Correlation between the distribution of smooth muscle or non muscle myosins and α‐smooth muscle actin in normal and pathological soft tissues

Abstract

The distribution of smooth muscle (SM) and non muscle myosins was compared with that of α‐SM actin in various normal and pathological tissues and in cultured cells by means of indirect immunofluorescence using a monoclonal antibody specific for α‐SM actin [anti‐αsm‐1, Skalli et al., 1986b] and two polyclonal antibodies raised against bovine aortic myosin (ABAM) and human platelet myosin (AHPM), respectively. In normal tissues ABAM stained vascular and parenchymal smooth muscle cells (SMC), myoepithelial cells and myoid cells of the testis in a pattern similar to that reported by other authors with antisera raised against non vascular SM myosin. Cells stained with ABAM were always positive for anti‐αsm‐1. In human and experimental atheromatous plaques, most cells were positive for AHPM; a variable proportion was also stained for ABAM plus anti‐αsm‐1. Myofibroblasts from rat granulation tissue, Dupuytren's nodule and stroma from breast carcinoma were constantly positive for AHPM and negative for ABAM; however, myofibroblasts from Dupuytren's nodule and breast carcinoma were anti‐αsm‐1 positive. Early primary cultures of rat aortic SMC were positive for ABAM and anti‐αsm‐1 and became negative for ABAM and positive for AHPM after a few days in culture. They remained positive for AHPM and anti‐αsm‐1 after passages; the staining of AHPM and anti‐αsm‐1 appeared to be colocalized along the same stress fibers. These results may be relevant for the understanding of SMC function and adaptation, and show that in non malignant SMC proliferation, α‐SM actin represents a more general marker of SM origin than SM myosin.