Thwarting of Lphn3 Functions in Cell Motility and Signaling by Cancer‐Related GAIN Domain Somatic Mutations

Cancer progression relies on cellular transition states accompanied by changes in the functionality of adhesion molecules. The gene for adhesion G Protein‐Coupled Receptor latrophilin‐3 (aG‐ PCR Lphn3 or ADGRL3) is targeted by tumor‐specific somatic mutations predominantly affecting the conserved GAIN domain where most aGPCRs are cleaved. However, it is unclear how these GAIN domain‐altering mutations impact Lphn3 function. Here, we studied Lphn3 cancer‐related mutations as a proxy for revealing unknown GAIN domain functions. We found that while intra‐GAIN cleavage efficiency was unaltered, most mutations produced a ligand‐specific impairment of Lphn3 intercellular adhesion profile paralleled by an increase in cell‐matrix actin‐dependent contact structures for cells expressing the select S810L mutation. Aberrant remodeling of the intermediate filament vimentin, which was found to coincide with Lphn3‐induced modification of nuclear morphology, had less impact on the nuclei of S810L expressing cells. Notoriously, receptor signaling through G13 protein was deficient for all variants bearing non‐homologous amino acid substitutions, including the S810L variant. Analysis of cell migration paradigms revealed a non‐cell‐autonomous impairment in collective cell migration indistinctly of Lphn3 or its cancer‐related variants expression, while cell‐autonomous motility was potentiated in the presence of Lphn3, but this effect was abolished in S810L GAIN mutant‐expressing cells. These data identify the GAIN domain as an important regulator of Lphn3‐dependent cell motility, thus furthering our understanding of cellular and molecular events linking Lphn3 genetic somatic mutations to cancer‐relevant pathogenesis mechanisms.