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Paresh P. Chothe, Santoshanand V. Thakkar, Jaya P. Gnana-Prakasam, Sudha Ananth, David R. Hinton, Ram Kannan, Sylvia B. Smith, Pamela M. Martin, Vadivel Ganapathy; Identification of a Novel Sodium-Coupled Oligopeptide Transporter (SOPT2) in Mouse and Human Retinal Pigment Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(1):413-420. doi: 10.1167/iovs.09-4048.
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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.
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.
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+.
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.
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