

Protein phosphatase 5 (PP5), a serine/threonine phosphatase, has a wide range of biological functions and exhibits elevated expression in tumor cells. We previously reported that pp5-deficient mice have altered ataxia-telangiectasia mutated (ATM)-mediated signaling and function. However, this regulation was likely indirect, as ATM is not a known PP5 substrate. In the current study, we found that pp5-deficient mice are hypersensitive to genotoxic stress. This hypersensitivity was associated with the marked up-regulation of the tumor suppressor tumor protein p53 and its downstream targets cyclin-dependent kinase inhibitor 1A (p21), MDM2 proto-oncogene (MDM2), and phosphatase and tensin homolog (PTEN) in pp5-deficient tissues and cells. These observations suggested that PP5 plays a role in regulating p53 stability and function. Experiments conducted with p53 ^+/- pp5 ^+/- or p53 ^+/- pp5 ^-/- mice revealed that complete loss of PP5 reduces tumorigenesis in the p53 ^+/- mice. Biochemical analyses further revealed that PP5 directly interacts with and dephosphorylates p53 at multiple serine/threonine residues, resulting in inhibition of p53-mediated transcriptional activity. Interestingly, PP5 expression was significantly up-regulated in p53-deficient cells, and further analysis of pp5 promoter activity revealed that p53 strongly represses PP5 transcription. Our results suggest a reciprocal regulatory interplay between PP5 and p53, providing an important feedback mechanism for the cellular response to genotoxic stress.

Wip1 knockout inhibits neurogenesis by affecting the Wnt/β-catenin signaling pathway in focal cerebral ischemia in mice

Neurogenesis correlates closely with the recovery of neural function after brain ischemia but the critical proteins and signaling pathways involved remain unclear. The phosphatase WIP1 has been shown to regulate neurogenesis in models of aging. However, it is not known if WIP1 affects neurogenesis and functional recovery after brain ischemia. To explore these questions, we performed permanent middle cerebral artery occlusion (MCAO) in mice and performed BrdU labeling, neurobehavioral testing, western blotting, and immunofluorescence staining. We found that ischemia induced WIP1 expression in the area bordering the injury. Compared to wild-type mice, the knockout of the Wip1 gene inhibited neurological functional recovery, reduced the expression of doublecortin, and inactivated the Wnt/β-Catenin signaling pathway in cerebral ischemia in mice. Pharmacological activation of the Wnt/β-Catenin signaling pathway compensated for the Wip1 knockout-induced deficit in neuroblast formation in animals with MCAO. These findings indicate that WIP1 is essential for neurogenesis after brain injury by activating the Wnt/β-Catenin signaling pathway.

Transcriptomic analysis reveals transgenerational effect of hypoxia on the neural control of testicular functions

There are over 400 hypoxic zones in the ocean worldwide. Both laboratory and field studies have shown that hypoxia causes endocrine disruption and reproductive impairments in vertebrates. More importantly, our recent study discovered that parental (F0) hypoxia exposure resulted in the transgenerational impairment of sperm quality in the F2 generation through the epigenetic regulation of germ cells. In the present study, we aim to test the hypothesis that the brain, as the major regulator of the brain-pituitary-gonad (BPG) axis, is also involved in the observed transgenerational effect. Using comparative transcriptomic analysis on brain tissues of marine medaka Oryzias melastigma, 45 common differentially expressed genes caused by parental hypoxia exposure were found in the hypoxic group of the F0 and F2 generations, and the transgenerational groups of the F2 generation. The bioinformatic analysis on this deregulated gene cluster further highlighted the possible involvement of the brain in the transgenerational effect of hypoxia on testicular structure, including abnormal morphologies of the epididymis and the seminal vesicle, and degeneration of the seminiferous tubule. This finding is concordant to the result of hematoxylin and eosin staining, which showed the reduction of testicular lobular diameter in the F0 and F2 generations. Our study demonstrated for the first time the involvement of the brain in the transgenerational effect of hypoxia.

Inhibition of WIP1 phosphatase sensitizes breast cancer cells to genotoxic stress and to MDM2 antagonist nutlin-3

PP2C family serine/threonine phosphatase WIP1 acts as a negative regulator of the tumor suppressor p53 and is implicated in silencing of cellular responses to genotoxic stress. Chromosomal locus 17q23 carrying the PPM1D (coding for WIP1) is commonly amplified in breast carcinomas and WIP1 was proposed as potential pharmacological target. Here we employed a cellular model with knocked out PPM1D to validate the specificity and efficiency of GSK2830371, novel small molecule inhibitor of WIP1. We have found that GSK2830371 increased activation of the DNA damage response pathway to a comparable level as the loss of PPM1D. In addition, GSK2830371 did not affect proliferation of cells lacking PPM1D but significantly supressed proliferation of breast cancer cells with amplified PPM1D. Over time cells treated with GSK2830371 accumulated in G1 and G2 phases of the cell cycle in a p21-dependent manner and were prone to induction of senescence by a low dose of MDM2 antagonist nutlin-3. In addition, combined treatment with GSK2830371 and doxorubicin or nutlin-3 potentiated cell death through a strong induction of p53 pathway and activation of caspase 9. We conclude that efficient inhibition of WIP1 by GSK2830371 sensitizes breast cancer cells with amplified PPM1D and wild type p53 to chemotherapy.

Wip1 phosphatase: between p53 and MAPK kinases pathways

Cells undergoing oncogenic transformation frequently inactivate tumor suppressor pathways that could prevent their uncontrolled growth. Among those pathways p53 and p38MAPK pathways play a critical role in regulation of cell cycle, senescence and cell death in response to activation of oncogenes, stress and DNA damage. Consequently, these two pathways are important in determining the sensitivity of tumor cells to anti-cancer treatment. Wild type p53-induced phosphatase, Wip1, is involved in governance of both pathways. Recently, strategies directed to manipulation with Wip1 activity proposed to advance current day anticancer treatment and novel chemical compounds synthesized to improve specificity of manipulation with Wip1 activity. Here we reviewed the history of Wip1 studies in vitro and in vivo, in genetically modified animal models that support Wip1 role in tumorigenesis through regulation of p53 and p38MAPK pathways. Based on our knowledge we propose several recommendations for future more accurate studies of Wip1 interactions with other pathways involved in tumorigenesis using recently developed tools and for adoption of Wip1 manipulation strategies in anti-cancer therapy.

Clinical Significance of the Wild Type p53-Induced Phosphatase 1 Expression in Invasive Breast Cancer

BACKGROUND

Wild type p53-induced phosphatase 1 (Wip1), encoded by the protein phosphatase magnesium dependent 1 delta (PPM1D), inhibits p53. PPM1D amplification has been reported in breast cancer. Breast cancer can sometimes develop without a tumor protein 53 (TP53) mutation. In these cases, the p53 pathway might be disrupted by alternative mechanisms, and Wip1 is reported to be a key molecule involved.

MATERIALS AND METHODS

Primary invasive ductal carcinoma specimens were obtained from 201 cases, for which archival tissue samples for immunohistochemistry were available. We evaluated Wip1 and p21 protein expression (201 cases), Wip1 mRNA expression (63 cases), PPM1D DNA copy number (71 cases) and TP53 status (36 cases) using available samples among the 201 cases, and analyzed their relationships with clinicopathological factors and prognosis.

RESULTS

The nuclear expression of Wip1 protein was positive in 21 cases (10.4%). The PPM1D DNA copy number was significantly correlated with Wip1 protein expression. All cases with PPM1D amplification by single-nucleotide polymorphism comparative genomic hybridization array showed positive nuclear Wip1 expression. Wip1 protein expression was positively correlated with p21 expression. The tumors with positive Wip1 and negative p21 expression showed the poorest prognosis among all tumor types.

CONCLUSION

The protein expression of Wip1 might be regulated by PPM1D amplification, independent of TP53 status. Positive Wip1 and negative p21 expression was associated with the poorest prognosis and suggests the loss of p53 function.

Inhibition of Ser/Thr phosphatase PPM1D induces neutrophil differentiation in HL-60 cells

Protein phosphatase Magnesium-dependent 1, Delta (PPM1D) is a wild-type p53-inducible Ser/Thr phosphatase that acts as a negative regulator of the p53 tumor suppressor. Gene amplification and overexpression of PPM1D have been reported in various cancers including leukemia and neuroblastoma. Therefore, PPM1D is a promising target in cancer therapy. It has been reported that PPM1D knockout mice exhibit neutrophilia in blood and show a defective immune response. Here, we found that inhibition of PPM1D induced neutrophil differentiation of human promyelocytic leukemia cell line HL-60. The combination of a PPM1D inhibitor and all-trans retinoic acid significantly increased their differentiation efficiency. The PPM1D inhibitor also induced G1 arrest in HL-60 cells. Our results suggest that PPM1D may be a potential therapeutic target for blood cell diseases including leukemia.

Wip1-dependent modulation of macrophage migration and phagocytosis

Macrophage accumulation within the vascular wall is a hallmark of atherosclerosis. Controlling macrophage conversion into foam cells remains a major challenge for treatment of atherosclerotic diseases. Here, we show that Wip1, a member of the PP2C family of Ser/Thr protein phosphatases, modulates macrophage migration and phagocytosis associated with atherosclerotic plaque formation. Wip1 deficiency increases migratory and phagocytic activities of the macrophage under stress conditions. Enhanced migration of Wip1^-/- macrophages is mediated by Rac1-GTPase and PI3K/AKT signalling pathways. Elevated phagocytic ability of Wip1^-/- macrophages is linked to CD36 plasma membrane recruitment that is regulated by AMPK activity. Our study identifies Wip1 as an intrinsic negative regulator of macrophage chemotaxis. We propose that Wip1-dependent control of macrophage function may provide avenues for preventing or eliminating plaque formation in atherosclerosis.

Wild-type p53-induced Phosphatase 1 Deficiency Exacerbates Myocardial Infarction-induced Ischemic Injury

BACKGROUND

Myocardial infarction (MI) is a major disease burden. Wild-type p53-induced phosphatase 1 (Wip1) has been studied extensively in the context of cancer and the regulation of different types of stem cells, but the role of Wip1 in cardiac adaptation to MI is unknown. We investigated the significance of Wip1 in a mouse model of MI.

METHODS

The study began in June 2014 and was completed in July 2016. We compared Wip1-knockout (Wip1-KO) mice and wild-type (WT) mice to determine changes in cardiac function and survival in response to MI. The heart weight/body weight (HW/BW) ratio and cardiac function were measured before MI. Mouse MI was established by ligating the left anterior descending (LAD) coronary artery under 1.5% isoflurane anesthesia. After MI, survival of the mice was observed for 4 weeks. Cardiac function was examined by echocardiography. The HW/BW ratio was analyzed, and cardiac hypertrophy was measured by wheat germ agglutinin staining. Hematoxylin and eosin (H&E) staining was used to determine the infarct size. Gene expression of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) was assessed by quantitative real-time polymerase chain reaction (qPCR), and the levels of signal transducers and activators of transcription 3 (stat3) and phosphor-stat3 (p-stat3) were also analyzed by Western blotting. Kaplan-Meier survival analysis, log-rank test, unpaired t-test, and one-way analysis of variance (ANOVA) were used for statistical analyses.

RESULTS

Wip1-KO mice had a marginally increased HW/BW ratio and slightly impaired cardiac function before LAD ligation. After MI, Wip1-deficient mice exhibited increased mortality (57.14% vs. 29.17%; n = 24 [WT], n = 35 [Wip1-KO], P< 0.05), increased cardiac hypertrophy (HW/BW ratio: 7 days: 7.25 ± 0.36 vs. 5.84 ± 0.18, n = 10, P< 0.01, and 4 weeks: 6.05 ± 0.17 vs. 5.87 ± 0.24, n = 10, P > 0.05; cross-sectional area: 7 days: 311.80 ± 8.29 vs. 268.90 ± 11.15, n = 6, P< 0.05, and 4 weeks: 308.80 ± 11.26 vs. 317.00 ± 13.55, n = 6, P > 0.05), and reduced cardiac function (ejection fraction: 7 days: 29.37 ± 1.38 vs. 34.72 ± 1.81, P< 0.05, and 4 weeks: 19.06 ± 2.07 vs. 26.37 ± 2.95, P< 0.05; fractional shortening: 7 days: 13.72 ± 0.71 vs. 16.50 ± 0.94, P< 0.05, and 4 weeks: 8.79 ± 1.00 vs. 12.48 ± 1.48, P< 0.05; n = 10 [WT], n = 15 [Wip1-KO]). H&E staining revealed a larger infarct size in Wip1-KO mice than in WT mice (34.79% ± 2.44% vs. 19.55% ± 1.48%, n = 6, P< 0.01). The expression of IL-6 and p-stat3 was downregulated in Wip1-KO mice (IL-6: 1.71 ± 0.27 vs. 4.46 ± 0.79, n = 6, P< 0.01; and p-stat3/stat3: 1.15 ± 0.15 vs. 1.97 ± 0.23, n = 6, P< 0.05).

CONCLUSION

The results suggest that Wip1 could protect the heart from MI-induced ischemic injury.

WIP1 phosphatase is a critical regulator of adipogenesis through dephosphorylating PPARγ serine 112

WIP1, as a critical phosphatase, plays many important roles in various physiological and pathological processes through dephosphorylating different substrate proteins. However, the functions of WIP1 in adipogenesis and fat accumulation are not clear. Here, we report that WIP1-deficient mice show impaired body weight growth, dramatically decreased fat mass, and significantly reduced triglyceride and leptin levels in circulation. This dysregulation of adipose development caused by the deletion of WIP1 occurs as early as adipogenesis. In contrast, lentivirus-mediated WIP1 phosphatase overexpression significantly increases the adipogenesis of pre-adipocytes via an enzymatic activity-dependent mechanism. PPARγ is a master gene of adipogenesis, and the phosphorylation of PPARγ at serine 112 strongly inhibits adipogenesis; however, very little is known about the negative regulation of this phosphorylation. Here, we show that WIP1 phosphatase plays a pro-adipogenic role by interacting directly with PPARγ and dephosphorylating p-PPARγ S112 in vitro and in vivo.

WIP1 phosphatase as pharmacological target in cancer therapy

DNA damage response (DDR) pathway protects cells from genome instability and prevents cancer development. Tumor suppressor p53 is a key molecule that interconnects DDR, cell cycle checkpoints, and cell fate decisions in the presence of genotoxic stress. Inactivating mutations in TP53 and other genes implicated in DDR potentiate cancer development and also influence the sensitivity of cancer cells to treatment. Protein phosphatase 2C delta (referred to as WIP1) is a negative regulator of DDR and has been proposed as potential pharmaceutical target. Until recently, exploitation of WIP1 inhibition for suppression of cancer cell growth was compromised by the lack of selective small-molecule inhibitors effective at cellular and organismal levels. Here, we review recent advances in development of WIP1 inhibitors and discuss their potential use in cancer treatment.

DNA damage-induced phosphatase Wip1 in regulation of hematopoiesis, immune system and inflammation

PP2C serine-threonine phosphatase, Wip1, is an important regulator of stress response. Wip1 controls a number of critical cellular functions: proliferation, cell cycle arrest, senescence and programmed cell death, apoptosis or autophagy. Ppm1d, the gene encoding Wip1 phosphatase, is expressed in hematopoietic progenitors, stem cells, neutrophils, macrophages B and T lymphocytes in bone marrow and peripheral blood. The Wip1-/- mice display immunodeficiency, abnormal lymphoid histopathology in thymus and spleen, defects in B- and T-cell differentiation, as well as susceptibility to viral infection. At the same time, Wip1 knockout mice exhibit pro-inflammatory phenotype in skin and intestine in the model of inflammatory bowel disease (IBD) with elevated levels of inflammation-promoting cytokines TNF-α, IL-6, IL-12, IL-17. Several Wip1 downstream targets can mediate Wip1 effects on hematopoietic system including, p53, ATM, p38MAPK kinase, NFkB, mTOR. Here, we summarized the current knowledge on the role of Wip1 in the differentiation of various hematopoietic lineages and how Wip1 deficiency affects the functions of immune cells.

WIP1 Phosphatase Plays a Critical Neuroprotective Role in Brain Injury Induced by High-Altitude Hypoxic Inflammation

The hypobaric hypoxic environment in high-altitude areas often aggravates the severity of inflammation and induces brain injury as a consequence. However, the critical genes regulating this process remain largely unknown. The phosphatase wild-type p53-induced phosphatase 1 (WIP1) plays important roles in various physiological and pathological processes, including the regulation of inflammation in normoxia, but its functions in hypoxic inflammation-induced brain injury remain unclear. Here, we established a mouse model of this type of injury and found that WIP1 deficiency augmented the release of inflammatory cytokines in the peripheral circulation and brain tissue, increased the numbers of activated microglia/macrophages in the brain, aggravated cerebral histological lesions, and exacerbated the impairment of motor and cognitive abilities. Collectively, these results provide the first in vivo evidence that WIP1 is a critical neuroprotector against hypoxic inflammation-induced brain injury.

Phosphatase Wip1 in Immunity: An Overview and Update

Wild-type p53-induced phosphatase 1 (Wip1) is a newly identified serine/threonine phosphatase, which belongs to the PP2C family. Due to its involvement in stress-induced networks and overexpression in human tumors, primary studies have mainly focused on the role of Wip1 in tumorigenesis. It now has also been implicated in regulating several other physiological processes such as organism aging and neurogenesis. Recent evidence highlights a new role of Wip1 in controlling immune response through regulating immune cell development and function, as well as through the interplay with inflammatory signaling pathways such NF-κB and p38 mitogen-activated protein kinase. In this short review, we will give an overview of Wip1 in immunity to better understand this important phosphatase.

WIP1 modulates responsiveness to Sonic Hedgehog signaling in neuronal precursor cells and medulloblastoma

High-level amplification of the protein phosphatase PPM1D (WIP1) is present in a subset of medulloblastomas (MBs) that have an expression profile consistent with active Sonic Hedgehog (SHH) signaling. We found that WIP1 overexpression increased expression of Shh target genes and cell proliferation in response to Shh stimulation in NIH3T3 and cerebellar granule neuron precursor cells in a p53-independent manner. Thus, we developed a mouse in which WIP1 is expressed in the developing brain under control of the Neurod2 promoter (ND2:WIP1). The external granule layer (EGL) in early postnatal ND2:WIP1 mice exhibited increased proliferation and expression of Shh downstream targets. MB incidence increased and survival decreased when ND2:WIP1 mice were crossed with an Shh-activated MB mouse model. Conversely, Wip1 knockout significantly suppressed MB formation in two independent mouse models of Shh-activated MB. Furthermore, Wip1 knockdown or treatment with a WIP1 inhibitor suppressed the effects of Shh stimulation and potentiated the growth inhibitory effects of SHH pathway-inhibiting drugs in Shh-activated MB cells in vitro. This suggests an important cross-talk between SHH and WIP1 pathways that accelerates tumorigenesis and supports WIP1 inhibition as a potential treatment strategy for MB.

Identification of PPM1D as an essential Ulk1 phosphatase for genotoxic stress-induced autophagy

Autophagy is an evolutionary conserved process that degrades subcellular constituents. Unlike starvation-induced autophagy, the molecular mechanism of genotoxic stress-induced autophagy has not yet been fully elucidated. In this study, we analyze the molecular mechanism of genotoxic stress-induced autophagy and identify an essential role of dephosphorylation of the Unc51-like kinase 1 (Ulk1) at Ser⁶³⁷, which is catalyzed by the protein phosphatase 1D magnesium-dependent delta isoform (PPM1D). We show that after exposure to genotoxic stress, PPM1D interacts with and dephosphorylates Ulk1 at Ser⁶³⁷ in a p53-dependent manner. The PPM1D-dependent Ulk1 dephosphorylation triggers Ulk1 puncta formation and induces autophagy. This happens not only in mouse embryonic fibroblasts but also in primary thymocytes, where the genetic ablation of PPM1D reduces the dephosphorylation of Ulk1 at Ser⁶³⁷, inhibits autophagy, and accelerates apoptosis induced by X-ray irradiation. This acceleration of apoptosis is caused mainly by the inability of the autophagic machinery to degrade the proapoptotic molecule Noxa. These findings indicate that the PPM1D-Ulk1 axis plays a pivotal role in genotoxic stress-induced autophagy.

Control of stress signaling in stem cells: crossroads of stem cells and cancer

Tumorigenesis is a relatively rare event in the human body considering the enormous number of cells composing our body and the frequent occurrence of genetic mutations in each cell. Nevertheless, the cells that happen to meet the minimum requirements can be transformed when stressed by a variety of oncogenic stimulations, then progress to form tumors. The vigorous competition between oncogenic signaling and tumor-suppressor defense is a critical determinant of cellular fate, which can be either tumorigenic transformation or cellular senescence/apoptosis depending on "who wins the battle." Recently, a number of cancers have been reported to originate from stem cells, whose self-renewing properties are normally reduced by innate tumor suppressors. Therefore, exploring the innate mechanism by which stem cells modulate tumor suppressors to maintain their "stemness" may provide valuable clues to characterize the distinctive oncogenic susceptibility of stem cells. This review is focused on the recent advances in the field of tumorigenesis of stem cells and on the associated molecular mechanisms.

Phosphatase Wip1 Masters IL-17-producing Neutrophil-mediated Colitis in Mice

Wild-type p53-induced phosphatase 1 (Wip1) is currently believed to be a promising drug target for cancer therapy. Our recent studies showed that deletion of Wip1 remarkably promoted neutrophil inflammatory response. Whether Wip1 is involved in the regulation of inflammatory bowel disease is unknown. In the present study, we found that Wip1 knockout (KO) mice were more susceptible to colitis induced by dextran sulphate sodium (DSS) than wild-type mice as substantiated by the lower mouse survival ratio, rapid bodyweight loss, increased disease activity index, shorter colon length, and more severe pathology of colons in Wip1KO mice. Using full bone marrow chimera mouse models, we demonstrated that Wip1 intrinsically controls inflammatory response of immune cells. Deletion of IL-17 (Wip1/IL-17 double KO mice) significantly rescued the pathology in Wip1KO mice. Neutrophils of DSS-treated wild-type and Wip1KO mice expressed significantly higher IL-17. After adoptive transfer of sorted Wip1KO or double KO neutrophils into IL-17KO mice, mice receiving double KO neutrophils were more resistant to DSS-induced colitis than mice receiving Wip1KO neutrophils. These data collectively indicate that Wip1 modulates host sensitivity to colitis by intrinsically regulating immune cells. The enhanced IL-17 expression in neutrophils contributed to the increased sensitivity and severity of colitis in Wip1KO mice. Thus, Wip1 may be used as a drug target to treat colitis.