The long-term goals are to determine how nutrients stimulate signal transduction pathways that regulate critical cellular functions. In particular, studies will focus on N-acetylglucosamine (GlcNAc). This amino sugar is a key component of GPI anchors and N-linked glycosylation on proteins, and is a core constituent of extracellular polymers, such as keratin or hyaluronan in humans and cell wall chitin in fungi and parasites. However, GlcNAc also activates signal transduction pathways that induce profound cellular changes in a wide range of organisms. Recent studies indicate that GlcNAc signaling underlies the pathology of many human diseases, including diabetes, cancer, and neurodegeneration. GlcNAc also stimulates the human fungal pathogen Candida albicans to induce the expression of virulence factors, including a switch from budding to hyphal growth. Therefore, C. albicans and related yeasts will be used as model systems to define novel mechanisms of GlcNAc signaling. These studies will take advantage of the recent discovery of a plasma membrane GlcNAc transporter (Ngt1) in C. albicans, which is the first eukaryotic GlcNAc transporter to be cloned. Preliminary studies indicate that additional components exist that enable GlcNAc to induce two separate signal pathways in C. albicans, but their identity is not known. Therefore, Aim 1 will be to define the pathway that stimulates the expression of the genes that encode the GlcNAc catabolic enzymes that are needed to break down GlcNAc. Aim 2 will be to identify the distinct pathway by which GlcNAc stimulates Ras1 and the cAMP pathway to induce cells to undergo hyphal growth and to turn on the expression of virulence genes. Aim 3 is to identify the intracellular form(s) of GlcNAc that induce the catabolic and hyphal pathways. Part of this aim will also test the hypothesis that cells modulate intracellular GlcNAc synthesis as part of a positive feedback loop with cAMP signaling in order to induce hyphal growth. Identification of novel mechanisms of GlcNAc signaling in C. albicans and related yeasts will serve as an important model for understanding how GlcNAc is sensed in other organisms, and will aid in the development of novel therapeutic approaches for pathogenic fungi. PUBLIC HEALTH RELEVANCE: Studies aimed at identifying the mechanisms by which the sugar N-acetylglucosamine (GlcNAc) activates cellular signaling are directly relevant to public health, because emerging data indicate that GlcNAc signaling underlies the pathology of many prevalent human diseases, such as diabetes, cancer, and neurodegeneration. GlcNAc also stimulates the human fungal pathogen Candida albicans to induce virulence factors. Therefore, identification of novel GlcNAc signaling mechanisms in C. albicans and related yeasts will serve as important models for understanding how GlcNAc signaling contributes to human diseases and will also aid in the development of novel therapeutic approaches for pathogenic fungi.