RESUMO
The A-kinase anchoring protein (AKAP) GSK3ß interaction protein (GSKIP) is a cytosolic scaffolding protein binding protein kinase A (PKA) and glycogen synthase kinase 3ß (GSK3ß). Here we show that both the AKAP function of GSKIP, i.e. its direct interaction with PKA, and its direct interaction with GSK3ß are required for the regulation of ß-catenin and thus Wnt signaling. A cytoplasmic destruction complex targets ß-catenin for degradation and thus prevents Wnt signaling. Wnt signals cause ß-catenin accumulation and translocation into the nucleus, where it induces Wnt target gene expression. GSKIP facilitates control of the ß-catenin stabilizing phosphorylation at Ser-675 by PKA. Its interaction with GSK3ß facilitates control of the destabilizing phosphorylation of ß-catenin at Ser-33/Ser-37/Thr-41. The influence of GSKIP on ß-catenin is explained by its scavenger function; it recruits the kinases away from the destruction complex without forming a complex with ß-catenin. The regulation of ß-catenin by GSKIP is specific for this AKAP as AKAP220, which also binds PKA and GSK3ß, did not affect Wnt signaling. We find that the binding domain of AKAP220 for GSK3ß is a conserved GSK3ß interaction domain (GID), which is also present in GSKIP. Our findings highlight an essential compartmentalization of both PKA and GSK3ß by GSKIP, and ascribe a function to a cytosolic AKAP-PKA interaction as a regulatory factor in the control of canonical Wnt signaling. Wnt signaling controls different biological processes, including embryonic development, cell cycle progression, glycogen metabolism, and immune regulation; deregulation is associated with diseases such as cancer, type 2 diabetes, inflammatory, and Alzheimer's and Parkinson's diseases.
Assuntos
Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Glicogênio Sintase Quinase 3 beta/metabolismo , Proteínas Repressoras/metabolismo , Via de Sinalização Wnt/fisiologia , beta Catenina/metabolismo , Proteínas de Ancoragem à Quinase A , Células A549 , Proteínas Quinases Dependentes de AMP Cíclico/genética , Glicogênio Sintase Quinase 3 beta/genética , Células HEK293 , Células HeLa , Humanos , Domínios Proteicos , Proteínas Repressoras/genética , beta Catenina/genéticaRESUMO
A-kinase anchoring proteins (AKAPs) represent a family of structurally diverse proteins, all of which bind PKA. A member of this family is glycogen synthase kinase 3ß (GSK3ß) interaction protein (GSKIP). GSKIP interacts with PKA and also directly interacts with GSK3ß. The physiological function of the GSKIP protein in vivo is unknown. We developed and characterized a conditional knock-out mouse model and found that GSKIP deficiency caused lethality at birth. Embryos obtained through Caesarean section at embryonic day 18.5 were cyanotic, suffered from respiratory distress, and failed to initiate breathing properly. Additionally, all GSKIP-deficient embryos showed an incomplete closure of the palatal shelves accompanied by a delay in ossification along the fusion area of secondary palatal bones. On the molecular level, GSKIP deficiency resulted in decreased phosphorylation of GSK3ß at Ser-9 starting early in development (embryonic day 10.5), leading to enhanced GSK3ß activity. At embryonic day 18.5, GSK3ß activity decreased to levels close to that of wild type. Our findings reveal a novel, crucial role for GSKIP in the coordination of GSK3ß signaling in palatal shelf fusion.
Assuntos
Quinase 3 da Glicogênio Sintase/metabolismo , Palato/embriologia , Palato/metabolismo , Proteínas Repressoras/metabolismo , Alelos , Animais , Fissura Palatina/embriologia , Fissura Palatina/enzimologia , Fissura Palatina/patologia , Perda do Embrião/metabolismo , Embrião de Mamíferos/anormalidades , Embrião de Mamíferos/embriologia , Embrião de Mamíferos/enzimologia , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Glicogênio Sintase Quinase 3 beta , Hemizigoto , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Palato/anormalidades , Palato/enzimologia , Fenótipo , Fosforilação , Fosfosserina/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Repressoras/deficiência , RespiraçãoRESUMO
The second messenger cyclic adenosine monophosphate (cAMP) can bind and activate protein kinase A (PKA). The cAMP/PKA system is ubiquitous and involved in a wide array of biological processes and therefore requires tight spatial and temporal regulation. Important components of the safeguard system are the A-kinase anchoring proteins (AKAPs), a heterogeneous family of scaffolding proteins defined by its ability to directly bind PKA. AKAPs tether PKA to specific subcellular compartments, and they bind further interaction partners to create local signalling hubs. The recent discovery of new AKAPs and advances in the field that shed light on the relevance of these hubs for human disease highlight unique opportunities for pharmacological modulation. This review exemplifies how interference with signalling, particularly cAMP signalling, at such hubs can reshape signalling responses and discusses how this could lead to novel pharmacological concepts for the treatment of disease with an unmet medical need such as cardiovascular disease and cancer.