Investigating the regulation of multidrug resistance by Cofilin in Saccharomyces cerevisiae.

The actin cytoskeleton is a dynamic structure which is capable of rapid assembly and disassembly, and has roles in the structural stability and migration of the cell. Cofilin 1 (Cof1) is an intracellular protein which depolymerises F-actin whilst inhibiting the polymerisation of G-actin, and as such dissembling the actin cytoskeleton, in a pH dependant way. Cofilin 1 has also been linked to the function and regulation of mitochondria in Saccharomyces cerevisiae. Mutations in the COF1 gene have been connected to drug resistance to numerous antifungals in Saccharomyces cerevisiae. One such mutant is the cof1-6 strain whose mutations are present outside of the charge - dependant PtdIns(4,5)P2 binding site of Cofilin 1, and has been linked to the up-regulation of several ABC transporters that have roles in drug resistance. We investigate the role of genes involved in lipid biosynthesis and the role of the mitochondrial outer membrane protein Porin 1 in cof1-6 linked drug resistance. We show that the Cof1-6 mediated drug resistance is PKC-regulated MAPK pathway independent. We further observe an increase in the expression of the sphingoid long chain base efflux pump Rsb1 in the cof1-6 strain. This up-regulation of Rsb1 is pH-independent but Porin dependent. Previous literature has demonstrated a link between peroxisomal and mitochondrial function. Our work suggests that peroxisome function does not regulate drug resistance whereas mitochondrial function is a key mediator in the resistance phenotype of the cof1-6 strain. Furthermore, we demonstrate that cof1-6 linked drug resistance is very complex with the ABC transporter Pdr5 involved in resistance to antifungals which operate through different modes of action. We hope that this work will further understanding into drug resistance against common antifungal drugs.