FoxA2 and RNA Pol II mediate human islet amyloid polypeptide turnover in ER-stressed pancreatic β-cells

Biochem J. 2021 Mar 26;478(6):1261-1282. doi: 10.1042/BCJ20200984.

Abstract

Here, we investigated transcriptional and trafficking mechanisms of human islet amyloid polypeptide (hIAPP) in normal and stressed β-cells. In high glucose-challenged human islets and rat insulinoma cells overexpressing hIAPP, cell fractionation studies revealed increased accumulation of hIAPP. Unexpectedly, a significant fraction (up to 22%) of hIAPP was found in the nuclear soluble and chromatin-enriched fractions of cultured human islet and rat insulinoma cells. The nucleolar accumulation of monomeric forms of hIAPP did not have any adverse effect on the proliferation of β-cells nor did it affect nucleolar organization or function. However, intact nucleolar organization and function were essential for hIAPP expression under normal and ER-stress conditions as RNA polymerase II inhibitor, α-amanitin, reduced hIAPP protein expression evoked by high glucose and thapsigargin. Promoter activity studies revealed the essential role of transcription factor FoxA2 in hIAPP promoter activation in ER-stressed β-cells. Transcriptome and secretory studies demonstrate that the biosynthetic and secretory capacity of islet β-cells was preserved during ER stress. Thus, the main reason for increased intracellular hIAPP accumulation is its enhanced biosynthesis under these adverse conditions.

Keywords: ER stress; FoxA2; islet amyloid polypeptide; nucleolus; trafficking; transcription.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Proliferation
  • Cells, Cultured
  • Endoplasmic Reticulum Stress*
  • Gene Expression Regulation*
  • Glucose / pharmacology*
  • Hepatocyte Nuclear Factor 3-beta / genetics
  • Hepatocyte Nuclear Factor 3-beta / metabolism*
  • Humans
  • Insulin-Secreting Cells / drug effects
  • Insulin-Secreting Cells / metabolism*
  • Insulin-Secreting Cells / pathology
  • Islet Amyloid Polypeptide / genetics
  • Islet Amyloid Polypeptide / metabolism*
  • RNA Polymerase II / genetics
  • RNA Polymerase II / metabolism*
  • Rats
  • Sweetening Agents

Substances

  • FOXA2 protein, human
  • Islet Amyloid Polypeptide
  • Sweetening Agents
  • Hepatocyte Nuclear Factor 3-beta
  • RNA Polymerase II
  • Glucose