Xenopus p21-activated kinase 5 regulates blastomeres' adhesive properties during convergent extension movements

Abstract

The p21-activated kinase (PAK) proteins regulate many cellular events including cell cycle progression, cell death and survival, and cytoskeleton rearrangements. We previously identified X-PAK5 that binds the actin and microtubule networks, and could potentially regulate their coordinated dynamics during cell motility. In this study, we investigated the functional importance of this kinase during gastrulation in Xenopus. X-PAK5 is mainly expressed in regions of the embryo that undergo extensive cell movements during gastrula such as the animal hemisphere and the marginal zone. Expression of a kinase-dead mutant inhibits convergent extension movements in whole embryos and in activin-treated animal cap by modifying behavior of cells. This phenotype is rescued in embryo by adding back X-PAK5 catalytic activity. The active kinase decreases cell adhesiveness when expressed in animal hemisphere and inhibits the calcium-dependent reassociation of cells, while dead X-PAK5 kinase localizes to cell-cell junctions and increases cell adhesion. In addition, endogenous X-PAK5 colocalizes with adherens junction proteins and its activity is regulated by extracellular calcium. Taken together, our results suggest that X-PAK5 regulates convergent extension movements in vivo by modulating the calcium-mediated cell-cell adhesion.

PAK6 targets to cell-cell adhesions via its N-terminus in a Cdc42-dependent manner to drive epithelial colony escape

“…We found that PAK4, PAK5 and PAK6 all target to cell-cell adhesions to varying degrees, indicating cell-cell adhesion targeting is not unique to PAK6 among the PAK family, but is a characteristic of type II PAKs. This is in agreement with previously published work showing that type II PAKs from other species, Xenopus PAK5 and Drosophila Mbt, also target to cell-cell adhesions (Schneeberger and Raabe, 2003;Faure et al, 2005). Further, while this manuscript was in preparation, a study was published confirming our observations that GFP-PAK4 localizes weakly to cell-cell adhesions (Selamat et al, 2015).…”

“…In keeping with this, we found that PAK6 constructs with altered catalytic activity (kinase-dead K436M, hyperactive P52L) but with intact N-termini still localize at cell-cell adhesions, indicating that PAK6 targeting to cell-cell adhesions is independent of catalytic activity. In agreement with our findings, the Xenopus type II PAK, PAK5 (also known as PAK7), targets to cell-cell junctions independent of catalytic activity (Faure et al, 2005).…”

Inca: a novel p21-activated kinase-associated protein required for cranial neural crest development

“…Knockdown of Inca expression by antisense morpholino oligonucleotides (MOs) in both Xenopus and zebrafish results in dramatic reductions in cranial NC-derived cartilage formation. We show that Inca interacts with PAK5, a p21-activated kinase downstream of the Rho GTPases Cdc42 and Rac1, previously implicated in cytoskeletal organization and apoptosis (Bokoch, 2003;Jaffer and Chernoff, 2002) as well as control of cell adhesion and convergent extension movements in Xenopus (Cau et al, 2001;Faure et al, 2005). Consistent with a role in cytoskeletal organization, Inca overexpression disrupts both cortical pigmentation in blastomeres and wound healing in Xenopus embryos.…”

“…Xenopus PAK5 is expressed maternally and, by the gastrula stages, expression overlaps that of Inca in the ectoderm, although it is not restricted to the inner, sensorial layer (Faure et al, 2005). At later stages, PAK5 expression appears ubiquitous (Fig.…”

“…PAK5 interacts with both microfilaments and microtubules in the Xenopus embryo, and interference with PAK5 function affects cell adhesion and convergent extension movements, both of which depend upon cytoskeletal integrity and Rho GTPase signaling (Faure et al, 2005;Kofron et al, 2002;Wunnenberg-Stapleton et al, 1999). To determine whether the Inca-PAK5 complex is also associated with the cytoskeleton, CHO cells were transiently cotransfected with Inca fused to GFP and PAK5 fused to red fluorescent protein (RFP) and observed with a confocal microscope.…”