Inositol-requiring enzyme 1 alpha (IRE1α)-dependent processing and endoplasmic reticulum (ER) association of XBP1u transcripts during stress. (A) Reporter construct design: Unspliceable (dark blue) and spliced (light blue) reporter transcripts are identical to XBP1 wild-type (WT; red) except for point mutations in the intron (unsplicable) or complete lack of it (spliced). (B) Representative live-cell images of XBP1 splice site mutant reporters (blue) in HeLa cells expressing NLS-stdMCP-stdHalo and Sec61b-SNAP as ER marker (gray). (C) Boxplot showing quantification of ER association from correlated diffusion and ER colocalization analysis for XBP1 WT (red), unspliceable (dark blue), and spliced (light blue) reporter transcripts. Different opacities represent experimental conditions: no treatment (Ctrl), ER stress induced with 3–4 hours of 5 µg/ml tunicamycin (TM), ER stress induced with 3–4 hours of 5 µg/ml TM under IRE1α inhibition with 4µ8C (TM + 4µ8C). Statistical test: unpaired t-test, p-values: (p≥0.05)=ns; (p<0.0001)=****. (D) Representative live-cell images of XBP1 WT reporter constructs (red) in HeLa cells expressing NLS-stdMCP-stdHalo and Sec61b-SNAP as ER marker (gray) under ER stress (5 µg/ml TM) as well as ER stress with IRE1α inhibition (5 µg/ml TM and 50 µM 4µ8C). All scale bars = 5 µm. Credit: eLife (2022). DOI: 10.7554/eLife.75580
FMI researchers developed an imaging approach that allowed them to visualize individual molecules involved in the cell's response to stress.
When a cell is exposed to stressors such as toxins, it switches on pathways aimed at repairing damage.
One of these pathways is called the "unfolded protein response," which senses unfolded or misfolded proteins in the endoplasmic reticulum—a cell organelle designated for folding proteins destined to other organelles or to be secreted by the cell.
The unfolded protein response relies on the enzyme IRE1a, which binds transcripts of the gene XBP1 and modifies them on the surface of the endoplasmic reticulum. Once modified, XBP1 transcripts are translated into proteins that travel to the nucleus and turn on genes involved in assisting protein folding and quality control.
Scientists led by Franka Voigt, a researcher in the Chao group at the FMI, developed an imaging approach that allowed them to take snapshots of individual XBP1 transcripts on the surface of the endoplasmic reticulum. This approach allowed the researchers to investigate how XBP1 transcripts are recruited and modified by IRE1a.
The findings, published in eLife, will help to better understand how cells respond to stress.
Credit: Friedrich Miescher Institute for Biomedical Research
More information:
Silvia Gómez-Puerta et al, Live imaging of the co-translational recruitment of XBP1 mRNA to the ER and its processing by diffuse, non-polarized IRE1α, eLife (2022). DOI: 10.7554/eLife.75580
Citation:
Video: Watching how cells deal with stress (2022, June 29)
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