DOCK8 controls survival of group 3 innate lymphoid cells in the gut through Cdc42 activation.

Innate lymphoid cells (ILCs) are a family of developmentally related leukocytes that rapidly secrete polarized sets of cytokines to combat infection and promote tissue repair at mucosal barriers. Among them, group 3 ILCs (ILC3s) play an important role in maintenance of the gut homeostasis by producing IL-22, and their development and function critically depend on the transcription factor RORγt. Although recent evidence indicates that RORγt+ ILC3s are reduced in the gut in the absence of the Cdc42 activator DOCK8 (dedicator of cytokinesis 8), the underlying mechanism remains unclear. We found that genetic deletion of Dock8 in RORγt+-lineage cells markedly reduced ILC3s in the lamina propria of the small intestine. By analyzing BrdU incorporation, it was revealed that DOCK8 deficiency did not affect the cell proliferation. Furthermore, when lineage marker-negative (Lin-) α4ß7+ CD127+ RORγt- fetal liver cells were cultured with OP9 stromal cells in the presence of stem cell factor (SCF) and IL-7 in vitro, RORγt+ ILC3s normally developed irrespective of DOCK8 expression. However, DOCK8-deficient ILC3s exhibited a severe defect in survival of ILC3s under the condition with or without IL-7. Similar defects were observed when we analyzed Dock8VAGR mice having mutations in the catalytic center of DOCK8, thereby failing to activate Cdc42. Thus, DOCK8 acts in cell-autonomous manner to control survival of ILC3s in the gut through Cdc42 activation.

Combined application of geranylgeranylacetone and amelogenin promotes angiogenesis and wound healing in human periodontal ligament cells.

Amelogenin directly binds to glucose-regulated protein 78 (Grp78). Cell migration activity is expected to increase when human periodontal ligament cells (hPDLCs) overexpressing Grp78 are treated with amelogenin. Geranylgeranylacetone (GGA) is a drug that induces the expression of heat shock protein and is routinely used to treat gastric ulcers. Here, we investigated the changes in the properties and behavior of hPDLCs in response to treatment with GGA and the synergistic effects of amelogenin stimulation in hPDLCs pretreated with GGA for the establishment of a novel periodontal tissue regenerative therapy. We observed that GGA treatment increased Grp78 protein expression in hPDLCs and enhanced cell migration. Microarray analysis demonstrated that increased Grp78 expression triggered the production of angiopoietin-like 4 and amphiregulin, which are involved in the enhancement of angiogenesis and subsequent wound healing via the activation of hypoxia-inducible factor 1α and peroxisome proliferator-activated receptors as well as the phosphorylation of cAMP response element-binding protein and protein kinase A. Moreover, the addition of recombinant murine amelogenin (rM180) further accelerated hPDLC migration and tube formation of human umbilical vein endothelial cells due to the upregulation of interleukin-8 (IL-8), monocyte chemotactic protein 1, and IL-6, which are also known as angiogenesis-inducing factors. These findings suggest that the application of GGA to gingival tissue and alveolar bone damaged by periodontal disease would facilitate the wound healing process by inducing periodontal ligament cells to migrate to the root surface and release cytokines involved in tissue repair. Additionally, supplementation with amelogenin synergistically enhanced the migratory capacity of these cells while actively promoting angiogenesis. Therefore, the combined application of GGA and amelogenin may establish a suitable environment for periodontal wound healing and further drive the development of novel therapeutics for periodontal tissue regeneration.

DOCK8 deficiency causes a skewing to type 2 immunity in the gut with expansion of group 2 innate lymphoid cells.

Dedicator of cytokinesis 8 (DOCK8) is a guanine nucleotide exchange factor (GEF) for Cdc42. In humans, homozygous or compound heterozygous deletions in DOCK8 cause a combined immunodeficiency characterized by various allergic diseases including food allergies. Although group 2 innate lymphoid cells (ILC2s) contribute to the development of allergic inflammation by producing interleukin (IL)-5 and IL-13, the role of ILC2s in DOCK8 deficiency has not been fully explored. With the use of cytometry by time-of-flight (CyTOF), we performed high-dimensional phenotyping of intestinal immune cells and found that DOCK8-deficient (Dock8-/-) mice exhibited expansion of ILC2s and other leukocytes associated with type 2 immunity in the small intestine. Moreover, IL-5- and IL-13-producing cells markedly increased in Dock8-/- mice, and the majority of them were lineage-negative cells, most likely ILC2s. Intestinal ILC2s expanded when DOCK8 expression was selectively deleted in hematopoietic cells. Importantly, intestinal ILC2 expansion was also observed in Dock8VAGR mice having mutations in the catalytic center of DOCK8, thereby failing to activate Cdc42. Our findings indicate that DOCK8 is a negative regulator of intestinal ILC2s to inhibit their expansion via Cdc42 activation, and that deletion of DOCK8 causes a skewing to type 2 immunity in the gut.

A conserved PI(4,5)P2-binding domain is critical for immune regulatory function of DOCK8.

DOCK8 is a Cdc42-specific guanine-nucleotide exchange factor that is essential for development and functions of various subsets of leukocytes in innate and acquired immune responses. Although DOCK8 plays a critical role in spatial control of Cdc42 activity during interstitial leukocyte migration, the mechanism remains unclear. We show that the DOCK homology region (DHR)-1 domain of DOCK8 binds specifically to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and is required for its recruitment to the plasma membrane. Structural and biochemical analyses reveal that DOCK8 DHR-1 domain consists of a C2 domain-like core with loops creating the upper surface pocket, where three basic residues are located for stereospecific recognition of phosphoinositides. Substitution of the two basic residues, K576 and R581, with alanine abolished PI(4,5)P2 binding in vitro, ablated the ability of DOCK8 to activate Cdc42 and support leukocyte migration in three-dimensional collagen gels. Dendritic cells carrying the mutation exhibited defective interstitial migration in vivo. Thus, our study uncovers a critical role of DOCK8 in coupling PI(4,5)P2 signaling with Cdc42 activation for immune regulation.

S100A4 Protein Is Essential for the Development of Mature Microfold Cells in Peyer's Patches.

Intestinal microfold cells (M cells) in Peyer's patches are a special subset of epithelial cells that initiate mucosal immune responses through uptake of luminal antigens. Although the cytokine receptor activator of nuclear factor-κB ligand (RANKL) expressed on mesenchymal cells triggers differentiation into M cells, other environmental cues remain unknown. Here, we show that the metastasis-promoting protein S100A4 is required for development of mature M cells. S100A4-producing cells are a heterogenous cell population including lysozyme-expressing dendritic cells and group 3 innate lymphoid cells. We found that in the absence of DOCK8, a Cdc42 activator critical for interstitial leukocyte migration, S100A4-producing cells are reduced in the subepithelial dome, resulting in a maturation defect of M cells. While S100A4 promotes differentiation into mature M cells in organoid culture, genetic inactivation of S100a4 prevents the development of mature M cells in mice. Thus, S100A4 is a key environmental cue that regulates M cell differentiation in collaboration with RANKL.