Description
It is a single-pass transmembrane protein composed of three extracellular Ig-like domains,a transmembrane region, and a tyrosine kinase domain (1, 2). Tyrosine-protein kinase that acts as cell-surface receptor for fibroblast growth factors and plays an essential role in the regulation of cell proliferation, differentiation and migration, and in regulation of lipid metabolism, bile acid biosynthesis, glucose uptake, vitamin D metabolism and phosphatehomeostasis (3, 4, 5, 6). Required for normal down-regulation of the expression of CYP7A1,the rate-limiting enzyme in bile acid synthesis, in response to FGF19. Phosphorylates PLCG1and FRS2. Ligand binding leads to the activation of several signalling cascades (6). Activation of PLCG1 leads to the production of the cellular signalling molecules diacylglycerol and inositol 1,4,5-trisphosphate. Phosphorylation of FRS2 triggersrecruitment of GRB2, GAB1, PIK3R1 and SOS1, and mediates activation of RAS,MAPK1/ERK2, MAPK3/ERK1 and the MAP kinase signalling pathway, as well as of the AKT1signalling pathway (7, 8, 9). Promotes SRC-dependent phosphorylation of the matrixprotease MMP14 and its lysosomal degradation (10). FGFR4 signalling is down-regulatedby receptor internalization and degradation; MMP14 promotes internalization anddegradation of FGFR4. Mutations that lead to constitutive kinase activation or impairnormal FGFR4 inactivation lead to aberrant signalling