Regulation of the expression of tropomyosins and actin cytoskeleton by ras transformation.

Neoplastic transformation by Ras proteins markedly suppresses the expression of certain isoforms of tropomyosins (TMs), which are important regulators of actin cytoskeleton. Downregulation of TMs and other actin-associated proteins is believed to result in the assembly of aberrant cytoskeleton, which in turn contributes to the malignant transformation by Ras. Oncogenic activation of ras, in addition to suppressing TMs by means of epigenetic mechanisms, also rapidly inhibits their cytoskeletal fractionation, leading to the disruption of cytoskeleton. Restoration of expression of certain isoforms of TMs reorganizes microfilaments and suppresses the malignant growth of ras-transformed cells. This chapter discusses some of the approaches to the analysis of TM isoform expression in normal and ras-transformed cells.