The immunoglobulin-repeat-containing receptor Ig-hepta/GPR116, member of the class B2 family of seven-transmembrane G protein-coupled receptors
GPR116 (also known as Ig-hepta) is an orphan receptor that belongs to group VI adhesion-GPCRs along with GPR110, GPR111, GPR113, and GPR115. The adhesion receptors are characterized by the presence of large N-terminal extracellular domains containing multiple adhesion motifs, which play critical roles in ligand recognition as well as cell-cell adhesion and cell-matrix interactions, linked by a stalk region to a class B seven-transmembrane domain. GPR116 has four I-set immunoglobulin-like repeats, which is found in the members of the immunoglobulin superfamily of cell surface proteins, and a SEA (sea urchin sperm protein, enterokinase, and a grin)-box, which is present in the extracellular domain of the transmembrane mucin (MUC) family and known to enhance O-glycosylation. GPR116 is highly expressed in fetal and adult lung, and it has been shown to regulate lung surfactant levels as well as to stimulate breast cancer metastasis through a G(q)-p63-RhoGEF-Rho GTPase signaling pathway. In addition, almost all adhesion receptors, except GPR123, contain an evolutionarily conserved GPCR-autoproteolysis inducing (GAIN) domain that undergoes autoproteolytic processing at the GPCR proteolysis site (GPS) motif located immediately N-terminal to the first transmembrane region, to generate N- and C-terminal fragments (NTF and CTF), which may serve important biological functions. However, several adhesion GPCRs, including GPR 111, GPR115, and CELSR1, are predicted to be non-cleavable at the GAIN domain because of the lack of a consensus catalytic triad sequence (His-Leu-Ser/Thr) within their GPS.
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