TGF-β downregulates PTEN via activation of NF-κB in pancreatic cancer cells

Chow JY, Ban M, Wu HL, Nguyen F, Huang M, Chung H, Dong H, Carethers JM. TGF-beta downregulates PTEN via activation of NF-kappa B in pancreatic cancer cells. Am J Physiol Gastrointest Liver Physiol 298: G275-G282, 2010. First published November 25, 2009; doi:10.1152/ajpgi.00344.2009.-TGF-beta utilizes receptor-activated SMAD signaling to mediate growth suppression; however, non-SMAD signaling that modulates the TGF-beta response in epithelial cells become apparent when the SMAD signaling is abrogated, a common occurrence in pancreatic cancers. Here, we examined whether TGF-beta utilized NF-kappa B to downregulate PTEN, a gene that is rarely mutated in pancreatic cancers. SMAD4-null BxPc3 and CAPAN-1 pancreatic cancer cells were treated with TGF-beta (10 ng/ml) and lysed, and cellular proteins were analyzed by Western blots using p-I kappa B, p65, and PTEN antibodies. PTEN promoter and NF-kappa B activities were assessed by PTEN-luc and p-NF-luc constructs, respectively. Dominant negative p-I kappa B alpha-M (NF-kappa B superrepressor) was used to block activation of NF-kappa B. Cell motility was assessed by Boyden chamber migration assay. TGF-beta induced I kappa B-alpha phosphorylation followed by NF-kappa B p65 subunit nuclear translocation and increased NF-kappa B activity. I kappa B-alpha-M blocked TGF-beta-induced NF-kappa B activity, reversed downregulated PTEN promoter activity and PTEN expression, and prevented augmentation of cell motility induced by TGF-beta. SMAD4 restoration, but not knockdown of SMAD2 and/or 3, reversed TGF-beta-induced NF-kappa B activity. Thus TGF-beta suppresses PTEN in pancreatic cancer cells through NF-kappa B activation and enhances cell motility and invasiveness in a SMAD4-independent manner that can be counteracted when TGF-beta-SMAD signaling is restored. The TGF-beta/NF-kappa B/PTEN cascade may be a critical pathway for pancreatic cancer cells to proliferate and metastasize.