Characterising the key role played by the sodium/ proton exchanger NHE8 in endosomal protein sorting. (360G-Wellcome-082871_Z_07_Z)

Protein sorting at the multivesicular body (MVB) is essential for many processes including growth factor down regulation and antigen presentation. In addition, many viruses including the human immunodeficiency virus (HIV) exploit the MVB sorting machinery during assembly and release. MVBs are formed by the inward budding of the endosomal membrane to form internal vesicles, and proteins sorted into these vesicles are destined for the lumen of the lysosome. My preliminary results suggest that N HE8 is the mammalian orthologue of Nhx1p, a sodium/ proton exchanger essential for MVB protein sorting in yeast. NHE8 is the first sodium/ proton exchanger implicated in MVB sorting in mammalian cells. This proposal focuses on the characterisation of NHE8 and its role in mammalian cell endosomal protein trafficking. As well as a further investigation of the role of NHE8 in MVB sorting using protein degradation and HIV budding assays, we will study the pH inside MVBs in cells depleted for NHE8 by siRNA. The localisation, trafficking and regulation of NHE8 will also be studied.