The Inflammatory Calcium Binding Protein S100A8 and Its N-Terminal Proteolytic Fragment Interact with Transforming Growth Factor-Beta1 (TGF-b1) and Alter Akt, mTOR and NF-kappa B Cancer Cell Signalling
Context S100A8 is highly expressed by stromal cells in pancreatic cancer when SMAD4 is not mutated or by cancer cells when SMAD4 is mutated, suggesting a link between TGF-β1 and S100A8 pathways. The proteolytic fragment of S100A8, NT-S100A8, highly abundant in pancreatic cancer, is involved in altering insulin secretion and action. Objective To ascertain whether S100A8 and NT-S100A8 interacts with TGF-β1 in altering intracellular calcium, NF-kappa B, Akt and mTOR signalling. Methods BxPC3 cells were stimulated with S100A8 (10 nM), NT-S100A8 (50 nM) alone or combined with TGF-β1 (0.02 ng/mL). Intracellular calcium was monitored by Fluo4 (epifluroescence). Akt (Ser473,Thr308), mTOR (Ser2448), NF-kappa B (p-IkB-a) were WB analyzed. Results NT-S100A8 evoked a train of intracellular calcium fluxes after 150-second lag time, which was reduced to few seconds in the presence of TGF-β1. S100A8 or TGF-β1 alone did not alter intracellular calcium. NF-kappa B signalling was activated in a calcium-dependent manner by S100A8 and by NT-S100A8 in the presence of TGF-β1. Akt Ser473 phosphorylation was reduced by NT-S100A8, TGF-β1 but mainly by their combination. AktThr308 was not affected by the studied molecules. mTOR phosphorylation (Ser2448) was induced by S100A8 and, at a lesser degree, by TGF-β1 and NT-S100A8. The phosphorylation (Ser235/236) of the downstream effector of mTORC1, S6RB, was reduced by TGF-β1 and NT-S100A8 independently, not by S100A8. Conclusion NT-S100A8 mimics TGF-β1 inhibitory effects on Akt and mTOR signalling. These two molecules co-operate in inhibiting Akt probably by altering intracellular calcium, while they co-operate in activating NF-kappa B in a calcium-independent manner mimicking the entire S100A8 molecule effect.
Copyright (c) 2014 Dania Bozzato, Stefania Moz, Andrea Padoan, Michele Scorzeto, Paola Fogar, Cosimo Sperti, Eliana Greco, Carlo Federico Zambon, Filippo Navaglia, Michele Pelloso, Elisa Rossi, Claudio Pasquali, Sergio Pedrazzoli, Carlo Reggiani, Mario Plebani, Daniela Basso
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