Differences in the stress fibers between fibroblasts and epithelial cells.

Abstract

In the stress fibers of 2 types of nonmuscle cells, epithelia (PtK2, bovine lens) and fibroblasts (Gerbil fibroma, WI-38, primary human) the spacing between sites of .alpha.-actinin localization differs by a factor of about 1.6 as determined by indirect immunofluorescence and ultrastructural localization with peroxidase-labeled antibody. Both methods reveal striations along the stress fibers with a center-to-center spacing in the range of 0.9 .mu.m in epithelial cells and 1.5 .mu.m in fibroblasts. Periodic densities spaced at comparable distances are seen in PtK2 and in gerbil fibroma cells when they are treated with tannic acid and examined in the EM. In such cells, densities are found not only along stress fibers but also at cell-cell junctions, attachment plaques and foci from which stress fibers radiate. These latter 3 sites all stain with .alpha.-actinin antibody on the light microscope and EM level. Stress fibers in the 2 cell types also vary in the periodicity produced by indirect immunofluorescence with tropomyosin antibodies. As is the case for .alpha.-actinin, the tropomyosin center-to-center banding is approximately 1.6 times as long in gerbil fibroma cells (1.7 .mu.m) as it is in PtK2 cells (1.0 .mu.m). The densities seen in the EM are sites of .alpha.-actin localization and the proteins in stress fibers have an arrangement similar to that in striated muscle. A sarcomeric model of stress fiber structure based on light microscopic and EM findings is proposed.