Gene silencing by S-adenosylmethionine in muscle differentiation.

A well-characterised experimental system, the myogenin gene in C2C12 muscle cell culture, was chosen to better understand the methylation mechanism underlying the regulation of gene expression. We already demonstrated that demethylation dynamics of a specific CpG site in the 5'-flanking region of myogenin well correlates with gene expression and terminal differentiation. Here we demonstrate that S-adenosylmethionine-sulphate-p-toluenesulphonate (SAM) inhibits myogenin expression and myoblast differentiation by delaying the demethylation of specific CpG in differentiating myoblasts. These results suggest new perspectives in methylation mechanisms and the use of SAM in the partial silencing of gene expression, as it could be required in disease treatment.

Potentiation of cADPR-induced Ca(2+)-release by methylxanthine analogues.

Caffeine and other methylxanthines are known to induce Ca(2+)-release from intracellular stores via the ryanodine receptor. In the present work, a range of caffeine analogues, in which methyl groups at the 1 and 7 positions were replaced with alkyl chains containing different functional groups (oxo, hydroxyl, propargyl, ester, and acids), were synthesized. These compounds were then screened for their ability to potentiate Ca(2+)-release induced by cADPR (an endogenous modulator of ryanodine receptors) in sea urchin egg homogenates. Two of the synthesized methylxanthines, 1, 3-dimethyl-7-(7-hydroxyoctyl)xanthine (37) and 3-methyl-7-(7-oxooctyl)-1-propargylxanthine (66), were shown to be more potent than caffeine in potentiating cADPR-induced Ca(2+)-release, while 1,3-dimethyl-7-(5-ethylcarboxypentyl)xanthine (14) was shown to be more efficacious. The development of new methylxanthine analogues may lead to a better understanding of ryanodine receptor function and could possibly provide novel therapeutic agents.