Relative Stabilität Lysin-gebundener Methylgruppen bei den argininreichen Histonen und ihren Unterfraktionen von Ehrlich-Ascites-Tumorzellen in vitro

Abstract

Zusammenfassung:Ehrlich-Ascites-Tumorzellen wurden in vitro mit [ 3 H]Methionin inkubiert, und der Radioaktivitätseinbau in einzelne gelelektrophoretisch trennbare Histonfraktionen untersucht. Die jeweiligen Histongruppen zeigten unterschiedliche Methionin-und Methyllysin-Radioaktivitäten, während die Unterfraktionen einer Gruppe sich gleich verhielten. Ebenso war das Verhältnis von Mono-zu Di-zu Trimethyllysin in den Unterfraktionen gleich, während es sich von Histongruppe zu -gruppe unterschied. Es ergaben sich Hinweise darauf, daß die Höhermethylierung bis zum Trimethyllysin nicht auf einmal, sondern schrittweise erfolgt. Im Chase-Experiment war kein Abfall der Methyllysin-Radioaktivität über eine Zeitdauer von 3 h zu verzeichnen, was bedeutet, daß kein rascher Methylgruppen-Turnover stattfindet. Relative stability of lysine-bound methyl groups in arginine-rich histones and their subffactions of Ehrlich ascites tumor cells in vitroSummary: Ehrlich ascites tumor cells were incubated /// vitro with [ 3 H]methionine, and the labelling of different histones and their subfractions, which can be separated on very long gels by analytical gel electrophoresis, was examined. The various histone groups showed different methionine and methyllysine radioactivities, while the bands of one group incorporated nearly identical radioactivities. The ratio of mono-to di-to trimethyllysine in the bands of one group was identical as well, but different from one group to another. There were indications that the methyl labelling from mono-to di-and trimethyllysine at one histone site occurred not at once but stepwise. In chase experiments no decrease of methyllysine activity could be observed over a period of 3 h, which means that no rapid methyl group turnover occurs.

Structural Investigations of the Nickel-Induced Inhibition of Truncated Constructs of the JMJD2 Family of Histone Demethylases Using X-ray Absorption Spectroscopy

“…Histone methylation can contribute to several biological processes including heterochromatin formation, X-inactivation, genome imprinting and silencing of homeotic genes (60 – 62). Histone methylation was considered as a permanent modification for a long time (63, 64). However, the identification of the H3K4 specific lysine demethylase (LSD1) suggested that histone methylation is reversible (65).…”

Excess histone levels mediate cytotoxicity via multiple mechanisms

“…For example, until the discovery of the first histone lysine demethylase a few years ago, 31 histone methylation marks were considered to be as stable as histone themselves. 32,33 There is a constant exchange of histones between the chromatin bound and free states as a result of transcriptional eviction, 34,35 the action of chromatin remodelling factors 36 and the opposing effects of chromatin assembly and disassembly. [37][38] We have recently obtained evidence that the tyrosine 99 residue of histone H3 may be phosphorylated only when histone H3 is not bound to the chromatin and this modification may serve as a mark to target this histone for degradation.…”

Reversal of Histone Lysine Trimethylation by the JMJD2 Family of Histone Demethylases

“…Unlike other histone modifications such as acetylation, methylation has long been considered a ''permanent'' modification. This view was based on the earlier observation that the half-lives of histones and total histone methyl groups were comparable, which led to the conclusion that histone methylation is stable and irreversible (Byvoet et al, 1972;Thomas et al, 1972). However, the identification of the H3-K4-specific histone demethylase LSD1 challenged this view and suggested that histone methylation is reversible and dynamically regulated (Shi et al, 2004).…”