title: CDK inhibitor p57 (Kip2)  is negatively regulated by COP9 signalosome subunit 6.
abstract: Subunit 6 of the COP9 signalosome complex, CSN6, is known to be critical to the regulation of the MDM2-p53 axis for cell proliferation and anti-apoptosis, but its many targets remain unclear. Here we show that p57 (Kip2)  is a target of CSN6, and that CSN6 is a negative regulator of p57 (Kip2) . CSN6 associates with p57 (Kip2) , and its overexpression can decrease the steady-state expression of p57 (Kip2) ; accordingly, CSN6 deficiency leads to p57 (Kip2)  stabilization. Mechanistic studies show that CSN6 associates with p57 (Kip2)  and Skp2, a component of the E3 ligase, which, in turn, facilitates Skp2-mediated protein ubiquitination of p57 (Kip2) . Loss of Skp2 compromised CSN6-mediated p57 (Kip2)  destabilization, suggesting collaboration between Skp2 and CSN6 in degradation of p57 (Kip2) . CSN6's negative impact on p57 (Kip2)  elevation translates into cell growth promotion, cell cycle deregulation and potentiated transformational activity. Significantly, univariate Kaplan-Meier analysis of tumor samples demonstrates that high CSN6 expression or low p57 expression is associated with poor overall survival. These data suggest that CSN6 is an important negative regulator of p57 (Kip2) , and that overexpression of CSN6 in many types of cancer could lead to decreased expression of p57 (Kip2)  and result in promoted cancer cell growth.
authors.affiliation: Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. chbyxl@163.com
authors.forename: Bo
authors.initials: B
authors.lastname: Chen
authors.forename: Ruiying
authors.initials: R
authors.lastname: Zhao
authors.forename: Chun-Hui
authors.initials: CH
authors.lastname: Su
authors.forename: Monica
authors.initials: M
authors.lastname: Linan
authors.forename: Chieh
authors.initials: C
authors.lastname: Tseng
authors.forename: Liem
authors.initials: L
authors.lastname: Phan
authors.forename: Lekuan
authors.initials: L
authors.lastname: Fang
authors.forename: Heng-Yin
authors.initials: HY
authors.lastname: Yang
authors.forename: Huiling
authors.initials: H
authors.lastname: Yang
authors.forename: Wenqian
authors.initials: W
authors.lastname: Wang
authors.forename: Xiaoyin
authors.initials: X
authors.lastname: Xu
authors.forename: Nan
authors.initials: N
authors.lastname: Jiang
authors.forename: Shouliang
authors.initials: S
authors.lastname: Cai
authors.forename: Feng
authors.initials: F
authors.lastname: Jin
authors.forename: Sai-Ching J
authors.initials: SC
authors.lastname: Yeung
authors.forename: Mong-Hong
authors.initials: MH
authors.lastname: Lee
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D000075686:COP9 Signalosome Complex; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D053208:Kaplan-Meier Estimate; D051379:Mice; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D041681:NIH 3T3 Cells; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000502:physiology
chemical_list: D050761:Cyclin-Dependent Kinase Inhibitor p57; D046912:Multiprotein Complexes; D010447:Peptide Hydrolases; D000075686:COP9 Signalosome Complex