title: PI 3-kinase activation in BCR/abl-transformed hematopoietic cells does not require interaction of p85 SH2 domains with p210 BCR/abl.
abstract: 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 interleukin-3-dependent hematopoietic cells. The mechanism of BCR/abl-mediated transformation of hematopoietic cells is poorly understood and involves activation of at least two signaling pathways, p21ras and PI 3-kinase. Here we report that PI 3,4-P2 and PI 3,4,5-P3, the enzymatic products of PI 3-kinase, accumulate in metabolically labeled transformed hematopoietic cells, in contrast to our previous report on the lack of accumulation of PI 3-kinase products in nontransformed NIH 3T3 fibroblasts that express p210 BCR/abl. Transformed cells also have increased PI 3-kinase activity in total cell extracts and membrane fractions. Activation of PI 3-kinase occurs by occupancy of SH2 domains of PI 3-kinase regulatory subunit, p85, by phosphorylated YXXM motifs. Therefore, 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 and with p85 SH2 domains was evident in hematopoietic cells that express the wt p210 BCR/abl. However, the binding of BCR/abl to p85 SH2 domains was abolished in cells expressing mutant, temperature-sensitive (ts) p210 BCR/abl in which the tyrosine in the YXXM motif of p210 BCR/abl was replaced by histidine. Despite lack of direct interaction with p85 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 immunoprecipitates. These data suggest that BCR/abl-induced activation of PI 3-kinase 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.
authors.affiliation: Department of Biomedical Research, St Elizabeth's Medical Center, Tufts University School of Medicine, Boston, MA 02135, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Jain
authors.forename: M
authors.initials: M
authors.lastname: Susa
authors.forename: M L
authors.initials: ML
authors.lastname: Keeler
authors.forename: N
authors.initials: N
authors.lastname: Carlesso
authors.forename: B
authors.initials: B
authors.lastname: Druker
authors.forename: L
authors.initials: L
authors.lastname: Varticovski
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004789:Enzyme Activation; D005347:Fibroblasts / Q000201:enzymology; D016044:Fusion Proteins, bcr-abl / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000201:enzymology*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D018909:src Homology Domains
chemical_list: D011993:Recombinant Fusion Proteins; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D016044:Fusion Proteins, bcr-abl