Association of α-Syn oligomer accumulation with ER stress response. Differentiated 3D5 cells with (α-Syn +) or without (α-Syn -) induced α-Syn expression were treated with 10 mM SB (10 mM), 40 μM salubrinal (Sal, an inhibitor of EIF2α dephosphorylation), 10 μg/ml tunicamycin (TM, an ER stress inducer), SB plus Sal (SBSal) or TM plus Sal (TMSal) for 36 hs. Cells without any drug treatment served as controls. (A) Cell viability. Significant differences were detected between drug treated and non-treated cultures [*P < 0.05 (e.g. SB/α-Syn + vs. Con/α-Syn +, SB/α-Syn - vs. Con/α-Syn -)], between drug treated α-Syn + and α-Syn- cultures [#P < 0.05 (e.g. SB/α-Syn + vs. SB/α-Syn -)] or between SB (or TM) and SB (or TM) plus Sal treated cultures [#P < 0.05 (e.g. SB/α-Syn + vs. SBSal/α-Syn +, TM/α-Syn + vs. TMSal/α-Syn +)]. (B) Western blotting. Samples from cultures with different treatments were probed with antibodies to α-Syn, six markers of ER stress, active caspase 3 and GAPDH. Exposure of α-Syn+ cultures to SB or TM promoted accumulation of α-Syn oligomers and expression of most ER stress markers. The presence of Sal, however, inhibited this effect (i.e. SB versus SBSal, or TM versus TMSal). Similar drug exposure affected the ER stress response less in α-Syn- cultures than in α-Syn+ cultures.