Thrombin effects on osteoblastic cells. II. Structure-function relationships.
Thrombin has been shown to cause in vitro bone resorption and to stimulate osteoblastic cell proliferation, phosphoinositide turnover and cytosolic calcium levels. In the present study, the role of the active site of thrombin in its action on osteoblastic cells was investigated. Either hirudin or (4-amidinophenyl)methanesulfonyl fluoride inhibited, in a dose-dependent manner, the effects of thrombin on human osteoblast-like osteosarcoma cells (G292 and Saos-2 cell lines) and on normal rat calvarial osteoblastic cells. Thrombin-induced stimulation of cell proliferation, cytosolic calcium increases, and stimulation of phosphoinositide metabolism were concomitantly, and to a proportionally similar extent, inhibited. The inhibitors, when present in the absence of thrombin, did not affect the basal levels of cell functions. Both zeta-thrombin and gamma-thrombin, forms resulting from proteolytic cleavage of alpha-thrombin, were capable of stimulating the osteoblastic cells. These data indicate that thrombin's actions on osteoblast-like cells are dependent on the availability of its catalytic site.
Tatakis
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DN
Department of Oral Biology, School of Dental Medicine, State University of New York, Buffalo 14214.
Dolce
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C
Dziak
R
R
Fenton
J W
JW
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002455:Cell Division; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D010011:Osteocytes / Q000187:drug effects*; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D013329:Structure-Activity Relationship; D013917:Thrombin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D006629:Hirudins; D010716:Phosphatidylinositols; D013917:Thrombin; D002118:Calcium