Spatiotemporal dimensions of signaling

Andreas Bock,

Rudolf-Boehm-Institute of Pharmacology and Toxicology, University of Leipzig, Germany

Optical mapping reveals spatiotemporal GPCR signaling at the nanoscale

G protein-coupled receptors (GPCRs) form the largest family of cell membrane receptors and modulate almost any (patho)physiological process in humans. GPCR signaling involves activation of distinct G-protein families, modulation of multiple intracellular second messengers, such as cAMP, and activation of kinases. Therefore, GPCRs orchestrate overwhelmingly complex intracellular signaling networks that are capable of precisely relaying signals in space and time to exert a myriad of specific cell functions.

To ensure signaling specificity, GPCRs and their downstream signals are compartmentalized in very small regions in the cell that are called nanodomains. In my talk, I will introduce the concept of signaling compartmentation and highlight our recent work on cAMP nanodomains. Disruption of GPCR signaling networks can lead to noncommunicable diseases such as heart failure and cancer, and I will briefly discuss potential roles of nanodomain signaling in such diseases.

Bianca Plouffe,

Queen’s University Belfast, Northern Ireland

The viral-encoded US28 receptor contributing to glioblastoma development constitutively activates Gq from early endosomes

Glioblastoma (GBM) is the most common and aggressive type of brain cancer. The human cytomegalovirus (HCMV) encodes US28, a viral chemokine GPCR. The constitutive activation of Gq by US28 is reported to induce oncomodulatory properties such as cell inflammation, proliferation, metabolic reprogramming and angiogenesis supporting GBM development. Due to the recent development of the technology allowing to monitor GPCR signalling with a subcellular resolution, accumulating evidence show that several GPCRs are able to activate G proteins from intracellular compartments. Unlike most GPCRs, US28 is mainly located at endosomes due to chronic internalisation. It was previously assumed that US28 signalling was mediated by the minor pool of receptors at the plasma membrane, but using a wide panel of assays in glioblastoma cells, our data demonstrate that US28 robustly and constitutively activates Gq from early endosomes instead. This finding has important therapeutical relevance as it suggests that targeting the endosomal compartment may represent a promising approach to robustly block US28 and its associated oncomodulatory signalling promoting GBM development in HCMV-positive patients

Shannon O'Brien,

University of Birmingham, England

Investigating GPCR signalling in adipocytes

It is now established that metabolites not only act as building blocks for biosynthetic pathways, but are also bona fide signaling molecules. The signaling functions of metabolites are largely dependent on their intra- and extracellular concentrations as well as their subcellular compartmentalisation. Notably, deregulation of metabolite signaling is implicated in numerous human diseases, including that of diabetes and obesity. In response, metabolite-sensing GPCRs have emerged as attractive therapeutic targets. Therefore, better understanding the physiological role as well as the underlying mechanism of metabolite sensing GPCRs is of great interest.

Here, we describe the use of mini-G protein (mG) probes (Wan et al., 2018), bioluminescence resonance energy transfer (BRET), and advanced imaging methods, to provide evidence that the free fatty acid receptor 4 (FFAR4)/GPR120, a GPCR responsive to medium and long chain fatty acids and known to be highly expressed in adipocytes, can signal from intracellular compartments in a Gαi/o dependent manner and FFAR4 compartmentalization is essential for its activation after the induction of lipolysis (Husted et al., 2020).

WAN, Q., OKASHAH, N., INOUE, A., NEHME, R., CARPENTER, B., TATE, C. G. & LAMBERT, N. A. 2018. Mini G protein probes for active G protein-coupled receptors (GPCRs) in live cells. J Biol Chem, 293, 7466-7473.

HUSTED, A. S., TRAUELSEN, M., RUDENKO, O., HJORTH, S. A. & SCHWARTZ, T. W. 2017. GPCR-Mediated Signaling of Metabolites. Cell Metab, 25, 777-796.