Localization of hepatocyte nuclear factor-4α in the nucleolus and nucleus is regulated by its C-terminus

Identification of Variants Responsible for Monogenic Forms of Diabetes in Brazil

Monogenic forms of diabetes mellitus may affect a significant number of patients of this disease, and it is an important molecular cause to be investigated. However, studies of the genetic causes of monogenic diabetes, especially in populations with mixed ethnic backgrounds, such as the one in Brazil, are scarce. The aim of this study was to screen several genes associated with monogenic diabetes in fifty-seven Brazilian patients with recurrence of the disease in their families and thirty-four relatives. Inclusion criteria were: Age of onset ≤ 40 years old, BMI < 30 kg/m², at least two affected generations and negative anti-GAD and anti-IA2 antibodies. MODY genes HNF4A, GCK, HNF1A, HNF1B, NEUROD1, KLF11, PAX4, INS, KCNJ11, and MT-TL1 were sequenced by Sanger sequencing. We identified a total of 20 patients with variants, 13 GCK-MODY, four HNF1A-MODY, and one variant in each of the following genes, HNF4A, HNF1B and MT-TL1. Segregation analysis was performed in 13 families. Four variants were novel, two in GCK (p.(Met115Val) [c.343A>G] and p.(Asp365GlufsTer95) [c.1094_1095insGCGA]) and two in HNF1A (p.(Tyr163Ter) [c.489C>G] and p.(Val380CysfsTer39) [c.1136_1137insC]). Here we highlight the importance of screening for monogenic diabetes in admixed populations.

Novel mechanisms of regulation of the expression and transcriptional activity of hepatocyte nuclear factor 4α

Hepatocyte nuclear factor 4α (HNF4α) is a master regulator of development and function of digestive tissues. The HNF4A gene uses two separate promoters P1 and P2, with P1 products predominant in adult liver, whereas P2 products prevalent in fetal liver, pancreas, and liver/colon cancer. To date, the mechanisms for the regulation of HNF4A and the dynamic switch of P1-HNF4α and P2-HNF4α during ontogenesis and carcinogenesis are still obscure. Our study validated the previously reported self-stimulation of P1-HNF4α but invalidated the reported synergism between HNF4α and HNF1α. HNF4A-AS1, a long noncoding RNA, is localized between the P2 and P1 promoters of HNF4A. We identified critical roles of P1-HNF4α in regulating the expression of HNF4A-AS1 and its mouse ortholog Hnf4a-os. Paired box 6 (PAX6), a master regulator of pancreas development overexpressed in colon cancer, cooperated with HNF1α to induce P2-HNF4α but antagonized HNF4α in HNF4A-AS1 expression. Thus, PAX6 may be important in determining ontogenic and carcinogenic changes of P2-HNF4α and HNF4A-AS1 in the pancreas and intestine. We also interrogated transactivation activities on multiple gene targets by multiple known and novel HNF4α mutants identified in patients with maturity onset diabetes of the young 1 (MODY1) and liver cancer. Particularly, HNF4α-D78A and HNF4α-G79S, two mutants found in liver cancer with mutations in DNA-binding domain, displayed highly gene-specific transactivation activities. Interestingly, HNF4α-Q277X, a MODY1 truncation mutant, antagonized the transactivation activities of HNF1α and farnesoid X receptor, key regulators of insulin secretion. Taken together, our study provides novel mechanistic insights regarding the transcriptional regulation and transactivation activity of HNF4α in digestive tissues.

Crosstalk of HNF4α with extracellular and intracellular signaling pathways in the regulation of hepatic metabolism of drugs and lipids

The liver is essential for survival due to its critical role in the regulation of metabolic homeostasis. Metabolism of xenobiotics, such as environmental chemicals and drugs by the liver protects us from toxic effects of these xenobiotics, whereas metabolism of cholesterol, bile acids (BAs), lipids, and glucose provide key building blocks and nutrients to promote the growth or maintain the survival of the organism. As a well-established master regulator of liver development and function, hepatocyte nuclear factor 4 alpha (HNF4α) plays a critical role in regulating a large number of key genes essential for the metabolism of xenobiotics, metabolic wastes, and nutrients. The expression and activity of HNF4α is regulated by diverse hormonal and signaling pathways such as growth hormone, glucocorticoids, thyroid hormone, insulin, transforming growth factor-β, estrogen, and cytokines. HNF4α appears to play a central role in orchestrating the transduction of extracellular hormonal signaling and intracellular stress/nutritional signaling onto transcriptional changes in the liver. There have been a few reviews on the regulation of drug metabolism, lipid metabolism, cell proliferation, and inflammation by HNF4α. However, the knowledge on how the expression and transcriptional activity of HNF4α is modulated remains scattered. Herein I provide comprehensive review on the regulation of expression and transcriptional activity of HNF4α, and how HNF4α crosstalks with diverse extracellular and intracellular signaling pathways to regulate genes essential in liver pathophysiology.