Cyclic AMP agonists increase levels of insulin-like growth factor (IGF) binding protein-6 in PC12 rat phaeochromocytoma cells.
The predominant insulin-like growth factor binding protein (IGFBP) synthesized by PC12 rat phaeochromocytoma cells is IGFBP-6. Since cAMP agonists regulate IGFBP-6 in other cells, and they may increase neurite outgrowth and catecholaminergic enzyme expression in PC12 cells, we studied regulation of IGFBP-6 by these agents. After 72 h incubation, forskolin and 8-(4-chlorophenylthio)-cAMP (CPT-cAMP) both increased IGFBP-6 protein levels in conditioned media to maximum levels of 231 +/- 40 and 275 +/- 30%, respectively. Incubation with forskolin resulted in a small, transient rise in IGFBP-6 mRNA levels which was insufficient to account for the increased protein levels. The increased protein levels also could not be attributed to increased cell number, protection of IGFBP-6 from proteolysis or release of IGFBP-6 from a cell-associated reservoir. These findings suggest that increased protein levels may have been due to increased translation of mRNA. Co-incubation of forskolin with dexamethasone (which decreases IGFBP-6 protein and mRNA) demonstrated that the effects of the latter were dominant. The effects of cAMP agonists and IGF-II, which increases IGFBP-6 protein but not mRNA levels, were not inhibited by rapamycin, suggesting that p70 S6 kinase is not involved. The effects of cAMP agonists on IGFBP-6 levels were not directly correlated with neurite outgrowth. These findings extend our knowledge of the molecular basis of the regulation of IGFBP-6 by cAMP agonists, and indicate a novel action of these agents in PC12 cells.
Bach
L A
LA
University of Melbourne, Department of Medicine, Austin and Repatriation Medical Centre, Heidelberg, Victoria, Australia. bach @austin.unimelb.edu.au
Leeding
K S
KS
Leng
S L
SL
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000819:agonists* / Q000031:analogs & derivatives* / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005109:Extracellular Matrix / Q000187:drug effects / Q000378:metabolism; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology; D016501:Neurites / Q000187:drug effects; D016716:PC12 Cells / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D020123:Sirolimus / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology*
D018976:Insulin-Like Growth Factor Binding Protein 6; D013873:Thionucleotides; D005576:Colforsin; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D007335:Insulin-Like Growth Factor II; D003907:Dexamethasone; D000242:Cyclic AMP; D020123:Sirolimus