Expression of ABCG2 mRNA and protein in KG-1a cells. The enriched cells had high expression of ABCG2 mRNA and protein. a, analysis by RT-PCR of expression of ABCG2 mRNA. b, analysis by Western blotting of the expression of ABCG2 protein. +5-FU: KG-1a cells incubated with 50 μg/mL of 5-FU for 4 d; -5-FU: KG-1a cells without 5-FU.