SHORT COMMUNICATION Relationship between E1A binding to cellular proteins, c-myc activation and S-phase induction S Baluchamy 1,3,4 , N Sankar 1,3 , A Navaraj 1,5 , E Moran 2 and B Thimmapaya 1 1 Department of Microbiology–Immunology Feinberg School of Medicine, Northwestern University, Chicago, IL, USA and 2 Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, PA, USA We recently showed that p300/CREB-binding protein (CBP) plays an important role in maintaining cells in G0/ G1 phase by keeping c-myc in a repressed state. Consistent with this, adenovirus E1A oncoprotein induces c-myc in a p300-dependent manner, and the c-myc induction is linked to S-phase induction. The induction of S phase by E1A is dependent on its binding to and inactivating several host proteins including p300/CBP. To determine whether there is a correlation between the host proteins binding to the N-terminal region of E1A, activation of c-myc and induction of S phase, we assayed the c-myc and S-phase induction in quiescent human cells by infecting them with Ad N-terminal E1A mutants with mutations that specifically affect binding to different chromatin-associated proteins including pRb, p300, p400 and p300/CBP-associated factor (PCAF). We show that the mutants that failed to bind to p300 or pRb were severely defective for c-myc and S-phase induction. The induction of c-myc and S phase was only moderately affected when E1A failed to bind to p400. Furthermore, analysis of the E1A mutants that fail to bind to p300, and both p300 and PCAF suggests that PCAF may also play a role in c-myc repression, and that the two chromatin- associated proteins may repress c-myc independently. In summary, these results suggest that c-myc deregulation by E1A through its interaction with these chromatin-asso- ciated proteins is an important step in the E1A-mediated cell cycle deregulation and possibly in cell transformation. Oncogene (2007) 26, 781–787. doi:10.1038/sj.onc.1209825; published online 24 July 2006 Keywords: E1A; p300; c-myc repression; cell cycle Cell transformation by the adenoviral E1A oncoprotein is dependent on its binding to and inactivating several host proteins including p400, p300, pRb, and the two Rb family proteins p130 and p107, PCAF, TRRAP and GCN5 (reviewed in Moran, 1993; Barbeau et al., 1994; Frisch and Mymryk, 2002); for an extensive list of references on this topic please refer to the web site http://www.geocities.com/jmymryk.geo/. These host proteins are found in distinct chromatin remodeling complexes that modulate gene expression either by activating or repressing transcription. In most cases, specific transcriptional targets of these complexes in the context of cell cycle and the mechanism by which E1A interferes in their function are not known. pRb, p130 and p107 proteins in association with histone deacety- lases repress E2F1 function that is critical for the induction of S phase (Harbour, 2001). p400 is a component of the human TIP60/NuA4 complex con- taining histone acetyl transferase (HAT) activity that modulates both transcriptional repression and activa- tion (Fuchs et al., 2001; Doyon et al., 2004). p300 and CREB-binding protein (CBP) are two large highly homologous nuclear phosphoproteins containing HAT activity that function as transcriptional coactivators and link chromatin remodeling with transcription (Goodman and Smolik, 2000). TRRAP is found in three distinct human HAT complexes including the TIP60 HAT complex and two other complexes that are similar to yeast SAGA (Spt-Ada-Gcn5-acetyl transferase complex) containing either GCN5 or PCAF (reviewed in Sterner and Berger, 2000). Until recently, the significance of E1A binding to p300 in the E1A-mediated cell cycle deregulation and cell transformation was not known. We recently showed that in quiescent human cells, p300/CBP plays an important role in keeping c-myc in a repressed state. Depletion and induction of p300/CBP in serum-starved cells led to induction and repression, respectively, of c-myc and DNA synthesis (Kolli et al., 2001; Baluchamy et al., 2003; Rajabi et al., 2005). Consistent with this, we showed that in quiescent cells, E1A induced c-myc in a p300-dependent manner indicating that E1A interferes with p300/CBP repression of c-myc (Kolli et al., 2001). To determine whether or not there is a correlation between E1A binding to host proteins, and induction of c-myc and S phase, we have studied a series of previously characterized E1A mutants for their capacity to induce Received 28 September 2005; revised 9 June 2006; accepted 11 June 2006; published online 24 July 2006 Correspondence: Dr B Thimmapaya, Department of Microbiology— Immunology, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Olson 8452, Chicago, IL 60611, USA. E-mail: b-thimmapaya@northwestern.edu 3 These two authors contributed equally to this work. 4 Current address: Department of Genetics and Biochemistry, Uni- versity of Illinois at Chicago, Chicago, IL, USA. 5 Current address: Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, USA. Oncogene (2007) 26, 781–787 & 2007 Nature Publishing Group All rights reserved 0950-9232/07 $30.00 www.nature.com/onc