Cdc42‐independent activation and translocation of the cytostatic p21‐activated protein kinase γ‐PAK by sphingosine

Abstract

Autophosphorylation of p21-activated protein kinase γ-PAK is stimulated at 10 μM sphingosine in vitro and is maximal at 100 μM. Sites autophosphorylated on γ-PAK in response to sphingosine are identical to those obtained with Cdc42(GTP). Autophosphorylation is paralleled by stimulation of γ-PAK activity as measured with peptide and protein substrates. In 3T3-L1 cells, sphingosine stimulates the autophosphorylation and activity of γ-PAK associated with the membrane-containing particulate fraction by 2.8-fold, but does not stimulate the activity of the soluble enzyme. Thus, γ-PAK is activatable via a Cdc42-independent mechanism, suggesting sphingosine has a role in γ-PAK activation under conditions of cell stress.