ERN1 and melanoma: Compared with that in HEMn-MP and HEMn-DP cells, higher levels of XBP1u (unspliced XBP1) mRNA were spliced into XBP1s (spliced XBP1) and then translated into the active form of the protein in the melanoma cells, thus indicating constitutive activation of the IRE1α-XBP1 branch in melanoma cell lines (Fig. 2a).