Fig. 5.

GTP-locked Arf1(Q71L) is sufficient to drive KDELR1 dispersion and ER chaperones to the cell surface. (A) The indicated cancer cell lines were transfected with the Arf1-HA(Q71L) mutant expression vector and were treated with Tg as indicated. The indicated proteins from the whole-cell lysate and the cell surface were analyzed by Western blot with GAPDH and EphB4 serving as loading controls. (B) As in A, except HeLa cells were transfected with the indicated expression vectors, and conditioned medium was collected and assayed for secreted F-GRP78. The band intensities of csF-GRP78 were quantified and graphed. (C) HeLa cells were transfected with the KDELR1-FLAG (KDELR1-F) expression vector alone or in combination with expression vectors for SRC531-His, HA-ASAP1, or Arf1-HA(Q71L), as indicated, and were subjected to immunofluorescent staining for the indicated proteins. GM130 served as the marker for cis-Golgi. (Scale bar, 5 µm.) (D) Summary of the ER stress-signaling cascade leading to the escape of ER luminal chaperones to the cell surface. *P < 0.05.