Polyamines modulate epithelial-to-mesenchymal transition.

Epithelial-to-mesenchymal transition and mesenchymal-to-epithelial transition are biologic processes responsible for conversion of epithelial cells into a mesenchymal phenotype or viceversa, respectively. They occur during embryo- and foetal-development and, in adult organisms, are involved in wound healing, in the genesis and progression of organ fibrosis as well as in the invasiveness of epithelial cancer cells. The key event of epithelial-to-mesenchymal transition is the loss of E-cadherin expression due to repressor activity of the transcriptional factor Snai1. Intracellular Snai1 levels are controlled through translational and post-translational events such as phosphorylation and de-phosphorylation, potentially modulated by polyamine content. Epithelial MDCK cells exposed to TGF-ß(1) acquired a fibroblastoid phenotype and expressed mesenchymal markers. These changes were emphasized in cells that were also exposed to DFMO in order to decrease the intracellular levels of polyamines. Addition of exogenous polyamines almost completely abolished the combined action of DFMO and TGF-ß(1) and rapidly reverted to epithelial phenotype MDCK cells previously undergone to mesenchymal phenotype. Nuclear extracts of cells treated with DFMO + TGF-ß(1) revealed the presence of Snai1 immunopositive bands in a range of molecular weight between 55 and 72 kDa, with additional positive bands detected at MW greater than 170 kDa. Same bands resulted positive to anti-Sumo 2/3 antibody, suggesting that an intracellular low level of polyamines favours Snai1 nuclear accumulation under the form of polysumoylated proteins.

Chronic exposure to agmatine results in the selection of agmatine-resistant hepatoma cells.

During our study of the cytostatic effect of agmatine, we were able to isolate an agmatine resistant clone from a parental hepatoma cell line, HTC. These cells, called Agres, had slower growth rate than the parental cells when cultured in normal medium. The modification in polyamine content induced by agmatine was much lower in these cells and ornithine decarboxylase, S-adenosylmethionine decarboxylase and spermidine/spermine acetyltransferase activities were much less affected. By investigating the mechanism responsible for these modifications, it was shown that agmatine and polyamines were not taken up by Agres cells. Their resistance to the antiproliferative effects of agmatine may thus arise from a lack of the polyamine transport system. Moreover, Agres cells were able to take up both glutamic acid and arginine at a rate significantly higher than that detected for HTC cells, most likely to provide components for compensatory increase of PA synthesis. These results emphasize the importance of polyamine transport for cell growth.