The analysis of PAR-3 in flow-mediated endothelial planar cell polarity
Final Report Abstract
Endothelial cells (ECs) have profound morphological adaptation to hemodynamic shear stress and show planar cell polarity (PCP) to the direction of blood flow. To establish functional vessels, dynamic changes of microtubules and the actin cytoskeleton are observed with maintaining blood flow. Cell shape is elongated along the axis of flow, and the microtubule organization centers (MTOCs) and the Golgi apparatus are aligned parallel to the flow direction. In contrast, regions of disrupted flow in the aorta often show roundish cell shape and disorganized Golgi orientation, which is highly associated with a pro-inflammatory condition. Although disrupted cell polarity plays a causative role in tumor initiation and progression, a causal link between compromised endothelial PCP and vascular inflammatory responses under flow has not been shown. Cell polarization is achieved by integrating of both extra- and intracellular signaling cascades controlling cytoskeletal dynamics. The signaling crosstalk among Rho family small GTPases, Cdc42, Rac1 and RhoA, regulates cytoskeletal reorganization mediated by the PAR polarity protein complex. Activated Cdc42 binds to the PAR-6/aPKC complex, leading to aPKC activation and promoting association with PAR-3. PAR-3 directly interacts with Rac1 activation factor, Tiam1/2 and further forms a complex with aPKC, PAR-6 and Cdc42, thereby mediating Cdc42-induced Rac1 activation. The RhoA effector Rhokinase/ROCK/ROK phosphorylates PAR-3 and disrupts the PAR complex, resulting in Rac1 inactivation. In addition, aPKC and PAR-6, but not PAR-3, forms a protein complex with Glycogen synthase kinase-3 beta (GSK3b) in migrating astrocytes and during epithelial cell death. aPKC/GSK3b complex formation inactivates GSK3b leading to the stabilization of microtubules and MTOC reorientation. In the cardiovascular system, it has been shown that PAR-3 regulates sprouting behavior of endothelial cells (ECs) during angiogenesis, meanwhile the role of PAR-3 in endothelial polarization in vivo was not shown. In line with these observations, we investigated the role of endothelial PAR-3 in EC polarization. EC specific inducible PAR-3 loss of function mice exhibit compromised PCP in a flow-rate dependent manner. Shear stress controls the spatio-temporal antagonism of the PAR-3/aPKC, complex versus the GSK3b/aPKC complex through the RhoA/Rho-kinase pathway, resulting in spatially controlled microtubules stabilization in the axis of flow. Moreover, vascular inflammatory responses are increased by regulating NF-kB, a key regulator of inflammation, nuclear localization downstream of GSK3b in PAR-3 loss of function conditions. Importantly, pharmacological suppression of GSK3b restored increased NF-kB nuclear localization but not endothelial PCP. Our results indicate an indirect relationship between endothelial PCP and vascular inflammation downstream of PAR- 3.
Publications
- PAR-3 controls endothelial planar polarity and vascular inflammation under laminar flow. EMBO Rep. 2018;19(9)
Hikita T, Mirzapourshafiyi F, Barbacena P, Riddell M, Pasha A, Li M, Kawamura T, Brandes RP, Hirose T, Ohno S, Gerhardt H, Matsuda M, Franco CA, Nakayama M
(See online at https://doi.org/10.15252/embr.201745253)
