An immediate response of ribosomal transcription to growth factor stimulation in mammals is mediated by ERK phosphorylation of UBF

Ribosomal transcription in mammals is regulated in response to growth, diff erentiation, disease, and aging, but the mechanisms of this regulation have remained unresolved. We show that epidermal growth factor induces immediat e, ERK1/2-dependent activation of endogenous ribosomal transcription, while inactivation of ERK1/2 causes an equally immediate reversion to the basal transcription level. ERK1/2 was found to phosphorylate the architectural tr anscription factor UBF at amino acids 117 and 201 within HMG boxes 1 and 2, preventing their interaction with DNA. Mutation of these sites inhibited t ranscription activation and abrogated the transcriptional response to ERK1/ 2. Thus, growth factor regulation of ribosomal transcription likely acts by a cyclic modulation of DNA architecture. The data suggest a central role f or ribosome biogenesis in growth regulation.