Deciphering the association between up‐regulation of glucose regulated protein of Mr‐78 kDa (GRP78) and hypersensitivity to cisplatin employing comparative genomics

Abstract

We previously demonstrated an excellent association between the induction of GRP78 and hypersensitivity to alkylating/platinating agents. However, the mechanisms of this association are still not clear. GRP78 is a strong Ca++ binding chaperone protein residing in the endoplasmic reticulum (ER). Thus, GRP78 induction can potentially alter Ca++ homeostasis in the ER resulting in alteration in the Ca++‐dependent signaling pathways. We verified this hypothesis by examining the transcript levels using human cDNA microarrays and pathway specific macroarrays. A549 human lung cancer cells were exposed to 10 mM 2‐deoxyglucose or 25 nM thapsigargin or 250 nM tunicamycin for 48 h to induce GRP78, followed by 60 μM cisplatin for 2 h. We show that GRP78 induction alone causes a decrease in the transcript levels of DNA repair genes, DNA damage check point genes and an increase in that of apoptotic genes. Further, cisplatin treatment after GRP78 induction is augmenting the mitochondria‐mediated apoptotic cascades through the activation of caspase‐2 and down‐regulation of many genes involved in DNA repair. These results were further confirmed by examining relevant protein levels and enzyme activity. Our study will hence reveal insight into the molecular mechanisms of association between GRP78 induction and hypersensitivity to cisplatin that will ultimately allow strategies for transferring bench side results to the bed.