Department of Morphology and Embryology and LTTA Centre, University of Ferrara, Ferrara, Italy.
J Cell Physiol. 2011 Sep;226(9):2279-86. doi: 10.1002/jcp.22564.
The soluble member of the TNF-R superfamily osteoprotegerin (OPG) is abundantly released under basal conditions by both mesenchymal stem cells (MSC) and fibroblasts and by endothelial cells upon stimulation with inflammatory cytokines. Since MSC, fibroblasts and endothelial cells represent key elements of the normal and tumor microenvironment and express detectable levels of surface TRAIL receptors, we investigated the effect of TRAIL on OPG release. Unexpectedly, recombinant TRAIL decreased the spontaneous OPG release in all cell types examined. Moreover, TRAIL decreased OPG release also in stromal cells co-cultured with lymphoma cells and counteracted the OPG induction by TN-alpha in HUVEC and MSC. Such down-regulation was not due to a masking effect in the ELISA quantification of the OPG released in the culture supernatants due to binding of OPG to its ligands (TRAIL and RANKL), as demonstrated by competition experiments with recombinant TRAIL and by the lack of RANKL release/induction. In addition, OPG down-regulation was not due to induction of cytotoxic effects by TRAIL, since the degree of apoptosis in response to TRAIL was negligible in all primary cell types. With regards to the possible molecular mechanism accounting for the down-regulation of OPG release by TRAIL, we found that treatment of MSC with TRAIL significantly decreased the phosphorylation levels of p38/MAPK. There is a suggestion that this pathway is involved in the stabilization of OPG mRNA. In this respect, the ability of TRAIL to decrease the release of OPG, in the absence of cell cytotoxicity, was mimicked by the p38/MAPK inhibitor SB203580.
肿瘤坏死因子受体超家族可溶性成员护骨素（OPG）在基础条件下由间充质干细胞（MSC）和成纤维细胞大量释放，内皮细胞受到炎性细胞因子刺激后也会释放 OPG。由于 MSC、成纤维细胞和内皮细胞是正常和肿瘤微环境的关键元素，并且表达可检测水平的表面 TRAIL 受体，我们研究了 TRAIL 对 OPG 释放的影响。出乎意料的是，重组 TRAIL 降低了所有检测细胞类型中自发的 OPG 释放。此外，TRAIL 还降低了基质细胞与淋巴瘤细胞共培养时的 OPG 释放，并抵消了 TN-α在 HUVEC 和 MSC 中诱导的 OPG。这种下调不是由于 ELISA 定量检测培养上清液中释放的 OPG 时由于 OPG 与其配体（TRAIL 和 RANKL）结合而产生的屏蔽效应，这一点通过与重组 TRAIL 的竞争实验和缺乏 RANKL 释放/诱导证明了这一点。此外，由于 TRAIL 诱导的细胞毒性作用程度在所有原代细胞类型中都可以忽略不计，因此 OPG 下调不是由于 TRAIL 诱导的细胞毒性作用所致。关于 TRAIL 下调 OPG 释放的可能分子机制，我们发现 TRAIL 处理 MSC 会显著降低 p38/MAPK 的磷酸化水平。有迹象表明，该途径参与了 OPG mRNA 的稳定。在这方面，TRAIL 在没有细胞毒性的情况下降低 OPG 释放的能力被 p38/MAPK 抑制剂 SB203580 模拟。
