Department of Hematopathology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
J Pathol. 2013 May;230(1):82-94. doi: 10.1002/path.4171. Epub 2013 Mar 14.
NPM-ALK chimeric oncogene is aberrantly expressed in an aggressive subset of T-cell lymphomas that frequently occurs in children and young adults. The mechanisms underlying the oncogenic effects of NPM-ALK are not completely elucidated. Inducible nitric oxide synthase (iNOS) promotes the survival and maintains the malignant phenotype of cancer cells by generating NO, a highly active free radical. We tested the hypothesis that iNOS is deregulated in NPM-ALK(+) T-cell lymphoma and promotes the survival of this lymphoma. In line with this possibility, an iNOS inhibitor and NO scavenger decreased the viability, adhesion, and migration of NPM-ALK(+) T-cell lymphoma cells, and an NO donor reversed these effects. Moreover, the NO donor salvaged the viability of lymphoma cells treated with ALK inhibitors. In further support of an important role of iNOS, we found iNOS protein to be highly expressed in NPM-ALK(+) T-cell lymphoma cell lines and in 79% of primary tumours but not in human T lymphocytes. Although expression of iNOS mRNA was identified in NPM-ALK(+) T-cell lymphoma cell lines and tumours, iNOS mRNA was remarkably elevated in T lymphocytes, suggesting post-transcriptional regulation. Consistently, we found that miR-26a contains potential binding sites and interacts with the 3'-UTR of iNOS. In addition, miR-26a was significantly decreased in NPM-ALK(+) T-cell lymphoma cell lines and tumours compared with T lymphocytes and reactive lymph nodes. Restoration of miR-26a in lymphoma cells abrogated iNOS protein expression and decreased NO production and cell viability, adhesion, and migration. Importantly, the effects of miR-26a were substantially attenuated when the NO donor was simultaneously used to treat lymphoma cells. Our investigation of the mechanisms underlying the decrease in miR-26a in this lymphoma revealed novel evidence that STAT3, a major downstream substrate of NPM-ALK tyrosine kinase activity, suppresses MIR26A1 gene expression.
NPM-ALK 嵌合癌基因在儿童和年轻成人中常发生的侵袭性 T 细胞淋巴瘤的一个亚群中异常表达。NPM-ALK 致癌作用的机制尚未完全阐明。诱导型一氧化氮合酶（iNOS）通过产生一氧化氮（一种高活性自由基）促进癌细胞的存活和维持恶性表型。我们检验了 iNOS 在 NPM-ALK(+)T 细胞淋巴瘤中失调并促进这种淋巴瘤存活的假说。符合这一可能性，iNOS 抑制剂和 NO 清除剂降低了 NPM-ALK(+)T 细胞淋巴瘤细胞的活力、黏附和迁移，而 NO 供体则逆转了这些效应。此外，NO 供体挽救了用 ALK 抑制剂处理的淋巴瘤细胞的活力。进一步支持 iNOS 发挥重要作用，我们发现 iNOS 蛋白在 NPM-ALK(+)T 细胞淋巴瘤细胞系和 79%的原发肿瘤中高度表达，但不在人 T 淋巴细胞中表达。虽然在 NPM-ALK(+)T 细胞淋巴瘤细胞系和肿瘤中鉴定出 iNOS mRNA 的表达，但 iNOS mRNA 在 T 淋巴细胞中显著升高，提示存在转录后调控。一致地，我们发现 miR-26a 含有潜在的结合位点并与 iNOS 的 3'-UTR 相互作用。此外，与 T 淋巴细胞和反应性淋巴结相比，miR-26a 在 NPM-ALK(+)T 细胞淋巴瘤细胞系和肿瘤中显著降低。在淋巴瘤细胞中恢复 miR-26a 表达可消除 iNOS 蛋白表达并降低 NO 产生和细胞活力、黏附和迁移。重要的是，当同时使用 NO 供体治疗淋巴瘤细胞时，miR-26a 的作用显著减弱。我们对这种淋巴瘤中 miR-26a 降低的机制的研究揭示了新的证据，表明 NPM-ALK 酪氨酸激酶活性的主要下游底物 STAT3 抑制 MIR26A1 基因表达。
