Phosphorylation of tyrosine 393 in the kinase domain of Bcr-Abl influences the sensitivity towards imatinib in vivo.
The Bcr-Abl fusion protein arising through the t(9;22)(q34;q11) reciprocal translocation is the causative agent in chronic myeloid leukemia and a subset of acute lymphocytic leukemia. Imatinib mesylate is a specific inhibitor of the Bcr-Abl kinase and has shown promising results in clinical studies. The structural relation between the Bcr-Abl oncogene and the tyrosine kinase inhibitor imatinib has recently been elucidated by an elegant crystal structure analysis, emphasizing the importance of dephosphorylated tyrosine 393 (Tyr393) in Bcr-Abl for access of the inhibitor to the kinase domain. By mutating this tyrosine to phenylalanine and thereby mimicking a constitutively dephosphorylated state, we now show that Ba/F3 cells transformed by this mutant demonstrate an increased sensitivity towards imatinib in vivo. This effect is not due to an impaired kinase activity of Bcr-Abl Y393F, since a synthetic substrate is phosphorylated with similar kinetics. Treatment of Ba/F3 cells transfected with Bcr-Abl wild type with a phosphatase inhibitor diminished the effect of imatinib, but did not influence the growth of Ba/F3 cells transfected with Bcr-AblY393F. The results support the findings of the crystal structure and indicate that Tyr393 indeed plays a significant role for the sensitivity of Bcr-Abl towards imatinib in vivo. These data implicate the regulation of Tyr393 phosphorylation as a potential mechanism of imatinib resistance.
Miething
C
C
Department of Internal Medicine III, Technical University of Munich, Munich, Germany.
Mugler
C
C
Grundler
R
R
Hoepfl
J
J
Bai
R-Y
RY
Peschel
C
C
Duyster
J
J
D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001549:Benzamides; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000378:metabolism; D008894:Milk Proteins; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D010879:Piperazines / Q000627:therapeutic use*; D011743:Pyrimidines / Q000627:therapeutic use*; D050799:STAT5 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism*
D000970:Antineoplastic Agents; D001549:Benzamides; D004268:DNA-Binding Proteins; D008894:Milk Proteins; D010879:Piperazines; D011743:Pyrimidines; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D014443:Tyrosine; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl