Background and Aim: We have previously observed that gliadin peptide P31-43 can induce proliferation of NIH3T3 cells and of enterocytes of untreated celiac mucosa due to an interference of this peptide with the degradation of the ligand loaded EGF receptor (1). We have also shown that in presence of P31-43 the EGF receptor stays longer activated as a consequence of a delay of the endocytic maturation. Aim of our study was to investigate whether proliferative effects induced by gliadin peptide P31-43 could be mediated also by activation of innate immunity. In particular we tested P31-43 effects on IL15 induction at level of transcription, translation, intracellular trafficking and role in P31-43 induced proliferation of both Caco2 cells and celiac enterocytes.Materials and Methods: Semi-quantitative and real time PCR were employed to investigate P31-43 effects on IL15 mRNA levels. FACS allowed analysis of the protein levels and distribution. Signalling downstream IL15 activation was examined by WB. BrdU (bromodeoxiuridine) incorporation was employed as proliferation marker, both in Caco 2 cells and in intestinal biopsies from untreated coeliac patients.Results: In Caco 2 cells P31-43 induces increase of IL15 mRNA levels after o/n treatment. By FACS analysis IL15 protein was found increased only on the cell surface; in fact, the percentage of IL15 positive cells on the surface rises from 18+/- 15%, of the untreated sample to 40+/-12% of the P31-43 o/n treated sample. This form of IL15 was not resistant to the acid treatment indicating that it is linked to the receptor. Erk and STAT5, two downstream effectors of the IL15 signalling and the IL15 receptor alfa (IL15Ra) itself are activated after P31-43 treatment. Anti-IL15 blocking antibodies can prevent P31-43 induced increase of proliferation in Caco2 cells and in enterocytes of biopsies from coeliac patients.Summary: P31-43 increases IL15 levels in the membranes and in the medium of Caco2 cells. IL15Ra and the downstream effectors Erk and Stat 5 are activated. Finally, P31-43 induced proliferation can be prevented by inhibitors of both EGF and IL15 pathway activation.Conclusion: P31-43 induced expression of IL15 contributes to gliadin effects on cell proliferation and activation of innate immunity.
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