FIGURE 6:

Glycogen phosphorylase inhibitors block ER stress–induced hexose-P mobilization and free glycan increases. (A) Scheme linking glycogenolysis and extracellular mannose to hexose-Ps and GDP-mannose. Three GP inhibitors are indicated. Determinations of (B) hexose-1-Ps, (C) hexose-6-Ps, and (D) free glycans. Where indicated, PERK^−/− MEFs were either left unstressed (white bars) or stressed with 2 mM DTT (black) or 150 nM TG (gray) for 1 h prior to saccharide harvest, in the absence or presence of 50–100 μM CP-91149, 5 mM caffeine, or 20 μM DAB (each for 2 h prior to saccharide harvest). Each panel includes one representative FACE gel (upper) and averaged data from four independent FACE experiments (lower), measuring total pools of hexose-Ps or the G₄–G₇ equivalent pool of free glycans. •, p < 0.001 for all inhibitor-free stressed samples compared with inhibitor-free unstressed controls. *, p < 0.001; #, p < 0.005; ∇, p < 0.01; +, p < 0.08 for inhibitor-treated stressed samples compared with inhibitor-free stressed samples.