gms | German Medical Science

Objective: Glioblastoma (GBM) is the most common form of malignant primary brain tumour. Only a dismal proportion of GBM patients achieve 5-year survival. Thus, it is critical to identify novel prognostic markers and molecular mechanisms, which could serve as targets for novel therapeutic strategies in this type of tumour. Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase 2 (PLOD2) is the key enzyme for mediating hydroxylation of collagen -the most abundant protein of the extracellular matrix (ECM)- thereby forming stabilized collagen cross-links. As a major component of the tumour microenvironment, the ECM plays a crucial role in tumour progression, invasion, migration and metastasis. The purpose of this study was to investigate the role of PLOD2 in GBM pathophysiology.

Methods: PLOD2 protein expression was assessed by immunohistochemistry in two independent cohorts of patients with primary GBM (n₁=233 and n₂=242, respectively). Additionally, H4 glioma cells were stably transfected to down-regulate PLOD2 levels in vitro. The transfected cells were subsequently tested in regard to proliferation (MTT assay), anchorage-independent growth (soft-agar clonogenic assay) and invasion (Oris^™ 3D Cell Invasion assay and matrix metalloprotease release). Furthermore, we tested potential downstream molecular mechanisms of PLOD2 by western blot.

Results: We found that high PLOD2 expression was associated with a shorter overall- (p₁=0.01; p₂= 0.01; log-rank) and progression-free (p₁=0.01; p₂=0.03; log-rank) survival of GBM patients in both cohorts and was an independent predictor of poor overall survival in multivariate Cox-regression models. In vitro, PLOD2 knockdown led to reduced proliferation, invasion and anchorage-independent growth. Mechanistically, inhibition of PLOD2 reduced the expression of MT1-MMP, CD44, CD99, Catenin D1 and the release of pro-invasive MMP2.

Conclusion: Our study identifies PLOD2 as an independent prognostic marker for the overall survival of GBM patients. Furthermore, we demonstrate the involvement of PLOD2 in GBM progression and identify novel downstream molecular mechanisms in the PLOD2 signalling pathway. Ultimately, these findings might foster the development of improved and personalized therapeutic strategies against this type of cancer.