Heparin inhibits mitogen-activated protein kinase-dependent and -independent c-fos induction in mesangial cells.
Heparin suppresses mitogenic responses in renal mesangial cells, and when quiescent mesangial cells are stimulated with serum, heparin blocks the induction of c-fos seen at 15 min. Because heparin is taken up by cells over a much longer time course, we addressed mechanisms whereby extracellular heparin might suppress c-fos induction at such early times. Quiescent cells were treated with serum, 12-O-tetradecanoylphorbol-13-acetate, or low concentrations of Ca2+ ionophores that produced increases in intracellular Ca2+ concentration ([Ca2+]i) in the physiological range. Each treatment caused an increase in c-fos mRNA, but they did so by different mechanisms. Serum activated mitogen-activated protein kinase (MAPK) and increased [Ca2+]i without affecting protein kinase C. Activation of protein kinase C with phorbol ester activated MAPK without much effect on [Ca2+]i. Ionophores increased [Ca2+]i without affecting basal levels of protein kinase C or MAPK. Heparin (1 microg/ml) suppressed the induction of c-fos initiated by all three treatments. It did not affect the activity of protein kinase C, but inhibited activation of MAPK by either serum or phorbol ester, suggesting a common site of action at or below the probable convergence of the induced signals at Ras/Raf-1 activation. Heparin also inhibited the serum-stimulated entry of extracellular Ca2+ to the same extent as verapamil, consistent with the ability of verapamil to block L-type Ca2+ channels and the known presence of these channels in mesangial cells. However, this effect does not appear to be related to heparin's ability to inhibit induction of c-fos. First, verapamil had no effect on induction of c-fos by serum. Second, heparin had no effect on changes in [Ca2+]i achieved by ionophores. We conclude that heparin suppresses induction of c-fos in mesangial cells by blocking at least two different points in signal transduction cascades, one upstream of MAPK and the other independent of MAPK, but dependent on intracellular Ca2+.
Miralem
T
T
Department of Clinical Biochemistry, University of Toronto, Toronto, Canada.
Wang
A
A
Whiteside
C I
CI
Templeton
D M
DM
D000595:Amino Acid Sequence; D000818:Animals; D001769:Blood; D015152:Blotting, Northern; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D003470:Culture Media; D004789:Enzyme Activation; D016762:Genes, fos / Q000187:drug effects*; D005920:Glomerular Mesangium / Q000187:drug effects / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology*; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D008969:Molecular Sequence Data; D009842:Oligopeptides; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D019908:Proto-Oncogene Proteins c-raf; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology; D018631:ras Proteins / Q000378:metabolism
D003470:Culture Media; D009842:Oligopeptides; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D000001:Calcimycin; D015759:Ionomycin; D006493:Heparin; D014700:Verapamil; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium