Interaction of the beta(IV)-tubulin isotype with actin stress fibers in cultured rat kidney mesangial cells

Microtubules and actin filaments are two of the major components of the cyt oskeleton. There is accumulating evidence for interaction between the two n etworks. Both the alpha- and beta -subunits of tubulin exist as numerous is otypes, some of which have been highly conserved in evolution. In an effort to better understand the functional significance of tubulin isotypes, we u sed a double immunofluorescence labeling technique to investigate the inter actions between the tubulin beta -isotypes and the actin stress fiber netwo rk in cultured rat kidney mesangial cells, smooth-muscle-like cells from th e renal glomerulus. Removal of the soluble cytoplasmic and nucleoplasmic pr oteins by detergent extraction caused the microtubule network to disappear while the stress fiber network was still present. In these extracted cells, the beta (I)- and beta (II)-tubulin isotypes were no longer present in the cytoplasm while the beta (IV)-isotype co-localized with actin stress fiber s. Co-localization between beta (IV)-tubulin and actin stress fibers was al so observed when the microtubule network was disrupted by the anti-tubulin drug colchicine and also by microinjection of the beta (IV)-tubulin antibod y. Our results suggest that the beta (IV) isotype of tubulin may be involve d in interactions between microtubules and actin. Cell Motil. Cytoskeleton 49:200-207, 2001. (C) 2001 Wiley-Liss, Inc.