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 (Km = 3.3 microM, Vmax = 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 C1- 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.