Cyclic GMP and lymphocyte proliferation: effects on DNA-dependent RNA polymerase I and II activities.

Cyclic GMP (guanosine 3′:5′-cyclic monophosphate) accumulation and Ca²⁺ influx have been correlated with early nuclear events associated with increases in RNA polymerase I activity and decreases in RNA polymerase II activity in phytohemagglutinin-stimulated lymphocytes. In the present study we demonstrate that cyclic GMP in the presence of Ca²⁺ stimulates RNA polymerase I activity in lymphocyte nuclei isolated from both non-stimulated and phytohemagglutinin-stimulated lymphocytes. In addition, cyclic GMP in the presence of Ca²⁺ decreases RNA polymerase II activity in both non-stimulated and phytohemagglutinin-stimulated lymphocyte nuclei. These observations suggest that cyclic GMP and Ca²⁺ may represent components of a plasma membrane-to-nucleus “mitogen signal sequence”.