James R. Hammond


James Hammond

PH.D. University of Alberta
B.Sc. University of Western Ontario
Office: Medical Sciences Building, Room 266
Phone: (519) 661-2111 Ext. 83780
Fax: (519) 661-3827
E-mail: james.hammond@schulich.uwo.ca
See Publications by James Hammond on PubMed

The research focus of this laboratory is on the pharmacological, functional and molecular characterization of the membrane transport systems responsible for the uptake and release of endogenous nucleosides and anticancer/antiviral nucleoside analogues by mammalian cells. Adenosine, the primary physiological substrate for these transporters, is an endogenous bioactive agent with inhibitory neuromodulator, cardioprotective and vasodilator activities. These actions of adenosine are mediated through extracellular components of specific membrane-located adenosine receptors. Uptake into cells via nucleoside transporters is the first step in the metabolism and inactivation of extracellular nucleosides and these transport systems thereby play a significant role in controlling the bioactivity of adenosine. Multiple subtypes of nucleoside transporters have been identified by both functional and molecular approaches that differ in their sensitivities to inhibition by agents such as nitrobenzylthioinosine (NBMPR) and dipyridamole, and by their dependence on ion (sodium) gradients. Four of these transporters have now been cloned (ENT1, ENT2, CNT1, CNT2), and we have recently cloned the mouse homologues of the two major subtypes of equilibrative transporters (ENT1, ENT2) as well as two novel splice variants of the ENT1 transporter. The physiological and pharmacological significance of the multiple transporter subtypes/variants has yet to be established. Nucleoside transporter heterogeneity is expected to impact significantly on the actions of many drugs that act through adenosine receptors or by modifying cellular nucleoside metabolism. This has particular relevance to the clinical activities of the cytotoxic nucleoside analogues used in cancer chemotherapy (e.g. cytosine arabinoside, gemcitabine, 2-chlorodeoxyadenosine).

Current research in our laboratory involves the analysis of the protein structural elements involved in the interaction of drugs and substrates with the multiple subtypes and isoforms of equilibrative nucleoside transporters. Studies involve the generation of chimeric recombinant transporters (between transporter subtypes and species orthologues) and point mutants (site-directed mutagenesis) and their expression in Xenopus laevis oocytes and transporter-deficient mammalian cell lines. Nucleoside transport activity of the native and recombinant proteins is measured directly by the cellular accumulation of radiolabelled substrates and indirectly using specific probes for the proteins associated with the transporter. We are also interested in the role of protein phosphorylation in the activity and membrane turnover of the equilibrative transporters. In this regard, we have recently cloned two isoforms of the mouse ENT1 that differ in the inclusion or deletion of a potential protein kinase CK2 phosphorylation site. In collaboration with Dr David Litchfield, Department of Biochemistry, we are conducting studies to elucidate the importance of this protein kinase CK2 site to the regulation of nucleoside transporter activity. The overall goal of these studies is to provide detailed information on the functional and molecular characteristics of the proteins involved in nucleoside translocation. It is expected that these studies will lead ultimately to the development of new sedatives, anti-epileptics, and vasodilators that act through manipulation of adenosinergic systems, as well as novel drugs for use in the on-going battle against cancer and various viral and parasitic diseases.

Robillard KR, Bone DB, Park JS, Hammond JR. Characterization of mENT1Delta11, a novel alternative splice variant of the mouse equilibrative nucleoside transporter 1. Mol Pharmacol. 2008 Jul;74(1):264-73. Epub 2008 Apr 15.  Abstract

Robillard KR, Bone DB, Hammond JR. Hypoxanthine uptake and release by equilibrative nucleoside transporter 2 (ENT2) of rat microvascular endothelial cells. Microvasc Res. 2008 Apr;75(3):351-7. Epub 2007 Oct 18.  Abstract

Bone DB, Hammond JR. Nucleoside and nucleobase transporters of primary human cardiac microvascular endothelial cells: characterization of a novel nucleobase transporter. Am J Physiol Heart Circ Physiol. 2007 Dec;293(6):H3325-32. Epub 2007 Oct 5.  Abstract

Bone DB, Robillard KR, Stolk M, Hammond JR. Differential regulation of mouse equilibrative nucleoside transporter 1 (mENT1) splice variants by protein kinase CK2. Mol Membr Biol. 2007 Jul-Aug;24(4):294-303.  Abstract

Stolk M, Cooper E, Vilk G, Litchfield DW, Hammond JR. Subtype-specific regulation of equilibrative nucleoside transporters by protein kinase CK2. Biochem J. 2005 Mar 1;386(Pt 2):281-9.  Abstract

Archer RG, Pitelka V, Hammond JR. Nucleoside transporter subtype expression and function in rat skeletal muscle microvascular endothelial cells. Br J Pharmacol. 2004 Sep;143(1):202-14. Epub 2004 Aug 2.  Abstract

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