The protein kinase C content is increased in the nuclear fraction of rat adrenal zona glomerulosa following long-term ACTH administration

Increased protein kinase C activity in myotrophin-induced myocyte growth

Myotrophin, a novel protein that has been shown to stimulate myocyte growth, has been isolated, purified, and sequenced from the hearts of spontaneously hypertensive rats and dilated cardiomyopathic human tissue. Recently, the cDNA clones encoding myotrophin have been isolated and expressed in Escherichia coli, and the recombinant myotrophin was found to be as biologically and immunologically active as natural myotrophin. The mechanism by which myotrophin stimulates protein synthesis and initiates myocardial hypertrophy is not known. To evaluate the involvement of protein kinase C (PKC) in myotrophin-induced hypertrophy, PKC activity and its distribution in the subcellular fraction were determined in cultured neonatal and adult myocytes. PKC activity was determined by measuring the incorporation of 32P into histone type III-S and PKCepsilon substrate peptide (epsilon(pep)) from [gamma-32P]ATP in neonatal myocytes. Myotrophin significantly stimulated PKC activity in neonatal myocytes and was associated with a significant increase in protein synthesis. The effect of myotrophin on the stimulation of PKC activity and [3H]leucine incorporation was abolished by pretreatment with either staurosporine or H-7, two selective, pharmacological PKC inhibitors. Pretreatment of myocytes with staurosporine also reduced the myotrophin-induced mRNA levels of c-fos and beta-myosin heavy chain. To evaluate the subcellular events whose occurrence was due to myotrophin and translocation of PKC, we studied the effect of genistein, a tyrosine kinase inhibitor, on myotrophin-induced neonatal myocyte growth. Genistein attenuated the [3H]leucine incorporation induced by myotrophin. To define the specificity of the PKC isoform(s) involved in myotrophin-stimulated myocyte growth, both neonatal and adult myocytes were treated with myotrophin, and Western blot analyses were performed by using the antibodies of different PKC isoforms. Results showed that both PKCalpha and PKCepsilon isoforms participated in the myotrophin-induced neonatal myocyte growth, whereas only the PKCepsilon isoform was involved in myotrophin-induced adult myocyte hypertrophy. PKCdelta and PKCzeta do not seem to participate in either neonatal or adult myocyte growth induced by myotrophin. Treatment with antisense oligonucleotides specific for PKCalpha and PKCepsilon isoforms further supported this result. PKCalpha is the major PKC isoform in neonatal myocytes and needs Ca2+ and phospholipids for its activation, and PKCepsilon (the Ca2+-independent PKC isoform) is present in both neonatal and adult myocytes; the 15-mer antisense oligodeoxynucleotides of each were used for this study. Treatment of neonatal myocytes with the PKCalpha and PKCepsilon antisense oligodeoxynucleotides for 5 days significantly reduced Ca2+-dependent and Ca2+-independent PKC activity, respectively, as well as the [3H]leucine incorporation induced by myotrophin. Furthermore, myotrophin-induced PKC activity was primarily located in the particulate fraction and did not result in a concomitant decrease in the cytosolic fraction. Myotrophin does not change PKC isoform expression (both Ca2+ dependent and independent PKC isoforms used in this study) in rat neonatal cardiac fibroblasts. Our data suggest that myotrophin exerts its action on protein synthesis, possibly through a tyrosine kinase-coupled pathway and translocation of PKC from the cytosol to the cell membrane.

Purification and isotype analysis of protein kinase C from rat liver nuclei

The properties and subtype composition of protein kinase C present in rat liver nuclei were studied in a Triton-X-100 extract of isolated purified nuclei. The enzyme activity was dependent on both Ca2+ and phosphatidylserine, but the phorbol ester 12-O-tetradecanoylphorbol 13-acetate gave only a partial stimulation. Both histone and myelin basic protein served as substrate. Purification of the Triton-X-100 extract followed by Q-Sepharose chromatography gave a preparation with a specific activity of 70 pmol/mg protein min. Western blotting of this preparation showed only the presence of the delta and zeta subtypes, but not the alpha-subtype, although the latter was present in rat liver homogenates. The beta, gamma and epsilon subtypes were not found in the homogenate nor in the nuclear extract. The specific activity of protein kinase C could be further increased up to 800 pmol/mg protein min after protamine agarose chromatography. Also in this preparation the presence of the delta and zeta subtypes could be established.

Role of tyrosine kinase and protein kinase C in the steroidogenic actions of angiotensin II, alpha-melanocyte-stimulating hormone and corticotropin in the rat adrenal cortex

The role of protein kinases in the steroidogenic actions of alpha-melanocyte-stimulating hormone (alpha-MSH), angiotensin II (AngII) and corticotropin (ACTH) in the rat adrenal zona glomerulosa was examined. Ro31-8220, a potent selective inhibitor of protein kinase C (PKC), inhibited both AngII- and alpha-MSH-stimulated aldosterone secretion but had no effect on aldosterone secretion in response to ACTH. The effect of Ro31-8220 on PKC activity was measured in subcellular fractions. Basal PKC activity was higher in cytosol than in membrane or nuclear fractions. Incubation of the zona glomerulosa with either alpha-MSH or AngII resulted in significant increases in PKC activity in the nuclear and cytosolic fractions and decreases in the membrane fraction. These effects were all inhibited by Ro31-8220. ACTH caused a significant increase in nuclear PKC activity only, and this was inhibited by Ro31-8220 without any significant effect on the steroidogenic response to ACTH, suggesting that PKC translocation in response to ACTH may be involved in another aspect of adrenal cellular function. Tyrosine phosphorylation has not previously been considered to be an important component of the response of adrenocortical cells to peptide hormones. Both AngII and alpha-MSH were found to activate tyrosine kinase, but ACTH had no effect, observations that have not been previously reported. Tyrphostin 23, a specific antagonist of tyrosine kinases, inhibited aldosterone secretion in response to AngII and alpha-MSH, but not ACTH. These data confirm the importance of PKC in the adrenocortical response to AngII and alpha-MSH, and, furthermore, indicate that tyrosine kinase may play a critical role in the steroidogenic actions of AngII and alpha-MSH in the rat adrenal zona glomerulosa.

Increased protein kinase C and isozyme redistribution in pressure-overload cardiac hypertrophy in the rat

Protein kinase C (PKC) activity and isozyme distribution were evaluated during development of pressure-overload-induced cardiac hypertrophy. Three-week-old rats were loosely banded on the ascending aorta (left ventricular hypertrophy [LVH] group). Two weeks later, when left ventricular mass was 50% greater than in the sham-operated control group and cardiac mass was still rapidly increasing beyond that of normal growth, PKC activity and [3H]phorbol 12,13-dibutyrate (PDBu) binding capacity were determined. In LVH, PKC activity was 119 +/- 14%, 158 +/- 17%, and 152 +/- 9% of the control value in cytosol, membrane, and nuclear-cytoskeletal fractions, respectively (n = 9 or 10). [3H]PDBu binding assay revealed increased PKC concentration in LVH cytosolic (control, 0.51 +/- 0.06 pmol/L per milligram; LVH, 0.78 +/- 0.09 pmol/L per milligram; n = 5; P < .05) and membrane fractions (control, 1.33 +/- 0.15; LVH, 2.32 +/- 0.39; n = 5; P < .05). Scatchard analysis indicated no difference in Kd values between control and LVH groups. Immunoblot analysis using PKC isoform-specific antibodies showed that both Ca(2+)-dependent (alpha and beta) and Ca(2+)-independent (delta, epsilon, and zeta) isoforms were present in the left ventricle. Compared with the control value, there was increased concentration in the membrane and nuclear-cytoskeletal fractions for beta 1,2 and epsilon and in the cytosol for beta 1,2. PKC-delta could be detected only in the nuclear-cytoskeletal fraction and was not changed in LVH. PKC-alpha and -zeta were present in all three fractions but were not altered in LVH. These data indicate that PKC activity and concentration increase during development of LVH induced by pressure overload. The increased PKC isozymes were mainly limited to PKC-beta 1,2 and PKC-epsilon, and the increase was present mainly in the membrane and nuclear-cytoskeletal fractions.

Substance P and adrenocorticotropic hormone do not affect T-lymphocyte adhesion to vascular endothelium or surface expression of adhesion receptors

Substance P (SP) and adrenocorticotropic hormone (ACTH) are peptides that have been shown to have both neurological and immunological effects. Because of the demonstrated effects upon immune function, we examined the effects of these peptides on T-lymphocyte adhesion to vascular endothelium and surface adhesion receptor expression. Neither the adhesion assays nor the expression assays showed any statistically significant effect of SP (10 microM) or ACTH (1 microM) for any incubation period used. We conclude that, while SP and ACTH have a variety of immunomodulatory effects, direct modulation of T-lymphocyte adhesion to vascular endothelium is probably not one of them.

Transcriptional activation of adrenocortical steroidogenic genes by high potassium or low sodium intake

We have previously shown that the long-term alterations in the intake of sodium and potassium which stimulated aldosterone production in the rat adrenal significantly increased cytochrome P450scc (P450scc) and P45011 beta (P45011 beta) mRNA's and also the mRNA of their electron donor adrenodoxin. In the present study run-on analyses showed an accumulation of nascent RNA in isolated nuclei of zona glomerulosa cells in K(+)-supplemented and Na(+)-depleted rats for P450scc (5- and 6-fold), 3 beta-HSD (3.6- and 2.0-fold) and P45011 beta (6.0- and 6.1-fold), but not for P450c21 (1.4- and 1.1-fold). In contrast, that of adrenodoxin decrease (0.6-fold) in high K+ and remained near control (1.3-fold) in low Na+ intake. Moderate variations in the rate of transcription of P450scc, P450c21, P45011 beta and adrenodoxin genes were observed in the zona fasciculata-reticularis cells of the treated rats. Our results thus demonstrated that positive modulators of aldosterone such as long-term K+ supplementation and Na+ restriction provoked an increase in transcription of the genes encoding key regulatory steroidogenic enzymes of aldosterone biosynthesis in the zona glomerulosa. The rates of transcription of the genes encoding 3 beta-HSD and P450c21, two enzymes catalyzing intermediate steps in the aldosterone pathway, were moderately affected by such treatments. However, according to the known stimulation of adrenodoxin mRNA levels following these treatments, a decreased turnover of the adrenodoxin mRNA rather than initiation of transcription of its gene might be involved in the response to K+ ions, and partially so in the response to Na+ restriction. Finally, the effects of salt-modified intake were mainly restricted to the zona glomerulosa cells, which are solely responsible for aldosterone production.