Protein kinase C isoenzymes: a review of their structure, regulation and role in regulating airways smooth muscle tone and mitogenesis.
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Animals↗
Biomedical subjects
B L Webb
Publications and source records attributed to B L Webb.
v-Src generates a p53-independent apoptotic signal.
Evasion of apoptosis appears to be a necessary event in tumor progression. Some oncogenes, such as c-myc and E1A, induce apoptosis in the absence of survival factors. However, others, such as bcl-2 and v-src, activate antiapoptotic pathways. For v-Src, these antiapoptotic pathways are dependent on the function of Ras, phosphatidylinositol (PI) 3-kinase, and Stat3. Here we asked whether v-Src can activate a proapoptotic signal when survival signaling is inhibited. We show that when the functions of Ras and PI 3-kinase are inhibited, v-src-transformed Rat-2 fibroblasts undergo apoptosis, evidenced by loss of adherence, nuclear fragmentation, and chromosomal DNA degradation. The apoptotic response is dependent on activation of caspase 3. Under similar conditions nontransformed Rat-2 cells undergo considerably lower levels of apoptosis. Apoptosis induced by v-Src is accompanied by a loss of mitochondrial membrane potential and release of cytochrome c and is blocked by overexpression of bcl-2, indicating that it is mediated by the mitochondrial pathway. However apoptosis induced by v-Src is not accompanied by an increase in the level of p53 and is not dependent on p53 function. Thus v-Src generates a p53-independent proapoptotic signal.
Amino Acid Chloromethyl Ketones↗
ATP hydrolysis and DNA binding by the Escherichia coli RecF protein.
The Escherichia coli RecF protein possesses a weak ATP hydrolytic activity. ATP hydrolysis leads to RecF dissociation from double-stranded (ds)DNA. The RecF protein is subject to precipitation and an accompanying inactivation in vitro when not bound to DNA. A mutant RecF protein that can bind but cannot hydrolyze ATP (RecF K36R) does not readily dissociate from dsDNA in the presence of ATP. This is in contrast to the limited dsDNA binding observed for wild-type RecF protein in the presence of ATP but is similar to dsDNA binding by wild-type RecF binding in the presence of the nonhydrolyzable ATP analog, adenosine 5'-O-(3-thio)triphosphate (ATPgammaS). In addition, wild-type RecF protein binds tightly to dsDNA in the presence of ATP at low pH where its ATPase activity is blocked. A transfer of RecF protein from labeled to unlabeled dsDNA is observed in the presence of ATP but not ATPgammaS. The transfer is slowed considerably when the RecR protein is also present. In competition experiments, RecF protein appears to bind at random locations on dsDNA and exhibits no special affinity for single strand/double strand junctions when bound to gapped DNA. Possible roles for the ATPase activity of RecF in the regulation of recombinational DNA repair are discussed.
Adenosine Triphosphatases↗
Expression and activation of protein kinase C-zeta in eosinophils after allergen challenge.
Protein kinase (PK) C is an increasingly diverse family of enzymes that has been implicated in a range of cellular functions within the eosinophil. Using isoform-specific polyclonal antibodies, we have explored the expression of PKC isoforms in circulating eosinophils. Initial studies demonstrated the presence of the alpha, betaI, betaII, and zeta and the low-level expression of the delta, epsilon, iota, and micro isoforms but no detectable expression of the gamma, eta, and theta isoforms in both normal and asthmatic subjects. There was no difference in the total protein expression between these two groups. Subsequent studies examined the expression and activation of PKC isoforms in circulating eosinophils from asthmatic patients before and 24 h after a late asthmatic response to an inhaled allergen. Cellular fractionation showed PKC-alpha and PKC-betaII to be mainly located in the cytosol, whereas PKC-betaI was constitutively more expressed in the membrane. No changes in expression or subcellular localization of these isoforms were seen after allergen challenge. In contrast, PKC-zeta expression was increased after allergen challenge, and we demonstrated a significant PKC-zeta translocation to the membrane, in keeping with activation of the enzyme. Our results suggest that 24 h after allergen exposure of asthmatic patients, there is increased expression and activation of eosinophil PKC-zeta that correlates with late asthmatic responses recorded between 4 and 10 h postallergen challenge.
Adult↗
The phosphorylation of eukaryotic initiation factor eIF4E in response to phorbol esters, cell stresses, and cytokines is mediated by distinct MAP kinase pathways.
Initiation factor eIF4E binds to the 5'-cap of eukaryotic mRNAs and plays a key role in the mechanism and regulation of translation. It may be regulated through its own phosphorylation and through inhibitory binding proteins (4E-BPs), which modulate its availability for initiation complex assembly. eIF4E phosphorylation is enhanced by phorbol esters. We show, using specific inhibitors, that this involves both the p38 mitogen-activated protein (MAP) kinase and Erk signaling pathways. Cell stresses such as arsenite and anisomycin and the cytokines tumor necrosis factor-alpha and interleukin-1beta also cause increased phosphorylation of eIF4E, which is abolished by the specific p38 MAP kinase inhibitor, SB203580. These changes in eIF4E phosphorylation parallel the activity of the eIF4E kinase, Mnk1. However other stresses such as heat shock, sorbitol, and H2O2, which also stimulate p38 MAP kinase and increase Mnk1 activity, do not increase phosphorylation of eIF4E. The latter stresses increase the binding of eIF4E to 4E-BP1, and we show that this blocks the phosphorylation of eIF4E by Mnk1 in vitro, which may explain the absence of an increase in eIF4E phosphorylation under these conditions.
Animals↗
Recombinational DNA repair: the RecF and RecR proteins limit the extension of RecA filaments beyond single-strand DNA gaps.
In the presence of both the RecF and RecR proteins, RecA filament extension from a single strand gap into adjoining duplex DNA is attenuated. RecR protein alone has no effect, and RecF protein alone has a reduced activity. The RecFR complexes bind randomly, primarily to the duplex regions of the DNA, and the extension of the RecA filament is halted at the first complex encountered. A very slow lengthening of RecA filaments observed in the presence of RecFR is virtually eliminated when RecF is replaced with an RecF mutant protein that does not hydrolyze ATP. These observations are incorporated into an expanded model for the functions of RecF, RecO, and RecR proteins in the early stages of postreplication DNA repair.
Bacterial Proteins↗
Identification of the protein kinase C isoenzymes in human lung and airways smooth muscle at the protein and mRNA level.
The protein kinase C (PKC) isoenzymes expressed by human peripheral lung and tracheal smooth muscle resected from individuals undergoing heart-lung transplantation were identified at the protein and mRNA level. Western immunoblot analyses of human lung identified multiple PKC isoenzymes that were differentially distributed between the soluble and particulate fraction. Thus, PKC alpha, PKC betaII, PKC epsilon, and PKC zeta were recovered predominantly in the soluble fraction whereas the eta isoform was membrane-associated together with trace amounts of PKC alpha and PKC epsilon. PKC beta1-like immunoreactivity was occasionally seen although the intensity of the band was uniformly weak. Immunoreactive bands corresponding to PKCs gamma, delta, or theta were never detected. Reverse transcription-polymerase chain reaction (RT-PCR) of RNA extracted from human lung using oligonucleotide primer pairs that recognise unique sequences in each of the PKC genes amplified cDNA fragments that corresponded to the predicted sizes of PKC alpha, PKC betaI, PKC betaII, PKC epsilon, PKC zeta, and PKC eta (consistent with the expression of PKC isoenzyme protein) and, in addition, mRNA for PKC delta; PCR fragments of the expected size for the supposedly muscle-specific isoform, PKC theta, or the atypical isoenzyme, PKC lambda, were never obtained. The complement and distribution of PKC isoforms in human trachealis were similar, but not identical, to human lung. Thus, immunoreactive bands corresponding to the alpha, betaI, betaII, epsilon, and zeta isoenzymes of PKC were routinely labelled in the cytosolic fraction. In the particulate material PKC alpha, PKC epsilon, PKC alpha, PKC eta, and PKC mu were detected by immunoblotting. With the exception of PKC zeta, RT-PCR analyses confirmed the expression of the PKC isoforms detected at the protein level and, in addition, identified mRNA for PKC delta. Collectively, these data clearly demonstrate the expression of multiple PKC isoenzymes in human lung and tracheal smooth muscle, suggesting that they subserve diverse multifunctional roles in these tissues.
Adult↗
Protein kinase C isoenzymes in airway smooth muscle.
The protein kinase C (PKC) isoenzymes expressed by bovine tracheal smooth muscle (BTSM) were identified at the protein and mRNA levels. Western immunoblot analyses reliably identified PKCalpha, PKCbetaI and PKCbetaII. In some experiments immunoreactive bands corresponding to PKCdelta, PKCepsilon and PKCTheta were also labelled, whereas the gamma, eta and zeta isoforms of PKC were never detected. Reverse transcriptase PCR of RNA extracted from BTSM using oligonucleotide primer pairs designed to recognize unique sequences in the PKC genes for which protein was absent or not reproducibly identified by immunoblotting, amplified cDNA fragments that corresponded to the predicted sizes of PKCdelta, PKCepsilon and PKCzeta, which was confirmed by Southern blotting. Anion-exchange chromatography of the soluble fraction of BTSM following homogenization in Ca2+-free buffer resolved two major peaks of activity. Using epsilon-peptide as the substrate, the first peak of activity was dependent upon Ca2+ and 4beta-PDBu (PDBu=phorbol 12, 13-dibutyrate), and represented a mixture of PKCs alpha, betaI and betaII. In contrast, the second peak of activity, which eluted at much higher ionic strength, also appeared to comprise a combination of conventional PKCs that were arbitrarily denoted PKCalpha', PKCbetaI' and PKCbetaII'. However, these novel enzymes were cofactor-independent and did not bind [3H]PDBu, but were equally sensitive to the PKC inhibitor GF 109203X compared with bona fide conventional PKCs, and migrated on SDS/polyacrylamide gels as 81 kDa polypeptides. Taken together, these data suggest that PKCs alpha', betaI' and betaII' represent modified, but not proteolysed, forms of their respective native enzymes that retain antibody immunoreactivity and sensitivity to PKC inhibitors, but have lost their sensitivity to Ca2+ and PDBu when epsilon-peptide is used as the substrate.
Animals↗
RecA protein filaments: end-dependent dissociation from ssDNA and stabilization by RecO and RecR proteins.
RecA protein filaments formed on circular (ssDNA) in the presence of ssDNA binding protein (SSB) are generally stable as long as ATP is regenerated. On linear ssDNA, stable RecA filaments are believed to be formed by nucleation at random sites on the DNA followed by filament extension in the 5' to 3' direction. This view must now be enlarged as we demonstrate that RecA filaments formed on linear ssDNA are subject to a previously undetected end-dependent disassembly process. RecA protein slowly dissociates from one filament end and is replaced by SSB. The results are most consistent with disassembly from the filament end nearest the 5' end of the DNA. The bound SSB prevents re-formation of the RecA filaments, rendering the dissociation largely irreversible. The dissociation requires ATP hydrolysis. Disassembly is not observed when the pH is lowered to 6.3 or when dATP replaces ATP. Disassembly is not observed even with ATP when both the RecO and RecR proteins are present in the initial reaction mixture. When the RecO and RecR proteins are added after most of the RecA protein has already dissociated, RecA protein filaments re-form after a short lag. The newly formed filaments contain an amount of RecA protein and exhibit an ATP hydrolysis rate comparable to that observed when the RecO and RecR proteins are included in the initial reaction mixture. The RecO and RecR proteins thereby stabilize RecA filaments even at the 5' ends of ssDNA, a fact which should affect the recombination potential of 5' ends relative to 3' ends. The location and length of RecA filaments involved in recombinational DNA repair is dictated by both the assembly and disassembly processes, as well as by the presence or absence of a variety of other proteins that can modulate either process.
Bacterial Proteins↗
Eukaryotic initiation factor 2B (eIF2B).
Eukaryotic initiation factor 2B (eIF2B) is a guanine nucleotide-exchange factor which mediates the exchange of GDP (bound to initiation factor eIF2) for GTP, thus regenerating the active [eIF2.GTP] complex that is required for peptide-chain initiation. The activity of eIF2B is a key control point for eukaryotic protein synthesis and is altered in response to viral infection, hormones, nutrients, growth factors and certain stresses. It may be regulated directly by its own phosphorylation, phosphorylation of its substrate, eIF2 and by allosteric effectors. Understanding its regulation will lead to a better knowledge of insulin action, regulation of the immune system and of insulin production in the pancreas.
Allosteric Regulation↗
Air National Guard promotes EMS training.
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Emergency Medical Technicians↗
Beta-Adrenoceptor-medicated down-regulation of M2 muscarinic receptors: role of cyclic adenosine 5'-monophosphate-dependent protein kinase and protein kinase C.
Stimulation of beta2-adrenoceptors with the selective beta2 agonist procaterol caused a biphasic decrease in cell surface M2 muscarinic receptor number in human embryonic lung 299 cells when measured with the hydrophilic antagonist [3H]N-methylscopolamine. In contrast, total muscarinic receptor number, measured with the lipophilic antagonist [3H]quinuclidinylbenzilate, decreased after only 24-hr treatments with procaterol. The loss in receptor number at 24 hr was mimicked with the use of forskolin and the cAMP analogue 8-bromo-cAMP, indicating a cAMP-mediated mechanism. Northern blot analysis showed a small and transient increase in m2-receptor mRNA levels up to 2 hr but no long term (24 hr) effect. Chronic (24 hr) treatment with 8-bromo-cAMP also had no effect on m2 muscarinic receptor mRNA, whereas forskolin caused a 50% reduction in the steady state levels of m2 mRNA that could be only partially blocked by the cAMP-dependent protein kinase inhibitor H-8 and the protein kinase C inhibitor GF 109203X. Procaterol-induced down-regulation of M2 receptors was fully blocked by N-[2-(methylamino)ethyl]-5'-isoquinoline-sulfonamide and 2-[1-(3-dimethylaminopropyl)-inol-3-yl]-3-(indol-3-yl)maleimide, implicating both of these kinases in the M2 muscarinic receptor down-regulation. Conversely, the forskolin- and 8-bromo-cAMP-induced down-regulation was only partially inhibited and unaffected by these inhibitors, respectively. In control cells and those treated with procaterol for < / = 2 hr, cAMP generation was significantly inhibited by carbachol. The inhibitory effect of carbachol was, however, lost after 24-hr exposure to procaterol. This desensitization was partially reversed by preincubations with H-8 and GF 109203X. Collectively, these results suggest that transregulation of M2 muscarinic receptors by beta2-adrenoceptor stimulation can be demonstrated at the protein level in human embryonic lung 299 cells. Furthermore, a role is suggested for cAMP-dependent kinase and PKC in M2 muscarinic receptor down-regulation and their functional desensitization.
Cyclic AMP-Dependent Protein Kinases↗
An interaction between the Escherichia coli RecF and RecR proteins dependent on ATP and double-stranded DNA.
The DNA binding and ATPase activities of RecF protein are modulated by RecR protein. Stoichiometric amounts of RecF protein bind to double-stranded (ds) DNA (about 1 RecF monomer/4-6 base pairs) in the presence of adenosine 5'-O-(3-thio)triphosphate (ATP gamma S), forming a homogeneous protein coating on the DNA. Little or no cooperativity is evident in the binding process. In the presence of ATP, RecF binding to dsDNA is much weaker, and no RecF protein coating forms. Instead, small numbers of RecF protomers are interspersed randomly along the DNA. RecR protein does not bind appreciably to the dsDNA under these same conditions. However, a protein coating, similar to that which was observed with RecF protein alone in the presence of ATP gamma S, was produced when both RecF and RecR proteins were incubated with dsDNA in the presence of ATP. An interaction between RecF and RecR enables both proteins to bind tightly to the dsDNA in an approximately 1:1 molar ratio. We also report a weak ATP hydrolytic activity of RecF which is stimulated by RecR.
Adenosine Triphosphatases↗
Inhibition of fetal calf serum-stimulated proliferation of rabbit cultured tracheal smooth muscle cells by selective inhibitors of protein kinase C and protein tyrosine kinase.
Severe chronic asthma is associated with structural changes in the airway wall including airway smooth muscle (ASM) hyperplasia. We have used cultured ASM cells isolated from rabbit trachealis as a model with which to investigate possible mechanisms of accelerated ASM growth to mitogenic stimuli. To elucidate the role that protein kinase C (PKC)- and protein tyrosine kinase (PTK)-dependent pathways play in the control of ASM mitogenesis, we have investigated the effect of reportedly selective inhibitors of PKC (3-[1-[3-(amidinothio)propyl]-3-indolyl]-4-(1-methyl-3-indolyl)-1H - pyrrole-2,5-dionemethanesulfonate [Ro31-8220] and 3-[1-(aminopropyl)indolyl]-4-(1-methyl-3-indolyl)-1H-pyrrole-2,5-dione acetate [Ro31-7549]) and PTK (alpha-cyano-3-ethoxy-4-hydroxy-5-phenylthiomethylcinnamamide [ST638]) on partially purified PKC, fetal calf serum (FCS)-stimulated protein phosphotyrosine content and on FCS-induced proliferation. Anion-exchange chromatography of lysed ASM cells resolved two peaks of Ca(2+)-activated, phospholipid-dependent PKC activity and one peak of Ca(2+)- and phospholipid-independent PKC activity. The selective PKC inhibitors, Ro31-8220 and Ro31-7549, abolished the main peak of PKC activity and the Ca(2+)- and phospholipid-independent peak that co-eluted with the main peak. The inhibition was dependent on the concentration of ATP in the reaction cocktail (IC50: 10 microM ATP: Ro31-8220 0.026 microM, Ro31-7549 0.073 microM; 100 microM ATP: Ro31-8220 0.065 microM, Ro31-7549 0.271 microM), consistent with these compounds inhibiting PKC at the ATP-binding site. Ro31-8220 was more potent (2- to 3-fold) than Ro31-7549. Concentrations of each inhibitor that produced maximal inhibition of the pooled kinase activity also abolished the second peak of Ca(2+)-dependent activity. The PTK inhibitor, ST638, had no effect on the kinase activity associated with any of the Ca(2+)-dependent or -independent peaks that eluted from the column. ST638, however, maximally inhibited FCS-stimulated PTK activity (IC50 25 microM). FCS-stimulated PTK was also inhibited by Ro31-8220 (IC50 0.15 microM), but only by 60%, revealing an Ro31-8220-insensitive component to the response. The ability of each protein kinase inhibitor to inhibit proliferation was also studied using four independent indices of ASM cell growth and division: 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) dye conversion, Coomassie blue protein determination, hemacytometer cell counts, and DNA synthesis. Ro31-8220 and Ro31-7549 produced concentration-dependent inhibition of FCS-stimulated proliferation of growth-arrested ASM cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗