Role of protein and RNA synthesis in the development of insulin binding sites on activated thymus-derived lymphocytes.

This study tested two theories that may explain the mechanism by which cellular activation leads to newly measurable receptors: 1) activation uncovers nascent receptors by alteration of membrane configuration or 2) activation initiates synthesis of the receptor or substances crucial to the integrity of the receptors.

Abstract

Quiescent T (thymus-derived) lymphocytes have no insulin receptors. Lymphocyte activation by alloantigen or mitogens stimulates receptor appearance. There are two theories that may explain the mechanism by which cellular activation leads to newly measurable receptors: 1) activation uncovers nascent receptors by alteration of membrane configuration or 2) activation initiates synthesis of the receptor or substances crucial to the integrity of the receptor. This study was designed to test the latter theory directly. T cells were activated with the mitogen phytohemagglutinin (PM) and treated with either mitomycin C (100 pg/ml), cycloheximide (0.5 mu), or actinomycin D (1 PM). Controls consisted of cells cultured with mitogen alone or with medium alone. Inhibitors reduced DNA synthesis 83% (r3H]thymidine), RNA synthesis 90% (r3H]uridine), and protein synthesis 88% (13H]leucine) in separate series of studies. Insulin binding after PHA interaction was 4.0 f 0.6 pg/106 in control and 3.93 + 0.1 in mitomycintreated cultures. In contrast, binding after PHA activation (75 gg/ml) fell from 6.3 + 1.3 to 0.4 + 0.2 pg/106 cells after RNA synthesis inhibition. Inhibition of DNAdependent, RNA synthesis by 96%, as measured by assay of RNA polymerase II, by cx-amanitin (1