Translational Control of Host Environmental Stress Responses in Candida albicans

PROJECT SUMMARY/ABSTRACT Candida albicans is a major human fungal pathogen responsible for a wide variety of systemic and mucosal infections. Immunocompromised individuals, including organ transplant recipients, AIDS patients and cancer patients on chemotherapy are highly susceptible to infection. A morphological transition from yeast to

filamentous cells and the ability to respond to a wide variety of host environmental stresses are critical for pathogenesis. While transcriptional and post-translational mechanisms that mediate C. albicans filamentation and stress responses have been well-characterized, considerably less is known about the role of translational

mechanisms. However, UME6, a key regulator of C. albicans morphogenesis, is controlled by a 5’ UTR- mediated translational efficiency mechanism. The eIF4F translation initiation complex is important for binding to the 5’ cap of mRNAs and contains helicase activity that unwinds complex secondary structures in 5’ UTRs to

promote ribosome accessibility. Fungal-specific C. albicans orthologs of the yeast eIF4E-binding proteins (eIF4E-BPs) Eap1 and Caf20, which function as negative regulators of the eIF4F complex, were shown to control morphogenesis and a variety of stress responses. Both C. albicans eIF4E-BPs are down-regulated in

response to membrane stress and orf19.7034 (the Eap1 ortholog) functions as a negative regulator of P- bodies (translationally inactive cellular compartments) under multiple stress conditions. Orf19.7034 and the eIF4E cap-binding protein, also control Ume6 protein levels in a 5’ UTR-dependent manner. Asc1, a key

virulence factor and phosphosignaling protein important for morphogenesis whose yeast ortholog forms a complex with Eap1 to translationally control target genes, also regulates a variety of C. albicans stress responses. We show genetic interactions between Asc1 and eIF4E-BPs with respect to control of morphology,

biofilm formation and/or stress responses. Using ribosome profiling, C. albicans morphogenesis and response to the drug stress fluconazole were also shown to be under widespread global translational regulation that does not simply parallel transcriptional control. Based on this evidence, and additional studies, our hypothesis

is that Asc1 and eIF4E-BPs function together to translationally regulate C. albicans morphology, stress responses and virulence by modulating activity of the eIF4F complex in response to host environmental cues. To address this hypothesis, we plan to: 1) determine how Asc1 and eIF4E-BPs control the ability to respond to

host filament-inducing and environmental stress conditions, 2) determine the mechanism by which Asc1 and eIF4E-BPs control C. albicans morphogenesis and Ume6 expression, 3) determine the functional relationship between Asc1 and eIF4E-BPs with respect to regulation of C. albicans target gene expression, pathogenesis

and virulence. These studies will provide a better understanding of translational mechanisms that control the response of C. albicans to a variety of filament-inducing and host environmental stress conditions, and could ultimately provide information leading to the development of new and more effective antifungals strategies.