Phenotype-dependent expression of alpha-smooth muscle actin in visceral smooth muscle cells

alpha-Smooth muscle actin is one of the molecular markers for a phenotype o f vascular smooth muscle cells, because the actin is a major isoform expres sed in vascular smooth muscle cells and its expression is upregulated durin g differentiation. Here, we first demonstrate that the phenotype-dependent expression of this actin in visceral smooth muscles is quite opposite to th at in vascular smooth muscles. This actin isoform is not expressed in adult chicken visceral smooth muscles including gizzard, trachea, and intestine except for the inner layer of intestinal muscle layers, whereas its express ion is clearly detected in these visceral smooth muscles at early stages of the embryo (10-day-old embryo) and is developmentally downregulated. In cu ltured gizzard smooth muscle cells maintaining a differentiated phenotype, cc-smooth muscle actin is not detected while its expression dramatically in creases during serum-induced dedifferentiation, Promoter analysis reveals t hat a sequence (-238 to -219) in the promoter region of this actin gene act s as a novel negative cis-element. In conclusion, the phenotype-dependent e xpression of ex-smooth muscle actin would be regulated by the sum of the co operative contributions of the negative element and well-characterized posi tive elements, purine-rich motif, and CArG boxes and their respective trans acting factors. (C) 1999 Academic Press.