ATF4 and breast carcinoma: Studies have also shown that the addition of ZFL to lung carcinoma and breast carcinoma cell lines could increase the levels of cytoplasmic Ca2+ and the endoplasmic reticulum (ER) stress-related proteins CHOP and ATF4, but the expression of ER stress markers was decreased after 24 h, and inhibition of CTSS failed to cause cell apoptosis (9).