Reverse transformation of vole cells transformed by avian sarcoma virus containing the src gene.

Vole cells transformed by avian sarcoma virus carrying the src gene lose their fibroblastic morphology, the organized cytoskeletal system of the normal fibroblastic cell, the typical fibronectin deposit around the cell membrane, and the ability to shut off multiplication when suspended in liquid medium. All of these transformation characteristics are reversed by treatment with cAMP derivatives. Moreover, the cAMP treatment does not cause loss of activity of the src gene product. These data imply that cAMP exerts its effect at or after the point in the metabolic pathway affected by the src gene product, pp60src. Presumably, the decision to adopt the transformed or the normal state is determined by the degree to which the src gene or cAMP-mediated kinase activities respectively predominante in the cell. The development of all four transformation characteristics as a result of introduction of the src gene, and their coordinate reversal by cAMP derivatives, supports the previous thesis that in the normal vole or CHO fibroblast all four properties are part of a common regulatory system.

Deposition of fibronectin in the course of reverse transformation of Chinese hamster ovary cells by cyclic AMP.

The Chinese hamster ovary (CHO) cell, like other transformed cells, has lost the fibronectin deposit around its membrane. Treatment with cyclic AMP derivatives restores the typical fibroblastic deposit of fibronectin. Thus, the reverse transformation process induced by cyclic AMP (cAMP) in the CHO cell restores this important property as well as other morphological, biochemical, and growth behavioral characteristics of the normal fibroblastic state. The fibronectin deposit occurs significantly later in time than do other characteristics of the reverse transformation reaction and may therefore reflect a metabolic action that requires other cAMP effect to precede it. The restoration of fibronectin deposition in response to cAMP derivatives is also exhibited by vole cells transformed by avian sarcoma virus, but it is not by HeLa cell. Addition of Colcemid, which disrupts microtubules, to CHO cells containing a fibronectin deposit induced by cAMP derivatives causes little or no erosion of the deposit, but cytochalasin B, which disrupts 5-nm microfilaments, eliminates it completely. Thus, various features of the action of cAMP derivatives on CHO and related cells require integrity of the cellular microfibrils--in some cases microtubules only, in some cases 5-nm microfilaments only, and in some cases both classes of fibrils.