Regulation by thyrotropin of acyl-CoA: cholesterol acyltransferase in cultured thyroid cells.
ACAT activity measured in microsomes of thyroid cells cultured for 4 days in the presence of TSH (1 mU/ml) was two or three times lower than that of the control cells cultured for the same period in the absence of TSH. The pool of cellular cholesterol which served as the ACAT substrate, was not exchangeable with exogenous cholesterol provided in the form of liposomes. However, the incubation of microsomes with liposomes made it possible to increase the cholesterol content in the microsomes by 35%, and this resulted in the activation of ACAT activity. Nevertheless, maximum activity measured after activation in the microsomes of the control cells remained higher than that of the microsomes of cells cultured in the presence of TSH. These findings would suggest that TSH acted by diminishing the cellular content in ACAT enzyme, as well as modifying the distribution of cholesterol in the intracellular membranes.
D000818:Animals; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D008081:Liposomes; D008861:Microsomes / Q000201:enzymology; D002785:Sterol O-Acyltransferase / Q000032:analysis*; D013961:Thyroid Gland / Q000201:enzymology*; D013972:Thyrotropin / Q000494:pharmacology*
D008081:Liposomes; D013972:Thyrotropin; D002784:Cholesterol; D002785:Sterol O-Acyltransferase