Inactivation/deficiency of DHODH induces cell cycle arrest and programed cell death in melanoma.

Malignant melanoma (MM) is one of the most malignant tumors and has a very poor prognosis. However, there are no effective drugs to treat this disease. As a kind of iron flavin dependent enzyme, dihydroorotate dehydrogenase (DHODH, EC 1.3.3.1) is the fourth and a key enzyme in the de novo biosynthesis of pyrimidines. Herein, we found that DHODH inactivation/deficiency inhibited melanoma cell proliferation, induced cell cycle arrest at S phase and lead to autophagy in human melanoma cells. Meanwhile, leflunomide treatment induced cell apoptosis and deficiency of DHODH sensitized cells to drug-induced apoptosis in BCL-2 deficient melanoma cells, while not in BCL-2 abundant melanoma cells. Then we found that BCL-2 could rescue apoptosis induced by DHODH inactivation/deficiency. Moreover, BCL-2 also showed to promote cell cycle arrest and to inhibit autophagy induced by leflunomide. To explore the mechanisms underlying autophagy induced by DHODH inhibition, we found that AMPK-Ulk1 axis was activated in this process. Besides, JNK was phosphorylated and activated to phosphorylate BCL-2, which abrogated the interaction between BCL-2 and Beclin1 and then abolished autophagy. Our findings provided evidences for the potential of DHODH used as a drug target for melanoma treatment.