BLOC1S1 and plasma cell myeloma: A similar inhibition was observed for the RIDD activity: in the presence of L827P protein, endogenous IRE1α was unable to cleave Blos1 in response to Tg treatment, whereas in the presence of WT IRE1GFP, Blos1 mRNA was reduced by 60% (Fig. 2C) in multiple myeloma cells.