PAK1 and Huntington disease: Furthermore, HTT negatively regulates PAK2 apoptotic functions by preventing PAK2 cleavage via caspases: this protective function is retained by mutated HTT. These studies suggest that PAK1 and PAK2 have completely different associations with Huntington disease, PAK1 increases the toxicity of mutated HTT while PAK2 possibly has protective effects (Luo and Rubinsztein, 2009).