High resolution

Module 7: Figure liver cell signalling

Hormonal control of liver cell function.

Liver function is regulated by a number of signalling pathways. Some of these, which use Ca2+ and cyclic AMP as messengers, activate glycogenolysis. The same messengers can also activate a transcriptional cascade initiated by the transcription factor CREB that results in an up-regulation of some of the key enzymes involved in gluconeogenesis. Insulin provides an inhibitory pathway to switch off the expression of peroxisome-proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α), which exerts a major control over gluconeogenesis. Free fatty acids (FFAs) contribute to this transcriptional cascade by activating the PPARα. Insulin counteracts the cyclic AMP signalling pathway by stimulating the phosphodiesterase PDE3B that hydrolyses cyclic AMP.