PAK1 and cancer: Rac1, Pak1 and Rock1, through the phosphorylation activation of the threonine residue within the LIMK1 ring, regulates the activity of LIMK1 and plays a role in cancer invasion and metastasis.22 LIMK is regulated by a variety of upstream signals, where the main upstream signal involved in the migration and invasion is the Rho GTP enzyme family.