X-linked inhibitor of apoptosis protein (XIAP) lacking RING domain localizes to the nuclear and promotes cancer cell anchorage-independent growth by targeting the E2F1/Cyclin E axis
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Zipeng Cao1,2, Xueyong Li3, Jingxia Li2, Wenjing Luo1, Chuanshu Huang2 and Jingyuan Chen1
1 Department of Occupational and Environmental Health and Ministry of Education Key Lab of Hazard Assessment and Control in Special Operational Environment, School of Public Health, Fourth Military Medical University, Xi’an, China
2 Nelson Institute of Environmental Medicine, New York University School of Medicine, Tuxedo, NY, USA
3 Department of Plastic and Burn Surgery, Tangdu Hospital, Fourth Military Medical University, Xi’an, China
Jingyuan Chen, email:
Chuanshu Huang, email:
Keywords: XIAP; RING domain; cell cycle progression; E2F1
Received: March 17, 2014 Accepted: July 16, 2014 Published: July 17, 2014
The inhibitor of apoptosis protein XIAP (X-linked inhibitor of apoptosis protein) is a well-documented protein that is located in cytoplasm acting as a potent regulator of cell apoptosis. Here, we showed that expressing XIAP with RING (Really Interesting New Gene) domain deletion (XIAP△RING) in cancer cells promoted cancer cell anchorage-independent growth and G1/S phase transition companied with increasing cyclin e transcription activity and protein expression. Further studies revealed that XIAP△RING was mainly localized in nuclear with increased binding with E2F1, whereas XIAP with BIR (Baculoviral IAP Repeat) domains deletion (XIAP△BIRs) was entirely presented in cytoplasma with losing its binding with E2F1, suggesting that RING domain was able to inhibit BIR domains nuclear localization, by which impaired BIRs binding with E2F1 in cellular nucleus in intact cells. These studies identified a new function of XIAP protein in cellular nucleus is to regulate E2F1 transcriptional activity by binding with E2F1 in cancer cells. Our current finding of an effect of XIAP△RING expression on cancer cell anchorage-independent growth suggests that overexpression of this protein may contribute to genetic instability associated with cell cycle and checkpoint perturbations, in addition to its impact on cellular apoptosis.
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