['Identification of multidrug resistance (MDR) factors is crucial for designing chemotherapeutic strategies. Aberrant expression and dysfunction of proteasome subunits have been involved in malignant transformation and in cell resistance to various cytotoxic drugs.', 'We analyzed the expression levels of the proteasome subunit Rpn11 in a panel of cancer cell lines, and studied the effect of Rpn11 overexpression on the resistance of mammalian cells to cytotoxic drugs in clonogenic cytotoxicity assay.', 'Rpn11 levels are highly variable in cancer cells; mammalian cells stably overexpressing Rpn11 display moderate resistance to vinblastine, cisplatin and doxorubicin, and also exhibit a slower proliferation rate when compared to the control cells.'] Does the essential 26S proteasome subunit Rpn11 confer multidrug resistance to mammalian cells?