Endoplasmic reticulum stress induces PRNP prion protein gene expression in breast cancer.

Abstract

INTRODUCTION:

High prion protein (PrP) levels are associated with breast, colon and gastric cancer resistance to treatment and with a poor prognosis for the patients. However, little is known about the underlying molecular mechanism(s) regulating human PrP gene (PRNP) expression in cancers. Because endoplasmic reticulum (ER) stress is associated with solid tumors, we investigated a possible regulation of PRNP gene expression by ER stress.

METHODS:

Published microarray databases of breast cancer tissues and breast carcinoma cell lines were analyzed for PrP mRNA and ER stress marker immunoglobulin heavy chain binding protein (BiP) levels. Breast cancer tissue microarrays (TMA) were immunostained for BiP and PrP. Breast carcinoma MCF-7, MDA-MB-231, HS578T and HCC1500 cells were treated with three different ER stressors - Brefeldin A, Tunicamycin, Thapsigargin - and levels of PrP mRNA or protein assessed by RT-PCR and Western blot analyses. A human PRNP promoter-luciferase reporter was used to assess transcriptional activation by ER stressors. Site-directed mutagenesis identified the ER stress response elements (ERSE). Chromatin immunoprecipitation (ChIP) analyses were done to identify the ER stress-mediated transcriptional regulators. The role of cleaved activating transcription factor 6α (ΔATF6α) and spliced X-box protein-1 (sXBP1) in PRNP gene expression was assessed with over-expression or silencing techniques. The role of PrP protection against ER stress was assessed with PrP siRNA and by using Prnp null cell lines.

RESULTS:

We find that mRNA levels of BiP correlated with PrP transcript levels in breast cancer tissues and breast carcinoma cell lines. PrP mRNA levels were enriched in the basal subtype and were associated with poor prognosis in breast cancer patients. Higher PrP and BiP levels correlated with increasing tumor grade in TMA. ER stress was a positive regulator of PRNP gene transcription in MCF-7 cells and luciferase reporter assays identified one ER stress response element (ERSE) conserved among primates and rodents and three primate-specific ERSEs that regulated PRNP gene expression. Among the various transactivators of the ER stress-regulated unfolded protein response (UPR), ATF6α and XBP1 transactivated PRNP gene expression, but the ability of these varied in different cell types. Functionally, PrP delayed ER stress-induced cell death.

CONCLUSIONS:

These results establish PRNP as a novel ER stress-regulated gene that could increase survival in breast cancers.

• Authors: Marc-André Déry, Julie Jodoin, Josie Ursini-Siegel, Olga Aleynikova, Cristiano Ferrario, Saima Hassan, Mark Basik, Andréa C LeBlanc
• Journal: Breast cancer research : BCR (Breast Cancer Res) Vol. 15 Issue 2 Pg. R22 (Mar 12 2013) ISSN: 1465-542X [Electronic] England
• PMID: 23497519 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• ATF6 protein, human
• Activating Transcription Factor 6
• DNA-Binding Proteins
• PRNP protein, human
• Prion Proteins
• Prions
• RNA, Messenger
• Regulatory Factor X Transcription Factors
• Transcription Factors
• X-Box Binding Protein 1
• XBP1 protein, human
• Luciferases

Topics

• Activating Transcription Factor 6 (genetics, metabolism)
• Apoptosis
• Blotting, Western
• Breast Neoplasms (pathology)
• DNA-Binding Proteins (genetics, metabolism)
• Endoplasmic Reticulum Stress
• Female
• Flow Cytometry
• Gene Expression Regulation, Neoplastic
• Humans
• Immunoenzyme Techniques
• Luciferases (metabolism)
• Prion Proteins
• Prions (genetics, metabolism)
• RNA, Messenger (genetics)
• Real-Time Polymerase Chain Reaction
• Regulatory Factor X Transcription Factors
• Reverse Transcriptase Polymerase Chain Reaction
• Tissue Array Analysis
• Transcription Factors (genetics, metabolism)
• Tumor Cells, Cultured
• X-Box Binding Protein 1