Tissue-specific transcription factor HNF4 alpha inhibits cell proliferation and induces apoptosis in the pancreatic INS-1 beta-cell line

Hepatocyte nuclear factor 4 alpha (HNF4 alpha) is a tissue-specific transcription factor expressed in many cell types, including pancreatic P-cells. Mutations in the HNF4a gene in humans give rise to maturity-onset diabetes of the young (MODY1) characterized by defective insulin secretion by p-cells. To elucidate the mechanism underlying this disease, we introduced the splice form HNF4 alpha 2 or HNF4 alpha 8 into the rat P-cell line INS-1. Upon tetracycline-induced expression, both HNF4 alpha. isoforms caused distinct changes in cell morphology and a massive loss of cell numbers that was correlated with reduced proliferation and induced apoptosis. This differential activity was reflected in oligonucleotide microarray analysis that identified more genes affected by HNF4 alpha 2 compared to HNF4 alpha 8, and suggests that both isoforms regulate largely the same set of genes, with HNF4 alpha 2 being a stronger transactivator. We verified the induction of selected transcripts by real-time RT-PCR, including KAl1 and AIF, both known to have apoptotic potential. By establishing cell lines with inducible expression of these target genes, we deduce that both factors are insufficient to induce apoptosis. We propose that the anti-proliferative and apoptotic properties of HNF4a may be an essential feature impaired in MODY1 and possibly also in type 2 diabetes.