del Fresno Carlos, Otero Karel, Gómez-García Lourdes, González-León Maria Carmen, Soler-Ranger Llanos, Fuentes-Prior Pablo, Escoll Pedro, Baos Rosa, Caveda Luis, García Felipe, Arnalich Francisco, López-Collazo Eduardo
Research Unit, Department of Surgical Research, La Paz Hospital, Madrid, Spain.
J Immunol. 2005 Mar 1;174(5):3032-40. doi: 10.4049/jimmunol.174.5.3032.
Although blood monocytes possess significant cytotoxic activity against tumor cells, tumor-infiltrating monocytes are commonly deactivated in cancer patients. Monocytes pre-exposed to tumor cells show significantly decreased expression levels of TNF-alpha, IL-12p40, and IL-1R-associated kinase (IRAK)-1. Activation of the Ser/Thr kinase IRAK-1 is an important event in several inflammatory processes. By contrast, another IRAK family member, IRAK-M, negatively regulates this pathway, and is up-regulated in cultures of endotoxin-tolerant monocytes and in monocytes from septic patients within the timeframe of tolerance. In this study, we show that IRAK-M expression is enhanced at the mRNA and protein level in human monocytes cultured in the presence of tumor cells. IRAK-M was induced in monocytes upon coculturing with different tumor cells, as well as by fixed tumor cells and medium supplemented with the supernatant from tumor cell cultures. Moreover, blood monocytes from patients with chronic myeloid leukemia and patients with metastasis also overexpressed IRAK-M. Low concentrations of hyaluronan, a cell surface glycosaminoglycan released by tumor cells, also up-regulated IRAK-M. The induction of IRAK-M by hyaluronan and tumor cells was abolished by incubation with anti-CD44 or anti-TLR4 blocking Abs. Furthermore, down-regulation of IRAK-M expression by small interfering RNAs specific for IRAK-M reinstates both TNF-alpha mRNA expression and protein production in human monocytes re-exposed to a tumor cell line. Altogether, our findings indicate that deactivation of human monocytes in the presence of tumor cells involves IRAK-M up-regulation, and this effect appears to be mediated by hyaluronan through the engagement of CD44 and TLR4.
尽管血液中的单核细胞对肿瘤细胞具有显著的细胞毒性活性，但肿瘤浸润的单核细胞在癌症患者中通常会失活。预先接触肿瘤细胞的单核细胞显示出肿瘤坏死因子-α、白细胞介素-12p40和白细胞介素-1受体相关激酶（IRAK）-1的表达水平显著降低。丝氨酸/苏氨酸激酶IRAK-1的激活是几个炎症过程中的一个重要事件。相比之下，另一个IRAK家族成员IRAK-M对该途径起负调节作用，并且在内毒素耐受单核细胞培养物以及脓毒症患者单核细胞处于耐受期时上调。在本研究中，我们表明在存在肿瘤细胞的情况下培养的人单核细胞中，IRAK-M的表达在mRNA和蛋白质水平均增强。与不同肿瘤细胞共培养时，以及与固定的肿瘤细胞和补充有肿瘤细胞培养上清液的培养基共培养时，单核细胞中均可诱导IRAK-M。此外，慢性髓性白血病患者和转移患者的血液单核细胞也过度表达IRAK-M。肿瘤细胞释放的一种细胞表面糖胺聚糖——低浓度透明质酸，也上调了IRAK-M。透明质酸和肿瘤细胞对IRAK-M的诱导作用可通过与抗CD44或抗TLR4阻断抗体孵育而消除。此外，用针对IRAK-M的小干扰RNA下调IRAK-M表达可恢复再次接触肿瘤细胞系的人单核细胞中肿瘤坏死因子-α mRNA表达和蛋白质产生。总之，我们的研究结果表明，在存在肿瘤细胞的情况下人单核细胞失活涉及IRAK-M上调，并且这种效应似乎是由透明质酸通过CD44和TLR4的结合介导的。
