Constitutive non-canonical NFkappaB signaling in pancreatic cancer cells.

Constitutive classical NFκB activation has been implicated in the development of pancreatic cancer, and inhibition of classical NFκB signaling sensitizes pancreatic cancer cells to apoptosis. However, the role of the more recently described non-canonical NFκB pathway has not been specifically addressed in pancreatic cancer. The non-canonical pathway requires stabilization of NIK and IKKα-dependent phosphorylation and processing of NFκB2/p100 to p52. This leads to the activation of p52-RelB heterodimers that regulate genes encoding lymphoid-specific chemokines and cytokines. We performed qRT-PCR to detect gene expression in a panel of pancreatic ductal adenocarcinoma cell lines (BxPC-3, PCA-2, PANC-1, Capan-1, Hs-766T, AsPC-1, MiaPACA-2) and found only modest elevation of classical NFκB-dependent genes. In contrast, each of the tumor cell lines displayed dramatically elevated levels of subsets of the non-canonical NFκB target genes CCL19, CCL21, CXCL12, CXCL13 and BAFF. Consistent with activation of the non-canonical pathway, p52 and RelB co-localized in adenocarcinoma cells in sections of pancreatic tumor tissue, and each of the tumor cell lines displayed elevated p52 levels. Furthermore, p52 and RelB co-immunoprecipitated from pancreatic cancer cells and immunoblotting revealed that NIK was stabilized and p100 was constitutively phosphorylated in a subset of the cell lines. Finally, stable overexpression of dominant negative IKKα significantly inhibited non-canonical target gene expression in BxPC-3 cells. These findings therefore demonstrate that the non-canonical NFκB pathway is constitutively active and functional in pancreatic cancer cells.