PI-3-KINASE ACTIVATION IN BCR ABL-TRANSFORMED HEMATOPOIETIC-CELLS DOES NOT REQUIRE INTERACTION OF P85 SH2 DOMAINS WITH P210 BCR/ABL/

BCR/abl is a chimeric oncogene implicated in the pathogenesis of human chronic myelogenous leukemia. Expression of the BCR/abl gene induces hematologic malignancies in transgenic mice and transformation of inte rleukin-3-dependent hematopoietic cells. The mechanism of BCR/abl-medi ated transformation of hematopoietic cells is poorly understood and in volves activation of at least two signaling pathways, p21(ras) and PI 3-kinase. Here we report that PI 3,4-P-2 and PI 3,4,5-P-3, the enzymat ic products of PI 3-kinase, accumulate in metabolically labeled transf ormed hematopoietic cells, in contrast to our previous report on the l ack of accumulation of PI 3-kinase products in nontransformed NIH 3T3 fibroblasts that express p210 BCR/abl. Transformed cells also have inc reased PI 3-kinase activity in total cell extracts and membrane fracti ons. Activation of PI 3-kinase occurs by occupancy of SH2 domains of P I 3-kinase regulatory subunit, p85, by phosphorylated YXXM motifs. The refore, we investigated whether BCR/abl binds to p85 and whether this binding is mediated by interaction of p85 SH2 domains with YXXM motif of BCR/abl. Association of p210 BCR/abl with p85 in immune complexes a nd with p85 SH2 domains was evident in hematopoietic cells that expres s the wt p210 BCR/abl. However, the binding of BCR/abl to p85 SH2 doma ins was abolished in cells expressing mutant, temperature-sensitive (f s) p210 BCR/abl in which the tyrosine in the YXXM motif of p210 BCR/ab l was replaced by histidine. Despite lack of direct interaction with p 85 SH2 domains, expression of ts p210 BCR/abl resulted in rapid, time- dependent activation of total and membrane-associated PI 3-kinase and increased PI 3-kinase activity in anti-P-tyr and anti-abl immunoprecip itates. These data suggest that BCR/abl-induced activation of PI 3-kin ase in hematopoietic cells does not require binding of p85 SH2 domains to BCR/abl gene product and involves interaction with other tyrosine phosphorylated intermediate proteins. (C) 1996 by The American Society of Hematology.