Department of Surgery, David Geffen School of Medicine at University of California, Los Angeles, CA 90095, USA.
Mary Crowley Cancer Research Center, Dallas, TX 75230, USA.
Genes (Basel). 2013 Jul 19;4(3):358-74. doi: 10.3390/genes4030358.
Transcription factor pancreatic and duodenal homeobox-1 (PDX-1) plays an essential role in pancreatic development, β-cell differentiation, maintenance of normal β-cell function and tumorigenesis. PDX-1 expression is tightly controlled through a variety of mechanisms under different cellular contexts. We report here that overexpression of Notch1 intracellular domain (NICD), an activated form of Notch1, enhanced PDX-1 expression in both PDX-1 stable HEK293 cells and mouse insulinoma β-TC-6 cells, while NICD shRNA inhibited the enhancing effect. NICD-enhanced PDX-1 expression was accompanied by increased insulin expression/secretion and cell proliferation in β-TC-6 cells, which was reversed by NICD shRNA. Cre activation-induced specific expression of NICD in islet β cells of transgenic βNICD+/+ mice induced increased expression of PDX-1, insulin and proliferating cell nuclear antigen (PCNA) and decreased expression of p27 with accompanied fasting hyperinsulinemia and hypoglycemia and altered responses to intraperitoneal glucose tolerance test. Systemically delivered NICD shRNA suppressed islet expression of PDX-1 and reversed the hypoglycemia and hyperinsulinemia. Moreover, expression levels of NICD were correlated with those of PDX-1 in human pancreatic neuroendocrine tumor. Thus, Notch1 acts as a positive regulator for PDX-1 expression, cooperates with PDX-1 in the development of insulin overexpression and islet cell neoplasia and represents a potential therapeutic target for islet neoplasia.
转录因子胰腺十二指肠同源盒-1（PDX-1）在胰腺发育、β细胞分化、维持正常β细胞功能和肿瘤发生中发挥着重要作用。PDX-1 的表达通过多种机制在不同的细胞环境中受到严格控制。我们在这里报告，Notch1 细胞内结构域（NICD）的过表达，即 Notch1 的激活形式，增强了 PDX-1 在 PDX-1 稳定 HEK293 细胞和小鼠胰岛素瘤β-TC-6 细胞中的表达，而 NICD shRNA 抑制了增强作用。NICD 增强的 PDX-1 表达伴随着β-TC-6 细胞中胰岛素的表达/分泌和细胞增殖增加，这被 NICD shRNA 逆转。转基因βNICD+/+ 小鼠胰岛β细胞中 Cre 激活诱导的 NICD 特异性表达诱导 PDX-1、胰岛素和增殖细胞核抗原（PCNA）的表达增加，p27 的表达减少，伴有空腹高胰岛素血症和低血糖，并改变了对腹腔内葡萄糖耐量试验的反应。系统递送的 NICD shRNA 抑制了胰岛 PDX-1 的表达，并逆转了低血糖和高胰岛素血症。此外，NICD 的表达水平与人胰腺神经内分泌肿瘤中的 PDX-1 表达水平相关。因此，Notch1 作为 PDX-1 表达的正调节剂，与 PDX-1 合作参与胰岛素过表达和胰岛细胞肿瘤的发生，并代表胰岛肿瘤的潜在治疗靶点。
