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J. Biol. Chem., Vol. 283, Issue 10, 6367-6374, March 7, 2008
Characterization of NAD Uptake in Mammalian Cells*From the Dipartimento di Scienze Chimiche, Alimentari, Farmaceutiche e Farmacologiche and the Drug and Food Biotechnology Center, Università del Piemonte Orientale, Via Bovio 6, Novara 28100, Italy Recent evidence has shown that NAD(P) plays a variety of roles in cell-signaling processes. Surprisingly, the presence of NAD(P) utilizing ectoenzymes suggests that NAD(P) is present extracellularly. Indeed, nanomolar concentrations of NAD have been found in plasma and other body fluids. Although very high concentrations of NAD have been shown to enter cells, it is not known whether lower, more physiological concentrations are able to be taken up. Here we show that two mammalian cell types are able to transport low NAD concentrations effectively. Furthermore, extracellular application of NAD was able to counteract FK866-induced cell death and restore intracellular NAD(P) levels. We propose that NAD uptake may play a role in physiological NAD homeostasis.
Received for publication, July 27, 2007 , and in revised form, January 4, 2008. * The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 To whom correspondence should be addressed. Tel.: 39-032-137-5835; Fax: 39-032-137-5821; E-mail: billington{at}pharm.unipmn.it.
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