Mouse Lymphoma Cells Destined to Undergo Apoptosis in Response to Thapsigargin Treatment Fail to Generate a Calcium-mediated grp78/grp94 Stress Response

Thomas S Mccormick,Karen S Mccoll,Clark W Distelhorst

doi:10.1074/jbc.272.9.6087

Thomas S Mccormick, Karen S Mccoll + Show 1 more

Open Access

https://doi.org/10.1074/jbc.272.9.6087

Copy DOI

Abstract

grp78/grp94 induction is critical for maintaining the viability of epithelial cells and fibroblasts following treatment with thapsigargin (TG), an inhibitor of Ca2+ uptake into the endoplasmic reticulum. In contrast to these cell types, WEHI7.2 mouse lymphoma cells undergo apoptosis when treated with TG, prompting us to examine the grp78/grp94 stress response in WEHI7.2 cells. TG treatment failed to induce grp78/grp94 transcription in WEHI7.2 cells, measured by Northern hybridization and nuclear run-on assays, even if the cells were protected from apoptosis by overexpressing bcl-2. However, grp78/grp94 transcription was induced by the glycosylation inhibitor tunicamycin, suggesting that there are at least two grp78/grp94 signaling pathways, one in response to TG-induced endoplasmic reticulum Ca2+ pool depletion, which is inoperable in WEHI7.2 cells, and one in response to glycosylation inhibition, which is operable in WEHI7.2 cells. Studies of additional lymphoid lines, as well as several nonlymphoid lines, suggested a correlation between grp78/grp94 induction and resistance to apoptosis following TG treatment. In conclusion, the vulnerability of TG-treated WEHI7.2 cells to apoptosis may be due to failure to signal a grp78/grp94 stress response.

Highlights

The endoplasmic reticulum (ER)1 is the major intracellular reservoir of Ca2ϩ in nonmuscle cells [1]
Grp78/grp94 transcription was induced by the glycosylation inhibitor tunicamycin, suggesting that there are at least two grp78/grp94 signaling pathways, one in response to TG-induced endoplasmic reticulum Ca2؉ pool depletion, which is inoperable in WEHI7.2 cells, and one in response to glycosylation inhibition, which is operable in WEHI7.2 cells
In contrast to epithelial cells and fibroblasts, we have found that WEHI7.2 mouse lymphoma cells undergo apoptosis in response to TG-induced ER Ca2ϩ loss, unless protected by overexpression of the anti-apoptotic oncogene bcl-2 [30]

Summary

Introduction

The endoplasmic reticulum (ER)1 is the major intracellular reservoir of Ca2ϩ in nonmuscle cells [1]. ER Ca2ϩ pool depletion, induced by either A23187 or TG, signals an increase in grp78/grp94 transcription, producing a 5–20-fold elevation of grp78/grp94 mRNA levels [25]. To determine whether or not the failure of TG treatment to increase grp78 mRNA levels in WEHI7.2 cells was secondary to early changes accompanying cell death, we examined the grp78 stress response in W.Hb12 cells, which are protected from apoptosis by bcl-2.

Results

Conclusion