Functional expression of breast cancer resistance protein and cholesterol effect in human erythrocyte membranes.

ABSTRACT

In human erythrocyte membranes, various influx and efflux transporters are functionally expressed. However, their transport characteristics and modulation under disease states are not fully understood. In this study, we first examined the expression and detailed transport characteristics of breast cancer resistance protein (BCRP), an efflux ABC transporter, using inside-out membrane vesicles (IOVs) prepared from human erythrocytes, and then studied the effect of membrane cholesterol on BCRP function. The expression of BCRP was confirmed by western blotting; most of them being homodimers. The uptake of lucifer yellow (LY), a fluorescent BCRP substrate, into IOVs was time-, temperature-, and ATP-dependent, and the concentration of ATP which induced half-maximal stimulation of LY uptake was calculated to be 0.39 mM. The uptake of LY by IOVs was saturable with a Km value of 166 µM, and was inhibited by various BCRP inhibitors and substrates, such as fumitremorgin C and mitoxantrone. When membrane cholesterol content was increased by treating IOVs with cholesteryl hemisuccinate, LY uptake decreased with increasing cholesterol content. These results suggest that transport activity of BCRP in human erythrocyte membranes may be suppressed under disease states, such as hypercholesterolemia, that increase membrane cholesterol content.