Department of Molecular Medicine, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA.
Virology and Gene Therapy Graduate Program, Mayo Clinic Graduate School of Biomedical Sciences, Rochester, MN 55905, USA.
Biol Chem. 2018 May 24;399(6):565-576. doi: 10.1515/hsz-2018-0109.
Glucokinase (GCK) is crucial to regulating glucose metabolism in the liver and in pancreatic β-cells. There are two major GCK isoforms, hepatic and pancreatic GCKs, which differ only in exon 1. However, the functional differences between the two GCK isoforms remain poorly understood. Here, we used a β-cell-targeted gene transfer vector to determine the impact of isoform-specific GCK overexpression on β-cells in vitro and in vivo. We showed that pancreatic GCK had a nuclear localization signal unique to the pancreatic isoform, facilitating its nuclear distribution in β-cells. Despite the difference in subcellular distribution, overexpression of GCK isoforms similarly enhanced glucose uptake and β-cell proliferation in vitro. Overexpression of hepatic or pancreatic GCK also similarly enhanced β-cell proliferation in normal diet mice without affecting fasting glucose and intraperitoneal glucose tolerance tests (IPGTT). Our further study on human GCK sequences identified disproportional GCK amino acid variants in exon 1, while mutations linked to maturity onset diabetes of the young type 2 (MODY2) were disproportionally found in exons 2 through 10. Our results therefore indicate functional conservation between the two major GCK isoforms despite their distinct subcellular distribution.
葡萄糖激酶（GCK）对于调节肝脏和胰腺β细胞中的葡萄糖代谢至关重要。有两种主要的 GCK 同工型，肝 GCK 和胰腺 GCK，它们仅在第 1 外显子上有所不同。然而，两种 GCK 同工型之间的功能差异仍知之甚少。在这里，我们使用一种β细胞靶向基因转移载体，来确定同工型特异性 GCK 过表达对体外和体内β细胞的影响。我们表明，胰腺 GCK 具有独特于胰腺同工型的核定位信号，有助于其在β细胞中的核分布。尽管亚细胞分布存在差异，但 GCK 同工型的过表达同样增强了体外的葡萄糖摄取和β细胞增殖。肝 GCK 或胰腺 GCK 的过表达也同样增强了正常饮食小鼠的β细胞增殖，而不影响空腹血糖和腹腔内葡萄糖耐量试验（IPGTT）。我们对人 GCK 序列的进一步研究确定了第 1 外显子中不成比例的 GCK 氨基酸变异，而与 2 型年轻发病型糖尿病（MODY2）相关的突变则不成比例地存在于第 2 至 10 外显子中。因此，我们的研究结果表明，尽管两种主要 GCK 同工型的亚细胞分布不同，但它们具有功能上的保守性。
