The Rap1A protein enhances protein kinase C activity in vitro.

The low molecular weight G protein Rap1A constitutes a major fraction of the GTP-binding proteins found in the plasma membrane and specific granules of the neutrophil; however, the function of Rap1A in neutrophil responses remains unclear. Protein kinase C assays were performed to examine the effects of Rap1A on protein kinase C activity. In the presence of recombinant Rap1A, the phosphorylation of protein kinase C substrates was significantly enhanced. The effect of the Rap1A on protein kinase C activity was concentration-dependent and specific. The low molecular weight G protein Rac 2 had no effect on protein kinase C activity. These results suggest that Rap1A may interact with protein kinases and regulate signal transduction.