Synthesis of Sterols and 5‐Lipoxygenase Products are Required for the G 1 ‐S Phase Transition of Interleukin‐2‐Dependent Lymphocyte Proliferation

A murine killer T cell line, G‐CTLL 1, whose proliferation depends on the presence of interleukin 2 (IL‐2), was used to analyze the mechanism of IL‐2 action with respect to sterol synthesis and arachidonate metabolism. De novo sterol synthesis was substantially enhanced much earlier than DNA synthesis, and the rate reached a maximum at 13 hr after the addition of IL‐2. Compactin, which is a potent competitive inhibitor of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase (HMG CoA reductase, the enzyme in the rate‐limiting step of the sterol synthesis), inhibited the IL‐2‐induced DNA synthesis. The addition of mevalonate, the product of HMG CoA reductase, prevented the inhibition of DNA synthesis by compactin, suggesting that the supply of a sufficient amount of sterol is an essential prerequisite for IL‐2 action. The IL‐2‐induced DNA synthesis was also inhibited by AA861, a specific inhibitor of arachidonate 5‐lipoxygenase, and by other lipoxygenase inhibitors such as nordihydroguaiaretic acid and esculetin. In contrast, indomethacin, an inhibitor of arachidonate cyclooxygenase, had no effect. These findings suggest that synthesis of 5‐lipoxygenase products is also a prerequisite. The inhibition of DNA synthesis was effectively inhibited only when compactin or lipoxygenase inhibitors were added early enough to block the synthesis of sterols or 5‐lipoxygenase products; addition of the reagents after 3 hr decreased the inhibition with time. Therefore, about 3 hr after the addition of IL‐2, several drastic intracellular changes are assumed to begin and to lead to DNA synthesis.