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At least 1,063 records · Page 59Linked to original sources
PubMed1993

Identification of a novel protein kinase C inhibitor in microsomes from phytohaemagglutinin activated human peripheral blood mononuclear cells.

A peptide inhibiting either corpuscolate or purified PKC has been identified from microsomes of PHA-activated human PBMC but it is not detectable in microsomes of resting PBMC. The peptide was obtained from a microsomal preparation in an oligomeric form that could be transformed into a monomeric form by beta-MSH. The active peptide (IN) was retained on a PC-11 chromatographic column and could be eluted with NaCl. IN is ineffective on PKC-dependent protamine phosphorylation of protamine and on Ca2+ and phospholipid-independent activity generated by mild hydrolysis with trypsin of PKC. Ca2+ binding is permissive for IN activity. IN inhibits particulate PKC in PHA-activated PBMC, but is ineffective after TPA activation. All these data indicate that IN acts at the regulatory domain of PKC.

Blood Proteins↗
PubMed2000

A review of current and future treatment strategies for malignant astrocytomas in adults.

BACKGROUND: For more than 20 years, after establishing the role of postoperative radiotherapy for malignant astrocytomas, no definitive improvement in survival rates could be observed, despite advances in established treatment modalities such as radiotherapy and chemotherapy. This review discusses available laboratory and clinical data as well as recent advances in our knowledge about prognostic factors (Table 1) and their implications for the design of future clinical trials. RESULTS: Elucidation of the biology of malignant astrocytomas allowed for development of rational new approaches, such as gene therapy and immunotherapy, which could interfere with established treatment regimens or being used independently. Possible strategies include the restoration of defective cancer-inhibitory genes, cell transduction or transfection with antisense DNA corresponding to genes coding for growth factors and their receptors, or with the so-called suicide genes. Several antiangiogenic approaches such as administration of thalidomide, protamine, or monoclonal antibodies against vascular endothelial growth factor have been developed, too. Further treatment possibilities include modulation of drug resistance, e.g. by P-glycoprotein antagonists or O6-alkyl-guanine-DNA-transferase inhibitors, inhibition of matrix metalloproteinases, inhibition of protein kinase C, and administration of agents such as phenylbutyrate or valproic acid that showed promising antiproliferative effects in vitro. CONCLUSIONS: Several rational new approaches are now entering clinical trials (Table 2). In the light of limited survival after standard treatment it is recommended that patients should be offered participation in such trials.

Adult↗
PubMedDate not supplied

Perspectives in the treatment of malignant gliomas in adults.

Over the last two decades, after establishing the role of postoperative radiotherapy for malignant gliomas, no definitive improvement in survival rate could be observed, despite advances in established treatment modalities such as radiotherapy and chemotherapy. Progress in exploration of the biology of these tumours allowed for translational research projects and the development of rational new approaches, such as gene therapy and immunotherapy, that could interfere with established treatment regimens or be used independently. Possible strategies include the restoration of defective cancer-inhibitory genes, cell transduction or transfection with antisense DNA corresponding to genes coding for growth factors and their receptors, or with the so-called 'suicide genes'. Several antiangiogenic approaches such as administration of thalidomide, protamine, or monoclonal antibodies against vascular endothelial growth factor have been developed, too. Further treatment possibilities include modulation of drug resistance, e.g. by P-glycoprotein antagonists or 06-alkyl-guanine-DNA-transferase inhibitors, inhibition of matrix metalloproteinases, inhibition of protein kinase C and administration of agents such as phenylbutyrate or valproic acid that showed promising antiproliferative effects in vitro. This review discusses the available laboratory and clinical data as well as recent advances in our knowledge about prognostic and predictive factors and their implications for the design of future clinical trials.

Adult↗
PubMed1983

Autophosphorylation of type 2 casein kinase TS at both its alpha- and beta-subunits. Influence of different effectors.

Rat liver casein kinase TS (Ck-TS) having quaternary structure alpha 2 beta 2, autophosphorylates at its 25 kDa, beta-subunits, incorporating up to 1.2 mol P/mol enzyme. According to their effects on the autophosphorylation pattern the effectors of Ck-TS activity can be grouped into 3 classes: (i) inhibitors, like heparin, which also prevent the autophosphorylation of the beta-subunit; (ii) stimulators possessing several amino groups (like spermine) which increase the autophosphorylation at the beta-subunit; (iii) stimulators possessing several guanido groups, like protamines and related peptides, which prevent the phosphorylation of the beta-subunit, while promoting the autophosphorylation of the 38 kDa alpha-subunit. In the presence of such polyarginyl effectors the 130 kDa Ck-TS is converted into forms with higher sedimentation coefficient.

Animals↗
PubMed1990

Purification and characterization of a novel calcium-dependent protein kinase from soybean.

A novel calcium-dependent protein kinase (CDPK) previously reported to be activated by the direct binding of Ca2+, and requiring neither calmodulin nor phospholipids for activity [Harmon, A.C., Putnam-Evans, C.L., & Cormier, M.J. (1987) Plant Physiol. 83, 830-837], was purified to greater than 95% homogeneity from suspension-cultured soybean cells (Glycine max, L. Wayne). Purification was achieved by chromatography on DEAE-cellulose, phenyl-Sepharose, Sephadex G-100, and Blue Sepharose. The purified enzyme (native molecular mass = 52,200 Da) resolved into two immunologically related protein bands of 52 and 55 kDa on 10% SDS gels. Enzyme activity was stimulated 40-100-fold by micromolar amounts of free calcium (K0.5 = 1.5 microM free calcium) and was dependent upon millimolar Mg2+. CDPK phosphorylated lysine-rich histone III-S and chicken gizzard myosin light chains but did not phosphorylate arginine-rich histone, phosvitin, casein, protamine, or Kemptide. Phosphorylation of histone III-S, but not autophosphorylation, was inhibited by KCl. CDPK displayed a broad pH optimum (pH 7-9), and kinetic studies revealed a Km for Mg2(+)-ATP of 8 microM and a Vmax of 1.7 mumol min-1 mg-1 with histone III-S (Km = 0.13 mg/mL) as substrate. Unlike many other protein kinases, CDPK was able to utilize Mg2(+)-GTP, in addition to Mg2(+)-ATP, as phosphate donor. The enzyme phosphorylated histone III-S exclusively on serine; however, CDPK autophosphorylated on both serine and threonine residues. These properties demonstrate that CDPK belongs to a new class of protein kinase.

Amino Acids↗
PubMed1981

[Isolation and study of the properties of the catalytic subunit of cAMP-dependent protein kinase of the small intestinal mucosa of the rabbit].

cAMP-dependent and casein proteinkinase were found in cytosol of the rabbit small intestine mucosa. cAMP-dependent proteinkinase of cytosol is represented by two forms of types I and II. The activity of enzymes of types I and II constitutes 10 and 90%, respectively. Casein proteinkinase is represented by a single form. The catalytic subunit of cAMP-dependent proteinkinase of type II was isolated in a homogenous state. The catalytic subunit phosphorylates histones H1, H2a, H2b and protamine and to a far less degree histones H3, H4 and casein (H2b greater than H1 greater than H2a greater than protamine much greater than H3 greater than casein). The Km value for histone H1 is equal to 65 mkM, and that for Mg-ATP 12 mkM. Chloromethylpyrophosphonate and adenosine p-fluorosulfobenzoate were studied as affine modifiers of the active center of the catalytic subunit from the small intestine mucosa. It was shown that only adenosine p-fluorosulfonate is an irreversible inhibitor of the catalytic subunit.

Animals↗
PubMed1992

Effects of insulin on diacylglycerol/protein kinase-C signalling and glucose transport in rat skeletal muscles in vivo and in vitro.

Insulin treatment in vivo provoked rapid dose-related increases in diacylglycerol content and/or translocation of protein kinase-C (PKC) from cytosol to membranes in rat soleus and gastrocnemius muscles. These effects were apparent with 1) insulin doses that provoked submaximal and maximal increases in glucose utilization, and 2) glucose-stimulated endogenous insulin secretion. Insulin-stimulated PKC translocation was evident when PKC was assayed by 1) histone or protamine phosphorylation after PKC purification by Mono Q column chromatography, and 2) immunoblotting for PKC beta and PKC epsilon. Dose-related effects of insulin on PKC translocation were also observed in the rat soleus in vitro, and this was associated with increased phosphorylation of 40- and 80-kilodalton proteins, which were also phosphorylated by phorbol ester treatment. A role for diacylglycerol-PKC signalling in insulin-stimulated glucose transport was suggested by studies of [3H]2-deoxyglucose ([3H]2-DOG) uptake in the rat soleus in vitro in that 1) PKC translocation and 2-DOG uptake were correlated; and 2) stimulatory effects of insulin and phorbol esters on 2-DOG uptake were apparently nonadditive.

Animals↗
PubMed2001

Spermatogenesis and the regulation of Ca(2+)-calmodulin-dependent protein kinase IV localization are not dependent on calspermin.

Calspermin and Ca(2+)-calmodulin-dependent protein kinase IV (CaMKIV) are two proteins encoded by the Camk4 gene. CaMKIV is found in multiple tissues, including brain, thymus, and testis, while calspermin is restricted to the testis. In the mouse testis, both proteins are expressed within elongating spermatids. We have recently shown that deletion of CaMKIV has no effect on calspermin expression but does impair spermiogenesis by disrupting the exchange of sperm basic nuclear proteins. The function of calspermin within the testis is unclear, although it has been speculated to play a role in binding and sequestering calmodulin during the development of the germ cell. To investigate the contribution of calspermin to spermatogenesis, we have used Cre/lox technology to specifically delete calspermin, while leaving kinase expression intact. We unexpectedly found that calspermin is not required for male fertility. We further demonstrate that CaMKIV expression and localization are unaffected by the absence of calspermin and that calspermin does not colocalize to the nuclear matrix with CaMKIV.

Animals↗
PubMed1989

Comparison of the effect of tautomycin and phorbol ester on protein kinase C in a cell-free system.

The effect of tautomycin (TM) on protein kinase C (PKC) was studied in a cell-free system. TM, like phorbol dibutyrate (PDBu), enhanced both base-line and Ca2+/phospholipids-dependent protein kinase activity. However, PDBu but not TM increased the affinity of the enzyme for calcium ions (Ca2+), suggesting that TM is a new activator of PKC, distinct from PDBu. In the presence of 10 micrograms/ml phosphatidyl inositol, the activity of PKC reached maximum at 10(-3) M Ca2+ concentration when the other co-factors were absent. Both TM and PDBu increased the maximum level of PKC activity at the optimum concentration of Ca2+, suggesting that they interacted with the site of PKC which is distinct from the site where Ca2+ interacts. TM and PDBu did not activate the enzyme when protamine sulfate in place of histone III-S was used as a substrate, indicating that they activate PKC by affecting the regulatory domain of the enzyme.

Antifungal Agents↗
PubMed1998

Inhibitory properties of the regulatory domains of human protein kinase Calpha and mouse protein kinase Cepsilon.

Two fusion proteins in which the regulatory domains of human protein kinase Calpha (Ralpha; amino acids 1-270) or mouse protein kinase Cepsilon (Repsilon; amino acids 1-385) were linked in frame with glutathione S-transferase (GST) were examined for their abilities to inhibit the catalytic activities of protein kinase Calpha (PKCalpha) and other protein kinases in vitro. Both GST-Ralpha and GST-Repsilon but not GST itself potently inhibited the activities of lipid-activated rat brain PKCalpha. In contrast, the fusion proteins had little or no inhibitory effect on the activities of the Ser/Thr protein kinases cAMP-dependent protein kinase, cGMP-dependent protein kinase, casein kinase II, myosin light chain kinase, and mitogen activated protein kinase or on the src Tyr kinase. GST-Ralpha and GST-Repsilon, on a molar basis, were 100-200-fold more potent inhibitors of PKCalpha activity than was the pseudosubstrate peptide PKC19-36. In addition, a GST-Ralpha fusion protein in which the first 32 amino acids of Ralpha were deleted (including the pseudosubstrate sequence from amino acids 19-31) was an effective competitive inhibitor of PKCalpha activity. The three GST-R fusion proteins also inhibited protamine-activated PKCalpha and proteolytically activated PKCalpha (PKM), two lipid-independent forms of PKCalpha; however, the IC50 values for inhibition were 1 order of magnitude greater than the IC50 values obtained in the presence of lipid. These results suggest that part of the inhibitory effect of the GST-R fusion proteins on lipid-activated PKCalpha may have resulted from sequestration of lipid activators. Nonetheless, as evidenced by their abilities to inhibit the lipid-independent forms of the enzyme, the GST-R fusion proteins also inhibited PKCalpha catalytic activity through direct interactions. These data indicate that the R domains of PKCalpha and PKCepsilon are specific inhibitors of protein kinase Calpha activity and suggest that regions of the R domain outside the pseudosubstrate sequence contribute to autoinhibition of the enzyme.

Amino Acid Sequence↗
PubMed1992

Protein kinase C group B members PKC-delta, -epsilon, -zeta and PKC-L(eta). Comparison of properties of recombinant proteins in vitro and in vivo.

Of the recently identified protein kinase C (PKC) types of group B (delta, epsilon, zeta, eta, PKC-L), only PKC-epsilon has been characterized in great detail. In order to compare the regulatory and catalytic properties of these new kinases, we have expressed PKC-delta, -epsilon, -zeta and PKC-L as recombinant proteins from their cDNAs in insect cells via baculovirus vectors and in mammalian COS-1 cells. After expression in insect cells, phorbol ester binding and kinase activities of the group B enzymes were compared with the respective activities of a member of group A, PKC-gamma. Although PKC-delta and PKC-L(eta) bind phorbol ester to a similar or the same extent as PKC-gamma, they show a distinctively different behaviour towards conventional PKC substrates such as histone, myelin basic protein, protamine and protamine sulphate, suggesting either that phorbol esters are not able to fully activate these enzymes or that their substrate specificities are very different from those of the group A enzymes. PKC-zeta, a polypeptide of 80 kDa, does not bind phorbol ester and does not phosphorylate these substrates to a significant extent. Consistent with their ability to bind phorbol ester, recombinant PKC-delta and PKC-epsilon are down-regulated in COS cells by prolonged treatment with phorbol ester, whereas PKC-zeta protein levels remain unaltered.

Animals↗
PubMed1989

Calmodulin as substrate for insulin-receptor kinase. Phosphorylation by receptors from rat skeletal muscle.

Calmodulin is a substrate for insulin-receptor kinase obtained from rat adipocytes and hepatocytes and human placenta. In this study, we demonstrate that insulin stimulates the phosphorylation of calmodulin via insulin receptors partially purified from rat skeletal muscle. Phosphorylation of calmodulin was maximal in the presence of Mg2+ and insulin and the absence of Ca2+. Free-Ca2+ concentrations greater than 0.1 microM progressively inhibited phosphorylation with almost total inhibition at 200 microM Ca2+. Insulin-stimulated phosphorylation of calmodulin was dose dependent and saturable with half-maximal effect obtained at approximately 5 x 10(-10) M insulin. There was an absolute requirement for certain basic proteins, e.g., polylysine or protamine sulfate, to obtain phosphate incorporation into calmodulin. Polylysine stimulated the phosphorylation of calmodulin independently of insulin, but this was increased up to sixfold by the addition of insulin. Phosphate incorporation into calmodulin increased with increasing concentration of the substrate up to a saturating concentration of 2.4 microM. The Km for calmodulin was approximately 0.2 microM. Up to 0.15 mol of phosphate was incorporated per mole of calmodulin with tyrosine the predominant amino acid phosphorylated. The observations that calmodulin is phosphorylated by insulin-receptor kinase from all three classic target organs for insulin confirm that calmodulin is a general substrate for this kinase and suggest that Ca2+ and calmodulin may be components of the insulin-signaling mechanism.

Amino Acids↗
PubMed1999

An unusual manifestation of diabetes mellitus.

MEDICAL HISTORY: Type 2 diabetes mellitus for five years; unexplained 35-lb weight loss three years ago; Bell's palsy on right side many years ago. MEDICATIONS: Glipizide, 10 mg/day. FAMILY HISTORY: Father died of leukemia at age 65; mother has kidney stones; no diabetes or neuromuscular disease. SOCIAL HISTORY: Insurance salesman; heterosexual, promiscuous, uses condoms; smokes (25 pack years); does not drink. PHYSICAL EXAMINATION: Well-nourished, well developed, not in acute distress; had difficulty rising from a sitting position because of right lower extremity weakness. Blood pressure, 154/74; pulse, 88; temperature, 36.6 degrees C; respiratory rate, 16. Head, eyes, ears, nose, and throat: normal. Neck: normal. Heart: S4. Lungs: clear. Abdomen: mildly obese. Extremities: no cyanosis, clubbing, or edema; atrophy and weakness of right thigh and both calves; wide-based gait; able to walk on toes but not heels. Neurologic responses: cranial nerves intact; deep tendon reflexes, 1 + symmetrically; plantar reflexes, flexor bilaterally. Skin: macular rash in sun-exposed areas. LABORATORY FINDINGS: Hemoglobin, 13.2 gm/dL; mean corpuscular volume, 80 micron 3; white blood cell count, 7,200/mm3 (normal differential); platelet count, 137,000/mm3. Serum: electrolytes, normal; blood urea nitrogen, 18 mg/dL; creatinine, 0.8 mg/dL; glucose, 308 mg/dL; total protein, albumin, liver enzymes, and creatine kinase, normal. Urine: 1 + glucose. Venereal disease test: nonreactive; HIV test: negative. DIFFERENTIAL DIAGNOSIS: Dermatomyositis; heavy-metal poisoning; diabetic amyotrophy. HOSPITAL COURSE: The patient was given 50 mg/day of oral amitriptyline to alleviate the painful paresthesias and was switched to 20 U/day of subcutaneously injected neutral protamine Hagedorn (NPH) insulin to normalize the blood glucose level. Histologic studies of skin and muscle showed sun damage and neuropathic changes, respectively. There was no evidence of vasculitis. Screening for heavy-metal toxins produced negative results.

Diabetes Mellitus, Type 2↗
PubMed1983

Histone H1-stimulated phosphorylase phosphatase from rabbit skeletal muscle.

A major rabbit skeletal muscle phosphorylase phosphatase activity which is markedly stimulated by histone H1 has been resolved from inhibitor-sensitive phosphorylase phosphatase (type-1 phosphatase), glycogen synthase kinase 3-activated phosphatase, phosphatase heat-stable inhibitor proteins, and alkaline phosphatase activity by various purification techniques. Evidence is presented that this phosphatase is a high-molecular weight form of a type-2 phosphatase. Our data suggest that this phosphatase may be regulated by histone H1, protamine or analogous polycationic compounds.

Animals↗