TRANSFECTED MUSCLE AND NONMUSCLE ACTINS ARE DIFFERENTIALLY SORTED BY CULTURED SMOOTH-MUSCLE AND NONMUSCLE CELLS

We have analyzed by immunolabeling the fate of exogenous epitope-tagge d actin isoforms introduced into cultured smooth muscle and non-muscle (i.e. endothelial and epithelial) cells by transfecting the correspon ding cDNAs in transient expression assays. Exogenous muscle actins did not produce obvious shape changes in transfected cells, In smooth mus cle cells, transfected striated and smooth muscle actins were preferen tially recruited into stress fibers. In non-muscle cells, exogenous st riated muscle actins mere rarely incorporated into stress fibers but r emained scattered within the cytoplasm and frequently appeared organiz ed in long crystal-like inclusions. Transfected smooth muscle actins w ere incorporated into stress fibers of epithelial cells but not of end othelial cells. Exogenous non-muscle actins induced alterations of cel l architecture and shape, All cell types transfected by non-muscle act in cDNAs showed an irregular shape and a poorly developed network of s tress fibers, beta- and gamma-cytoplasmic actins transfected into musc le and non-muscle cells were dispersed throughout the cytoplasm, often accumulated at the cell periphery and rarely incorporated into stress fibers, These results show that isoactins are differently sorted: not only muscle and non-muscle actins are differentially distributed with in the cell but also, according to the cell type, striated and smooth muscle actins can be discriminated for, Our observations support the a ssumption of isoactin functional diversity.