title: A Bcr/Abl-independent, Lyn-dependent form of imatinib mesylate (STI-571) resistance is associated with altered expression of Bcl-2.
abstract: The relationship between the Src kinase Lyn and Bcl-2 expression was examined in chronic myelogenous leukemia cells (K562 and LAMA84) displaying a Bcr/Abl-independent form of imatinib mesylate resistance. K562-R and LAMA-R cells that were markedly resistant to induction of mitochondrial dysfunction (e.g. loss of mitochondrial membrane potential, Bax translocation, cytochrome c, and apoptosis-inducing factor release) and apoptosis by imatinib mesylate exhibited a pronounced reduction in expression of Bcr/Abl, Bcl-x(L), and STAT5 but a striking increase in levels of activated Lyn. Whereas basal expression of Bcl-2 protein was very low in parental cells, imatinib-resistant cells displayed a marked increase in Bcl-2 mRNA and/or protein levels. Treatment of LAMA-R cells with the Src kinase inhibitor PP2 significantly reduced Lyn activation as well as Bcl-2 mRNA and protein levels. Transient or stable transfection of LAMA84 or K562 cells with a constitutively active Lyn (Y508F), but not with a kinase-dead mutant (K275D), significantly increased Bcl-2 protein expression and protected cells from lethality of imatinib mesylate. Ectopic expression of Bcl-2 protected K562 and LAMA84 cells from imatinib mesylate- and PP2-mediated lethality. Conversely, interference with Bcl-2 function by co-administration of the small molecule Bcl-2 inhibitor HA14-1 or down-regulation of Bcl-2 expression by small interfering RNA or antisense strategies significantly increased mitochondrial dysfunction and apoptosis induced by imatinib mesylate and the topoisomerase inhibitor VP-16 in LAMA-R cells. In marked contrast, these interventions had little effect in parental LAMA84 cells that display low basal levels of Bcl-2. Together, these findings indicate that activation of Lyn in leukemia cells displaying a Bcr/Abl-independent form of imatinib mesylate resistance plays a functional role in Bcl-2 up-regulation and provide a theoretical basis for the development of therapeutic strategies targeting Bcl-2 in such a setting.
authors.affiliation: Department of Medicine, Virginia Commonwealth University/Medical College of Virginia, Richmond, VA 23298, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Mohamed
authors.initials: M
authors.lastname: Rahmani
authors.forename: Seth J
authors.initials: SJ
authors.lastname: Corey
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D017209:Apoptosis; D051033:Apoptosis Inducing Factor; D001549:Benzamides; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D004396:Coloring Agents / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005420:Flavoproteins / Q000378:metabolism; D005434:Flow Cytometry; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D006801:Humans; D000068877:Imatinib Mesylate; D020014:K562 Cells; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000378:metabolism; D008894:Milk Proteins; D008928:Mitochondria / Q000378:metabolism; D009154:Mutation; D010879:Piperazines / Q000494:pharmacology*; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050799:STAT5 Transcription Factor; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: C412373:AG 1879; C494829:AIFM1 protein, human; D051033:Apoptosis Inducing Factor; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D001549:Benzamides; D004396:Coloring Agents; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005420:Flavoproteins; D008565:Membrane Proteins; D008894:Milk Proteins; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011743:Pyrimidines; D012333:RNA, Messenger; D050799:STAT5 Transcription Factor; D013778:Tetrazolium Salts; D013844:Thiazoles; D015534:Trans-Activators; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D000068877:Imatinib Mesylate; D045304:Cytochromes c; D016044:Fusion Proteins, bcr-abl; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; C022616:thiazolyl blue