School of Medical Science and Molecular Basis of Disease Program, Menzies Health Institute Queensland, Griffith University, Gold Coast, Parklands Drive, Southport, QLD 4222, Australia
Wiskott-Aldrich Syndrome Protein-Interacting Protein (WIP) interacts with Wiskott-Aldrich Syndrome Protein (WASP) to activate the Arp2/3 complex and promote the nucleation of branched actin filaments. Dysfunction of WIP and WASP in humans is implicated in a range of diseases such as the inherited immunodeficiency disease WAS (Wiskott-Aldrich Syndrome) and cancer. In Saccharomyces cerevisiae (baker's yeast), the Src Homology 3 (SH3) domain of Hof1p, a key regulator of the yeast cell cycle, binds proline-rich motifs in yeast WIP (verprolin/Vrp1p). In the absence of yeast WIP, the Hof1p SH3 domain has a toxic effect and appears to inhibit actin-dependent processes such as cytokinesis and endocytosis. Yeast cells lacking yeast WIP can be rescued by the expression of human WIP. If interactions between the SH3 domains of yeast Hof1p and its human equivalents and proline-rich motifs in human and yeast WIP have been conserved and mediate similar functions in actin-dependent processes, then the results of this study could aid in finding new treatments for WAS and elucidating the roles of WASP and WIP in tumor-suppression. The yeast two-hybrid system and in vitro pull-down assays using purified recombinant proteins were employed to test if the yeast Hof1p SH3 domain binds human WIP. We found that the yeast Hof1p SH3 domain interacts with two proline-rich motifs in the C-terminus of human WIP one of which is already reported to be important for human WIP function in yeast. This result indicates that these protein interactions have been conserved from yeasts to humans.