Enhanced expression of the human multidrug resistance protein 3 by bile salt in human enterocytes. A transcriptional control of a plausible bile acid transporter

The enterohepatic circulation is essential for the maintenance of bile acids and cholesterol homeostasis. The ileal bile acid transporter on the apical membrane of enterocytes mediates the intestinal uptake of bile salts, but little is known about the bile salt secretion from the basolateral membrane of enterocytes into blood. In the basolateral membrane of enterocytes, an ATP-binding cassette transporter, multidrug resistance protein 3 (MRP3), is expressed, which has the ability to transport bile salts. We hypothesized that MRP3 might play a role in the enterohepatic circulation of bile salts by transporting them from enterocytes into circulating blood through the up-regulation of MRP3 expression, so we investigated the transcriptional control of MRP3 in response to bile salts. MRP3 mRNA levels were increased about 3-fold in human colon cells by chenodeoxycholic acid (CDCA), in a dose- and time-dependent manner. In the promoter assay, the promoter activity of MRP3 was increased about 3-fold over the basal promoter activity when treated with CDCA, and the putative bile salt-responsive elements exist in the region -229/-138 including two alpha-1 fetoprotein transcription factor (FTF)-like elements. Constructs with a specific mutation in the consensus sequence of FTF elements showed no increase in basal transcriptional activity following CDCA treatment. In electrophoretic mobility shift assay with nuclear extracts, specific binding of FTF to FTF-like elements was observed when treated with CDCA. The expression of FTF mRNA levels were also markedly enhanced in response to CDCA, and overexpression of FTF specifically activated the MRP3 promoter activity about 4-fold over the basal promoter activity. FTF thus might play a key role not only in the bile salt synthetic pathway in hepatocytes but also in the bile salt excretion pathway in enterocytes through the regulation of MRP3 expression. MRP3 may contribute as a plausible bile salt-exporting transporter to the enterohepatic circulation of bile salts.

Decreased expression of an ATP-binding cassette transporter, MRP2, in human livers with hepatitis C virus infection

BACKGROUND/AIMS

To understand hepatic injury during the process of hepatitis viral infection, determination of liver-specific functions at molecular levels is critical. Because the transport of endogenous/exogenous toxic substances is an intrinsically important hepatic function, we examined whether expression of the ATP-binding cassette (ABC) transporter gene was affected in patients with hepatitis viral infection.

METHODS

To determine which ABC transporter was expressed differently in patients with hepatic viral infection, we assayed the expression of MDR1, MDR3, MRP1, MRP2, and MRP3 in non-cancerous regions in the liver of 42 patients with hepatic tumors using both quantitative RT-PCR and immunological staining analysis, and compared the hepatic expression levels between patients with hepatitis viral infection and non-infected controls.

RESULTS

Of the five ABC transporter genes studied, the mRNAs of MRP2 and MRP3 were highly expressed in the human liver. There was a significant reduction in MRP2 expression to 29% in the virus-infected liver. Treatment of hepatic cells with inflammatory cytokines resulted in decreased mRNA levels of MRP2 and decreased MRP2 promoter activity.

CONCLUSIONS

The down-regulation of MRP2 might induce a failure in the transport of various genotoxic substances in the liver with hepatitis virus infection.

The nutritional advantages of proximal gastrectomy for early gastric cancer

BACKGROUND/AIMS

Total gastrectomy has generally been performed for the treatment of early gastric cancers involving the upper third of the stomach. However, proximal gastrectomy has also been used for the treatment of cardial early gastric cancer.

METHODOLOGY

To compare the nutritional parameters after proximal gastrectomy with the parameters after total gastrectomy, and to also determine the advantages of the postoperative nutritional states, a retrospective analysis was made to evaluate the nutritional status of patients with early gastric cancer who underwent proximal gastrectomy with those undergoing total gastrectomy. Forty-nine patients were studied for one year after surgery; 9 underwent proximal gastrectomy while 40 had a total gastrectomy.

RESULTS

Proximal gastrectomy allowed the patient to better maintain both their nutritional parameters and body weight.

CONCLUSIONS

Proximal gastrectomy was thus found to be a beneficial modality for early gastric cancer patients regarding terms of the postoperative nutritional status, in comparison to total gastrectomy.

Involvement of the multidrug resistance protein 3 in drug sensitivity and its expression in human glioma

The multidrug resistance protein (MRP) family belongs to the ATP-binding cassette superfamily (ABC) of transporters, which are involved in ATP-dependent transport of hydrophobic compounds. One of the MRP family, MRP1, is partially associated with the multidrug resistance phenotype in brain tumors. In this study, we asked whether another MRP family gene, MRP3, could affect drug sensitivity to anticancer agents in human glioma cell lines and clinical glioma specimens. We first produced two antisense transfectants by introduction of antisense MRP3 cDNA into the glioma cell line NHG2, which endogenously expresses MRP3. The two MRP3 antisense transfectants showed 2- to 5-fold increases in drug sensitivity to etoposide and cisplatin compared with NHG2 cells, but their sensitivity to vincristine or nitrosourea was not changed. Two MRP3 cDNA sense transfectants of pig kidney cell lines showed 4- to 6-fold drug resistance to etoposide, but only 1.4- to 1.5-fold to cisplatin. We next compared the mRNA levels of four ABC transporters, multidrug resistance 1 (MDR1), MRP1, MRP2 and MRP3 in clinical samples, including 34 patients with gliomas, by quantitative RT-PCR analysis. In some of the clinical samples, increased expression of MRP1 and MRP3 was apparent in malignant gliomas. In situ hybridization revealed that glioma cells were stained with MRP3 probe. MRP3 may modulate drug sensitivity to certain anticancer agents in human gliomas.

Increased expression of an ATP-binding cassette superfamily transporter, multidrug resistance protein 2, in human colorectal carcinomas

The expression of ATP-binding cassette superfamily transporter genes, such as P-glycoprotein/multidrug resistance (MDR) 1 and MDR protein (MRP) 1, is often up-regulated in various tumor types and is involved in responses to some anticancer chemotherapeutic agents. Five human MRP subfamily members (MRP2-6) with structural similarities to MRP1 have been identified. The relationships between MRP2-6 mRNA levels and drug resistance are not well understood. Data on 45 patients with colorectal cancer were analyzed. Of the ATP-binding cassette superfamily genes, we asked whether mRNA levels of MDR1, MRP1, MRP2, and MRP3 correlated with drug resistance to anticancer agents. For this analysis, we used quantitative reverse transcription-PCR, and the sensitivity to anticancer agents in surgically resected colon carcinomas was determined using the in vitro succinate dehydrogenase inhibition test. MDR1, MRP1, and MRP3 were highly expressed in normal colorectal mucosa, and the relative mRNA levels of MDR1, MRP1, and MRP3 in cancerous tissues compared with noncancerous tissues were decreased or unchanged. By contrast, MRP2 mRNA expression was low in normal colorectal mucosa and specifically increased in cancer regions compared with noncancerous regions. Of the anticancer agents prescribed for patients with colorectal cancers, including doxorubicin, mitomycin C, cisplatin, 5-fluorouracil, etoposide, and a camptothecin derivative, mRNA expression of MRP2 was significantly associated with resistance to cisplatin. MRP2 may be important for resistance to cisplatin treatment in colorectal cancer.

The human multidrug resistance protein 2 gene: functional characterization of the 5'-flanking region and expression in hepatic cells

The human multidrug resistance protein 2 (MRP2), also termed as the canalicular multispecific organic anion transporter (cMOAT), is a member of the adenosine triphosphate-binding cassette transporter superfamily. In the liver, MRP2 mediates the multispecific efflux of various types of organic anions, including glucuronate, sulfate, and glutathione conjugates, across the canalicular hepatocyte membrane to the bile. To investigate how the MRP2 gene is expressed in liver cells, the 5'-flanking region of the human MRP2 gene was isolated from a human placental genomic library. Sequence analysis of the MRP2 promoter showed a number of consensus binding sites for both ubiquitous and liver-enriched transcription factors. Transfection of human hepatic HepG2 cells with a series of 5'-deleted promoter luciferase constructs identified a putative silencer element localized in the -1,659/-491 region and a liver-specific positive regulatory element localized in the -491/-258 region. This latter region contained the liver-abundant transcription factor CCAAT-enhancer binding protein beta (C/EBPbeta). The transcriptional activity of the promoter construct containing a mutation in the C/EBPbeta binding site was significantly decreased in HepG2 cells. This study suggests that C/EBPbeta (-356 to -343) may regulate the liver expression of the MRP2 gene.

Duodenal metastasis from large cell carcinoma of the lung: report of a case

Duodenal metastasis from primary lung cancer is extremely rare. It rarely shows any symptoms, and the prognosis for this condition is poor. We herein describe the case of a 46-year-old woman with primary lung cancer who underwent a left upper lobectomy. Severe anemia was observed about 20 days after lobectomy. Gastroduodenoscopy showed duodenal metastasis. Simultaneously, brain metastasis was also detected using magnetic resonance imaging. The patient underwent a local resection of the duodenum and a tumor resection of the brain. Postoperative irradiation of the brain metastases and systemic chemotherapy of the lung metastases were performed, and complete remission occurred. However, abdominal lymph node metastasis recurred, and the patient died 1 year after the lobectomy.

Pre-operative imaging can diagnose torsion of the gallbladder: report of a case

Torsion of the gallbladder is a rare disease and pre-operative diagnosis of the disease is uncommon. About 400 cases have been reported, but only 4 were diagnosed by pre-operative imaging. We report on a case of gallbladder volvulus diagnosed pre-operatively using pre-operative imaging with ultrasound and computed tomography.

Isolation of a novel human canalicular multispecific organic anion transporter, cMOAT2/MRP3, and its expression in cisplatin-resistant cancer cells with decreased ATP-dependent drug transport

The human multidrug resistance protein (MRP) gene encodes a membrane protein involved in the ATP-dependent transport of hydrophobic compounds. We previously isolated a canalicular multispecific organic anion transporter, cMOAT1/MRP2, that belongs to the ATP binding cassette (ABC) superfamily, which is specifically expressed in liver, and cMOAT1/MRP2 is responsible for the defects in hyperbilirubinemia II/Dubin-Johnson syndrome. In this study, we isolated a new cDNA of the ABC superfamily designated cMOAT2/MRP3 that is homologous to human MRP1 and cMOAT1/MRP2: cMOAT2/MRP3 is 56% identical to MRP1 and 45% identical to cMOAT1/MRP2, respectively. Fluorescence in situ hybridization demonstrated the chromosomal locus of this gene on chromosome 17q22. The human cMOAT2 cDNA hybridized to a 6.5-kb mRNA that was mainly expressed in liver and to a lesser extent in colon, small intestine, and prostate. The cMOAT2/MRP3 gene was not overexpressed in cisplatin-resistant cell lines with increased ATP-dependent transport of cisplatin over their parental counterparts derived from human head and neck cancer and human prostatic cancer cell lines. The human cMOAT2/MRP3, a novel member of the ABC superfamily, may function as a membrane transporter in liver, colon, and prostate.