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. Examine RNAs bound to hnRNPA1 in cytosol, mitochondria, and total cell lysates by using RIPseq. Examine differential gene expression by hnRNPA1 knockdown using RNA sequencing