Polarized expression of monocarboxylate transporters in human retinal pigment epithelium and ARPE-19 cells.
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PURPOSE: To evaluate the expression and subcellular distribution of proton-coupled monocarboxylate transporters (MCTs) in human RPE in vivo and determine whether ARPE-19 cells retain the ability to express and differentially polarize these transporters. METHODS: Total RNA was prepared from human donor eyes and from ARPE-19 cell cultures. Expression of MCT transcripts was evaluated by RT-PCR amplification. Expression of MCT proteins in human RPE and ARPE-19 cells was evaluated by immunolocalization and Western blot analysis with isoform-specific anti-peptide antibodies. RESULTS: The expression of MCTs in human RPE was investigated by immunofluorescence analysis on frozen sections of human donor eyes. MCT1 antibody labeled the apical membrane of the RPE intensely, whereas MCT3 labeling was restricted to the basolateral membrane. MCT4 was detected in the neural retina but not in the RPE. ARPE-19 cells constitutively expressed MCT1 and MCT4 mRNAs. Expression of MCT3 mRNA increased over time as ARPE-19 cells established a differentiated phenotype. Western blot analysis revealed that ARPE-19 cells expressed high levels of MCT1 and MCT4 but very little MCT3 protein. Sections of differentiated ARPE-19 cells were labeled with MCT1, MCT4, and glucose transporter-1 antibodies. MCT1 was polarized to the apical membrane and MCT4 to the basolateral membrane, whereas GLUT1 was expressed in both membrane domains. CD147, which is necessary for targeting MCTs to the plasma membrane, was detected in the apical and basolateral membranes of human RPE in situ and ARPE-19 cells. CONCLUSIONS: These studies demonstrate for the first time that human RPE expresses two proton-coupled monocarboxylate transporters: MCT1 in the apical membrane and MCT3 in the basolateral membrane. The coordinated activities of these two transporters could facilitate the flux of lactate from the retina to the choroid. ARPE-19 cells express two MCT isoforms, polarized to different membrane domains: MCT1 to the apical membrane and MCT4 to the basolateral membrane. The polarized expression of MCTs in ARPE-19 demonstrates that these cells retain the cellular machinery necessary for transepithelial transport of lactate. (+info)
Overexpression of extracellular matrix metalloproteinase inducer in multidrug resistant cancer cells.
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Multidrug resistant (MDR) cancer cells overexpressing P-glycoprotein (P-gp) display variations in invasive and metastatic behavior. We previously reported that these properties of MDR cancer cell lines overexpressing P-gp could be altered by chemotherapeutic drugs or MDR modulators (R. S. Kerbel et al., Cancer Surv., 7: 597-629, 1988). To attempt to clarify the mechanism(s) underlying these observations, we studied the expression of extracellular matrix metalloproteinase inducer (EMMPRIN), a glycoprotein enriched on the surface of tumor cells that can stimulate the production of matrix metalloproteinases (MMPs), in sensitive and MDR cancer cells. Using immunofluorescence staining and fluorescence-activated cell sorting analysis, we found that EMMPRIN expression was increased in MDR carcinoma cell lines, MCF-7/AdrR, KBV-1, and A2780Dx5, as compared to their parental counterparts. The MDR cell lines produced more matrix metalloproteinase-1 (MMP-1), matrix metalloproteinase-2 (MMP-2), and matrix metalloproteinase-9 (MMP-9), as determined by zymography, Western blot, and reverse transcription-PCR. Treatment of MDR cells with an anti-EMMPRIN antibody inhibited the activity of MMP-1, MMP-2, and MMP-9. In MDR cell line MCF-7/AdrR, an increased in vitro invasive ability was observed as compared with the sensitive line MCF-7, and EMMPRIN antibody could inhibit the in vitro invasion in drug-resistant cells. In addition, the expression and activity of MMP-1, MMP-2, and MMP-9 in MDR cells were decreased by treatment with U-0126, an inhibitor of mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/Erk). Our results suggest that during the development of MDR, the expression of EMMPRIN is responsible for the increased activity of MMP in MDR cell lines. (+info)
Regulation of multidrug resistance in cancer cells by hyaluronan.
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Multidrug resistance in cancer cells is often due to ATP-dependent efflux pumps, but is also linked to alterations in cell survival and apoptotic signaling pathways. We have found previously that perturbation of hyaluronan-tumor cell interaction by treatment with hyaluronan oligosaccharides suppresses the phosphoinositide 3-kinase/Akt cell survival signaling pathway in cancer cells and reduces tumor growth in vivo. Here we find that these oligomers suppress both the MAP kinase and phosphoinositide 3-kinase pathways in multidrug resistant tumor cells and sensitize these cells to a variety of chemotherapeutic drugs. On the other hand, increased hyaluronan production induces resistance in drug-sensitive tumor cells. Likewise, increased expression of emmprin, which is a glycoprotein that is present on the surface of most malignant cancer cells and that stimulates hyaluronan production, also induces increased resistance. Thus, perturbation of hyaluronan signaling may provide a dual therapeutic role, since it has intrinsic suppressive effects on tumor growth as well as sensitizing cancer cells to chemotherapeutic agents. (+info)
Selective inhibition of T cell activation via CD147 through novel modulation of lipid rafts.
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The plasma membrane is compartmentalized into microdomains and the association/dissociation of receptors and signaling molecules with/from these membrane domains is a major principle for regulation of signal transduction. By following the reorganization of microdomains on living cells and performing biochemical studies, we show that Ab targeting of the T cell activation-associated Ag CD147 prevents TCR stimulation-dependent reorganization and clustering of microdomains. Triggering CD147 induces a displacement of the GPI-anchored coreceptors CD48 and CD59 from microdomains in human T lymphocytes. This perturbation of microdomains is accompanied by a selective inhibition of TCR-mediated T cell proliferation. The CD147-inhibited cells secret normal levels of IL-2 but acquire reduced amounts of the IL-2 receptor alpha-chain CD25. These results indicate that negative regulating signals can modulate microdomains and suggest a general mechanism for inhibition of receptor signaling. (+info)
Retina-specific expression of 5A11/Basigin-2, a member of the immunoglobulin gene superfamily.
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PURPOSE: 5A11/Basigin has recently been identified as a critical glycoprotein for full maturity and function of the mouse retina. However, the biological function of 5A11/Basigin has yet to be determined. Previous reports indicate the presence of multiple 5A11/Basigin polypeptides within the retina. Therefore, in an effort to determine the function of 5A11/Basigin, the molecular diversity of its expression was evaluated. METHODS: Northern blot and immunoblot techniques were used to evaluate the number of forms of 5A11/Basigin in the mouse retina. cDNA cloning, using a mouse retina library or RT-PCR from rat, chicken, zebrafish, and human retina, was performed to determine the sequence of 5A11/Basigin transcripts. A peptide was generated, based on the deduced amino acid sequence, for subsequent antibody production. Localization of 5A11/Basigin expression was evaluated by immunoblot, immunohistochemistry, and real-time RT-PCR. RESULTS: Two 5A11/Basigin transcripts of approximately 1.5 kb and approximately 1.8 kb, which correspond to glycosylated proteins of approximately 45 and approximately 55 kDa, respectively, were identified in mouse retina. The shorter form was previously cloned. However, the longer form, a splice variant of mouse 5A11/Basigin, is a member of the immunoglobulin gene superfamily and has been named 5A11/Basigin-2. Homologous transcripts were also cloned from rat, chicken, zebrafish, and human retina. 5A11/Basigin-2 expression was limited to the retina, specifically to photoreceptor cells, where it appeared to be most concentrated in the inner segments. CONCLUSIONS: The specific and limited expression of 5A11/Basigin-2 explicitly within photoreceptor cells implies that this glycoprotein plays a fundamental role within the retina. However, its role remains to be determined. (+info)
Inhibitory effects of antisense RNA of HAb18G/CD147 on invasion of hepatocellular carcinoma cells in vitro.
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AIM: To study the inhibitory effects of antisense RNA of HAb18G/CD147 on invasion of hepatocellular carcinoma(HCC) cells in vitro. METHODS: Antisense RNA of HAb18G/CD147 vector PCI-asHAb18G was constructed by reversely inserting HAb18G/CD147 cDNA to eukaryotic expression vector PCI-neo. The HCC cell line HHCC was transfected by PCI-asHAb18G via cation liposome. Expression of HAb18G/CD147 of transfected cells selected by G418 (geneticin) was observed by immuno-histochemical SP staining and FACS (fluorescence activated cell sorting). Gelatin zymography was used to determine the effect of PCI-asHAb18G on reducing secretions of MMP-2 and MMP-9 of the transfected cells. Boyden chamber was employed to test the invasion of HCC cells in vitro. RESULTS: The construction of antisense RNA vector PCI-asHAb18G was verified correct by partial nucleotide sequencing and restricted endonuclease digestion. The expression of HAb18G/CD147 in transfected HHCC was inhibited by PCI-asHAb18G. Secretions of MMP-2 and MMP-9 of transfected HHCC were reduced and the invasion of transfected HHCC was inhibited compared to HHCC, respectively. CONCLUSION: Invasion of HCC cells can be inhibited by antisense RNA of HAb18G/CD147. HAb18G/CD147 may be used as a potential target of drugs for anti-invasion and metastasis of HCC. (+info)
A novel form of the membrane protein CD147 that contains an extra Ig-like domain and interacts homophilically.
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BACKGROUND: CD147 is a broadly distributed integral membrane glycoprotein with two Ig-like domains implicated in a wide range of functions. It is associated at the cell surface with the monocarboxylate transporters MCT1 and 4 but interactions of the extracellular region have not been characterised. RESULTS: We report the characterisation of a form of CD147 with an additional membrane-distal Ig-like domain. In contrast to the two domain form, this three domain form of CD147 interacts homophilically. Surface plasmon resonance analysis using recombinant proteins showed that the interaction was of low affinity (KD approximately 40 microM) and this is typical of many interactions between membrane proteins. cDNA for the 3 domain form are rare but have been identified in human and mouse retina. CONCLUSION: The finding that the three domain form of CD147 has an extracellular ligand, that is it interacts homophilically, suggests this interaction may be important in aligning lactate transporters in the retina where lactate is an important metabolite. (+info)
MCT1 and its accessory protein CD147 are differentially regulated by TSH in rat thyroid cells.
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In thyroid cells, basal and TSH-stimulated glycolysis is associated with lactic acid efflux. In this report, we address whether monocarboxylate transporters (MCTs) are present in thyroid tissue for exporting excess lactic acid generated by aerobic glycolysis. Using immunostaining techniques, we show that MCT4 localizes with its accessory protein CD147 in the basolateral membrane of rat thyroid follicular cells. In cultured rat thyroid (FRTL-5) cells, MCT1 rather than MCT4 is expressed. CD147 colocalizes and coimmunoprecipitates with MCT1. TSH upregulates MCT1/CD147 expression as a function of time through a cAMP-dependent mechanism as forskolin reproduces the effect of TSH. TSH enhances protein expression of both MCT1 and CD147 in FRTL-5 cells. Whereas MCT1 protein expression is controlled at the level of transcription, CD147 protein expression is regulated by a posttranscriptional mechanism. Results of these studies suggest that hormone stimulation of lactate transport is mediated by regulating MCT1 transcription. (+info)