The dual-coding gene SLC35A4 protects against oxidative stress.

Alternative proteins (AltProts) represent a newly recognized class of biologically active proteins encoded from alternative open reading frames (AltORFs) within already annotated genes. This study focuses on the SLC35A4 gene, which encodes both the reference protein SLC35A4 and the alternative protein AltSLC35A4. Using a combination of microscopy and biochemical analyses, we confirmed the presence of AltSLC35A4 in the inner mitochondrial membrane, resolving previous conflicting reports. Previous studies employing ribosome profiling have revealed that during oxidative stress induced by sodium arsenite, the reference coding sequence of SLC35A4 exhibits the largest increase in translational efficiency among all cellular mRNAs. Our results confirmed this translational upregulation, with the emergence of SLC35A4 protein isoforms during oxidative stress in an upstream ORF-dependent manner. Notably, the expression of AltSLC35A4 remained unchanged during oxidative stress. Knock out of SLC35A4 or AltSLC35A4 enhanced sensitivity to oxidative stress in a rescuable manner, indicating a direct implication for these proteins in stress resistance. In conclusion, our research provides compelling evidence for the functional significance of the dual-coding nature of SLC35A4 for resistance to oxidative stress and highlights the importance of considering AltProts in the functional study of eukaryotic genes.