Mechanism of Differentiation of Pancreatic β Cells

为了阐明胰腺β细胞分化的分子机制，我们研究了胰腺AR42J细胞向胰岛素生成细胞分化过程中各种转录因子的表达变化。这些细胞是淀粉酶分泌肿瘤细胞，并在激活素A和肝细胞生长因子（HGF）的作用下分化为胰岛素分泌细胞。我们利用RT-PCR技术研究了胰岛中各种转录因子的表达变化。在所研究的转录因子中，Pax4和neurogenin3 （ngn3）的表达在分化过程中显著升高。因此，在初始AR42J细胞中检测不到Pax4和ngn3的表达，但在激活素A和HGF处理后可诱导表达。激活素A而非HGF诱导Pax4和ngn3的表达。为了评估这些转录因子的功能意义，我们在未成熟的AR42J细胞中引入了Pax4或ngn3的cDNA，并检测了各种分化标记物的形态和表达变化。我们还研究了引入反义cDNA的效果。当Pax 4被引入幼稚的AR42J细胞时，没有发生任何变化。此外，反义cDNA的引入对激活素A和HGF诱导的分化没有影响。相比之下，转染Pax4到未成熟的AR42J细胞会引起形态学改变。因此，细胞延长神经突样突起。此外，转染ngn3诱导胰腺多肽的表达。此外，ngn3表达的降低导致AR42J向胰岛素分泌细胞的分化受到抑制。我们得出结论，激活素A诱导ngn3表达对AR42J细胞分化至关重要。

To elucidate the molecular mechanism for differentiation of pancreatic β cells, we studied the changes in the expression of various transcription factors during differentiation of pancreatic AR42J cells to insulin-producing cells. These cells are amylase-secreting tumor cells and differentiate to insulin-secreting cells in response to activin A and hepatocyte growth factor (HGF). We studied the changes in the expression of variou transcription factors expressed in pancreatic islets by RT-PCR.Among various transcription factors studied, expression of Pax4 and neurogenin3 (ngn3) was markedly increased during the differentiation. Thus, the expression of Pax4 and ngn3 was not detectable in naive AR42J cells but induced after the treatment with activin A and HGF.It was activin A but not HGF that induced the expression of Pax4 and ngn3. To assess the functional significance of these transcription factors, we introduced cDNA for Pax4 or ngn3 in naive AR42J cells and examined the changes in morphology and expression of various differentiation markers. We also studied the effect of introducing antisense cDNA.When Pax 4 was introduced into naive AR42J cells, nothing happened. Furthermore, introduction of antisense cDNA did not affect the ddiferentiation induced by activin A and HGF.In contrast, transfection of Pax4 to naive AR42J cells induced morphological changes. Thus, cells extended neurite-like processes, Also, expression of pancreatic polypeptide was induced by transfection of ngn3. Additionally, reduction of ngn3 expression resulted in the inhibition of differentation of AR42J into insulin-secreting cells. We conclude that induction of ngn3 expression is critical in differentiation of AR42J cells by activin A.