Presence of growth factors-induced type III @entity9117 5-deiodinase in cultured XXXX brown adipocytes.

@entity35 @entity9117 @entity664 @entity73282
We found low T3 concentrations in @entity35 brown adipocytes differentiated in vitro. This might be due to the high metabolic rate of T3, possibly caused by elevated type III @entity9117 5-deiodinase activity ( @entity73282 ), induced by serum growth factors. We tested the ability of several growth factors to induce @entity73282 activity. Epidermal growth factor and basic and acidic fibroblast growth factors produced a strong induction of @entity73282 activity (25, 45-, and 50-fold, respectively). This process required gene transcription and de novo protein synthesis. The half-life of @entity73282 was approximately 3 h. Heparin was required for full acidic fibroblast growth factor activity. Platelet-derived growth factor, vasopressin, and insulin-like growth factor-I induced lower @entity73282 activities (3- to 6-fold). Vasopressin amplified @entity664 and epidermal growth factor inductions when used at submaximal doses. We found a Km of 22.5 nM using T3 as substrate. Although brown adipose tissue has undetectable @entity73282 activities in vivo, the present data explain the low T3 concentrations found in cultured @entity35 brown adipocytes and suggest that growth factors, by stimulating @entity73282 , may lead to low T3 concentrations and indirectly inhibit the expression of some genes regulated by T3, e.g. the @entity35 uncoupling protein.
