G-protein-coupled receptors (GPCRs) remain one of the most successful targets for therapeutic drugs approved by the US Food and Drug Administration (FDA). Many novel orphan GPCRs have been identified by human genome sequencing and considered as putative targets for refractory diseases. Of note, a series of studies have been carried out involving GPCR 158 (or GPR158) since its identification in 2005, predominantly focusing on the characterization of its roles in the progression of cancer and mental illness. However, advances towards an in-depth understanding of the biological mechanism(s) involved for clinical application of GPR158 are lacking. In this paper, we clarify the origin of the GPR158 evolution in different species and summarize the relationship between GPR158 and different diseases towards potential drug target identification, through an analysis of the sequences and substructures of GPR158. Further, we discuss how recent studies set about unraveling the fundamental features and principles, followed by future perspectives and thoughts, which may lead to prospective therapies involving GPR158.

Background: Tumor cells typically rely on paracrine stromal signals to guide malignant behavior, yet whether they gain signaling autonomy and thereby reduce microenvironment dependency during metastasis remains unclear. Methods: Gremlin 1 (GREM1) and activin A receptor type 1C (ACVR1C) expression levels and cellular distribution were analyzed by immunohistochemistry, immunofluorescence (IF) staining, and single-cell transcriptomics in colorectal cancer (CRC) specimens across stages I–IV. The GREM1–ACVR1C interaction was identified and validated by interaction proteomics, co-immunoprecipitation, IF, and microscale thermophoresis (MST). Functional roles of the GREM1–ACVR1C axis in epithelial–mesenchymal transition (EMT) and metastasis were examined by transcriptomic profiling, pathway analysis, immunoblotting, reverse transcription quantitative PCR (RT–qPCR), scratch and transwell assays, and genetically engineered and xenograft mouse models. An inhibitory peptide targeting the GREM1–ACVR1C interface was designed and evaluated. Results: While GREM1 remains restricted to stromal cells in earlier-stage (I–III) CRC, its ectopic expression in tumor epithelium increases markedly in stage IV. Mechanistically, we identify ACVR1C as a direct, high-affinity epithelial receptor for GREM1. Their interaction, independent of canonical transforming growth factor β receptor (TGFβR) and bone morphogenetic protein (BMP) signaling, activates SMAD2/3, which in turn induces the transcription of SNAI1 and GREM1 , thereby establishing a self-sustaining autocrine loop that amplifies EMT. Disrupting this loop via stromal GREM1 deletion, epithelial ACVR1C knockdown, kinase inhibition, or a novel GREM1-blocking peptide targeting the GREM1–ACVR1C binding interface significantly impairs CRC metastasis in vivo. Remarkably, while stromal GREM1 is required to initiate this loop, epithelial-derived GREM1 is sufficient to maintain metastatic progression. Clinically, epithelial GREM1 or ACVR1C expression predicts aggressive disease and poor survival. Conclusions: Our findings define a paradigm wherein CRC cells hijack the stromal factor GREM1 to establish a tumor-autonomous GREM1–ACVR1C autocrine loop. This loop licenses signaling independence, drives sustained EMT, and represents a novel, actionable vulnerability in advanced CRC.