Association of the src-gene product of rous sarcoma virus with a pyruvate-kinase inactivating factor

Abstract

A casein-kmase preparation was isolated from extracts of mouse tumors induced by Rous sarcoma virus with the aid of affinity chromatography. The preparation was several hundredfold enriched with respect to casein-inase as well as pp60 src-kinase activity and contained a pyruvate-kinase inactivating factor. The pp60 src- kinase is expressed by a phosphoprotein ( pp60 src) which is the product of the transforming src gene of the Rous sarcoma virus (RSV). The pp60 src- kinase phosphorylates IgG from sera of rabbits bearing the RSV tumor (TBR sera) in free solution exclusively in tyrosine residues. The activity of pp60 src- kinase, as well as casein phosphorylation, was inhibited by μmolar concentrations of quercetin. The protein-kinase preparation caused MgATP-dependent inactivation of co-eluting pyruvate kinase. The activation of pyruvate kinase was blocked by phosphoribosyl pyrophosphate, fructose 1,6-diphosphate and P 1, p 5-di (adenosine-5')-pentaphosphate. These compounds also inhibited tyrosine phosphorylation of TBR-IgG and the casein-kinase activity. Immunoadsorption of the protein-kinase preparation by TBR-IgG was accompanied by a loss of the protein-kinase preparation's ability to cause MgATP-dependent inactivation of pyruvate kinase. Essentially the same results were obtained when tumor extracts were first passed over Blue Sepharose and subsequently over the casein-affinity column. Inactivation of purified chicken-liver pyruvate kinase, type M 2, was observed with an 800-fold purified pp60 src-kinase preparation obtained from RSV-transformed chicken-embryo fibroblasts. Incubation of the pyruvate kinase with pp60 srcin the presence of MgATP resulted in increased tyrosine phosphorylation of proteins with sub-unit molecular weights of 52 000 and 56 000 dalton. The latter corresponded to the sub-unit molecular weight of chicken-liver pyruvate kinase. The results show that the pyruvate-kinase inactivating factor is closely associated with pp60 src-kinase. The findings support the hypothesis that substrates of pp60 src, essential for cell proliferation, are among the enzymes that control glycolysis.