Caffeine activates HOG-signalling and inhibits pseudohyphal growth in Saccharomyces cerevisiae

Caffeine has a wide range of effects in humans and other organisms. Caffeine activates p38 MAPK, the human homolog to the Hog1 protein that orchestrates the high-osmolarity glycerol (HOG) response to osmotic stress in the yeast Saccharomyces cerevisiae. Caffeine has also been used as an inducer of cell-wall stress in yeast via its activation of the Pkc1-mediated cell wall integrity (CWI) pathway. In this study, using immunodetection of phosphorylated Hog1, microscopy to score nuclear localisation of GFP-tagged Hog1 and a pseudohyphal growth assays, the effect of caffeine on the HOG-pathway and filamentous growth in yeast was studied.

It was found that caffeine causes rapid, strong and transient Hog1 dual phosphorylation with statistically significant increases at 20, 30 and 40 mM caffeine. In response to caffeine treatment Hog1 was also rapidly localized to the nucleus, supporting the caffeine-induced phosphorylation and activation of Hog1. We also found that caffeine inhibited the pseudohyphal/filamentous growth in diploid cells, but had no effect on invasive growth in haploids. Our data thus highlights that the HOG signalling pathway is activated by caffeine, which has implications for interpreting caffeine responses in yeast and fungi.