Dual mode of glucagon receptor internalization: role of PKCα, GRKs and β-arrestins.
Dual mode of glucagon receptor internalization: role of PKCα, GRKs and β-arrestins.
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DOI：
10.1016/j.yexcr.2011.10.001
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发表时间：
2011-12-10
影响因子：
3.7
通讯作者：
Bouscarel, Bernard
中科院分区：
文献类型：
--
作者：
Krilov, Lada;Amy Nguyen;Miyazaki, Teruo;Unson, Cecilia G.;Williams, Russell;Lee, Norman H.;Ceryak, Susan;Bouscarel, Bernard
胰高血糖素水平在糖尿病和一些肝脏疾病中升高。胰高血糖素分泌增加导致胰高血糖素受体（GR）的异常刺激和随后肝脏中葡萄糖产生的升高。已经提出阻断胰高血糖素受体信号传导作为糖尿病和与高血糖症相关的其他病症的潜在治疗选择。阐明GR脱敏和下调的机制可能有助于确定除GR本身以外的新药物靶点。本研究探讨GR内化的机制以及PKCα、GPCR激酶（GRKs）和β-arrestins在其中的作用。我们以前曾报道过PKCα介导GR磷酸化和脱敏。虽然PKC激动剂PMA在单独测试时不影响GR内化，但其在表达GR的HEK-293细胞（HEK-GR细胞）中使胰高血糖素介导的GR内化增加25-40%。在原代肝细胞和HEK-GR细胞中，胰高血糖素处理将PKCα募集到质膜上，在那里它与GR共定位。我们还观察到GRK 2、GRK 3或GRK 5的过表达增强了GR的内化。此外，我们发现GR利用网格蛋白和小窝蛋白介导的内吞作用在HEK-GR细胞。胰高血糖素触发β-arrestin 1和β-arrestin 2从胞质移位到膜周区域，并且β-arrestin 1和β-arrestin 2的过表达增加GR内化。此外，β-arrestin 1和β-arrestin 2与GR和Cav-1共定位，表明这些arrestins可能参与GR内化。
Glucagon levels are elevated in diabetes and some liver diseases. Increased glucagon secretion leads to abnormal stimulation of glucagon receptors (GRs) and consequent elevated glucose production in the liver. Blocking glucagon receptor signaling has been proposed as a potential treatment option for diabetes and other conditions associated with hyperglycemia. Elucidating mechanisms of GR desensitization and downregulation may help identify new drug targets besides GR itself. The present study explores the mechanisms of GR internalization and the role of PKCα, GPCR kinases (GRKs) and β-arrestins therein. We have reported previously that PKCα mediates GR phosphorylation and desensitization. While the PKC agonist, PMA, did not affect GR internalization when tested alone, it increased glucagon-mediated GR internalization by 25–40% in GR-expressing HEK-293 cells (HEK-GR cells). In both primary hepatocytes and HEK-GR cells, glucagon treatment recruited PKCα to the plasma membrane where it colocalized with GR. We also observed that overexpression of GRK2, GRK3, or GRK5 enhanced GR internalization. In addition, we found that GR utilizes both clathrin- and caveolin-mediated endocytosis in HEK-GR cells. Glucagon triggered translocation of both β-arrestin1 and β-arrestin2 from the cytosol to the perimembrane region, and overexpression of β-arrestin1 and β-arrestin2 increased GR internalization. Furthermore, both β-arrestin1 and β-arrestin2 colocalized with GR and with Cav-1, suggesting the possible involvement of these arrestins in GR internalization.
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