Harada Kazuki, Kitaguchi Tetsuya, Kamiya Taichi, Aung Kyaw Htet, Nakamura Kazuaki, Ohta Kunihiro, Tsuboi Takashi
From the Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan.
Cell Signaling Group, Waseda Bioscience Research Institute in Singapore (WABIOS), Singapore 138667, Singapore.
J Biol Chem. 2017 Jun 30;292(26):10855-10864. doi: 10.1074/jbc.M117.788653. Epub 2017 May 22.
The lysophosphatidylinositol (LPI) has crucial roles in multiple physiological processes, including insulin exocytosis from pancreatic islets. However, the role of LPI in secretion of glucagon-like peptide-1 (GLP-1), a hormone that enhances glucose-induced insulin secretion, is unclear. Here, we used the murine enteroendocrine L cell line GLUTag and primary murine small intestinal cells to elucidate the mechanism of LPI-induced GLP-1 secretion. Exogenous LPI addition increased intracellular Ca concentrations ([Ca] ) in GLUTag cells and induced GLP-1 secretion from both GLUTag and acutely prepared primary intestinal cells. The [Ca] increase was suppressed by an antagonist for G protein-coupled receptor 55 (GPR55) and by silencing of GPR55 expression, indicating involvement of G and G signaling pathways in the LPI-induced increased [Ca] levels and GLP-1 secretion. However, GPR55 agonists did not mimic many of the effects of LPI. We also found that phospholipase C inhibitor and Rho-associated kinase inhibitor suppressed the [Ca] increase and that LPI increased the number of focal adhesions, indicating actin reorganization. Of note, blockage or silencing of transient receptor potential cation channel subfamily V member 2 (TRPV2) channels suppressed both the LPI-induced [Ca] increase and GLP-1 secretion. Furthermore, LPI accelerated TRPV2 translocation to the plasma membrane, which was significantly suppressed by a GPR55 antagonist. These findings suggest that TRPV2 activation via actin reorganization induced by G and G signaling is involved in LPI-stimulated GLP-1 secretion in enteroendocrine L cells. Because GPR55 agonists largely failed to mimic the effects of LPI, its actions on L cells are at least partially independent of GPR55 activation.
溶血磷脂酰肌醇（LPI）在多种生理过程中发挥着关键作用，包括胰腺胰岛的胰岛素胞吐作用。然而，LPI在胰高血糖素样肽-1（GLP-1）分泌中的作用尚不清楚，GLP-1是一种可增强葡萄糖诱导的胰岛素分泌的激素。在此，我们使用小鼠肠内分泌L细胞系GLUTag和原代小鼠小肠细胞来阐明LPI诱导GLP-1分泌的机制。添加外源性LPI可增加GLUTag细胞内的钙离子浓度（[Ca] ），并诱导GLUTag细胞和急性制备的原代肠细胞分泌GLP-1。G蛋白偶联受体55（GPR55）拮抗剂以及GPR55表达沉默可抑制[Ca] 的升高，这表明G 和G 信号通路参与了LPI诱导的[Ca] 水平升高和GLP-1分泌。然而，GPR55激动剂并不能模拟LPI的许多作用。我们还发现磷脂酶C抑制剂和Rho相关激酶抑制剂可抑制[Ca] 的升高，并且LPI增加了粘着斑的数量，表明肌动蛋白发生了重组。值得注意的是，瞬时受体电位阳离子通道亚家族V成员2（TRPV2）通道的阻断或沉默可同时抑制LPI诱导的[Ca] 升高和GLP-1分泌。此外，LPI加速了TRPV2向质膜的转位，而这一过程被GPR55拮抗剂显著抑制。这些发现表明，G 和G 信号诱导的肌动蛋白重组所激活的TRPV2参与了肠内分泌L细胞中LPI刺激的GLP-1分泌。由于GPR55激动剂在很大程度上无法模拟LPI的作用，其对L细胞的作用至少部分独立于GPR55的激活。
