Identification of a mammalian silicon transporter.
Silicon (Si) has long been known to play a major physiological and structural role in certain organisms, including diatoms, sponges, and many higher plants, leading to the recent identification of multiple proteins responsible for Si transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding about the biochemical pathways that enable Si homeostasis. Here we report the identification of a mammalian efflux Si transporter, namely Slc34a2 (also termed NaPiIIb), a known sodium-phosphate cotransporter, which was upregulated in rat kidney following chronic dietary Si deprivation. Normal rat renal epithelium demonstrated punctate expression of Slc34a2, and when the protein was heterologously expressed inXenopus laevisoocytes, Si efflux activity (i.e., movement of Si out of cells) was induced and was quantitatively similar to that induced by the known plant Si transporterOsLsi2 in the same expression system. Interestingly, Si efflux appeared saturable over time, but it did not vary as a function of extracellular [Formula: see text] or Na+concentration, suggesting that Slc34a2 harbors a functionally independent transport site for Si operating in the reverse direction to the site for phosphate. Indeed, in rats with dietary Si depletion-induced upregulation of transporter expression, there was increased urinary phosphate excretion. This is the first evidence of an active Si transport protein in mammals and points towards an important role for Si in vertebrates and explains interactions between dietary phosphate and silicon.
Medical Research Council Elsie Widdowson Laboratory, Cambridge, United Kingdom.
Sarah
S
Ratcliffe
Medical Research Council Elsie Widdowson Laboratory, Cambridge, United Kingdom.|Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom.
Ravin
R
Jugdaohsingh
Département de Phytologie-Faculté des Sciences de l'Agriculture et de l'Alimentation, Centre de Recherche en Horticulture, Université Laval, Quebec City, Quebec, Canada.
Julien
J
Vivancos
Department of Zoology, University of Cambridge, Cambridge United Kingdom.
Alan
A
Marron
Department of Zoology, University of Cambridge, Cambridge United Kingdom.
Rupesh
R
Deshmukh
Institute of Plant Science and Resources, Okayama University, Kurashiki, Japan.
Jian Feng
JF
Ma
Institute of Plant Science and Resources, Okayama University, Kurashiki, Japan.
Namiki
N
Mitani-Ueno
Medical Research Council Elsie Widdowson Laboratory, Cambridge, United Kingdom.
Jack
J
Robertson
Mechanistic Studies Division, Environmental Health Sciences & Research Bureau, Health Canada, Ottawa, Ontario, Canada.
John
J
Wills
Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
Mark V
MV
Boekschoten
Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
Michael
M
Müller
Department of Chemistry, Lakehead University, Thunder Bay, Canada; and.
Robert C
RC
Mawhinney
Department of Chemistry, Lakehead University, Thunder Bay, Canada; and.
Stephen D
SD
Kinrade
Nephrology Group L'Hôtel-Dieu de Québec Institution, Department of Medicine, Faculty of Medicine, Université Laval, Quebec City, Quebec, Canada.
Paul
P
Isenring
Département de Phytologie-Faculté des Sciences de l'Agriculture et de l'Alimentation, Centre de Recherche en Horticulture, Université Laval, Quebec City, Quebec, Canada.
Richard R
RR
Bélanger
Medical Research Council Elsie Widdowson Laboratory, Cambridge, United Kingdom; jonathan.powell@mrc-ewl.cam.ac.uk jjp37@cam.ac.uk.|Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom.
Jonathan J
JJ
Powell
D000818:Animals; D005260:Female; D010710:Phosphates / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012825:Silicon / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb / Q000737:chemistry* / Q000378:metabolism*; D013045:Species Specificity
D010710:Phosphates; C493559:Slc34a2 protein, rat; D050614:Sodium-Phosphate Cotransporter Proteins, Type IIb; D012964:Sodium; D012825:Silicon
Slc34a2; Xenopus laevis oocytes; rat kidneys; silicon; transport