The Role of Multi-Drug Resistance ABC Transporters in Murine Prostate Epithelial Differentiation
Samant, Mugdha D.
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Multi-drug resistance (MDR)-ATP binding cassette (ABC) transporters, ABCB1, ABCC1 and ABCG2 participate in the efflux of steroid hormones, estrogens and androgens that regulate prostate development and differentiation. The role of MDR-ABC efflux transporters in prostate epithelial proliferation and differentiation remains elusive. The hypothesis of the thesis is that MDR-ABC transporters regulate prostate differentiation and epithelium regeneration. Prostate epithelial differentiation was studied using histology, sphere formation assay and the tissue recombination assay, whereas prostate regeneration was studied by repeated androgen withdrawal and replacement. Embryonic deletion of Abcg2 resulted in a decreased number of luminal cells in the prostate and increased sphere formation efficiency, indicating an imbalance in the prostate epithelial differentiation pattern. Decreased luminal cell number in the Abcg2 null prostate implies reduced luminal differentiation. Enhanced sphere formation efficiency in Abcg2 null prostate cells implies activation of the stem/progenitor cells. The spheres and grafts in tissue recombination assay generated from Abcg2 null prostate cells displayed enhanced divisions towards p63 - phenotype. Although prostate regeneration was not impaired in Abcg2 null mice, was associated with profound increase in sphere formation efficiency suggesting activation of the stem/progenitor cells. Moreover, Abcg2 null prostate stem/progenitor cells demonstrated heightened response to dihydrotestosterone (DHT) suggesting the critical importance of Abcg2 in DHT mediated differentiation. Abcg2 null prostates had side population phenotype indicating presence of MDR-ABC efflux function. Since, embryonic deletion of Abcg2 resulted in the compensation by other MDR-ABC transporters, pharmacological inhibition of MDR-ABC efflux was performed. Pharmacological inhibition of MDR-ABC efflux enhanced prostate luminal differentiation in sphere culture and during prostate regeneration in WT and Abcg2 null prostate cells. Abcg2 null prostate cells are highly sensitized to MDR-ABC efflux inhibition indicating the critical role of Abcg2 in prostate stem/progenitor cells. In conclusion, Abcg2 deletion leads to activation of the stem/progenitor cells and enhanced differentiating divisions; and pharmacological inhibition of MDR-ABC efflux leads to augmented luminal differentiation. Our study demonstrates for the first time that MDR-ABC efflux transporter inhibition results in enhanced prostate epithelial cell differentiation.