ERN1 and melanoma: To identify relevant cell types activating IRE1 RNase in tumors, we analyzed the immune composition of B16 melanoma tumors of ERAI mice, a mouse strain that reports IRE1 RNase activity through expression of Venus Fluorescent Protein (VenusFP) fused with the sequence of Xbp1s (33) [validated in (21, 22, 31)].