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

Abstract

IntroductionHigh 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.MethodsPublished 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.ResultsWe 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.ConclusionsThese results establish PRNP as a novel ER stress-regulated gene that could increase survival in breast cancers.

Cellular prion protein controls stem cell-like properties of human glioblastoma tumor-initiating cells

“…Interestingly, PrP C displays a significant plasticity in human tumors and thus it represents a potential therapeutic target. For example, PrP C overexpression is induced in breast cancer cells by endoplasmic reticulum stress, conferring to tumor cells increased resistance to cytotoxic stimuli [85]. All in all, the induction of GBM CSC differentiation by PrP C down-regulation, or its functional inhibition, could represent a relevant novel approach in this field.…”

Autocrine and paracrine STIP1 signaling promote osteolytic bone metastasis in renal cell carcinoma

“…Although a direct binding assay was not performed to confirm the interaction between STIP1 and PrPc in the osteoclast precursor cells, the results from several functional studies were supportive to our conclusion, i.e., 1) a dose-dependent induction of PrPc expression by hrSTIP1; 2) the anti-PrPc antibody impeded the hrSTIP1-induced osteoclast differentiation; and 3) the combination of anti-STIP1 and anti-PrPc antibodies inhibited the CTSK expression significantly. In vivo , several cancer-associated conditions, including hypoxia and oxidative or endoplasmic reticulum stresses can activate PrPc transcription [37, 38], which also been shown to increase osteoclast activity [39, 40]. Thus, the STIP1-PrPc signaling in osteolysis might be augmented and an in vivo verification in the bone metastasis RCC animal model or patient specimens would be needed.…”

“…The initial release of osteolytic mediators by tumor cells leads to bone degradation, release of growth factors from degraded bone, increased tumor cell proliferation, and finally further release of osteolytic mediators, which forms a tumor-enhancing feedback cycle. It has been noted that the physical properties of bone matrix, including low oxygen content, acidic pH, plus growth factors, create an environment favorable for tumor growth [42], and also activate the PrPc transcription to transduce the STIP1 stimulation for osteoclast differentiation [37, 38]. Thus, the tumor STIP1-ALK2 signaling and osteoclast STIP1-PrPc signaling aggravate the vicious cycle in osteolytic bone metastasis from RCC.…”

Physiological Functions of the Cellular Prion Protein

“…These regulatory sequences presumably enable dynamic control of PrP C expression in response to various stimuli, for example, treatment of cultured cells with nerve growth factor, insulin or insulin-like growth factor induces PrP C expression (Kuwahara et al, 2000; Zawlik et al, 2006; Liu et al, 2013). Additionally, endoplasmic reticulum (ER) stress, oxidative stress and genotoxic stress are all reported to cause upregulation of PrP C expression (Dery et al, 2013; Cichon and Brown, 2014; Bravard et al, 2015). …”