FIG. 4.
Thapsigargin retards early-late and late protein accumulation. (A) HFF cells were infected (MOI = 2.5) for 48, 72, and 96 h under normal conditions, and a parallel set of infected cultures was treated with thapsigargin for the 24-h periods between 48 and 72 hpi (48-72 Th.) and between 72 and 96 hpi (72-96 Th.). Total protein was extracted from the infected cells, and the steady-state levels of the MIEPs, the pp52 early protein, and the pp65 early-late protein were determined by Western analysis. To assure that thapsigargin had induced the UPR, we measured the levels of the chaperone Bip, which is induced when the UPR is activated by thapsigargin (18, 21). (B) Using an identical approach but extending the infection time to 120 h, the accumulation level of the pp28 late protein was determined.