Functional inhibition of HIKESHI, a nuclear import carrier protein for HSP70, has been reported to enhance the heat sensitivity of cancer cells. In this study, we aimed to elucidate the molecular mechanisms underlying this increased heat sensitivity by comparing gene expression profiles between wild-type (WT) and HIKESHI-knockout (KO) human oral squamous cell carcinoma (OSCC) HSC-3 cells exposed to mild hyperthermia (MHT) at 42 ℃. Immunocytochemical analysis revealed that MHT-induced translocation of HSP70 from the cytoplasm to the nucleus was significantly suppressed in HIKESHI KO cells compared with WT cells. Comprehensive gene expression analysis using the GeneChip® system demonstrated that numerous probe sets exhibited altered expression in response to MHT in both cell types. Furthermore, Ingenuity® Pathway Analysis (IPA) identified gene networks associated with the heat shock response (HSR) and unfolded protein response (UPR). Functional prediction based on activation Z-scores in IPA indicated activation of the UPR in WT cells, whereas no such activation was predicted in KO cells. Real-time quantitative PCR confirmed that expression of UPR-related genes, including DNAJB1, HSPA1A, HSPA5, and HSPH1, was significantly reduced in KO cells. In addition, the level of spliced XBP1, a key regulator of the UPR, was markedly decreased in KO cells. These findings suggest that the UPR is impaired in HIKESHI-deficient OSCC HSC-3 cells and that this impairment may contribute, at least in part, to the enhanced MHT sensitivity resulting from HIKESHI deficiency.
Tabuchi et al. (Sun,) studied this question.