O(6)-Methylguanine-DNA Methyltransferase Is a Novel Negative Effector of Invasion in Glioblastoma Multiforme

Abstract

The dismal prognosis of glioblastoma multiforme (GBM) is mostly due to the high propensity of GBM tumor cells to invade. We reported an inverse relationship between GBM angiogenicity and expression of the DNA repair protein O 6 -methylguanine-DNA methyltransferase (MGMT), which has been extensively characterized for its role in resistance to alkylating agents used in GBM treatment. In the present study, given the major role of angiogenesis and invasion in GBM aggressiveness, we aimed to investigate the relationship between MGMT expression and GBM invasion. Stable overexpression of MGMT in the U87MG cell line significantly decreased invasion, altered expression of invasion-related genes, decreased expression of a 5 b 1 integrin and focal adhesion kinase, and reduced their spindle-shaped morphology and migration compared with the empty vector control. Conversely, short hairpin RNA-mediated stable knockdown of MGMT or its pharmacologic depletion in the MGMT-positive T98G cell line were required for increased invasion. The inverse relationship between MGMT and invasion was further validated in primary GBM patient-derived cell lines. Using paraffin-embedded tumors from patients with newly diagnosed GBM (n ¼ 59), tumor MGMT promoter hypermethylation (MGMT gene silencing) was significantly associated with increased immunohistochemical expression of the proinvasive matricellular protein secreted protein acidic and rich in cysteine (SPARC; P ¼ 0.039, x 2 test). Taken together, our findings highlight for the first time the role of MGMT as a negative effector of GBM invasion. Future studies are warranted to elucidate the role of SPARC in the molecular mechanisms underlying the inverse relationship between MGMT and GBM invasion and the potential use of MGMT and SPARC as biomarkers of GBM invasion.

Interrogation of gossypol therapy in glioblastoma implementing cell line and patient-derived tumour models

“…Some synergism was observed in the U87MG-luc2 cell line (MGMT-expressing) as also previously reported ( Voss et al , 2010 ). Nevertheless, U373 (MGMT-low level) and U251 (MGMT-negative) GBM cell lines ( Chahal et al , 2012 ) demonstrated additive and antagonistic response to combined drug treatment. Interestingly, it has previously been reported that U251 and U373 GBM cell line express low Mcl-1 levels ( Day et al , 2011 ), whereas U87 and U343 cell lines exhibit high Mcl-1 expression levels ( Hetschko et al , 2008 ; Day et al , 2011 ; Murphy et al , 2014 ).…”

Integrin α5β1, the Fibronectin Receptor, as a Pertinent Therapeutic Target in Solid Tumors

“…Interaction of MMP-2 with α5β1 integrin was shown to regulate the IL-6/STAT3 survival signaling in glioma [115]. The expression of the DNA repair protein, O6-Methylguanine-DNA Methyltransferase (MGMT), was inversely related to invasion capacity of glioma and to α5β1 integrin expression [116]. …”

Differential response to ablative ionizing radiation in genetically distinct non-small cell lung cancer cells

“…Cell migration and invasion was assessed using modified Boyden chambers (8-mm pore, BD Biosciences, CA) according to previously established methods. 34 Chambers were either non-coated for migration or pre-coated with BD Matrigel basement membrane for invasion studies. Assays were performed 5 d after exposure to AIR or FIR.…”