Occurrence of caldesmon (a calmodulin-binding protein) in cultured cells: comparison of normal and transformed cells.

Publisher Website
Google Scholar
Abstract
Caldesmon is a calmodulin-binding and F-actin-binding protein originally purified from chicken gizzard smooth muscle. This protein binds to F-actin filaments in a Ca2+- and calmodulin-dependent flip-flop fashion, thereby regulating the function of actin filaments. Various lines of cultured cells [rat cell no. 7, S7-1, 68-N2 clone, chick embryo fibroblast, C3H-2K] contain a MW 77,000 protein that specifically reacts with the affinity-purified caldesmon antibody raised against chicken gizzard caldesmon. Among the fibroblast proteins that were pulse-labeled with [35S]Met, the MW 77,000 protein was the only protein band detected on the NaDodSO4 [sodium dodecyl sulfate] gel that reacted with the anticaldesmon. The subcellular distribution of the MW 77,000 protein was investigated by the indirect immunofluorescence technique using the anticaldesmon. In all fibroblast cell lines examined, the immunofluorescence localized along the cellular stress fibers and in leading edges of the cell. In Rous sarcoma virus-transformed cells (S7-1) the distribution of the fluorescence changed to a diffuse and blurred appearance. These staining patterns of anticaldesmon obtained with the normal and transformed cells coincided with those of antiactin in the corresponding states, strongly suggesting the functional linkage between the MW 77,000 protein and actin filaments. This MW 77,000 protein may be referred to as caldesmon77. The cellular level of caldesmon77 n transformed S7-1 cells decreased to about 1/3 of that in their normal counterparts (cell line no. 7). Essentially the same result was obtained with normal rat kidney cells infected with the temperature-sensitive transformation mutant Schmidt-Ruppin strain of Rous sarcoma virus (68 N2 clone). The cellular level of caldesmon77 observed at a permissive temperature (35.degree. C) was about 1/3 of that at a nonpermissive temperature (38.5.degree. C). These changes of caldesmon77 in transformed cells may correlate with the loss of Ca2+ regulation in the transformed state.