Figure 5.

Changes in ER Ca²⁺ alters nSREBP activity. (A) ER luminal Ca²⁺ (thapsigargin releasable pool of Ca²⁺) in wild-type cells, Calr ^−/− cells and Calr ^−/− cells expressing full length recombinant calreticulin (Calr), the calreticulin Ca²⁺ binding domain or the calreticulin chaperone domain. **Indicates statistically significant differences: wild-type vs. Calr ^−/− cells, p-value < 0.05 (ANOVA). *Indicates statistically significant differences: Calr ^−/− vs. Calr ^−/− cells expressing rCalr, p-value < 0.05 (ANOVA); Calr ^−/− vs. Calr ^−/− cells expressing calreticulin Ca²⁺ binding domain, p-value < 0.05 (ANOVA). Representative of 3 biological replicates. NS, not significant. (B) nSREBP activity in wild-type cells, Calr ^−/− cells and Calr ^−/− cells expressing full length recombinant calreticulin (rCalr), the calreticulin chaperone domain or the calreticulin Ca²⁺ binding domain. *Indicates statistically significant differences: wild-type vs. Calr ^−/− cells, p-value < 0.05 (ANOVA); Calr ^−/− vs. Calr ^−/− cells expressing full length recombinant calreticulin (rCalr), p-value < 0.05 (ANOVA); wild-type vs. Calr ^−/− expressing calreticulin Ca²⁺ binding domain, p-value < 0.05 (ANOVA). Representative of 3 biological replicates. NS, not significant. (C) nSREBP activity in wild-type cells exposed to decreasing extracellular Ca²⁺ concentration to deplete ER Ca²⁺ stores. Ca²⁺ replete represents 2.17 mM extracellular Ca²⁺ concentration. *Indicates statistically significant differences, wild-type vs. Calr ^−/− cells in control conditions, p-value < 0.05 (ANOVA); wild-type cells in control vs. 150 µM Ca²⁺, p-value < 0.05 (ANOVA). Representative of 7 biological replicates. NS, not significant. See “Experimental Procedures” for additional details.