FORSKOLIN INDUCES THE REORGANIZATION OF EXTRACELLULAR-MATRIX FIBRONECTIN AND CYTOARCHITECTURE IN 3T3-F442A ADIPOCYTES - ITS EFFECT ON FIBRONECTIN GENE-EXPRESSION

We studied the effect of forskolin on fibronectin and actin gene expre ssion in 3T3-F442A adipogenic cell line. The structural organizations of extracellular matrix fibronectin and actin cytoskeleton were invest igated in parallel. Immunofluorescence experiments showed that preadip ocytes treated for 48 h with 10 mu M forskolin exhibited an intensifie d network of both actin and fibronectin when compared to control. A si milar picture was obtained with adipocytes given long-term exposure to forskolin. As determined by Western analysis, fibronectin protein lev els were increased by 50-75% over control, both in preadipocytes and a dipocytes. A parallel increase of fibronectin mRNA content was observe d in forskolin-treated cells. In contrast, forskolin treatment of prea dipocytes and adipocytes did not elicit any change in the steady-state level of either actin mRNA or protein. Nuclear run-on experiments sho wed that forskolin increased the fibronectin gene transcription rate b ut left that of the actin gene in adipocytes unchanged. These findings suggest the reorganization of the actin network in forskolin-treated adipocytes to be a consequence of fibronectin-enhanced biosynthesis an d reorganization.