Rap-linked cAMP signaling Epac proteins: Compartmentation, functioning and disease implications

Breckler, Magali; Berthouze, Magali; Laurent, Anne‐Coline; Crozatier, Bertrand; Morel, Éric; Lezoualc’h, Frank

doi:10.1016/j.cellsig.2011.03.007

Cited by 108 publications

(119 citation statements)

References 162 publications

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“…As cAMP is the main downstream messenger of GLP-1, it can be deduced that the EPAC-1 enhancement was due to GLP-1R activation. Interestingly, EPAC-1 plays an important role in the maintenance of the endothelial barrier and neuronal functions [20][21][22][23], and therefore its upregulation after DPP-IV inhibition indicates this pathway as a new mechanism contributing to the protective vasculotropic actions of GLP-1R activation.…”

Section: Discussionmentioning

confidence: 99%

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Topical administration of DPP-IV inhibitors prevents retinal neurodegeneration in experimental diabetes

et al. 2017

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Aims/hypothesis The main aims of the present study were: (1) to assess the expression and content of dipeptidyl peptidase IV (DPP-IV) in human and db/db mouse retinas, and in human vitreous fluid; and (2) to determine whether the topical administration of the DPP-IV inhibitors (DPP-IVi) would prevent retinal neurodegeneration and vascular leakage in db/db mice by reducing endogenous glucagon-like peptide 1 (GLP-1) degradation. Methods To assess the expression and content of DPP-IV, human samples of vitreous fluid and retinas were obtained from participants with type 2 diabetes (n = 8) and agematched non-diabetic individuals (n = 8), as well as from db/db (n = 72) and db/+ (n = 28) mice. The interventional study, which included 72 db/db mice, consisted of the topical administration (eye drops) of saxagliptin, sitagliptin or vehicle for 14 days. DPP-IV mRNA levels were assessed by RT-PCR, and protein content was measured by ELISA or western blotting. GLP-1 was assessed by immunofluorescence, and its downstream effector exchange protein activated by cAMP-1 (EPAC-1) was used as a measure of GLP-1 receptor activation. Retinal analyses were performed in vivo by electroretinography and ex vivo by RT-PCR (Epac-1, Iba-1 [also known as Aif1]), western blotting (EPAC-1, glial fibrillar acidic protein [GFAP], glutamate−aspartate transporter [GLAST]) and immunofluorescence measurements (GLP-1, GFAP, ionised calcium binding adaptor molecule 1 [IBA-1], TUNEL, GLAST, albumin and collagen IV). Glutamate was quantified by HPLC. In addition, vascular leakage was examined by the Evans Blue method. Results DPP-IV was present in human vitreous fluid but in a range 100-fold less than in plasma. Both mRNA levels and protein content were much lower in the retina than in the liver or bowel, but were significantly higher in retinal pigment epithelium (RPE) from diabetic donors in comparison to non-diabetic donors (p < 0.05). Topical treatment with DPP-IVi prevented glial activation, apoptosis and vascular leakage induced by diabetes in db/db mice (p < 0.05). Moreover, it also significantly prevented diabetes-induced functional abnormalities in the electroretinogram. A significant increase of both GLP-1 and EPAC-1 was found after treatment with DPP-IVi (p < 0.05). Furthermore, GLAST downregulation induced by diabetes was prevented, resulting in a significant reduction of extracellular glutamate concentrations. All these effects were observed without any changes in blood glucose levels. Conclusions/interpretation The topical administration of DPP-IVi is effective in preventing neurodegeneration and vascular leakage in the diabetic retina. These effects can be attributed to an enhancement of GLP-1, but other mechanisms unrelated to the prevention of GLP-1 degradation cannot be ruled out.

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Section: Discussionmentioning

confidence: 99%

“…2d) for exchange protein activated by cAMP-1 (EPAC-1). This protein is a downstream cAMP signalling mediator and plays an important role in the maintenance of the endothelial barrier and neuronal functions [20][21][22][23].…”

Section: Topical Administration Of Dpp-ivi Increases the Ocular Contementioning

confidence: 99%

Topical administration of DPP-IV inhibitors prevents retinal neurodegeneration in experimental diabetes

et al. 2017

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“…Until the discovery of Epac proteins in 1998 the effects of the secondary messenger cAMP were considered to be mediated only by PKA and cyclic nucleotide gated ion channels [50]. Representing a novel category of cAMP mediators, Epac proteins act as specific guanine nucleotide exchange factors (GEFs) for the Ras GTPase family members Rap1 and Rap2 and consequently mediate a wide array of cellular functions including cell division, differentiation, secretion and growth [51].…”

Section: Discussionmentioning

confidence: 99%

Mechanical loading stimulates chondrogenesis via the PKA/CREB-Sox9 and PP2A pathways in chicken micromass cultures

Juhász

Matta

Somogyi

et al. 2014

Cellular Signalling

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Biomechanical stimuli play important roles in the formation of articular cartilage during early foetal life, and optimal mechanical load is a crucial regulatory factor of adult chondrocyte metabolism and function. In this study, we undertook to analyse mechanotransduction pathways during in vitro chondrogenesis. Chondroprogenitor cells isolated from limb buds of 4-day-old chicken embryos were cultivated as high density cell cultures for 6 days. Mechanical stimulation was carried out by a self-designed bioreactor that exerted uniaxial intermittent cyclic load transmitted by the culture medium as hydrostatic pressure and fluid shear to differentiating cells. The loading scheme (0.05 Hz, 600 Pa; for 30 min) was applied on culturing days 2 and 3, when final commitment and differentiation of chondroprogenitor cells occurred in this model. The applied mechanical load significantly augmented cartilage matrix production and elevated mRNA expression of several cartilage matrix constituents, including collagen type II and aggrecan core protein, as well as matrixproducing hyaluronan synthases through enhanced expression, phosphorylation and nuclear signals of the main chondrogenic transcription factor Sox9. Along with increased cAMP levels, a significantly enhanced protein kinase A (PKA) activity was also detected and CREB, the archetypal downstream transcription factor of PKA signalling, exhibited elevated phosphorylation levels and stronger nuclear signals in response to mechanical stimuli. All the above effects were diminished by the PKA-inhibitor H89. Inhibition of the PKA-independent cAMP-mediators Epac1 and Epac2 with HJC0197 resulted in enhanced cartilage formation, which was additive to that of the mechanical stimulation, implying that the chondrogenesispromoting effect of mechanical load was independent of Epac. At the same time, PP2A activity was reduced following mechanical load and treatments with the PP2A-inhibitor okadaic acid were able to mimic the effects of the intervention. Our results indicate that proper mechanical stimuli augment in vitro cartilage formation via promoting both Juhász and Matta et al. 3 differentiation and matrix production of chondrogenic cells, and the opposing regulation of the PKA/CREB-Sox9 and the PP2A signalling pathways is crucial in this phenomenon.

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“…For example, PKA can inhibit Rap1-dependent angiogenesis, acting downstream of Rap1 (40). cAMP-dependent activation of Epac can regulate Rap1-dependent adhesion and migration (27,(41)(42)(43)(44). PKA and other kinases can decrease the signaling actions of Epac by regulating the availability of cAMP through phosphodiesterases (45)(46)(47)(48).…”

Section: Discussionmentioning

confidence: 99%

Protein Kinase A-dependent Phosphorylation of Rap1 Regulates Its Membrane Localization and Cell Migration

Takahashi

Dillon

Liu

et al. 2013

Journal of Biological Chemistry

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Background:The small G protein Rap1 is phosphorylated within its carboxyl terminus by the cAMP-dependent protein kinase PKA. Results: This phosphorylation removes Rap1 from the plasma membrane to limit Rap1 signaling. Conclusion: Rap1 phosphorylation switches Rap1 off the membrane and terminates its activation. Significance: Carboxyl-terminal phosphorylation may be common among small G proteins to regulate GTP/GDP cycling and downstream signaling.

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Rap-linked cAMP signaling Epac proteins: Compartmentation, functioning and disease implications

Cited by 108 publications

References 162 publications

Topical administration of DPP-IV inhibitors prevents retinal neurodegeneration in experimental diabetes

Topical administration of DPP-IV inhibitors prevents retinal neurodegeneration in experimental diabetes

Mechanical loading stimulates chondrogenesis via the PKA/CREB-Sox9 and PP2A pathways in chicken micromass cultures

Protein Kinase A-dependent Phosphorylation of Rap1 Regulates Its Membrane Localization and Cell Migration

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