Control of Transcription of RNA Rich in Polyadenylic Acid in Human Lymphocytes

Rapidly labeled polyribosomal RNA rich in poly(A) has been isolated from cultures of highly purified human peripheral blood lymphocytes. Messenger RNA function for this RNA is suggested by its ability to direct [3H]Met-tRNA binding to ribosomes and incorporation of amino acids into protein in a cell-free preparation. Phytohemagglutinin and low concentrations of dibutyryl cAMP (40 nM) increase poly(A)-rich RNA synthesis 40% within 2 hr, and 100-300% by 12 hr; the percent poly(A) content and the size of the poly(A)-rich portion remain constant. Higher concentrations of dibutyryl cAMP (1 mM), which prevent morphological transformation of lymphocytes by phytohemagglutinin, inhibit synthesis of poly(A)-rich RNA in phytohemagglutinin-treated lymphocytes without damaging cells. Cortisol (0.1 mM), which also prevents lymphocyte transformation, inhibits poly(A)-rich RNA synthesis by 80%. Cycloheximide (5 μ g/ml), which decreases protein synthesis by 90%, decreases poly(A)-rich RNA synthesis 80% in cells stimulated by phytohemagglutinin. These studies demonstrate that, as part of the early molecular events of their action, phytohemagglutinin and cortisol regulate transcription of adenylate-rich RNA in human lymphocytes, and that similar transcriptional effects can be produced by dibutyryl cAMP.