title: The anti-apoptotic form of tyrosine kinase Lyn that is generated by proteolysis is degraded by the N-end rule pathway.
abstract: The activation of apoptotic pathways results in the caspase cleavage of the Lyn tyrosine kinase to generate the N-terminal truncated LynΔN. This LynΔN fragment has been demonstrated to exert negative feedback on imatinib induced apoptosis in chronic myelogenous leukemia (CML) K562 cells. Our investigations focus on LynΔN stability and how reduced stability reduces imatinib resistance. As the proteolytical generated LynΔN has a leucine as an N-terminal amino acid, we hypothesized that LynΔN would be degraded by the N-end rule pathway. We demonstrated that LynΔN is unstable and that its stability is dependent on the identity of its N-terminus. Additionally we established that LynΔN degradation could be inhibited by inhibiting either the proteasome or knocking down the UBR1 and UBR2 ubiquitin E3 ligases. Importantly, we also demonstrate that LynΔN degradation by the N-end rule counters the imatinib resistance of K562 cells provided by LynΔN expression. Together our data suggest a possible mechanism for the N-end rule pathway having a link to imatinib resistance in CML. With LynΔN being an N-end rule substrate, it provides the first example that this pathway can also provide a pro-apoptotic function as previous reports have currently only demonstrated anti-apoptotic roles for the N-end rule pathway.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton Alberta Canada.
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Eldeeb
authors.forename: Richard P
authors.initials: RP
authors.lastname: Fahlman
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides / Q000494:pharmacology*; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D005434:Flow Cytometry; D006801:Humans; D000068877:Imatinib Mesylate; D007124:Immunoenzyme Techniques; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010879:Piperazines / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000378:metabolism; D059748:Proteolysis; D011743:Pyrimidines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics; D014407:Tumor Cells, Cultured; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D034741:RNA, Small Interfering; D000068877:Imatinib Mesylate; D044767:Ubiquitin-Protein Ligases; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D020169:Caspases; D046988:Proteasome Endopeptidase Complex