Common gene expression patterns responsive to mild temperature hyperthermia in normal human fibroblastic cells.

PURPOSE: Heat stress induces complex cellular responses, and its detailed molecular mechanisms still remain to be clarified. The objective of this study was to investigate the molecular mechanisms underlying cellular responses to mild hyperthermia (MHT) in normal human fibroblastic (NHF) cells. MATERIALS AND METHODS: Cells were treated with MHT (41°C, 30 min) and then cultured at 37°C. Gene expression was determined by the GeneChip® system and bioinformatics tools. RESULTS: Treatment of the NHF cell lines, Hs68 and OUMS-36, with MHT did not affect the cell viability or cell cycle. In contrast, many probe sets were differentially expressed by >1.5-fold in both cell lines after MHT treatment. Of the 1,196 commonly and differentially expressed probe sets analysed by k-means clustering, three gene clusters, Up-I, Down-I and Down-II, were observed. Interestingly, two gene networks were obtained from the up-regulated genes in cluster Up-I. The gene network E contained DDIT3 and HSPA5 and was mainly associated with the biological process of endoplasmic reticulum stress, while the network S contained HBEGF and LIF and was associated with the biological process of cell survival. Eighteen genes were validated by quantitative real-time polymerase chain reaction, consistent with the microarray data, in four kinds of NHF cells. CONCLUSIONS: Common genes that were differentially expressed and/or acted within a gene network in response to MHT in NHF cells were identified. These findings provide the molecular basis for a further understanding of the mechanisms of the MHT response in NHF cells.

A microRNA-27a mimic sensitizes human oral squamous cell carcinoma HSC-4 cells to hyperthermia through downregulation of Hsp110 and Hsp90.

Hyperthermia (HT) is an important modality in cancer treatment; however, the acquisition of thermal resistance in cancer cells due to the elevation of heat shock proteins (HSPs) makes HT less effective. Accumulating evidence suggests that microRNAs (miRNAs) play an important role in regulating cellular stress sensitivities, such as drug sensitivity and radio-sensitivity, in cancer cells. However, few studies have investigated the involvement of miRNAs in thermal sensitivity. The aim of this study was thus to investigate the contribution of miRNAs to the thermal sensitivity of human oral squamous cell carcinoma (OSCC) cells. When the HSC-2, HSC-3 and HSC-4 OSCC cell lines were treated with HT at 44˚C for 60 min, a significant increase in cell death was observed in HSC-2 and HSC-3 cells but not HSC-4 cells, suggesting that HSC-4 cells were thermally resistant under the present experimental conditions. Moreover, the expression levels of HSPs were most elevated in HSC-4 cells. When the basal expression levels of miRNAs were monitored using two different microarray systems in thermal-sensitive HSC-2 and HSC-3 cells and thermal-resistant HSC-4 cells, five miRNAs that were differentially expressed were identified. Among these miRNAs, the expression level of miR-27a in HSC-4 cells was markedly reducec compared to the expression levels in HSC-2 and HSC-3 cells. Interestingly, treatment of HSC-4 cells with a miR-27a mimic oligonucleotide significantly enhanced HT-induced cell death. Furthermore, the miR-27a mimic oligonucleotide suppressed the elevation of the expression of Hsp90 and Hsp110 in HSC-4 cells, suggesting that these HSPs may be involved in a mechanism of thermal resistance. From these findings, we concluded that in OSCC cells, miR-27a may contribute to thermal sensitivity by modulating the HSP expression.

Development of oral epithelial cell line ROE2 with differentiation potential from transgenic rats harboring temperature-sensitive simian virus40 large T-antigen gene.

We have developed an immortalized oral epithelial cell line, ROE2, from fetal transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen gene. The cells grew continuously at either a permissive temperature of 33°C or an intermediate temperature of 37°C. At the nonpermissive temperature of 39°C, on the other hand, growth decreased significantly, and the Sub-G1 phase of the cell cycle increased, indicating that the cells undergo apoptosis at a nonpermissive temperature. Histological and immunocytochemical analyses revealed that ROE2 cells at 37°C had a stratified epithelial-like morphology and expressed cytokeratins Krt4 and Krt13, marker proteins for oral nonkeratinized epithelial cells. Global-scale comprehensive microarray analysis, coupled with bioinformatics tools, demonstrated a significant gene network that was obtained from the upregulated genes. The gene network contained 16 genes, including Cdkn1a, Fos, Krt13, and Prdm1, and was associated mainly with the biological process of skin development in the category of biological functions, organ development. These four genes were validated by quantitative real-time polymerase chain reaction, and the results were nearly consistent with the microarray data. It is therefore anticipated that this cell line will be useful as an in vitro model for studies such as physiological functions, as well as for gene expression in oral epithelial cells.

The combination of silencing BAG3 and inhibition of the JNK pathway enhances hyperthermia sensitivity in human oral squamous cell carcinoma cells.

Hyperthermia (HT) is a widely used physical treatment for various cancers, but its effect is often insufficient because of cytoprotective effects of heat shock proteins. BAG3, a co-chaperone of the heat shock protein 70, is a stress-inducible protein and demonstrates a cytoprotective property against various stresses, including heat stress. Here, we examined the effects of silencing the BAG3 on the sensitivity to HT in human oral squamous cell carcinoma (OSCC) HSC-3 cells. HT (44 °C, 90 min) was significantly increased in apoptotic cells concomitant with the activations of caspase-3 and c-Jun N-terminal kinase (JNK) pathway. Furthermore, the sensitivity to HT was remarkably enhanced in BAG3-downregulated HSC-3 cells. Interestingly, the effects of this combination treatment were significantly enhanced in the cells pretreated with a JNK inhibitor, SP600125. These findings indicated that the disruption of functions of both BAG3 and the JNK pathway may become an option in HT therapy in OSCC cells.

Identification of common gene networks responsive to mild hyperthermia in human cancer cells.

Hyperthermia (HT) has been used as a possible treatment modality for various types of malignant tumors. Due to its pleiotropic effects, its combined use with radiotherapy and/or chemotherapy has proven to be beneficial. However, the molecular mechanisms underling the cellular responses to heat stress remain unclear. Therefore, the aim of this study was to identify common gene expression patterns responsive to mild HT (MHT) in human cancer cells. HeLa human cervical squamous cell carcinoma (SCC) and HSC-3 human oral SCC cells were exposed to MHT at 41˚C for 30 min, followed by culture at 37˚C for 0-24 h. MHT did not affect cell viability or the cell cycle. GeneChip microarray analysis clearly revealed that many probe sets were differentially expressed by a factor of ≥1.5 in both cell lines following exposure to MHT. Of the many differentially expressed probe sets, 114 genes were found to be commonly upregulated in both HeLa and HSC­3 cells, and two significant gene networks were obtained from the commonly upregulated genes. Gene network A included several heat shock proteins, as well as BCL2-associated athanogene 3 (BAG3), and was found to be mainly associated with the biological functions of cellular function and maintenance. Gene network B included several anti-cell death genes, such as early growth response 1 (EGR1) and endothelin 1 (EDN1) and was found to be associated with the biological functions of cell death and survival. Real­time quantitative polymerase chain reaction demonstrated that the gene expression patterns of the 12 genes selected were consistent with the microarray data in four cancer cell lines. These findings may provide further insight into the detailed molecular mechanisms of the MHT response in cancer cells.

Inactivation of DNA-dependent protein kinase promotes heat-induced apoptosis independently of heat-shock protein induction in human cancer cell lines.

The inhibition of DNA damage response pathway seems to be an attractive strategy for cancer therapy. It was previously reported that in rodent cells exposed to heat stress, cell growth was promoted by the activity of DNA-dependent protein kinase (DNA-PK), an enzyme involved in DNA non-homologous end joining (NHEJ) required for double-strand break repair. The absence of a functioning DNA-PK was associated with down regulation of heat shock protein 70 (HSP70). The objective of this study is thus to investigate the role of DNA-PK inhibition in heat-induced apoptosis in human cell lines. The inhibitors of phosphorylation of the DNA-PK catalytic subunit (DNA-PKcs) at Ser2056, such as NU7026 and NU7441, were utilized. Furthermore, knock down of DNA-PKcs was carried out using small interfering RNA (siDNA-PKcs). For heat exposure, cells were placed in water bath at 44°C for 60 min. Apoptosis was evaluated after 24 h incubation flow cytometrically. Proteins were extracted after 24 h and analyzed for HSP70 and HSP40 expression by Western blotting. Total RNA was extracted 6 h after treatment and analyzed using a GeneChip® microarray system to identify and select the up-regulated genes (≥1.5 fold). The results showed an enhancement in heat-induced apoptosis in absence of functioning DNA-PKcs. Interestingly, the expression levels of HSP70 and HSP40 were elevated in the absence of DNA-PKcs under heat stress. The results of genetic network analysis showed that HSPs and JUN genes were up-regulated independently of DNA-PKcs in exposed parent and knock out cells. In the presence of functioning DNA-PKcs, there was an observed up-regulation of anti-apoptotic genes, such as NR1D1, whereas in the absence of DNA-PKcs the pro-apoptotic genes, such as EGR2, were preferentially up-regulated. From these findings, we concluded that in human cells, the inactivation of DNA-PKcs can promote heat-induced apoptosis independently of heat-shock proteins.