ERN1 and plasma cell myeloma: To confirm the phosphospecificity of our anti–phospho-S729 antibody, we treated 5TGM1 mouse multiple myeloma cells with SubAB immunoprecipitated IRE1 using an anti–IRE1 antibody and incubated immunoprecipitated IRE1 with λPPase or CIP before immunoblotting using the anti–phospho-S729 antibody.