MT-ND1 and breast cancer: Since ornithine decarboxylase activity is a marker for cell growth, it appears that a signal transduction pathway for estrogen-induced cell growth may originate from the mitochondria assuming that rotenone inhibition is specific to complex I. The antitumor arotinoid, mofarotene (Ro 40-8757), has been demonstrated to down-regulate mitochondrial encoded NADH dehydrogenase subunit 1 (MtND1) expression in breast cancer cell lines MDA-MB-231, ZR-75-I, and MCF7 [141].