title: Enhancement of cellular radiation sensitivity through degradation of Chk1 by the XIAP-XAF1 complex.
abstract: X-linked inhibitor of apoptosis (XIAP) and Chk1 are potential molecular targets in radiotherapy. However, their molecular association in the regulation of radiation sensitivity has been rarely studied. Here, we show that XIAP modulates radiation sensitivity by regulating stability of Chk1 in lung cancer cells. Both Chk1 and XIAP are highly expressed in various lung cancer cells. Overexpression of XIAP increased cell survival following genotoxic treatments by preventing downregulation of Chk1. However, XIAP reversed Chk1-protective activity in the presence of XIAP-associated factor 1 (XAF1) by degrading Chk1 via ubiquitination-dependent proteasomal proteolysis. The XIAP-XAF1 complex-mediated Chk1 degradation also required CUL4A and DDB1. Chk1 or XIAP was associated with DDB1 and CUL4A. Depletion of CUL4A or DDB1 prevented the XIAP-XAF1-mediated Chk1 degradation suggesting involvement of a CUL4A/DDB1-based E3 ubiquitin ligase in the process or its collaboration with XIAP E3 ligase activity. Taken together, our findings show that XIAP plays a dual role in modulation of Chk1 stability and cell viability following IR. In the absence of XAF1, XIAP stabilizes Chk1 under IR with corresponding increase of cell viability. By contrast, when XAF1 is overexpressed, XIAP facilitates Chk1 degradation, which leads to enhancement of radiation sensitivity. This selective regulation of Chk1 stability by XIAP and XAF1 could be harnessed to devise a strategy to modulate radiation sensitivity in lung cancer cells.
authors.affiliation: a Division of Radiation Effects; Korea Institute of Radiological and Medical Sciences ; Seoul , Republic of Korea.
authors.forename: Kwang Seok
authors.initials: KS
authors.lastname: Kim
authors.forename: Jong-Ik
authors.initials: JI
authors.lastname: Heo
authors.forename: Kyu Jin
authors.initials: KJ
authors.lastname: Choi
authors.forename: Sangwoo
authors.initials: S
authors.lastname: Bae
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D044842:Cullin Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D009153:Mutagens / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011494:Protein Kinases / Q000378:metabolism*; D059748:Proteolysis; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics; D011839:Radiation, Ionizing; D054875:Ubiquitination; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C114234:CUL4A protein, human; D044842:Cullin Proteins; C091435:DDB1 protein, human; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009153:Mutagens; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D051636:X-Linked Inhibitor of Apoptosis Protein; C417551:XAF1 protein, human; D007371:Interferon-gamma; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1
keywords: Chk1; Chk1, Checkpoint kinase 1; DDR, DNA damage responses; DNA damage response; IFN-γ, interferon-gamma; IR, ionizing radiation; RING domain; XAF1; XAF1, XIAP-associated factor 1; XIAP; XIAP, X-linked inhibitor of apoptosis; radiation sensitivity; synthetic lethality