Activation of pp90rsk and early growth response-1 gene expression by pokeweed mitogen in human B cells.

The present studies have examined the effects of pokeweed mitogen (PWM) on the induction of early growth response-1 gene (EGR-1) in normal human B cells. PWM regulates EGR-1 gene expression by both transcriptional and post-transcriptional mechanisms. Transient transfection assays with EGR-1 promoter fragments linked to the chloramphenicol acetyltransferase (CAT) gene demonstrated that PWM induced EGR-1 transcription is conferred by the CArG motif (C C[AT]6GG) in the EGR-1 promoter. The results further demonstrated the activation of S6 kinase (pp90rsk), evidenced by phosphorylation of S6 and serum response factor (SRF) peptides, in PWM treated B cells. Taken together, these findings suggest that PWM is able to initiate an intracytoplasmic signalling cascade and EGR-1 induction in normal human B cells.