p21-Activated Kinase 2 Regulates Endothelial Development and Function through the Bmk1/Erk5 Pathway

Abstract

p21-activated kinases (Paks) have been shown to regulate cytoskeleton rearrangements, cell proliferation, attachment, and migration in a variety of cellular contexts, including endothelial cells. However, the role of endothelial Pak in embryo development has not been reported, and currently, there is no consensus on the endothelial function of individual Pak isoforms, in particular p21-activated kinase 2 (Pak2), the main Pak isoform expressed in endothelial cells. In this work, we employ genetic and molecular studies that show that Pak2, but not Pak1, is a critical mediator of development and maintenance of endothelial cell function. Endothelial depletion of Pak2 leads to early embryo lethality due to flawed blood vessel formation in the embryo body and yolk sac. In adult endothelial cells, Pak2 depletion leads to severe apoptosis and acute angiogenesis defects, and in adult mice, endothelial Pak2 deletion leads to increased vascular permeability. Furthermore, ubiquitous Pak2 deletion is lethal in adult mice. We show that many of these defects are mediated through a newly unveiled Pak2/Bmk1 pathway. Our results demonstrate that endothelial Pak2 is essential during embryogenesis and also for adult blood vessel maintenance, and they also pinpoint the Bmk1/Erk5 pathway as a critical mediator of endothelial Pak2 signaling.

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00630-15.

ACKNOWLEDGMENTS

We thank Luisa Iruela-Arispe for providing the VEC-CreER^T2 mice, Jun-Ichi Abe for adenovirus expressing constitutively active Mek5, the Transgenic Facility and the Lab Animal Facility at the Fox Chase Cancer Center and Genentech for assistance with production of Pak2^fl/fl mice, the Imaging Facility at the Fox Chase Cancer Center and the Center for Advanced Light Microscopy at Genentech for assistance with immunofluorescence experiments, and Ailey Crow for assistance with actin stress fiber quantification.

This work was supported by grants from the NIH (R01 CA148805 and R01 CA098830), Department of Defense (NF130108), and Children's Tumor Foundation to Jonathan Chernoff, NIH CORE Grant CA06927, and an appropriation from the state of Pennsylvania to the Fox Chase Cancer Center.