Characterization of the major phosphoinositide-specific phospholipase C of human amnion.
Most of the phosphoinositide-specific phospholipase C activity in human amnion at term was found to be attributable to a single isoform (Mr 85,000). Phospholipase C purified from amnion catalyzed the calcium-dependent hydrolysis of both phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate. The high phospholipase C activity of amnion cells isolated at 38-41 weeks of gestation declined greater than 80% during the initial 2-5 days of culture to values characteristic of amnion tissue in early gestation. Activities of phospholipase A2 and phosphatidylinositol synthase remained essentially unaltered during this period of culture. Loss of phospholipase C activity was apparently due neither to the appearance of an inhibitor nor to the loss of an activator and most likely reflected a decrease in the amount of enzyme in amnion cells. Basal production of prostaglandin E2 (PGE2) by amnion cells also declined greatly during the period of loss of phospholipase C activity. Involvement of phospholipase C in the regulation of amnion prostaglandin production was also supported by the finding that the phospholipase C inhibitor, U-73122, potently inhibited amnion cell PGE2 production. In contrast, vasopressin, which appears to stimulate prostaglandin production in amnion cells by a phospholipase C-dependent mechanism, was equipotent in stimulating PGE2 production by amnion cells on Day 2 and Day 5 of culture, even though phospholipase C activity had declined by more than 75%. Furthermore, epidermal growth factor stimulation of PGE2 production by amnion cells appeared to be largely attributable to an increase in prostaglandin H synthase activity and did not involve an increase in phospholipase C activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Bala
G A
GA
Department of Cell Biology, Upjohn Company, Kalamazoo, Michigan 49001.
Thakur
N R
NR
Bleasdale
J E
JE
D000650:Amnion / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D010716:Phosphatidylinositols / Q000378:metabolism / Q000502:physiology*; D011247:Pregnancy; D011453:Prostaglandins / Q000378:metabolism; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000032:analysis* / Q000378:metabolism / Q000502:physiology
D010716:Phosphatidylinositols; D011453:Prostaglandins; D010738:Type C Phospholipases