The basic helix-loop-helix transcription factor Cph2 regulates hyphal development in Candida albicans partly via Tec1

Candida albicans undergoes a morphogenetic switch from budding yeast to hyp hal growth form in response to a variety of stimuli and growth conditions. Multiple signaling pathways, including a Cph1-mediated mitogen-activated pr otein kinase pathway and an Efg1-mediated cyclic AMP/protein kinase A pathw ay, regulate the transition. Here we report the identification of a basic h elix-loop-helix transcription factor of the Myc subfamily (Cph2) by its abi lity to promote pseudohyphal growth in Saccharomyces cerevisiae. Like stero l response element binding protein 1, Cph2 has a Tyr instead of a conserved Arg in the basic DNA binding region. Cph2 regulates hyphal development in C. albicans, as cph2/cph2 mutant strains show medium-specific impairment in hyphal development and in the induction of hypha-specific genes. However, many hypha-specific genes do not have potential Cph2 binding sites in their upstream regions. Interestingly, upstream sequences of all known hypha-spe cific genes are found to contain potential binding sites for Tec1, a regula tor of hyphal development. Northern analysis shows that TEC1 transcription is highest in the medium in which cph2/cph2 displays a defect in hyphal dev elopment, and Cph2 is necessary for this transcriptional induction of TEC1. In vitro gel mobility shift experiments show that Cph2 directly binds to t he two sterol regulatory element I-like elements upstream of TEC1 Furthermo re, the ectopic expression of TEC1 suppresses the defect of cph2/cph2 in hy phal development. Therefore, the function of Cph2 in hyphal transcription i s mediated, in part, through Tec1. We further show that this function of Cp h2 is independent of the Cph1- and Efg1-mediated pathways.