A Naturally Occurring Lgr4 Splice Variant Encodes a Soluble Antagonist Useful for Demonstrating the Gonadal Roles of Lgr4 in Mammals

Abstract

Leucine-rich repeat containing G protein-coupled receptor 4 (LGR4) promotes the Wnt signaling through interaction with R-spondins or norrin. Using PCR amplification from rat ovarian cDNAs, we identified a naturally occurring Lgr4 splice variant encoding only the ectodomain of Lgr4, which was named Lgr4-ED. Lgr4-ED can be detected as a secreted protein in the extracts from rodent and bovine postnatal gonads, suggesting conservation of Lgr4-ED in mammals. Recombinant Lgr4-ED purified from the conditioned media of transfected 293T cells was found to dose-dependently inhibit the LGR4-mediated Wnt signaling induced by RSPO2 or norrin, suggesting that it is capable of ligand absorption and could have a potential role as an antagonist. Intraperitoneal injection of purified recombinant Lgr4-ED into newborn mice was found to significantly decrease the testicular expression of estrogen receptor alpha and aquaporin 1, which is similar to the phenotype found in Lgr4-null mice. Administration of recombinant Lgr4-ED to superovulated female rats can also decrease the expression of estrogen receptor alpha, aquaporin 1, LH receptor and other key steroidogenic genes as well as bring about the suppression of progesterone production. Thus, these findings suggest that endogenously expressed Lgr4-ED may act as an antagonist molecule and help to fine-tune the R-spondin/norrin-mediated Lgr4-Wnt signaling during gonadal development.

Wnt, RSPO and Hippo Signalling in the Intestine and Intestinal Stem Cells

“…LGR5 and related LGR4 and LGR6 proteins represent the B subgroup of LGR transmembrane proteins, related to the G-protein-coupled receptors (GPCRs) of the hormone receptor class. All LGRs contain a large N-terminal extracellular domain; however, in contrast to LGR4/5/6, the other members of the LGR A and C subgroups bind hormones [ 81 , 82 , 83 ]. LGR4/5/6 proteins are highly homologous; nevertheless, their expression pattern appears to be only partially overlapping.…”

LGR4 Is a Direct Target of MicroRNA-34a and Modulates the Proliferation and Migration of Retinal Pigment Epithelial ARPE-19 Cells

“…[16] Hsu et al identified a LGR4 splice variant which encodes a soluble secreted protein that can inhibit LGR4 mediated Wnt signaling. [27] Furthermore, a nonsense mutation of LGR4 (c.376C>T) has been reported to be strongly associated with low bone marrow density, electrolyte imbalance, reduced testosterone levels and increased risk of squamous cell carcinoma of the skin. [28] Therefore, identifying regulators of LGR4 expression and activity may have a significant impact in clinical practice.…”

Inhibitory effect of AQP1 silencing on adhesion and angiogenesis in ectopic endometrial cells of mice with endometriosis through activating the Wnt signaling pathway

“…AQP1 gene expression was up-regulated in endometriosis (Figure 1(b)). AQP1 was then predicted to interact with topoisomerase 2-beta (TOP2B) by PPI (Figure 1 (c)), which was correlated to the Wnt/β-catenin signaling pathway [12,26,27]. All in all, AQP1 gene is highly expressed in endometriosis and is related to Wnt signaling pathway in silico.…”