Mammalian steroid hormones are substrates for the major RND- and MFS-type tripartite multidrug efflux pumps of Escherichia coli

Abstract

A steroid-hormone-dependent growth suppression was observed in Escherichia coli efflux-deficient backgrounds containing mutations in the major RND- and MFS-type tripartite multidrug efflux systems, AcrAB-TolC and EmrAB-TolC, respectively. In addition to their previously known natural steroid spectrum, which includes bile acids, both systems were shown to transport the hormones estradiol and progesterone, whereas hydrocortisone served as a substrate of only AcrAB-TolC. Furthermore, at least two other RND-type pumps, YhiV and AcrD, were capable of transporting such hormones when overexpressed on plasmid vectors (with some demonstrable specificity observed with AcrD). When this activity was examined in a wild-type background, cell-associated estradiol levels remained largely unaffected by competition with exogenous bile acids and hydrocortisone, in contrast to progesterone, which produced a significant modulation in estradiol uptake.

FIG. 1.

Uptake of various tritium-labeled steroid molecules by E. coli AG102 and its efflux-deficient derivatives. Error bars represent standard deviations from three replicates with the same bacterial suspension.

FIG. 2.

Uptake of tritium-labeled steroid molecules by HNCE4 cells complemented with pSportI plasmid-encoded RND pumps from the E. coli genome. Of the six RND-type pumps encoded within the E. coli genome, AcrD and YhiV were previously shown to function heterologously with AcrA to produce a drug resistance phenotype (5, 6).

FIG. 3.

Effect of exogenous, unlabeled steroids on the uptake of tritium-labeled estradiol by fully efflux-proficient wild-type AG102 cells.