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Objectives: We aimed to determine the role of dihydroorotate dehydrogenase (DHODH) in pathogenesis of adult T‐cell leukemia (ATL) caused by human T‐cell leukemia virus type 1 (HTLV‐1) and the effects of its inhibition on the de novo pyrimidine biosynthesis pathway. Methods: Cell proliferation, viability, cycle, and apoptosis were analyzed using WST‐8 assays, flow cytometry, and Hoechst 33342 staining. To elucidate the molecular mechanisms involved in the anti‐ATL effects of DHODH knockdown and inhibition, RT‐PCR and immunoblotting were conducted. Results: HTLV‐1‐infected T‐cell lines aberrantly expressed DHODH. Viral infection and the oncoprotein, Tax, enhanced DHODH expression, while knockdown of DHODH decreased HTLV‐1‐infected T‐cell growth. In addition, BAY2402234, a DHODH inhibitor, exerted an anti‐proliferative effect, which was reversed by uridine supplementation. BAY2402234 induced DNA damage and S phase arrest by downregulating c‐Myc, CDK2, and cyclin A and upregulating p53 and cyclin E. It also induced caspase‐mediated apoptosis by the upregulation of pro‐apoptotic and downregulation of anti‐apoptotic proteins. Furthermore, BAY2402234 induced caspase‐independent ferroptosis and necroptosis. It decreased phosphorylation of IKK, IκBα, PTEN, Akt, and its downstream targets, suggesting that inhibition of NF‐κB and Akt signaling is involved in its anti‐ATL action. Conclusion: These findings highlight DHODH as a potential therapeutic target for treating ATL. [ABSTRACT FROM AUTHOR]

AbstractAdult T-cell leukemia (ATL), caused by HTLV-1, is the most lethal hematological malignancy. NEDD8-activating enzyme (NAE) is a component of the NEDD8 conjunction pathway that regulates cullin-RING ubiquitin ligase (CRL) activity. HTLV-1-infected T cells expressed higher levels of NAE catalytic subunit UBA3 than normal peripheral blood mononuclear cells. NAE1 knockdown inhibited proliferation of HTLV-1-infected T cells. The NAE1 inhibitor MLN4924 suppressed neddylation of cullin and inhibited the CRL-mediated turnover of tumor suppressor proteins. MLN4924 inhibited proliferation of HTLV-1-infected T cells by inducing DNA damage, leading to S phase arrest and caspase-dependent apoptosis. S phase arrest was associated with CDK2 and cyclin A downregulation. MLN4924-induced apoptosis was mediated by the upregulation of pro-apoptotic and downregulation of anti-apoptotic proteins. Furthermore, MLN4924 inhibited NF-κB, AP-1, and Akt signaling pathways and activated JNK. Therefore, neddylation inhibition is an attractive strategy for ATL therapy. Our findings support the use of MLN4924 in ATL clinical trials. [ABSTRACT FROM AUTHOR]