Figure 1.

A. The expression of let-7 and miR-34 variants is reduced in lung cancer cell lines. Total RNA from lung cancer cell lines was isolated, and the levels of let-7a, let-7b, miR-34a, miR-34b and miR-34c were determined using quantitative reverse transcription PCR (RT-qPCR). Expression levels are normalized to Rnu6B and plotted relative to the expression levels in a non-cancerous human bronchial epithelial cell line (HBEC3). Plotted: mean ± s.d.; n = 4 ; **P < 0.01, Student's t-test. B. let-7 and miR-34 potentiate the cytotoxic effect of erlotinib. Lung cancer cell lines were transfected with 25 nM of a control miRNA mimic, 25 nM of mimics of let-7b, miR-34a, or a half dose of each let-7b + miR-34a, or left untreated. 48 hours after transfection, the cells were treated with erlotinib at the experimentally determined EC₅₀ for each line (Fig. S1). 72 hours after drug exposure, cell survival was determined via the sulforhodamine-B (SRB) assay. The absorbance measurements for each erlotinib + miRNA mimic treatment were normalized relative to the group treated with erlotinib + control miRNA mimic, while the measurements for the DMSO + miRNA mimic treatments were normalized to the DMSO + control mimic group. Plotted: mean ± s.d.; n = 4 ; *P < 0.05, **P < 0.01, Student's t-test.