PHOSPHATIDYLINOSITOL-3 KINASE-ACTIVITY IS REGULATED BY BCR ABL AND ISREQUIRED FOR THE GROWTH OF PHILADELPHIA-CHROMOSOME-POSITIVE CELLS/

The BCR/ABL oncogenic tyrosine kinase is responsible for initiating an d maintaining the leukemic phenotype of Philadelphia chromosome (Ph(1) )-positive cells, Phosphatidylinositol-3 (PI-3) kinase is known to int eract with and be activated by receptor and nonreceptor tyrosine kinas es. We investigated whether PI-3 kinase associates with and/or is regu lated by BCR/ABL, whether this interaction is functionally significant for Ph(1) cell proliferation, acid, if so, whether inhibition of PI-3 kinase activity can be exploited to eliminate Ph(1)-positive cells fr om bone marrow, We show that the p85 alpha subunit of PI-3 kinase asso ciates with BCR/ABL and that transient expression of BCR/ABL in fibrob lasts and downregulation of BCR/ABL expression using antisense oligode oxynucleotides (ODNs) in Ph(1) cells activates and inhibits, respectiv ely, PI-3 kinase enzymatic activity. The use of specific ODNs or antis ense constructs to downregulate p85 alpha expression showed a requirem ent for p85 alpha subunit in the proliferation of BCR/ABL-dependent ce ll lines and chronic myelogenous leukemia (CML) primary cells. Similar ly, wortmannin, a specific inhibitor of the enzymatic activity of the p110 subunit of PI-3 kinase, inhibited growth of these cells, The grow th of normal bone marrow and erythromyeloid, but not megakaryocyte, pr ogenitors was inhibited by p85 alpha antisense [S]ODNs, but wortmannin , at the concentrations tested, did not affect normal hematopoiesis. T he proliferation of two BCR/ABL- and growth factor-independent cell li nes was not affected by downregulation of the expression of the p85 al pha subunit or inhibition of p110 enzymatic activity, confirming the s pecificity of the observed effects on Ph(1) cells. Thus, PI-3 kinase i s one of the downstream effecters of BCR/ABL tyrosine kinase in CML ce lls. Moreover, reverse transcriptase-polymerase chain reaction perform ed on single colonies to detect BCR-ABL transcripts showed that wortma nnin was able to eliminate selectively CML-blast crisis cells from a m ixture of normal bone marrow and Ph(1) cells, (C) 1995 by The American Society of Hematology.