Effects of vanadate on tyrosine phosphorylation and the pattern of glycosaminoglycan synthesis in rabbit chondrocytes in culture

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Abstract
The present study examined the effects of high doses of vanadate on glycosami-noglycan (GAG) synthesis and tyrosine phosphorylation in rabbit chondrocytes in confluent cultures. Although 6 μM vanadate increased the incorporation of [3H] glucosamine into chondroitin sulfate proteoglycans twofold, 40–60 μM vanadate suppressed this incorporation fourfold. Although 6 μM vanadate had little effect on [3H] glucosamine incorporation into hyaluronate, 40–60 μM vanadate increased this incorporation threefold. Chemical analyses confirmed that the increase in ∥3H∥glucosamine incorporation into hyaluronate and the decrease in the incorporation into chondroitin sulfate proteoglycan correlated with increased hyaluronate content and decreased chondroitin sulfate content in the cell layers of vanadate-transformed cells. Chondrocytes exposed to 40–60 μM vanadaje became typically transformed spindlelike cells. Furthermore, vanadate, at 6 and 60 μM, increased the overall level of phosphotyrosine by 8- and 31-fold, respectively, and 60 μM vanadate enhanced phosphorylation of many phosphotyrosine-containing proteins. These observations suggest that vanadate induces transformation-associated changes in the pattern of GAG synthesis when it induces excess phosphorylation on tyrosine in chondrocyte proteins.