TITLE:
Intracellular Localization of ABC Transporter TAPL Differs between Transient and Stable Expression
AUTHORS:
Yu Motohashi, Ayako Ohashi-Kobayashi, Mayumi Nakanishi-Matsui, Yasuyuki Fujimoto, Masatomo Maeda
KEYWORDS:
ABCB9, Lysosome, Membrane Localization, Stable Expression, TAPL, Transfection
JOURNAL NAME:
CellBio,
Vol.3 No.2,
June
12,
2014
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 determine 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 fusion proteins, i.e., TAPL(M1 -A766)-GFP, TAPL(M1-S275)-GFP, TAPL(M1-K182 )-GFP, TAPL(M 1-R141)-GFP and TAPL(M1-G75), were co-localized with an ER marker, PDI. However, the fluorescence of all of them except for TAPL(M1-G 75)-GFP and TAPL(M1-S275)-GFP overlapped with a lysosome marker, cathepsin D, upon stable expression. Lysosomal localization was similarly observed with TAPL(M1- A766)-DsRed, which was stably expressed. These results suggest that TAPL is sorted to the lysosomal 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 transmembrane helices may not be enough to function as such a signal.