Research Article

4-Phenylbutyric Acid Reduces Endoplasmic Reticulum Stress in Chondrocytes That Is Caused by Loss of the Protein Disulfide Isomerase ERp57

Figure 2

Thapsigargin is a potent inductor of ER stress in C28/I2 cells. (a) RT-PCR analysis of C28/I2 micromass cultures stimulated with rising concentrations of the ER stress inductor Thapsigargin (Tg). mRNA expression levels of BiP, Chop, XBP1 spliced (XBP1s), ATF6, ATF4, and ERp57 relative to GAPDH are shown with mRNA levels of unstimulated cells set as 1. The PCR results demonstrate a dose-dependent increase of both ER stress markers with increasing Tg concentrations. , , , and . (b) Immunoblot analysis of C28/I2 micromass cultures stimulated with 10 μM of the ER stress inductor Thapsigargin (Tg). Relative to GAPDH as internal control, all investigated marker proteins BiP, Chop, IRE1, XBP1s, ATF6, and ERp57 are significantly increased in C28/I2 cells in the presence of 10 μM Tg compared to nonstimulated control cells set as 1. , , , and . (c) Transmission electron microscopic analysis of C28/I2 control cells cultured in micromasses in the presence or absence of 10 μM Tg. C28/I2 cells w/o Tg (control) reveal regular stacks of rough ER (>). Thapsigargin stimulation of C28/I2 cells leads to distended ER structures () suggesting an accumulation of un- or misfolded proteins in the ER. All .
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