PTPH1 dephosphorylates and cooperates with p38gamma MAPK to increase ras oncogenesis through PDZ-mediated interaction

Phosphorylation of cell cycle and apoptosis regulatory protein-1 by stress activated protein kinase P38γ is a novel mechanism of apoptosis signaling by genotoxic chemotherapy

CARP-1, a perinuclear phospho-protein, regulates cell survival and apoptosis signaling induced by genotoxic drugs. However, kinase(s) phosphorylating CARP-1 and down-stream signal transduction events remain unclear. Here we find that CARP-1 Serine (S)626 and Threonine (T)627 substitution to Alanines (AA) inhibits genotoxic drug-induced apoptosis. CARP-1 T627 is followed by a Proline (P), and this TP motif is conserved in vertebrates. Based on these findings, we generated affinity-purified, anti-phospho-CARP-1 T627 rabbit polyclonal antibodies, and utilized them to elucidate chemotherapy-activated, CARP-1-dependent cell growth signaling mechanisms. Our kinase profiling studies revealed that MAPKs/SAPKs phosphorylated CARP-1 T627. We then UV cross-linked protein extracts from Adriamycin-treated HeLa cervical cancer cells with a CARP-1 (614-638) peptide, and conducted liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses of the peptide-bound protein complexes. This experiment revealed SAPK p38γ interaction with CARP-1 (614-638) peptide. Our studies further established that SAPK p38γ, but not other MAPKs, phosphorylates CARP-1 T627 in cancer cells treated with genotoxic drugs. Loss of p38γ abrogates CARP-1 T627 phosphorylation, and results in enhanced survival of breast cancer cells by genotoxic drugs. CARP-1 T627 phosphorylation was also noted in breast tumors from patients treated with radiation or endocrine therapies. We conclude that genotoxic drugs activate p38γ-dependent CARP-1 T627 phosphorylation to inhibit cell growth.

G-quadruplex structural dynamics at MAPK12 promoter dictates transcriptional switch to determine stemness in breast cancer

P38γ (MAPK12) is predominantly expressed in triple negative breast cancer cells (TNBC) and induces stem cell (CSC) expansion resulting in decreased survival of the patients due to metastasis. Abundance of G-rich sequences at MAPK12 promoter implied the functional probability to reverse tumorigenesis, though the formation of G-Quadruplex (G4) structures at MAPK12 promoter is elusive. Here, we identified two evolutionary consensus adjacent G4 motifs upstream of the MAPK12 promoter, forming parallel G4 structures. They exist in an equilibria between G4 and duplex, regulated by the binding turnover of Sp1 and Nucleolin that bind to these G4 motifs and regulate MAPK12 transcriptional homeostasis. To underscore the gene-regulatory functions of G4 motifs, we employed CRISPR-Cas9 system to eliminate G4s from TNBC cells and synthesized a naphthalene diimide (NDI) derivative (TGS24) which shows high-affinity binding to MAPK12-G4 and inhibits MAPK12 transcription. Deletion of G4 motifs and NDI compound interfere with the recruitment of the transcription factors, inhibiting MAPK12 expression in cancer cells. The molecular basis of NDI-induced G4 transcriptional regulation was analysed by RNA-seq analyses, which revealed that MAPK12-G4 inhibits oncogenic RAS transformation and trans-activation of NANOG. MAPK12-G4 also reduces CD44High/CD24Low population in TNBC cells and downregulates internal stem cell markers, arresting the stemness properties of cancer cells.

The effects of HPV oncoproteins on host communication networks: Therapeutic connotations

Human papillomavirus (HPV) infections are a leading cause of viral-induced malignancies worldwide, with a prominent association with cervical and head and neck cancers. The pivotal role of HPV oncoproteins, E5, E6, and E7, in manipulating cellular events, which contribute to viral pathogenesis in various ways, has been extensively documented. This article reviews the influence of HPV oncoproteins on cellular signaling pathways within the host cell, shedding light on the underlying molecular mechanisms. A comprehensive understanding of these molecular alterations is essential for the development of targeted therapies and strategies to combat HPV-induced premalignancies and prevent their progress to cancer. Furthermore, this review underscores the intricate interplay between HPV oncoproteins and some of the most important cellular signaling pathways: Notch, Wnt/β-catenin, MAPK, JAK/STAT, and PI3K AKT/mTOR. The treatment efficacies of the currently available inhibitors on these pathways in an HPV-positive context are also discussed. This review also highlights the importance of continued research to advance our knowledge and enhance therapeutic interventions for HPV-associated diseases.

P38 kinase in gastrointestinal cancers

Gastrointestinal cancers are a leading cause of cancer morbidity and mortality worldwide with 4.2 million new cases and 3.2 million deaths estimated in 2020. Despite the advances in primary and adjuvant therapies, patients still develop distant metastases and require novel therapies. Mitogen‑activated protein kinase (MAPK) cascades are crucial signaling pathways that regulate many cellular processes, including proliferation, differentiation, apoptosis, stress responses and cancer development. p38 Mitogen Activated Protein Kinases (p38 MAPKs) includes four isoforms: p38α (MAPK14), p38β (MAPK11), p38γ (MAPK12), and p38δ (MAPK13). p38 MAPK was first identified as a stress response protein kinase that phosphorylates different transcriptional factors. Dysregulation of p38 pathways, in particular p38γ, are associated with cancer development, metastasis, autophagy and tumor microenvironment. In this article, we provide an overview of p38 and p38γ with respect to gastrointestinal cancers. Furthermore, targeting p38γ is also discussed as a potential therapy for gastrointestinal cancers.

p38γ MAPK Inflammatory and Metabolic Signaling in Physiology and Disease

p38γ MAPK (also called ERK6 or SAPK3) is a family member of stress-activated MAPKs and has common and specific roles as compared to other p38 proteins in signal transduction. Recent studies showed that, in addition to inflammation, p38γ metabolic signaling is involved in physiological exercise and in pathogenesis of cancer, diabetes, and Alzheimer's disease, indicating its potential as a therapeutic target. p38γphosphorylates at least 19 substrates through which p38γ activity is further modified to regulate life-important cellular processes such as proliferation, differentiation, cell death, and transformation, thereby impacting biological outcomes of p38γ-driven pathogenesis. P38γ signaling is characterized by its unique reciprocal regulation with its specific phosphatase PTPH1 and by its direct binding to promoter DNAs, leading to transcriptional activation of targets including cancer-like stem cell drivers. This paper will review recent findings about p38γ inflammation and metabolic signaling in physiology and diseases. Moreover, we will discuss the progress in the development of p38γ-specific pharmacological inhibitors for therapeutic intervention in disease prevention and treatment by targeting the p38γ signaling network.

Interactions of the protein tyrosine phosphatase PTPN3 with viral and cellular partners through its PDZ domain: insights into structural determinants and phosphatase activity

The human protein tyrosine phosphatase non-receptor type 3 (PTPN3) is a phosphatase containing a PDZ (PSD-95/Dlg/ZO-1) domain that has been found to play both tumor-suppressive and tumor-promoting roles in various cancers, despite limited knowledge of its cellular partners and signaling functions. Notably, the high-risk genital human papillomavirus (HPV) types 16 and 18 and the hepatitis B virus (HBV) target the PDZ domain of PTPN3 through PDZ-binding motifs (PBMs) in their E6 and HBc proteins respectively. This study focuses on the interactions between the PTPN3 PDZ domain (PTPN3-PDZ) and PBMs of viral and cellular protein partners. We solved the X-ray structures of complexes between PTPN3-PDZ and PBMs of E6 of HPV18 and the tumor necrosis factor-alpha converting enzyme (TACE). We provide new insights into key structural determinants of PBM recognition by PTPN3 by screening the selectivity of PTPN3-PDZ recognition of PBMs, and by comparing the PDZome binding profiles of PTPN3-recognized PBMs and the interactome of PTPN3-PDZ. The PDZ domain of PTPN3 was known to auto-inhibit the protein's phosphatase activity. We discovered that the linker connecting the PDZ and phosphatase domains is involved in this inhibition, and that the binding of PBMs does not impact this catalytic regulation. Overall, the study sheds light on the interactions and structural determinants of PTPN3 with its cellular and viral partners, as well as on the inhibitory role of its PDZ domain on its phosphatase activity.

Structural and biochemical analysis of the PTPN4 PDZ domain bound to the C-terminal tail of the human papillomavirus E6 oncoprotein

High-risk genotypes of human papillomaviruses (HPVs) are directly implicated in various abnormalities associated with cellular hyperproliferation, including cervical cancer. E6 is one of two oncoproteins encoded in the HPV genome, which recruits diverse PSD-95/Dlg/ZO-1 (PDZ) domain-containing human proteins through its C-terminal PDZ-binding motif (PBM) to be degraded by means of the proteasome pathway. Among the three PDZ domain-containing protein tyrosine phosphatases, protein tyrosine phosphatase non-receptor type 3 (PTPN3) and PTPN13 were identified to be recognized by HPV E6 in a PBM-dependent manner. However, whether HPV E6 associates with PTPN4, which also has a PDZ domain and functions as an apoptosis regulator, remains undetermined. Herein, we present structural and biochemical evidence demonstrating the direct interaction between the PBM of HPV16 E6 and the PDZ domain of human PTPN4 for the first time. X-ray crystallographic structure determination and binding measurements using isothermal titration calorimetry demonstrated that hydrophobic interactions in which Leu158 of HPV16 E6 plays a key role and a network of intermolecular hydrogen bonds sustain the complex formation between PTPN4 PDZ and the PBM of HPV16 E6. In addition, it was verified that the corresponding motifs from several other high-risk HPV genotypes, including HPV18, HPV31, HPV33, and HPV45, bind to PTPN4 PDZ with comparable affinities, suggesting that PTPN4 is a common target of various pathogenic HPV genotypes.

The Role of p38γ in Cancer: From review to outlook

p38γ is a member of the p38 Mitogen Activated Protein Kinases (p38 MAPKs). It contains four subtypes in mammalian cells encoded by different genes including p38α (MAPK14), p38β (MAPK11), p38γ (MAPK12), and p38δ (MAPK13). Recent studies revealed that p38γ may exhibit a crucial role in tumorigenesis and cancer aggressiveness. Despite the large number of published literatures, further researches are demanded to clarify its role in cancer development, the tissue-specific function and associated novel treatment strategies. In this article, we provide the latest view on the connection between p38γ and malignant tumors, highlighting the function of p38γ. The clinical value of p38γ is also discussed, helping the translation into the remarkable therapeutic strategy in tumor diseases.

Targeting the non-ATP-binding pocket of the MAP kinase p38γ mediates a novel mechanism of cytotoxicity in cutaneous T-cell lymphoma (CTCL)

We describe here for the first time a lipid‐binding‐domain (LBD) in p38γ mitogen‐activated protein kinase (MAPK) involved in the response of T cells to a newly identified inhibitor, CSH71. We describe how CSH71, which binds to both the LBD and the ATP‐binding pocket of p38γ, is selectively cytotoxic to CTCL Hut78 cells but spares normal healthy peripheral blood mononuclear (PBMC) cells, and propose possible molecular mechanisms for its action. p38γ is a key player in CTCL development, and we expect that the ability to regulate its expression by specifically targeting the lipid‐binding domain will have important clinical relevance. Our findings characterize novel mechanisms of gene regulation in T lymphoma cells and validate the use of computational screening techniques to identify inhibitors for therapeutic development.

Molecular basis of the interaction of the human tyrosine phosphatase PTPN3 with the hepatitis B virus core protein

Interactions between the hepatitis B virus core protein (HBc) and host cell proteins are poorly understood, although they may be essential for the propagation of the virus and its pathogenicity. HBc has a C-terminal PDZ (PSD-95, Dlg1, ZO-1)-binding motif (PBM) that is responsible for interactions with host PDZ domain-containing proteins. In this work, we focused on the human protein tyrosine phosphatase non-receptor type 3 (PTPN3) and its interaction with HBc. We solved the crystal structure of the PDZ domain of PTPN3 in complex with the PBM of HBc, revealing a network of interactions specific to class I PDZ domains despite the presence of a C-terminal cysteine in this atypical PBM. We further showed that PTPN3 binds the HBc protein within capsids or as a homodimer. We demonstrate that overexpression of PTPN3 significantly affects HBV infection in HepG2 NTCP cells. Finally, we performed proteomics studies on both sides by pull-down assays and screening of a human PDZ domain library. We identified a pool of human PBM-containing proteins that might interact with PTPN3 in cells and that could be in competition with the HBc PBM during infection, and we also identified potential cellular partners of HBc through PDZ-PBM interactions. This study opens up many avenues of future investigations into the pathophysiology of HBV.

p38γ Activation and BGP (Biliary Glycoprotein) Induction in Primates at Risk for Inflammatory Bowel Disease and Colorectal Cancer-A Comparative Study with Humans

Colorectal cancer (CRC) is a common cause of cancer-related deaths largely due to CRC liver metastasis (CRLM). Identification of targetable mechanisms continues and includes investigations into the role of inflammatory pathways. Of interest, MAPK is aberrantly expressed in CRC patients, yet the activation status is not defined. The present study assessed p38γ activation in CRC patients, cancer cells, and tissues of cotton top tamarin (CTT) and common marmoset (CM). The primate world is an overlooked resource as colitis-CRC-prone CTT are usually inure to liver metastasis while CM develop colitis but not CRC. The results demonstrate that p38γ protein and phosphorylation levels are significantly increased in CRC patients compared to normal subjects and CTT. Furthermore, p38γ phosphorylation is significantly elevated in human CRC cells and hepatoblastoma cells but not in CM colon. Additionally, carcinoembryonic antigen (CEA) and biliary glycoprotein (BGP) are induced in the CRC patients that showed p38γ phosphorylation. Inhibition of p38 MAPK in CRC cells showed a significant decline in cell growth with no effect on apoptosis or BGP level. Overall, p38γ is activated in CRC tumorigenesis and likely involves CEA antigens during CRLM in humans but not in the CTT or CM, that rarely develop CRLM.

p38γ MAPK Is Essential for Aerobic Glycolysis and Pancreatic Tumorigenesis

KRAS is mutated in most pancreatic ductal adenocarcinomas (PDAC) and yet remains undruggable. Here, we report that p38γ MAPK, which promotes PDAC tumorigenesis by linking KRAS signaling and aerobic glycolysis (also called the Warburg effect), is a novel therapeutic target. p38γ interacted with a glycolytic activator PFKFB3 that was dependent on mutated KRAS. KRAS transformation and overexpression of p38γ increased expression of PFKFB3 and glucose transporter GLUT2, conversely, silencing mutant KRAS, and p38γ decreased PFKFB3 and GLUT2 expression. p38γ phosphorylated PFKFB3 at S467, stabilized PFKFB3, and promoted their interaction with GLUT2. Pancreatic knockout of p38γ decreased p-PFKFB3/PFKFB3/GLUT2 protein levels, reduced aerobic glycolysis, and inhibited PDAC tumorigenesis in KPC mice. PFKFB3 and GLUT2 depended on p38γ to stimulate glycolysis and PDAC growth and p38γ required PFKFB3/S467 to promote these activities. A p38γ inhibitor cooperated with a PFKFB3 inhibitor to blunt aerobic glycolysis and PDAC growth, which was dependent on p38γ. Moreover, overexpression of p38γ, p-PFKFB3, PFKFB3, and GLUT2 in PDAC predicted poor clinical prognosis. These results indicate that p38γ links KRAS oncogene signaling and aerobic glycolysis to promote pancreatic tumorigenesis through PFKFB3 and GLUT2, and that p38γ and PFKFB3 may be targeted for therapeutic intervention in PDAC. SIGNIFICANCE: These findings show that p38γ links KRAS oncogene signaling and the Warburg effect through PFKBF3 and Glut2 to promote pancreatic tumorigenesis, which can be disrupted via inhibition of p38γ and PFKFB3.

Prognostic Significance of Metastatic Lymph Nodes Ratio (MLNR) Combined with Protein-Tyrosine Phosphatase H1 (PTPH1) Expression in Operable Breast Invasive Ductal Carcinoma

Purpose

The metastatic lymph node ratio (MLNR) is one of the most important factors in prognostic analysis of breast cancer. The objective of this study was to determine if MLNR combined with protein-tyrosine phosphatase H1 (PTPH1) pathological expression can be used to predict the prognosis of patients with breast invasive ductal carcinoma (IDC) better than one factor only.

Patients and Methods

A total of 136 patients with invasive ductal carcinoma (IDC) of breast who underwent modified radical mastectomy and were treated with chemotherapy after operation at Qilu Hospital of Shandong University from December 2008 to October 2011 were included. PTPH1 expression was evaluated by immunohistochemistry in surgical specimens retrospectively collected from patients with histologically proven invasive ductal breast cancer. Kaplan–Meier survival analysis and Cox regression analysis were performed to assess the prognostic significance of PTPH1 expression. A prognostic factor for disease-free survival (DFS) was identified by univariate and multivariate analyses. ROC analysis was used to evaluate the performance of single factors and combined feature.

Results

One hundred and thirty-six patients were included in the analysis. By cut-point survival analysis, MLNR cut-off was designed as 0.2. On multivariate analysis, a MLNR>0.2 was associated with a worse DFS (HR=2.581, 95% CI=1.303–5.113, P=0.007). PTPH1 overexpression is correlated with a better DFS (HR=0.391, 95% CI=0.162–0.945, P=0.037). In addition, MLNR and PTPH1 combined feature had better performance in predicting clinical outcomes after surgery long before recurrence had occurred (Area under the curve=0.795 [95% CI=0.694–0.896], P<0.001).

Conclusion

These findings indicate that both PTPH1 and MLNR are accurate independent prognostic parameters in patients with IDC of the breast. Better information on IDC prognosis could be obtained from the combined feature.

PTPN3 Inhibits the Growth and Metastasis of Clear Cell Renal Cell Carcinoma via Inhibition of PI3K/AKT Signaling

The underlying molecular mechanism driving clear cell renal cell carcinoma (ccRCC) progression is still to be explored. The significant downregulation of protein tyrosine phosphatase nonreceptor type 3 (PTPN3) expression in the tumor tissues suggested its protective role in ccRCC progression. IHC analysis of PTPN3 protein in 172 ccRCC tissue revealed that PTPN3 was an independently favorable prognostic factor for progression-free survival (P = 0.0166) and overall survival (P = 0.0343) of patients. The ccRCC cell lines SN12C, 1932, ACHN, and Caki-1 were used to evaluate, both in vitro and in vivo, the biological roles of PTPN3. We observed that overexpression of PTPN3 significantly inhibited the proliferation, migration, and invasion of ccRCC cells. In contrast, the knocking down of PTPN3 elicited opposite effects. Overexpressing PTPN3 inhibited xenograft tumor growth and lung metastasis displayed by the in vivo mice models. PTPN3 inhibited tumor cell motility by suppressing the phosphorylation of AKT, and subsequently inactivating the PI3K/AKT signaling pathway of renal cell carcinoma cells. Furthermore, the inhibition of phospho-AKT^Thr308 and phospho-AKT^Ser473 reversed PTPN3-induced silencing in tumor cell migration. Our work revealed that the overexpression of PTPN3 could suppress kidney cancer progression by negatively regulating the AKT signaling pathway, and served as a favorable prognostic factor in patients with ccRCC. Our findings provided insight that PTPN3 could be a potential target for therapy aiming to inhibit the malignant behaviors of ccRCC. IMPLICATIONS: PTPN3 is an independent favorable prognostic factor for patients with ccRCC and could be a potential target for therapy aiming to inhibit the malignant behaviors of ccRCC.

MicroRNA-574-5p in gastric cancer cells promotes angiogenesis by targeting protein tyrosine phosphatase non-receptor type 3 (PTPN3)

We elucidate in this study that up-regulation of miR-574-5p in gastric cancer cells under hypoxic conditions contributed to angiogenesis. We found that miR-574-5p and HIF-1α were up-regulated in gastric cancer cells cultured under 2% O₂ or in medium containing CoCl_2, and in muscle tissues of mice injected with NaNO₂, indicating up-regulation of miR-574-5p in vitro or in vivo in response to hypoxic conditions. We hypothesized that up-regulation of miR-574-5p could promote angiogenesis. Transfection of gastric cancer cells with miR-574-5p mimics or inhibitor resulted in increase or decrease in the expression of VEGFA. Viability, migration, invasion and tube formation of HUVECs cultured with conditioned medium from SGC/574 cells transfected with miR-574-5p inhibitor were reduced. Tube formation of HUVECs cultured with conditioned medium from SGC-7901 cells transfected with miR-574-5p mimics was increased. An in vivo study demonstrated that inhibition of miR-574-5p in the tumor xenografts of mice reduced the expression of CD31 one of the endothelial cell markers. We identified PTPN3 a tyrosine phosphatase as a target of miR-574-5p that bound to the 3'UTR of PTPN3 mRNA to inhibit the expression of PTPN3. Furthermore, the data in this study demonstrated that inhibition of PTPN3 in gastric cancer cells enhanced phosphorylation of p44/42 MAPKs and promoted angiogenesis. We conclude that miR-574-5p in gastric cancer cells promoted angiogenesis via enhancing phosphorylation of p44/42 MAPKs by miR-574-5p inhibition of PTPN3 expression.

p38γ MAPK contributes to left ventricular remodeling after pathologic stress and disinhibits calpain through phosphorylation of calpastatin

Despite the high and preferential expression of p38γ MAPK in the myocardium, little is known about its function in the heart. The aim of the current study was to elucidate the physiologic and biochemical roles of p38γ in the heart. Expression and subcellular localization of p38 isoforms was determined in mouse hearts. Comparisons of the cardiac function and structure of wild-type and p38γ knockout (KO) mice at baseline and after abdominal aortic banding demonstrated that KO mice developed less ventricular hypertrophy and that contractile function is better preserved. To identify potential substrates of p38γ, we generated an analog-sensitive mutant to affinity tag endogenous myocardial proteins. Among other proteins, this technique identified calpastatin as a direct p38γ substrate. Moreover, phosphorylation of calpastatin by p38γ impaired its ability to inhibit the protease, calpain. We have identified p38γ as an important determinant of the progression of pathologic cardiac hypertrophy after aortic banding in mice. In addition, we have identified calpastatin, among other substrates, as a novel direct target of p38γ that may contribute to the protection observed in p38γKO mice.-Loonat, A. A., Martin, E. D., Sarafraz-Shekary, N., Tilgner, K., Hertz, N. T., Levin, R., Shokat, K. M., Burlingame, A. L., Arabacilar, P., Uddin, S., Thomas, M., Marber, M. S., Clark, J. E. p38γ MAPK contributes to left ventricular remodeling after pathologic stress and disinhibits calpain through phosphorylation of calpastatin.

Protein tyrosine phosphatases: promising targets in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer. It is the fourth leading cause of cancer-related death and is associated with a very poor prognosis. KRAS driver mutations occur in approximately 95% of PDAC cases and cause the activation of several signaling pathways such as mitogen-activated protein kinase (MAPK) pathways. Regulation of these signaling pathways is orchestrated by feedback loops mediated by the balance between protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), leading to activation or inhibition of its downstream targets. The human PTPome comprises 125 members, and these proteins are classified into three distinct families according to their structure. Since PTP activity description, it has become clear that they have both inhibitory and stimulatory effects on cancer-associated signaling processes and that deregulation of PTP function is closely associated with tumorigenesis. Several PTPs have displayed either tumor suppressor or oncogenic characteristics during the development and progression of PDAC. In this sense, PTPs have been presented as promising candidates for the treatment of human pancreatic cancer, and many PTP inhibitors have been developed since these proteins were first associated with cancer. Nevertheless, some challenges persist regarding the development of effective and safe methods to target these molecules and deliver these drugs. In this review, we discuss the role of PTPs in tumorigenesis as tumor suppressor and oncogenic proteins. We have focused on the differential expression of these proteins in PDAC, as well as their clinical implications and possible targeting for pharmacological inhibition in cancer therapy.

Structural and functional characterization of the PDZ domain of the human phosphatase PTPN3 and its interaction with the human papillomavirus E6 oncoprotein

The human protein tyrosine phosphatase non-receptor type 3 (PTPN3) is a PDZ (PSD-95/Dlg/ZO-1) domain-containing phosphatase with a tumor-suppressive or a tumor-promoting role in many cancers. Interestingly, the high-risk genital human papillomavirus (HPV) types 16 and 18 target the PDZ domain of PTPN3. The presence of a PDZ binding motif (PBM) on E6 confers interaction with a number of different cellular PDZ domain-containing proteins and is a marker of high oncogenic potential. Here, we report the molecular basis of interaction between the PDZ domain of PTPN3 and the PBM of the HPV E6 protein. We combined biophysical, NMR and X-ray experiments to investigate the structural and functional properties of the PDZ domain of PTPN3. We showed that the C-terminal sequences from viral proteins encompassing a PBM interact with PTPN3-PDZ with similar affinities to the endogenous PTPN3 ligand MAP kinase p38γ. PBM binding stabilizes the PDZ domain of PTPN3. We solved the X-ray structure of the PDZ domain of PTPN3 in complex with the PBM of the HPV E6 protein. The crystal structure and the NMR chemical shift mapping of the PTPN3-PDZ/peptide complex allowed us to pinpoint the main structural determinants of recognition of the C-terminal sequence of the E6 protein and the long-range perturbations induced upon PBM binding.

The Protein Tyrosine Phosphatase H1 PTPH1 Supports Proliferation of Keratinocytes and is a Target of the Human Papillomavirus Type 8 E6 Oncogene

Human papillomaviruses (HPV) replicate their DNA in the suprabasal layer of the infected mucosa or skin. In order to create a suitable environment for vegetative viral DNA replication HPV delay differentiation and sustain keratinocyte proliferation that can lead to hyperplasia. The mechanism underlying cell growth stimulation is not well characterized. Here, we show that the E6 oncoprotein of the βHPV type 8 (HPV8), which infects the cutaneous skin and is associated with skin cancer in Epidermodysplasia verruciformis patients and immunosuppressed organ transplant recipients, binds to the protein tyrosine phosphatase H1 (PTPH1), which resulted in increased protein expression and phosphatase activity of PTPH1. Suppression of PTPH1 in immortalized keratinocytes reduced cell proliferation as well as the level of epidermal growth factor receptor (EGFR). Furthermore, we report that HPV8E6 expressing keratinocytes have increased level of active, GTP-bound Ras. This effect was independent of PTPH1. Therefore, HPV8E6-mediated targeting of PTPH1 might result in higher level of EGFR and enhanced keratinocyte proliferation. The HPV8E6-mediated stimulation of Ras may be an additional step to induce cell growth. Our results provide novel insights into the mechanism how βHPVE6 proteins support proliferation of infected keratinocytes, thus creating an environment with increased risk of development of skin cancer particularly upon UV-induced DNA mutations.

High Expression of PTPN3 Predicts Progression and Unfavorable Prognosis of Glioblastoma

Background

PTPN3 was demonstrated to be involved in the progression of several types of cancers, such as gastric adenocarcinoma, lung cancer, and intrahepatic cholangiocarcinoma. However, its clinical significance in glioblastoma (GBM) has not been elucidated.

Material/Methods

We investigated the expression of PTPN3 in 95 cases of GBM with immunohistochemistry and in 8 pairs of fresh GBMs and their adjacent tissues with qualitative polymerase chain reaction. Moreover, the correlation between PTPN3 and clinicopathological factors was evaluated by chi-square test. The prognostic value of PTPN3 was investigated with univariate analysis and multivariate analysis. With MTT assay and Transwell assay, the oncogenic functions of PTPN3 in GBM proliferation and invasion were further investigated.

Results

Expression of PTPN3 in GBM tissues was significantly higher than in their corresponding adjacent tissues. High expression of PTPN3 was significantly associated with unfavorable prognosis of GBM. Moreover, in GBM cell lines, PTPN3 promoted cell proliferation and invasion, and the PTP common inhibitor pervanadate suppressed GBM proliferation and invasion.

Conclusions

Our experiments show that PTPN3 is an independent prognostic factor in GBM and indicated that postoperative detection of PTPN3 can be used to identify high-risk patients and guide individual treatment.

Targeting an oncogenic kinase/phosphatase signaling network for cancer therapy

Protein kinases and phosphatases signal by phosphorylation and dephosphorylation to precisely control the activities of their individual and common substrates for a coordinated cellular outcome. In many situations, a kinase/phosphatase complex signals dynamically in time and space through their reciprocal regulations and their cooperative actions on a substrate. This complex may be essential for malignant transformation and progression and can therefore be considered as a target for therapeutic intervention. p38γ is a unique MAPK family member that contains a PDZ motif at its C-terminus and interacts with a PDZ domain-containing protein tyrosine phosphatase PTPH1. This PDZ-coupled binding is required for both PTPH1 dephosphorylation and inactivation of p38γ and for p38γ phosphorylation and activation of PTPH1. Moreover, the p38γ/PTPH1 complex can further regulate their substrates phosphorylation and dephosphorylation, which impacts Ras transformation, malignant growth and progression, and therapeutic response. This review will use the p38γ/PTPH1 signaling network as an example to discuss the potential of targeting the kinase/phosphatase signaling complex for development of novel targeted cancer therapy.

NOTCH3 inactivation increases triple negative breast cancer sensitivity to gefitinib by promoting EGFR tyrosine dephosphorylation and its intracellular arrest

Notch dysregulation has been implicated in numerous tumors, including triple-negative breast cancer (TNBC), which is the breast cancer subtype with the worst clinical outcome. However, the importance of individual receptors in TNBC and their specific mechanism of action remain to be elucidated, even if recent findings suggested a specific role of activated-Notch3 in a subset of TNBCs. Epidermal growth factor receptor (EGFR) is overexpressed in TNBCs but the use of anti-EGFR agents (including tyrosine kinase inhibitors, TKIs) has not been approved for the treatment of these patients, as clinical trials have shown disappointing results. Resistance to EGFR blockers is commonly reported. Here we show that Notch3-specific inhibition increases TNBC sensitivity to the TKI-gefitinib in TNBC-resistant cells. Mechanistically, we demonstrate that Notch3 is able to regulate the activated EGFR membrane localization into lipid rafts microdomains, as Notch3 inhibition, such as rafts depletion, induces the EGFR internalization and its intracellular arrest, without involving receptor degradation. Interestingly, these events are associated with the EGFR tyrosine dephosphorylation at Y1173 residue (but not at Y1068) by the protein tyrosine phosphatase H1 (PTPH1), thus suggesting its possible involvement in the observed Notch3-dependent TNBC sensitivity response to gefitinib. Consistent with this notion, a nuclear localization defect of phospho-EGFR is observed after combined blockade of EGFR and Notch3, which results in a decreased TNBC cell survival. Notably, we observed a significant correlation between EGFR and NOTCH3 expression levels by in silico gene expression and immunohistochemical analysis of human TNBC primary samples. Our findings strongly suggest that combined therapies of TKI-gefitinib with Notch3-specific suppression may be exploited as a drug combination advantage in TNBC treatment.

The vitamin D receptor is involved in the regulation of human breast cancer cell growth via a ligand-independent function in cytoplasm

Vitamin D has pleiotropic effects on multiple tissues, including malignant tumors. Vitamin D inhibits breast cancer growth through activation of the vitamin D receptor (VDR) and via classical nuclear signaling pathways. Here, we demonstrate that the VDR can also function in the absence of its ligand to control behaviour of human breast cancer cells both outside and within the bone microenvironment. Stable shRNA expression was used to knock down VDR expression in MCF-7 cells, generating two VDR knockdown clonal lines. In ligand-free culture, knockdown of VDR in MCF-7 cells significantly reduced proliferation and increased apoptosis, suggesting that the VDR plays a ligand-independent role in cancer cell growth. Implantation of these VDR knockdown cells into the mammary fat pad of nude mice resulted in reduced tumor growth in vivo compared with controls. In the intra-tibial xenograft model, VDR knockdown greatly reduced the ability of the cells to form tumors in the bone microenvironment. The in vitro growth of VDR knockdown cells was rescued by the expression of a mutant form of VDR which is unable to translocate to the nucleus and hence accumulates in the cytoplasm. Thus, our data indicate that in the absence of ligand, the VDR promotes breast cancer growth both in vitro and in vivo and that cytoplasmic accumulation of VDR is sufficient to produce this effect in vitro. This new mechanism of VDR action in breast cancer cells contrasts the known anti-proliferative nuclear actions of the VDR-vitamin D ligand complex.

Tumor suppressive protein phosphatases in human cancer: Emerging targets for therapeutic intervention and tumor stratification

Aberrant protein phosphorylation is one of the hallmarks of cancer cells, and in many cases a prerequisite to sustain tumor development and progression. Like protein kinases, protein phosphatases are key regulators of cell signaling. However, their contribution to aberrant signaling in cancer cells is overall less well appreciated, and therefore, their clinical potential remains largely unexploited. In this review, we provide an overview of tumor suppressive protein phosphatases in human cancer. Along their mechanisms of inactivation in defined cancer contexts, we give an overview of their functional roles in diverse signaling pathways that contribute to their tumor suppressive abilities. Finally, we discuss their emerging roles as predictive or prognostic markers, their potential as synthetic lethality targets, and the current feasibility of their reactivation with pharmacologic compounds as promising new cancer therapies. We conclude that their inclusion in clinical practice has obvious potential to significantly improve therapeutic outcome in various ways, and should now definitely be pushed forward.

Stepping out of the shadows: Oncogenic and tumor-promoting protein tyrosine phosphatases

Protein tyrosine phosphorylation is critical for proper function of cells and organisms. Phosphorylation is regulated by the concerted but generically opposing activities of tyrosine kinases (PTKs) and tyrosine phosphatases (PTPs), which ensure its proper regulation, reversibility, and ability to respond to changing physiological situations. Historically, PTKs have been associated mainly with oncogenic and pro-tumorigenic activities, leading to the generalization that protein dephosphorylation is anti-oncogenic and hence that PTPs are tumor-suppressors. In many cases PTPs do suppress tumorigenesis. However, a growing body of evidence indicates that PTPs act as dominant oncogenes and drive cell transformation in a number of contexts, while in others PTPs support transformation that is driven by other oncogenes. This review summarizes the known transforming and tumor-promoting activities of the classical, tyrosine specific PTPs and highlights their potential as drug targets for cancer therapy.

The K-Ras effector p38γ MAPK confers intrinsic resistance to tyrosine kinase inhibitors by stimulating EGFR transcription and EGFR dephosphorylation

Mutations in K-Ras and epidermal growth factor receptor (EGFR) are mutually exclusive, but it is not known how K-Ras activation inactivates EGFR, leading to resistance of cancer cells to anti-EGFR therapy. Here, we report that the K-Ras effector p38γ MAPK confers intrinsic resistance to small molecular tyrosine kinase inhibitors (TKIs) by concurrently stimulating EGFR gene transcription and protein dephosphorylation. We found that p38γ increases EGFR transcription by c-Jun-mediated promoter binding and stimulates EGFR dephosphorylation via activation of protein-tyrosine phosphatase H1 (PTPH1). Silencing the p38γ/c-Jun/PTPH1 signaling network increased sensitivities to TKIs in K-Ras mutant cells in which EGFR knockdown inhibited growth. Similar results were obtained with the p38γ-specific pharmacological inhibitor pirfenidone. These results indicate that in K-Ras mutant cancers, EGFR activity is regulated by the p38γ/c-Jun/PTPH1 signaling network, whose disruption may be a novel strategy to restore the sensitivity to TKIs.

Protein tyrosine phosphatase PTPN3 promotes drug resistance and stem cell-like characteristics in ovarian cancer

The current standard treatment for ovarian cancer is aggressive surgery followed by platinum-based combination chemotherapy. Recurrence and chemotherapeutic drug resistance are the two main factors that account for the high mortality of most ovarian cancers. Liposomal doxorubicin is primarily used for the treatment of ovarian cancer when the disease has progressed after platinum-based chemotherapy. However, relatively little is known about the genomic changes that contribute to both cisplatin and doxorubicin resistance in high-grade serous ovarian cancer (HGSC) under the selective pressure of chemotherapy. Here, we found that protein tyrosine phosphatase PTPN3 gene expression was substantially increased in both cisplatin and doxorubicin-resistant ovarian cancer cells. Silencing of PTPN3 restored sensitivity to cisplatin and doxorubicin in resistant ovarian cancer cells. Down-regulation of PTPN3 also inhibited cell cycle progression, migration, stemness in vitro and the tumorigenicity of resistant ovarian cancer cells in vivo. Meanwhile, the expression of PTPN3 was found to be regulated by miR-199 in resistant ovarian cancer cells. These findings suggest that PTPN3 promotes tumorigenicity, stemness and drug resistance in ovarian cancer, and thus is a potential therapeutic target for the treatment of ovarian cancer.

Cell Signaling and Stress Responses

Stress-signaling pathways are evolutionarily conserved and play an important role in the maintenance of homeostasis. These pathways are also critical for adaptation to new cellular environments. The endoplasmic reticulum (ER) unfolded protein response (UPR) is activated by biosynthetic stress and leads to a compensatory increase in ER function. The JNK and p38 MAPK signaling pathways control adaptive responses to intracellular and extracellular stresses, including environmental changes such as UV light, heat, and hyperosmotic conditions, and exposure to inflammatory cytokines. Metabolic stress caused by a high-fat diet represents an example of a stimulus that coordinately activates both the UPR and JNK/p38 signaling pathways. Chronic activation of these stress-response pathways ultimately causes metabolic changes associated with obesity and altered insulin sensitivity. Stress-signaling pathways, therefore, represent potential targets for therapeutic intervention in the metabolic stress response and other disease processes.

Molecular Basis of the Interaction of the Human Protein Tyrosine Phosphatase Non-receptor Type 4 (PTPN4) with the Mitogen-activated Protein Kinase p38γ

The human protein tyrosine phosphatase non-receptor type 4 (PTPN4) prevents cell death induction in neuroblastoma and glioblastoma cell lines in a PDZ·PDZ binding motifs-dependent manner, but the cellular partners of PTPN4 involved in cell protection are unknown. Here, we described the mitogen-activated protein kinase p38γ as a cellular partner of PTPN4. The main contribution to the p38γ·PTPN4 complex formation is the tight interaction between the C terminus of p38γ and the PDZ domain of PTPN4. We solved the crystal structure of the PDZ domain of PTPN4 bound to the p38γ C terminus. We identified the molecular basis of recognition of the C-terminal sequence of p38γ that displays the highest affinity among all endogenous partners of PTPN4. We showed that the p38γ C terminus is also an efficient inducer of cell death after its intracellular delivery. In addition to recruiting the kinase, the binding of the C-terminal sequence of p38γ to PTPN4 abolishes the catalytic autoinhibition of PTPN4 and thus activates the phosphatase, which can efficiently dephosphorylate the activation loop of p38γ. We presume that the p38γ·PTPN4 interaction promotes cellular signaling, preventing cell death induction.

p38γ and p38δ Mitogen Activated Protein Kinases (MAPKs), New Stars in the MAPK Galaxy

The protein kinases p38γ and p38δ belong to the p38 mitogen-activated protein kinase (MAPK) family. p38MAPK signaling controls many cellular processes and is one of the most conserved mechanisms in eukaryotes for the cellular response to environmental stress and inflammation. Although p38γ and p38δ are widely expressed, it is likely that they perform specific functions in different tissues. Their involvement in human pathologies such as inflammation-related diseases or cancer is starting to be uncovered. In this article we give a general overview and highlight recent advances made in defining the functions of p38γ and p38δ, focusing in innate immunity and inflammation. We consider the potential of the pharmacological targeting of MAPK pathways to treat autoimmune and inflammatory diseases and cancer.

Tyrosine dephosphorylation enhances the therapeutic target activity of epidermal growth factor receptor (EGFR) by disrupting its interaction with estrogen receptor (ER)

Protein-protein interactions can increase or decrease its therapeutic target activity and the determining factors involved, however, are largely unknown. Here, we report that tyrosine-dephosphorylation of epidermal growth factor receptor (EGFR) increases its therapeutic target activity by disrupting its interaction with estrogen receptor (ER). Protein tyrosine phosphatase H1 (PTPH1) dephosphorylates the tyrosine kinase EGFR, disrupts its interaction with the nuclear receptor ER, and increases breast cancer sensitivity to small molecule tyrosine kinase inhibitors (TKIs). These effects require PTPH1 catalytic activity and its interaction with EGFR, suggesting that the phosphatase may increase the sensitivity by dephosphorylating EGFR leading to its dissociation with ER. Consistent with this notion, a nuclear-localization defective ER has a higher EGFR-binding activity and confers the resistance to TKI-induced growth inhibition. Additional analysis show that PTPH1 stabilizes EGFR, stimulates the membranous EGFR accumulation, and enhances the growth-inhibitory activity of a combination therapy of TKIs with an anti-estrogen. Since EGFR and ER both are substrates for PTPH1 in vitro and in intact cells, these results indicate that an inhibitory EGFR-ER protein complex can be switched off through a competitive enzyme-substrate binding. Our results would have important implications for the treatment of breast cancer with targeted therapeutics.

Genetic profiling of intrahepatic cholangiocarcinoma and its clinical implication in targeted therapy

Intrahepatic cholangiocarcinoma (iCCA) is a treatment-refractory primary liver cancer with an increasing incidence and mortality worldwide in recent years. Lack of a stereotyped genetic signature and limited understanding of genomic landscape make the development of effective targeted therapies challenging. Recent application of advanced technologies such as next-generation sequencing (NGS) has broadened our understanding of genetic heterogeneity in iCCA and many potentially actionable genetic alterations have been identified. This review explores the recent advances in defining genetic alterations in iCCAs, which may present potent therapeutic targets. Chromatin remodeling genes and genes encoding isocitrate dehydrogenase and tyrosine kinase receptors as well as their downstream effectors are among the most frequently altered genes. Clinical trials testing the effect of new targeted agents on iCCA patients, especially those with the above genetic markers are under way. However, the complex interplay of environmental and evolutionary factors contributing to the genetic variability in iCCA calls for a more cautionary use of NGS in tailoring targeted regimen to the patients. Next-generation functional testing may complement NGS to execute precision medicine in future.

p38γ MAPK Is a Therapeutic Target for Triple-Negative Breast Cancer by Stimulation of Cancer Stem-Like Cell Expansion

Triple-negative breast cancer (TNBC) is highly progressive and lacks established therapeutic targets. p38γ mitogen-activated protein kinase (MAPK) (gene name: MAPK12) is overexpressed in TNBC but how overexpressed p38γ contributes to TNBC remains unknown. Here, we show that p38γ activation promotes TNBC development and progression by stimulating cancer stem-like cell (CSC) expansion and may serve as a novel therapeutic target. p38γ silencing in TNBC cells reduces mammosphere formation and decreases expression levels of CSC drivers including Nanog, Oct3/4, and Sox2. Moreover, p38γ MAPK-forced expression alone is sufficient to stimulate CSC expansion and to induce epithelial cell transformation in vitro and in vivo. Furthermore, p38γ depends on its activity to stimulate CSC expansion and breast cancer progression, indicating a therapeutic opportunity by application of its pharmacological inhibitor. Indeed, the non-toxic p38γ specific pharmacological inhibitor pirfenidone selectively inhibits TNBC growth in vitro and/or in vivo and significantly decreases the CSC population. Mechanistically, p38γ stimulates Nanog transcription through c-Jun/AP-1 via a multi-protein complex formation. These results together demonstrate that p38γ can drive TNBC development and progression and may be a novel therapeutic target for TNBC by stimulating CSC expansion. Inhibiting p38γ activity with pirfenidone may be a novel strategy for the treatment of TNBC.

p38γ MAPK is required for inflammation-associated colon tumorigenesis

Chronic inflammation has long been considered to causatively link to colon cancer development. However, signal transduction pathways involved remain largely unidentified. Here, we report that p38γ mitogen-activated protein kinase mediates inflammatory signaling to promote colon tumorigenesis. Inflammation activates p38γ in mouse colon tissues and intestinal epithelial cell-specific p38γ knockout (KO) attenuates colitis and inhibits pro-inflammatory cytokine expression. Significantly, p38γ KO inhibits tumorigenesis in a colitis-associated mouse model. The specific p38γ pharmacological inhibitor pirfenidone also suppresses pro-inflammatory cytokine expression and colon tumorigenesis. The tumor-promoting activity of epithelial p38γ was further demonstrated by xenograft studies. In addition, p38γ is required for β-catenin/Wnt activities and p38γ stimulates Wnt transcription by phosphorylating β-catenin at Ser605. These results show that p38γ activation links inflammation and colon tumorigenesis. Targeting p38γ may be a novel strategy for colon cancer prevention and treatment.

Identification of a ternary protein-complex as a therapeutic target for K-Ras-dependent colon cancer

A cancer phenotype is driven by several proteins and targeting a cluster of functionally interdependent molecules should be more effective for therapeutic intervention. This is specifically important for Ras-dependent cancer, as mutated (MT) Ras is non-druggable and targeting its interaction with effectors may be essential for therapeutic intervention. Here, we report that a protein-complex activated by the Ras effector p38γ MAPK is a novel therapeutic target for K-Ras-dependent colon cancer. Unbiased proteomic screening and immune-precipitation analyses identified p38γ interaction with heat shock protein 90 (Hsp90) and K-Ras in K-Ras MT, but not wild-type (WT), colon cancer cells, indicating a role of this complex in Ras-dependent growth. Further experiments showed that this complex requires p38γ and Hsp90 activity to maintain MT, but not WT, K-Ras protein expression. Additional studies demonstrated that this complex is activated by p38γ-induced Hsp90 phosphorylation at S595, which is important for MT K-Ras stability and for K-Ras dependent growth. Of most important, pharmacologically inhibition of Hsp90 or p38γ activity disrupts the complex, decreases K-Ras expression, and selectively inhibits the growth of K-Ras MT colon cancer in vitro and in vivo. These results demonstrated that the p38γ-activated ternary complex is a novel therapeutic target for K-Ras-dependent colon cancer.

Strategies to interfere with PDZ-mediated interactions in neurons: What we can learn from the rabies virus

PDZ (PSD-95/Dlg/ZO-1) domains play a major role in neuronal homeostasis in which they act as scaffold domains regulating cellular trafficking, self-association and catalytic activity of essential proteins such as kinases and phosphatases. Because of their central role in cell signaling, cellular PDZ-containing proteins are preferential targets of viruses to hijack cellular function to their advantage. Here, we describe how the viral G protein of the rabies virus specifically targets the PDZ domain of neuronal enzymes during viral infection. By disrupting the complexes formed by cellular enzymes and their ligands, the virus triggers drastic effect on cell signaling and commitment of the cell to either survival (virulent strains) or death (vaccinal strains). We provide structural and biological evidences that the viral proteins act as competitors endowed with specificity and affinity in an essential cellular process by mimicking PDZ binding motif of cellular partners. Disruption of critical endogenous protein-protein interactions by viral protein drastically alters intracellular protein trafficking and catalytic activity of cellular proteins that control cell homeostasis. This work opens up many perspectives to mimic viral sequences and developing innovative therapies to manipulate cellular homeostasis.

Reciprocal allosteric regulation of p38γ and PTPN3 involves a PDZ domain-modulated complex formation

The mitogen-activated protein kinase p38γ (also known as MAPK12) and its specific phosphatase PTPN3 (also known as PTPH1) cooperate to promote Ras-induced oncogenesis. We determined the architecture of the PTPN3-p38γ complex by a hybrid method combining x-ray crystallography, small-angle x-ray scattering, and chemical cross-linking coupled to mass spectrometry. A unique feature of the glutamic acid-containing loop (E-loop) of the phosphatase domain defined the substrate specificity of PTPN3 toward fully activated p38γ. The solution structure revealed the formation of an active-state complex between p38γ and the phosphatase domain of PTPN3. The PDZ domain of PTPN3 stabilized the active-state complex through an interaction with the PDZ-binding motif of p38γ. This interaction alleviated autoinhibition of PTPN3, enabling efficient tyrosine dephosphorylation of p38γ. Our findings may enable structure-based drug design targeting the PTPN3-p38γ interaction as an anticancer therapeutic.

Regulation of the catalytic activity of the human phosphatase PTPN4 by its PDZ domain

The human protein tyrosine phosphatase non-receptor type 4 (PTPN4) prevents cells death. Targeting its PDZ domain abrogates this protection and triggers apoptosis. We demonstrate here that the PDZ domain inhibits the phosphatase activity of PTPN4. The mere binding of a PDZ ligand is sufficient to release the catalytic inhibition. We combined analytical ultracentrifugation, small angle X-ray scattering and NMR to understand how the PDZ domain controls PTPN4 activity. We show that the physiologically active PTPN4 two-domain, encompassing the PDZ and the phosphatase domains, adopts a predominant compact conformation in solution. The PDZ ligand binding restores the catalytic competence of PTPN4 disrupting the transient interdomain communication. This study strengthens the emerging notion that PDZ domains can act as regulators of enzyme activity and therefore are active players in the dynamic regulation of signaling pathways.

Anti-proliferation effects of interferon-gamma on gastric cancer cells

IFN-γ plays an indirect anti-cancer role through the immune system but may have direct negative effects on cancer cells. It regulates the viability of gastric cancer cells, so we examined whether it affects their proliferation and how that might be brought about. We exposed AGS, HGC-27 and GES-1 gastric cancer cell lines to IFN-γ and found significantly reduced colony formation ability. Flow cytometry revealed no effect of IFN-γ on apoptosis of cell lines and no effect on cell aging as assessed by β-gal staining. Microarray assay revealed that IFN-γ changed the mRNA expression of genes related to the cell cycle and cell proliferation and migration, as well as chemokines and chemokine receptors, and immunity-related genes. Finally, flow cytometry revealed that IFN-γ arrested the cells in the G1/S phase. IFN-γ may slow proliferation of some gastric cancer cells by affecting the cell cycle to play a negative role in the development of gastric cancer.

Activating mutations in PTPN3 promote cholangiocarcinoma cell proliferation and migration and are associated with tumor recurrence in patients

BACKGROUND & AIMS

The pathogenesis of intrahepatic cholangiocarcinoma (ICC), the second most common hepatic cancer, is poorly understood, and the incidence of ICC is increasing worldwide. We searched for mutations in human ICC tumor samples and investigated how they affect ICC cell function.

METHODS

We performed whole exome sequencing of 7 pairs of ICC tumors and their surrounding nontumor tissues to detect somatic alterations. We then screened 124 pairs of ICC and nontumor samples for these mutations, including 7 exomes. We compared mutations in PTPN3 with tumor recurrence in 124 patients and PTPN3 expression levels with recurrence in 322 patients (the combination of both in 86 patients). The functional effects of PTPN3 variations were determined by RNA interference and transgenic expression in cholangiocarcinoma cell lines (RBE, HCCC-9810, and Huh28).

RESULTS

Based on exome sequencing, pathways that regulate protein phosphorylation were among the most frequently altered in ICC samples and genes encoding protein tyrosine phosphatases (PTPs) were among the most frequently mutated. We identified mutations in 9 genes encoding PTPs in 4 of 7 ICC exomes. In the prevalence screen of 124 paired samples, 51.6% of ICCs contained somatic mutations in at least 1 of 9 PTP genes; 41.1% had mutations in PTPN3. Transgenic expression of PTPN3 in cell lines increased cell proliferation, colony formation, and migration. PTPN3(L232R) and PTPN3(L384H), which were frequently detected in ICC samples, were found to be gain-of-function mutations; their expression in cell lines further increased cell proliferation, colony formation, and migration. ICC-associated variants of PTPN3 altered phosphatase activity. Patients whose tumors contained activating mutations or higher levels of PTPN3 protein than nontumor tissues had higher rates of disease recurrence than patients whose tumors did not have these characteristics.

CONCLUSIONS

Using whole exome sequencing of ICC samples from patients, we found that more than 40% contain somatic mutations in PTPN3. Activating mutations in and high expression levels of PTPN3 were associated with tumor recurrence.

The regulatory roles of phosphatases in cancer

The relevance of potentially reversible post-translational modifications required for controlling cellular processes in cancer is one of the most thriving arenas of cellular and molecular biology. Any alteration in the balanced equilibrium between kinases and phosphatases may result in development and progression of various diseases, including different types of cancer, though phosphatases are relatively under-studied. Loss of phosphatases such as PTEN (phosphatase and tensin homologue deleted on chromosome 10), a known tumour suppressor, across tumour types lends credence to the development of phosphatidylinositol 3-kinase inhibitors alongside the use of phosphatase expression as a biomarker, though phase 3 trial data are lacking. In this review, we give an updated report on phosphatase dysregulation linked to organ-specific malignancies.

p38γ overexpression in gliomas and its role in proliferation and apoptosis

The objective of this study was to confirm the biological role of p38γ in human gliomas. The expression profiles of p38γ and hTERT in human glioma samples were detected by Western Blot and immunohistochemistry. RNA interference was performed in U251 cells by p38γ silencing. Cell proliferation and apoptosis were assayed by CCK-8 and flow cytometric analysis, and then RNA and protein expression levels were measured by real-time RT-PCR and Western Blot, respectively. Telomerase activity assays and Caspase-3,-9 activation assays were also conducted. The results showed p38γ had a positive correlation with the glioma's malignancy grade and that the treatment of U251 cells with p38γ-siRNA inhibited proliferation and induced apoptosis. Correspondingly, hTERT expression and telomerase activity were down regulated and Caspase-3 and -9 activities were elevated. In conclusion, p38γ may serve as an oncogenic factor promoting the growth and progression of gliomas and may become a useful therapeutic target.

Protein tyrosine phosphatases as novel targets in breast cancer therapy

Breast cancer is linked to hyperactivation of protein tyrosine kinases (PTKs), and recent studies have unveiled that selective tyrosine dephosphorylation by protein tyrosine phosphatases (PTPs) of specific substrates, including PTKs, may activate or inactivate oncogenic pathways in human breast cancer cell growth-related processes. Here, we review the current knowledge on the involvement of PTPs in breast cancer, as major regulators of breast cancer therapy-targeted PTKs, such as HER1/EGFR, HER2/Neu, and Src. The functional interplay between PTKs and PTK-activating or -inactivating PTPs, and its implications in novel breast cancer therapies based on targeting of specific PTPs, are discussed.