Id3 is a novel regulator of p27kip1 mRNA in early G1 phase and is required for cell-cycle progression

Abstract

P27kip is a key inhibitory protein of the cell-cycle progression, which is rapidly downregulated in early G1 phase by a post-translational mechanism involving the proteosomal degradation. In this study, using a wounding model that induces cell-cycle entry of human dermal fibroblasts, we demonstrate that p27mRNA is downregulated when cells progress into the G1 phase, and then it returns to its basal level when cells approach the S phase. By using a quantitative polymerase chain reaction screening we identified inhibitors of differentiation (Id3), a bHLH transcriptional repressor, as a candidate mediator accounting for p27 mRNA decrease. Id3 silencing, using an small interfering RNA approach, reversed the injury mediated p27 downregulation demonstrating that Id3 is involved in the transcriptional repression of p27. Reporter gene experiments and a chromatin immunoprecipitation assay showed that Id3 likely exerts its repressive action through ELK1 inhibition. By inhibiting early p27 downregulation, Id3 depletion blocked (i) the G1-phase progression as assessed by the inhibition of pRb phosphorylation and p130 degradation and (ii) the G1/S transition as observed by the inhibition of cyclin A induction, demonstrating that p27 mRNA decrease is required for cell proliferation. Apart from its effect on the early p27 diminution, Id3 appears also involved in the control of the steady-state level of p27 at the G1/S boundary. In conclusion, this study identifies a novel mechanism of p27 regulation which besides p27 protein degradation also implicates a transcriptional mechanism mediated by Id3.

Targeting Id protein interactions by an engineered HLH domain induces human neuroblastoma cell differentiation

“…This may explain the 13I effect on SH-EP cells, at least partly, as E47 activity prevents cell cycle progression in neuroblastoma cells (Rothschild et al, 2006). Finally, 13I affected the expression of the Id targets p27 kip1 and VEGF (Lasorella et al, 2005;Chassot et al, 2007), by turning the first on and the second off. Such a deregulation was reversed by over-producing ID2.…”

“…Through the HLH domain, Ids associate with the ubiquitous bHLHs, the E proteins, preventing DNA binding and complex formation with tissue-specific bHLHs (Ruzinova and Benezra, 2003). They also interact with non-bHLH proteins such as PAX, ETS, ELK and underphosphorylated RB (Iavarone et al, 1994;Ohtani et al, 2001;Roberts et al, 2001;Chassot et al, 2007).…”

Id3 upregulates BrdU incorporation associated with a DNA damage response, not replication, in human pancreatic β-cells

“…[56][57][58] Conversely, Id knockdown is associated in many cell types with increased expression of CDKIs. 53,56,[59][60][61][62][63] Recently we reported that E47 directly activates p57…”

Inhibition of tumourigenicity of small cell lung cancer cells by suppressing Id3 expression

“…Using a wounding model as an inducer of cell cycle entry for human dermal fibroblasts, when Id3 was silenced, the expected down-regulation of p27 did not occurred, suggesting that transcription repression of p27 was regulated by Id3. It was also found that both G1 phase progression and G1/S transition were blocked by Id3 depletion (14).…”

“…These inhibitors sequestrate CDKs and therefore stop them from phosphorylating pRB, hence having an indirect anti-proliferation effect (13). Id3 specifically regulates P27 through an ETS domain factor called ELK1 (14). Id1 and Id3 have also been identified as downstream targets of MYC (15).…”