Glucagon is a peptide hormone generated by pancreatic α cells. It is the counterpart of insulin and plays an essential role in the regulation of blood glucose level. Therefore, a tight regulation of glucagon levels is pivotal to maintain homeostasis of blood glucose. However, little is known about the mechanisms regulating glucagon biosynthesis. In this study, we demonstrate that the RNA-binding protein HuD regulates glucagon expression in pancreatic α cells. HuD was found in α cells from mouse pancreatic islet and mouse glucagonoma αTC1 cell line. Ribonucleoprotein immunoprecipitation analysis, followed by RT-qPCR showed the association of HuD with glucagon mRNA. Knockdown of HuD resulted in a reduction in both proglucagon expression and cellular glucagon level by decreasing its de novo synthesis. Reporter analysis using the EGFP reporter containing 3′ untranslated region (3′UTR) of glucagon mRNA showed that HuD regulates proglucagon expression via its 3′UTR. In addition, the relative level of glucagon in the islets and plasma was lower in HuD knockout (KO) mice compared to age-matched control mice. Taken together, these results suggest that HuD is a novel factor regulating the biosynthesis of proglucagon in pancreatic α cells.

胰高血糖素是由胰腺α细胞产生的肽激素。它是胰岛素的对应物，在血糖水平的调节中起着至关重要的作用。因此，严格调节胰高血糖素水平对于维持血糖的稳态至关重要。然而，关于调节胰高血糖素生物合成的机制知之甚少。在这项研究中，我们证明了RNA结合蛋白HuD调节胰岛α细胞中胰高血糖素的表达。在来自小鼠胰岛和小鼠胰高血糖素瘤αTC1细胞系的α细胞中发现了HuD。核糖蛋白免疫沉淀分析，然后进行RT-qPCR，显示了HuD与胰高血糖素mRNA的关联。降低HuD导致从头降低胰高血糖素原表达和细胞胰高血糖素水平合成。使用含有胰高血糖素mRNA的3'非翻译区（3'UTR）的EGFP报告基因进行的报告基因分析表明，HuD通过其3'UTR调节胰高血糖素原的表达。此外，与年龄匹配的对照小鼠相比，HuD基因敲除（KO）小鼠的胰岛和血浆中胰高血糖素的相对水平较低。综上所述，这些结果表明HuD是调节胰高血糖素在胰腺α细胞中生物合成的新因素。