Functional analysis of genetically encoded aGPCR signaling states
Tobias Langenhan, Leipzig University
Adhesion-GPCRs (aGPCRs) possess a highly modular architecture displaying protein regions that permit adhesion and target recognition through protein interactions, and G protein signaling through a heptahelical transmembrane unit (7TM). Evidence from several aGPCRs suggests that these receptors differentially engage with at least two independent activity contexts. In principle, this renders aGPCRs a receptor entity capable to handle multiple signals. These activities molecularly differ from each other in that one depends on the presence of the 7TM and intracellular domain (ICD), whereas the other one functions 7TM-independently provided that its extracellular domain (ECD) remains anchored to the cell membrane, e.g. through a single transmembrane helix. Genetic complementation experiments with full and truncated aGPCR homologs revealed a picture on aGPCR signalling, which is consistent with a hybrid receptor model, in which the ECD of an aGPCR is required for biological activities that differ from the activities exerted by the 7TM/ICD (i.e. adhesion vs transmembrane signaling, trans vs cis-protein interactions). However, if and how these bimodal activities are differentially regulated under physiological conditions is unclear thus far. Further, it is unknown whether an aGPCR molecule can receive its different signal inputs simultaneously, or if stimulus encounter restricts the receptor to one signaling state. This project centres on the hypothesis that splicing constitutes a mechanism to control the production of different dCirl mRNA species. Preliminary data show that at least two different types of dCirl transcripts are expressed in the fly resulting in two disparate receptor isoforms: a full-length receptor (dCIRL7TM), and a shortened receptor protein, which contains the ECD, a single transmembrane helix and an alternative ICD (dCIRL1TM). During the project the hypothesis will be tested that these dCIRL isoforms correspond to naturally occuring 7TM-dependent or 7TM-independent receptor states. The endogenous function of each isoform will be studied within an in vivo environment using Drosophila.
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