Analysis of expression of cMOAT (MRP2), MRP3, MRP4, and MRP5, homologues of the multidrug resistance-associated protein gene (MRP1), in human cancer cell lines

By screening databases of human expressed sequence tags, we have identified three new homologues of MRP1, the gene encoding the multidrug resistance-associated protein, and cMOAT (or MRP2), the canalicular multispecific organic anion transporter gene. We call these new genes MRP3, MRP4, and MRP5. MRP3, like cMOAT, is mainly expressed in the liver. MRP4 is expressed only at very low levels in a few tissues, and MRP5, like MRP1, is expressed in almost every tissue tested. To assess a possible role of these new MRP homologues in multidrug or cisplatin resistance, a large set of resistant cell lines was examined for the (over)expression of MRP1, cMOAT, MRP3, MRP4, and MRP5. We find that even in cells selected for a low level of resistance, several MRP-related genes can be up-regulated simultaneously. However, MRP4 is not overexpressed in any of the cell lines we analyzed; MRP3 and MRP5 are only overexpressed in a few cell lines, and the RNA levels do not seem to correlate with resistance to either doxorubicin or cisplatin. cMOAT is substantially overexpressed in several cell lines, and cMOAT RNA levels correlate with cisplatin but not doxorubicin resistance in a subset of resistant cell lines. Our results emphasize the need for gene-specific blocks in gene expression to define which transporter contributes to resistance in each resistant cell lin

The N-terminus of the human copper transporter 1 (hCTR1) is localized extracellularly, and interacts with itself.

We have used indirect immunofluorescense studies and glycosylation-site insertion and deletion mapping to characterize the topology of human copper transporter 1 (hCTR1), the putative human high-affinity copper-import protein. Both approaches indicated that hCTR1 contains three transmembrane domains and that the N-terminus of hCTR1, which contains several putative copper-binding sites, is localized extracellularly, whereas the C-terminus is exposed to the cytosol. Based on previous observations that CTR1 proteins form high-molecular-mass complexes, we investigated directly whether CTR1 proteins interact with themselves. Yeast two-hybrid studies showed that interaction of yeast, mouse, rat and human CTR1 occurs at the sites of their N-terminal domains, and is not dependent on the copper concentration in the growth media. Analysis of deletion constructs indicated that multiple regions in the N-terminus are essential for this self-interaction. In contrast, the N-terminal tail of the presumed low-affinity copper transporter, hCTR2, does not interact with itself. Taken together, these results suggest that CTR1 spans the membrane at least six times, permitting formation of a channel, which is consistent with its proposed role as a copper transporter

FIC1, the protein affected in two forms of hereditary cholestasis, is localized in the cholangiocyte and the canalicular membrane of the hepatocyte

BACKGROUND/AIMS: FIC1 (familial intrahepatic cholestasis 1) is affected in two clinically distinct forms of hereditary cholestasis, namely progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis. Here we examined the subcellular localization of this protein within the liver. METHODS: Antibodies raised against different epitopes of human FIC1 were used for immunoblot analysis and immunohistochemical detection of FICI. RESULTS: Immunoblot analysis of intestine and liver tissue extracts from human, rat and mouse origin indicated that the antibodies raised against FIC1 specifically detected FIC1 as a 140-kDa protein. In the liver homogenate of a PFIC1 patient, FIC1 could not be detected. Analysis of isolated rat liver membrane vesicles indicated that this protein is predominantly present in the canalicular membrane fraction. Immunohistochemical detection of the protein in liver sections confirmed that FIC1 was present in the canalicular membrane, whereas no staining was observed in the PFIC1 patients liver. Double label immunofluorescence of murine liver revealed that FIC1 colocalized with cytokeratin 7 in cholangiocytes. CONCLUSIONS: The localization of FIC1 in the canalicular membrane and cholangiocytes suggests that it may directly or indirectly play a role in bile formation since mutations in FICI are associated with severe symptoms of cholestasi

Fine-resolution mapping by haplotype evaluation:the examples of PFIC1 and BRIC

Loci for two inherited liver diseases, benign recurrent intrahepatic cholestasis (BRIC) and progressive familial intrahepatic cholestasis type 1 (PFIC1), have previously been mapped to 18q21 by a search for shared haplotypes in patients in two isolated populations. This paper describes the use of further haplotype evaluation with a larger sample of patients for both disorders, drawn from several different populations. Our assessment places both loci in the same interval of less than 1 cM and has led to the discovery of the PFIC1/BRIC gene, FIC1; this discovery permits retrospective examination of the general utility of haplotype evaluation and highlights possible caveats regarding this method of genetic mapping

Fine-resolution mapping by haplotype evaluation: the examples of PFIC1 and BRIC

Loci for two inherited liver diseases, benign recurrent intrahepatic cholestasis (BRIC) and progressive familial intrahepatic cholestasis type 1 (PFIC1), have previously been mapped to 18q21 by a search for shared haplotypes in patients in two isolated populations. This paper describes the use of further haplotype evaluation with a larger sample of patients for both disorders, drawn from several different populations. Our assessment places both loci in the same interval of less than 1 cM and has led to the discovery of the PFIC1/BRIC gene, FIC1; this discovery permits retrospective examination of the general utility of haplotype evaluation and highlights possible caveats regarding this method of genetic mapping