Figure 5

Constitutive HSP90A expression sensitizes cells to apoptosis. (a) Protein extracts were prepared from control parental HC11 or heat shock protein 90 alpha (HSP90α)-HC11 (line 2) cells that were cultured as undifferentiated (U), competent (C) or differentiated (D) cells. (b, c) Differentiated parental HC11 and two different pools of HC11-HSP90α cells (lines 1 and/or 2) were induced to differentiate and then starved of lactogenic hormones and serum for the time indicated. Equal amounts of protein were resolved by SDS-PAGE (15%). An antibody was used to detect phosphorylated-histone 2A.X, and an antibody against GRB2 was used as a loading control. (d) Differentiated control HC11 and HC11-HSP90α cells (line 2) were starved or not apoptosis was assessed by the relative quantities of mono- and oligo-nucleosomes (apoptotic index). Each bar represents the average of three experiments with standard deviation. t-test, *p = 0.02 at 24 hours, **p = 0.00004 at 48 hours.