Protein Kinase A Subunit Balance Regulates Lipid Metabolism in Caenorhabditis elegans and Mammalian Adipocytes

Abstract

Protein kinase A (PKA) is a cyclic AMP (cAMP)-dependent protein kinase composed of catalytic and regulatory subunits and involved in various physiological phenomena, including lipid metabolism. Here we demonstrated that the stoichiometric balance between catalytic and regulatory subunits is crucial for maintaining basal PKA activity and lipid homeostasis. To uncover the potential roles of each PKA subunit, Caenorhabditis elegans was used to investigate the effects of PKA subunit deficiency. In worms, suppression of PKA via RNAi resulted in severe phenotypes, including shortened life span, decreased egg laying, reduced locomotion, and altered lipid distribution. Similarly, in mammalian adipocytes, suppression of PKA regulatory subunits RI␣ and RII␤ via siRNAs potently stimulated PKA activity, leading to potentiated lipolysis without increasing cAMP levels. Nevertheless, insulin exerted anti-lipolytic effects and restored lipid droplet integrity by antagonizing PKA action. Together, these data implicate the importance of subunit stoichiometry as another regulatory mechanism of PKA activity and lipid metabolism.Protein kinase A (PKA) is a cyclic AMP (cAMP)-dependent serine/threonine kinase that mediates various cellular responses, including lipolysis. Since its discovery in the 1950s (1-4), the cAMP-PKA system has become one of the best understood signaling pathways in terms of biochemical properties. PKA is composed of catalytic subunits and cAMP-binding regulatory subunits (5). In the absence of cAMP stimulation, PKA forms an inactive tetramer composed of four subunits with two regulatory and two catalytic subunits. Upon nutritional deprivation or hormonal stimulation, activated adenylyl cyclase produces cAMP from ATP. Then, the regulatory subunit of PKA binds cAMP, causing a conformational change that decreases its affinity for catalytic subunits by ϳ10 4 -fold and leads to the release of active catalytic subunits to phosphorylate target proteins (6, 7).PKA has a wide range of substrates that regulate a number of physiological processes. To date, several hundred PKA target proteins have been identified, and yet new PKA substrates are continually being reported (8, 9). In mammalian adipocytes, numerous studies over the last 40 years have revealed that the cAMP-PKA axis forms a critical node in the regulation of lipolysis. For instance, major components of lipolytic pathways, including hormone-sensitive lipase (Hsl) 2 and perilipin 1 (Plin1), are direct targets of PKA (10, 11). Recently, adipose triglyceride lipase (Atgl) was also reported to be a target of PKA (12, 13). Upon receiving activation signals from molecules such as catecholamine and glucagon, activated PKA phosphorylates Plin1 and HSL to promote the recruitment of HSL to lipid droplets (14, 15). In addition, phosphorylated Plin1 releases comparative gene identification-58 (CGI-58; Abhd5), a coactivator of Atgl, to mediate lipolysis upon PKA activation (16 -20). On the contrary, insulin can activate phosphodiesterase 3B (Pde3b) and reduce cAMP levels (1...

Multi‐omics identify xanthine as a pro‐survival metabolite for nematodes with mitochondrial dysfunction

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“…Since genes in sugar metabolism seem particularly enriched in both the transcriptome and the proteome, we measured simple and complex carbohydrates using the phenol-sulfuric acid colorimetric assay. In C. elegans, kin-1 encodes the catalytic subunit of PKA, whereas kin-2 encodes for the regulatory one (Lee et al, 2016). We then overlapped IPA predictions from both transcriptomics and proteomics.…”

Transcription profiles of age-at-maturity-associated genes suggest cell fate commitment regulation as a key factor in the Atlantic salmon maturation process

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Gα/GSA-1 works upstream of PKA/KIN-1 to regulate calcium signaling and contractility in theCaenorhabditis elegansspermatheca

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