Metabolic regulator betaKlotho interacts with fibroblast growth factor receptor 4 (FGFR4) to induce apoptosis and inhibit tumor cell proliferation.
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abstract
In organs involved in metabolic homeostasis, transmembrane and klothos direct FGFR signaling to control of metabolic pathways. Coordinate expression of klotho and FGFR4 is a property of mature hepatocytes. Genetic deletion of FGFR4 or klotho in mice disrupts hepatic cholesterol/bile acid and lipid metabolism. The deletion of FGFR4 has no effect on the proliferative response of hepatocytes after liver injury. However, its absence results in accelerated progression of dimethynitrosamine-initiated hepatocellular carcinomas, indicating that FGFR4 suppresses hepatoma proliferation. The mechanism underlying the FGFR4-mediated hepatoma suppression has not been addressed. Here we show that klotho expression is more consistently down-regulated in human and mouse hepatomas than FGFR4. Co-expression and activation by either endocrine FGF19 or cellular FGF1 of the FGFR4 kinase in a complex with klotho restricts cell population growth through induction of apoptotic cell death in both hepatic and nonhepatic cells. The klotho-FGFR4 partnership caused a depression of activated AKT and mammalian target of rapamycin while activating ERK1/2 that may underlie the pro-apoptotic effect. Our results show that klotho not only interacts with heparan sulfate-FGFR4 to form a complex with high affinity for endocrine FGF19 but also impacts the quality of downstream signaling and biological end points activated by either FGF19 or canonical FGF1. Thus the same klotho-heparan sulfate-FGFR4 partnership that mediates endocrine control of hepatic metabolism plays a role in cellular homeostasis and hepatoma suppression through negative control of cell population growth mediated by pro-apoptotic signaling.
