MAPK3 and hepatocellular carcinoma: In differentiated 3T3-L1 adipocytes that co-express predominantly the FGFR1-KLB, FGF19, FGF21 and FGF1 activate the ERK1/2 to an equal extent, while in hepatoma cells co-expressing preferentially the FGFR4-KLB but not FGFR1-KLB, FGF21 is unable to activate the ERK1/2 response as compared to FGF19 and FGF1 (Figure 5B).