Role of SUMO-1 modification in transcriptional activation

Genetic transcription;Genetic code;Genetic regulation

Pinto Desterro, Maria Joana ; Hay, Ron ; Hay, Ron

University:University of St Andrews

Department:Biology (School of)

关键词: Genetic transcription;    Genetic code;    Genetic regulation;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/2724/MariaJPintoDesterroPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

In unstimulated cells, the transcription factor NF-κB is held in thecytoplasm in an inactive state by IκB inhibitor proteins. Activation of NF--KB ismediated by signal induced degradation of IκBα via the ubiquitin proteasome-dependentpathway. Targeting the proteins for ubiquitin-mediated proteolysis is anirrevocable decision, and as such, the process needs to be highly specific and tightlyregulated. This task is achieved by conjugation and deconjugation enzymes that actin a dynamic and coordinated mechanism.In a yeast two hybrid screen designed to identify proteins involved in IκBαsignalling Ubch9 was found to interact with the N-terminal regulatory region ofIκBα. Although Ubch9 is an enzyme homologous to E2 ubiquitin conjugatingenzymes we have shown that is unable to form a thioester with ubiquitin but it iscapable to form a thioester with the small ubiquitin-like protein SUMO- 1. To fullycharacterise the SUMO-1 modification reaction we have purified the proteins andcloned the genes encoding the SUMO-1 activating enzyme (SAEl/SAE2) andshown that it is homologous to enzymes involved in the activation of ubiquitin,Smt3p, the yeast SUMO-1 homologue, and Rublp/Nedd8, another ubiquitin-likeprotein. SUMO-1 is conjugated to target proteins by a pathway that is distinct from,but analogous to, ubiquitin conjugation.SUMO-1 was efficiently conjugated, both in vivo and in vitro, to IκBα onlysine 21, which is also utilised for ubiquitin modification. Thus, by blockingubiquitination SUMO-1 modification acts antagonistically to generate a pool ofIκBα resistant to proteasome-mediated degradation which consequently inhibitsNF-κB dependent transcription activation.In view of several lines of similarity between NF-kB and p53, theinvolvement of SUMO-1 modification in the metabolism of the tumour supressorp53 was investigated. We have shown that p53 is modified by SUMO-1 at a singlesite, lysine 386 in the C-terminus of p53. Although p53 is regulated byubiquitination, SUMO-1 and ubiquitin modification do not compete for the samelysine in p53. However, overexpression of SUMO-1 activates the transcriptionalactivity of wild type p53, but not K386R p53 where the SUMO-1 acceptor site hasbeen mutated.A consensus sequence was obtained by comparison of the sequencessurrounding the SUMO-1 acceptor lysine in proteins that have been shown to bemodified by SUMO-1 and revealed a possible recognition site for SUMO-1conjugation machinery.Tagging of proteins with SUMO-1 regulates transcriptional activation, eitherby interfering with subcellular location or with the ubiquitination pathway. Thepathway may represent a novel target for drug development.