dAKAP1: A mitochondrial AKAP that coordinates local translation

Abstract

A-Kinase anchoring proteins (AKAPs) are a structurally diverse family of proteins defined by the ability to bind protein kinase A (PKA). AKAPs process and integrate a variety of intracellular signals by sequestering PKA with other signaling enzymes such as kinases, phosphodiesterases, and phosphatases. dAKAP1 tethers both PKA and protein phosphatase 1 (PP1) to the outer mitochondrial membrane and contains RNA and protein interaction domains that permit the clustering of signaling enzymes with the post-transcriptional machinery. The function of RNA binding by dAKAP1 at the outer mitochondrial membrane, however, is largely unresolved. I investigated two main questions: what are the protein and RNA binding partners of dAKAP1? and what is the physiological significance of the association of these molecules with dAKAP1? In order to answer the first question, I utilized mass spectrometry to identify protein interacting partners of dAKAP1 and discovered that dAKAP1 interacts with protein subcomplexes with RNA regulatory functions. I validated the interaction of one of these subcomplexes, LARP4/PABPC1, and determined that dAKAP1 binding of RNA is required for its localization to the outer mitochondrial membrane. I utilized RNA-Seq to identify RNA interacting partners of dAKAP1 and discovered that dAKAP1 can interact with RNAs that encode mitochondrial proteins. In order to answer the second question, I investigated the local translation of proteins encoded by RNA interacting partners of dAKAP1 at the mitochondria. I observed that dAKAP1-mediated anchoring of the SDHA mRNA directly correlates with mitochondrial SDHA protein levels. Though alternation of this anchoring is not sufficient to drive metabolic change, I also correlate a decrease of SDHA with a decrease in dAKAP1 levels across four different breast cancer cell lines. Collectively, my work suggests that dAKAP1 anchoring of both RNA and RNA-regulatory proteins is important for the local translation of at least one protein, SDHA, involved in the critical mitochondrial function of oxidative phosphorylation.