Nischarin inhibits Rac induced migration and invasion of epithelial cells by affecting signaling cascades involving PAK.

Nischarin, a cytosolic protein that binds the alpha5beta1 integrin, plays an important role in fibroblast migration, and in regulation of the actin cytoskeleton. The effect of Nischarin on Rac induced migration and invasion by breast and colon epithelial cell lines has been determined. In these cells, Rac potently induced migration, as well as invasion of matrix; both of these events were strongly inhibited by overexpression of Nischarin. To understand the mechanism of Nischarin's inhibitory role in Rac induced cell migration, several effector domain mutants of Rac1 were employed. Nischarin was able to inhibit migration induced by Rac effector mutants that can activate PAK and JNK, but not migration stimulated by other Rac mutants. Further, Nischarin inhibited PAK induced cell migration, while not affecting migration induced by MEKK1, a Rac effector in the JNK pathway. In addition, Nischarin failed to inhibit migration induced by MEK1, a downstream effector in the Ras-Raf-MEK-Erk signaling cascade. Furthermore, Nischarin does not affect Rac mediated JNK and PI3K activities. However, Rac induced migration and invasion were effectively blocked by pharmacological inhibitors of PI-3 kinase and MEK. These results suggest that several pathways contribute to cell migration, but that Nischarin selectively inhibits Rac driven signaling cascades that affect migration through PAK.