Fig. 4.

Resistance of estrogen receptor–positive (ER⁺) MCF-7 cells to doxorubicin after down-regulation of endogenous Hsp22 expression. MCF-7 cells grown in complete medium were electroporated to take up control pCH1 vector (light bars) or the pCH1–short hairpin (sh)Hsp22 vector (dark bars). Approximately 15 000 electroporated cells were seeded into each well of 24-well plates containing complete Dulbecco modified Eagle medium (DMEM). Twenty-four hours later, doxorubicin was added as indicated, and after additional 72 hours, cell viability was determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Error bars represent standard deviation. The inset shows Western blots for Hsp22, Hsp27, and β-actin of untreated control cells (lane 1) and of cells electroporated with the pCH1 control vector (lane 2) or the pCH1-shHsp22 vector (lane 3). A representative experiment is shown. Although the down-regulation of Hsp22 was effective, the resistance of MCF-7 cells to doxorubicin was not affected