Tropomyosin Isoform Switching in Tumorigenic Human Fibroblasts

Abstract

We identified six tropomyosin (Tm) isoforms in diploid human fibroblasts. We used computerized microdensitometry of 2-dimensional protein profiles to measure the relative rates of synthesis and abundance of the individual Tm isoforms and actin, the two major structural constituents of microfilaments. In carcinogen-transformed human fibroblasts (HuT-14), the rates of synthesis of three Tm isoforms (Tm1, Tm2, and Tm6) were greatly decreased relative to normal diploid parental fibroblasts and to actin. In contrast, related nontumorigenic HuT fibroblasts which are "immortalized" and anchorage independent exhibited both slight down-regulation of Tm1 and Tm6 and 3.5-fold up-regulation of Tm3. Thus, Tm isoform switching from the predominance of the larger more avid Tm isoforms (Tm1, Tm2, Tm3, and Tm6) to the smaller, less avid Tm isoforms (Tm4 and Tm5) in microfilaments was a transformation-induced change correlated with tumorigenicity in human fibroblasts.

Isolation and Characterization of a cDNA That Encodes Mouse Fibroblast Tropomyosin Isoform 2

“…In striated muscle, they, in concert with troponins, regulate the calcium-sensitive interaction with actin and myosin (6). In nonmuscle cells, they are associated with cytoskeletal actin in microfilaments (8,15). Their function in these filaments is not clear but has been suggested to be stabilization of the actin filament network, (1,3).…”