Functional dissection of transmembrane domains of human TAP-like (ABCB9)

Intracellular Localization of ABC Transporter TAPL Differs between Transient and Stable Expression

“…TAPL( )-GFP as well as TAPL-DsRed expressed stably in CHO-K1 cells were co-localized with a lysosome marker protein, cathepsin D, rather than an endoplasmic reticulum marker, PDI. This localization is consistent with our previous findings [4] [10], and that for a SKOV3 cell line derived from human ovaries [18]. The expression level would be too high upon transient expression, resulting in inhibition of the normal targeting pathway from the ER to lysosomes because various components for lysosomal targeting [19], limiting amounts of which are present in the ER, could be saturated by the excess TAPL molecules.…”

“…Previously, TAPL(M 1 -A 766 )-GFP and TAPL(M 1 -R 141 )-GFP were suggested to be localized to lysosomes, as determined by organelle staining with a fluorescent dye [4]. In this study, we detected the immunofluorescence of organelle marker proteins such as cathepsin D (a lysosome marker) and PDI (an ER marker) on microscopy.…”

“…TAPL is a half-type ABC transporter that forms a homo-dimer [3] [4]. The TAPL molecule is highly homologous to each subunit of TAP composed of a hetero-dimer of TAP1 and TAP2 [3].…”

“…The downstream six transmembrane helices and the ABC domain of TAPL form a core domain essential for homo-dimerization, while its N-terminal four transmembrane helices do not participate in the dimer formation by TAPL [4]. When the fusion protein comprising TAPL with the green fluorescent protein (GFP) at its C-terminus was stably expressed in Chinese hamster ovary (CHO)-K1 cells, it was localized on the lysosomal membrane [4] [10]. It is further suggested that the N-terminal four transmembrane helices of TAPL comprise an unidentified lysosomal targeting signal [4].…”

“…When the fusion protein comprising TAPL with the green fluorescent protein (GFP) at its C-terminus was stably expressed in Chinese hamster ovary (CHO)-K1 cells, it was localized on the lysosomal membrane [4] [10]. It is further suggested that the N-terminal four transmembrane helices of TAPL comprise an unidentified lysosomal targeting signal [4].…”