H⁺-peptide cotransport in the human bile duct epithelium cell line SK-ChA-1

Abstract

This study describes for the first time the presence of H+-peptide cotransport in cells of the bile duct. Uptake of [glycine-1-14C]glycylsarcosine ([14C]Gly-Sar) in human extrahepatic cholangiocarcinoma SK-ChA-1 cells was stimulated sevenfold by an inwardly directed H+ gradient. Transport was mediated by a low-affinity system with a transport constant ( K t) value of 1.1 mM. Several dipeptides, cefadroxil, and δ-aminolevulinic acid, but not glycine and glutathione, were strong inhibitors of Gly-Sar uptake. SK-ChA-1 cells formed tight, polarized monolayers on permeable membranes. The transepithelial electrical resistance was 856 ± 29 Ω × cm2. The transepithelial flux of [14C]Gly-Sar in apical-to-basolateral direction exceeded the basolateral-to-apical flux 11-fold. Uptake was 20-fold higher from the apical side. RT-PCR analysis using primer pairs specific for the intestinal-type peptide transporter (PEPT1) or kidney-type (PEPT2) revealed that the transport system expressed in SK-ChA-1 and also in cells of the native rabbit bile duct is PEPT1. Immunohistochemistry localized PEPT1 to the apical membrane of cholangiocytes of mouse extrahepatic biliary duct. We conclude that the cells of the mammalian extrahepatic biliary tract epithelium express the intestinal-type H+-peptide cotransporter in their apical membrane. SK-ChA-1 cells represent a convenient model to study the physiological and clinical aspects of peptide transport in cholangiocytes.

Association of PepT1 with lipid rafts differently modulates its transport activity in polarized and nonpolarized cells

“…Human PepT1 (hPepT1), which mediates this peptide transport activity (6,8,9), cotransports peptides with H ϩ (12,17,21,24) and has a broad specificity including many di/tripeptides and peptide-derived drugs (42,43). Functional expression of hPepT1 in Xenopus laevis oocytes induces H ϩ -dependent peptide-transport activity, therefore recapitulating the transport activity observed in natural gut epithelia (30,40).…”

“…PepT1 is mainly expressed in brush border membranes (BBMs) of enterocytes in small intestine, in proximal tubular cells of the S1 segment of kidney, and in bile duct epithelial cells (1,9,17,34,35,38). Expression of PepT1 mRNA or protein is low (46) or not detected (25,34) in the colon but is transiently expressed in normal rat colon cells during the first few days after birth (35).…”

PepT1-Mediated Tripeptide KPV Uptake Reduces Intestinal Inflammation

“…The specificity of hPepT1 is broad and includes many di-and tripeptides in addition to various peptide-derived drugs (3)(4)(5)(6)(7)(8). PepT1 is mainly expressed in brush-border membranes of enterocytes in the small intestine, in proximal tubular cells of the S1 segment of the kidney, and in bile-duct epithelial cells (4,5,(9)(10)(11)(12)(13)(14)(15). By contrast, in the colon, expression of PepT1 mRNA and protein is low (16) and sometimes cannot be detected (10,15,17).…”

Cancer Detection Using a PET Tracer, 11C-Glycylsarcosine, Targeted to H+/Peptide Transporter

“…Gonzalez et al reported that human pancreatic carcinoma cell lines AsPC-1 and Capan-2 also possess peptide transport activity and express PEPT1 (13). Subsequently, our group (11) and Knütter et al (14) reported that human gastric cancer cell line MKN45, human osteosarcoma cell line MG-63, human bladder cancer cell line T24, and human extrahepatic cholangiocarcinoma cell line SKChA-1 also exhibit peptide transport activity. These findings suggest that the PEPTs may be a promising target for cancer imaging using PET.…”