GRM4 and neoplasm: Although it is currently unknown that if mGluR4 can regulate the expression and function of Gli-1 in tumor cells, a study in rat cerebellar granular cell precursors indicated mGluR4 activation inhibited the expression of Gli-1 (Canudas et al., 2004), which may suggest a potential intracellular molecule of mGluR4 in regulation of tumor growth.