Transforming growth factor beta 1 treatment leads to an epithelial-mesenchymal transdifferentiation of pancreatic cancer cells requiring extracellular signal-regulated kinase 2 activation

The aim of this study was to examine the effects of transforming growth fac tor (TGF) beta1 on the phenotype and the biological behavior of pancreatic cancer cell lines with and without mutations in the TGF-beta signaling path way and to elucidate whether the Ras signaling cascade participates in medi ating these effects of TGF-beta1, TGF-beta -responsive (PANC-1, COLO-357, a nd IMIM-PC1) and nonresponsive (CAPAN1 and IMIM-PC2) pancreatic cancer cell Lines with activating mutations of the Iii-Rns oncogene were treated with 10 ng/ml TGF-beta1 over time. Phenotypic alterations were studied by electr on and phase contrast microscopy and by immunohistochemistry and expression analyses of differentiation markers. The influence of TGF-beta on tumor ce ll scattering, migration, and invasion was determined. The role of the Ras- mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulate d kinase (ERK) cascade in mediating TGF-beta -induced morphological and fun ctional effects were studied by pretreatment with the MEK1 inhibitor PD 980 59 and by measuring ERK2 activation using immune complex kinase assays. TGF -beta1 led to a reversible and time-dependent epithelial-mesenchymal transd ifferentiation (EMT) in TGF-beta -responsive pancreatic cancer cell lines, characterized by a fibroblastoid morphology and an up-regulation of mesench ymal markers and a down-regulation of epithelial markers, EMT was associate d with an increase in tumor cell migration, invasion, and scattering. In th e responsive cell lines, TGF-beta1 induced a moderate but sustained activat ion of ERK2, EMT, the concomitant changes in gene expression, and the invas ive and migratory potential were reduced or abolished by pretreatment with the selective MEK1 inhibitor. Thus, in TGF-beta -responsive pancreatic canc er cells with activating Ki;Rns mutations, TGF-beta1 treatment caused an EM T associated with a more invasive phenotype. Cross-talk with the Ras-MEK-ER K-signaling cascade appears to be essential for mediating these effects of TGF-beta1.