title: Cullin 4B protein ubiquitin ligase targets peroxiredoxin III for degradation.
abstract: Cullin 4B (CUL4B) is a scaffold protein that assembles cullin-RING ubiquitin ligase (E3) complexes. Recent studies have revealed that germ-line mutations in CUL4B can cause mental retardation, short stature, and many other abnormalities in humans. Identifying specific CUL4B substrates will help to better understand the physiological functions of CUL4B. Here, we report the identification of peroxiredoxin III (PrxIII) as a novel substrate of the CUL4B ubiquitin ligase complex. Two-dimensional gel electrophoresis coupled with mass spectrometry showed that PrxIII was among the proteins up-regulated in cells after RNAi-mediated CUL4B depletion. The impaired degradation of PrxIII observed in CUL4B knockdown cells was confirmed by Western blot. We further demonstrated that DDB1 and ROC1 in the DDB1-CUL4B-ROC1 complex are also indispensable for the proteolysis of PrxIII. In addition, the degradation of PrxIII is independent of CUL4A, a cullin family member closely related to CUL4B. In vitro and in vivo ubiquitination assays revealed that CUL4B promoted the polyubiquitination of PrxIII. Furthermore, we observed a significant decrease in cellular reactive oxygen species (ROS) production in CUL4B-silenced cells, which was associated with increased resistance to hypoxia and H(2)O(2)-induced apoptosis. These findings are discussed with regard to the known function of PrxIII as a ROS scavenger and the high endogenous ROS levels required for neural stem cell proliferation. Together, our study has identified a specific target substrate of CUL4B ubiquitin ligase that may have significant implications for the pathogenesis observed in patients with mutations in CUL4B.
authors.affiliation: Key Laboratory of Experimental Teratology, Ministry of Education, Institute of Medical Genetics, Shandong University School of Medicine, Jinan, Shandong 250012, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Li
authors.forename: Defen
authors.initials: D
authors.lastname: Lu
authors.forename: Fengjuan
authors.initials: F
authors.lastname: He
authors.forename: Haibin
authors.initials: H
authors.lastname: Zhou
authors.forename: Qiao
authors.initials: Q
authors.lastname: Liu
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Changshun
authors.initials: C
authors.lastname: Shao
authors.forename: Yaoqin
authors.initials: Y
authors.lastname: Gong
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D049109:Cell Proliferation / Q000187:drug effects; D044842:Cullin Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D055785:Gene Knockdown Techniques; D018095:Germ-Line Mutation; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008607:Intellectual Disability / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D058953:Neural Stem Cells / Q000378:metabolism* / Q000473:pathology; D016877:Oxidants / Q000494:pharmacology; D061105:Peroxiredoxin III / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D054875:Ubiquitination; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: C517832:CUL4B protein, human; D002352:Carrier Proteins; D044842:Cullin Proteins; C091435:DDB1 protein, human; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; D016877:Oxidants; C479529:RBX1 protein, human; D034741:RNA, Small Interfering; D006861:Hydrogen Peroxide; D061105:Peroxiredoxin III