RISE IN CYTOSOLIC CA2-LIPASE STIMULATED BY GROWTH-HORMONE( ABOLISHES IN PREADIPOSE CELLS THE EXPRESSION OF LIPOPROTEIN)

Lipoprotein lipase (LPL) is known to be an early marker of adipose cel l differentiation. Growth hormone (GH) stimulates in preadipose Ob1771 cells the expression of LPL gene and this effect is mediated at least in part by c-fos protooncogene, the expression of which is transientl y activated by a protein kinase C-dependent pathway (Barcellini-Couget et al., Endocrinology, 1993, 132: 55-60). Since GH stimulates the for mation of diacylglycerol from phosphatidylcholine independently of Ca2 + mobilization, the role of Ca2+ was studied in regard to LPL gene exp ression stimulated by GH. The results obtained in the presence of Ca2 ionophores show that a rise in intracellular free Ca2+ abolishes this expression but has no effect on the expression of various adipose-rel ated genes, including the transient expression of c-fos protooncogene. Therefore, the inability of preadipose cells to mobilize Ca2+ in resp onse to GH, at an early stage of the differentiation process, appears as a prerequisite for the maximal expression of LPL. (C) 1994 Academic Press, Inc.