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Title: Characterising the function of ubiquitin associated protein 1 (UBAP1)
Author: Stefani, Flavia
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2013
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Inactivating EGF signalling is key to modulating cell growth and avoiding cancer. To do this, the EGF receptor is ubiquitinated, internalized and sorted to lysosome for degradation. This latter process is coordinated by the endosomal sorting complex required for transport (ESCRT) machinery, a multi-complex protein machinery divided into four groups: ESCRT-0, I, II, III. ESCRTs recognise ubiquitinated cargoes and sort them from the limiting membrane of intermediate vesicles of maturing endosomes. In mammalian cells, the ESCRT machinery is also involved in other membrane related events, such as cytokinesis and viral budding. Certain ESCRTs, such as ESCRT-0, seem to be specifically required for cargo sorting to lysosomes, whereas other downstream ESCRTs, such as ESCRT-I, are required for all the cellular processes where the ESCRT machinery is involved. The existence of multiple variants of ESCRT-I components may suggest that ESCRT-I itself exists in different variants, each specific for a different membrane-based event. A bioinformatic study suggested Ubiquitin Associated Protein1 (UBAP1)as a novel variant of the ESCRT-I component MVB12. Moreover, a preliminary Y2H study identified UBAP1 as a potential binding partner of the ESCRT machinery regulator, HDPTP. This study aims to characterise UBAP1 as a variant MVB12 and a novel member of ESCRT-I. The results show that loss of UBAP1 impairs EGFR trafficking to lysosomes and causes the accumulation of ubiquitinated proteins on aberrant vacuolar structures. In cells, UBAP1 is incorporated in a complex with the ESCRT-I members TSG101, VPS28 and VPS37A. Importantly, UBAP1 uses three tandem ubiquitin associated (UBA) domains to bind ubiquitin and this activity is key for UBAP1 to function in cells. UBAP1 binds HDPTP via a peptide motif located about 100 aa. proximal to the tandem UBA domains. Altogether, the data shown in this thesis suggest that UBAP1 represents a subunit of an endosome-specific ESCRT-I complex, whose function may be coordinated by the ESCRT machinery regulator HDPTP.
Supervisor: Woodman, Philip ; Petersen, Janni Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ubiquitin ; ESCRT machinery ; UBAP1 ; HDPTP ; TSG101