4.9. Chromatin Immunoprecipitation (ChIP)

ChIP was performed according to the manufacturer’s instructions. Briefly, 6 × 10⁶ A549/T cells were fixed by 1.42% formaldehyde. STAT3-DNA was immunoprecipitated with anti-STAT3 antibody (Santa Cruz, #sc-482, 1 µg per 200 µg protein) overnight. Then anti-STAT3/STAT3/DNA complex was captured by protein A/G agarose beads (Thermo Fisher, Rockford, IL, USA), and reversely cross-linked, then DNA was purified by DNA column following manufacture’s instruction (Thermo Fisher, #26156). 50 µg cross-linked genomic DNA was used for qPCR to test with specific primers (Table 1) across MDR1 −198 bp to +43 bp around TSS promoter region and −504 bp~−398 bp of MRP1 promoter region.