title: Casitas B-cell lymphoma (Cbl) proteins protect mammary epithelial cells from proteotoxicity of active c-Src accumulation.
abstract: Casitas B-cell lymphoma (Cbl) family ubiquitin ligases negatively regulate tyrosine kinase-dependent signal transduction by promoting degradation of active kinases. We and others previously reported that loss of Cbl functions caused hyperproliferation in lymphoid and hematopoietic systems. Unexpectedly, Cbl deletion in Cbl-b-null, Cbl-c-null primary mouse mammary epithelial cells (MECs) (Cbl triple-deficiency) induced rapid cell death despite enhanced MAP kinase and AKT activation. Acute Cbl triple-deficiency elicited distinct transcriptional and biochemical responses with partial overlap with previously described cellular reactions to unfolded proteins and oxidative stress. Although the levels of reactive oxygen species were comparable, detergent-insoluble protein aggregates containing phosphorylated c-Src accumulated in Cbl triple-deficient MECs. Treatment with a broad-spectrum kinase inhibitor dasatinib blocked protein aggregate accumulation and restored in vitro organoid formation. This effect is most likely mediated through c-Src because Cbl triple-deficient MECs were able to form organoids upon shRNA-mediated c-Src knockdown. Taking these data together, the present study demonstrates that Cbl family proteins are required to protect MECs from proteotoxic stress-induced cell death by promoting turnover of active c-Src.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198.
authors.forename: Chandrani
authors.initials: C
authors.lastname: Mukhopadhyay
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198.
authors.forename: Aleata
authors.initials: A
authors.lastname: Triplett
authors.affiliation: Department of Genetics, Cell Biology, and Anatomy, College of Medicine, University of Nebraska Medical Center, Omaha, NE 68198.
authors.forename: Tom
authors.initials: T
authors.lastname: Bargar
authors.affiliation: Department of Biological Sciences, College of Arts and Sciences, Bowling Green State University, Bowling Green, OH 43403.
authors.forename: Carol
authors.initials: C
authors.lastname: Heckman
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198.|Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, NE 68198.
authors.forename: Kay-Uwe
authors.initials: KU
authors.lastname: Wagner
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198; mnaramura@unmc.edu.|Department of Genetics, Cell Biology, and Anatomy, College of Medicine, University of Nebraska Medical Center, Omaha, NE 68198.|Fred and Pamela Buffett Cancer Center, University of Nebraska Medical Center, Omaha, NE 68198.
authors.forename: Mayumi
authors.identifier: 0000-0003-3658-0767
authors.initials: M
authors.lastname: Naramura
mesh_terms: D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D000069439:Dasatinib / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism*; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D016393:Lymphoma, B-Cell / Q000378:metabolism*; D008297:Male; D051379:Mice; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D015398:Signal Transduction; D054875:Ubiquitination; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D050721:Proto-Oncogene Proteins c-cbl; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; C493849:Cbl protein, mouse; D000069439:Dasatinib
keywords: CBL; protein degradation; stress response; tyrosine kinase; ubiquitin ligase