title: Biotin availability regulates expression of the sodium-dependent multivitamin transporter and the rate of biotin uptake in HepG2 cells.
abstract: In human cells, biotin is essential to maintain metabolic homeostasis and as regulator of gene expression. The enzyme holocarboxylase synthetase (HCS) transforms biotin into its active form 5'-biotinyl-AMP and this compound is used to biotinylate five biotin-dependent carboxylases or to activate a soluble guanylate cyclase (sGC) and a cGMP-dependent protein kinase (PKG). The HCS-sGC-PKG pathway is responsible for maintaining the mRNA levels of enzymes involved in biotin utilization including HCS, carboxylases, and a biotin carrier known as sodium-dependent multivitamin transporter (SMVT). To understand the role of SMVT in the control of biotin utilization, we have studied the effect of biotin availability on SMVT protein and mRNA expression levels in HepG2 cells by Western blot analysis and rtPCR, respectively; and their functional impact on the rate of [3H]biotin uptake in human cells. Our results showed that human HepG2 cells grown in a biotin-deficient medium have a lower rate of biotin uptake than normal cells. The impairment in biotin uptake is associated with a reduction in the amount of both SMVT protein mass and mRNA levels. Transfection of HepG2 cells with a vector containing a luciferase reporter gene under the control of the rat SMVT promoter demonstrated that its transcriptional activity is regulated by biotin availability through activation of the HCS-sGC-PKG pathway. Our results support the proposed role of SMVT in the altruistic regulation of biotin utilization in liver cells that has been associated with sparing biotin depletion of the brain.
authors.affiliation: Department of Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico D.F. 04510, Mexico.
authors.forename: Diana
authors.initials: D
authors.lastname: Pacheco-Alvarez
authors.forename: R Sergio
authors.initials: RS
authors.lastname: Solórzano-Vargas
authors.forename: Alfonso
authors.initials: A
authors.lastname: González-Noriega
authors.forename: Colette
authors.initials: C
authors.lastname: Michalak
authors.forename: Janos
authors.initials: J
authors.lastname: Zempleni
authors.forename: Alfonso
authors.initials: A
authors.lastname: León-Del-Río
mesh_terms: D000818:Animals; D001710:Biotin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D019921:Biotinylation; D015153:Blotting, Western; D018929:Cell Culture Techniques; D017869:Cyclic GMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D006801:Humans; D008099:Liver / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D051272:Glucose Transporter Type 1; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; C495677:SLC2A1 protein, human; D027981:Symporters; C119981:biotin transporter; D001710:Biotin; D017869:Cyclic GMP-Dependent Protein Kinases