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Reddy PN , Radu M , Xu K , Wood J , Harris CE , Chernoff J , Williams DA
P21 activated kinase 2 regulates HSPC cytoskeleton, migration and homing via CDC42 activation and interaction with beta-Pix
Blood. 2016 Mar 1;127(16) :1967-75
PMID: 26932803    PMCID: PMC4841040    URL: http://www.ncbi.nlm.nih.gov/pubmed/26932803
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Cytoskeletal remodeling of hematopoietic stem/progenitor cells (HSPCs) is essential for homing to the bone marrow. The Rac/CDC42 GTPase effector p21 activated kinase (Pak2) has been implicated in HSPC homing and engraftment. However, the molecular pathways mediating Pak2 functions in HSPCs are unknown. Here, we demonstrate that both Pak2 kinase activity and its interaction with the exchange factor beta-Pix are required to reconstitute defective Pak2Delta/Delta HSPC homing to the bone marrow. Pak2 serine/threonine kinase activity is required for stromal derived factor-1 (SDF1alpha) chemokine-induced HSPC directional migration, while Pak2 interaction with beta-Pix is required to regulate the velocity of HSPC migration and precise F-actin assembly. Lack of SDF1alpha-induced filopodia and associated abnormal cell protrusions seen in Pak2Delta/Delta HSPC were rescued by full length Pak2 (WT) but not by a Pak2-kinase dead mutant (KD). Expression of beta-Pix interaction deficient mutant of Pak2 rescued filopodia formation but led to abnormal F-actin bundles detected by confocal microscopy. While CDC42 has previously been considered an upstream regulator of Pak2 we found a paradoxical decrease in baseline activation of CDC42 in Pak2 Delta/Delta HSPC. This dysregulated activation of CDC42 was rescued by expression of Pak2-WT but not by Pak2-KD, and defective homing of Pak2-deleted HSPC was rescued by constitutive active CDC42. These data demonstrate that both Pak2 kinase activity and its interaction with beta-Pix are essential for Pak2 regulation of HSPC filopodia formation, cytoskeletal integrity, and homing via activation of CDC42. Taken together we provide mechanistic insights into the role of Pak2 in HSPC migration and homing.
Reddy, Pavankumar N G Radu, Maria Xu, Ke Wood, Jenna Harris, Chad E Chernoff, Jonathan Williams, David A Blood. 2016 Mar 1. pii: blood-2016-01-693572.