L1CAM–integrin interaction induces constitutive NF-κB activation in pancreatic adenocarcinoma cells by enhancing IL-1β expression

L1 cell adhesion molecule (L1CAM) overexpression is often associated with bad prognosis in various human carcinomas. Recent studies also suggest a role of L1CAM in pancreatic ductal adenocarcinomas (PDAC). To further address its contribution, we expressed functional domains of L1CAM in PT45-P1 PDAC cells. We found that L1CAM that is full length (L1-FL), but neither the soluble ectodomain (L1ecto) nor the cytoplasmic part (L1cyt), could enhance cell proliferation or tumour growth in mice. Expression of L1-FL resulted in constitutive activation of NF-κB, which was abolished by L1CAM knockdown. We showed that the expression of IL-1β was selectively upregulated by L1-FL, and increased IL-1β levels were instrumental for sustained NF-κB activation. IL-1β production and NF-κB activation were abolished by knockdown of α5-integrin and integrin-linked kinase, but insensitive to depletion of L1CAM cleavage proteinases. Supporting these data, PT45-P1 cells transduced with an L1CAM mutant deficient in integrin binding (L1-RGE) did not support the described L1-FL functions. Our results suggest that membranous L1CAM interacts with RGD&!minus;-binding integrins, leading to sustained NF-κB activation by IL-1β production and autocrine/paracrine signalling. The unravelling of this novel mechanism sheds new light on the important role of L1CAM expression in PDAC cells.