Pancreatic cancer is a notorious disease with a poor prognosis and low survival rates, which is due to limited advances in understanding of the molecular mechanism and inadequate development of effective treatment options over the decades. In previous studies, we demonstrated that a novel soluble protein named pancreatic adenocarcinoma up-regulated factor (PAUF) acts on tumor and immune cells and plays an important role in metastasis and progression of pancreatic cancer. Here we show that PAUF promotes adhesiveness of pancreatic cancer cells to various extracellular matrix (ECM). Our results further support a positive correlation of activation and expression of focal adhesion kinase (FAK), a key player in tumor cell metastasis and survival, with PAUF expression. PAUF-mediated adhesiveness was significantly attenuated upon blockade of the FAK pathway. Moreover, PAUF appeared to enhance resistance of pancreatic cancer cells to anoikis via modulation of FAK. Our results suggest that PAUF-mediated FAK activation plays an important role in pancreatic cancer progression.
Anoikis/genetics ; Cell Line, Tumor ; Focal Adhesion Protein-Tyrosine Kinases/*metabolism ; Focal Adhesions/genetics/*metabolism ; Humans ; Lectins/genetics/*metabolism ; Pancreatic Neoplasms/enzymology/genetics/*metabolism ; Proto-Oncogene Proteins pp60(c-src)/metabolism ; Signal Transduction/genetics

CD98, a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein, regulates beta 1 integrin- mediated cell adhesion. However, the molecular mechanisms underlying CD98-mediated activation of beta 1 integrin are presently unclear. In this study, the effects of CD98 signaling on the expression and clustering of beta 1 integrin were investigated. Activation of CD98 augmented surface expression of beta 1 integrin on MCF-7 cells. Cross-linking CD98 induced clustering of beta 1 integrins. Inhibition of phosphorylation of focal adhesion kimase (FAK) by PP2, an inhibitor of Src family kinase, reduced cell-extracellular matrix adhesion, but not surface expression and clustering of beta1 integrin on MCF-7 cells. This result was confirmed by over-expression of dominant negative forms of FAK. In addition, phalloidin or cytochalasin D inhibited CD98-mediated induction of cell-ECM adhesion, but not surface expression and clustering of b1 integrins. The inhibitory effects of PP2, cytochalasin D or phalloidin on CD98-stimulated cell adhesion were diminished by pretreatment of cells with Mn2+, which is shown to induce conformational change of integrins. These results provide the first evidence that CD98 activation increases not only beta1 integrin affinity but also its surface expression and clustering and the latter is independent of FAK/Src and cytoskeleton.
Antigens, CD29/*biosynthesis/genetics ; Antigens, CD98/agonists/*metabolism ; Cell Line, Tumor ; Cytochalasin D/pharmacology ; Cytoskeleton/drug effects/enzymology ; Focal Adhesion Kinase 2/genetics/*metabolism ; Focal Adhesions/drug effects/enzymology ; Humans ; Microscopy, Confocal ; Multiprotein Complexes/*biosynthesis/genetics ; Mutant Proteins/genetics/metabolism ; Phalloidine/pharmacology ; Phosphorylation/drug effects ; Protein Binding ; Pyrimidines/pharmacology ; Signal Transduction/physiology ; Transfection