G protein-coupled receptors: a gateway to targeting oncogenic EVs?

Abstract

Dysregulated intercellular communication is a key feature driving cancer progression. Recently, extracellular vesicles (EVs) have added a new channel to this dense communication network. Despite solid evidence that EVs are central mediators of dysregulated signaling in onco-pathological settings, this has yet to be translated into clinically actionable strategies. The heterogeneity of EV cargo molecules, plasticity of biogenesis routes, and large overlap with their role in physiological communication, complicate a potential targeting strategy. However, recent work has linked EV biology to perhaps the "most druggable" proteins - G protein-coupled receptors (GPCRs). GPCR targeting accounts for ~60% of drugs in development and more than a third of all currently approved drugs, spanning almost all areas of medicine. Although several GPCRs have been linked to cancer initiation and progression, relatively few agents have made it into oncological regimes, suggesting that their potential is underexploited. Herein, we examine the molecular mechanisms linking GPCRs to EV communication in cancer settings. We propose that GPCRs hold potential in the search for EV-targeting in oncology.

Keywords: G protein-coupled receptors (GPCRs); extracellular vesicles (EVs); oncogenic signaling; therapeutic targeting.

Figure 1

Schematic overview of GPCR signaling. (1) GPCR in its inactive state, where the heterotrimeric G protein complex, consisting of a Gα-subunit and a Gβγ-subunit, is still associated and GDP bound; (2) Ligand binding induces the GPCR to undergo a conformational change that initiates G protein coupling. The heterotrimeric G protein complex is activated by GDP exchange for GTP. For a constitutively active GPCR, the G protein constantly couples to the receptor; (3) Subsequently, the subunits dissociate and interact with their corresponding effector proteins, regulating downstream signaling; (4) GPCR signaling is downregulated by G protein-coupled receptor kinase (GRK)-mediated phosphorylation of the C-terminus. Subsequent arrestin binding initiates receptor endocytosis, which can lead to receptor degradation or recycling back to the plasma membrane, as well as endosomal signaling propagation. GPCR: G protein-coupled receptor; AC: adenylyl cyclase; PLCβ: phospholipase C-beta; GRK: G protein-coupled receptor kinase; Arr: arrestin; GDP: guanosine diphosphate; GTP: guanosine triphosphate.

Figure 2

Interplay between GPCRs and EVs during cancer development, highlighting their therapeutic potential. (I) Mutated or oncogenic GPCRs mediate abnormal signaling pathways that can affect protein sorting, leading to a change in EV cargo, or modulate tumor EV biogenesis and secretion, or a combination of the two. (II) EV-mediated functional horizontal transfer of GPCRs can propagate oncogenic signaling in the recipient cells. (III) Uptake of oncogenic EVs, either via endocytosis (c) or perhaps direct membrane fusion (d), can affect endogenously expressed GPCR signaling, contributing to cancer development. Additionally, GPCRs can modulate EV uptake, for example, via docking to the GPCR via its ligand (e). Thus, GPCRs pose an interesting point of interception to target tumor EV-mediated cancer development and progression. a: microvesicle secretion; b: exosome secretion; c: EV endocytosis; d: EV-plasma membrane fusion; e: GPCR-mediated EV docking. GPCR: G protein-coupled receptor; MVB: multivesicular body; EV: extracellular vesicle; EE: early endosome.

Figure 3

Illustrative examples of EV-GPCR oncomodulation. (A) MV3 melanoma cell-derived EVs activate primary neutrophils to adopt a pro-tumor/N2-phenotype by increasing the expression of chemokine receptor CXCR4. This allows the neutrophils to migrate toward the tumor cells in a CXCL12-dependent manner, promoting tumor cell survival; (B) Osteopathic melanoma LCP-derived EVs alter the osteotropism of other melanoma cells. EV exposure of SK-Mel28 and WM-266 cells induces plasma membrane ACKR3 expression, resulting in a CXCL12-dependent tumor cell migration toward the bone; (C) EVs derived from prostate cancer cells are rich in PKM2, a kinase that induces CXCL12 production and secretion in bone marrow stem cells. Increased CXCL12 section induces migration of cancer cells toward the bone marrow in a chemokine receptor CXCR4-dependent manner; (D) Breast cancer cells can increase the migration and invasion of other breast cancer cells via EV-mediated transfer of MMP1. MMP1 is a protease that can activate PAR1 receptors on the receiving breast cancer cells in an autocrine manner, resulting in increased migration. PKM2: pyruvate kinase muscle isozyme 2; MMP1: matrix metalloprotease 1; BMSCs: bone marrow stem cells.