Analysis of human c-Abl tyrosine kinase activity and regulation in S. pombe.

c-Abl protein tyrosine kinase activity is tightly regulated in vertebrate cells. Several mutations, including deletions of the SH3 domain, can activate abl and convert it into an oncogene. To study c-Abl activity in a cellular environment likely to lack specific regulators, we have expressed human c-Abl in Schizosaccharomyces pombe in an inducible fashion. c-Abl, but not a kinase inactive form of the molecule, causes growth arrest followed by death of the cells. Concomitant to Abl expression we observed extensive phosphorylation of endogenous proteins on tyrosine. Mutations in the SH2 domain or in the autophosphorylation site dramatically reduce the ability of Abl to confer the growth arrest phenotype and to phosphorylate endogenous proteins, suggesting a fundamental role of these structures in the activity of the enzyme. An SH3 domain deletion mutant of Abl is equally active as wild type c-Abl in yeast, even under conditions allowing detection of subtle differences. These results demonstrate that there is no intrinsic regulation of c-Abl kinase activity via the SH3 domain and suggest that the inhibitory effect of the SH3 domain observed in mammalian cells is medicated by a factor that is absent in fission yeast. Expression of Ab1 S.pombe provides a novel quantitative assay for ab1 activity and regulation.