Cloning of the rabbit homologue of mouse 'basigin' and rat 'OX-47': kidney cell type-specific expression, and regulation in collecting duct cells

Intestinal OCTN2- and MCT1-targeted drug delivery to improve oral bioavailability

Various drug transporters are widely expressed throughout the intestine and play important roles in absorbing nutrients and drugs, thus providing high quality targets for the design of prodrugs or nanoparticles to facilitate oral drug delivery. In particular, intestinal carnitine/organic cation transporter 2 (OCTN2) and mono-carboxylate transporter protein 1 (MCT1) possess high transport capacities and complementary distributions. Therefore, we outline recent developments in transporter-targeted oral drug delivery with regard to the OCTN2 and MCT1 proteins in this review. First, basic information of the two transporters is reviewed, including their topological structures, characteristics and functions, expression and key features of their substrates. Furthermore, progress in transporter-targeting prodrugs and nanoparticles to increase oral drug delivery is discussed, including improvements in the oral absorption of anti-inflammatory drugs, antiepileptic drugs and anticancer drugs. Finally, the potential of a dual transporter-targeting strategy is discussed.

How, with whom and when: an overview of CD147-mediated regulatory networks influencing matrix metalloproteinase activity

Matrix metalloproteinases (MMPs) comprise a family of 23 zinc-dependent enzymes involved in various pathologic and physiologic processes. In cancer, MMPs contribute to processes from tumour initiation to establishment of distant metastases. Complex signalling and protein transport networks regulate MMP synthesis, cell surface presentation and release. Earlier attempts to disrupt MMP activity in patients have proven to be intolerable and with underwhelming clinical efficacy; thus targeting ancillary proteins that regulate MMP activity may be a useful therapeutic approach. Extracellular matrix metalloproteinase inducer (EMMPRIN) was originally characterized as a factor present on lung cancer cells, which stimulated collagenase (MMP-1) production in fibroblasts. Subsequent studies demonstrated that EMMPRIN was identical with several other protein factors, including basigin (Bsg), all of which are now commonly termed CD147. CD147 modulates the synthesis and activity of soluble and membrane-bound [membrane-type MMPs (MT-MMPs)] in various contexts via homophilic/heterophilic cell interactions, vesicular shedding or cell-autonomous processes. CD147 also participates in inflammation, nutrient and drug transporter activity, microbial pathology and developmental processes. Despite the hundreds of manuscripts demonstrating CD147-mediated MMP regulation, the molecular underpinnings governing this process have not been fully elucidated. The present review summarizes our present knowledge of the complex regulatory systems influencing CD147 biology and provides a framework to understand how CD147 may influence MMP activity.

The roles of CD147 and/or cyclophilin A in kidney diseases

CD147 is a widely expressed integral plasma membrane glycoprotein and has been involved in a variety of physiological and pathological activities in combination with different partners, including cyclophilins, caveolin-1, monocarboxylate transporters, and integrins. Recent data demonstrate that both CyPA and CD147 significantly contribute to renal inflammation, acute kidney injury, renal fibrosis, and renal cell carcinoma. Here we review the current understanding of cyclophilin A and CD147 expression and functions in kidney diseases and potential implications for treatment of kidney diseases.

Localization of members of MCT monocarboxylate transporter family Slc16 in the kidney and regulation during metabolic acidosis

The monocarboxylate transporter family (MCT) comprises 14 members with distinct transport properties and tissue distribution. The kidney expresses several members of the MCT family, but only little is known about their exact distribution and function. Here, we investigated selected members of the MCT family in the mouse kidney. MCT1, MCT2, MCT7, and MCT8 localized to basolateral membranes of the epithelial cells lining the nephron. MCT1 and MCT8 were detected in proximal tubule cells whereas MCT7 and MCT2 were located in the thick ascending limb and the distal tubule. CD147, a β-subunit of MCT1 and MCT4, showed partially overlapping expression with MCT1 and MCT2. However, CD147 was also found in intercalated cells. We also detected SMCT1 and SMCT2, two Na+-dependent monocarboxylate cotransporters, on the luminal membrane of type A intercalated cells. Moreover, mice were given an acid load for 2 and 7 days. Acidotic animals showed a marked but transient increase in urinary lactate excretion. During acidosis, a downregulation of MCT1, MCT8, and SMCT2 was observed at the mRNA level, whereas MCT7 and SMCT1 showed increased mRNA abundance. Only MCT7 showed lower protein abundance whereas all other transporters remained unchanged. In summary, we describe for the first time the localization of various MCT transporters in mammalian kidney and demonstrate that metabolic acidosis induces a transient increase in urinary lactate excretion paralleled by lower MCT7 protein expression.

Cyclophilin-CD147 interactions: a new target for anti-inflammatory therapeutics

CD147 is a widely expressed plasma membrane protein that has been implicated in a variety of physiological and pathological activities. It is best known for its ability to function as extracellular matrix metalloproteinase inducer (hence the other name for this protein, EMMPRIN), but has also been shown to regulate lymphocyte responsiveness, monocarboxylate transporter expression and spermatogenesis. These functions reflect multiple interacting partners of CD147. Among these CD147-interacting proteins cyclophilins represent a particularly interesting class, both in terms of structural considerations and potential medical implications. CD147 has been shown to function as a signalling receptor for extracellular cyclophilins A and B and to mediate chemotactic activity of cyclophilins towards a variety of immune cells. Recent studies using in vitro and in vivo models have demonstrated a role for cyclophilin-CD147 interactions in the regulation of inflammatory responses in a number of diseases, including acute lung inflammation, rheumatoid arthritis and cardiovascular disease. Agents targeting either CD147 or cyclophilin activity showed significant anti-inflammatory effects in experimental models, suggesting CD147-cyclophilin interactions may be a good target for new anti-inflammatory therapeutics. Here, we review the recent literature on different aspects of cyclophilin-CD147 interactions and their role in inflammatory diseases.

Extracellular matrix metalloproteinase inducer is expressed in the proximal tubular epithelial cells of the human kidney

AIM

Matrix metalloproteinases (MMP) affect matrix remodelling, and extracellular matrix metalloproteinase inducer (EMMPRIN) has been reported to increase the levels of several MMP. However, the expression of EMMPRIN in the human kidney and its regulatory mechanisms are not well known. In this study, we examined EMMPRIN expression in the human kidney with the biopsied specimens, cultured proximal tubular epithelial cells (PTEC) and human mesangial cells (HMC).

METHODS

EMMPRIN expression was examined by immunofluorescent (IF) study, reverse transcription polymerase chain reaction, western blotting and enzyme-linked immunosorbent assay. We also examined soluble EMMPRIN in the conditioned medium of PTEC stimulated by various agents and its effect in the activities of MMP-2 and MMP-9. Also, IF study in the several kidney diseases was performed to elucidate its role in pathological condition.

RESULTS

EMMPRIN expression was diffusely observed in the tubular epithelial cells of most patients and healthy adults, but was never observed in glomeruli. Cultured PTEC expressed EMMPRIN, while HMC did not. Soluble EMMPRIN was also detected by enzyme-linked immunosorbent assay in the conditioned medium of PTEC. Epidermal growth factor (50 ng/mL) and phorbol 12-myristate 13-acetate (10(-7) mol/L) stimulated the secretion of soluble EMMPRIN and increased the MMP-2 activity, although these agents did not increase the level of EMMPRIN mRNA. From the IF study, EMMPRIN expression was shown to decrease in tubulointerstitial nephritis.

CONCLUSION

EMMPRIN is widely distributed in the tubular epithelial cells of the adult human kidney and may regulate MMP-2 activity via its secretion from PTEC.

Dealing with the family: CD147 interactions with cyclophilins

CD147 is a widely expressed plasma membrane protein that has been implicated in a variety of physiological and pathological activities. It is best known for its ability to function as extracellular matrix metalloproteinase inducer (hence the other name for this protein, EMMPRIN), but has also been shown to regulate lymphocyte responsiveness, monocarboxylate transporter expression and spermatogenesis. These functions reflect multiple interacting partners of CD147. Recently, interaction of CD147 with proteins of the cyclophilin family has been demonstrated and activity of CD147 as a signalling receptor to extracellular cyclophilins A and B has been shown. Given that extracellular cyclophilins are potent chemotactic agents for various immune cells, further studies of the role of cyclophilin-CD147 interaction in inflammation followed. They demonstrated that agents targeting CD147 or cyclophilin had a significant anti-inflammatory effect in animal models of acute or chronic lung diseases and rheumatoid arthritis. Here, we review the current knowledge about interactions between CD147 and cyclophilins.

Basigin (CD147) is the target for organomercurial inhibition of monocarboxylate transporter isoforms 1 and 4: the ancillary protein for the insensitive MCT2 is EMBIGIN (gp70)

Translocation of monocarboxylate transporters MCT1 and MCT4 to the plasma membrane requires CD147 (basigin) with which they remain tightly associated. However, the importance of CD147 for MCT activity is unclear. MCT1 and MCT4 are both inhibited by the cell-impermeant organomercurial reagent p-chloromercuribenzene sulfonate (pCMBS). Here we demonstrate by site-directed mutagenesis that removal of all accessible cysteine residues on MCT4 does not prevent this inhibition. pCMBS treatment of cells abolished co-immunoprecipitation of MCT1 and MCT4 with CD147 and enhanced labeling of CD147 with a biotinylated-thiol reagent. This suggested that CD147 might be the target of pCMBS, and further evidence for this was obtained by treatment of cells with the bifunctional organomercurial reagent fluorescein dimercury acetate that caused oligomerization of CD147. Site-directed mutagenesis of CD147 implicated the disulfide bridge in the Ig-like C2 domain of CD147 as the target of pCMBS attack. MCT2, which is pCMBS-insensitive, was found to co-immunoprecipitate with gp70 rather than CD147. The interaction between gp70 and MCT2 was confirmed using fluorescence resonance energy transfer between the cyan fluorescent protein- and yellow fluorescent protein-tagged MCT2 and gp70. pCMBS strongly inhibited lactate transport into rabbit erythrocytes, where MCT1 interacts with CD147, but not into rat erythrocytes where it interacts with gp70. These data imply that inhibition of MCT1 and MCT4 activity by pCMBS is mediated through its binding to CD147, whereas MCT2, which associates with gp70, is insensitive to pCMBS. We conclude that ancillary proteins are required to maintain the catalytic activity of MCTs as well as for their translocation to the plasma membrane.

Animal models of implantation

Implantation is an intricately timed event necessary in the process of viviparous birth that allows mammals to nourish and protect their young during early development. Human implantation begins when the blastocyst both assumes a fixed position in the uterus and establishes a more intimate relationship with the endometrium. Due to the impracticalities of studying implantation in humans, animal models are necessary to decipher the molecular and mechanical events of this process. This review will discuss the differences in implantation between different animal models and describe how these differences can be utilized to investigate discrete implantation stages. In addition, factors that have been shown to be involved in implantation in the human and other various animal models including growth factors, cytokines, modulators of cell adhesion, and developmental factors will be discussed, and examples from each will be given.

The immunoglobulin-superfamily molecule basigin is a binding protein for oligomannosidic carbohydrates: an anti-idiotypic approach

Recognition molecules that carry carbohydrate structures regulate cell interactions during development and play important roles in synaptic plasticity and regeneration in the adult. Glycans appear to be involved in these interactions. We have searched for binding proteins for oligomannosidic structures using the L3 antibody directed against high mannose-type glycans in an anti-idiotypic approach. A selected monoclonal anti-idiotype antibody was used for affinity chromatography and identified basigin as a binding protein from mouse brain detergent lysates. Basigin was found to bind to high mannose-carrying cell recognition molecules, such as myelin-associated glycoprotein, L1, the beta2-subunit of Na+/K+-ATPase and an oligomannosidic neoglycolipid. Furthermore, basigin was involved in outgrowth of astrocytic processes in vitro. A striking homology between the first immunoglobulin (Ig)-like domain of basigin and the fourth Ig-like domain of NCAM, previously shown to bind to oligomannosidic glycans, and the lectin domain of the mannose receptor confirms that basigin is an oligomannose binding lectin. To our knowledge this is the first report that anti-idiotypic antibodies can be used to identify binding partners for carbohydrates.

Expression of Basigin in human fetal, infantile and adult skin and in basal cell carcinoma

BACKGROUND

Basigin is a glycosylated transmembrane protein belonging to the immunoglobulin superfamily and is thought to be associated with cell development and differentiation. We investigated the relation between Basigin expression and epidermal development in this study.

METHODS

Basigin expression was immunohistochemically investigated during organogenesis of human skin and in human basal cell carcinoma (BCC).

RESULTS

Human fetal skin showed negative staining at 10 weeks of gestation. At 20 weeks, the cytoplasm and membranes of adnexal germ and hair follicular cells were strongly positive, while epidermal basal cells showed weakly positive staining. After birth, basal cells, suprabasal cells, anagen hair follicular cells and eccrine glandular cells showed positive staining. Membranes of basal cells expressed more Basigin compared to other cell components. Basigin was not detectable in granular cells and telogen hair follicular cells. Sixteen of 30 BCCs were entirely negative for Basigin. However, cells at budding areas of tumor masses were positive in 14 of the 30 BCCs.

CONCLUSIONS

These findings suggest that 1) Basigin is associated with epidermal proliferation and differentiation, 2) most parts of BCCs might be derived from early fetal epidermal basal cells, and 3) that a part, only the budding area of BCCs, has the characteristics of epithelial germ cells.

Red blood cell surface adhesion molecules: their possible roles in normal human physiology and disease

Human erythrocytes express a relatively large number of known adhesion receptors, despite the fact that red blood cells (RBCs) are generally considered to be nonadhesive for endothelial cell surfaces. Some of these adhesion receptors are expressed by many other tissues, while others have more limited tissue distribution. Some adhesion receptors, including CD36 and VLA-4, are only expressed by immature erythroid cells, while others are present on mature erythrocytes. The structure and function of these proteins is reviewed here. LW, CD36, CD58, and CD147 have been shown in other tissues to mediate cell-cell interaction. Other receptors, such as CD44, VLA-4, and B-CAM/LU, can mediate adhesion to components of extracellular matrix. In addition, their roles in normal erythropolesis, as well as in the pathophysiology of human disease, are summarized. The most convincing evidence for a pathophysiologic role for any of these receptors on erythrocytes comes from studies of cells from patients homozygous for hemoglobin S, as RBC adhesion is thought to contribute to vaso-occlusion. Thus, receptors such as B-CAM/LU may become targets for future therapy aimed at preventing or ameliorating this thrombotic process.

Increased expression of extracellular matrix metalloproteinase inducer in rheumatoid synovium

OBJECTIVE

To investigate the expression of extracellular matrix metalloproteinase inducer (EMMPRIN) in the synovial membrane of patients with rheumatoid arthritis (RA) and osteoarthritis (OA).

METHODS

Mouse monoclonal antibody against human EMMPRIN was applied according to an avidin-biotin-peroxidase complex method to reveal EMMPRIN expression. Western blotting and reverse transcriptase-polymerase chain reaction (RT-PCR) were performed to check for the presence of EMMPRIN protein and messenger RNA (mRNA).

RESULTS

EMMPRIN immunoreactivity was more intense in RA than in OA synovial membrane (P < 0.01). EMMPRIN staining was more widespread in RA than in OA, especially in association with macrophage infiltrates. RT-PCR of synovial membrane samples disclosed the presence of EMMPRIN mRNA. Nucleotide sequencing of the PCR amplification products confirmed the identity of the amplified bands. Immunoblot analysis revealed 55-kd glycosylated EMMPRIN bands, which were particularly prominent in RA samples.

CONCLUSION

The expression of EMMPRIN is upregulated in the rheumatoid synovial membrane. EMMPRIN can induce local production of at least MMPs 1, 2, and 3, and can thereby play a role in joint destruction in RA.

Increased expression of EMMPRIN in the tissue around loosened hip prostheses

Matrix metalloproteinases (MMPs) have been shown to play a role in aseptic loosening of total hip replacement (THR). Extracellular matrix metalloproteinase inducer (EMMPRIN) can upregulate expression of several MMPs but has little effect on their tissue inhibitor (TIMP). Using the avidin-biotin-peroxidase complex immunostaining method, we detected strong immunoreactivity of EMMPRIN in the lining-like layers, sublining area and vascular endothelium of synovial membrane-like interface tissue around loosened prostheses. In contrast, EMMPRIN staining was very weak in the synovial samples from patients with hip arthrosis. Double immunofluorescence labeling revealed EMMPRIN/MMP-1 double-positive cells in lining-like layers and the sublining area of interface tissue. Our findings indicate that EMMPRIN expression is upregulated in interface tissue, and that locally accumulated EMMPRIN may modulate MMP-1 expression. An imbalance in the activity of MMPs and TIMP may lead to tissue destruction and periprosthetic osteolysis. These biological responses, combined with mechanical stress caused by micromotion and oscillating fluid pressure, may eventually cause aseptic loosening of THR.

Lactate transport in skeletal muscle - role and regulation of the monocarboxylate transporter

Skeletal muscle is the major producer of lactic acid in the body, but its oxidative fibres also use lactic acid as a respiratory fuel. The stereoselective transport of L-lactic acid across the plasma membrane of muscle fibres has been shown to involve a proton-linked monocarboxylate transporter (MCT) similar to that described in erythrocytes and other cells. This transporter plays an important role in the pH regulation of skeletal muscle. A family of eight MCTs has now been cloned and sequenced, and the tissue distribution of each isoform varies. Skeletal muscle contains both MCT1 (the only isoform found in erythrocytes but also present in most other cells) and MCT4. The latter is found in all fibre types, although least in more oxidative red muscles such as soleus, whereas expression of MCT1 is highest in the more oxidative muscles and very low in white muscles that are almost entirely glycolytic. The properties of MCT1 and MCT2 have been described in some detail and the latter shown to have a higher affinity for substrates. MCT4 has been less well characterized but has a lower affinity for L-lactate (i.e. a higher Km of 20 mM) than does MCT1 (Km of 5 mM). MCT1 expression is increased in response to chronic stimulation and either endurance or explosive exercise training in rats and humans, whereas denervation decreases expression of both MCT1 and MCT4. The mechanism of regulation is not established, but does not appear to be accompanied by changes in mRNA concentrations. However, in other cells MCT1 and MCT4 are intimately associated with an ancillary protein OX-47 (also known as CD147). This protein is a member of the immunoglobulin superfamily with a single transmembrane helix, whose expression is known to be increased in a range of cells when their metabolic activity is increased.

T cell activation-associated epitopes of CD147 in regulation of the T cell response, and their definition by antibody affinity and antigen density

CD147 is a broadly expressed cell surface glycoprotein of the Ig superfamily whose expression is up-regulated upon T cell activation. In order to elucidate a possible role of CD147 in T cell biology, we established 15 specific mAb. Seven distinct epitopes were defined by the mAb panel. Most of the mAb bound only to phytohemagglutinin (PHA)-activated but not resting T cells. We demonstrate that this was not because of true expression of activation-dependent neoepitopes but rather due to bivalent binding of the relatively low-affinity mAb (affinity constant KA values between 2.25 x 10(8) and 7 x 10(9) M-1) to the more densely expressed and/or more clustered CD147 molecules on the activated T cells. In contrast, the mAb with higher affinity (KA > 7 x 10(9) M-1) could stably bind in a monovalent fashion even to the relatively low dense CD147 molecules on resting T cells. This model might more generally explain the nature of 'activation epitopes' described previously in other leukocyte surface molecules. Finally, we provide evidence that induction of ordered dimerization of CD147 by a mAb directed to a unique epitope results in strong inhibition of CD3-mediated T cell activation.

CD147 monoclonal antibodies induce homotypic cell aggregation of monocytic cell line U937 via LFA-1/ICAM-1 pathway

CD147 is a 50 000-60 000 MW glycoprotein of the immunoglobulin superfamily broadly expressed on haemopoietic cell lines and peripheral blood cells. In the present study, six monoclonal antibodies (mAbs) directed against the CD147 protein were generated. The antigen defined by the generated CD147 mAbs is widely expressed on haemopoietic cell lines, peripheral blood cells and is a lymphocyte activation-associated cell surface molecule. The generated CD147 mAbs precipitated a broad protein band from U937 cells of 45 000-65 000 MW under reducing conditions. Functional analysis indicated that the CD147 mAbs markedly induced homotypic cell aggregation of U937 cells, but not K562 cells. The CD147 mAb-induced cell aggregation was inhibited by leucocyte function-antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) mAbs. However, the expression of LFA-1 and ICAM-1 molecules on U937 was not altered by CD147 mAb treatment. The U937 cell aggregation induced by CD147 mAb was also inhibited by ethylenediamine tetra-acetic acid (EDTA), sodium azide and when incubated at 4 degrees. We therefore propose that the binding of CD147 mAb to CD147 molecule, which mimics the natural ligand binding, may generate intracellular signals that activate LFA-1/ICAM-1 intercellular adhesion pathway.

Interaction of the erythrocyte lactate transporter (monocarboxylate transporter 1) with an integral 70-kDa membrane glycoprotein of the immunoglobulin superfamily

Treatment of intact erythrocytes with 4,4'-diisothiocyanostilbene-2, 2'-disulfonate (DIDS) causes irreversible inhibition and chemical labeling of the lactate transporter, monocarboxylate transporter 1 (MCT1) (Poole, R. C., and Halestrap, A. P. (1992) Biochem. J. 283, 855-862). In rat erythrocytes DIDS also causes cross-linking of MCT1 to another protein in the membrane to give a product of 130 kDa on SDS-polyacrylamide gel electrophoresis. Cross-linking is markedly reduced by those compounds that protect against irreversible inhibition of lactate transport by DIDS and enhanced by imposition of a pH gradient across the plasma membrane to recruit the substrate binding site of MCT1 to an exofacial conformation. These data indicate that DIDS cross-linking is via the same site on MCT1 as is responsible for inhibition of transport. Antibodies raised against the cross-linked conjugate react with proteins of approximately 40 kDa (MCT1) and 70 kDa on Western blots of erythrocyte membranes and an additional band of 130 kDa after treatment of erythrocytes with 100 microM DIDS. The 70-kDa protein that is cross-linked to MCT1 was purified and shown to contain N-linked carbohydrate; the apparent core molecular mass is 40 kDa. Amino acid sequencing showed that the protein is the rat equivalent of the membrane-spanning mouse teratocarcinoma glycoprotein GP-70, a member of the immunoglobulin superfamily related to basigin (Ozawa, M., Huang, R. P., Furukawa, T. , and Muramatsu, T. (1988) J. Biol. Chem. 263, 3059-3062). Possible implications of the specific interaction between MCT1 and this protein are discussed.

The Oka blood group antigen is a marker for the M6 leukocyte activation antigen, the human homolog of OX-47 antigen, basigin and neurothelin, an immunoglobulin superfamily molecule that is widely expressed in human cells and tissues

The high-frequency blood group antigen Ok(a) is carried on a red cell membrane glycoprotein (gp) of 35-69 kDa that is widely distributed on malignant cells of different origins. Immunostaining of hemopoietic cells and a range of normal human tissues demonstrated a wide distribution of the Ok(a) gp that appears to be nonlineage-restricted, although certain tissues show differentiation-related expression. Ok(a) gp was purified from red cell membranes by immunoaffinity chromatography using mAb A103 and amino acid sequence analysis was performed. The N-terminal 30 amino acids are identical to the predicted sequence of M6 leukocyte activation antigen (M6), a member of the Ig superfamily (IgSF) with two IgSF domains. There are homologs in rat (MRC OX-47 or CE9), in mouse (basigin or gp42), and in chicken (HT7 or neurothelin). The molecular basis of the Ok(a) mutation was established by sequencing M6 cDNA derived from normal and Ok(a-) EBV-transformed B cell lines. A point mutation in the translated portion of M6 cDNA, G331AG-->AAG gives rise to a predicted E92-->K amino acid change in the first Ig-like domain of the Ok(a-) form of the protein. Transfection of mouse NS-0 cells with normal or Ok(a-) cDNA confirmed the identity of the protein and only the Ok(a-) transfectants failed to react with monoclonal anti-Ok(a) Ab.