Serum and growth factors stimulate ribosomal RNA processing in Syrian hamster embryo cells: Divergence of this signalling pathway from immediate-early gene expression

Abstract

Growth factor stimulation of cells results in multiple intracellular biochemical changes including increases in calcium levels, phosphatidylinositol turnover, protein phosphorylation, immediate-early gene transcription and intracellular pH alterations. We report here that serum and growth factor stimulation of Syrian hamster embryo (SHE)-derived cell lines increases the ribosomal RNA (rRNA) processing rates. In addition, in several transformed SHE cell lines, the immediate-early response of fos/actin transcription could be separated from the immediate-early rRNA processing response. These results indicate that in these cell lines a mutation(s) which uncouples these responses has occured. This is the first report describing (i) rRNA processing as an immediate-early effect following growth factor stimulation and (ii) the identification of a mutation(s) which can uncouple two immediate-early signalling responses.