Modulation of p120E4F transcriptional activity by the Gam1 adenoviral early protein

Abstract

Gam1, an early adenoviral CELO protein, is required for viral replication. Consistent with its ability to inhibit histone deacetylation by HDAC1, Gam1 activates transcription. In this report, we identify the cellular transcription factor p120 E4F as a Gam1 interaction partner. p120 E4F is a low-abundance transcription factor that represses the adenovirus E4 promoter. Here we demonstrate that p120 E4F interacts with HDAC1 in vivo and in vitro, and that E4F-mediated transcriptional repression is alleviated by the HDAC inhibitor trichostatin A or by overexpressing Gam1. A mutant E4 promoter unresponsive to E4F-mediated transcriptional repression is also not stimulated by Gam1. Moreover, our cofractionation experiments demonstrate that p120 E4F , HDAC1 and Gam1 may be concomitantly present in protein complexes. We conclude that Gam1 activates E4-dependent transcription possibly by inactivating HDAC1.

Viral control of the SUMO pathway: Gam1, a model system

“…In fact, the double substitutions L258A and L265A (LL/AA) impair totally the Gam1 binding capability both in vitro and in vivo. Interestingly, this double point mutant was initially identified as the inactive version of Gam1 protein that failed in many phenotypes induced by this viral protein [3,4,7,8,11,20]. We therefore predicted that by recruiting cullin E3 ligase complexes through its BC-box, Gam1 could allow the specific and non-physiological degradation of specific cellular proteins to carry out its functions.…”

The LIM-only protein FHL2 is a negative regulator of E4F1

“…in vitro effect of FHL2 on E4F-binding activity to DNA, or direct binding of FHL2 to DNA (Paul and Sardet, unpublished observations). Moreover, we also considered that FHL2 might interfere with the association of E4F1 with the corepressor histone deacetylase HDAC1 (Colombo et al, 2003), assuming that this would prevent nucleosome deacetylation and transcriptional repression at E4F-regulated promoters. However, we were unable to test this hypothesis because, unlike others (Colombo et al, 2003), we did not detect E4F-HDAC1 complexes in our cell systems (Paul and Sardet., unpublished observations).…”

“…Moreover, we also considered that FHL2 might interfere with the association of E4F1 with the corepressor histone deacetylase HDAC1 (Colombo et al, 2003), assuming that this would prevent nucleosome deacetylation and transcriptional repression at E4F-regulated promoters. However, we were unable to test this hypothesis because, unlike others (Colombo et al, 2003), we did not detect E4F-HDAC1 complexes in our cell systems (Paul and Sardet., unpublished observations). A better knowledge of E4F1 communication with the polymerase II holoenzyme and with the chromatin remodeling machinery in U2OS will be required to further explore the mechanisms of this FHL2-mediated inhibition of E4F1 transcriptional activity.…”

“…p50 E4F1 transactivates expression of the adenoviral E4 gene through multiple CRE-like elements in an E1A-dependent fashion (Fernandes et al, 1997). On the contrary, p120 E4F1 , at least when overexpressed, is likely to play a role of repressor for the adenoviral E4 and E1A promoters (Fognani et al, 1993;Fernandes et al, 1997) and for the cellular cyclin A2 gene (Fajas et al, 2001;Tessari et al, 2003;Ahmed-Choudhury et al, 2005), a property that might rely on its direct interaction with histone deacetylase 1 (Colombo et al, 2003).…”

The E4F Protein Is Required for Mitotic Progression during Embryonic Cell Cycles

“…Thus, while p50 E4F is believed to act as a transcriptional activator, overexpression of p120 E4F was shown to repress transcription of the viral E4 and E1A genes (9) and of the cellular cyclin A2 gene (4). This repressive action of p120 E4F might rely on E4F's direct interaction with histone deacetylase 1 (2). Unlike the well-described cellular roles of other E1A targets, the physiological function of E4F remains largely unknown.…”