The essential role of vitamin B12 (Cbl) in recycling folate and thereby in DMA synthesis and single carbon metabolism and in the generation of methionine, the precursor for biological methylations is indicated by the clinical presentation of megaloblastic anemia and neurologic abnormalities in Cbl deficiency. The two metabolites, homocysteine (HCY) and methylmalonic acid (MMA) that is elevated in both Cbl and folate deficiency have been implicated in vascular damage and neurologic abnormalities respectively. The incidence of these elevated metabolites in the elderly population is a cause for concern. In the absence of dietary deficiency and malabsorption, the cellular uptake of Cbl is the likely cause of elevated HCY and MMA. Transcobalamin (TC), the Cbl transporter secreted by the vascular endothelium into the blood and the membrane receptor (TCR) for the uptake of TC-Cbl are the two proteins involved in this process. Many aspects of TC are being investigated at this time, however, very little are known about TCR, a protein expressed in actively dividing cells and appear to be cell cycle regulated. We have purified and determined the primary structure of TCR and have identified the gene encoding this protein. Our goal is to understand the genetic regulation of TCR expression and the mechanism by which it binds and mediates the cellular uptake of TC-Cbl to maintain intracellular Cbl. This information will be used in devising strategies to target TCR in cancer therapy, to devise therapeutic and preventive strategies for cellular Cbl deficiency and to study the effects of Cbl deficiency in an animal model. Towards achieving these goals the following specific aims are proposed. 1. To characterize the regulation of TCR gene expression. 2. To determine the synthesis, translocation and functions of TCR in the uptake of TCCbl. 3. To evaluate the effects of functional ablation of TCR at the cellular level and in the whole organism. The rationale for the proposed studies is that understanding how this gene functions will allow us to identify differences in expression or control mechanisms between normal replicating cells and cancer cells and an animal model will allow us to examine the metabolic and structural changes due to Cbl deficiency. We expect these studies to reveal new information on the expression of TCR, whether this pathway could be targeted in cancer therapy and provided a model to understand the metabolic basis for the neuropathological presentation of Cbl deficiency.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
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Integrative Nutrition and Metabolic Processes Study Section (INMP)
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May, Michael K
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Suny Downstate Medical Center
Schools of Medicine
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Arora, Kaveri; Sequeira, Jeffrey M; Quadros, Edward V (2017) Maternofetal transport of vitamin B12: role of TCblR/CD320 and megalin. FASEB J 31:3098-3106
Jiang, Wenxia; Nakayama, Yasumi; Sequeira, Jeffrey M et al. (2013) Mapping the functional domains of TCblR/CD320, the receptor for cellular uptake of transcobalamin-bound cobalamin. FASEB J 27:2988-94
Lai, Shao-Chiang; Nakayama, Yasumi; Sequeira, Jeffrey M et al. (2013) The transcobalamin receptor knockout mouse: a model for vitamin B12 deficiency in the central nervous system. FASEB J 27:2468-75
Quadros, Edward V; Sequeira, Jeffrey M (2013) Cellular uptake of cobalamin: transcobalamin and the TCblR/CD320 receptor. Biochimie 95:1008-18
Quadros, Edward V; Nakayama, Yasumi; Sequeira, Jeffrey M (2013) Saporin Conjugated Monoclonal Antibody to the Transcobalamin Receptor TCblR/CD320 Is Effective in Targeting and Destroying Cancer Cells. J Cancer Ther 4:1074-1081
Lai, Shao-Chiang; Nakayama, Yasumi; Sequeira, Jeffrey M et al. (2011) Down-regulation of transcobalamin receptor TCblR/CD320 by siRNA inhibits cobalamin uptake and proliferation of cells in culture. Exp Cell Res 317:1603-7
Jiang, Wenxia; Nakayama, Yasumi; Sequeira, Jeffrey M et al. (2011) Characterizing monoclonal antibodies to antigenic domains of TCblR/CD320, the receptor for cellular uptake of transcobalamin-bound cobalamin. Drug Deliv 18:74-8
Arendt, Johan Frederik Berg; Quadros, Edward V; Nexo, Ebba (2011) Soluble transcobalamin receptor, sCD320, is present in human serum and relates to serum cobalamin - establishment and validation of an ELISA. Clin Chem Lab Med 50:515-9
Quadros, Edward V; Lai, Shao-Chiang; Nakayama, Yasumi et al. (2010) Positive newborn screen for methylmalonic aciduria identifies the first mutation in TCblR/CD320, the gene for cellular uptake of transcobalamin-bound vitamin B(12). Hum Mutat 31:924-9
Pangilinan, F; Mitchell, A; VanderMeer, J et al. (2010) Transcobalamin II receptor polymorphisms are associated with increased risk for neural tube defects. J Med Genet 47:677-85

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