Transforming growth factor-beta1 regulation of resting zone chondrocytes is mediated by two separate but interacting pathways.
Previous studies have shown that transforming growth factor-beta1 (TGF-beta1) stimulates protein kinase C (PKC) via a mechanism that is independent of phospholipase C or tyrosine kinase, but involves a pertussis toxin-sensitive G-protein. Maximal activation occurs at 12 h and requires new gene expression. To understand the signaling pathways involved, resting zone chondrocytes were incubated with TGF-beta1 and PKC activity was inhibited with chelerythrine, staurosporine or H-7. [(35)S]Sulfate incorporation was inhibited, indicating that PKC mediates the effects of TGF-beta1 on matrix production. However, there was little, if any, effect on TGF-beta1-dependent increases in [(3)H]thymidine incorporation, and TGF-beta1-stimulated alkaline phosphatase was unaffected, indicating that these responses to the growth factor are not regulated via PKC. TGF-beta1 caused a dose-dependent increase in prostaglandin E(2) (PGE(2)) production which was further increased by PKC inhibition. The increase was regulated by TGF-beta1-dependent effects on phospholipase A(2) (PLA(2)). Activation of PLA(2) inhibited TGF-beta1 effects on PKC, and inhibition of PLA(2) activated TGF-beta1-dependent PKC. Exogenous arachidonic acid also inhibited TGF-beta1-dependent increases in PKC. The effects of TGF-beta1 on PKC involve genomic mechanisms, but not regulation of existing membrane-associated enzyme, since no direct effect of the growth factor on plasma membrane or matrix vesicle PKC was observed. These results support the hypothesis that TGF-beta1 modulates its effects on matrix production through PKC, but its effects on alkaline phosphatase are mediated by production of PGE(2) and protein kinase A (PKA). Inhibition of PKA also decreases TGF-beta1-dependent proliferation. We have previously shown that PGE(2) stimulates alkaline phosphatase through its EP2 receptor, whereas EP1 signaling causes a decrease in PKC. Thus, there is cross-talk between the two pathways.
Sylvia
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VL
Department of Orthopaedics, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, USA.
Schwartz
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Dean
D D
DD
Boyan
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BD
D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000470:Alkaloids; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D053119:Benzophenanthridines; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D019902:Chondrocytes / Q000187:drug effects* / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D010617:Phenanthridines / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D019311:Staurosporine / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D000470:Alkaloids; D053119:Benzophenanthridines; D004791:Enzyme Inhibitors; D010617:Phenanthridines; D011509:Proteoglycans; D016212:Transforming Growth Factor beta; D016718:Arachidonic Acid; C016299:chelerythrine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010741:Phospholipases A; D000469:Alkaline Phosphatase; D019311:Staurosporine; D015232:Dinoprostone