Insulin
Insulin is the pancreatic hormone that signals nutrient abundance: it tells tissues to absorb glucose, store energy, and grow, and its signaling pathway is the evolutionary ancestor of the aging-control systems studied in worms and flies.
Function
Insulin is secreted by pancreatic β-cells when blood glucose rises after a meal. It binds the insulin receptor, a tyrosine kinase that recruits IRS proteins and activates two main routes: the PI3K–AKT arm, which moves GLUT4 transporters into muscle and fat cell membranes and drives glycogen and lipid storage; and the MAPK arm, which drives growth. Between meals, insulin falls and the body mobilizes stores — the hormone’s absence is as physiologically important as its presence.
In aging and cancer
Reduced insulin/IGF signaling extends lifespan across species, through an evolutionarily conserved pathway whose downstream effectors — FOXO transcription factors and mTOR — mediate that extension. Chronic insulin elevation (insulin resistance, metabolic syndrome) raises IGF-1 signaling, mitotic drive, and cancer risk. Hyperinsulinemia is a recognized tumor-promoting condition, particularly for colorectal and endometrial cancer.
Notes
- Human gene symbol: INS; UniProt P01308; 110 amino acids (preproinsulin); mature insulin is a two-chain peptide.
- First protein to be sequenced (Sanger, 1955) and first recombinant human therapeutic (1982).