Received for publication June 7, 2006.
Revised December 10, 2006.
Accepted for publication December 12, 2006.

Up-regulation of 150-kDa Oxygen-regulated Protein (ORP150) By Celecoxib in Human Gastric Carcinoma Cells

Abstract

Induction of apoptosis by non-steroidal anti-inflammatory drugs (NSAIDs), such as celecoxib, is involved in their anti-tumor activity. An endoplasmic reticulum (ER) chaperone, 150-kDa oxygen-regulated protein (ORP150) is essential for the maintenance of cellular viability under hypoxia and is reported to be over-expressed in clinically isolated tumors. We here found that ORP150 was up-regulated by celecoxib in human gastric carcinoma cells. In conjunction with the suppression of tumor growth, orally administered celecoxib up-regulated ORP150 in xenograft tumors. Both the ATF4- and ATF6-pathways were activated by celecoxib, and suppression of ATF4 and ATF6 mRNA expression by small interfering RNA (siRNA) inhibited the celecoxib-dependent up-regulation of ORP150. Celecoxib administration led to an increase in the intracellular concentration of Ca²⁺, while BAPTA-AM, an intracellular Ca²⁺ chelator, inhibited the up-regulation of ORP150 and the activation of the ATF4- and ATF6-pathways. These results suggest that these Ca²⁺-activated pathways are involved in the celecoxib-mediated up-regulation of ORP150. Clones over-expressing ORP150 were less susceptible to celecoxib-induced, but not staurosporine-induced, apoptosis and displayed less up-regulation of CHOP, a transcription factor with apoptosis-inducing activity. In contrast, siRNA for ORP150 stimulated apoptosis and expression of CHOP in the presence of celecoxib but not staurosporine. These results suggest that up-regulation of ORP150 in cancer cells inhibits celecoxib-induced apoptosis, thereby decreasing the potential anti-tumor activity of celecoxib.

Key words: Apoptosis, Mechanisms of cell killing/apoptosis