A50
Nucleolar translocation of NF-κB/RelA and apoptosis as a consequence of proteasome stress
Hazel Thoms, Carolyn Loveridge, Alexandra Clipson, Karina Reinhardt, Malcolm Dunlop, Lesley Stark
University of Edinburgh, Edinburgh, UK
Compartmentalization of transcription-associated proteins within nuclear bodies is increasingly recognized as an important mechanism for regulating gene expression and apoptosis. We have previously demonstrated that upon stimulation of the NF-κB pathway, the RelA component of NF-kB is compartmentalised to the nucleoplasm or nucleolus, dependent on the stimuli. Furthermore we demonstrated that nucleolar sequestration of RelA is causally involved in the induction of apoptosis while nucleoplasmic sequestration generally inhibits apoptosis. Understanding the mechanisms that regulate the nuclear/nucleolar distribution of RelA is highly desirable because, it may allow the development of molecules that target RelA to the nucleolar compartment to induce apoptosis of cancer cells.
Here we make the novel observation that RelA is compartmentalised within the nucleolus in response to the proteasome inhibitors MG132 and lactacystin. This occurs in a time and dose dependent manner and is causally involved in the apoptotic response to these agents. Furthermore, proteasome inhibitor-mediated nucleolar translocation of RelA is preceded by ubiqutinylation of the protein. We demonstrate that aspirin, an agent we have previously shown to induce nucleolar translocation of RelA, causes partial proteasome inhibition and ubiquitinylation of the protein which again, precedes nucleolar translocation. We show that deleting amino acids 27-30 of RelA blocks both ubiquitinylation and nucleolar targeting of the protein in response to aspirin and MG132 while increased expression of COMMD1, a component of the RelA ubiquitin ligase complex, promotes this effect. Together, these data identify a mechansim that regulates the nuclear/nucleolar distribution of RelA and apoptosis involving the ubiquitin-proteasome system and suggests a potential role for NF-κB/RelA in surveillance of proteasome function. These data have substantial relevance to the chemoprevention and therapy of cancer.
