Diacylglycerol kinase zeta is associated with chromatin, but dissociates from condensed chromatin during mitotic phase in NIH3T3 cells

Diacylglycerol kinase (DGK) converts diacylglycerol (DG) to phosphatidic acid, both of which act as second messengers to mediate a variety of cellular mechanisms. Therefore, DGK contributes to the regulation of these messengers in cellular signal transduction. Of DGK isozymes cloned, DGKzeta is characterized by a nuclear localization signal that overlaps with a sequence similar to the myristoylated alanine-rich C-kinase substrate. Previous studies showed that nuclear DG is differentially regulated from plasma membrane DG and that the nuclear DG levels fluctuate in correlation with cell cycle progression, suggesting the importance of nuclear DG in cell cycle control. In this connection, DGKzeta has been shown to localize to the nucleus in fully differentiated cells, such as neurons and lung cells, although it remains elusive how DGK behaves during the cell cycle in proliferating cells. Here we demonstrate that DGKzeta localizes to the nucleus during interphase including G1, S, and G2 phases and is associated with chromatin although it dissociates from condensed chromatin during mitotic phase in NIH3T3 cells. Furthermore, this localization pattern is also observed in proliferating spermatogonia in the testis. These results suggest a reversible association of DGKzeta with histone or its related proteins in cell cycle, plausibly dependent on their post-translational modifications.     

CaM kinase control of AKT and LNCaP cell survival

AKT and its substrate BAD have been shown to promote prostate cancer cell survival. Agonists, such as carbachol, and hormones that increase intracellular calcium concentration can activate AKT leading to cancer cell survival. The LNCaP prostate cancer cells express the carbachol-sensitive M(3) -subtype of G protein-coupled receptors that cause increases in intracellular calcium and activate the family of Ca(2+) /calmodulin-dependent protein kinases (CaM Ks). One type of CaM Kinase, CaM Kinase Kinase (CaM KK), phosphorylates several substrates including AKT on threonine 308. AKT phosphorylation and activation enhances cell survival through phosphorylation of BAD protein and the subsequent blockade of caspase activation. Our goals were to examine the mechanism of carbachol activation of AKT and BAD in LNCaP prostate cancer cells and evaluate whether CaM KK may be mediating carbachol's activation of AKT and cell survival. Our results suggest that carbachol treatment of LNCaP cells promoted cell survival through CaM KK and its phosphorylation of AKT. The bacterial toxin anisomycin triggered caspase-3 activation in LNCaP cells that was blocked by carbachol in a CaM KK- and AKT-dependent manner. AKT and BAD phosphorylation were blocked by the selective CaM KK inhibitor, STO-609, as well as siRNA directed against CaM KK. BAD phosphorylation was also blocked by treating cells with the AKT inhibitor, AKT-X, as well as siRNA to AKT. Additionally, epinephrine promoted LNCaP cell survival through activation of AKT that was insensitive to STO-609. Taken together these data suggest a survival role for CaM KK operating through AKT and BAD in LNCaP prostate cancer cells.     

Targeting PKC-mediated signal transduction pathways using enzastaurin to promote apoptosis in acute myeloid leukemia-derived cell lines and blast cells

Recent studies in acute myeloid leukemia (AML) suggest activation of pro-proliferative signaling cascades including those mediated by protein kinase C (PKC) represent a poor prognostic factor for patients. The classical PKC isoforms α and β generally support survival signaling and have emerged as important targets for anti-cancer therapy. Enzastaurin is a PKC β inhibitor and is in clinical trials for lymphomas, gliomas, and lung cancer. Presently, it is not known if enzastaurin could be effective against AML. In the current study, we found that high dose enzastaurin was found to promote apoptosis in the AML-derived cell lines and in blast cells from AML patients. The mechanism of cell death, however, likely does not involve PKC β as another PKC β inhibitor was not toxic to AML cell lines and did not promote enzastaurin-induced cell killing. While enzastaurin is fairly specific for PKC β, the agent can inhibit other PKC isoforms at higher concentrations. Enzastaurin was effective at inhibiting PKC α phosphorylation and membrane localization in the AML cell lines and suppressed phosphorylation of BCL2. Furthermore, enzastaurin suppressed activation of ERK (which can be activated by PKC α). Analysis of the serine/threonine phosphorylation profile in HL60 cells after enzastaurin treatment revealed that the drug inhibits the phosphorylation of a distinct set of proteins while promoting phosphorylation of another set of proteins. This suggests the drug may regulate multiple signaling pathways. Taken together, these findings suggest that enzastaurin could be effective in the therapy of AML.     

Reaction of peroxynitrite with L-tryptophan

Summary

The reaction between peroxynitrous acid (hydrogen oxoperoxonitrate) and L-tryptophan is 130 M^?1s^?1 at 25°C. The pH dependence of the second-order rate constant shows a maximum at pH 5.1. The enthalpy and entropy of activation at pH 7.1 are 10.6 ± 0.4 kcal.mol^?1 and -16 ± 2 cal.mol^?1K^?1 respectively. High-performance liquid chromatography analysis revealed a number of reaction products, two of which were identified as 5- and 6- nitrotryptophan. Hydroxytryptophans were not observed, even at low peroxynitrite concentrations where most of the peroxynitrite decays to nitrate via a first-order process. These results support the hypothesis that isomerization of protonated peroxynitrite to nitrate does not involve formation of the hydroxyl radical.     

Cyclic GMP/protein kinase G type-Iα (PKG-Iα) signaling pathway promotes CREB phosphorylation and maintains higher c-IAP1, livin, survivin, and Mcl-1 expression and the inhibition of PKG-Iα kinase activity synergizes with cisplatin in non-small cell lung cancer cells

Previously, our laboratory showed that nitric oxide (NO)/cyclic GMP (cGMP)/protein kinase G type‐Iα (PKG‐Iα) signaling pathway plays an important role in preventing spontaneous apoptosis and promoting cell proliferation in both normal cells (bone marrow stromal cells and vascular smooth muscle cells) and certain cancer cells (ovarian cancer cells). In the present study, we investigated the novel role of the cGMP/PKG‐Iα pathway in preventing spontaneous apoptosis, promoting colony formation and regulating phosphorylation of cAMP response element binding (CREB) protein and protein expression of inhibitor of apoptosis proteins (IAPs) and anti‐apoptotic Bcl‐2‐related proteins in NCI‐H460 and A549 non‐small cell lung cancer (NSCLC) cells. 1H‐(1,2,4)oxadiazolo(4,3‐a)quinoxalin‐1‐one (ODQ), which blocks endogenous NO‐induced activation of cGMP/PKG‐Iα, induced apoptosis and decreased colony formation. ODQ also decreased CREB ser133 phosphorylation and protein expression of c‐IAP1, livin, and survivin. DT‐2 (inhibitor of PKG‐Iα kinase activity) increased apoptosis by twofold and decreased CREB ser133 phosphorylation and c‐IAP1, livin, and survivin expression. Gene knockdown of PKG‐Iα expression using small‐interfering RNA increased apoptosis and decreased CREB ser133 phosphorylation, and c‐IAP1, livin, survivin, and Mcl‐1 expression. Inhibition of PKG‐Iα kinase activity with DT‐2 dramatically enhanced pro‐apoptotic effects of the chemotherapeutic agent cisplatin. Combined treatment of DT‐2 and cisplatin increased apoptosis compared with cisplatin or DT‐2 alone, showing a synergistic effect. The data suggest that the PKG‐Iα kinase activity is necessary for maintaining higher levels of CREB phosphorylation at ser133 and protein expression of c‐IAP1, livin, survivin, and Mcl‐1, preventing spontaneous apoptosis and promoting colony formation in NSCLC cells, which may limit the effectiveness of chemotherapeutic agents like cisplatin. J. Cell. Biochem. 113: 3587–3598, 2012. © 2012 Wiley Periodicals, Inc.     

Cell rounding in cultured human astrocytes and vascular endothelial cells upon inhibition of CK2 is mediated by actomyosin cytoskeleton alterations

Protein kinase CK2 participates in a wide range of cellular events, including the regulation of cellular morphology and migration, and may be an important mediator of angiogenesis. We previously showed that in the retina, CK2 immunolocalizes mostly to vascular endothelium and astrocytes in association with the cytoskeleton. Additionally, CK2 inhibitors significantly reduced retinal neovascularization and stem cell recruitment in the mouse model of oxygen-induced proliferative retinopathy. We have also shown that CK2 and F-actin co-localized in actin stress fibers in microvascular endothelial cells, and that highly specific CK2 inhibitors caused cell rounding in astrocytes and microvascular endothelial cells, which was alleviated by serum that promotes spreading by Rho/Rho-kinase (RhoK) activation of myosin II. Therefore, we examined a possible role of CK2 in the regulation of actin-myosin II-based contractility. Treatment with CK2 inhibitors correlated with disassembly of actomyosin stress fibers and cell shape changes, including cytoplasmic retraction and process formation that were similar to those occurring during astrocyte stellation. Low doses of specific inhibitors of kinases (RhoK and MLCK) that phosphorylate myosin light chain (MLC) enhanced the effect of suboptimal CK2 inhibition on cell shape. Such striking stellation-like alteration was accompanied by decreased level of phospho-MLC, thus implying a CK2 role in regulation of actomyosin cytoskeleton. Our results suggest an important role of CK2 in the control of cell contractility and motility, which may account for suppressing effect of CK2 inhibition on retinal neovascularization. Together, our data implicate protein kinase CK2 for the first time in stellation-like morphological transformation.     

Level of nitrated proteins in the plasma,platelets and liver of patients with liver cirrhosis

Abstract

Over-expression of nitric oxide synthase (NOS) and nitric oxide (NO) formation are associated with the pathogenesis of liver cirrhosis. NO-related stress alters the functions of biomolecules, especially proteins, probably as a result of nitration. The aim of this study was to assess the level of protein nitration and its correlation with the severity of the disease. Liver cirrhosis patients with different grades of severity (grades A, B, and C according to the Child–Pugh classification) were enrolled in this study. Nitroprotein content, arginine, citrulline, NO in terms of total nitrite, nitrosothiol (RSNO) and protein carbonyls were measured in blood. Immunohistochemical detection of nitroprotein was carried out in liver sections of cirrhosis patients. A significant elevation in the levels of serum and platelet arginine, arginase, citrulline, plasma, and platelet nitroproteins, RSNO, total nitrite, protein carbonyls and also a significant amount of nitrated proteins by immunohistochemical detection in tissue were observed in cirrhosis patients. The alterations were highly significant in grade C patients with bleeding complications when compared to those of grade B and A patients. In platelets, both cytosolic and cytoskeletal proteins were found to be nitrated significantly. The level of nitrite seems to have positive correlation with the level of nitroproteins in different grades of cirrhosis. The level of nitroproteins in plasma, platelets and liver tissue can be correlated with the severity of liver cirrhosis.