Basic FGF-induced down-regulation of IGF-I mRNA in cultured rat Müller cells.
Interactions among growth factors are important in a variety of physiological and pathological processes. The regulation of IGF-I mRNA expression by bFGF was investigated in cultured rat Müller cells and the mechanism of regulation studied. Müller cells from 1- to 3-day-old Sprague-Dawley rats were isolated and cultured with Eagle MEM+10% FCS. Cultured cells were identified by immunocytochemistry using antibodies against vimentin, carbonic anhydrase C, and glutamine synthetase. Cells of passage 1-4 were treated with bFGF, the PKC inhibitor H-7, calphostin C, the PKC activator PMA or the PKA inhibitor H-89, as well as the adenylate cyclase activator forskolin, or adenylate cyclase inhibitor SQ22536. IGF-I and bFGF expression levels were assessed by Northern blot analysis. The addition of bFGF to culture medium down-regulated IGF-I expression in a dose- and time-dependent manner. Decrease of IGF-I expression started at a bFGF concentration of 1 ng ml-1. IGF-I mRNA level declined to 44% of baseline level at 10 ng ml-1 of bFGF, and reached a trough of 40% at 50 ng ml-1. At 10 ng ml-1 of bFGF, down-regulation of IGF-I expression was observed as early as 4 hr (60%) after treatment, and reached a trough of 42% by 8 hr. The temporal and concentration dependence of IGF-I expression by addition of the PKC activator PMA, to culture medium was similar to that due to the addition of bFGF. The down-regulation of IGF-I expression by bFGF (10 ng ml-1) and PMA (0.1 microM) was blocked by the PKC inhibitors H-7 (30 microM) and calphostin C (1 microM). Forskolin (5 microM), an adenylate cyclase activator, had activator, had no effect on IGF-I expression. SQ22536 (100 microM), an adenylate cyclase inhibitor, and H-89, a PKA inhibitor, had no inhibitory effect on bFGF-induced down-regulation of IGF-I expression. These results indicate that bFGF down-regulates IGF-I expression in cultured rat M uller cells through PKC activation.
Li
F
F
Dean A. McGee Eye Institute, University of Oklahoma, Oklahoma City, USA.
Cao
W
W
Steinberg
R H
RH
LaVail
M M
MM
D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D009457:Neuroglia / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D015290:Second Messenger Systems; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology