title: RB family tumor suppressor activity may not relate to active silencing of E2F target genes.
abstract: The retinoblastoma protein pRB and its two homologs p130 and p107 form the family of pocket proteins and play a major role in cell-cycle regulation and suppression of human and mouse tumorigenesis. Pocket proteins regulate the activity of E2F transcription factors during G1-S transition. Two mechanisms have been described: (i) pocket protein binding blocks the transactivation domain of activator E2Fs, inhibiting E2F-dependent transcription and (ii) E2F-bound pocket proteins can recruit chromatin remodeling proteins containing an LxCxE motif (x encoding any amino acid), resulting in active repression of E2F target genes. To investigate the importance of pRB's LxCxE-interacting motif in cell-cycle control and tumor suppression, we generated mouse embryonic fibroblasts and mice expressing a mutant pRB protein carrying an asparagine for phenylalanine substitution at position 750, abrogating LxCxE binding. Because p130 may compensate for loss of pRB, we studied pRB(N750F) activity in the presence and absence of p130. The pRB-LxCxE interaction was not required for cell-cycle arrest upon mitogen deprivation and cell-cell contact, but did contribute to RAS(V12)- and radiation-induced cell-cycle arrest. Remarkably, the pRB-LxCxE interaction was not required for suppression of in vitro and in vivo transformation, even in the absence of p130. These results indicate that pRB's tumor suppressor activity is not effectuated by active silencing of E2F target genes, but rather by regulation of activator E2Fs or another unidentified mechanism. Furthermore, the in vitro response of pocket protein-perturbed cells to mitogen deprivation and cell-cell contact seems a better predictor of tumor development than the response to ectopic RAS(V12) expression. Cancer Res; 74(18); 5266-76. ©2014 AACR.
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Tinke L
authors: TL
authors: Vormer
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Kamila
authors: K
authors: Wojciechowicz
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Marleen
authors: M
authors: Dekker
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Sandra
authors: S
authors: de Vries
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Anja
authors: A
authors: van der Wal
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Elly
authors: E
authors: Delzenne-Goette
authors: Division of Immunology, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Sjalin H
authors: SH
authors: Naik
authors: Department of Animal Pathology, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Ji-Ying
authors: JY
authors: Song
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands.
authors: Jan-Hermen
authors: JH
authors: Dannenberg
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands. Department of Biology, University of Copenhagen, Copenhagen, Denmark. h.t.riele@nki.nl jacob.hansen@bio.ku.dk.
authors: Jacob B
authors: JB
authors: Hansen
authors: Division of Biological Stress Response, The Netherlands Cancer Institute, Amsterdam, the Netherlands. h.t.riele@nki.nl jacob.hansen@bio.ku.dk.
authors: Hein
authors: H
authors: Te Riele
mesh_terms: D000818:Animals; D048708:Cell Growth Processes / Q000235:genetics; D050684:E2F Transcription Factors / Q000235:genetics* / Q000378:metabolism; D020868:Gene Silencing; D006801:Humans; D051379:Mice; D016160:Retinoblastoma Protein / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: D050684:E2F Transcription Factors; D016160:Retinoblastoma Protein