In some aspects, the disclosure provides methods of modulating the level of proteasome inhibitor resistance of a cell, the methods comprising manipulating the level of expression or activity of a subunit of the 19S proteasome in the cell. In some aspects, cells in which the level of a 19S subunit is modulated, e.g., reduced, are provided. In some aspects, methods of identifying agents that reduce proteasome inhibitor resistance are provided. In some aspects, methods of classifying cancers according to predicted proteasome inhibitor resistance are provided. In some aspects, methods of killing or inhibiting proliferation of cancer cells, e.g., proteasome inhibitor resistant cancer cells, are provided. In some aspects, methods of treating cancer, e.g., proteasome inhibitor resistant cancer, are provided.