hnRNPA is a novel regulator of a mitochondrial microprotein expression

Mitochondrial-derived peptides (MDPs) are microproteins that are encoded by short open reading frames within the mitochondrial genome. Several MDPs have been identified in recent years; however, the transcriptional and translational regulation of MDPs remain poorly understood. Here we discovered an RNA binding protein of an MDP called humanin. By conducting RNA pull-down assays from mitochondrial extracts, we confidently pinpointed three humanin RNA binding partners that regulate translation: heterogeneous nuclear ribonucleoproteins A1 (hnRNPA1), hnRNPA2, and hnRNPA3. We also identified a novel post-translational modification in the form of succinylation in hnRNPA1 at lysine residue K-106. Succinylation of hnRNPA1 plays an important role in mitochondrial translocation and binding affinity of hnRNPA1 to humanin mRNA. Furthermore, hnRNPA1 and humanin are highly co-expressed in prostate cancer. We provide the first evidence of mRNA binding proteins modulating the expression of a mitochondrial microprotein. This study articulates important new roles of ribonucleoproteins in modulating microprotein expression in mitochondria.