Serglycin activates pro-tumorigenic signaling and controls glioblastoma cell stemness, differentiation and invasive potential

Dimitra Manou; Panagiotis Bouris; Dimitris Kletsas; Martin Götte; Burkhard Greve; Aristidis Moustakas; Nikos K Karamanos; Achilleas D Theocharis

doi:10.1016/j.mbplus.2020.100033

Serglycin activates pro-tumorigenic signaling and controls glioblastoma cell stemness, differentiation and invasive potential

Matrix Biol Plus. 2020 Mar 11:6-7:100033. doi: 10.1016/j.mbplus.2020.100033. eCollection 2020 May.

Authors

Dimitra Manou¹, Panagiotis Bouris¹, Dimitris Kletsas², Martin Götte³, Burkhard Greve⁴, Aristidis Moustakas⁵, Nikos K Karamanos¹, Achilleas D Theocharis¹

Affiliations

¹ Biochemistry, Biochemical Analysis & Matrix Pathobiology Research Group, Laboratory of Biochemistry, Department of Chemistry, University of Patras, Greece.
² Laboratory of Cell Proliferation & Ageing, Institute of Biosciences & Applications, National Centre for Scientific Research 'Demokritos', Athens, Greece.
³ Department of Gynecology and Obstetrics, University Hospital, Muenster, Germany.
⁴ Department of Radiotherapy-Radiooncology, University Hospital, Muenster, Germany.
⁵ Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, Uppsala University, Sweden.

Abstract

Despite the functional role of serglycin as an intracellular proteoglycan, a variety of malignant cells depends on its expression and constitutive secretion to advance their aggressive behavior. Serglycin arose to be a biomarker for glioblastoma, which is the deadliest and most treatment-resistant form of brain tumor, but its role in this disease is not fully elucidated. In our study we suppressed the endogenous levels of serglycin in LN-18 glioblastoma cells to decipher its involvement in their malignant phenotype. Serglycin suppressed LN-18 (LN-18^shSRGN) glioblastoma cells underwent astrocytic differentiation characterized by induced expression of GFAP, SPARCL-1 and SNAIL, with simultaneous loss of their stemness capacity. In particular, LN-18^shSRGN cells presented decreased expression of glioma stem cell-related genes and ALDH1 activity, accompanied by reduced colony formation ability. Moreover, the suppression of serglycin in LN-18^shSRGN cells retarded the proliferative and migratory rate, the invasive potential in vitro and the tumor burden in vivo. The lack of serglycin in LN-18^shSRGN cells was followed by G2 arrest, with subsequent reduction of the expression of cell-cycle regulators. LN-18^shSRGN cells also exhibited impaired expression and activity of proteolytic enzymes such as MMPs, TIMPs and uPA, both in vitro and in vivo. Moreover, suppression of serglycin in LN-18^shSRGN cells eliminated the activation of pro-tumorigenic signal transduction. Of note, LN-18^shSRGN cells displayed lower expression and secretion levels of IL-6, IL-8 and CXCR-2. Concomitant, serglycin suppressed LN-18^shSRGN cells demonstrated repressed phosphorylation of ERK1/2, p38, SRC and STAT-3, which together with PI3K/AKT and IL-8/CXCR-2 signaling control LN-18 glioblastoma cell aggressiveness. Collectively, the absence of serglycin favors an astrocytic fate switch and a less aggressive phenotype, characterized by loss of pluripotency, block of the cell cycle, reduced ability for ECM proteolysis and pro-tumorigenic signaling attenuation.

Keywords: ALDH1, aldehyde dehydrogenase 1; Astrocytic differentiation; CXCR, C-X-C chemokine receptor; ECM, extracellular matrix; EMT, epithelial to mesenchymal transition; ERK, extracellular-signal-regulated kinase; GFAP, glial fibrillary acid protein; Glioblastoma; IL, interleukin; Interleukins; MAPK, mitogen-activated protein kinase; MMPs, metalloproteinases; PGs, proteoglycans; PI3K, phosphoinositide 3-kinase; Proteoglycans; Proteolytic enzymes; SRGN, serglycin; STAT-3, signal transducer and activator of transcription 3; Serglycin; Signaling; Stemness; TIMPs, tissue inhibitors of metalloproteinases; uPA, urokinase plasminogen activator.