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LmrA is an ATP binding cassette (ABC) multidrug transporter in Lactococcus lactis

The emergence of multidrug resistant cancer cells is a serious problem in the chemotherapeutic treatment of human tumors. In mammals, multidrug resistance based on the active extrusion of cytotoxic drugs from the cell is mediated by several members of the ATP-binding cassette (ABC) 1 superfamily. These include the multidrug resistance P-glycoprotein MDR1 (also termed ABCB1) and the protein MRP1 (multidrug resistance-associated protein 1, also termed ABCC1) (1). The breast cancer resistance protein (BCRP, also termed MXR, ABCP, or ABCG2) is one of the more recently discovered ABC multidrug transporters in human cancer cells. BCRP confers resistance on cells to (i) toxic ions such as rhodamine 123, (ii) anticancer agents including mitoxantrone and the anthracyclines daunomycin and doxorubicin, and (iii) the camptothecins topotecan and SN-38 (2-7). Overexpression of BCRP has been observed in several human cancer cell lines selected for drug resistance (2, 5, 8) as well as in tumor samples of cancer patients (9 -11). Recently, fumitremorgin C (FTC), a novel chemosensitizing agent, was identified and shown to reverse drug resistance in human BCRP-expressing cancer cells by inhibiting BCRP-mediated drug transport (12).BCRP is a 655-amino acid, 72.1-kDa protein and is the second member of the G subfamily of ABC transporters. Members of the G subfamily are all half-transporters and include among others (i) the Drosophila white, brown, and scarlet proteins, which are involved in the transport of eye pigment (13); (ii) ABCG1, which is thought to be involved in the transport of cholesterol and phospholipids (14); and (iii) heterodimeric ABCG5/ABCG8, which has been implicated in the transport of cholesterol and plant sterols (15). In contrast to P-glycoprotein MDR1 and MRP1, which are full size transporters, BCRP most likely functions as a homodimer (16).In normal tissue, high expression of the BCRP is found in stem cells (17), epithelial cells of small and large intestines, ducts and lobules of the breast, endothelial cells of veins and capillaries (18), and synchitiotrophoblastic cells of the placenta (19). The localization of BCRP suggests that it could have a potential role in protection against toxins. The recent observation in BCRP knock-out mice that BCRP protects against a chlorophyll-derived dietary phototoxin and protoporphyria is consistent with this notion (20).Previously, we have characterized the molecular basis of the drug specificity of LmrA, a half-transporter homologue of human P-glycoprotein MDR1, in the Gram-positive bacterium Lactococcus lactis (21,22). To allow a detailed comparison of BCRP and LmrA, human BCRP was functionally expressed in L. lactis using the nisin A-induced expression system that is used for the expression of LmrA. BCRP was active as an ATPdependent multidrug transporter in L. lactis and was able to interact with sterols. We conclude that the substrate specificity of BCRP partly overlaps with that proposed for ABCG1 and ABCG5/ABCG8. Our observations may suggest a physiological role f...

Nasopharyngeal carcinoma (NPC) is an uncommon cancer, which has a distinctive ethnic and geographic distribution. Etiology of NPC is considered to be related with a complex interaction of environmental and genetic factors as well as Epstein-Barr virus infection. Since NPC is located in the silent painless area, the disease is usually therefore diagnosed at the advanced stages; hence early detection of NPC is difficult. Furthermore, understanding in molecular pathogenesis is still lacking, pondering the identification of effective prognostic and diagnostic biomarkers. Dysregulation of signaling molecules in intracellular signal transduction, which regulate cell proliferation, apoptosis, and adhesion, underlines the basis of NPC pathogenesis. In this paper, the molecular signaling pathways in the NPC are discussed for the holistic view of NPC development and progression. The important insights toward NPC pathogenesis may offer strategies for identification of novel biomarkers for diagnosis and prognosis.

Clostridium difficile is a gram-positive, spore-forming enteric anaerobe which can infect humans and a wide variety of animal species. Recently, the incidence and severity of human C. difficile infection has markedly increased. In this study, we evaluated the genomic content of 73 C. difficile strains isolated from humans, horses, cattle, and pigs by comparative genomic hybridization with microarrays containing coding sequences from C. difficile strains 630 and QCD-32g58. The sequenced genome of C. difficile strain 630 was used as a reference to define a candidate core genome of C. difficile and to explore correlations between host origins and genetic diversity. Approximately 16% of the genes in strain 630 were highly conserved among all strains, representing the core complement of functional genes defining C. difficile. Absent or divergent genes in the tested strains were distributed across the entire C. difficile 630 genome and across all the predicted functional categories. Interestingly, certain genes were conserved among strains from a specific host species, but divergent in isolates with other host origins. This information provides insight into the genomic changes which might contribute to host adaptation. Due to a high degree of divergence among C. difficile strains, a core gene list from this study offers the first step toward the construction of diagnostic arrays for C. difficile.

Clostridium difficile is well recognized as the most common infectious cause of nosocomial diarrhea. The incidence and severity of C. difficile infection (CDI) is increasing worldwide. Here, we examined the transcriptional changes in the human colorectal epithelial Caco-2 cells and C. difficile simultaneously following the infection. A total of 271 transcripts in Caco-2 cells and 207 transcripts in C. difficile were significantly differentially-expressed in at least one time point during CDI. We utilized the gene ontology annotations and protein-protein network interactions to underline a framework of target molecules that could potentially play a key role during CDI. These genes included those associated with cellular metabolism, transcription, transport, cell communication, and signal transduction. Our data identified certain key factors that have previously been reported to be involved in CDI as well as novel determinants that may participate in a complex mechanism underlying host response to infection, bacterial adaptation and pathogenesis.

The ATP-binding cassette (ABC) transporter superfamily is one of the largest protein families with representatives in all kingdoms of life. Members of this superfamily are involved in a wide variety of transport processes with substrates ranging from small ions to relatively large polypeptides and polysaccharides. The G subfamily of ABC transporters consists of half-transporters, which oligomerise to form the functional transporter. While ABCG1, ABCG4 and ABCG5/8 are involved in the ATP-dependent translocation of steroids and, possibly, other lipids, ABCG2 (also termed the breast cancer resistance protein) has been identified as a multidrug transporter that confers resistance on tumor cells. Evidence will be summarized suggesting that ABCG2 can also mediate the binding/transport of non-drug substrates, including free and conjugated steroids. The characterization of the substrate specificities of ABCG proteins at a molecular level might provide further clues about their potential physiological role(s), and create new opportunities for the modulation of their activities in relation to human disease.

Microarray-based comparative genome hybridisations (CGH) and genome sequencing of Clostridium difficile isolates have shown that the genomes of this species are highly variable. To further characterize their genome variation, we employed integration of data from CGH, genome sequencing and putative cellular pathways. Transcontinental strain comparison using CGH data confirmed the emergence of a human-specific hypervirulent cluster. However, there was no correlation between total toxin production and hypervirulent phenotype, indicating the possibility of involvement of additional factors towards hypervirulence. Calculation of C. difficile core and pan genome size using CGH and sequence data estimated that the core genome is composed of 947 to 1,033 genes and a pan genome comprised of 9,640 genes. The reconstruction, annotation and analysis of cellular pathways revealed highly conserved pathways despite large genome variation. However, few pathways such as tetrahydrofolate biosynthesis were found to be variable and could be contributing to adaptation towards virulence such as antibiotic resistance.