Heterotrimeric G-protein subunit function in Candida albicans: both the alpha and beta subunits of the pheromone response G protein are required for mating.
A pheromone-mediated signaling pathway that couples seven-transmembrane-domain (7-TMD) receptors to a mitogen-activated protein kinase module controls Candida albicans mating. 7-TMD receptors are typically connected to heterotrimeric G proteins whose activation regulates downstream effectors. Two Galpha subunits in C. albicans have been identified previously, both of which have been implicated in aspects of pheromone response. Cag1p was found to complement the mating pathway function of the pheromone receptor-coupled Galpha subunit in Saccharomyces cerevisiae, and Gpa2p was shown to have a role in the regulation of cyclic AMP signaling in C. albicans and to repress pheromone-mediated arrest. Here, we show that the disruption of CAG1 prevented mating, inactivated pheromone-mediated arrest and morphological changes, and blocked pheromone-mediated gene expression changes in opaque cells of C. albicans and that the overproduction of CAG1 suppressed the hyperactive cell cycle arrest exhibited by sst2 mutant cells. Because the disruption of the STE4 homolog constituting the only C. albicans gene for a heterotrimeric Gbeta subunit also blocked mating and pheromone response, it appears that in this fungal pathogen the Galpha and Gbeta subunits do not act antagonistically but, instead, are both required for the transmission of the mating signal.
Dignard
Daniel
D
NRC Biotechnology Research Institute, 6100 Royalmount Ave., Montreal, Quebec, Canada H4P 2R2.
André
Dominique
D
Whiteway
Malcolm
M
D002176:Candida albicans / Q000235:genetics / Q000502:physiology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism*; D044387:GTP-Binding Protein beta Subunits / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D020411:Oligonucleotide Array Sequence Analysis; D010675:Pheromones / Q000378:metabolism*; D051964:Receptors, Mating Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic
D005656:Fungal Proteins; D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D010675:Pheromones; D051964:Receptors, Mating Factor