Mitochondrial AKAP121 Links cAMP and src Signaling to Oxidative Metabolism

Abstract

AKAP121 focuses distinct signaling events from membrane to mitochondria by binding and targeting cAMP-dependent protein kinase (PKA), protein tyrosine phosphatase (PTPD1), and mRNA. We find that AKAP121 also targets src tyrosine kinase to mitochondria via PTPD1. AKAP121 increased src-dependent phosphorylation of mitochondrial substrates and enhanced the activity of cytochrome c oxidase, a component of the mitochondrial respiratory chain. Mitochondrial membrane potential and ATP oxidative synthesis were enhanced by AKAP121 in an src-and PKA-dependent manner. Finally, siRNA-mediated silencing of endogenous AKAP121 drastically impaired synthesis and accumulation of mitochondrial ATP. These findings indicate that AKAP121, through its role in enhancing cAMP and tyrosine kinase signaling to distal organelles, is an important regulator in mitochondrial metabolism. INTRODUCTIONProtein kinase A (PKA) is an essential mediator in most cAMP-dependent signaling pathways. A family of proteins named A-kinase anchor proteins (AKAPs) has been identified that enhance cAMP-dependent PKA signaling pathways (Rubin, 1994;Gray et al., 1998;McKnight et al., 1998;Feliciello et al., 2001;Houslay and Adams, 2003;Tasken and Aandahl, 2004;Taylor et al., 2004;Wong and Scott, 2004). AKAP121 (also called D-AKAP1), AKAP149, and AKAP84 arise from a single gene by alternative pre-mRNA splicing (Lin et al., 1995;Trendelenburg et al., 1996;Chen et al., 1997;Huang et al., 1997Huang et al., , 1999Furusawa et al., 2002). AKAP121 and AKAP84 tether PKA to the mitochondrial outer surface. This localization is mediated by the interaction of AKAP121 and AKAP84 with ␤ tubulin, an integral component of mitochondrial outer membrane (Cardone et al., 2002). AKAP121 is widely expressed in several tissues and its accumulation is regulated at the transcriptional level by the cAMP/PKA pathway (Feliciello et al., 1998). Anchoring of PKA to mitochondria supports cAMP signaling and suppresses apoptosis (Harada et al., 1999;Affaitati et al., 2003). AKAP121, via a KH domain at its COOH-terminus, binds at least two mRNAs that encode mitochondrial proteins Ranganathan et al., 2005). This multicomponent system, reminiscent of other AKAP complexes at cell membranes, ensures efficient translation and import of nuclear-encoded mitochondrial proteins. It is suggested that PKA may phosphorylate some of these proteins cotranslationally, as well as acting on AKAP121 itself to regulate the stability of the RNA-AKAP121 complex Feliciello et al., 2005).In addition, AKAP121 and AKAP84 bind the central core of PTPD1, a classical nonreceptor protein tyrosine phosphatase (Moller et al., 1994). PTPD1 binds to and activates src, enhancing EGF-dependent mitogenic signaling (Cardone et al., 2004). By translocating PTPD1 to the outer membrane of mitochondria, AKAP121 inhibits PTPD1-dependent EGF signaling to the nucleus. These data suggest a model whereby AKAP121, by targeting PTPD1/src complex to mitochondria, may shift the focus of tyrosine kinase signaling from membrane to specific distal...

Localization of PTP-1B, SHP-2, and Src Exclusively in Rat Brain Mitochondria and Functional Consequences

“…8, 9, 13 and the present work) ruled out the possibility that they were washed out. However, recent observations indicate that the protein kinase A anchor protein AKAP121 associates with Src and another tyrosine phosphatase, PTP-1D, on the outer membrane of mitochondria in a human embryonic kidney cell line, HEK293, in response to epidermal growth factor (14,15). The authors proposed that Src translocated inside the mitochondria to regulate tyrosine phosphorylation.…”

“…Low Src levels or compensation by other tyrosine kinases in mitochondria from mouse muscle were deduced from studies showing no change in complex IV enzymatic activity in Src Ϫ/Ϫ mice, whereas activity was reduced in liver and kidney mitochondria (13). Other reports evoked the possibility that Src translocated within mitochondria in a human kidney cell line (14,15). Therefore, this tissue-specific distribution of mitochondrial kinases and phosphatases could be correlated to functional tissue differences.…”

Dual effects of sodium tungstate on adipocyte biology: inhibition of adipogenesis and stimulation of cellular oxygen consumption

“…Increasing reports over the past few years suggest a direct regulation of mitochondrial activity by phosphorylation events in several cell types, in which some classical cytosolic kinases are found in mitochondria [32][33][34][35] acting on different subunits of the respiratory chain complexes. [36][37][38][39][40][41] We cannot exclude a direct regulation of mitochondrial activity by sodium tungstate.…”

Molecular chaperone TRAP1 regulates a metabolic switch between mitochondrial respiration and aerobic glycolysis

“…Unexpectedly, we found TRAP1 to be tyrosine phosphorylated (Fig. 3A, Left), which caused us to examine c-Src, a kinase reported to be present in mitochondria (14,15,(30)(31)(32)(33). We probed TRAP1 immunoprecipitates for c-Src association and we identified c-Src as a TRAP1-interacting protein in HCT116 cells (Fig.…”