GNA11 Q209L Mouse Model Reveals RasGRP3 as an Essential Signaling Node in Uveal Melanoma

Abstract

SUMMARY Uveal melanoma (UM) is characterized by mutually exclusive activating mutations in GNAQ, GNA11, CYSLTR2, and PLCB4, four genes in a linear pathway to activation of PLCβ in almost all tumors and loss of BAP1 in the aggressive subset. We generated mice with melanocyte-specific expression of GNA11Q209L with and without homozygous Bap1 loss. The GNA11Q209L mice recapitulated human Gq-associated melanomas, and they developed pigmented neoplastic lesions from melanocytes of the skin and non-cutaneous organs, including the eye and leptomeninges, as well as at atypical sites, including the lymph nodes and lungs. The addition of Bap1 loss increased tumor proliferation and cutaneous melanoma size. Integrative transcriptome analysis of human and murine melanomas identified RasGRP3 to be specifically expressed in GNAQ/GNA11-driven melanomas. In human UM cell lines and murine models, RasGRP3 is specifically required for GNAQ/GNA11-driven Ras activation and tumorigenesis. This implicates RasGRP3 as a critical node and a potential target in UM.

Oncogenic signaling in uveal melanoma

“…DAG binds and activates PKC and RasGRP3 at the plasma membrane and phosphorylation of RasGRP3 at Thr‐133 by PKC enhances RasGRP3 activity (Aiba et al., ; Zheng et al., ). RasGRP3 transcription is also increased in a PKC‐dependent manner in response to GNAQ activation in UM (Chen et al., ; Moore et al., ). Thus, the upregulation and activation of RasGRP3 in response to oncogenic Gα q/11 signaling stimulates the formation of GTP‐bound active RAS and MAPK pathway activation.…”

“…KCN1, a novel small molecule, was able to suppress protein expression of p‐MET, p‐MAPK, and p‐STAT3 in preclinical models to suggest a potential therapeutic agent in metastatic UM (Zhang, Yang, Kaluz, Van Meir, & Grossniklaus, ). More recently, RasGRP3, which is transcriptionally upregulated by oncogenic Gα q/11 signaling and is activated via PKC‐dependent phosphorylation and PKC‐independent DAG‐mediated membrane recruitment, has been identified as a potential therapeutic target (Figure ) (Chen et al., ; Moore et al., ).…”

Mouse models of uveal melanoma: Strengths, weaknesses, and future directions

“…Second, they illuminate differences between the pigment cell‐specific promoters used in induction. The constitutive expression of Mitf‐cre beginning at E15.5 likely explains the earlier onset of tumor formation in the GNAQ Q209L model as compared to the GNA11 Q209L model in which Tyr‐creER T2 is induced in 4‐week‐old mice (Huang et al, ; Moore et al, ). Interestingly, induction of Tyr‐creER in 8‐week‐old mice in the GNAQ Q209L model did not produce overt uveal melanoma.…”

“…Despite these advancements in genetic models of uveal melanoma, the inherent differences in tumor biology between mice and humans cannot be ignored. Putative metastases that have been observed in published genetic models occur in the lungs, not the liver (Huang et al, ; Moore et al, ). Additionally, the loss of Bap1 did not enhance the aggressiveness of uveal melanomas; in fact, the ocular phenotype was weaker, and there was no increase in size or incidence of lung lesions compared with mice expressing GNA11 Q209L alone (Moore et al, ).…”

Uveal Melanoma OncogeneCYSLTR2Encodes a Constitutively Active GPCR Highly Biased Toward Gq Signaling

“…The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) targets PKC and stimulated the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway. In UVM cells, PKC phosphorylates the Ras guanylyl-releasing protein 3 (RasGRP3) and activates the Ras-Raf-MEK-ERK pathway 55 . Activation of this pathway is essential for growth of UVM cells, and also for the TPA-dependent growth of melan-a cells.…”