# Cytochrome c Oxidase Subunit COX4-1 Reprograms Erastin-Induced Cell Death from Ferroptosis to Apoptosis: A Transmitochondrial Study

## TL;DR

This study shows that the mitochondrial protein COX4-1 changes how glioma cells die in response to erastin, shifting from ferroptosis to apoptosis.

## Contribution

The study reveals that COX4-1 isoform in mitochondria determines cell death type, offering new insights into glioblastoma therapy resistance.

## Key findings

- COX4-1-containing mitochondria restore CcO activity and confer resistance to ferroptosis.
- COX4-1 cybrids undergo apoptosis instead of ferroptosis despite low SLC7A11 and GPX4 levels.
- Mitochondrial COX4-1 isoform alters redox metabolism and cell death signaling.

## Abstract

Ferroptosis is an iron-dependent, oxidative form of regulated cell death that has emerged as a therapeutic vulnerability in glioblastoma; however, the mitochondrial determinants that govern ferroptotic sensitivity remain poorly defined. Cytochrome c oxidase (CcO/Complex IV), a key regulator of mitochondrial respiration, contains two isoforms of subunit IV (COX4): COX4-1, a housekeeping isoform, and COX4-2, a stress-inducible variant. We previously found that COX4-1 expression protects glioma cells from erastin-induced ferroptosis, suggesting that mitochondria influence cell-death decisions independently of canonical ferroptotic regulators. Here, we used CRISPR-generated POLG-knockout ρ0 cells and transmitochondrial cybrids to isolate mitochondrial from nuclear contributions to ferroptosis sensitivity. Cybrids reconstituted with COX4-1-containing mitochondria restored CcO activity and recapitulated the ferroptosis-resistant phenotype, whereas COX4-2 cybrids remained insensitive to erastin. COX4-1 cybrids exhibited reduced labile iron, diminished cystine uptake, and low expression of SLC7A11 and GPX4, yet underwent apoptosis rather than ferroptosis upon erastin treatment. These findings demonstrate that mitochondrial COX4-1 rewires redox metabolism and diverts cell-death signaling away from ferroptosis toward apoptosis. Our results identify isoform-specific mitochondrial composition as a previously unrecognized determinant of regulated cell death and highlight COX4-1-driven mitochondrial remodeling as a potential mechanism of therapeutic resistance in glioblastoma.