Regulation of VASP by phosphorylation: consequences for cell migration

Abstract

Phosphorylations control all aspects of vasodilator-stimulated phospho-protein (VASP) function. Mapped phosphorylation sites include Y39, S157, S239, T278, and S322, and multiple kinases have been shown to mediate their phosphorylation. Recently, Protein Kinase D1 (PKD1) as a direct kinase for S157 and S322 joined this group. While S157 phosphorylation generally seems to serve as a signal for membrane localization, phosphorylations at S322 or at S239 and T278 have opposite effects on F-actin accumulation. In migrating cells, S322 phosphorylation increases filopodia numbers and length, while S239/T278 phosphorylations decrease these and also disrupt formation of focal adhesions. Therefore, the kinases mediating these phosphorylations can be seen as switches needed to facilitate cell motility.

Keywords: VASP; cytoskeleton; filopodium; leading edge; migration; phosphorylation.

Figure 1. VASP domains, interacting proteins, phosphorylation sites, and upstream kinases. (A) VASP consists of a WH1/EVH1 domain (aa2-aa113), a prolin-rich domain (aa118-aa216), and an EVH2 domain (aa225-aa377). The EVH1 domain interacts with WASP, vinculin, zyxin, LPP, and actA; the prolin-rich (PR) domain with profilin and SH3 domains of Abl and Src; the EVH2 domain binds to F- and G-actin, but also is required for tetramerization of VASP. Multiple phosphorylation sites have been mapped including Y39 (phosphorylated by Abl) in the EVH1 domain, S157 in the PR domain (mediated by PKA, PKG, and PKD1), as well as S239 and T278 (mediated by RSK1, PKA, PKG, and AMPK, as indicated) and S322 (mediated by PKD1 and AMPK) in the EVH2 domain. (B) The VASP “phosphorylation code” with respect to its functions in regulating cell motility. Phosphorylation at Y39 decreases localization at the focal adhesions. Phosphorylation at S157 mediates membrane localization. Additional phosphorylation at S322 mediates F-actin accumulation and increases numbers of filopodia, while additional phosphorylation at S239 (and phosphorylation at T278) prevents F-actin bundling, decreases F-actin accumulation and decreases filopodia formation.