Department of Cell Biology and Histology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands; Division of Neurobiology, Barrow Brain Tumor Research Center, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013, USA.
Department of Genetic Toxicology and Cancer Biology, National Institute of Biology, Večna pot 111, 1000 Ljubljana, Slovenia.
Biochim Biophys Acta Mol Cell Res. 2017 Mar;1864(3):594-603. doi: 10.1016/j.bbamcr.2016.12.021. Epub 2016 Dec 28.
Glioblastoma (GBM) is the most aggressive primary brain tumor with poor patient survival that is at least partly caused by malignant and therapy-resistant glioma stem-like cells (GSLCs) that are protected in GSLC niches. Previously, we have shown that the chemo-attractant stromal-derived factor-1α (SDF-1α), its C-X-C receptor type 4 (CXCR4) and the cysteine protease cathepsin K (CatK) are localized in GSLC niches in glioblastoma. Here, we investigated whether SDF-1α is a niche factor that through its interactions with CXCR4 and/or its second receptor CXCR7 on GSLCs facilitates their homing to niches. Furthermore, we aimed to prove that SDF-1α cleavage by CatK inactivates SDF-1α and inhibits the invasion of GSLCs. We performed mass spectrometric analysis of cleavage products of SDF-1α after proteolysis by CatK. We demonstrated that CatK cleaves SDF-1α at 3 sites in the N-terminus, which is the region of SDF-1α that binds to its receptors. Confocal imaging of human GBM tissue sections confirmed co-localization of SDF-1α and CatK in GSLC niches. In accordance, 2D and 3D invasion experiments using CXCR4/CXCR7-expressing GSLCs and GBM cells showed that SDF-1α had chemotactic activity whereas CatK cleavage products of SDF-1α did not. Besides, CXCR4 inhibitor plerixafor inhibited invasion of CXCR4/CXCR7-expressing GSLCs. In conclusion, CatK can cleave and inactivate SDF-1α. This implies that CatK activity facilitates migration of GSLCs out of niches. We propose that activation of CatK may be a promising strategy to prevent homing of GSLCs in niches and thus render these cells sensitive to chemotherapy and radiation.
胶质母细胞瘤（GBM）是最具侵袭性的原发性脑肿瘤，患者生存情况较差，至少部分原因是恶性和治疗耐药的神经胶质瘤干细胞样细胞（GSLCs）在 GSLC 龛位中受到保护。以前，我们已经表明，趋化因子基质衍生因子-1α（SDF-1α）、其 C-X-C 受体型 4（CXCR4）和半胱氨酸蛋白酶组织蛋白酶 K（CatK）定位于胶质母细胞瘤中的 GSLC 龛位。在这里，我们研究了 SDF-1α 是否是一种龛位因子，通过其与 GSLC 上的 CXCR4 和/或其第二受体 CXCR7 的相互作用，促进它们归巢到龛位。此外，我们旨在证明 CatK 对 SDF-1α 的切割使其失活并抑制 GSLC 侵袭。我们对 CatK 蛋白水解后 SDF-1α 的切割产物进行了质谱分析。我们证明 CatK 在 SDF-1α 的 N 端 3 个位点切割 SDF-1α，这是 SDF-1α 与受体结合的区域。对人 GBM 组织切片的共聚焦成像证实了 SDF-1α 和 CatK 在 GSLC 龛位中的共定位。相应地，使用表达 CXCR4/CXCR7 的 GSLC 和 GBM 细胞进行的 2D 和 3D 侵袭实验表明，SDF-1α 具有趋化活性，而 SDF-1α 的 CatK 切割产物则没有。此外，CXCR4 抑制剂plerixafor 抑制了表达 CXCR4/CXCR7 的 GSLC 的侵袭。总之，CatK 可以切割并使 SDF-1α 失活。这意味着 CatK 活性促进 GSLC 从龛位中迁移。我们提出，激活 CatK 可能是一种有前途的策略，可以防止 GSLC 归巢到龛位中，从而使这些细胞对化疗和放疗敏感。
