Signalling by insulin and IGF receptors: supporting acts and new players

The signalling pathways utilised by insulin receptor (IR) and IGF receptor to transduce their diverse effects on cellular metabolism, growth and survival are well established in broad outline, but many details remain to be elucidated. Tyrosine phosphorylation of IR substrates and Shc initiates signalling via canonical phosphoinositide 3-kinase/Akt and Ras/MAP kinase pathways, which together mediate many of the actions of insulin and IGFs. However, a variety of additional substrates and scaffolds have been described that may play roles in modulating the canonical pathways or in specific biological responses. This review will focus on recent studies that have extended our understanding of insulin/IGF signalling pathways, and the elements that may contribute to specificity.