Alien inhibits E2F1 gene expression and cell proliferation

Abstract

Recently, using a proteomic approach we have identified the corepressor Alien as a novel interacting factor of the cell cycle regulator E2F1. Unclear was whether this interaction influences cell proliferation and endogenous E2F1 target gene expression. Here, we show by chromatin immunoprecipitation (ChIP) that Alien is recruited in vivo to the E2F binding sites present in the E2F1 gene promoter, inhibits the transactivation of E2F1 and represses endogenous E2F1 gene expression. Interestingly, using synchronized cells to assess the expression of Alien profile during cell cycle the levels of endogenous Alien are increased during G1, G1/S and G2 phase. Furthermore, stable transfection of Alien leads to reduction of cell proliferation. Thus, the data suggest that Alien acts as a corepressor for E2F1 and is involved in cell cycle regulation.

COPS2 (COP9 constitutive photomorphogenic homolog subunit 2 (Arabidopsis))

“…pRB represses E2F1 transcriptional activation. It is not yet known whether Alien is able to substitute pRB function during cell cycle progression (Tenbaum et al, 2007). Furthermore, a direct interaction between Alien and pRB is detected.…”

“…In line with this, Alien represses cell cycle progression. Remarkably, the inhibition of E2F1-mediated transactivation is independent of retinoblastoma protein pRB (Tenbaum et al, 2007). pRB represses E2F1 transcriptional activation.…”

The corepressor Alien as a novel tumor suppressor?

“…Further insights of Alien-mediated corepressor function were gained by using an in vivo proteomic approach to identify novel Alien interacting partners (28)(29)(30). Interestingly, conserved cell cycle factors were among proteins that interact with Alien.…”

“…Interestingly, other factors such as two transcription factor IIH (TFIIH) subunits, XBP and XPD/p44, were identified by in vivo proteomic approaches (28)(29)(30). TFIIH is an eukaryotic multiprotein complex exhibiting exceptional evolutionary conservation of its structure.…”

The coregulator Alien

“…Protein-protein interaction techniques are a powerful method to detect protein complexes in a cell. An in vivo proteomic approach was assessed to identify Alien-interacting partners, combining detection of protein interactions of solely endogenously-expressed proteins with surface-enhanced laser desorption/ionization - mass spectrometry (SELDI-MS) and immunological techniques [ Escher et al, 2007 ; Kob et al, 2007 ; Tenbaum et al, 2007 ]. Using this in vivo approach in addition to HDACs, several members of the E2F transcription factor family were identified as interacting partners of Alien ( Figure 1 and [ Escher et al, 2007 ]).…”