Pak1 kinase activity affects the character of cell morphology and movement

Abstract

As described in the review by Bagrodia and Cerione1xBagrodia, S. and Cerione, R. Trends Cell Biol. 1999; 9: 350–355Abstract | Full Text | Full Text PDF | PubMed | Scopus (323)See all References1, inducible expression of different forms of Pak1 in NIH3T3 cells leads to changes in cell morphology and pattern of movement2xSells, M.A. et al. J. Cell Biol. 1999; 145: 837–849Crossref | PubMed | Scopus (291)See all References2. This figure shows wild-type cells (a), and cells overexpressing either an active form of Pak1 (b) or a kinase-dead form (c). The cells expressing constitutively active Pak1 have large, polarized lamellipodia at their leading edge and are more motile than the control cells (Fig. 1Fig. 1). Sells and colleagues also observed that these cells moved more rapidly in response to a collagen gradient when plated on a fibronectin surface. By contrast, the cells expressing the kinase-dead form of Pak1 had several lamellipodia projecting in different directions simultaneously. They were highly motile, but in a more random manner, and their ability to respond to the collagen gradient by directional movement was impaired. These movement differences correlated with changes in the organization of the actin cytoskeleton and are consistent with previous findings. Sells et al. also found that cells expressing the constitutively active form of Pak1 showed increased myosin light chain (MLC) phosphorylation and proposed that this is involved in the regulation of cell movement by Pak1. However, as described by Bagrodia and Cerione1xBagrodia, S. and Cerione, R. Trends Cell Biol. 1999; 9: 350–355Abstract | Full Text | Full Text PDF | PubMed | Scopus (323)See all References1, this does not agree with previous results in other cell types, where activated Pak reduced MLC phosphorylation. The influence of Pak, both direct and indirect, on MLC phosphorylation and the role of this modification in influencing cell movement both require further investigation.FIGURE 1Pak1 expression was induced in Pak1-overexpressing NIH 3T3 cells by removing tetracycline from the growth medium for 16 hours. The cells were then trypsinized and, after a 30-minute incubation on plates coated with bovine serum albumin, the cells were transferred to fibronectin-coated plates. Phase-contrast micrographs were taken 95 min later. The cells shown express: (a) empty vector (control cells), (b) Pak1L83,L86 (constitutively active) and (c) Pak1R299 (kinase dead). Bar, 50 μm.View Large Image | Download PowerPoint Slide