ATF4 and neoplasm: Shikonin (Compound 25), a naturally naphthoquinone derived from the roots of Lithospermum erythrorhizon, has been shown by Qi H et al. to exert anti-tumor effects through the activation of ER stress via the PERK/eIF2α/ATF4/CHOP and IRE1α/JNK signaling pathways.