G protein-coupled receptors (GPCRs) constitute a super-family of cell surface receptors that regulate a variety of cell functions. Defective export trafficking of GPCRs from the endoplasmic reticulum (ER) through the Golgi to the cell surface is associated with the pathogenesis of a variety of human diseases, nephrogenic diabetes insipidus being one of the best-studied examples. However, the molecular mechanism underlying the export of GPCRs remains poorly understood. Our overall objective is to define the molecular mechanism of GPCR export trafficking and its functional role in regulating cellular responses to hormones and drugs. Under this broad objective, this proposal focuses on two important questions: 1) how GPCRs export from the ER? 2) How GPCRs transport from the ER to the Golgi? Our preliminary data have demonstrated that the motif consisting of a phenylalanine (F) and double leucine (L) spaced by six residues {F(x)6LL} is required for export of the alpha2B-adrenergic (AR) and angiotensin ll-type 1 (AT1R) receptors from the ER. This motif is highly conserved in many GPCRs and thus may provide a common mechanism for their export. Our data also indicate that different GPCRs may use different routes to move to the cell surface in neuroblastoma- glioma NG108 and human embryonic kidney HEK293 cell lines. Non-glycosylated alpha2B-AR uses a novel, as yet undefined pathway.
The Specific Aims are: 1) To define the mechanism of the F(x)6LL motif in mediating GPCR export from the ER. We will determine if the F(x)6LL motif is a common code for GPCR export from the ER, determine if the F(x)6LL motif functions as an ER export signal and/or regulates receptor folding, and define the structure-function relationship of the F(x)6LL motif. 2) To define the novel pathway for alpha2B-AR transport from the ER to the Golgi. We will define intracellular compartments and transport vesicles involved in alpha2B-AR transport and determine if glycosylation alters alpha2B-AR transport pathway. These studies will provide new and important information regarding the molecular mechanisms underlying GPCR export and its control on receptor function. Such information may help exploit the possibility of developing new therapeutic strategies for treating disease by targeting GPCR transport.
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