ucn-1028-c and Hypertrophy

The transcription factor nuclear factor-kappaB (NF-kappaB) regulates expression of a variety of genes involved in immune responses, inflammation, proliferation, and programmed cell death (apoptosis). Here, we show that in rat neonatal ventricular cardiomyocytes, activation of NF-kappaB is involved in the hypertrophic response induced by myotrophin, a hypertrophic activator identified from spontaneously hypertensive rat heart and cardiomyopathic human hearts. Myotrophin treatment stimulated NF-kappaB nuclear translocation and transcriptional activity, accompanied by IkappaB-alpha phosphorylation and degradation. Consistently, myotrophin-induced NF-kappaB activation was enhanced by wild-type IkappaB kinase (IKK) beta and abolished by the dominant-negative IKKbeta or a general PKC inhibitor, calphostin C. Importantly, myotrophin-induced expression of two hypertrophic genes (atrial natriuretic factor [ANF] and c-myc) and also enhanced protein synthesis were partially inhibited by a potent NF-kappaB inhibitor, pyrrolidine dithio-carbamate (PDTC), and calphostin C. Expression of the dominant-negative form of IkappaB-alpha or IKKbeta also partially inhibited the transcriptional activity of ANF induced by myotrophin. These findings suggest that the PKC-IKK-NF-kappaB pathway may play a critical role in mediating the myotrophin-induced hypertrophic response in cardiomyocytes.

Topics: Alkaloids; Animals; Animals, Newborn; Benzophenanthridines; Blotting, Northern; Blotting, Western; Cell Nucleus; Cells, Cultured; Cytoplasm; DNA, Complementary; Dose-Response Relationship, Drug; Enzyme Activation; Genes, Dominant; Growth Substances; Hypertrophy; I-kappa B Proteins; Immunohistochemistry; Intercellular Signaling Peptides and Proteins; Luciferases; Microscopy, Confocal; Microscopy, Fluorescence; Myocardium; Naphthalenes; NF-kappa B; NF-KappaB Inhibitor alpha; Phenanthridines; Phosphorylation; Protein Binding; Protein Kinase C; Protein Transport; Rats; Rats, Sprague-Dawley; Rats, Wistar; RNA, Messenger; Time Factors; Transcription, Genetic; Transfection

It is not certain whether activation of the Ras/mitogen-activated protein (MAP) kinase pathway is involved in cardiac hypertrophy. 3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, such as lovastatin, prevent farnesylation of the Ras protein, which is critical for Ras's membrane localization and function. Therefore, the present study was undertaken to investigate the role of the Ras pathway, which is linked to mevalonate metabolism, in the mechanism of stretch-induced myocyte hypertrophy. Myocytes isolated from 1- to 2-day-old rats were cultured at 4.1 x 10(6) cells per well in a deformable silicon dish and incubated with serum-free medium for 7 days. The cultures were stretched by 15% on culture day 4. Stretch increased the RNA/DNA ratio by 20% to 26% on culture days 5 and 6 and the protein/DNA ratio by 18% to 20% on culture days 6 and 7. Stretch accelerated rates of protein synthesis by 24% on culture day 6. Stretch increased protein kinase C (PKC) activity, MAP kinase activity, and c-fos mRNA expression. A selective PKC inhibitor, calphostin C (1 x 10(-6) M), prevented the stretch-induced increase in PKC activity, but lovastatin (7.5 x 10(-6) M) did not. Lovastatin as well as calphostin C partially but significantly inhibited the stretch-induced increases in MAP kinase activity, c-fos mRNA expression, and protein synthesis. Pretreatment with both lovastatin and calphostin C completely inhibited the increases in these variables caused by stretch. Lovastatin as well as calphostin C prevents stretch-induced cardiac hypertrophy. These results suggest that mechanical stretch may activate the Ras pathway, which is linked to mevalonate metabolism, in cultured neonatal rat heart cells.

Topics: Animals; Animals, Newborn; Cells, Cultured; Enzyme Activation; Enzyme Inhibitors; Gene Expression; Heart; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Hypertrophy; Lovastatin; Mevalonic Acid; Mitogen-Activated Protein Kinase 1; Myocardium; Naphthalenes; Physical Stimulation; Protein Biosynthesis; Protein Kinase C; Proteins; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; RNA, Messenger; Signal Transduction; Stress, Mechanical