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Most mitogens are secreted signal proteins that bind to cell-surface receptors. When activated by mitogen binding, these receptors initiate various intracellular signaling pathways that stimulate cell division.

These signaling pathways act mainly by releasing the molecular brakes that block the transition from the G1 phase of the cell cycle into S phase.

Most mitogens have been identified and characterized by their effects on cells in culture. One of the first mitogens identified in this way was platelet-derived growth factor, or PDGF, the effects of which are typical of many others discovered since. When blood clots form (in a wound, for example), blood platelets incorporated in the clots are stimulated to release PDGF.

PDGF then binds to receptor tyrosine kinases in surviving cells at the wound site, stimulating these cells to proliferate and help heal the wound. In a similar way, if part of the liver is lost through surgery or acute injury, a mitogen called hepatocyte growth factor helps stimulate the surviving liver cells to proliferate.

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