ATF6 and head and neck squamous cell carcinoma: However, the opposite effect could also be seen in head and neck squamous cell carcinoma where knockdown of CerS6 and depletion of its product C16:0-ceramide induced UPR and subsequent apoptosis through decreased ER Ca2+, fusion of the ER and Golgi, and activation of ATF6 signaling (30, 58).