Kinase domain mutants of Bcr enhance Bcr-Abl oncogenic effects.
Bcr-Abl acquires its transforming ability through its upregulated Abl tyrosine kinase activity. Bcr is a phosphoprotein with a novel serine/threonine kinase activity encoded by its first exon. In chronic myelogenous leukemia (CML) cells, Bcr-Abl phosphorylates Bcr on tyrosine residues reducing its kinase activity. Overexpression of BCR in BCR-ABL+ cells produces a phosphoserine form of Bcr, which inhibits the oncogenic effects of BCR-ABL. To investigate the inhibitory effects of Bcr on Bcr-Abl, we expressed BCR/GFP in TonB210 cells, which contain a tetracycline-inducible BCR-ABL. In nude mice injected with cell clones of TonB210/BCR/GFP, tumor formation was delayed, and tumors were 50% smaller compared with the TonB210/GFP. In addition, TonB210/ BCR/GFP cells had little colony-forming ability in soft agar compared with TonB210/GFP cells. In contrast, a point mutant of BCR (Y360F), which disrupts its kinase activity, not only blocked Bcr's inhibitory effects but also enhanced the oncogenic effects of Bcr-Abl in a solid tumor model and in soft agar colony assays. Similar effects were observed with a second BCR kinase domain mutant, S354A. These results indicate that the inhibitory function of Bcr directed toward Bcr-Abl requires its kinase function.
Perazzona
B
B
Department of Molecular Pathology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Lin
H
H
Sun
T
T
Wang
Y
Y
Arlinghaus
R
R
D000818:Animals; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D002478:Cells, Cultured; D016044:Fusion Proteins, bcr-abl / Q000235:genetics* / Q000502:physiology; D016259:Genes, myc; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D050505:Mutant Proteins / Q000502:physiology; D010770:Phosphotransferases / Q000235:genetics*; D017434:Protein Structure, Tertiary / Q000235:genetics; D051562:Proto-Oncogene Proteins c-bcr / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D014162:Transfection; D014410:Tumor Stem Cell Assay
D050505:Mutant Proteins; D010770:Phosphotransferases; D016044:Fusion Proteins, bcr-abl; C496613:BCR protein, human; D051562:Proto-Oncogene Proteins c-bcr