Candida albicans is the most common fungal pathogen in humans and the third most common nosocomial infectious agent. Signaling pathways control processes critical for adaptation, survival, and pathogenesis. Our long-term research goal is to understand the roles of signaling pathways in C. albicans survival in response to environmental stress and antifungal drugs. We discovered that transcription factor Sko1 plays a novel role as a major regulator of the cell wall damage response caused by the antifungal drug caspofungin. In addition, we found a conserved role of Sko1 as a regulator of the osmotic stress response. Our objective in this proposal is to identify and functionally characterize the Sko1 transcriptional network underlying the response to successive hyperosmotic stress and caspofungin-induced cell wall damage. Our transcriptional profiling studies uncovered the genetic network underlying Sko1-dependent osmotic stress signaling and caspofungin-induced signaling; however, the direct gene targets remain unknown. Moreover, numerous Sko1-dependent genes have not been functionally characterized. Our central hypothesis is that Sko1 binding to the DNA promoter sequences ATAGCAAT(C/T)A and G(A/T)GATGAGATG confers caspofungin tolerance when cells are pre-exposed to hyperosmotic environments, and Sko1-dependent genes involved in carbohydrate and cation transport are required for adaptive cell growth. This hypothesis is based on three observations. First, our in silico findings show that the aforementioned DNA sequences were enriched in Sko1-dependent genes. Second, strains containing mutations to several Sko1-dependent genes including the carbohydrate transporter HGT6 are hypersensitive to caspofungin. Third, C. albicans wild-type cells pre- treated with sodium chloride have increased tolerance to caspofungin. We propose the following specific aims to test our central hypothesis: 1) To determine the promoter sequences required for Sko1 gene regulation and 2) To determine the role of carbohydrate and cation transporters in the osmotic and cell wall damage stress responses. We will utilize a genomics and high-throughput molecular genetics approach that is cost-effective and time-saving. Caspofungin has limited activity against C. albicans infections in hyperosmotic environments such as the kidneys and urine, the cerebrospinal fluid, and the eyes. Hence, this proposal is innovative in the identification of an adaptive mechanism to successive stress. Moreover, it will provide a framework of genetic targets that can propel development of novel antifungal agents that can be used synergistically with caspofungin. John Jay College (CUNY) is the largest Hispanic-serving institution in the northeastern U.S. and funding of this proposal will expand biomedical research to a student population that currently lacks opportunities in this critical area.
Candida albicans is the major fungal pathogen of humans and the 3rd most common nosocomial infective agent in the US alone with a high mortality rate amongst candidemia patients. Signaling pathways are critical for adaptation, survival, and pathogenesis. This proposal is relevant, as we will determine the signaling mechanisms that govern the response to successive stress caused by osmotic shock and antifungal drugs.
