FIG. 1.

Hypoxia and HP activate the UPR. HP activates an hsp-4 promoter-GFP fusion reporter (A and B) and the endogenous hsp-4 gene (C). (B) After HP, the level of GFP increased significantly after a 4-h recovery (*, P < 0.001, two-tailed t test), and it returned to the control level after 16 more hours. (C) The level of hsp-4 mRNA was measured by qRT-PCR and was significantly elevated after a 2- and 4-h recovery from 4 h of hypoxia (P < 0.05, two-tailed t test), while hypoxia alone (up to 8 h) or a shorter HP incubation had no effect. (D) Hypoxia induced eIF2α phosphorylation. The level of phosphorylated eIF2α increased after 1 h of hypoxia and remained high under hypoxic conditions but rapidly returned to baseline during normoxic recovery. Relative band intensities normalized to no hypoxia are given. β-Actin levels decreased relative to total protein during the hypoxic incubation, thus the p-eIF2α/β-actin ratio increased greatly. The 0-h hypoxia/0 recovery and the 4-h hypoxia/0 recovery conditions were repeated for a total of four trials, and the relative p-eIF2α induction (1.96 ± 0.29) was statistically significant (P < 0.01, paired t test).