In this study, we report that commonly used methods of transient transfection induce the cellular stress response and a recovery period is required following transfection when analyzing cellular stress responsive genes. Four transfection methods were examined for their ability to induce the stress response by measuring the expression of heat shock protein (hsp) 72. We demonstrate that electroporation increases expression of hsp 72 in HUT 78 cells. Additionally, DEAE-dextran and liposome-mediated transfection resulted in increased hsp 72 expression in an adherent cell line (HeLa). Liposome-mediated transfection differentially induced cell stress, dependent on the transfection time in serum-free culture conditions. The stress responsiveness of two viral promoters, the HTLV-1 long terminal repeat and CMV immediate early transcriptional unit were examined. We found the maximal stress-mediated enhancement of transcription with both promoters did not occur until the cells recovered for 24 h following transfection.
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