ATF6 and Miyoshi myopathy: Quantitative RT-PCR analysis showed that ixazomib treated cells only slightly increased mRNA expression of EIF2AK3 and ATF6 while the XBP1s mRNA level was strongly up-regulated upon treatment with ixazomib (Fig. 1B, C) suggesting that MM cells activate the IRE1α-XBP1 axis as an adaptive pathway shielding against ixazomib-induced cell death.