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The SIT4 Gene Encoding a Protein Phosphatase of the 2A Family is Involved in MDR Phenotype in Saccharomyces cerevisiae
Miranda, M.N.1; Masuda, C.A.1; Carvajal, E.2; Montero-Lomeli, M.M.1
1Instituto de Bioquímica Médica, IBqM – UFRJ, RJ; 2Departamento de Biologia Celular e Genética, IB – UERJ, RJ.
Multidrug resistance (MDR) is defined as the cell ability to survive in the presence of lethal doses of more than one drug. This phenomenom has been conserved through the evolutionary scale and in humans is associated with the failure in cancer treatment. S. cerevisiae is widely used as an eukaryotic model system due to its known genome and easy manipulation. There are at least 60 MDR genes in S. cerevisiae. Among them, there are genes belonging to the ABC (ATP binding cassette) and MF (major facilitator) families encoding membrane proteins that pump out a great number of cytotoxic compounds, genes related with lipid and cell wall metabolism, stress response and transcriptional activators that regulate the expression of these genes. Little is known whether posttranscriptional regulation is involved in MDR phenotype, however proteins from the ABC family Pdr5, Snq2, Yor1, Pdr12 and Ycf1, which contributes to MDR phenotype in S.cerevisiae are in vitro phosphorylated and this regulation is been associated with MDR. The objective of this work is to characterize new MDR genes from S. cerevisiae. We are now reporting that SIT4, a gene encoding a serine/threonine protein phosphatase associated with cell cycle regulation is also involved in MDR phenotype. S. cerevisiae cells carrying a disrupted sit4 allele were sensitive to fluconazole, ketoconazole, cycloheximide and hydrogen peroxide when compared to wild type cells. Interestingly, overexpression of SIT4 in wild type cells enhanced azole resistance. β-galactosidase assay revealed higher expression of PDR5 in cells lacking SIT4, indicating that resistance mediated by SIT4 requires other MDR genes. SIT4 can also modulate the expression of Candida albicans MDR genes, since wild type S. cerevisiae cells carrying plasmids containing CDR1, CaMDR1 and FLU1 were more resistant to fluconazole and cycloheximide than Dsit4 cells carrying the same plasmids. These findings indicate that Sit4 is a potential target for inhibition of multidrug resistance.
Supported by FAPERJ.
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