Caffeine induces tumor cytotoxicity via the regulation of alternative splicing in subsets of cancer-associated genes.

Caffeine causes a diverse range of pharmacological effects that are time- and concentration-dependent and reversible. The detailed mechanisms of caffeine in tumor suppression via tumor suppressor protein p53 remain unclear. The isoforms of p53 are physiological proteins that are expressed in normal cells and generated via alternative promoters, splicing sites and/or translational initiation sites. In this study, we investigated how caffeine modulated cell cycle arrest and apoptosis via the expression of various alternatively spliced p53 isoforms. Caffeine reduced p53α expression and induced the expression of p53β, which contains an alternatively spliced p53 C-terminus. In HeLa cells, the expression levels of many serine/arginine-rich splicing factors, including serine/arginine-rich splicing factors 2 and 3, were altered by caffeine. Serine/arginine-rich splicing factor 3 was a promising candidate for the serine/arginine-rich splicing factors responsible for the alternative splicing of p53 in response to caffeine treatment. In addition to p53-dependent functions, multiple target genes of serine/arginine-rich splicing factor 3 suggest that caffeine can regulate epithelial-mesenchymal-transition and hypoxic conditions to inhibit the survival of tumor cells. In summary, our data provide a new pathway of caffeine-modulated tumor suppression via the alternative splicing of the target genes of serine/arginine-rich splicing factor 3.