Dynamic assembly of chromatin complexes during cellular senescence: implications for the growth arrest of human melanocytic nevi

Abstract

Summary The retinoblastoma (RB)/p16INK4a pathway regulates senescence of human melanocytes in culture and oncogeneinduced senescence of melanocytic nevi in vivo . This senescence response is likely due to chromatin modifications because RB complexes from senescent melanocytes contain increased levels of histone deacetylase (HDAC) activity and tethered HDAC1. Here we show that HDAC1 is prominently detected in p16 INK4a -positive, senescent intradermal melanocytic nevi but not in proliferating, recurrent nevus cells that localize to the epidermal/ dermal junction. To assess the role of HDAC1 in the senescence of melanocytes and nevi, we used tetracyclinebased inducible expression systems in cultured melanocytic cells. We found that HDAC1 drives a sequential and cooperative activity of chromatin remodeling effectors, including transient recruitment of Brahma (Brm1) into RB/HDAC1 mega-complexes, formation of heterochromatin protein 1β β β β (HP1β β β β )/SUV39H1 foci, methylation of H3-K9, stable association of RB with chromatin and significant global heterochromatinization. These chromatin changes coincide with expression of typical markers of senescence, including the senescent-associated β β β β -galactosidase marker. Notably, formation of RB/HP1β β β β foci and early tethering of RB to chromatin depends on intact Brm1 ATPase activity. As cells reached senescence, ejection of Brm1 from chromatin coincided with its dissociation from HP1β β β β /RB and relocalization to protein complexes of lower molecular weight. These results provide new insights into the role of the RB pathway in regulating cellular senescence and implicate HDAC1 as a likely mediator of early chromatin remodeling events.

Microphthalmia-Associated Transcription Factor Controls the DNA Damage Response and a Lineage-Specific Senescence Program in Melanomas

“…INK4A -proficient (501 mel) and p16 INK4A -deficient melanoma cells (WM9 and B16) and that genetic ablation of p16 INK4A in 501 mel cells does not abrogate the senescence growth arrest phenotype in agreement with previous reports (31). Additionally, CDK2 and p27 KIP1 , two other cell cycle regulators deregulated on MITF depletion and involved in cellular senescence (32,33), do not seem as key mediators of MITF siRNA prosenescing effect.…”

H1 histone subtype constitution and phosphorylation state of the ageing cell system of human peripheral blood lymphocytes

“…Moreover, Lezhava (2001) What may be the relationship of our findings to the increase in heterochromatin believed to occur during ageing by the results from Narita et al (2003), Lezhava (2001) and others (Bandyopadhyay et al, 2007;Herbig et al, 2006;Jeyapalan et al, 2007;Imai and Kitano, 1998) and also indicated from the increase in HP1α in the lymphocytes of the elderly group observed in this investigation? As described in the Introduction section of this work, recent in vitro and in vivo results support that dephosphorylation of H1 is associated with the maintenance of the H1 subtypes on chromatin or the close association of the H1 subtypes on chromatin and the formation of, or stabilization of condensed structures (Roth and Allis, 1992;Dou et al, 2006).…”

Unrepairable DNA double-strand breaks that are generated by ionising radiation determine the cell fate of normal human cells

“…The formation of facultative heterochromatin foci (Narita et al, 2003;Bandyopadhyay et al, 2007;Sedivy et al, 2008), which are known as the senescenceassociated heterochromatin foci (SAHF), occurs on each chromosome (Zhang et al, 2007). SAHF contain HP1 proteins, which modulate histone modifications and epigenetic silencing.…”