ACTIN-ISOFORM PATTERN AS A MARKER OF NORMAL OR PATHOLOGICAL SMOOTH-MUSCLE AND FIBROBLASTIC TISSUES

The relative proportions of actin isoforms present in smooth-muscle (SM) and fibroblastic human and non-human tissue extracts were examined by densitometric evaluation of Coomassie-Blue-stained spots in two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) as well as by quantification of radiolabeled actin NH2-terminal peptide spots separated by two-dimensional paper electrophoresis. SM tissues contained .alpha.- and .gamma.-SM as well as .beta.- and .gamma.-cytoplasmic (CY) actins in different proportions in different organs. Species differences with respect to the ratios of the isoactins were also observed. Moreover, during pregnancy, both human and rat myometrium exhibited a changed actin-isoform pattern, there being an increased proportion of .gamma.-actin. Analysis of the NH2-terminal peptides showed that, in human myometrium, this was essentially due to an increase in the amount of the .gamma.-SM isoform. Fibroblastic tissues were found to contain only the .beta.- and .gamma.-CY isoforms, the ratio being approximately 2.6:1. Thus, the presence or absence of .alpha.-action provides a reliable biochemical criterion for distinguishing between fibroblastic and SM cell populations and/or tissues. This distinction and the evaluation of changes in isoactin ratios may be useful in the study of differentiation as well as physiological and pathological phenomena, and for determining the origin of certain soft-tissue tumours.