CASC3 and leukemia: First, from marine biology studies, characterization of proteasome subunits of the PI Salinosporamide A (NPI-0052, Marizomib) producing actinobacterium Salinispora tropica revealed the same Ala49Val and Met45Phe mutations in the β5 subunit homologue as in BTZ-resistant leukemia cells.