Repression of GADD153/CHOP by NF-kappaB: a possible cellular defense against endoplasmic reticulum stress-induced cell death

Our plain-English summary of Repression of GADD153/CHOP by NF-kappaB: a possible cellular defense against endoplasmic reticulum stress-induced cell death, by S. Nozaki, G.W. Sledge, H. Nakshatri (Oncogene, 2001).

The study

• Authors: S. Nozaki, G.W. Sledge, H. Nakshatri
• Journal: Oncogene
• Published: 2001;20(17):2178-85
• Cited by: 101 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Exposure of mammalian cells to ultraviolet light, nutrient deprived culture media, hypoxia, environmental toxicants such as methyl mercury, methyl methanesulfonate, crocodilite asbestos or the agents that disrupt the function of endoplasmic reticulum (ER) leads to activation of the pro-apoptotic transcription factor GADD153/CHOP. Paradoxically, several of these agents also induce the anti-apoptotic transcription factor NF-kappaB. In this report, we demonstrate that NF-kappaB inhibits GADD153 activation in breast cancer cells exposed to nutrient deprived media, tunicamycin (which blocks protein folding in ER) or calcium ionopore (which depletes calcium stores in ER). Basal and calcium ionopore-induced GADD153 expression was more pronounced in fibroblasts obtained from mouse embryos lacking in p65 subunit of NF-kappaB compared to fibroblasts from wild type littermate embryos. Moreover, p65-/- fibroblasts were killed more efficiently by calcium ionopore and tunicamycin but not hydrogen peroxide compared to wild type fibroblasts. We also show that parthenolide, a NF-kappaB inhibitor, sensitizes breast cancer cells to tunicamycin. Transient transfection assay revealed that the p65 subunit but not the p50 subunit of NF-kappaB represses GADD153 promoter activity. These results establish a correlation between repression of pro-apoptotic genes by NF-kappaB and increased cell survival during ER stress as well as identify a distinct NF-kappaB regulated cell survival pathway.

In plain English

This was a laboratory study of cells, not of people or of asbestos. The article mentions crocidolite asbestos (spelled "crocodilite") only as background in its abstract and introduction; it did not test asbestos. The authors asked whether NF-kappaB, a protein that helps cells survive, holds down GADD153, a protein that promotes cell death, when cells are under stress. They used human breast cancer cell lines (MDA-MB-231 and MDA-MB-435) in which NF-kappaB was blocked, and fibroblasts from mouse embryos lacking the p65 part of NF-kappaB. GADD153 levels were higher when NF-kappaB was blocked. Among serum-starved MDA-MB-231 cells, for example, expression was about 3.5-fold higher in NF-kappaB-blocked cells than in empty-vector cells. Mouse fibroblasts lacking p65 were at least four times more sensitive to A23187 than normal fibroblasts, and more sensitive to tunicamycin. In transfected breast cancer cells, p65, but not p50, lowered the activity of a GADD153 promoter reporter. The authors wrote that these results suggest NF-kappaB protects breast cancer cells against cell death caused by stress in the endoplasmic reticulum, the cell's protein-folding compartment.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory cell-culture experiments (gene expression, cell survival and reporter transfection assays); not a study of human subjects or of asbestos exposure
• Who was studied: Human breast cancer cell lines MDA-MB-231 and MDA-MB-435, engineered to block NF-kappaB (IkBaSR clones) or carrying an empty vector; fibroblast cell lines from mouse embryos lacking the p65 subunit of NF-kappaB and from normal littermate embryos
• Exposure: Laboratory stressors of the endoplasmic reticulum and cell growth: serum starvation, growth to confluency, tunicamycin, the calcium ionophore A23187, and hydrogen peroxide; the NF-kappaB inhibitor parthenolide. Asbestos ("crocodilite") is mentioned only as background, in the abstract and introduction, and was not tested.
• Main results:
  • In serum-starved MDA-MB-231 breast cancer cells, GADD153 expression was about 3.5-fold higher in cells with NF-kappaB blocked (IkBaSR cells) than in vector-only LxSN11 cells; after A23187 treatment it was 1.5-fold higher in IkBaSR cells than in LxSN11 cells
  • In MDA-MB-435 cells with NF-kappaB blocked, GADD153 expression was higher than in vector-only cells, about 15-fold under serum starvation and confluent growth
  • In MDA-MB-231 cells, after 5 hours of A23187, GADD153 expression was twofold higher in cells pretreated with the NF-kappaB inhibitor parthenolide than in ethanol-treated cells
  • In mouse fibroblasts lacking p65, A23187-induced GADD153 expression was two times higher (n=3) than in wild type fibroblasts
  • Fibroblasts lacking p65 were at least four times more sensitive to A23187 than wild type fibroblasts, were also more sensitive to tunicamycin (less pronounced), and were more resistant to hydrogen peroxide
  • In MDA-MB-231 cells, parthenolide combined with A23187 killed more cells than either drug alone (more than additive)
  • In MDA-MB-231 and MDA-MB-435 cells, GADD153 antisense oligonucleotides substantially lowered tunicamycin-induced cell death compared with control oligonucleotides
  • In transfected MDA-MB-231 cells, the p65 subunit caused a dose-dependent decrease in GADD153 promoter (reporter) activity, while the p50 subunit marginally increased it
• The authors' conclusion: The authors wrote that their results suggest NF-kappaB protects breast cancer cells against endoplasmic reticulum stress-induced cell death; separately, they concluded that GADD153 is required for that cell death
• Limitations the authors state:
  • Both breast cancer cell lines carried mutated p53, so the authors did not know whether NF-kappaB represses GADD153 only in cells lacking normal p53
  • The mechanism by which p65 represses GADD153 was not known, and the authors could not rule out that the inhibition is post-transcriptional

Topics

Medical terms in this study, explained in our Lexicon: Hypoxia, Fibroblast.

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