Methylation of secreted frizzle-related protein (SFRP) genes activates Wnt/?-catenin signaling and promotes tumor development. This study investigated whether SFRP5 gene methylation causes multidrug resistance (MDR) in leukemia through the Wnt/?-catenin signaling, leading to the upregulation of the mdr1 gene and its product, P-glycoprotein (P-gp). Methylation-specific PCR identified SFRP5 gene methylation in cultured bone mononuclear cells from 7/12 patients with acute leukemia and in four human leukemia cell lines (HL-60, Raji, U937 and KG1a). Western blotting revealed absent SFRP5 protein expression in cells from 5/7 patients with SFRP5 gene methylation and in all cell lines. Treatment with a demethylation agent (DAC) rescued SFRP5 expression. mdr1 mRNA and P-gp protein were detected in cells from 3/5 patients with absent SFRP5, and in the KG1a cell line; these cells also had the highest levels of activated ?-catenin. In cells from these three patients, DAC rescued SFRP5 expression and downregulated mdr1 and P-gp. SFRP5 protein expression was rescued in transgenic KG1a/SFRP5 cells, compared with KG1a/eGFP or untransfected KG1a cells. mdr1 and P-gp in KG1a/SFRP5 cells were downregulated. Doxorubicin IC50 values were significantly lower in KG1a/SFRP5 (0.573±0.131 ìM) than in KG1a (0.963±0.115) or KG1a/eGFP (0.917±0.138) cells (P<0.05). We conclude that SFRP5 gene methylation in leukemia cells activates Wnt/?-catenin signaling to upregulate mdr1/P-gp expression and cause MDR. Recovery of SFRP5 expression reversed MDR in the KG1a leukemia cell line. Our results suggest that modulating SFRP5 methylation could decrease MDR in leukemia patients.
ATP Binding Cassette Transporter, Subfamily B ATP Binding Cassette Transporter, Subfamily B, Member 1