Hyperosmolarity shifts fas signaling pathway from apoptosis to proliferation by activation of p38 in gastric mucosal cell

Abstract

BackgroundAerative response to FasL was determined in control medium or hyperosmotic medium (40mM or 80 mM sodium chloride) via a combination of FACS, DNA fragmentation assay, BrdU incorporation, NF-KB activation an_alysis, and WST-1 assay. Western blot. with phosphor-specific antibody was used to quami~ate the phosphorylation status of p38 MAPK as an index of p38 activation. Results. Exposure to hypemsmotic medium for 10 rain resulted in a marked increase in p38 MAPK phosphorylation which was inhibited by pretreannent witb SB203580, a specific inhibitor of p38 phosphoryiation. NF-KB activation increased 1.5 and 4 4 fold in cells exposed to 40 or 80mM NaCI respectively, an effect that was cnmpletdy aboliahed by the addition of SB203580. Low abundance clones increased proliferation (BrdU incorporation) in response to Fas L (12.5 ng/ml for 24 hours) from 10.09% to 14.42% which was dramatically augmented by NaCt 40ram in the presence of Fas L (2611%) but not in its absence (11.03%), and was dependent on p38 activation (NaC140raM, Fas L 12.5 ng/ml, SB203580 = I4.63%) To test if NaCI exposure could also protect against Fas mediated apoptosis, we employed a high Fas abundance clone which is highly sensitive to Fas mediated apoptosis After 24 hours exposure to 50ng/ml FasL, 76 -+ 0.03% of cells were apoptotic. This level decreased dramatically to 10.2 _+ 0.02% with the addition of 40 mM NaCI. This protective effect of NaCI was completely reversed by tire addition at SB203580 (79 -+ 0.04% apoptosis) WST-I assay confirmed increased cell survival in the NaCI treated group Conclusions. Hyperosnmlarity in the physiological range can active p38 MAPK signal, which may enhance Fas proliteeative signaling, and inhibit Fas apoptotic signaling. This growth signaling imbalance may contribute to the association between high salt diets and gasu'ic cancer,