The role of the transferrin receptor in lymphocyte activation

Blockade of the transferrin receptors whose expression is induced in lymphocytes incubated with the mitogenic lectin phytohaemagglutinin (PHA) does not affect the initial stimulation of protein synthesis but does strongly and progressively inhibit the subsequent induction of DNA synthesis. When the effects of transferrin receptor blockade on the induction of the enzymes uridine kinase (whose induction begins early in G1 phase of the cell cycle) and thymidine kinase (whose induction is closely associated with DNA synthesis) were examined, both enzymes were found to be induced normally. This indicates that the function of the transferrin receptor is directly to provide a component essential for DNA synthesis itself (probably iron) rather than to act as the receptor for a general signal required to initiate entry into S-phase.