title: Interplay between kinase domain autophosphorylation and F-actin binding domain in regulating imatinib sensitivity and nuclear import of BCR-ABL.
abstract: BACKGROUND
  The constitutively activated BCR-ABL tyrosine kinase of chronic myeloid leukemia (CML) is localized exclusively to the cytoplasm despite the three nuclear localization signals (NLS) in the ABL portion of this fusion protein. The NLS function of BCR-ABL is re-activated by a kinase inhibitor, imatinib, and in a kinase-defective BCR-ABL mutant. The mechanism of this kinase-dependent inhibition of the NLS function is not understood.
  
  
  RESULTS
  By examining the subcellular localization of mutant BCR-ABL proteins under conditions of imatinib and/or leptomycin B treatment to inhibit nuclear export, we have found that mutations of three specific tyrosines (Y232, Y253, Y257, according to ABL-1a numbering) in the kinase domain can inhibit the NLS function of kinase-proficient and kinase-defective BCR-ABL. Interestingly, binding of imatinib to the kinase-defective tyrosine-mutant restored the NLS function, suggesting that the kinase domain conformation induced by imatinib-binding is critical to the re-activation of the NLS function. The C-terminal region of ABL contains an F-actin binding domain (FABD). We examined the subcellular localization of several FABD-mutants and found that this domain is also required for the activated kinase to inhibit the NLS function; however, the binding to F-actin per se is not important. Furthermore, we found that some of the C-terminal deletions reduced the kinase sensitivity to imatinib.
  
  
  CONCLUSIONS
  Results from this study suggest that an autophosphorylation-dependent kinase conformation together with the C-terminal region including the FABD imposes a blockade of the BCR-ABL NLS function. Conversely, conformation of the C-terminal region including the FABD can influence the binding affinity of imatinib for the kinase domain. Elucidating the structural interactions among the kinase domain, the NLS region and the FABD may therefore provide insights on the design of next generation BCR-ABL inhibitors for the treatment of CML.
authors.affiliation: Division of Hematology-Oncology and Moores Cancer Center, Department of Medicine, University of California San Diego School of Medicine, La Jolla, California, United States of America.
authors.forename: Martin
authors.initials: M
authors.lastname: Preyer
authors.forename: Paolo
authors.initials: P
authors.lastname: Vigneri
authors.forename: Jean Y J
authors.initials: JY
authors.lastname: Wang
mesh_terms: D000199:Actins / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus / Q000187:drug effects*; D000818:Animals; D001549:Benzamides; D019556:COS Cells; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D016044:Fusion Proteins, bcr-abl / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000068877:Imatinib Mesylate; D008958:Models, Molecular; D016296:Mutagenesis; D009154:Mutation; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D017510:Protein Folding / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D011743:Pyrimidines / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D000199:Actins; D001549:Benzamides; D019913:Nuclear Localization Signals; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D014443:Tyrosine; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl