Polyamine production is downstream and upstream of oncogenic PI3K signalling and contributes to tumour cell growth

Author:

Rajeeve Vinothini1,Pearce Wayne2,Cascante Marta3,Vanhaesebroeck Bart2,Cutillas Pedro R.1

Affiliation:

1. Analytical Signaling Group, Centre for Cell Signaling, Barts Cancer Institute, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, U.K.

2. Cell Signalling Group, Centre for Cell Signaling, Barts Cancer Institute, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, U.K.

3. Department of Biochemistry and Molecular Biology, Biology Faculty, Biomedicine Institute (IBUB), Universitat de Barcelona, and Associated Unit with CSIC (Consejo Superior de Investigaciones Científicas), Barcelona 08028, Spain

Abstract

PI3K (phosphoinositide 3-kinase) signalling pathways regulate a large array of cell biological functions in normal and cancer cells. In the present study we investigated the involvement of PI3K in modulating small molecule metabolism. A LC (liquid chromatography)-MS screen in colorectal cancer cell lines isogenic for oncogenic PIK3CA mutations revealed an association between PI3K activation and the levels of polyamine pathway metabolites, including 5-methylthioadenosine, putrescine and spermidine. Pharmacological inhibition confirmed that the PI3K pathway controls polyamine production. Despite inducing a decrease in PKB (protein kinase B)/Akt phosphorylation, spermidine promoted cell survival and opposed the anti-proliferative effects of PI3K inhibitors. Conversely, polyamine depletion by an ornithine decarboxylase inhibitor enhanced PKB/Akt phosphorylation, but suppressed cell survival. These results suggest that spermidine mediates cell proliferation and survival downstream of PI3K/Akt and indicate that these two biochemical pathways control each other's activities, highlighting a mechanism by which small molecule metabolism feeds back to regulate kinase signalling. Consistent with this feedback loop having a functional role in these cell models, pharmacological inhibitors of PI3K and ornithine decarboxylase potentiated each other in inhibiting tumour growth in a xenograft model. The results of the present study support the notion that the modulation of spermidine concentrations may be a previously unrecognized mechanism by which PI3K sustains chronic proliferation of cancer cells.

Publisher

Portland Press Ltd.

Subject

Cell Biology,Molecular Biology,Biochemistry

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