Opposing effects of Ets and Id proteins on p16INK4a expression during cellular senescence

Abstract

The p16INK4a cyclin-dependent kinase inhibitor is implicated in replicative senescence, the state of permanent growth arrest provoked by cumulative cell divisions or as a response to constitutive Ras-Raf-MEK signalling in somatic cells. Some contribution to senescence presumably underlies the importance of p16INK4a as a tumour suppressor but the mechanisms regulating its expression in these different contexts remain unknown. Here we demonstrate a role for the Ets1 and Ets2 transcription factors based on their ability to activate the p16INK4a promoter through an ETS-binding site and their patterns of expression during the lifespan of human diploid fibroblasts. The induction of p16INK4a by Ets2, which is abundant in young human diploid fibroblasts, is potentiated by signalling through the Ras-Raf-MEK kinase cascade and inhibited by a direct interaction with the helix-loop-helix protein Id1 (ref. 11). In senescent cells, where the Ets2 levels and MEK signalling decline, the marked increase in p16INK4a expression is consistent with the reciprocal reduction of Id1 and accumulation of Ets1.

Site-specific DNA methylation by a complex of PU.1 and Dnmt3a/b

“…Moreover, there is no report indicating that PU.1-mediated transcriptional repression is mediated by DNA hypermethylation. The promoter region of the p16 gene, a cyclin-dependent kinase inhibitor gene, has several Etsbinding sites (Ohtani et al, 2001) and many CpG sites (Figure 7a). Therefore, we examined whether PU.1 regulates transcription of the p16 gene negatively through hypermethylation of the CpG site in the promoter.…”

A population of BJ fibroblasts escaped from Ras-induced senescence susceptible to transformation

“…Currently OIS is known to be induced by various kinds of oncogenic stimulation [4]. Subsequently, cell cycle arrest by p16 has been shown to be one of the important mechanisms for OIS, regulated by combination of Ets and Id1 [5]. p16 downregulation is able to prevent RAS-induced senescence [5; 6; 7], and p16 determines the sensitivity of HDFs to transformation by cooperating oncogenes [8].…”

Interference of the dominant negative helix–loop–helix protein ID1 with the proteasomal subunit S5A causes centrosomal abnormalities

“…ID proteins form DNA-binding incompetent heterodimers with bHLH transcription factors thereby inhibiting their transcriptional activities (Benezra et al, 1990). Individual ID-proteins have been linked to inhibiting cellular differentiation, inhibition of bHLHand other transcription factors (Benezra et al, 1990;Jen et al, 1992;Kreider et al, 1992;Ohtani et al, 2001;Roberts et al, 2001), modulating apoptosis (Florio et al, 1998;Ling et al, 2003), cooperating with the retinoblastoma tumor suppressor pathway (Iavarone et al, 1994;Hara et al, 1996), extending cellular life span (Alani et al, 1999;Nickoloff et al, 2000;Tang et al, 2002), regulating angiogenesis (Lyden et al, 2001) as well as cardiac development (Fraidenraich et al, 2004), and stem cell maintenance (Ying et al, 2003). ID expression is induced as part of the immediate-early transcriptional response to growth factors and is regulated in a cell cycle-dependent manner.…”