CellBio, 2014, 3, 50-59 Published Online June 2014 in SciRes. http://www.scirp.org/journal/cellbio http://dx.doi.org/10.4236/cellbio.2014.32006 How to cite this paper: Motohashi, Y., Ohashi-Kobayashi, A., Nakanishi-Matsui, M., Fujimoto, Y. and Maeda, M. (2014) Intracellular Localization of ABC Transporter TAPL Differs between Transient and Stable Expression. CellBio, 3, 50-59. http://dx.doi.org/10.4236/cellbio.2014.32006 Intracellular Localization of ABC Transporter TAPL Differs between Transient and Stable Expression Yu Motohashi 1 , Ayako Ohashi-Kobayashi 2 , Mayumi Nakanishi-Matsui 3 , Yasuyuki Fujimoto 4 , Masatomo Maeda 4* 1 Laboratory of Biochemistry and Molecular Biology, Graduate School of Pharmaceutical Sciences, Osaka University, Suita, Japan 2 Department of Immunology, School of Pharmacy, Iwate Medical University, Shiwa-Gun, Japan 3 Department of Biochemistry, School of Pharmacy, Iwate Medical University, Shiwa-Gun, Japan 4 Department of Molecular Biology, School of Pharmacy, Iwate Medical University, Shiwa-Gun, Japan Email: * mmaeda@iwate-med.ac.jp Received 23 April 2014; revised 26 May 2014; accepted 2 June 2014 Copyright © 2014 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract Transporter associated with antigen processing (TAP)-like (TAPL; ABCB9) is a half-type ABC transporter with sequence similarity to TAP1 and TAP2 that function in the ER membrane. To de- termine the cellular localization, TAPL and truncated forms of it were tagged with GFP at their car- boxyl termini. Intracellular localization of these fusion proteins was compared between transient and stable expression in CHO-K1 cells. When they were expressed transiently, the fluorescence of the fusion proteins was detected on the intracellular membrane, mainly in the ER, and all the fu- sion proteins, i.e., TAPL(M 1 -A 766 )-GFP, TAPL(M 1 -S 275 )-GFP, TAPL(M 1 -K 182 )-GFP, TAPL(M 1 -R 141 )-GFP and TAPL(M 1 -G 75 ), were co-localized with an ER marker, PDI. However, the fluorescence of all of them except for TAPL(M 1 -G 75 )-GFP and TAPL(M 1 -S 275 )-GFP overlapped with a lysosome marker, ca- thepsin D, upon stable expression. Lysosomal localization was similarly observed with TAPL(M 1 - A 766 )-DsRed, which was stably expressed. These results suggest that TAPL is sorted to the lyso- somal membrane when expressed stably in CHO-K1 cells. Furthermore, the lysosomal targeting signal may comprise the N-terminal four transmembrane helices since the N-terminal two trans- membrane helices may not be enough to function as such a signal. Keywords ABCB9, Lysosome, Membrane Localization, Stable Expression, TAPL, Transfection * Corresponding author.