FIG. 4.

The DNA-damaging agent CPT does not induce ER stress in HNSCC cells. (A) UMSCC-23 or UMSCC-14A cells were treated with CPT (10 μM) or PS-341 for the indicated time periods. The phosphorylation of PERK was detected by Western blot analysis as described in the legend to Fig. 3A. (B) Cells were treated with PS-341 or CPT for the indicated time periods. The expression of ATF-4 and GADD-34 was examined by Western blot analysis as described in the legend to Fig. 3A.