ATF4 and prostate cancer: It is overexpressed in prostate cancer tissues and promotes prostate cancer growth; mechanism analysis suggests that androgen increases STEAP4 expression; then STEAP4 promotes prostate cancer growth through catalyzing reduction of Fe3+ to Fe2+, and increasing NADP levels; NADP increases ROS levels, in turn promoting ATF4 expression; and ATF4 promotes prostate cancer growth [12, 13].