The trafficking and signaling of HCMV encoded chemokine receptors

Abstract

In my thesis I demonstrate that the viral receptor US28 is targeted to late endosomes/lysosomes by a direct interaction with the GPCR-associated sorting protein (GASP-1). The prevention of the US28/GASP-1 significantly delays the degradation and prmotes the recycling of US28. Furthermore, the modification of endogenous GASP -1 levels is directly connected with an alteration of the constitutive signaling capacity of US28. When GASP-1 is overexpressed, the inositol phosphate accumulation and the activation of transcription factors NF-κB and CREB are significantly increased. On the other hand, the disruption of the GASP-1/US28 interaction significantly reduces the signaling capacity of US28. Hence, this study shows for the first time the existence of a direct connection between GASP-1 dependent receptor sorting and the signaling activity of the receptor. In addition to the regulation through sorting processes, the trafficking and signaling properties of receptors can be altered through heteromerization. I provide evidence that the signaling capacity of US28 is controlled by the interaction with other receptors. Co-expression of US28 with the orphan HCMV encoded receptors UL33 and UL78 decreases the activation of transcription factors by US28. In contrast, co-expression of US27 significantly enhances the signaling activity of US28. Hence, it seems that US27, UL33 and UL78 encoded by HCMV are able to differentially modulate the signaling of US28. Further on, I demonstrate that US28 is able to interact with endogenous 7TM/GPCRs, such as histamine 4 receptor (H4R) or CC chemokine receptor 5 (CCR5). Co-expression of US28 reduces the overall expression level of H4R and both receptors co-localize in the endoplasmatic reticulum (ER). Hence, the heteromerization with US28 might inhibit the export of H4R to the plasma membrane. Interestingly, the internalization-deficient US28∆300 does not alter the surface expression of H4R, suggesting that the constitutive endocytosis/trafficking of US28 is involved in the ER retention of H4R. Moreover, US28 is also able to heteromerize with endogenous CCR5. Transient expression of US28 in stable transfected CCR5 cells decreases the surface expression of CCR5 and leads to its retention in the ER. Finally, the interaction with CCR5 also significantly reduces the activation of the transcription factor NF-κB by US28. Summarized, I provide evidence that the activity of US28 is tightly regulated by various processes, such as (i) the direct interaction with GASP-1 and (ii) the heteromerization with HCMV-encoded and endogenous 7TM/GPCRs.

Datum der Bewilligung	2011
Originalsprache	Englisch
Gradverleihende Hochschule	Medizinische Universität Graz
Betreuer/-in	Akos Heinemann (Betreuer*in) & Maria Waldhoer (Betreuer*in)