Moreover, we show for the first time that GRM signalling can influence vesicular trafficking and, specifically, that GRM3 activation fosters the endosomal trafficking of a pro-invasive transmembrane matrix metalloprotease—a process dependent on Rab27, a GTPase linked to poor prognosis and metastasis in breast cancer and glioma32,33. The gene discussed is GRM3; the disease is breast carcinoma.