Cloning and Functional Analysis of the Rhesus Macaque ABCG2 Gene

ABCG2 regulates the pattern of self-renewing divisions in cisplatin-resistant non-small cell lung cancer cell lines

Overexpression of ABCG2 is considered a major mechanism of cancer drug resistance. Recent studies have shown that ABCG2 can regulate the switch between symmetric and asymmetric cell division in adult stem cells; however, the relationship between ABCG2 and cell division in drug-resistant cancer cells remains to be determined. In the present study, we demonstrated that ABCG2 is involved in the cell division of drug-resistant cancer cells. We first established drug-resistant H460 and A549 cell lines by repeated exposure to cisplatin and found that the expression of ABCG2 in these cell lines was significantly increased. As evidenced by PKH-26 staining, these drug-resistant cell lines favored symmetric division, which differed from the asymmetric division of the parental cells. Furthermore, we established stable ABCG2‑overexpressing and stable shRNA-ABCG2‑knockdown cell lines to evaluate the potential role of ABCG2 in cancer cell division. The results showed that overexpression of ABCG2 in A549 parental cells significantly increased the proportion of symmetric division, whereas knockdown of ABCG2 in drug-resistant A549 cells significantly increased the proportion of asymmetric division. Taken together, our findings suggest that ABCG2 is involved in the modulation of cancer drug resistance by regulating the pattern of cell division. The present study provides novel insight into the role of ABCG2 in cancer treatment resistance.

Side populations from cervical-cancer-derived cell lines have stem-cell-like properties

The target cells for the transforming mutations caused by high-risk human papillomavirus (HPV) infection could be the stem cells of the uterine cervical epithelium, generating particular cancer stem cells (CSCs). The aim of this study was to identify and characterize the CSCs from cervical-cancer-derived cell lines. The ability of SiHa, CaLo, and C-33A cell lines to efflux Hoechst 33342 was evaluated by flow cytometry and cells from the corresponding side populations (SPs) and nonside populations (NSPs) were analyzed for their cell-cycle status (pyronin Y) and their mRNA levels of ABC transporter family members (with qPCR). Specific markers (α6-integrin(bri)/CD71(dim), CK17) of normal epithelial stem cells were evaluated by flow cytometry. The biological properties of these cells were analyzed, including their colony heterogeneity, repopulation, and anchorage-independent colony formation. We identified SPs (around 3 %) in the SiHa and CaLo cell lines, more than 70 % of which were in G0 phase and strongly expressed ABC transporters (predominantly ABCG2 and ABCB1). The SP from CaLo cells showed an α6-integrin(bri)/CD(dim) pattern, whereas the SP from the SiHa cells showed an α6-integrin(-)/CD(dim) pattern. Recultured cells from the SPs of both cell lines generated both SPs and NSPs, and had higher clonogenic potential to form mainly holoclones and greater colony-forming efficiency under anchorage-independent growth conditions than the cells from the NSPs or total cell populations. Interestingly, we identified no SP in the HPV-uninfected C-33A cell line, and it did not express ABCG2 or other members of the ABC transporters (ABCB1, ABCC1, or ABCA3).

Glutathione transport is a unique function of the ATP-binding cassette protein ABCG2

Glutathione (GSH) transport is vital for maintenance of intracellular and extracellular redox balance. Only a few human proteins have been identified as transporters of GSH, glutathione disulfide (GSSG) and/or GSH conjugates (GS-X). Human epithelial MDA1586, A549, H1975, H460, HN4, and H157 cell lines were exposed to 2',5'-dihydroxychalcone, which induces a GSH efflux response. A real-time gene superarray for 84 proteins found in families that have a known role in GSH, GSSG, and/or GS-X transport was employed to help identify potential GSH transporters. ABCG2 was identified as the only gene in the array that closely corresponded with the magnitude of 2',5'-dihydroxychalcone (2',5'-DHC)-induced GSH efflux. The role of human ABCG2 as a novel GSH transporter was verified in a Saccharomyces cerevisiae galactose-inducible gene expression system. Yeast expressing human ABCG2 had 2.5-fold more extracellular GSH compared with those not expressing ABCG2. GSH efflux in ABCG2-expressing yeast was abolished by the ABCG2 substrate methotrexate (10 microM), indicating competitive inhibition. In contrast, 2',5'-DHC treatment of ABCG2-expressing yeast increased extracellular GSH levels in a dose-dependent manner with a maximum 3.5-fold increase in GSH after 24 h. In addition, suppression of ABCG2 with short hairpin RNA or ABCG2 overexpression in human epithelial cells decreased or increased extracellular GSH levels, respectively. Our data indicate that ABCG2 is a novel GSH transporter.

Side population cells in developing human liver are primarily haematopoietic progenitor cells

Side population (SP) cells have recently been identified in a number of tissues although their phenotype and functional abilities are poorly understood. Surface marker characterisation and functional assessment of developing liver SP cells might allow for their isolation and manipulation using clinically relevant techniques. It was hypothesised that SP cells are present early during human liver development and contribute to haematopoietic and epithelial lineage generation. Whilst the SP population remained positive for CD34 during the 1st and 2nd trimester, 1st trimester SP cells were more highly enriched for haematopoietic and epithelial progenitor activity than those from the 2nd trimester in vitro. Marker expression and functional similarities indicate that SP cells in developing human liver may share a temporal relationship with oval/progenitor cells, responsible for liver regeneration after massive or chronic hepatic injury. Furthermore, modification of SP integrin expression during development suggests a potential adaptive interaction with niche components such as fibronectin. Improved understanding of developing human liver SP cells will contribute to the generation of novel cell-based therapies for liver disease.

BCRP/ABCG2 in the placenta: expression, function and regulation

Knowledge concerning transport of maternally administered drugs across the placental barrier is essential for determining potential toxicity of drugs to the fetus and the value of drug therapy during pregnancy. An important determinant for fetal drug exposure is the expression of efflux transporters in the placenta. Among human tissues, the ATP-binding cassette efflux transporter BCRP (gene symbol ABCG2) is most abundantly expressed in the apical membrane of placental syncytiotrophoblasts. Although the precise physiological role of BCRP in the placenta is still unclear, existing data strongly suggest that BCRP plays an important role in protecting the fetus against the potential toxicity of drugs, xenobiotics, and metabolites by expelling them across the placental barrier. In this review, we summarize the current knowledge with respect to the expression, function, and polymorphisms of BCRP, as well as transcriptional and posttranscriptional regulation of the transporter in the placenta. Finally, clinical significance of BCRP in the placenta for drug therapy in pregnant women is discussed.

Cloning, sequence and functional analysis of goat ATP-binding cassette transporter G2 (ABCG2)

ATP-binding cassette transporter G2 (ABCG2) gene encodes a protein that has a wide variety of substrates and is responsible for the active secretion of clinically and toxicologically important molecules into milk. Although known in many species, this marks the first time this gene product has been reported in goats. In this study, we cloned and sequenced goat ABCG2 gene complete coding sequence and predicted its putative translated protein structure with implicative functional domains. One six-transmembrane span on C-terminal region and at least one coiled-coil domain on N-terminal were predicted and compared primarily with those of other closely related species. In addition, three conserved cysteines (in positions 595, 606, and 611) were determined toward the C-terminal of goat's ABCG2. Two known functional motifs were identified in goat's protein through comparative studies with other species. The goat ABCG2 relative expression profile revealed that the gene expression was a function of lactation stage and parallel to goat lactation curve.

Characterization and localization of side population (SP) cells in zebrafish kidney hematopoietic tissue

We previously showed that side population (SP) cells, characterized by specific Hoechst dye efflux pattern in flow cytometric analysis, were present in teleost kidney hematopoietic tissue, and that kidney SP cells were enriched in hematopoietic stem cells (HSCs). ABCG2/Abcg2 is an ATP-binding cassette (ABC) transporter that is known to be associated with Hoechst dye efflux activity of mammalian HSCs. In the present study, we examined the expression and function of Abcg2 in kidney SP cells from zebrafish (Danio rerio). Although the zebrafish genome has 4 paralogous copies of ABCG2 (zAbcg2a, b, c, and d), zAbcg2a and zAbcg2c mRNA was expressed in kidney SP cells. Transfection of COS-7 cells with zAbcg2a and zAbcg2c showed that zAbcg2a was directly associated with the SP phenotype. These results indicate that zAbcg2a mRNA is a useful marker for zebrafish HSCs. In situ hybridization in kidney tissue showed that zAbcg2a-positive cells were sporadically localized on the surface of renal tubules, and tightly adhered to renal tubule epithelial cells. This result suggests that teleost HSCs adhere to the surface of renal tubules, and that renal tubule epithelial cells are a key component of HSC niche in teleosts.

ATP-binding-cassette transporters in hematopoietic stem cells and their utility as therapeutical targets in acute and chronic myeloid leukemia

ATP-binding-cassette (ABC) transporters are evolutionary extremely well-conserved transmembrane proteins that are highly expressed in hematopoietic stem cells (HSCs). The physiological function in human stem cells is believed to be protection against genetic damage caused by both environmental and naturally occurring xenobiotics. Additionally, ABC transporters have been implicated in the maintenance of quiescence and cell fate decisions of stem cells. These physiological roles suggest a potential role in the pathogenesis and biology of stem cell-derived hematological malignancies such as acute and chronic myeloid leukemia. This paper reviews the (patho)physiological role of ABC transporters in human normal and malignant HSCs and discusses its implications for their utility as therapeutical targets to eradicate leukemic stem cells in these diseases.

ABC transporters, neural stem cells and neurogenesis – a different perspective

Stem cells intrigue. They have the ability to divide exponentially, recreate the stem cell compartment, as well as create differentiated cells to generate tissues. Therefore, they should be natural candidates to provide a renewable source of cells for transplantation applied in regenerative medicine. Stem cells have the capacity to generate specific tissues or even whole organs like the blood, heart, or bones. A subgroup of stem cells, the neural stem cells (NSCs), is characterized as a self-renewing population that generates neurons and glia of the developing brain. They can be isolated, genetically manipulated and differentiated in vitro and reintroduced into a developing, adult or a pathologically altered central nervous system. NSCs have been considered for use in cell replacement therapies in various neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. Characterization of genes with tightly controlled expression patterns during differentiation represents an approach to understanding the regulation of stem cell commitment. The regulation of stem cell biology by the ATP-binding cassette (ABC) transporters has emerged as an important new field of investigation. As a major focus of stem cell research is in the manipulation of cells to enable differentiation into a targeted cell population; in this review, we discuss recent literatures on ABC transporters and stem cells, and propose an integrated view on the role of the ABC transporters, especially ABCA2, ABCA3, ABCB1 and ABCG2, in NSCs' proliferation, differentiation and regulation, along with comparisons to that in hematopoietic and other stem cells.

Progress and prospects: cell based regenerative therapy for cardiovascular disease

Experimental and clinical studies are progressing simultaneously to investigate the mechanisms and efficacy of progenitor cell treatment after an acute myocardial infarction and in chronic congestive heart failure. Multipotent progenitor cells appear to be capable of improving cardiac perfusion and/or function; however, the mechanisms still are unclear, and the issue of whether or not trans-differentiation occurs remains unsettled. Both experimentally and clinically, cells originating from different tissues have been shown capable of restoring cardiac function, but more recently multiple groups have identified resident cardiac progenitor cells that seem to participate in regenerating the heart after injury. Clinically, cells originating from blood or bone marrow have been proven to be safe whereas injection of skeletal myoblasts has been associated with the occurrence of ventricular arrhythmias. Myoblasts can transform into rapidly beating myotubes; however, thus far convincing evidence for electro-mechanical coupling between myoblasts and cardiomyocytes is lacking. Moving forward, mechanistic studies will benefit from the use of genetic markers and Cre/lox reporter systems that are less prone to misinterpretation than fluorescent antibodies, and a more convincing answer regarding therapeutic efficacy will come from adequately powered randomized placebo controlled trials.

Role of ABCG2/BCRP in biology and medicine

The protein variously named ABCG2/BCRP/MXR/ABCP is a recently described ATP-binding cassette (ABC) transporter originally identified by its ability to confer drug resistance that is independent of Mrp1 (multidrug-resistance protein 1) and Pgp (P-glycoprotein). Unlike Mrp1 and Pgp, ABCG2 is a half-transporter that must homodimerize to acquire transport activity. ABCG2 is found in a variety of stem cells and may protect them from exogenous and endogenous toxins. ABCG2 expression is upregulated under low-oxygen conditions, consistent with its high expression in tissues exposed to low-oxygen environments. ABCG2 interacts with heme and other porphyrins and protects cells and/or tissues from protoporphyrin accumulation under hypoxic conditions. Individuals who carry ABCG2 alleles that have impaired function may be more susceptible to porphyrin-induced toxicity. Abcg2 knock-out models have allowed in vivo studies of Abcg2 function in host and cellular defense. In combination with immunohistochemical analyses, these studies have revealed how ABCG2 influences the absorption, distribution, and excretion of drugs and cytotoxins.