latrunculin-b and Hypertrophy

The low molecular weight GTPase Rho mediates a variety of cytoskeleton-dependent cell functions and stretch- and G(q) protein-induced hypertrophic responses in cardiac myocytes. Although ROCK, one of Rho's effectors, has been suggested to mediate hypertrophic signals, the relationship of Rho/ROCK with downstream signals is unknown. A zinc finger transcription factor, GATA-4, is activated by extracellular signal-regulated kinase 1/2 and is required for the up-regulation of the endothelin-1 gene during myocardial cell hypertrophy. However, it is unknown whether Rho/ROCK signals are linked to downstream GATA-4. By transient transfection assays using a dominant-negative mutant and an activated derivative of ROCK-I, we showed that ROCK-I participates in GATA-4-dependent endothelin-1 transcription. Inhibition of the Rho/ROCK pathway by Y-27632, a selective inhibitor of ROCK, suppressed phenylephrine-stimulated phosphorylation of extracellular signal-regulated kinase 1/2 and increased the DNA binding activity of cardiac GATA-4. Interestingly, latrunculin B, which inhibits actin polymerization, also prevents phenylephrine-induced responses. These findings demonstrate that the Rho/ROCK pathway is linked to downstream GATA-4 via the activation of extracellular signal-regulated kinases during myocardial cell hypertrophy. The results also suggest that changes in actin dynamics provide a convergence point for Rho/ROCK to the downstream signals during this process.

Topics: 3T3 Cells; Actins; Amides; Animals; Blotting, Northern; Bridged Bicyclo Compounds, Heterocyclic; Cells, Cultured; COS Cells; DNA-Binding Proteins; Enzyme Activation; GATA4 Transcription Factor; Hypertrophy; Immunohistochemistry; Intracellular Signaling Peptides and Proteins; Luciferases; Mice; Microscopy, Fluorescence; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Mutation; Myocardium; Phenylephrine; Phosphorylation; Plasmids; Protein Binding; Protein Serine-Threonine Kinases; Pyridines; Rats; rho-Associated Kinases; Thiazoles; Thiazolidines; Transcription Factors; Transcription, Genetic; Transfection; Zinc Fingers