Accelerated degradation of HIF-1α in Psen1-/- fibroblasts. Psen1+/+ and Psen1-/- fibroblasts were treated with cycloheximide. In panel A, a representative experiment is shown with cells treated for the indicated times. Due to the difference in basal HIF-1α levels between Psen1 +/+ and Psen1-/- cells, total protein loaded (15 μg for Psen1+/+ and 30 μg for Psen1 -/-) and blot exposure times were adjusted so that the signal at time 0' would be of similar intensity in Psen1+/+ and Psen1-/- cells to facilitate comparison. In panel B, the % HIF-1α remaining at each time point normalized to β-tubulin is shown. Data is derived from the average of three independently performed experiments.