Puf4 Mediates Post-transcriptional Regulation of Cell Wall Biosynthesis and Caspofungin Resistance in Cryptococcus neoformans.

The human fungal pathogen is intrinsically resistant to the echinocandin antifungal drug caspofungin, which targets the β-1,3-glucan synthase encoded by Echinocandins have been on the market for 20 years, yet they are the newest class of antifungal drugs. Analysis of a Δ mutant, lacking the pumilio/FBF RNA binding protein family member Puf4, revealed exacerbated caspofungin resistance. In contrast, overexpression of resulted in caspofungin sensitivity. The mRNA contains three Puf4-binding elements (PBEs) in its 5' untranslated region. Puf4 binds with specificity to this region of The mRNA was destabilized in the Δ mutant, and the abundance of the mRNA was reduced compared to wild type, suggesting that Puf4 is a positive regulator of mRNA stability. In addition to , the abundance of additional cell wall biosynthesis genes, including chitin synthases (, , and ) and deacetylases (, , and ) as well as a β-1,6-glucan synthase gene (), was regulated by Puf4. The use of fluorescent dyes to quantify cell wall components revealed that the Δ mutant had increased chitin content, suggesting a cell wall composition that is less reliant on β-1,3-glucan. Overall, our findings suggest a mechanism by which caspofungin resistance, and more broadly, cell wall biogenesis, is regulated post-transcriptionally by Puf4. is an environmental fungus that causes pulmonary and central nervous system infections. It is also responsible for 15% of AIDS-related deaths. A significant contributor to the high morbidity and mortality statistics is the lack of safe and effective antifungal therapies, especially in resource-poor settings. Yet, antifungal drug development has stalled in the pharmaceutical industry. Therefore, it is essential to understand the mechanism by which is resistant to caspofungin to design adjunctive therapies to potentiate the drug's activity toward this important pathogen.