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Published on: December 27, 2016
Utilization of biotin in proliferating human lymphocytes
1Department of Pediatrics, University of Arkansas for Medical Sciences/Arkansas Children's Hospital Research Institute, Little Rock 72202, USA.
Insights
Proliferating lymphocytes significantly increase biotin uptake by synthesizing more transporters, ensuring sufficient coenzyme for biotin-dependent carboxylases. This enhanced nutrient transport supports immune cell function.
Area of Science:
- Immunology
- Cell Biology
- Nutritional Biochemistry
Background:
- Lymphocytes are key immune cells that proliferate upon antigenic stimulation.
- Understanding nutrient transport in activated immune cells is crucial for immune function.
- Biotin is an essential vitamin involved in various metabolic processes.
Purpose of the Study:
- To investigate if proliferating lymphocytes enhance biotin cellular uptake.
- To elucidate the mechanisms behind increased biotin uptake in stimulated lymphocytes.
- To determine if increased biotin uptake supports metabolic demands of proliferating lymphocytes.
Main Methods:
- Human peripheral blood lymphocytes were isolated and stimulated to proliferate using mitogens (pokeweed lectin, concanavalin A, phytohemagglutinin).
- Biotin uptake was quantified using radiolabeled [3H]biotin, with confirmation of minimal biotin metabolism.
- Kinetic analysis and the effect of cycloheximide (protein synthesis inhibitor) were assessed.
Main Results:
- Biotin uptake increased by 278-722% in proliferating lymphocytes compared to non-proliferating controls.
- The increase in uptake was attributed to a higher number of biotin transporters on the cell surface, not altered affinity.
- Inhibition of protein synthesis abolished the mitogen-induced increase in biotin transport.
- Biotin-dependent beta-methylcrotonyl-CoA carboxylase activity was 2.5-fold higher in stimulated lymphocytes.
Conclusions:
- Mitogen-stimulated lymphocytes increase biotin uptake primarily by upregulating the synthesis of biotin transporters.
- This enhanced uptake likely provides necessary biotin coenzyme for increased carboxylase activity in proliferating immune cells.
- The findings highlight a specific nutrient transport adaptation in activated lymphocytes to meet metabolic demands.
Abstract:
Lymphocytes are part of the immune system and respond to antigenic stimulation with proliferation. We sought to determine whether mitogen-stimulated, proliferating lymphocytes increase the cellular uptake of biotin and, if so, to identify mechanisms that mediate the increase. Lymphocytes were isolated from human peripheral blood; proliferation of lymphocytes was induced by incubation with pokeweed lectin, concanavalin A or phytohemagglutinin. Biotin uptake was quantitated by determination of [3H] uptake into the lymphocytes during incubation with [3H]biotin after establishing that [3H]biotin is not metabolized within the lymphocytes during the incubation period (<5%). Biotin uptake into proliferating lymphocytes increased to 278-722% of the control values for nonproliferating lymphocytes. Kinetic analysis of biotin transport provided evidence that the increase is mediated by an increased number of transporters on the cell surface rather than by an increase in transporter affinity. Cycloheximide, an inhibitor of protein synthesis, completely suppressed the mitogen-stimulated increase in biotin transport. This observation is consistent with the hypothesis that proliferating lymphocytes increase biotin uptake by increasing the synthesis of new transporters. Biotin affinity and structural specificity were similar in proliferating and nonproliferating lymphocytes, suggesting that mitogens induced an increase in the number of the same transporter molecule that mediates transport in unstimulated lymphocytes. Mitogen-stimulated lymphocytes exhibited 2.5 times greater activities of biotin-dependent beta-methylcrotonyl-CoA carboxylase compared with time 0 (at 72 h after addition of mitogen). This observation is consistent with the hypothesis that proliferating lymphocytes increase biotin uptake at least in part to provide adequate coenzyme for biotin-dependent carboxylases.
