Regulation of β cell function by tyrosine kinase pathways. There is evidence for participation of tyrosine kinase signaling in different β cell functions. Interestingly, activation of PI 3-kinase is thought to be important for cell size control, neogenesis and proliferation, apoptosis, and insulin synthesis or secretion. However, the pathways activated by PI 3-kinase appear to diverge, with Akt contributing to growth and size control but not to insulin secretion. It is unclear how PI 3-kinase signaling is linked to insulin synthesis or secretion, since insulin regulation is unaffected by loss of p70^s6k1. On the other hand, phosphorylation of eIF2α on Ser⁵¹ by the kinase gene Perk is thought to play an important role in insulin mRNA translation.