Regulation of intracellular levels of calmodulin and tubulin in normal and transformed cells.

Abstract

Transformation of mammalian tissue culture cells by oncogenic viruses results in a 2-fold increase in the intracellular concentration of calmodulin quantitated by radioimmunoassay. The two pairs of companion cell lines used in this study were the Swiss mouse 3T3/simian virus 40-transformed 3T3 cells and the normal rat kidney (NRK)/Rous sarcoma virus-transformed NRK cells. The increased intracellular levels of calmodulin in the transformed cells are due to a greater increase in the rate of synthesis (3-fold) relative to the change in the rate ofdegradation (1.4-fold). On the other hand, no increases were observed in tubulin levels as quantitated by a colchicine-binding assay. The lack of change in tubulin concentration was accounted for by a 2-fold increase in the rate of degradation that is compensated by a similar increase in the rate of synthesis. The consequence of such changes in both transformed cell types is a 2-fold increase in the calmodulin-to-tubulin protein ratio relative to that in their nontransformed counterparts. 996The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

Activity and regulation by growth factors of calmodulin-dependent protein kinase III (elongation factor 2-kinase) in human breast cancer

“…In this regard, CaM-dependent pathways represent a compelling area for investigation into the proliferative responses of malignant cells. Numerous studies have suggested the importance of CaM-mediated signalling in cell proliferation and malignant transformation (Chafouleas et al, 1981;MacManus et al, 1981;Veigl et al, 1984;Means, 1987, 1989;Lu and Means, 1993). Early studies from our laboratory and others detected increased CaM in malignant cells (Hait and DeRosa, 1988;Rasmussen and Means, 1989;Lu and Means, 1993), and demonstrated that drugs that bind directly to CaM and inhibit its function were both antiproliferative and cytotoxic to breast cancer cells (Hait and Lee, 1985;Ford et al, 1989).…”

“…In this regard, calmodulin (CaM), a ubiquitous mediator of calcium-dependent signal transduction, represents a compelling area for investigation into the proliferative responses of malignant cells (Hait and Lazo, 1986;Lu and Means, 1993). For example, Chafouleas et al (1981) reported that CaM was required for re-entry of quiescent Chinese hamster ovary (CHO) cells into the cell cycle. Rasmussen and Means (1987) demonstrated that overexpression of CaM increased cell proliferation by decreasing the G 1 /S transit time, and that CaM antisense blocked this effect (Rasmussen and Means, 1989).…”

“…Rasmussen and Means (1987) demonstrated that overexpression of CaM increased cell proliferation by decreasing the G 1 /S transit time, and that CaM antisense blocked this effect (Rasmussen and Means, 1989). Although CaM is a constitutively expressed protein in nondividing cells (Veigl et al, 1984), cellular transformation to malignancy has been associated with increases in intracellular CaM (Chafouleas et al, 1981). In addition, a positive correlation between CaM levels and the growth rate of malignant cells has been demonstrated (MacManus et al, 1981).…”

Intracellular levels of calmodulin are increased in transformed cells

“…Although Chafouleas et al had clarified the true increase of CaM referring to the change of tubulin [5], an increase of the tubulin level during cell cycle has also been reported [14].…”

“…However, an increase in the amount of CaM relative to total protein has been reported in chicken embryo fibroblasts transformed by Rous sarcoma virus, with CaM level quantified by either densitometric scanning of polyacrylamide gels [3] or bioassay [4], but it has not been verified if this increase was true in individual cells. In 1981,by the means of radioimmunoassay, it was reported that the transformation by oncogenic viruses resulted in an increase in the number of CaM molecules per cell by preferentially stimulating the synthesis of this protein, whereas no such elevation was observed in case of tubulin; and the increase of CaM in transformed cells amounted to 2 folds [5].…”