Suppression of the p53- or pRB-mediated G1 checkpoint is required for E2F-induced S-phase entry

Marina Lomazzi, M. Cristina Moroni, Michael R. Jensen, Emanuela Frittoli, Kristian Helin

Research output: Contribution to journalArticlepeer-review


Deregulation of the retinoblastoma protein (pRB) pathway is a hallmark of cancer. In the absence of other genetic alterations, this deregulation results in lack of differentiation, hyperproliferation and apoptosis. The pRB protein acts as a transcriptional repressor by targeting the E2F transcription factors, whose functions are required for entry into S phase. Increased E2F activity can induce S phase in quiescent cells-this is a central element of most models for the development of cancer. We show that although E2F1 alone is not sufficient to induce S phase in diploid mouse and human fibroblasts, increased E2F1 activity can result in S-phase entry in diploid fibroblasts in which the p53-mediated G1 checkpoint is suppressed. In addition, we show that E2F1 can induce S phase in primary mouse fibroblasts lacking pRB. These results indicate that, in addition to acting as an E2F-dependent transcriptional repressor, pRB is also required for the cells to retain the G1 checkpoint in response to unprogrammed proliferative signals.

Original languageEnglish
Pages (from-to)190-194
Number of pages5
JournalNature Genetics
Issue number2
Publication statusPublished - Jun 2002

ASJC Scopus subject areas

  • Genetics(clinical)
  • Genetics


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