Serine/Threonine Protein Phosphatase-5 Accelerates Cell Growth and Migration in Human Glioma

Impact of Co-chaperones and Posttranslational Modifications Toward Hsp90 Drug Sensitivity

Posttranslational modifications (PTMs) regulate myriad cellular processes by modulating protein function and protein-protein interaction. Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone whose activity is responsible for the stabilization and maturation of more than 300 client proteins. Hsp90 is a substrate for numerous PTMs, which have diverse effects on Hsp90 function. Interestingly, many Hsp90 clients are enzymes that catalyze PTM, demonstrating one of the several modes of regulation of Hsp90 activity. Approximately 25 co-chaperone regulatory proteins of Hsp90 impact structural rearrangements, ATP hydrolysis, and client interaction, representing a second layer of influence on Hsp90 activity. A growing body of literature has also established that PTM of these co-chaperones fine-tune their activity toward Hsp90; however, many of the identified PTMs remain uncharacterized. Given the critical role of Hsp90 in supporting signaling in cancer, clinical evaluation of Hsp90 inhibitors is an area of great interest. Interestingly, differential PTM and co-chaperone interaction have been shown to impact Hsp90 binding to its inhibitors. Therefore, understanding these layers of Hsp90 regulation will provide a more complete understanding of the chaperone code, facilitating the development of new biomarkers and combination therapies.

MiR-520a-5p/PPP5C regulation pattern is identified as the key to gemcitabine resistance in pancreatic cancer

Objective

To explore the effects of the expression level of miR-520-5p/PPP5C in pancreatic cancer cells and exosomes on cell viability, angiogenesis, autophagy, which involved in the mechanism of gemcitabine resistance in pancreatic cancer.

Methods

APSC-1 cell line was treated with gemcitabine, after which its exosomes were extracted for NTA assay. Subsequently, the drug resistance of APSC-1 cells was assayed using CCK8, as well as the activity of HUVEC cells treated with exosomes from each group of APSC-1 cells after drug resistance treatment as well as overexpression treatment. Five groups of HUVEC cells treated with exosomes were subjected to in vitro tubule formation assay. levels of PPP5C in each group of ASPC-1 cells and their exosomes, levels of overexpressed PPP5C, and related exosomal proteins were examined by WB. mRNA expression levels of PPP5C and levels of miR-520a were examined by qPCR The relationship between miR-520a-5p and PPP5C was investigated. After that, the autophagy of PPP5C was detected. Finally, it was analyzed by TCGA database for survival prognosis analysis.

Results

APSC-1 cells had an IC50 value of 227.1 μM for gemcitabine, elevated PPP5C expression, drug resistance, and enhanced HUVEC cell activity; exosomes CD9, CD63, and CD81 were significantly expressed in all groups; meanwhile, enhanced PPP5C expression not only promoted in vitro tubule formation but also increased autophagy levels; meanwhile, its relationship with miR-520-5p and There was a targeted inhibitory relationship between its level and miR-520-5p and PPP5C, and its elevated level also led to a decrease in the survival level of patients over 3-5 years.

Conclusion

PPP5C has a prognostic role in pancreatic cancer by promoting the value-added and invasion of pancreatic cancer cells, and a targeted inhibitory relationship between miR-520-5p and PPP5C was found.

Review of PP2A Tumor Biology and Antitumor Effects of PP2A Inhibitor LB100 in the Nervous System

Simple Summary

Central and peripheral nervous system tumors represent a heterogenous group of neoplasms which often demonstrate resistance to treatment. Given that these tumors are often refractory to conventional therapy, novel pharmaceutical regimens are needed for successfully treating this pathology. One such therapeutic is the serine/threonine phosphatase inhibitor, LB100. LB100 is a water-soluble competitive protein phosphtase inhibitor that has demonstrated antitumor effects in preclinical and clinical trials. In this review, we aim to summarize current evidence demonstrating the efficacy of LB100 as an inhibitor of nervous system tumors. Furthermore, we review the involvement of the well-studied phosphatase, protein phosphatase 2A, in oncogenic cell signaling pathways, neurophysiology, and neurodevelopment.

Abstract

Protein phosphatase 2A (PP2A) is a ubiquitous serine/threonine phosphatase implicated in a wide variety of regulatory cellular functions. PP2A is abundant in the mammalian nervous system, and dysregulation of its cellular functions is associated with myriad neurodegenerative disorders. Additionally, PP2A has oncologic implications, recently garnering attention and emerging as a therapeutic target because of the antitumor effects of a potent PP2A inhibitor, LB100. LB100 abrogation of PP2A is believed to exert its inhibitory effects on tumor progression through cellular chemo- and radiosensitization to adjuvant agents. An updated and unifying review of PP2A biology and inhibition with LB100 as a therapeutic strategy for targeting cancers of the nervous system is needed, as other reviews have mainly covered broader applications of LB100. In this review, we discuss the role of PP2A in normal cells and tumor cells of the nervous system. Furthermore, we summarize current evidence regarding the therapeutic potential of LB100 for treating solid tumors of the nervous system.

The role of PP5 and PP2C in cardiac health and disease

Protein phosphatases are important, for example, as functional antagonists of β-adrenergic stimulation of the mammalian heart. While β-adrenergic stimulations increase the phosphorylation state of regulatory proteins and therefore force of contraction in the heart, these phosphorylations are reversed and thus force is reduced by the activity of protein phosphatases. In this context the role of PP5 and PP2C is starting to unravel. They do not belong to the same family of phosphatases with regard to sequence homology, many similarities with regard to location, activation by lipids and putative substrates have been worked out over the years. We also suggest which pathways for regulation of PP5 and/or PP2C described in other tissues and not yet in the heart might be useful to look for in cardiac tissue. Both phosphatases might play a role in signal transduction of sarcolemmal receptors in the heart. Expression of PP5 and PP2C can be increased by extracellular stimuli in the heart. Because PP5 is overexpressed in failing animal and human hearts, and because overexpression of PP5 or PP2C leads to cardiac hypertrophy and KO of PP5 leads to cardiac hypotrophy, one might argue for a role of PP5 and PP2C in heart failure. Because PP5 and PP2C can reduce, at least in vitro, the phosphorylation state of proteins thought to be relevant for cardiac arrhythmias, a role of these phosphatases for cardiac arrhythmias is also probable. Thus, PP5 and PP2C might be druggable targets to treat important cardiac diseases like heart failure, cardiac hypertrophy and cardiac arrhythmias.

Structure and function of the co-chaperone protein phosphatase 5 in cancer

Protein phosphatase 5 (PP5) is a serine/threonine protein phosphatase that regulates many cellular functions including steroid hormone signaling, stress response, proliferation, apoptosis, and DNA repair. PP5 is also a co-chaperone of the heat shock protein 90 molecular chaperone machinery that assists in regulation of cellular signaling pathways essential for cell survival and growth. PP5 plays a significant role in survival and propagation of multiple cancers, which makes it a promising target for cancer therapy. Though there are several naturally occurring PP5 inhibitors, none is specific for PP5. Here, we review the roles of PP5 in cancer progression and survival and discuss the unique features of the PP5 structure that differentiate it from other phosphoprotein phosphatase (PPP) family members and make it an attractive therapeutic target.

Protein Phosphatases-A Touchy Enemy in the Battle Against Glioblastomas: A Review

Glioblastoma (GBM) is the most common malignant tumor arising from brain parenchyma. Although many efforts have been made to develop therapies for GBM, the prognosis still remains poor, mainly because of the difficulty in total resection of the tumor mass from brain tissue and the resistance of the residual tumor against standard chemoradiotherapy. Therefore, novel adjuvant therapies are urgently needed. Recent genome-wide analyses of GBM cases have clarified molecular signaling mechanisms underlying GBM biology. However, results of clinical trials targeting phosphorylation-mediated signaling have been unsatisfactory to date. Protein phosphatases are enzymes that antagonize phosphorylation signaling by dephosphorylating phosphorylated signaling molecules. Recently, the critical roles of phosphatases in the regulation of oncogenic signaling in malignant tumor cells have been reported, and tumorigenic roles of deregulated phosphatases have been demonstrated in GBM. However, a detailed mechanism underlying phosphatase-mediated signaling transduction in the regulation of GBM has not been elucidated, and such information is necessary to apply phosphatases as a therapeutic target for GBM. This review highlights and summarizes the phosphatases that have crucial roles in the regulation of oncogenic signaling in GBM cells.

The Antitumor Drug LB-100 Is a Catalytic Inhibitor of Protein Phosphatase 2A (PPP2CA) and 5 (PPP5C) Coordinating with the Active-Site Catalytic Metals in PPP5C

LB-100 is an experimental cancer therapeutic with cytotoxic activity against cancer cells in culture and antitumor activity in animals. The first phase I trial (NCT01837667) evaluating LB-100 recently concluded that safety and efficacy parameters are favorable for further clinical testing. Although LB-100 is widely reported as a specific inhibitor of serine/threonine phosphatase 2A (PP2AC/PPP2CA:PPP2CB), we could find no experimental evidence in the published literature demonstrating the specific engagement of LB-100 with PP2A in vitro, in cultured cells, or in animals. Rather, the premise for LB-100 targeting PP2AC is derived from studies that measure phosphate released from a phosphopeptide (K-R-pT-I-R-R) or inferred from the ability of LB-100 to mimic activity previously reported to result from the inhibition of PP2AC by other means. PP2AC and PPP5C share a common catalytic mechanism. Here, we demonstrate that the phosphopeptide used to ascribe LB-100 specificity for PP2A is also a substrate for PPP5C. Inhibition assays using purified enzymes demonstrate that LB-100 is a catalytic inhibitor of both PP2AC and PPP5C. The structure of PPP5C cocrystallized with LB-100 was solved to a resolution of 1.65Å, revealing that the 7-oxabicyclo[2.2.1]heptane-2,3-dicarbonyl moiety coordinates with the metal ions and key residues that are conserved in both PP2AC and PPP5C. Cell-based studies revealed some known actions of LB-100 are mimicked by the genetic disruption of PPP5C These data demonstrate that LB-100 is a catalytic inhibitor of both PP2AC and PPP5C and suggest that the observed antitumor activity might be due to an additive effect achieved by suppressing both PP2A and PPP5C.

Serine/threonine protein phosphatase 5 is a potential therapeutic target in cholangiocarcinoma

BACKGROUND & AIMS

Few molecules are currently verified to be actionable drug targets in cholangiocarcinoma (CCA). Serine/threonine protein phosphatase 5 (PP5) dysregulation is related to several malignancies. However, the role of PP5 in CCA is poorly defined.

METHODS

Colony and tumorsphere formation assays were conducted to establish the role of PP5 in CCA tumorigenesis. Cantharidin (CTD) and norcantharidin (NCTD), both potent PP5 inhibitors, were used in in vitro and in vivo experiments to validate the potential therapeutic role of PP5.

RESULTS

Increased cell growth, colony formation and tumorsphere formation were observed in PP5-overexpressing CCA cells, whereas PP5 knockdown by shRNA decreased cell growth and colony formation. Tumours from HuCCT1 xenograft-bearing mice treated with PP5-shRNA showed decreased growth and increased AMP-activated protein kinase (AMPK) phosphorylation. Furthermore, CTD treatment decreased cell viability, reduced PP5 activity and enhanced AMPK phosphorylation in CCA cell lines. Overexpressing PP5 or enhancing PP5 activity suppressed AMPK phosphorylation and decreased CTD-induced cell death. Suppressing p-AMPK with siRNA or inhibitors also decreased CTD-induced cell death, suggesting a pivotal role for PP5-AMPK cascades in CCA. Immunoprecipitation revealed that PP5 interacted with AMPK. Importantly, treatment of HuCCT1 xenograft-bearing mice with NCTD, a CTD analogue with a lower systemic toxicity in vivo, suppressed PP5 activity, increased p-AMPK and reduced tumour volume.

CONCLUSIONS

Protein phosphatase 5 negatively regulates AMPK phosphorylation and contributes to CCA aggressiveness; thus, PP5 may be a potential therapeutic target in CCA.

PPP5C promotes cell proliferation and survival in human prostate cancer by regulating of the JNK and ERK1/2 phosphorylation

Background

Prostate cancer (PCa) is one of the most common malignancies and a major leading cause of cancer-related deaths in males. And it is necessary to explore new molecular targets to enhance diagnosis and treatment level of the PCa. Serine/threonine protein phosphatase 5 (PPP5C) is a vital molecule that Involve in complex cell physiological activity.

Purpose

The objective of this study was to detecte the expression level of PPP5C in the tissue of prostate cancer patients and further discussed the PPP5C biological function and mechanisms on the PCa.

Methods

The expression level of PPP5C was analyzed by immunohistochemistry and ONCOM-INE datasets. Lentivirus-mediated short hairpin RNA (shRNA) was constructed to silence the expression of PPP5C in prostate cancer cell. Cell viability and proliferation were measured using MTT and colony formation, and the cell cycle and apoptosis was analyszed by flow cytometry. The changes of downstream protein level and protein phosphorylation level were detected by western blot.

Results

PPP5C was highly expressed in PCa tissue as analyzed by immunohistochemistry and ONCOMINE datasets. PPP5C Knockdown inhibited cell proliferation and colony formation in PCa cells. Flow cytometry analysis showed that DU145, PC3 and 22RV1 PCa cells deprived of PPP5C were arrested in G0/G1 phase and became apoptotic. Western blot analysis indicated that PPP5C knockdown could promote JNK and ERK phosphorylation.

Conclusion

Our study indicated that the PPP5C may become a new potential diagnostic biomarker and therapeutic target for the PCa.

Knockdown of serine/threonine protein phosphatase 5 enhances gemcitabine sensitivity by promoting apoptosis in pancreatic cancer cells in vitro

The targeting protein of serine/threonine protein phosphatase 5 (PPP5C) has been reported to be present in various malignancies. However, its functional role in pancreatic cancer (PC) remains unknown. In the present study, the function of PPP5C in PC cells treated with the first-line drug gemcitabine (GEM) was investigated. Short hairpin (sh)RNA targeting PPP5C was constructed to knockdown PPP5C in PANC-1 cells. Cell cycle and apoptosis analyses were performed in order to investigate the mechanisms underlying the effects induced by PPP5C silencing combined with GEM treatment. Western blot analysis was applied to detect the expression of certain key regulators of cell apoptosis in PANC-1 cells treated with GEM. shRNA against PPP5C effectively suppressed the proliferation of PANC-1 cells treated with GEM. Additionally, cell cycle analysis indicated that PPP5C knockdown resulted in a higher number of PANC-1 cells treated with GEM in G₀/G₁ phase arrest. Knockdown of PPP5C increased the expression of associated apoptotic markers, including cleaved caspase 3, poly (ADP-ribose) polymerase and phosphorylated (p)-p53. In addition, the combination of treatment with GEM and PPP5C silencing significantly increased the apoptosis of PANC-1 cells by affecting the expression levels of p-c-Jun N-terminal kinases and p-p38. The present study suggests that PPP5C may be a potential target for the treatment of PC and that it may enhance the gemcitabine sensitivity of PC cells.

Phosphatases and solid tumors: focus on glioblastoma initiation, progression and recurrences

Phosphatases and cancer have been related for many years now, as these enzymes regulate key cellular functions, including cell survival, migration, differentiation and proliferation. Dysfunctions or mutations affecting these enzymes have been demonstrated to be key factors for oncogenesis. The aim of this review is to shed light on the role of four different phosphatases (PTEN, PP2A, CDC25 and DUSP1) in five different solid tumors (breast cancer, lung cancer, pancreatic cancer, prostate cancer and ovarian cancer), in order to better understand the most frequent and aggressive primary cancer of the central nervous system, glioblastoma.