Identification of a novel sodium-coupled oligopeptide transporter (SOPT2) in mouse and human retinal pigment epithelial cells.
OBJECTIVE
A sodium-coupled oligopeptide transporter (SOPT1) was described originally in ARPE-19 cells. The transporter is inducible by HIV-1 Tat. Recent studies of conjunctival epithelial cells have identified a second oligopeptide transporter (SOPT2). This study was conducted to determine whether the newly discovered SOPT2 is expressed in ARPE-19 cells, to examine whether the new transporter is also inducible by HIV-1 Tat, and to find out whether this transporter is expressed in primary RPE cells.


METHODS
The transport activity of SOPT2 was monitored in control and Tat-expressing ARPE-19 cells and in primary mouse and human fetal RPE cells by the uptake of the synthetic opioid peptide DADLE ((H-Tyr-D-Ala-Gly-Phe-D-Leu-OH) and by its susceptibility to inhibition by small peptides. Substrate selectivity was examined by competition studies and kinetic parameters were determined by saturation analysis.


RESULTS
ARPE-19 cells express DADLE uptake activity that is inhibited by small peptides, indicating expression of SOPT2 in these cells. The activity of SOPT2 is induced by HIV-1 Tat. SOPT2 accepts endogenous and synthetic opioid peptides as substrates, but nonpeptide opiate antagonists are excluded. An 11-amino-acid HIV-1 Tat peptide also serves as a high-affinity substrate for the transporter. Primary cultures of mouse and human fetal RPE cells express SOPT2. The transporter is partially Na(+)-dependent with comparable substrate selectivity and inhibitor specificity in the presence and absence of Na(+).


CONCLUSIONS
ARPE-19 cells as well as primary mouse and human fetal RPE cells express the newly discovered oligopeptide transporter SOPT2, and the transporter is induced by HIV-1 Tat in ARPE-19 cells.
Chothe
Paresh P
PP
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA.
Thakkar
Santoshanand V
SV
Gnana-Prakasam
Jaya P
JP
Ananth
Sudha
S
Hinton
David R
DR
Kannan
Ram
R
Smith
Sylvia B
SB
Martin
Pamela M
PM
Ganapathy
Vadivel
V
D000818:Animals; D001693:Biological Transport, Active; D002478:Cells, Cultured; D016308:Enkephalin, Leucine-2-Alanine / Q000378:metabolism; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism*; D051379:Mice; D009842:Oligopeptides / Q000378:metabolism*; D018847:Opioid Peptides / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*; D014162:Transfection; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000378:metabolism
D026901:Membrane Transport Proteins; D009842:Oligopeptides; D018847:Opioid Peptides; D010446:Peptide Fragments; D054322:tat Gene Products, Human Immunodeficiency Virus; C497137:tat peptide (47-57), Human immunodeficiency virus 1; D016308:Enkephalin, Leucine-2-Alanine; D012964:Sodium