COX4-1 promotes mitochondrial supercomplex assembly and limits reactive oxide species production in radioresistant GBM

Abstract

Glioblastoma (GBM) is a fatal disease with recurrences often associated with radioresistance. Although often effective at treating newly diagnosed GBM, increasing evidence suggests that radiotherapy-induced alterations in tumor metabolism promote GBM recurrence and aggressiveness. Using isogenic radiosensitive and radioresistant GBM cell lines and patient-derived xenolines, we found that acquired radioresistance is associated with a shift from a glycolytic metabolism to a more oxidative metabolism marked by a substantial increase in the activity of the mitochondrial res-piratory chain complex cytochrome c oxidase (CcO). This elevated CcO ac-tivity was associated with a switch in the isoform expression of the CcO regulatory subunit COX4, from COX4-2 to COX4-1, assembly of CcO-containing mitochondrial supercomplexes (SCs), and reduced superoxide (O2●-) production. Overexpression of COX4-1 in the radiosensitive cells was sufficient to promote the switch from glycolytic to oxidative metabolism and the incorporation of CcO into SCs, with a concomitant reduction in O2●- production. Conversely, silencing of COX4-1 expression in normally radiore-sistant cells reduced CcO activity, promoted the disassembly of mitochon-drial SCs, and increased O2●- production. Additionally, gain or loss of COX4-1 expression was sufficient to induce the radioresistant or radiosensitive phenotype, respectively. Our results demonstrate that COX4-1 promotes SC assembly in GBM cells, and SC assembly may in turn regulate the pro-duction of reactive oxygen species and thus the acquisition of radiore-sistance in GBM.

Glioblastoma initiation, migration, and cell types are regulated by core bHLH transcription factors ASCL1 and OLIG2

“…We saw significant upregulation of both nuclear (Cox4i1, Cox5a, Cox5b, Cox6c, Cox7a, Cox7c, Cox8a) and mitochondrial (mt-Co1, mt-Co2, mt-Co3) genes encoding for the 13 subunits of cytochrome c oxidase in the electron transport chain, the key regulator of oxidative phosphorylation 104,105 . More specifically, increases in COX4I1 isoforms are implicated in poorer prognosis, supercomplex formation, increased tumor growth and metastases, and radioresistance [106][107][108] . Therefore, through upregulation of cytochrome c oxidase subunits, especially Cox4i1, ASCL1 increases the efficiency of oxidative phosphorylation and, ultimately, confers a GSC phenotype.…”

Metabolic Roles of HIF1, c-Myc, and p53 in Glioma Cells

“…HIF1 activates the components of complex IV through the expression of the cytochrome-c-oxidase (COX) subunit 4-2 (COX4-2) isoform and the mitochondrial protease LON, which degrades COX4-1. Then, COX4-2 substitutes for COX4-1 in cytochrome c oxidase (complex IV), resulting in a more efficient electron transfer to oxygen without increasing ROS levels [194,198], as COX4-1 expression correlates with elevated complex IV activity and increased ROS production [199]. COX4-1 is involved in the formation of mitochondrial supercomplexes containing CTE complex IV, thus promoting an increased rate of respiration and an OXPHOS phenotype in radioresistant cells [199].…”

“…Then, COX4-2 substitutes for COX4-1 in cytochrome c oxidase (complex IV), resulting in a more efficient electron transfer to oxygen without increasing ROS levels [194,198], as COX4-1 expression correlates with elevated complex IV activity and increased ROS production [199]. COX4-1 is involved in the formation of mitochondrial supercomplexes containing CTE complex IV, thus promoting an increased rate of respiration and an OXPHOS phenotype in radioresistant cells [199]. Oliva et al reported a strong association of COX4-1 levels with poor prognosis in cancer patients, whereas higher COX4-2 concentrations were not correlated in such a way [200].…”

Mitoferrin-1 Promotes Proliferation and Abrogates Protein Oxidation via the Glutathione Pathway in Glioblastoma

“…Mitochondria fractions were prepared as previously described [28,[34][35][36]. The activity of ETC complexes and citrate synthase was measured in mitochondrial extracts, as previously described [37].…”