Stable inducible expression of a functional rat liver organic anion transport protein in HeLa cells

Recently we expression cloned a rat liver organic anion transport protein in Xenopus laevis oocytes (Jacquemin, E., Hagenbuch, B., Stieger, B., Wolkoff, A. W., and Meier, P. J. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 133-137). In the present study, we have stably transfected the cDNA encoding this protein into HeLa cells by using a vector containing a zinc-inducible promoter. The parent cells have virtually no baseline transport of [³⁵S]sulfobromophthalein, whereas the induced transfected cells express a novel 74-kDa protein and avidly transport this ligand. Transport by these cells is saturable (K(m) = 3.3 μM, V(max) = 257 pmol/min/mg protein), bidirectional, and highly temperature-dependent. In the presence of albumin, uptake of [³⁵S]sulfobromophthalein requires the presence of extracellular Cl^-, whereas in the absence of albumin, this Cl^- dependence is not seen. These studies indicate that cellular uptake of sulfobromophthalein does not result from direct interaction with the plasma membrane lipid bilayer but rather requires the presence of a specific plasma membrane transporter.