Silencing Heat Shock Transcription Factor 1 Using Small Interfering RNA Enhances Mild Hyperthermia and Hyperthermia Sensitivity in Human Oral Squamous Cell Carcinoma Cells

Abstract

Hyperthermia (HT) for various types of malignant tumor is a promising agent in anti-tumor action. However, the acquisition of thermotolerance in carcinoma cells due to the induction of heat shock proteins (HSPs) makes HT less effective. Recent findings suggest that a decrease in heat shock transcription factor 1 (HSF1) elicits sensitivity to HT in some kinds of carcinoma cells. Here we evaluated the effects of knockdown of HSF1 by small interfering RNA (siRNA) on the sensitivity to mild hyperthermia (MHT) and HT in human oral squamous cell carcinoma (OSCC) cells. Treatment of human OSCC HSC-3 cells with siHSF1-2, a siRNA for HSF1, effectively decreased the protein expression level of HSF1 in a time-dependent manner at 37°C, and almost complete knockdown of HSF1 was observed at 48 h post treatment. Moreover, although a remarkable elevation of protein expression of HSPs such as Hsp70, Hsp40 and Hsp27 was detected in HSC-3 cells treated with MHT at 42°C and HT at 44°C for 90 min, expression of these HSPs was significantly decreased in HSF1-silenced cells under normal and hyperthermic conditions. In HSC-3 cells, knockdown of HSF1 significantly decreased the number of viable cells at 37°C, suggesting that HSF1 may be required for normal cell growth. In addition, sensitivity to MHT or HT was markedly enhanced in HSF1-silenced HSC-3 cells. Moreover, we observed an increase in sensitivity to these hyperthermic treatments by silencing of HSF1 in human OSCC cell lines HO-1-N-1, HO-1-u-1 and SAS. These findings indicate that silencing of HSF1 enhances sensitivity to MHT and HT in human OSCC cells, and that hyperthermic treatment combined with HSF1 silencing has potential significance in OSCC therapy.