Transcriptional Autoregulation Controls Pancreatic Ptf1a Expression during Development and Adulthood

Abstract

The basic helix-loop-helix (bHLH) transcription factor PTF1a is critical to the development of the embryonic pancreas. It is required early for the formation of the undifferentiated tubular epithelium of the nascent pancreatic rudiment and then becomes restricted to the differentiating acinar cells, where it directs the transcriptional activation of the secretory digestive enzyme genes. Here we report that the complex temporal and spatial expression of Ptf1a is controlled by at least three separable gene-flanking regions. A 14.8-kb control domain immediately downstream of the last Ptf1a exon is highly conserved among mammals and directs expression in the dorsal part of the spinal cord but has very little activity in the embryonic or neonatal pancreas. A 13.4-kb proximal promoter domain initiates limited expression in cells that begin the acinar differentiation program. The activity of the proximal promoter domain is complemented by an adjacent 2.3-kb autoregulatory enhancer that is able to activate a heterologous minimal promoter with high-level penetrance in the pancreases of transgenic mice. During embryonic development, the enhancer initiates expression in the early precursor epithelium and then superinduces expression in acinar cells at the onset of their development. The enhancer contains two evolutionarily conserved binding sites for the active form of PTF1a, a trimeric complex composed of PTF1a, one of the common bHLH E proteins, and either RBPJ or RBPJL. The two sites are essential for acinar cell-specific transcription in transfected cell lines and mice. In mature acinar cells, the enhancer and PTF1a establish an autoregulatory loop that reinforces and maintains Ptf1a expression. Indeed, the trimeric PTF1 complex forms dual autoregulatory loops with the Ptf1a and Rbpjl genes that may maintain the stable phenotype of pancreatic acinar cells.

Neurog2 is a direct downstream target of the Ptf1a-Rbpj transcription complex in dorsal spinal cord

“…The PTF1 target site consensus is CANNTG(N 4/5 )WTTCCCA (Beres et al, 2006). In the developing pancreas before the appearance of Rbpjl, the PTF1-J form of PTF1 is active on targets that include Rbpjl and Ptf1a itself (Masui et al, 2007;Masui et al, 2008). Examination of the PTF1-J target sites, including the neural PTF1-J target identified in Neurog2, shows that there is no obvious distinction in consensus site for PTF1-J versus PTF1-L.…”

Id3 modulates cellular localization of bHLH Ptf1‐p48 protein

“…Ptf1-p48 controls its own expression by transcriptional autoregulation notably by the presence of PTF1 complex binding site in the enhancer of the Ptf1-p48 gene. 45 The Ptf1-p48 cytoplasmic mislocalization may set up a feedback response that further decreases its expression. In addition, we have shown that in parallel to cytoplasmic mislocalization and loss of Ptf1-p48, Id3 is overexpressed in acino-ductal metaplastic structures and greatly increased in PanIN and IPMN lesions.…”

The E3 Ubiquitin Ligase Thyroid Hormone Receptor-interacting Protein 12 Targets Pancreas Transcription Factor 1a for Proteasomal Degradation

“…PTF1a protein level is also decreased in acute and chronic pancreatitis (23,24). Recently, gene-associated sequences and transcriptional mechanisms regulating spatial and temporal expression of PTF1a were identified (25,26). Functional modulation of PTF1a transcriptional activity by interaction with HES (Hairy/Enhancer of Split) family of transcriptional repressors or recruitment of the transcriptional co-activators p/CAF (p300/cAMP-response element-binding protein-binding protein-associated factor) was reported (27,28).…”