MUC2 and Merkel cell skin cancer: In this study, we first demonstrated that MCC and high MUC2 producing cells (dnTCF4-LS174T exposed to doxycycline) had elevated basal ERS levels compared to NMCC and low MUC2 producing cancer cells, and that the mucinous nature of these tumors (excessive MUC2 protein production) was responsible for the high basal ERS levels.