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Biochemical and Molecular Actions of Nutrients
Research Communication

Monocarboxylate Transporter 1 Mediates Biotin Uptake in Human Peripheral Blood Mononuclear Cells¹

Rachel L. Daberkow^*, Brett R. White, Rebecca A. Cederberg, Jacob B. Griffin^* and Janos Zempleni^*,,**,2

Departments of ^* Nutritional Science and Dietetics, Animal Science and ^** Biochemistry, University of Nebraska at Lincoln, Lincoln, NE

²To whom correspondence should be addressed. E-mail: jzempleni2{at}unl.edu.

	ABSTRACT

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Here the hypothesis was tested that monocarboxylate transporters (MCT) mediate biotin transport in human lymphoid cells. Uptake of [³H]biotin was measured in human lymphoid cells [peripheral blood mononuclear cells (PBMC) and Jurkat cells] under conditions known to affect MCT-mediated transport. When biotin uptake into PBMC was measured in the presence of excess concentrations of competitors (MCT substrates) and MCT inhibitors, transport rates decreased significantly to <75 and <67%, respectively, of controls. Biotin uptake correlated with the concentration of protons in culture media, consistent with cotransport of protons and the carboxylate biotin by MCT. Efflux of biotin from PBMC was stimulated by extracellular lactate (a known substrate for MCT), consistent with countertransport of the two substrates by the same transporter. PBMC responded to proliferation with parallel increases of transport rates for both biotin and lactate, providing circumstantial evidence that the same transporter mediates uptake of the two substrates in PBMC. Transfection of Jurkat cells with an expression vector encoding MCT1 caused a 50% increase in biotin uptake; in contrast, overexpression of MCT1 did not affect biotin uptake in various nonlymphoid cell lines. These findings are consistent with the hypothesis that MCT mediate biotin uptake in human lymphoid cells.

KEY WORDS: • biotin • human • monocarboxylate transporter • peripheral blood mononuclear cells • transport

In mammals, biotin serves as a covalently bound coenzyme for acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase (1). These carboxylases catalyze essential steps in the metabolism of glucose, amino acids and fatty acids. Furthermore, human cells bind biotin to histones (2,3); biotinylation of histones may play a role in cell proliferation and DNA repair (3,4).

Consistent with these essential roles for biotin in metabolism, biotin status may affect cellular growth, proliferation and differentiation. For example, biotin deficiency causes arrest of HeLa cells in the G1 phase of the cell cycle (5). Abnormal cellular growth and differentiation might cause the fetal malformations (6) and impaired immune function (7) observed in biotin-deficient animals.

Research has provided evidence that the sodium-dependent multivitamin transporter (SMVT)² might mediate biotin uptake into human cells (8–10). SMVT binds biotin, pantothenic acid and lipoic acid with similar affinity. Notwithstanding the potential role for SMVT in biotin transport, our studies (11–14) provided evidence that unidentified transporters other than SMVT might also mediate biotin uptake in human cells, based on the following lines of evidence: 1) the Michaelis-Menten constant for biotin transport in human peripheral blood mononuclear cells (PBMC) is 1000 times smaller than the Michaelis-Menten constant for biotin transport by SMVT (8,10,11,15,16); 2) lipoic acid and pantothenic acid do not compete with biotin for uptake into PBMC (11,12); 3) an inborn error in biotin transport does not affect pantothenic acid transport in PBMC (13); and 4) human lymphoid cells (Jurkat cells) respond to biotin deficiency with increased rates of biotin uptake but not with increased expression of SMVT (14).

Chemically, biotin is a monocarboxylic acid (1). Uptake of monocarboxylic acids (e.g., lactate and pyruvate) into human cells is mediated by monocarboxylic acid transporters (MCT) (17). Currently, nine MCT-related sequences have been identified in humans. Here we tested the hypothesis that biotin uptake into human cells is mediated by MCT.

	MATERIALS AND METHODS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Subjects.

Healthy Caucasian adults (n = 2 men, 4 women), aged 25–51 y, participated in this study. All subjects were nonsmokers; none had knowingly consumed any vitamin supplements for at least 3 wk before initiation of the study. Pregnant women and individuals treated with anticonvulsants were not eligible for study participation (1). This study was approved by the Institutional Review Board for the Protection of Human Subjects at the University of Nebraska-Lincoln.

Cell isolation and culture.

PBMC were isolated from heparinized venous blood by gradient centrifugation (11); this procedure provides cultures of predominantly quiescent (nonproliferating) cells (18). Cell viability (>96%) was monitored by Trypan blue exclusion; cell density in culture media was adjusted to 3 x 10⁹ cells/L. If nutrient transport was to be quantified in proliferating cells, PBMC were cultured with 20 mg/L concanavalin A for 2 d to induce proliferation (18).

The following cell lines were purchased from American Type Culture Collection (Manassas, VA): Jurkat cells (clone E6–1), a human leukemia T-cell line; NCI-H69 cells, a human small cell lung cancer cell line; and JAr cells, a human choriocarcinoma cell line. These cells were cultured in RPMI-1640 containing 0.1 L fetal bovine serum (Mediatech, Herndon, VA), 100 kU penicillin, and 100 mg streptomycin per liter of medium (14). T3–1 cells, a gonadotrope-derived cell line, were generously provided by Pamela Mellon (Salk Institute, La Jolla, CA) and were cultured in high-glucose DMEM (Mediatech) supplemented with 0.05 L fetal bovine serum, 0.05 L horse serum (Gibco, Grand Island, NY), 100 kU penicillin, 100 mg streptomycin and 2 mmol glutamine per liter of medium. T3–1 cells were collected by trypsination when cultures reached 70% confluence. All cells were cultured in humidified atmosphere (5% CO₂, 37°C). Culture media were replaced with fresh media every 48 h.

Biotin transport.

Cells were washed and transferred into PBS immediately before transport studies; PBS did not contain unlabeled biotin. Rates of biotin transport into cells were quantified using a physiologic concentration of [³H]biotin (475 pmol/L) (11); the physiologic range of biotin compounds in human plasma is 300–600 pmol/L (19). In competition studies, we determined whether the following substrates of MCT compete with biotin for cellular uptake: acetoacetate, L-(+)-lactate, D,L-ß-hydroxybutyrate, -ketoisocaproate, hexanoate, acetate and pyruvate (Sigma, St. Louis, MO). These competitors were added to cell suspensions immediately before transport studies at a final concentration of 25 mmol/L; this concentration is at least 7 times greater than the Michaelis-Menten constant of the various MCT for their substrates, i.e., competitors and biotin were in excess of available substrate-binding sites (20).

In inhibitor studies, we determined whether the following inhibitors of MCT decreased cellular biotin uptake: probenecid (2.5 mmol/L final concentration), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.2 mmol/L and 2 mmol/L), sulfinpyrazone (2.5 mmol/L), and p-chloromercuribenzenesulfonic acid (0.1 mmol/L) (Sigma). Incubation times of PBMC with these MCT inhibitors were as described (17,21).

MCT cotransport organic anions and protons; thus, MCT-mediated transport depends on the availability of protons (20,21). Here we determined whether transport rates of biotin correlated inversely with pH, consistent with MCT-mediated transport. PBMC were suspended in the following isotonic buffers: 1) citrate-phosphate buffer (36.6 mL of 50 mmol/L citric acid plus 63.4 mL of 100 mmol/L disodium hydrogen phosphate, pH 6.0); 2) phosphate buffer (78 mL of 100 mmol/L monosodium dihydrogen phosphate plus 122 mL of 100 mmol/L disodium hydrogen phosphate, pH 7.0); or 3) Tris-HCl buffer (27.2 mL of 100 mmol/L hydrochloric acid, 50 mL of 100 mmol/L Tris base, and 22.8 mL of water; pH 8.0). Biotin transport was quantified as described above.

Lactate transport.

Transport rates of [¹⁴C]L-lactate were quantified as described for biotin (11) using a final concentration of 5 µmol/L lactate. Lactate uptake increased linearly with time for 15 min (data not shown). Thus, cells were incubated with lactate for up to 10 min in the transport studies described here.

Trans-stimulation of biotin transport.

Theoretically, if two substrates are transported by the same transporter, efflux of one of these substrates from cells can be stimulated by the addition of the other substrate to the extracellular medium ("trans-stimulation"). We determined whether efflux of biotin from PBMC was stimulated by extracellular lactate in analogy to our previous studies (22). Briefly, PBMC were incubated with 475 pmol/L [³H]biotin at 37°C for 2 h to load the cells with biotin. Aliquots were collected to quantify intracellular [³H]biotin by liquid scintillation counting. Cells from the remaining suspension were collected by centrifugation (250 x g for 10 min) and were resuspended in biotin-free PBS containing 25 mmol/L lactate; controls were suspended in lactate-free saline. Incubation was continued for 12 min when [³H]biotin remaining in cells was quantified by liquid scintillation counting. The addition of lactate to the medium did not affect cell viability as judged by Trypan blue exclusion (data not shown).

RT-PCR.

MCT in PBMC were identified by PCR. Total RNA from PBMC was reverse transcribed (23). First-strand DNA was amplified by PCR using the following oligonucleotide primers (Integrated DNA Technologies, Coralville, IA): 1) 5'-ACC AGC AGT TGG AGG TCC AGT TGG ATA-3' and 5'-AAC TGA TTA ATT GTT TGG AAG ACT GAT-3' for human MCT1 (GenBank accession number L31801); 2) 5'-ACT GAG CTC ATG CCA CCA ATG CCA AGT GCC-3' and 5'-AGA GGT ACC TTA AAT GTT AGT TTC TCT TTC-3' for human MCT2 (GenBank AF049608); 3) 5'-CGC TGG CGG CCC CCG GCG GGG CGA GGG-3' and 5'-GTC CAG CAG GCG CCG GCG GGG CCG GAC-3' for human MCT3 (GenBank AF132610); 4) 5'-AGG GGC CGT GGT GGA CGA GGG CCC CAC-3' and 5'-GAC GAA GAG CCC CAG CAC CAT GAC CGA-3' for human MCT4 (GenBank U81800); 5) 5'-ACT CCG CGG AAG GGA TCT TCT GCA TTT AAAA-3' and 5'-AGA CTC GAG TTT AGG TTT TCT TTT GTT TAGC-3' for human MCT5 (GenBank U59185); 6) 5'-CCA GGC CCT GGA GCG TGC AGA TGG CAG-3' and 5'-ACC CAG TAT GTA CAC GCA GTA GCC TGT-3' for human MCT6 (GenBank U59299); 7) 5'-CCA AAA TAA ATT AAA GCT TTG TTC CAA-3' and 5'-TAG TTC TAC TCC TGA GTC AAT GGA GTC-3' for human MCT7 (GenBank U79745); and 8) 5'-GAG GGA CCG TCT GTC GCG GGA CGG GCT-3' and 5'-GAG GCC AAT GAA AGC AAC GGC AGC CCC-3' for human MCT8 (GenBank U05315).

PCR was performed using the following conditions per cycle for 35 cycles (23): 94°C for 1 min (denaturating), 55°C for 1 min (annealing), and 72°C for 2 min (extending). Samples were electrophoresed using agarose gels (15 g agarose/L). DNA on gels was visualized with ethidium bromide and analyzed using the Kodak EDAS 290 Documentation and Analysis System (Rochester, NY).

Transfection of cells with MCT1.

An expression vector encoding hamster MCT1 (pMCT1) was obtained from American Type Culture Collection; in this plasmid, expression of MCT1 is driven by the ubiquitous cytomegalovirus promoter. Jurkat cells, NCI-H69 cells and JAr cells were transfected with 10 µg pMCT1 as described previously (24). T3–1 cells were transfected using Polyfect (Qiagen, Valencia, CA) according to the manufacturer’s instructions. Forty-eight hours after transfection, cells were collected and transport rates of biotin and lactate were quantified.

Statistics.

Homogeneity of variances among groups was tested using Bartlett’s test (25). Whenever variances were heterogeneous, data were log-transformed before further statistical testing. Significance of differences among groups was tested by one-way ANOVA. Fisher’s Protected Least Significant Difference procedure was used for post-hoc testing (25). When significance of difference between only two groups was tested, the paired t test was used. StatView 5.0.1 (SAS Institute, Cary, NC) was used to perform all calculations. Differences were considered significant if P < 0.05. Data are expressed as mean ± SD.

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Competitor studies.

Compounds known to be transported by MCT competed with biotin for uptake into freshly isolated (quiescent) PBMC. For example, uptake of biotin decreased to 69 ± 2.3% of competitor-free controls if measured in the presence of excess concentrations of L-(+)-lactate (Fig. 1). Similarly, uptake of biotin decreased to <75% of control values if measured in the presence of D,L-betahydroxybutyrate, -ketoisocaproate, hexanoate, acetate and pyruvate. Biotin uptake in the presence of acetoacetate was 82 ± 25% of controls, but this decrease was not significant (P = 0.14). Taken together, these observations suggest that biotin and other organic acids compete for binding to the same transporter.

View larger version (20K): [in this window] [in a new window]   FIGURE 1 Substrates of monocarboxylate transporters (panels A and B) compete with [3H]biotin for uptake into PBMC. (A) Effects of acetoacetate, lactate, ß-hydroxybutyrate (ß-HB) and -ketoisocaproate (-KIC) (all at 25 mmol/L) on the transport of [3H]biotin (475 pmol/L). (B) Effects of hexanoate, acetate and pyruvate (all at 25 mmol/L) on the transport of [3H]biotin (475 pmol/L). Values are means ± SD, n = 6 independent experiments. a,b,cBars without a common letter differ (P < 0.05).

In freshly isolated PBMC, rates of biotin uptake decreased to <67% of control values if cells were treated with the following inhibitors of MCT-mediated transport: 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, probenecid, sulfinpyrazone and p-chloromercuribenzenesulfonic acid (Fig. 2). These observations suggest that biotin uptake into PBMC is mediated by MCT.

View larger version (16K): [in this window] [in a new window]   FIGURE 2 Inhibitors of monocarboxylate transporters decrease uptake of [3H]biotin into PBMC. Cells were treated with the following inhibitors before quantifying uptake of [3H]biotin: 2.5 mmol/L probenecid, 0.2 or 2.0 mmol/L 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), 2.5 mmol/L sulfinpyrazone and 0.1 mmol/L p-chloromercuribenzenesulfonic acid (pCMBS). Values are means ± SD, n = 9 independent experiments. a,bBars without a common letter differ (P < 0.05).

Biotin uptake into quiescent PBMC correlated positively with the concentration of protons in culture media. For example, biotin uptake at pH 6.0 [106 ± 3.6 amol biotin/(10⁶ cells · 30 min)] was significantly greater (P < 0.01) than biotin uptake at pH 8.0 [43 ± 1.4 amol biotin/(10⁶ cells · 30 min)]. Similarly, biotin uptake at pH 6.0 tended to be greater than biotin uptake at pH 7.0 [86 ± 2.9 amol biotin/(10⁶ cells · 30 min)] (n = 3 independent experiments; P = 0.13). These data suggest that biotin uptake into PBMC involves cotransport of protons.

Trans-stimulation of biotin transport.

Biotin efflux from PBMC was stimulated by extracellular L-(+)-lactate. Cells were loaded with [³H]biotin in lactate-free medium for 2 h; intracellular concentrations of [³H]biotin reached a plateau at 415 ± 32 amol/10⁶ cells. When these cells were transferred into biotin-free medium containing 25 mmol/L lactate and incubation was continued for 12 min at 37°C, cells retained only 22 ± 7.2% of their [³H]biotin; in contrast, cells incubated in lactate-free and biotin-free medium retained 53 ± 9.1% of their [³H]biotin (n = 6 independent experiments; P < 0.01). Trans-stimulation of biotin efflux by extracellular lactate suggests that biotin and lactate are transported by the same transporter.

PBMC express genes encoding MCT.

PBMC express at least three distinct MCT. RNA from PBMC was reverse transcribed and fragments of MCT were amplified by PCR, using primers specific for eight known human MCT. The following MCT were expressed in PBMC, as judged by PCR amplification of DNA of the expected size: MCT1 (749 bp), MCT2 (726 bp), and MCT5 (726 bp; data not shown).

Effects of cell proliferation on lactate transport.

Previous studies suggested that biotin uptake into PBMC increases by 500% in response to cell proliferation, and that increased uptake is mediated by an increased number of biotin transporters on the cell surface; the identity of these transporters remains uncertain (18). In the present study, cells responded to proliferation with increased rates of lactate uptake: proliferating PBMC = 23 ± 13 pmol/(10⁶ cells · 5 min); quiescent controls = 3.8 ± 0.8 pmol/(10⁶ cells · 5 min) (n = 6 independent experiments; P < 0.01). Thus, uptake of both biotin and lactate increases to a similar extent in response to cell proliferation. This observation provides circumstantial evidence that uptake of both compounds is mediated by the same transporter.

Transfection of cells with MCT1.

Transport rates of biotin increased significantly in response to transfection of lymphoid (Jurkat) cells with an expression vector (pMCT1) encoding MCT1 [units = amol/(10⁶ cells · 30 min)]: transfected cells = 101 ± 44; nontransfected controls = 65 ± 28 (P < 0.01; n = 3 independent experiments). This observation is consistent with the hypothesis that MCT1 mediates biotin uptake into human immune cells. Lactate uptake was used as a positive control in these studies to verify expression of functional MCT1; rates of lactate transport increased by 57% in response to transfection of Jurkat cells with pMCT1 [units = pmol/(10⁶ cells · 10 min)]: transfected cells = 4.1 ± 0.4; nontransfected controls = 2.8 ± 0.6 (P < 0.01; n = 5 independent experiments).

Biotin transport by MCT1 is specific for lymphoid cells and, perhaps, some other cell lines. Transfection of JAr cells, NCI-H69 cells and T3–1 cells with pMCT1 did not increase biotin uptake despite increased lactate uptake compared with nontransfected controls (data not shown).

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
The present study provides evidence that MCT1 mediates biotin uptake into human lymphoid cells. This conclusion is based on the following lines of evidence: 1) substrates of MCT compete with biotin for uptake into PBMC; 2) inhibitors of MCT-mediated transport decrease biotin uptake into PBMC; 3) the concentration of protons in culture media correlates with biotin uptake; 4) extracellular lactate stimulates the efflux of biotin from PBMC; 5) PBMC express genes encoding MCT1, MCT2 and MCT5; 6) transport rates of biotin and lactate increase in parallel in response to cell proliferation; and 7) overexpression of MCT1 in Jurkat cells causes increased transport rates of biotin. Biotin transport by MCT1 is physiologically meaningful given the broad tissue distribution and large transport capacity of MCT (17,20).

MCT other than MCT1 are also likely to mediate biotin transport. Substrates for most MCT are characterized by having an aliphatic chain with a carboxyl group (26); biotin also carries an aliphatic chain with a carboxyl group, i.e., valeric acid. Modifications of the aliphatic chain typically do not impair binding of organic acids to MCT. For example, lactate, pyruvate, ß-hydroxybutyrate and acetate all bind to MCT1 and MCT2 with high affinity (17,20,27). Structurally, the biotin molecule is an -substituted valeric acid. In contrast to other MCT, MCT4 exhibits relatively high substrate specificity; L-lactate is the preferred substrate for MCT4 (28). Thus, MCT4 might not transport biotin.

The present study provided evidence that MCT1 mediates the uptake of biotin into lymphoid cells but not into placental (JAr) cells, lung (NCI-H69) cells and gonadotrope-derived (T3–1) cells. The reason for the tissue specificity of biotin transport by MCT1 is uncertain. We speculate that lymphoid cells might express accessory membrane proteins, which facilitate biotin uptake by MCT1. Notwithstanding this tissue specificity, we hypothesize that MCT might play a role in biotin uptake in tissues other than immune cells. For example, recent studies suggested that human keratinocytes express a biotin transporter that is very similar to the biotin transporter described in lymphoid cells (15).

Potentially, MCT play a causal role in an inborn error of biotin transport identified in humans. In this inborn error, biotin uptake into immune cells is severely diminished (13). Mutations in the coding sequence of the "classical" biotin transporter SMVT have been excluded as a cause for this defect (13). Abnormal sequence or expression of the MCT1 gene is a plausible explanation for this defect, based on the studies described here. Future studies will investigate the role of MCT in inborn errors of biotin transport.

	FOOTNOTES

 
¹ Supported by National Institutes of Health grant DK 60447 and the U.S. Department of Agriculture/National Research Initiative Competitive Grants Program project award 2001–35200-10187. A contribution of the University of Nebraska Agricultural Research Division, Lincoln, NE 68583. Journal Series No. 14054.

³ Abbreviations used: MCT, monocarboxylate transporter; PBMC, peripheral blood mononuclear cells; SMVT, sodium-dependent multivitamin transporter.

Manuscript received 4 April 2003. Initial review completed 31 May 2003. Revision accepted 12 June 2003.

	LITERATURE CITED

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 

1. Zempleni, J. (2001) Biotin. Bowman, B. A. Russell, R. M. eds. Present Knowledge in Nutrition 2001 ILSI Press Washington, DC. .

2. Hymes, J., Fleischhauer, K. & Wolf, B. (1995) Biotinylation of histones by human serum biotinidase: assessment of biotinyl-transferase activity in sera from normal individuals and children with biotinidase deficiency. Biochem. Mol. Med. 56:76-83.[Medline]

3. Stanley, J. S., Griffin, J. B. & Zempleni, J. (2001) Biotinylation of histones in human cells: effects of cell proliferation. Eur. J. Biochem. 268:5424-5429.[Medline]

4. Peters, D. M., Griffin, J. B., Stanley, J. S., Beck, M. M. & Zempleni, J. (2002) Exposure to UV light causes increased biotinylation of histones in Jurkat cells. Am. J. Physiol. 283:C878-C884.

5. Dakshinamurti, K., Chalifour, L. E. & Bhullar, R. J. (1985) Requirement for biotin and the function of biotin in cells in culture. Dakshinamurti, K. Bhagavan, H. N. eds. Biotin 1985 New York Academy of Science New York, NY. .

6. Watanabe, T., Dakshinamurti, K. & Persaud, T. V. N. (1995) Biotin influences palatal development of mouse embryos in organ culture. J. Nutr. 125:2114-2121.

7. Báez-Saldaña, A., Díaz, G., Espinoza, B. & Ortega, E. (1998) Biotin deficiency induces changes in subpopulations of spleen lymphocytes in mice. Am. J. Clin. Nutr. 67:431-437.[Abstract]

8. Prasad, P. D., Wang, H., Kekuda, R., Fujita, T., Fei, Y.-J., Devoe, L. D., Leibach, F. H. & Ganapathy, V. (1998) Cloning and functional expression of a cDNA encoding a mammalian sodium-dependent vitamin transporter mediating the uptake of pantothenate, biotin, and lipoate. J. Biol. Chem. 273:7501-7506.[Abstract/Free Full Text]

9. Wang, H., Huang, W., Fei, Y.-J., Xia, H., Fang-Yeng, T. L., Leibach, F. H., Devoe, L. D., Ganapathy, V. & Prasad, P. D. (1999) Human placental Na⁺-dependent multivitamin transporter. J. Biol. Chem. 274:14875-14883.[Abstract/Free Full Text]

10. Prasad, P., Wang, H., Huang, W., Fei, Y.-J., Leibach, F. H., Devoe, L. D. & Ganapathy, V. (1999) Molecular and functional characterization of the intestinal Na⁺-dependent multivitamin transporter. Arch. Biochem. Biophys. 366:95-106.[Medline]

11. Zempleni, J. & Mock, D. M. (1998) Uptake and metabolism of biotin by human peripheral blood mononuclear cells. Am. J. Physiol. 275:C382-C388.[Medline]

12. Zempleni, J. & Mock, D. M. (1999) Human peripheral blood mononuclear cells: inhibition of biotin transport by reversible competition with pantothenic acid is quantitatively minor. J. Nutr. Biochem. 10:427-432.

13. Mardach, R., Zempleni, J., Wolf, B., Cannon, M. J., Jennings, M. L., Cress, S., Boylan, J., Roth, S., Cederbaum, S. & Mock, D. M. (2002) Biotin dependency due to a defect in biotin transport. J. Clin. Investig. 109:1617-1623.[Medline]

14. Manthey, K. C., Griffin, J. B. & Zempleni, J. (2002) Biotin supply affects expression of biotin transporters, biotinylation of carboxylases, and metabolism of interleukin-2 in Jurkat cells. J. Nutr. 132:887-892.[Abstract/Free Full Text]

15. Grafe, F., Wohlrab, W., Neubert, R. H. & Brandsch, M. (2003) Transport of biotin in human keratinocytes. J. Investig. Dermatol. 120:428-433.[Medline]

16. Prasad, P. D., Ramamoorthy, S., Leibach, F. H. & Ganapathy, V. (1997) Characterization of a sodium-dependent vitamin transporter mediating the uptake of pantothenate, biotin and lipoate in human placental choriocarcinoma cells. Placenta 18:527-533.[Medline]

17. Halestrap, A. P. & Price, N. T. (1999) The proton-linked monocarboxylate transporter (MCT) family: structure, function and regulation. Biochem. J. 343:281-299.

18. Zempleni, J. & Mock, D. M. (1999) Mitogen-induced proliferation increases biotin uptake into human peripheral blood mononuclear cells. Am. J. Physiol. 276:C1079-C1084.[Medline]

19. Mock, D. M., Lankford, G. L. & Mock, N. I. (1995) Biotin accounts for only half of the total avidin-binding substances in human serum. J. Nutr. 125:941-946.

20. Broer, S., Broer, A., Schneider, H. P., Stegen, C., Halestrap, A. P. & Deitmer, J. W. (1999) Characterization of the high-affinity monocarboxylate transporter MCT2 in Xenopus laevis oocytes. Biochem. J. 341:529-535.

21. Loike, J. D., Kaback, E., Silverstein, S. C. & Steinberg, T. H. (1993) Lactate transport in macrophages. J. Immunol. 150:1951-1958.[Abstract]

22. Zempleni, J. & Mock, D. M. (1999) The efflux of biotin from human peripheral blood mononuclear cells. J. Nutr. Biochem. 10:105-109.

23. Wiedmann, S., Eudy, J. D. & Zempleni, J. (2003) Biotin supplementation causes increased expression of genes encoding interferon-, interleukin-1ß, and 3-methylcrotonyl-CoA carboxylase, and causes decreased expression of the gene encoding interleukin-4 in human peripheral blood mononuclear cells. J. Nutr. 133:716-719.[Abstract/Free Full Text]

24. Rodriguez-Melendez, R., Camporeale, G., Griffin, J. B. & Zempleni, J. (2003) Interleukin-2 receptor -dependent endocytosis depends on biotin in Jurkat cells. Am. J. Physiol. 284:C415-C421.

25. SAS Institute (1999) StatView Reference 1999 SAS Publishing Cary, NC.

26. Rahman, B., Schneider, H., Broer, A., Deitmer, J. W. & Broer, S. (1999) Helix 8 and helix 10 are in substrate recognition in the rat monocarboxylate transporter MCT1. Biochem. J. 38:11577-11584.

27. McCullagh, K. J., Poole, R. C., Halestrap, A. P., O’Brien, M. & Bonen, A. (1996) Role of the lactate transporter (MCT1) in skeletal muscles. Am. J. Physiol. 271:E143-E150.[Medline]

28. Dimmer, K. S., Friedrich, B., Lang, F., Deitmer, J. W. & Broer, S. (2000) The low-affinity monocarboxylate transporter MCT4 is adapted to the export of lactate in highly glycolytic cells. Biochem. J. 350:219-227.

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