Mouse protein kinase C-delta, the major isoform expressed in mouse hemopoietic cells: sequence of the cDNA, expression patterns, and characterization of the protein

Phorbol 12-myristate 13-acetate-stimulated phosphorylation of erythrocyte membrane skeletal proteins is blocked by calpain inhibitors: possible role of protein kinase M

Human erythrocytes contain cytosolic protein kinase C (PKC) which, when activated by phorbol 12-myristate 13-acetate (PMA), induces the phosphorylation of the membrane skeletal proteins band 4.1, band 4.9 and adducin. We found that brief treatments of erythrocytes with PMA resulted in a decrease in cytosolic PKC content and in the transient appearance in the cytosol of a Ca(2+)- and phospholipid-independent 55 kDa fragment of PKC, called PKM. Prolonged treatment with PMA resulted in the complete and irreversible loss of erythrocyte PKC. To investigate the possible role of calpain in this process, the calpain inhibitors leupeptin and E-64 were sealed inside erythrocytes by reversible haemolysis. Both inhibitors prolonged the lifetime of PKC in PMA-treated cells, and leupeptin was shown to block the PMA-stimulated appearance of PKM in the cytosol. Significantly, leupeptin also completely blocked PMA-stimulated phosphorylation of membrane and cytosolic substrates. This effect was mimicked by other calpain inhibitors (MDL-28170 and calpain inhibitor I), but did not occur when other protease inhibitors such as phenylmethanesulphonyl fluoride, pepstatin A or chymostatin were used. In addition, the phosphorylation of exogenous histone sealed inside erythrocytes was also blocked by leupeptin. Immunoblotting showed that leupeptin did not prevent the PMA-induced translocation of PKC to the erythrocyte membrane. Thus inhibition of PKC phosphorylation of membrane skeletal proteins by calpain inhibitors was not due to inhibition of PKC translocation to the membrane. Our results suggest that PMA treatment of erythrocytes results in the translocation of PKC to the plasma membrane, followed by calpain-mediated cleavage of PKC to PKM. This cleavage, or some other leupeptin-inhibitable process, is a necessary step for the phosphorylation of membrane skeletal substrates, suggesting that the short-lived PKM may be responsible for membrane skeletal phosphorylation. Our results suggest a potential mechanism whereby erythrocyte PKC may be subject to continual down-regulation during the lifespan of the erythrocyte due to repeated activation events, possibly related to transient Ca2+ influx. Such down-regulation may play an important role in erythrocyte survival or pathophysiology.

Regulation of delta protein kinase C during rat ovarian differentiation

Studies were undertaken to classify protein kinase C (PKC) forms present in rat corpora lutea and to begin to evaluate their regulation during ovarian differentiation. Hydroxyapatite (HAP) column chromatography of rat luteal tissue revealed the presence of multiple forms of PKC (alpha, beta, delta, zeta). Identification of the PKC isoforms was based upon elution positions from HAP column chromatography and immunoreactivity. The delta PKC isoform was identified as the major Ca(2+)-independent form of PKC present in rat luteal tissue. The Ca(2+)-independent, lipid-dependent phosphorylation of the 80-kDa delta PKC was readily detectable in soluble luteal extracts and was shown to reflect autophosphorylation of delta PKC. To evaluate the regulation of PKC isoforms during ovarian differentiation, PKC protein levels were compared between preovulatory follicle-enriched ovaries and corpora lutea obtained on day 16 of pregnancy. Levels of delta PKC protein were greatly elevated in corpora lutea compared to levels in preovulatory follicles. In contrast, levels of alpha and beta PKC protein remained constant while levels of zeta PKC were slightly higher in the follicular than the luteal extract. Levels of delta PKC mRNA were also higher in corpora lutea than in preovulatory follicles. These results are the first to demonstrate the physiological regulation of delta PKC with follicular differentiation into corpora lutea and implicate a role for this prominent PKC form in the corpus luteum during pregnancy.

Molecular and biochemical characterization of a recombinant human PKC-delta family member

Two cDNA clones coding for the human protein kinase C-delta (PKC-delta) were fortuitously isolated during the process of screening a human library for a cDNA clone of an unrelated protein, the nucleolar protein fibrillarin. The two human homologues have about 88% nucleotide sequence identity to the rat and mouse PKC-delta cDNA clones. A comparison of the predicted amino acid sequences of the two human PKC-delta clones with the rat and mouse homologues indicated a greater degree of sequence divergence (89-90% homology) compared to the high degree of sequence conservation observed with other human PKC family members and their mammalian counterparts. Expression of the clones in the baculovirus insect-cell expression system indicated that both proteins exhibited phorbol ester binding activity, and were dependent upon phosphatidylserine and diacylglycerol for maximal activation. Further characterization of the properties of the human PKC-delta revealed substrate and lipid dependencies distinct from other members of the protein kinase C family; including PKC-deltas isolated from other species. The dissimilarities in the predicted amino acid sequences between the human and other mammalian species could account in part for some of these observed biochemical differences.

Unique expression pattern of protein kinase C-theta: high mRNA levels in normal mouse testes and in T-lymphocytic cells and neoplasms

A 2.2-kb cDNA that contains the entire coding region of mouse protein kinase C-theta (PKC-theta) was cloned from skeletal muscle mRNA using reverse transcription and the polymerase chain reaction (PCR). This clone was used as a probe to study the expression of this PKC isoform in normal and transformed hemopoietic cells and other normal tissues. By far the highest steady-state level of PKC-theta mRNA was found as a 2.8-kb transcript on a Northern blot of poly(A)+ RNA from testes. High levels were also found in skeletal muscle, spleen, T lymphomas and purified normal T lymphocytes, but these tissues and cells expressed two transcripts, 3.3 kb and 3.8 kb. Lower levels of similar size transcripts were found in normal brain, B lymphocytes and B-lymphocytic tumors and cell lines.

An okadaic acid-sensitive protein phosphatase counteracts protein kinase C-induced phosphorylation in SH-SY5Y cells

Protein phosphorylation and subsequent dephosphorylation was studied in digitonin-permeabilized neuroblastoma SH-SY5Y cells by measuring the incorporation of [32P]phosphate into myelin basic protein (MBP). 1,2-Dioctanoyl-sn-glycerol (DOG) and calcium synergistically induced phosphorylation of MBP, which was inhibited by the protein kinase C (PKC) pseudosubstrate peptide (PKC19-36). The phosphorylation increased for 10 min when a net dephosphorylation started to appear. The dephosphorylation was inhibited by okadaic acid. Regardless of calcium concentration, the presence of DOG was necessary for significant effects of okadaic acid on MBP phosphorylation. H7 and staurosporine dose-dependently inhibited the phosphorylation of MBP, induced by DOG and calcium in the presence of okadaic acid. Different PKC pseudosubstrate peptides were applied and all showed an inhibitory effect on the phosphorylation of MBP under these conditions. These results demonstrate the presence, in SH-SY5Y cells, of a protein phosphatase, possibly protein phosphatase 2A, with a high basal activity that counteracts PKC-induced phosphorylation.

Protein kinase C isoenzymes: divergence in signal transduction?

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Phosphatidylcholine hydrolysis and c-myc expression are in collaborating mitogenic pathways activated by colony-stimulating factor 1

Stimulation of diglyceride production via phospholipase C (PLC) hydrolysis of phosphatidylcholine was an early event in the mitogenic action of colony-stimulating factor 1 (CSF-1) in the murine macrophage cell line BAC1.2F5 and was followed by a second phase of diglyceride production that persisted throughout the G1 phase of the cell cycle. Addition of phosphatidylcholine-specific PLC (PC-PLC) from Bacillus cereus to the medium of quiescent cells raised the intracellular diglyceride concentration and stimulated [3H]thymidine incorporation, although PC-PLC did not support continuous proliferation. PC-PLC treatment did not induce tyrosine phosphorylation or turnover of the CSF-1 receptor. The major protein kinase C (PKC) isotype in BAC1.2F5 cells was PKC-delta. Diglyceride production from PC-PLC did not target PKC-delta, since unlike phorbol esters, PC-PLC treatment neither decreased the electrophoretic mobility of PKC-delta nor increased the amount of GTP bound to Ras, and PC-PLC was mitogenically active in BAC1.2F5 cells in which PKC-delta was downregulated by prolonged treatment with phorbol ester. PC-PLC mimicked CSF-1 action by elevating c-fos and junB mRNAs to 40% of the level induced by CSF-1; however, PC-PLC induced c-myc mRNA to only 5% of the level in CSF-1-stimulated cells. PC-PLC addition to CSF-1-dependent BAC1.2F5 clones that constitutively express c-myc increased [3H]thymidine incorporation to 86% of the level evoked by CSF-1 and supported slow growth in the absence of CSF-1. Therefore, PC-PLC is a component of a signal transduction pathway leading to transcription of c-fos and junB that collaborates with c-myc and is independent of PKC-delta and Ras activation.

Phosphatidylcholine hydrolysis and c-myc expression are in collaborating mitogenic pathways activated by colony-stimulating factor 1

Stimulation of diglyceride production via phospholipase C (PLC) hydrolysis of phosphatidylcholine was an early event in the mitogenic action of colony-stimulating factor 1 (CSF-1) in the murine macrophage cell line BAC1.2F5 and was followed by a second phase of diglyceride production that persisted throughout the G1 phase of the cell cycle. Addition of phosphatidylcholine-specific PLC (PC-PLC) from Bacillus cereus to the medium of quiescent cells raised the intracellular diglyceride concentration and stimulated [3H]thymidine incorporation, although PC-PLC did not support continuous proliferation. PC-PLC treatment did not induce tyrosine phosphorylation or turnover of the CSF-1 receptor. The major protein kinase C (PKC) isotype in BAC1.2F5 cells was PKC-delta. Diglyceride production from PC-PLC did not target PKC-delta, since unlike phorbol esters, PC-PLC treatment neither decreased the electrophoretic mobility of PKC-delta nor increased the amount of GTP bound to Ras, and PC-PLC was mitogenically active in BAC1.2F5 cells in which PKC-delta was downregulated by prolonged treatment with phorbol ester. PC-PLC mimicked CSF-1 action by elevating c-fos and junB mRNAs to 40% of the level induced by CSF-1; however, PC-PLC induced c-myc mRNA to only 5% of the level in CSF-1-stimulated cells. PC-PLC addition to CSF-1-dependent BAC1.2F5 clones that constitutively express c-myc increased [3H]thymidine incorporation to 86% of the level evoked by CSF-1 and supported slow growth in the absence of CSF-1. Therefore, PC-PLC is a component of a signal transduction pathway leading to transcription of c-fos and junB that collaborates with c-myc and is independent of PKC-delta and Ras activation.

Isolation and sequence of a mouse brain cDNA coding for protein kinase C-gamma isozyme

The regulatory enzyme, protein kinase C (PKC), is characterized by a family of related isozymes. Currently, nucleotide (nt) sequences for seven members of this family have been reported from the bovine, human and rat genomes. Only four of these seven PKC isoforms have been isolated in mouse: alpha, beta II, delta and epsilon. Here, we report the cDNA sequence encoding mouse PKC-gamma isolated from a C57BL/6 brain cDNA library. The mouse and rat PKC-gamma nt and deduced amino acid sequences share 97 and 100% identity, respectively.

Localization and developmental expression of a novel protein kinase C delta gene

The expression and localization of a novel protein kinase C delta (nPKC delta) mRNA were investigated using Northern blotting and in situ hybridization in the developmental process of mouse brain. In adult mice, nPKC delta was abundantly expressed in the thalamus, moderately in the pons and the cerebellum, but faintly in the cerebral cortex and the spinal cord. By in situ hybridization, the signals were observed specifically at the sensory and motor relay nuclei of the thalamus, the dorsal cochlear nuclei of the pons, and the molecular layer of the cerebellum. When developmental changes in the expression of nPKC delta gene were analyzed by in situ hybridization, it was not detectable in embryonic and neonatal brains, very weakly expressed in the thalamus in the first week, and highly expressed at two weeks of age. These results suggest that the gene expression of nPKC delta is strictly controlled by both the cell type and the developmental process.

The cDNA sequence, expression pattern and protein characteristics of mouse protein kinase C-zeta

A 2199-bp complementary DNA (cDNA) that encodes protein kinase C-zeta (PKC-zeta) has been isolated from mouse brain by a combination of reverse transcription and primer extension. The predicted PKC-zeta protein consists of 592 amino acids which are 99% identical to those of rat PKC-zeta. Northern blots that were probed with this cDNA revealed abundant 2200-nucleotide (nt) and 4200-nt PKC-zeta mRNAs in mouse brain in roughly equal amounts. PKC-zeta mRNA was also abundant in normal lung, kidney, and testes, and in several hemopoietic tumor lines. In all other mouse tissues and cell lines that were examined, at least faint levels of PKC-zeta mRNAs could also be detected. In tissues other than brain, the amount of PKC-zeta mRNA was less, and the smaller species generally predominated. Furthermore, in these tissues, both PKC-zeta mRNAs appear to be approximately 200 nt longer than the two mRNAs found in the brain. When the cDNA is expressed in insect cells via a baculovirus expression vector, a 75-kDa protein is synthesized which, unlike other PKC isoforms, does not bind phorbol ester, even at very high concentrations.

Cell division arrest induced by phorbol ester in CHO cells overexpressing protein kinase C-delta subspecies

Several lines of CHO cells stably overexpressing protein kinase C (PKC) subspecies to various extents were established by the DNA-mediated transfer. Upon treatment with phorbol 12-myristate 13-acetate, the growth of the cells expressing the PKC-delta subspecies was markedly inhibited, whereas cell lines expressing PKC-alpha, PKC-beta II, and PKC-zeta subspecies were not significantly affected. Flow cytometric analysis indicated that all cell lines overexpressing PKC-delta subspecies accumulated in G2/M phase in response to phorbol 12-myristate 13-acetate. In these arrested cells, dikaryons were predominant, implying that phorbol ester-induced inhibition of cell division is specific to telophase. These results suggest PKC-delta subspecies may play a role in the normal cell cycle progression.

A new member of the protein kinase C family, nPKC theta, predominantly expressed in skeletal muscle

A new protein kinase C (PKC)-related cDNA with unique tissue distribution has been isolated and characterized. This cDNA encodes a protein, nPKC theta, which consists of 707 amino acid residues and showed the highest sequence similarity to nPKC delta (67.0% in total). nPKC theta has a zinc-finger-like cysteine-rich sequence (C1 region) and a protein kinase domain sequence (C3 region), both of which are common in all PKC family members. However, nPKC theta lacks a putative Ca2+ binding region (C2 region) that is seen only in the conventional PKC subfamily (cPKC alpha, -beta I, -beta II, and -gamma) but not in the novel PKC subfamily (nPKC delta, -epsilon, -zeta, and -eta). Northern (RNA) blot analyses revealed that the mRNA for nPKC theta is expressed predominantly in skeletal muscle. Furthermore, nPKC theta mRNA is the most abundantly expressed PKC isoform in skeletal muscle among the nine PKC family members. nPKC theta expressed in COS1 cells serves as a phorbol ester receptor. By the use of an antipeptide antibody specific to the D2-D3 region of the nPKC theta sequence, nPKC theta was recognized as a 79-kDa protein upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis in mouse skeletal muscle extract and also in an extract from COS1 cells transfected with an nPKC theta cDNA expression plasmid. Autophosphorylation of immunoprecipitated nPKC theta was observed; it was enhanced by phosphatidylserine and 12-O-tetradecanoylphorbol-13-acetate but attenuated by the addition of Ca2+. These results clearly demonstrate that nPKC theta should be considered a member of the PKC family of proteins that play crucial roles in the signal transduction pathway.

A new member of the protein kinase C family, nPKC theta, predominantly expressed in skeletal muscle

A new protein kinase C (PKC)-related cDNA with unique tissue distribution has been isolated and characterized. This cDNA encodes a protein, nPKC theta, which consists of 707 amino acid residues and showed the highest sequence similarity to nPKC delta (67.0% in total). nPKC theta has a zinc-finger-like cysteine-rich sequence (C1 region) and a protein kinase domain sequence (C3 region), both of which are common in all PKC family members. However, nPKC theta lacks a putative Ca2+ binding region (C2 region) that is seen only in the conventional PKC subfamily (cPKC alpha, -beta I, -beta II, and -gamma) but not in the novel PKC subfamily (nPKC delta, -epsilon, -zeta, and -eta). Northern (RNA) blot analyses revealed that the mRNA for nPKC theta is expressed predominantly in skeletal muscle. Furthermore, nPKC theta mRNA is the most abundantly expressed PKC isoform in skeletal muscle among the nine PKC family members. nPKC theta expressed in COS1 cells serves as a phorbol ester receptor. By the use of an antipeptide antibody specific to the D2-D3 region of the nPKC theta sequence, nPKC theta was recognized as a 79-kDa protein upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis in mouse skeletal muscle extract and also in an extract from COS1 cells transfected with an nPKC theta cDNA expression plasmid. Autophosphorylation of immunoprecipitated nPKC theta was observed; it was enhanced by phosphatidylserine and 12-O-tetradecanoylphorbol-13-acetate but attenuated by the addition of Ca2+. These results clearly demonstrate that nPKC theta should be considered a member of the PKC family of proteins that play crucial roles in the signal transduction pathway.

Immunocharacterization of delta- and zeta-isoenzymes of protein kinase C in rat renal mesangial cells

The isoforms of protein kinase C (PKC) present in rat mesangial cells were identified by immunoblot analysis with antibody raised against isotype-specific peptides. In addition to the previously observed alpha- and epsilon-subspecies, mesangial cells also express the delta- and zeta-isoenzymes of PKC. On exposure to phorbol 12,13-dibutyrate (PDB) a complete depletion of PKC-delta is observed within 8 h. Removal of PDB results in a recovery of PKC-delta. In contrast, PKC-zeta is unaffected by addition or removal of PDB.

Transcripts encoding protein kinase C-alpha, -delta, -epsilon, -zeta, and -eta are expressed in basal and differentiating mouse keratinocytes in vitro and exhibit quantitative changes in neoplastic cells

The protein kinase C (PKC) family of phospholipid-dependent serine-threonine kinases has been implicated in keratinocyte differentiation and neoplastic transformation. To determine if Ca(2+)-mediated keratinocyte differentiation is associated with changes in PKC isozyme gene expression, RNA was isolated from primary mouse keratinocytes grown in medium with 0.05, 0.12, or 1.4 mM Ca2+. Based on northern blot analysis, primary keratinocytes expressed mRNA encoding PKC-alpha, -delta, -epsilon, -zeta, and -eta, but not PKC-beta or -gamma. Relatively little change was detected in the level of these transcripts in cells induced to differentiate by exposure to elevated extracellular Ca2+. Interestingly, the PKC-zeta transcripts detected in RNA isolated from keratinocytes were approximately 200 nucleotides longer than those from mouse brain, suggesting the existence of an alternative form of this isozyme. An early change in benign neoplastic transformation of keratinocytes is the inability to differentiate in response to Ca2+ or the PKC activator 12-O-tetradecanoylphorbol-13-acetate, which is consistent with altered PKC function in these cells. The PKC isozyme mRNA profile was examined in two benign neoplastic keratinocyte cell lines, 308 and SP-1, which contain an activating mutation of the c-Ha-ras gene. Like normal keratinocytes. 308 and SP-1 cells expressed mRNA encoding PKC-alpha, -delta, -epsilon, -zeta, and -eta. However, the abundance of PKC-zeta transcripts in both cell lines was reduced by 74-89% when compared with normal keratinocytes at similar Ca2+ levels. In addition, SP-1 but not 308 cells exhibited a sevenfold increase in PKC-eta mRNA when cultured in medium with 1.4 mM Ca2+. To address whether these changes were related to the presence of an activated ras gene, RNA was isolated from primary keratinocytes transduced to a benign neoplastic phenotype with the v-Ha-ras oncogene. As with normal, 308, and SP-1 cells, v-Ha-ras keratinocytes expressed mRNA encoding PKC-alpha, -delta, -epsilon, -zeta and -eta. The level of PKC-zeta transcripts was similar in normal and v-Ha-ras keratinocytes, indicating that reduction of this mRNA in both 308 and SP-1 cells was not a direct result of ras activation. As in SP-1 cells, PKC-eta in v-Ha-ras keratinocytes was responsive to extracellular Ca2+, with a four-fold increase in transcript abundance in 0.12 mM Ca2+ medium relative to 0.05 mM Ca2+ medium.(ABSTRACT TRUNCATED AT 400 WORDS)

Protein kinase C isozymes epsilon and alpha in murine erythroleukemia cells

Protein kinase C (PKC) has a role in signal transduction during hexamethylene bisacetamide (HMBA)-induced differentiation of murine erythroleukemia cells (MELC). Separation of MELC PKC isozymes by hydroxylapatite chromatography yields a major peak (III) and a minor peak (II) of PKC activity, previously reported to contain the PKC alpha and beta isozymes, respectively. In the present study, we confirm that peak III activity is PKC alpha but show that peak II contains PKC epsilon and little or no PKC beta. Immunoblot analysis with isozyme-specific anti-alpha and anti-epsilon PKC antibodies detected PKC alpha in peak III and PKC epsilon in peak II. Peak III activity was markedly enhanced (up to 20-fold) by phosphatidylserine, diolein, and Ca2+, whereas addition of these cofactors to the reaction mixture stimulated peak II activity only 2- to 4-fold. RNase protection analysis of MELC RNA showed that PKC alpha and PKC epsilon RNAs were in a ratio of approximately 2:1, but PKC beta RNA was barely detectable. Taken together, these data indicate that MELC contain PKC alpha and PKC epsilon but little or no PKC beta.