Dendritic Cell Motility and T Cell Activation Requires Regulation of Rho-Cofilin Signaling by the Rho-GTPase Activating Protein Myosin IXb

Abstract

Directed migration of stimulated dendritic cells (DCs) to secondary lymphoid organs and their interaction with Ag-specific T cells is a prerequisite for the induction of primary immune responses. In this article, we show that murine DCs that lack myosin IXB (Myo9b), a motorized negative regulator of RhoA signaling, exhibit increased Rho signaling activity and downstream acto-myosin contractility, and inactivation of the Rho target protein cofilin, an actin-depolymerizing factor. On a functional level, Myo9b−/− DCs showed impaired directed migratory activity both in vitro and in vivo. Moreover, despite unaltered Ag presentation and costimulatory capabilities, Myo9b−/− DCs were poor T cell stimulators in vitro in a three-dimensional collagen matrix and in vivo, associated with altered DC–T cell contact dynamics and T cell polarization. Accordingly, Myo9b−/− mice showed an attenuated ear-swelling response in a model of contact hypersensitivity. The impaired migratory and T cell stimulatory capacity of Myo9b−/− DCs was restored in large part by pharmacological activation of cofilin. Taken together, these results identify Myo9b as a negative key regulator of the Rho/RhoA effector Rho-kinase [Rho-associated coiled-coil–forming kinase (ROCK)]/LIM domain kinase signaling pathway in DCs, which controls cofilin inactivation and myosin II activation and, therefore may control, in part, the induction of adaptive immune responses.

Mouse Macrophages Completely Lacking Rho Subfamily GTPases (RhoA, RhoB, and RhoC) Have Severe Lamellipodial Retraction Defects, but Robust Chemotactic Navigation and Altered Motility

“…6A). Active RhoA (RhoA-GTP) levels, but not total RhoA, are known to be increased in mouse macrophages (1) and dendritic cells (38). We found that total RhoB levels were markedly reduced in Myo9b Ϫ/Ϫ macrophages, when compared with WT cells (Fig.…”

“…Ϫ/Ϫ Macrophages-The motorized RhoGAP Myo9b is a key negative regulator of Rho in leukocytes (1,38). We next tested whether genetic deletion of RhoB rescued the motility defect of macrophages lacking Myo9b (1).…”

T‐cell activation RhoGTPase‐activating protein plays an important role in TH17‐cell differentiation

“…RhoGAPs rapidly convert RhoGTPases to their GDP‐bound inactive state. Although ~80 RhoGAPs are encoded by the human genome, 6 , 7 the function of RhoGAP in T cells has not been extensively investigated 8 , 9 …”

Noncanonical Myo9b-RhoGAP Accelerates RhoA GTP Hydrolysis by a Dual-Arginine-Finger Mechanism

“…Myo9b-deficient macrophages fail to spread and remain in a round shape [11]. Additionally, Myo9b-depleted dendritic cells and T-cells are also defective in chemotactic migration [12,13]. It has been proposed that Myo9b acts as a single-headed myosin motor that is capable of moving along actin filaments [14,15].…”