ABSTRACT
The transcription factor p73, a member of the p53 family, mediates cell-cycle arrest and apoptosis in response to DNA damage-induced cellular stress, acting thus as a proapoptotic gene. Similar to p53, p73 activity is regulated by post-translational modification, including phosphorylation, acetylation and ubiquitylation. In C. elegans, the F-box protein FSN-1 controls germline apoptosis by regulating CEP-1, the single ancestral p53 family member. Here we report that FBXO45, the human ortholog of FSN-1, binds specifically to p73 triggering its proteasome-dependent degradation. Importantly, SCF(FBXO45) ubiquitylates p73 both in vivo and in vitro. Moreover, siRNA-mediated depletion of FBXO45 stabilizes p73 and concomitantly induces cell death in a p53-independent manner. All together, these results show that the orphan F-box protein FBXO45 regulates the stability of p73, highlighting a conserved pathway evolved from nematode to human by which the p53 members are regulated by an SCF-dependent mechanism.
Subject(s)
DNA-Binding Proteins/metabolism , F-Box Proteins/metabolism , Nuclear Proteins/metabolism , Proteasome Endopeptidase Complex/metabolism , Tumor Suppressor Proteins/metabolism , Animals , Breast Neoplasms/pathology , CHO Cells , Cell Death/genetics , Cell Line , Cell Line, Transformed , Cell Line, Tumor , Cricetinae , Cricetulus , F-Box Proteins/genetics , Green Fluorescent Proteins/metabolism , HeLa Cells , Hemagglutinins/metabolism , Humans , Kidney/cytology , Leupeptins/pharmacology , Mutation , Neuroblastoma/pathology , Proteasome Inhibitors , Protein Binding , RNA, Small Interfering/metabolism , Substrate Specificity , Temperature , Transfection , Tumor Protein p73 , Ubiquitin-Protein Ligases/metabolism , UbiquitinationABSTRACT
The HECT-type E3 ubiquitin ligase (E3) Itch is absent in the non-agouti-lethal 18H or Itchy mice, which develop a severe immunological disease, including lung and stomach inflammation and hyperplasia of lymphoid and hematopoietic cells. The involvement of Itch in multiple signaling pathways and pathological conditions is presently an area of extensive scientific interest. This review aims to bring together a growing body of work exploring Itch-regulated biological processes, and to highlight recent discoveries on the regulatory mechanisms modulating its catalytic activity and substrate recognition capability. Our contribution is also an endeavor to correlate Itch substrate specificity with the pathological defects manifested by the mutant Itchy mice.
