XBP1 and chronic obstructive pulmonary disease: However, when comparing the same ER stress markers in NHBE cells isolated from nonsmokers, smokers, and COPD donors, expressions of ATF4, XBP1, GRP78, GRP94, EDEM1, and CHOP were all increased in cells isolated from COPD subjects (Figure 1(c)). EDEM1 gene expression was significantly enhanced in cells isolated from smokers (Figure 1(c)).