Functional characterization of the human multidrug transporter, ABCG2, expressed in insect cells

ABCG2 (also called MXR (3), BCRP (4), or ABCP (5)) is a recently-identified ABC half-transporter, which causes multidrug resistance in cancer. Here we report that the expression of the ABCG2 protein in Sf9 insect cells result ed in a high-capacity, vanadate-sensitive ATPase activity in isolated membr ane preparations. ABCG2 was expressed underglycosylated, and its ATPase act ivity was stimulated by daunorubicin, doxorubicin, mitoxantrone, prazosin a nd rhodamine 123, compounds known to be transported by this protein. ABCG2- ATPase was inhibited by low concentrations of Na-orthovanadate, N-ethylmale imide and cyclosporin A Verapamil had no effect, while Fumitremorgin C, rev ersing ABCG2-dependent cancer drug resistance, strongly inhibited this ATPa se activity. The functional expression of ABCG2 in this heterologous system indicates that no additional partner protein is required for the activity of this multidrug transporter, probably working as a homodimer, We suggest that the Sf9 cell membrane ATPase system is an efficient tool for examining the interactions of ABCG2 with pharmacological agents. (C) 2001 Academic P ress.