TY - JOUR T1 - Activation of Cyclosporin A Transport by a Novel λ Light Chain of Human Ig Surface Antigen-Related Gene in <em>Xenopus laevis</em> Oocytes JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1427 LP - 1435 DO - 10.1124/dmd.109.030916 VL - 38 IS - 9 AU - Yasuna Kobayashi AU - Takahiro Umemoto AU - Masayuki Ohbayashi AU - Noriko Kohyama AU - Yutaka Sanada AU - Toshinori Yamamoto Y1 - 2010/09/01 UR - http://dmd.aspetjournals.org/content/38/9/1427.abstract N2 - In the present study, we isolated and determined the pharmacological characteristics of a novel gene encoding the λ light chain of human Ig surface antigen-related gene (IgLC-rG). The isolated cDNA consisted of 693 base pairs that encoded a 232-amino acid protein. Northern blot analysis revealed that the IgLC-rG mRNA is expressed in the adult spleen and small intestine but not in fetal tissues. When expressed in Xenopus laevis oocytes, IgLC-rG mediated the high-affinity transport of [3H]cyclosporin A (CsA) (Km = 189.7 ± 123.5 nM) in a sodium-dependent manner; however, other organic solutes such as p-aminohippuric acid and TEA were not transported via IgLC-rG. The transport of [3H]CsA by IgLC-rG was sensitive to pH. The uptake of [3H]CsA was trans-stimulated by CsA and GSH. Immunohistochemical analysis revealed that the IgLC-rG protein is localized at the brush border membrane in the human small intestine. Although the isolated IgLC-rG gene is a member of the human Ig λ light chain surface antigen superfamily, our findings suggest that IgLC-rG functions as a novel transport peptide responsible for CsA in the human body. Our results should provide insight into the novel function of membrane-bound proteins, such as Igs. ER -