The G-protein coupled receptor 56, expressed in colonic stem and cancer cells, binds progastrin to promote proliferation and carcinogenesis

Abstract

Overexpression of human progastrin increases colonic mucosal proliferation and colorectal cancer progression in mice. The G-protein coupled receptor 56 (GPR56) is known to regulate cell adhesion, migration, proliferation and stem cell biology, but its expression in the gut has not been studied. We hypothesized that the promotion of colorectal cancer by progastrin may be mediated in part through GPR56. Here, we found that GPR56 expresses in rare colonic crypt cells that lineage trace colonic glands consistent with GPR56 marking long-lived colonic stem-progenitor cells. GPR56 was upregulated in transgenic mice overexpressing human progastrin. While recombinant human progastrin promoted the growth and survival of wild-type colonic organoids in vitro, colonic organoids cultured from GPR56−/− mice were resistant to progastrin. We found that progastrin directly bound to, and increased the proliferation of, GPR56-expressing colon cancer cells in vitro, and proliferation was increased in cells that expressed both GPR56 and the cholecystokinin-2 receptor (CCK2R). In vivo, deletion of GPR56 in the mouse germline abrogated progastrin-dependent colonic mucosal proliferation and increased apoptosis. Loss of GPR56 also inhibited progastrin-dependent colonic crypt fission and colorectal carcinogenesis in the azoxymethane (AOM) mouse model of colorectal cancer. Overall, we found that progastrin binds to GPR56 expressing colonic stem cells, which in turn promotes their expansion, and that this GPR56-dependent pathway is an important driver and potential new target in colorectal carcinogenesis.

Stachel-independent modulation of GPR56/ADGRG1 signaling by synthetic ligands directed to its extracellular region

“…For example, the aGPCR GPR56/ADGRG1 is involved in cortex development, oligodendrocyte development, muscle cell development, innate immunity, and cancer progression (11)(12)(13)(14)(15)(16)(17). Recent studies have highlighted the role of GPR56 in promoting progression of acute myeloid leukemia (18) and progastrin-dependent colon cancer (19) and suggested that a GPR56 inhibitor would be clinically desirable.…”

Anti-GPR56 monoclonal antibody potentiates GPR56-mediated Src-Fak signaling to modulate cell adhesion

“…Previous studies have demonstrated that loss of GPR56 in CRC cells lead to decreased migration, invasion, and resistance to chemotherapy (12, 13,16); all of which may potentially be regulated through the Src-Fak pathway. In fact, therapeutic inhibitors of Src have been shown to suppress CRC cell growth and adhesion and sensitize cells to chemotherapy (49)(50)(51).…”

“…Analysis of clinical data revealed a significant correlation between high GPR56 levels and poor outcome in acute myeloid leukemia, ovarian cancer, and colorectal cancer (CRC) (10)(11)(12)(13)(14)(15). In CRC, GPR56 was shown to promote drug resistance and drive tumor growth (12,13,16). On the contrary, GPR56 has been shown to be downregulated in metastatic melanoma and inhibitory to melanoma growth and metastasis (17).…”

“…Alternatively, the stalk-independent model suggests that a ligand-induced conformational change of the ECD (incorporating the NTF and the stalk region), which promotes interaction with the 7TM, is required to stimulate signaling activity (20,23). GPR56 has been shown to interact with proteins such as collagen III (24), transglutaminase 2 (TG2) (17), and progastrin (16); however receptor-specific ligands have yet to be fully validated. Several studies have established that GPR56 is coupled to the Gα12/13 class of heterotrimeric G-proteins to promote RhoA activation (13,22,(24)(25)(26).…”

Adhesion G-protein coupled receptors: Implications for metabolic function

“…cross-linking enzyme transglutaminase 2 (TG2) in HEK293 cells (Xu et al, 2006), the anticoagulant heparin in A375 melanoma cells (Chiang et al, 2016) and the stomach prohormone progastrin in colorectal cancer cells (Jin et al, 2017). Whereas activation of GPR56 by collagen III or an antibody directed against its N-terminal has been shown to couple to RhoA through G12/13 (Iguchi et al, 2008;Luo et al, 2011Luo et al, , 2014, recruitment of downstream signalling has not been demonstrated so far for TG2, heparin or progastrin, suggesting that collagen III is the main endogenous agonist of GPR56.…”