β Cell–intrinsic β-arrestin 1 signaling enhances sulfonylurea-induced insulin secretion
Luiz F. Barella, Mario Rossi, Lu Zhu, Yinghong Cui, Fang C. Mei, Xiaodong Cheng, Wei Chen, Vsevolod V. Gurevich, Jürgen Wess
Luiz F. Barella, Mario Rossi, Lu Zhu, Yinghong Cui, Fang C. Mei, Xiaodong Cheng, Wei Chen, Vsevolod V. Gurevich, Jürgen Wess
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Concise Communication Endocrinology

β Cell–intrinsic β-arrestin 1 signaling enhances sulfonylurea-induced insulin secretion

Abstract

β-Arrestin 1 and 2 (Barr1 and Barr2, respectively) are intracellular signaling molecules that regulate many important metabolic functions. We previously demonstrated that mice lacking Barr2 selectively in pancreatic β cells showed pronounced metabolic impairments. Here we investigated whether Barr1 plays a similar role in regulating β cell function and whole-body glucose homeostasis. Initially, we inactivated the Barr1 gene in β cells of adult mice (β-barr1-KO mice). β-barr1-KO mice did not display any obvious phenotypes in a series of in vivo and in vitro metabolic tests. However, glibenclamide and tolbutamide, 2 widely used antidiabetic drugs of the sulfonylurea (SU) family, showed greatly reduced efficacy in stimulating insulin secretion in the KO mice in vivo and in perifused KO islets in vitro. Additional in vivo and in vitro studies demonstrated that Barr1 enhanced SU-stimulated insulin secretion by promoting SU-mediated activation of Epac2. Pull-down and coimmunoprecipitation experiments showed that Barr1 can directly interact with Epac2 and that SUs such as glibenclamide promote Barr1/Epac2 complex formation, triggering enhanced Rap1 signaling and insulin secretion. These findings suggest that strategies aimed at promoting Barr1 signaling in β cells may prove useful for the development of efficacious antidiabetic drugs.

Authors

Luiz F. Barella, Mario Rossi, Lu Zhu, Yinghong Cui, Fang C. Mei, Xiaodong Cheng, Wei Chen, Vsevolod V. Gurevich, Jürgen Wess

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Figure 4

Glibenclamide promotes the interaction of Barr1 with Epac2 and stimulates Rap1 activation in a Barr1-dependent fashion.

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Glibenclamide promotes the interaction of Barr1 with Epac2 and stimulate...
(A) Coimmunoprecipitation was performed with MIN6-K8 cells infected with adenoviruses encoding Barr1 and Epac2-FLAG. Cells were stimulated with 1 μM glibenclamide (GLB) for 30 or 60 minutes. Cell lysates were incubated with an anti-FLAG antibody or rabbit IgG (negative control), and immunoprecipitated proteins were probed with an anti-Barr1 antibody by Western blotting. Data from a representative experiment are shown. (B) Quantification of the amount of Barr1 detected by Western blotting in the coimmunoprecipitation studies shown in A. Data are mean ± SEM of 3 independent experiments. (C) Efficient knockdown of Barr1 gene expression in MIN6-K8 cells by the use of Barr1 siRNA (n = 4). Con, scrambled control siRNA. (D) GLB treatment promotes the formation of Rap1-GTP in a Barr1-dependent fashion in MIN6-K8 cells. MIN6-K8 cells treated with scrambled control or Barr1 siRNA were incubated with GLB (100 nM) for 30 minutes and Rap1-GTP and total Rap1 levels were determined by Western blotting. Representative blots are shown. (E) Quantification of the Western blotting data shown in D. Data are mean ± SEM of 4 independent experiments. *P < 0.05; NS, no statistically significant difference (B, Kruskal-Wallis test; C, 2-tailed Student’s t test; E, 2-way ANOVA followed by Tukey’s post hoc test). See complete unedited blots in the supplemental material.