Saturday, September 7, 2024
9/7/2024
PROJECT SUMMARY Fatty liver potentiates alcohol-associated liver disease (ALD) development. AKAP12 (A-kinase anchoring protein 12) is a scaffolding protein in signal transduction by anchoring protein kinases (PKA, PKC), cyclin-D1 and heat shock protein 47. Our recent proteomics studies showed that AKAP12 exhibited decreased interaction with kinases and increased interaction with phosphatases by alcohol in mouse models and human ALD. This led us to examine whether alcohol regulated AKAP12 phosphorylation. By phospho-peptide mapping we determined that alcohol strongly inhibited AKAP12 phosphorylation in mouse liver. AKAP12’s alcohol-sensitive phospho- sites were mainly PKA-predicted substrates. Mutating these phospho-sites reduced the stability of AKAP12 protein, suggesting that phosphorylation stabilized AKAP12. The AKAP12 interactome revealed its interactions with proteins known to regulate lipid homeostasis such as PKA, 2-adrenergic receptor (2-AR) and lipolytic enzymes, adipose-triglyceride lipase (ATGL). We therefore assessed the functional role of this AKAP12 interactome in hepatocytes. It was shown previously that AKAP12-mediated PKA scaffolding recruits it to 2- AR. The signalosome of AKAP12, PKA and 2-AR regulates cAMP levels through the process of 2-AR de- sensitization/re-sensitization and may involve AKAP12 phosphorylation. 2-AR/PKA/cAMP signaling limits lipid accumulation and enhances lipolysis. Our novel preliminary data indicates that alcohol exposure dysregulates several components of the AKAP12/PKA/2-AR signalosome. Alcohol inhibited the interaction between PKA and 2-AR. AKAP12 was highly phosphorylated at a S696-S698 PKA-phospho-site that was previously published to facilitate AKAP12-2-AR binding. This site exhibited decreased phosphorylation upon alcohol exposure and mutating this AKAP12 site reduced its scaffolding towards both PKA and 2-AR. This AKAP12 mutation also reduced 2-AR protein stability. Alcohol interfered with AKAP12-2-AR interaction and facilitated AKAP12 and 2-AR lysosomal degradation. Based on these data, we hypothesize that decreased AKAP12 phosphorylation following alcohol exposure might interfere with AKAP12/PKA/2-AR signalosome, causing alterations in cAMP signaling, which in turn could dysregulate lipid homeostasis. Preliminary data that support this hypothesis are: 1) Enhancing endogenous AKAP12 levels reverses the inhibitory effect of alcohol on PKA-2-AR interaction; 2) AKAP12 induction inhibits alcohol-mediated increase of triglyceride levels; 3) AKAP12 induction reverses alcohol’s suppressive effect on fatty acid oxidation. Induction of AKAP12 also reverses alcohol’s suppressive effect on the activity of lipolytic enzyme, ATGL. Whether the AKAP12/PKA/2-AR scaffold controls lipid homeostasis is unknown. We hypothesize that dysregulation of the AKAP12 signalosome favors lipid accumulation. This proposal will evaluate how alcohol-sensitive AKAP12 phosphorylation destabilizes AKAP12, impairs its scaffolding activities and contributes to dysregulation of lipid homeostasis. The therapeutic benefit of AKAP12 phospho-stabilization in ameliorating lipid dysfunction will be tested in mouse models of ALD.
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