GENETIC REQUIREMENT FOR RAS IN THE TRANSFORMATION OF FIBROBLASTS AND HEMATOPOIETIC-CELLS BY THE BCR-ABL ONCOGENE

To determine the functional importance of Ras in transformation by Ab1 oncogenes, we used a genetic approach to measure the effect of impaired Ras activity on the ability of Bcr-Ab1 or v-Ab1 to transform cells. Expression of the catalytic domain of the GTPase activating protein for Ras (Gap C terminus) impaired soft agar colony formation by fibroblasts expressing v-Ab1 or Bcr-Ab1 by 70-80%. To test Ras function in a model that more closely resembles clinical diseases involving Bcr-Ab1 double gene retroviruses expressing Bcr-Ab1 paired with the Gap C terminus or dominant negative Ras were introduced into naive mouse bone marrow cells. Transformation by Bcr-Ab1 was completely blocked in both situations. Coexpression of normal c-H-Ras accelerated the transforming activity of Bcr-Ab1. These findings shaw that Ras activation is essential: for the leukemogenic activity of Ab1 oncogenes in two distinct model systems. The results genetically define a connection between the Bcr-Ab1 cytoplasmic tyrosine kinase and Ras and add to the accumulating evidence that deregulation of Ras is a central event in the genesis of a number of molecularly distinct forms of human myeloid leukemia.