Phosphoprotein Phosphatases ; Kinetics ; Protein Phosphatase 2/metabolism*

The 26S proteasome at the center of the ubiquitin-proteasome system (UPS) is essential for virtually all cellular processes of eukaryotes. A common misconception about the proteasome is that, once made, it remains as a static and uniform complex with spontaneous and constitutive activity for protein degradation. Recent discoveries have provided compelling evidence to support the exact opposite insomuch as the 26S proteasome undergoes dynamic and reversible phosphorylation under a variety of physiopathological conditions. In this review, we summarize the history and current understanding of proteasome phosphorylation, and advocate the idea of targeting proteasome kinases/phosphatases as a new strategy for clinical interventions of several human diseases.
Animals ; Humans ; Phosphoprotein Phosphatases ; genetics ; metabolism ; Phosphorylation ; genetics ; Proteasome Endopeptidase Complex ; genetics ; metabolism ; Protein Kinases ; genetics ; metabolism

This study was aimed to investigate the effect of AG490, a JAK2 inhibitor, on expression of PHLPP and p-Akt in K562. K562 cells were treated with different concentrations of AG490. The proliferation of K562 cells was examined by WST-1 assay and apoptosis of K562 cells was detected by flow cytometry with Annexin V-FITC/PI double staining. The expressions of PHLPP, phosphorate-Akt (p-Akt) and total Akt protein were detected by Western blot. The results indicated that AG490 inhibited the proliferation of K562 cells in concentration-and time-dependent manners, with the IC(50) 338.0 µmol/L in 48 h. AG490 100 µmol/L also induced apoptosis of K562 cells in a time-dependent manner. AG490 100 µmol/L time-dependently down-regulated the protein expression of p-Akt and PHLPP, but without significant effect on expression of total Akt. It is concluded that AG490 can inhibit proliferation and induce apoptosis of K562 cells through down-regulation of p-Akt expression, but inhibiting efficacy of AG490 on K562 proliferation also may be limited due to the down-regulation of p-Akt regulatory protein PHLPP expression.
Cell Proliferation ; drug effects ; Down-Regulation ; Humans ; K562 Cells ; Nuclear Proteins ; metabolism ; Phosphoprotein Phosphatases ; metabolism ; Tyrphostins ; pharmacology

OBJECTIVEEosinophils play a pivotal role in asthmatic airway inflammation. We previously found a significantly high expression of Slingshot-1L (SSH-1L) in peripheral eosinophils in acute exacerbations of asthma. Objective To investigate the expression and localization patterns of SSH-1L in peripheral blood eosinophils of asthmatic patients and their changes after treatment with inhaled corticosteroids.

METHODSWe recruited 4 outpatients with acute exacerbations of asthma who received no previous corticosteroid treatment and 1 healthy volunteer. From all the subjects 30 ml peripheral venous blood samples were collected before and after a 3-month treatment with inhaled fluticasone. The eosinophils were isolated, purified and counted, and the expressions of SSH-1L in the eosinophils were examined by RT-PCR and Western blotting. The localization of SSH-1L phosphatases in the peripheral eosinophils was detected by immunofluorescence assay in one patient.

RESULTSSSH-1L phosphatases distributed diffusely in the cytoplasm, especially dense near the membrane of the peripheral eosinophils. Glucocorticoids treatment resulted in a significant reduction in both the SSH-1L mRNA expression (0.7403∓0.1124 vs 0.4101∓0.0363, P=0.001) and SSH-1L protein expression (0.3410∓0.1337 vs 0.1543∓0.0551, P=0.039).

CONCLUSIONA high expression of SSH-1L in peripheral eosinophils in acute exacerbations of asthma may play a role in the activation and migration of eosinophils. The efficacy of inhaled corticosteroids in asthma control might be partly attributed to a down-regulated expression of SSH-1L.

Adult ; Aged ; Asthma ; blood ; drug therapy ; Eosinophils ; metabolism ; Female ; Glucocorticoids ; therapeutic use ; Humans ; Male ; Middle Aged ; Phosphoprotein Phosphatases ; metabolism

OBJECTIVETo investigate the constituent expression of PH domain leucine-rich repeat protein phosphatase 1 (PHLPP1) in human umbilical vein endothelial cells (HUVECs) and the effect of PHLPP1 gene transfer on the proliferation of the cells in vitro.

METHODSCultured HUVECs were transfected with pcDNA3-GFP or pcDNA3HA-PHLPP1 via lipofectamine 2000. The cell proliferation ability was determined by cell counting and MTT colorimetric assay, and Western blotting was used to detect the protein expression of PHLPP1 in the cells.

RESULTSNo PHLPP1 protein was detected in the non-transfected cells or pcDNA3-GFP-transfected cells. pcDNA3HA-PHLPP1 gene transfection significantly increased PHLPP1 expression in the HUVECs (P<0.01), but the cell proliferation status remained unchanged (P>0.05). The absorbance of the cells measured by MTT assay was 0.134-/+0.0152, 0133-/+0.014 and 0.137-/+0.016, with cell counts of (8.293-/+0.962)x10(5), (7.937-/+0.101)x10(5) and (8.127-/+0.112)x10(5), respectively, showing no significant differences between the 3 groups (P>0.05).

CONCLUSIONSPhosphatase PHLPP1 may not be the most important signal protein in the regulation of HUVEC proliferation.

Cell Proliferation ; Gene Transfer Techniques ; Human Umbilical Vein Endothelial Cells ; cytology ; metabolism ; Humans ; Nuclear Proteins ; genetics ; Phosphoprotein Phosphatases ; genetics ; Transfection

BACKGROUNDAdvances in the understanding of cardiovascular pathogenesis have highlighted that inflammation plays a central role in atherosclerotic coronary heart disease. Therefore, exploring pharmacologically based anti-inflammatory treatments to be used in cardiovascular therapeutics is worthwhile to promote the discovery of novel ways of treating cardiovascular disorders.

METHODSThe myocardial cell line H9c2(2-1) was exposed to lipopolysaccharide (LPS) in culture and resulted in a cellular pro-inflammation status. miR-21 microRNA levels were detected using quantitative real-time polymerase chain reaction (Q-RT-PCR). The influence of lovastatin on miR-21 under normal and pro-inflammatory conditions was tested after being added to the cell culture mixture for 24 hours. Conditional gene function of two predicted cardiovascular system relevant downstream targets of miR-21, protein phosphatase 1 regulatory subunit 3A (PPP1R3A) and signal transducer and activator of transcription 3 (STAT3), were analyzed with immunoblotting.

RESULTSForty-eight hours of LPS treatment significantly increased the miR-21 to 170.71%± 34.32% of control levels (P = 0.002). Co-treatment with lovastatin for 24 hours before harvesting attenuated the up-regulation of miR-21 (P = 0.013). Twenty-four hours of lovastatin exposure up-regulated PPP1R3A to 143.85%± 21.89% of control levels in cardiomyocytes (P = 0.023). Lovastatin up-regulated the phosphorylation level of STAT3 compared to the background LPS pretreatment (P = 0.0077), this effect was significantly (P = 0.018) blunted when miR-21 was functionally inhibited.

CONCLUSIONSmiR-21 plays a major role in the regulation of the cellular anti-inflammation effects of lovastatin.

Blotting, Western ; Cell Line ; Humans ; Lipopolysaccharides ; pharmacology ; Lovastatin ; pharmacology ; MicroRNAs ; genetics ; Myocardium ; metabolism ; Myocytes, Cardiac ; drug effects ; metabolism ; Phosphoprotein Phosphatases ; metabolism ; Phosphorylation ; STAT3 Transcription Factor ; metabolism

OBJECTIVETo study the changes in expression and activity of protein phosphatases type 2A (PP2A ) during differentiation of NB4 and NB4-MR2 cells induced by all-trans retinoic acid (ATRA), and evaluate the role of PP2A in MR2 resistance to ATRA.

METHODSATRA, okadaic acid (OKA) and ATRA + OKA at the same dosage were incubated with NB4 and MR2 cells respectively. Wright's staining and NBT reduction test were employed to evaluate the change in the cells. The CD11b expression was measured by flow cytometry. The activity of PP2A was evaluated by serine/threonine phosphatase assay system, and the level of PP2A subunits was detected by Western blot.

RESULTS1) Wright's staining, NBT reduction test and flow cytometry results showed OKA could augment the differentiation of NB4 induced by ATRA, and OKA + ATRA induced slight differentiation of MR2 cells. 2) Phosphatase assay showed a decrease in PP2A phosphatase activity [(534 +/- 43) pmol x min(-1) x microg protein(-1)] in NB4 after ATRA treatment, accompanied with that activity [(959 +/- 83) pmol x min(-1) x microg protein(-1)] in untreated NB4 cells. OKA enhanced the inhibitory effect of ATRA on the activity in NB4. When OKA + ATRA was incubated with MR2, PP2A in the cells was significantly decreased [(229 +/- 23) pmol x min(-1) x microg protein(-1)]. 3) Western blot analysis showed that the level of PP2A catalytic subunit (PP2A/C) was decreased during the course of ATRA-induced NB4 cell differentiation, whereas expressions of every subunits of PP2A in MR2 cells were somewhat unaltered.

CONCLUSIONExpression of PP2A/C and activity of PP2A is decreased during differentiation of NB4 induced by ATRA, and no repression of the PP2 activity maybe related to MR2 resistance to ATRA.

Cell Differentiation ; drug effects ; Cell Line, Tumor ; Humans ; Leukemia, Promyelocytic, Acute ; metabolism ; pathology ; Okadaic Acid ; pharmacology ; Phosphoprotein Phosphatases ; metabolism ; Protein Phosphatase 2 ; antagonists & inhibitors ; metabolism ; Tretinoin ; pharmacology

Objective To investigate the expression level of serine/threonine phosphoprotein phosphatase 4C(PPP4C)in gastric cancer,and analyze its relationship with prognosis and the underlying regulatory mechanism.Methods The clinical data of 104 gastric cancer patients admitted to the First Affiliated Hospital of Bengbu Medical College between January 2012 and August 2016 were collected.Immunohistochemical staining was employed to determine the expression levels of PPP4C and Ki-67 in the gastric cancer tissue.The gastric cancer cell lines BGC823 and HGC27 were cultured and transfected with the vector for PPP4C knockdown,the vector for PPP4C overexpression,and the lentiviral vector(control),respectively.The effects of PPP4C on the cell cycle and proliferation were analyzed and the possible regulatory mechanisms were explored.Results PPP4C was highly expressed in gastric cancer(P<0.001),and its expression promoted malignant progression of the tumor(all P<0.01).Univariate and Cox multivariate analysis clarified that high expression of PPP4C was an independent risk factor affecting the 5-year survival rate of gastric cancer patients(P=0.003).Gene ontology and Kyoto encyclopedia of genes and genomes enrichment analysis suggested that PPP4C may be involved in the cell cycle.The correlation analysis showed that the expression of PPP4C was positively correlated with that of Ki-67 in gastric cancer(P<0.001).The up-regulation of PPP4C expression increased the proportion of tumor cells in the S phase,alleviated the G2/M phase arrest,and promoted the proliferation of gastric cancer cells and the expression of cyclin D1 and cyclin-dependent kinase 6(CDK6)(all P<0.05).The down-regulation of PPP4C decreased the proportion of gastric cancer cells in the S phase,promoted G2/M phase arrest,and inhibited cell proliferation and the expression of cyclin D1,CDK6,and p53(all P<0.05).p53 inhibitors promoted the proliferation of BGC823 and HGC27 cells in the PPP4C knockdown group(P<0.001,P<0.001),while p53 activators inhibited the proliferation of BGC823 and HGC27 cells in the PPP4C overexpression group(P<0.001,P=0.002).Conclusions PPP4C is highly expressed in gastric cancer and affects the prognosis of the patients.It may increase the proportion of gastric cancer cells in the S phase and alleviate the G2/M phase arrest by inhibiting p53 signaling,thereby promoting cell proliferation.
Humans ; Stomach Neoplasms/genetics* ; Cyclin D1/metabolism* ; Tumor Suppressor Protein p53 ; Phosphoproteins/metabolism* ; Ki-67 Antigen ; Cell Line, Tumor ; Prognosis ; Cell Proliferation ; Phosphoprotein Phosphatases/metabolism* ; Threonine ; Serine

The serine/threonine phosphatase (PP1) isoform PP1 gamma 2, predominantly expressed in the testis, is a key enzyme in spermatozoa. High PP1 gamma 2 catalytic activity holds motility in check in immature spermatozoa. Inhibition of PP1 gamma 2 causes motility initiation in immature spermatozoa and motility stimulation and changes in flagellar beat parameters in mature spermatozoa. The PP1 gamma 2 isoform is present in all mammalian spermatozoa studied: mouse, rat, hamster, bovine, non-human primate and man. We have now identified at least four of its regulatory proteins that regulate distinct pools of PP1 gamma 2 within spermatozoa. Our studies provide new insights into biochemical mechanisms underlying development and regulation of sperm motility. We hypothesize that changes in sperm PP1 gamma 2 activity as a result of phosphorylation and reversible binding of the regulatory proteins to the catalytic subunit are critical in the development and regulation of motility and the ability of sperm to fertilize eggs. Targeted disruption of the Ppp1cc gene, which encodes the PP1 gamma 1 or PP1 gamma 2 isoforms, causes male infertility in mice as a result of impaired spermiogenesis. Our observations suggest that, in addition to motility, the protein phosphatase PP1 gamma 2 might play an isoform-specific function in the development of specialized flagellar structures of mammalian spermatozoa.
Animals ; Cattle ; Cricetinae ; Epididymis ; enzymology ; physiology ; Homeostasis ; Humans ; Male ; Mice ; Phosphoprotein Phosphatases ; genetics ; metabolism ; Sperm Motility ; physiology ; Spermatozoa ; enzymology ; physiology ; Testis ; enzymology

Programmed necrosis, also known as necroptosis, has recently drawn great attention. As an important cellular regulation mechanism, knowledge of its signaling components is expanding. Necroptosisis demonstrated to be regulated by the RIP1 and RIP3 kinases, and its pathophysiological importance has been confirmed in a number of disease models. Here we review the new members of this necroptosis pathway, MLKL, PGAM5, Drp1 and DAI, and discuss some of their possible applications according to recent findings.
Animals ; Carrier Proteins ; metabolism ; DNA-Binding Proteins ; metabolism ; GTP Phosphohydrolases ; metabolism ; Humans ; Microtubule-Associated Proteins ; metabolism ; Mitochondrial Proteins ; metabolism ; Necrosis ; Phosphoprotein Phosphatases ; Protein Kinases ; chemistry ; metabolism ; Receptor-Interacting Protein Serine-Threonine Kinases ; metabolism ; Signal Transduction ; Tumor Necrosis Factors ; metabolism