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P016. ABCG2 down regulation in active inflammatory bowel disease is due to incorrect protein folding

J. Deuring, C. de Haar, C. Koelewijn, E.J. Kuipers, M. Peppelenbosch, C.J. van der Woude

Erasmus MC, Rotterdam, The Netherlands

Background and Aim: The expression of ABCG2 is dramatically reduced in intestinal epithelium during active inflammation. Proper protein folding of ATP-binding cassette transporter proteins, such as ABCG2, is crucial for proper membrane localisation and function. As such, inflammation induced protein misfolding could affect correct ABCG2-protein folding thereby reducing its apical expression. Here we studied whether elevated levels of nitric oxide (NO) produced by the innate immune system during active inflammation could affect folding and function of ABCG2 leading to activation of the endoplasmic reticulum (ER) stress pathways in the intestinal epithelium cells.

Methods: The expression of ABCG2 and the misfolded protein response (ER stress) marker, glucose-regulated protein 78 (GRP78), were studied histochemically in colon biopsies from healthy individuals (n = 9), patients with inactive (n = 67) or active (n = 55) inflammatory bowel disease, ischemic colitis (n = 10), or infectious colitis (n = 14) and in small bowel biopsies from healthy individuals (n = 27), and patients with inactive (n = 9) or active (n = 25) Crohns disease. The effect of NO on protein folding, as well as ABCG2 expression and function was studied in GFP-ABCG2 transgenic HEK293t cells using live-cell imaging on a confocal microscope.

Results: In all biopsies from actively inflamed mucosa the ABCG2 expression was significantly decreased whereas the GRP78 expression was increased. No significant differences were seen between the locations of inflammation or between the different diseases. Nitric oxide induced protein misfolding leading to ER stress in HEK293t cells. This was associated with reduced membrane localisation and transport activity of GFP-ABCG2.

Conclusion: NO induced ER stress, by affecting proper protein folding, is likely involved in the reduced expression and function of ABCG2 in the intestinal epithelial cells during mucosal inflammation.