Functional defect of truncated hepatocyte nuclear factor-1α (G554fsX556) associated with maturity-onset diabetes of the young

Defective functions of HNF1A variants on BCL2L1 transactivation and beta-cell growth

Maturity-onset diabetes of the young type 3 (MODY3) is caused by mutations in a gene encoding transcription factor hepatocyte nuclear factor 1-alpha (HNF1A). Although the roles of HNF1A in regulation of hepatic and pancreatic genes to maintain glucose homeostasis were investigated, the functions of HNF1A are not completely elucidated. To better understand the functions of HNF1A, we characterized mutations of HNF1A in Thai MODY3 patients and studied the functions of wild-type HNF1A and variant proteins. We demonstrate for the first time that HNF1A upregulates transactivation of an anti-apoptotic gene BCL2 Like 1 (BCL2L1) and that all the identified HNF1A variants including p.D80V, p.R203C, p.P475L, and p.G554fsX556, reduce this ability. The four HNF1A variants impair HNF1A function in promoting INS-1 cell transition from G1 to S phase of cell cycle, which thereby retard cell growth. This finding indicates the role of HNF1A in beta-cell viability by upregulation of anti-apoptotic gene expression and also reaffirms its role in beta-cell growth through cell cycle control.

Roles of HNF1α and HNF4α in pancreatic β-cells: lessons from a monogenic form of diabetes (MODY)

Mutations in the genes encoding hepatocyte nuclear factor (HNF)1α and HNF4α cause a monogenic form of diabetes mellitus known as maturity-onset diabetes of the young (MODY). The primary cause of MODY is an impairment of glucose-stimulated insulin secretion by pancreatic β-cells, indicating the important roles of HNF1α and HNF4α in β-cells. Large-scale genetic studies have clarified that the common variants of HNF1α and HNF4α genes are also associated with type 2 diabetes, suggesting that they are involved in the pathogenesis of both diseases. Recent experimental studies revealed that HNF1α controls both β-cell function and growth by regulating target genes such as glucose transporter 2, pyruvate kinase, collectrin, hepatocyte growth factor activator, and HNF4α. In contrast, HNF4α mainly regulates the function of β-cells. Although direct target genes of HNF4α in β-cells are largely unknown, we recently identified Anks4b as a novel target of HNF4α that regulates β-cell susceptibility to endoplasmic reticulum stress. Studies of MODY have led to a better understanding of the molecular mechanism of glucose-stimulated insulin secretion by pancreatic β-cells.