Role of PAK1 and PAK2 kinases in Snail phosphorylation and in the epithelial-mesenchymal transition

1025 The epithelial-mesenchymal transition (EMT) can convert epithelial tumor cells to a more metastatic phenotype characterized by enhanced cell migration and invasion, increased resistance to anoikis and apoptosis, and greater resistance to chemotherapy or molecular targeted therapeutics. PAK1 was reported to phosphorylate Snail, a transcriptional repressor that acts as a master regulator of the epithelial-mesenchymal transition, on serine 246. Ser246 phosphorylation by PAK1 in MCF7 breast cancer cells was reported to be important for Snail translocation to the nucleus where it could repress target genes such as E-cadherin, aromatase, and occludin. Here we present supporting evidence for a positive role of both PAK1 and PAK2 kinases in a TGFβ-driven EMT model. We show that TGFβ treatment of the epithelial H358 NSCLC cell line results in downregulation of epithelial markers (E-cadherin, ErbB3) and upregulation of mesenchymal markers (N-cadherin, Snail, ZEB1). siRNA oligos targeting both PAK1 and PAK2 abolished many of the EMT marker changes induced by TGFβ, whereas siRNA oligos targeting only PAK1 or PAK2 alone were insufficient to suppress these EMT marker changes. Importantly this effect was correlated with the inhibition of Snail phosphorylation on Ser246, translocation to the nuclear compartment, and protein accumulation. In addition, expression of the PAK1 auto-inhibitory domain (AID), which acts as a dominant negative inhibitor of both PAK1 and PAK2 function, was demonstrated to inhibit Snail phosphorylation and nuclear localization in HeLa cells. These findings indicate that dual inhibition of PAK1 and PAK2 may be a promising approach to inhibit Snail-mediated EMT for treatment of cancer.