Inhibition of collagen synthesis by prostaglandins in the immortalized rat osteoblastic cell line pyla: Structure-activity relations and signal transduction mechanisms

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Abstract
We previously showed that prostaglandin E2 (PGE2) can selectively inhibit collagen synthesis and gene transcription in the immortalized rat osteoblastic clonal cell line Py1a, particularly in the presence of insulin-like growth factor I (IGF-I). In the present study, we examined the structure-activity relations for this effect. PGF2α was approximately 100 times more potent than PGE2. The prostaglandin F receptor (FP) selective agonist, fluprostenol, was the most potent agonist tested, significantly inhibiting incorporation of [3H]proline into both collagen and noncollagen protein at 10−11 M, with more than 90% inhibition of collagen synthesis at 10−8 M. The PGE2 analog, sulprostone, and PGD2 showed activity similar to that of PGE2. PGI2 and its stable analog, carbacyclin, were the least effective. Parathyroid hormone (PTH), forskolin, and isobutylmethylxanthine (IBMX) were ineffective. Phorbol myristate acetate (PMA) inhibited collagen synthesis in a manner similar to that of the prostanoids. The inhibitory effects of PGF2α, fluprostenol, and PMA show a similar time course on α1 (I) procollagen mRNA levels. The inhibition appeared to be caused by a decrease in collagen gene transcription as measured by nuclear run-on analysis. Further evidence for a transcriptional effect was obtained with COLIA1 promoter-CAT reporter constructs, although these showed somewhat smaller effects of prostanoids on CAT activity than on mRNA levels or labeling. Based on these results, we conclude that in the Py1a cell line prostanoids inhibit collagen synthesis by a pathway involving activation of protein kinase C that is not dependent on adenylate cyclase. The structure-activity relations for this response suggest that it is mediated by an FP receptor and is distinctly different from the stimulatory effects on bone resorption and formation.
Funding Information
  • USPHS (AR18063, AR38933)

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