The Basic Helix-Loop-Helix Transcription Factor Cph2 Regulates Hyphal Development in CandidaalbicansPartly via Tec1

Abstract

Candida albicans undergoes a morphogenetic switch from budding yeast to hyphal growth form in response to a variety of stimuli and growth conditions. Multiple signaling pathways, including a Cph1-mediated mitogen-activated protein kinase pathway and an Efg1-mediated cyclic AMP/protein kinase A pathway, regulate the transition. Here we report the identification of a basic helix-loop-helix transcription factor of the Myc subfamily (Cph2) by its ability to promote pseudohyphal growth in Saccharomyces cerevisiae. Like sterol 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, ascph2/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-specific genes are found to contain potential binding sites for Tec1, a regulator of hyphal development. Northern analysis shows that TEC1 transcription is highest in the medium in which cph2/cph2 displays a defect in hyphal development, and Cph2 is necessary for this transcriptional induction of TEC1. In vitro gel mobility shift experiments show that Cph2 directly binds to the two sterol regulatory element 1-like elements upstream of TEC1. Furthermore, the ectopic expression of TEC1 suppresses the defect ofcph2/cph2 in hyphal development. Therefore, the function of Cph2 in hyphal transcription is mediated, in part, through Tec1. We further show that this function of Cph2 is independent of the Cph1- and Efg1-mediated pathways.

ACKNOWLEDGMENTS

The cloning of CPH2 was performed in the Fink Laboratory while H. Liu was a postdoctoral fellow. We thank Tim Osborne for helpful suggestions, discussions, and critical reading of the manuscript; the members of the Osborne and Dai Laboratories for advice and reagents for GST-Cph2 recombinant protein expression and purification and subsequent gel mobility shift experiments; Jiangye Chen for assistance with the cph2 deletion; and Gerald Fink, William Fonzi, and Joachim Ernst for strains and plasmids.

S. Lane is a predoctoral fellow supported by an NIH Carcinogenesis training grant, and S. Zhou is a predoctoral fellow supported by a training grant from the UC Systemwide Biotechnology Research and Education program. This work was supported by funds from Burroughs Wellcome and NIH (grant GM55155).