POLYAMINE
TRANSPORT AND CANCER
Polyamines (putrescine, spermidine and spermine) are ubiquitous cellular components with various essential functions. These functions include the control of macromolecular biosynthesis and growth-related processes, as well as ion channel activity. Both increased polyamine biosynthesis and uptake from extracellular sources favor cellular transformation and tumor progression. The polyamine biosynthetic pathways have been described in considerable molecular details and therapeutic tools have been developped that efficiently block polyamine biosynthesis resulting in complete growth arrest. However, the marked increased in polyamine membrane transport that accompanies carcinogenesis pre-empts the antitumor effect of polyamine synthesis inhibitors in vivo. The molecular structure of polyamine carriers is still unknown.
Our research program aims at 1) identifying the molecular structure and physiopathological functions of polyamine membrane carrier systems in eukaryotes, and 2) developping specific antagonists of polyamine transport as therapeutic tools to enhance the antitumor effect of polyamine biosynthesis inhibitors in various neoplasias. The molecular cloning of polyamine transporters in human and yeast cells was carried out using mutagenesis and expression cloning approaches in polyamine transport-deficient cell lines. Our studies have revealed that a novel family of serine/threonine protein kinases controls the expression of polyamine transporters in yeast, and we are currently determining the mode of action of these kinases. Our drug development program includes the organic synthesis and biochemical evaluation of novel polyamine analogs which act as polyamine transport inhibitors in various in vitro and in vivo cancer models. These studies are being conducted jointly with Drs. Marie Audette and René Charest-Gaudreault (from the Departments of Medical Biology and Pharmacology, respectively).
These projects are supported by the Medical Research Council of Canada and the Natural Sciences and Engineering Research Council of Canada.
Huber M, Pelletier J, Torossian K, Dionne P, Gamache I, Charest-Gaudreault R, Audette M, Poulin R (1996). 2,2'-Dithiobis(N-ethyl-spermine-5-carboxamide) is a high affinity, membrane-impermeant antagonist of the mammalian polyamine transport system. J Biol Chem 271 27556-27563.
Kaouass M, Audette M, Ramotar D, Torossian K, Gamache I, DeMontigny D, Verma S, Poulin R (1997). The STK2 gene, which encodes a putative serine/threonine protein kinase, is required for high-affinity spermidine transport in Saccharomyces cerevisiae. Mol. Cell. Biol. 17, 2994-3004.
Kaouass M, Gamache I, Ramotar D, Audette M, Poulin R (1998) The spermidine transport system is regulated by ligand inactivation, endocytosis, and by the Npr1p Ser/Thr protein kinase in Saccharomyces cerevisiae. J Biol Chem 273: 2109-2117.
Poulin R, Zhao C, Verma S, Charest-Gaudreault R, Audette M (1998) Dependence of mammalian putrescine and spermidine transport on membrane potential: identification of an amiloride binding site on the putrescine carrier. Biochem J 330 : 1283-1291.
Torossian K, Audette M, Poulin R (1998) Substrate protection against inactivation of the mammalian polyamine transport system by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. Biochem J 319 : 21-26.