title: The E3 Ligase CHIP Mediates p21 Degradation to Maintain Radioresistance.
abstract: Lung cancer resists radiotherapy, making it one of the deadliest forms of cancer. Here, we show that human lung cancer cell lines can be rendered sensitive to ionizing radiation (IR) by RNAi knockdown of C-terminus of Hsc70-interacting protein (CHIP/STUB1), a U-box-type E3 ubiquitin ligase that targets a number of stress-induced proteins. Mechanistically, ubiquitin-dependent degradation of the cyclin-dependent kinase (CDK) inhibitor, p21 protein, is reduced by CHIP knockdown, leading to enhanced senescence of cells in response to exposure to IR. Cellular senescence and sensitivity to IR is prevented by CRISPR/Cas9-mediated deletion of the p21 gene (CDKN1A)in CHIP knockdown cells. Conversely, overexpression of CHIP potentiates p21 degradation and promotes greater radioresistance of lung cancer cells.In vitroand cell-based assays demonstrate that p21 is a novel and direct ubiquitylation substrate of CHIP that also requires the CHIP-associated chaperone HSP70. These data reveal that the inhibition of the E3 ubiquitin ligase CHIP promotes radiosensitivity, thus suggesting a novel strategy for the treatment of lung cancer.Implications:The CHIP-HSP70-p21 ubiquitylation/degradation axis identified here could be exploited to enhance the efficacy of radiotherapy in patients with non-small cell lung cancer.Mol Cancer Res; 15(6); 651-9. ©2017 AACR.
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia.
authors.forename: Kuntal
authors.initials: K
authors.lastname: Biswas
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia.
authors.forename: Sukumar
authors.initials: S
authors.lastname: Sarkar
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia.
authors.forename: Kangping
authors.initials: K
authors.lastname: Du
authors.affiliation: Center for Cell Signaling and Department of Microbiology, Immunology & Cancer Biology, University of Virginia, Charlottesville, Virginia.
authors.forename: David L
authors.initials: DL
authors.lastname: Brautigan
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia.|Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia.
authors.forename: Tarek
authors.initials: T
authors.lastname: Abbas
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia. jml2p@virginia.edu.
authors.forename: James M
authors.initials: JM
authors.lastname: Larner
mesh_terms: D064113:CRISPR-Cas Systems; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy*; D059748:Proteolysis / Q000528:radiation effects; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C467728:STUB1 protein, human; D044767:Ubiquitin-Protein Ligases