Talin1 Methylation Is Required for Neutrophil Infiltration and Lipopolysaccharide-Induced Lethality

Abstract

Talin1, a well-established integrin coactivator, is critical for the transmigration of neutrophils across the vascular endothelium into various organs and the peritoneal cavity during inflammation. Several posttranslational modifications of talin1 have been proposed to play a role in this process. In this study, we show that trimethylation of talin1 at Lys2454 by cytosolic Ezh2 is substantially increased in murine peritoneal neutrophils upon induction of peritonitis. By reconstituting talin1-deficient mouse myeloid cells with wild-type, methyl-mimicking, or unmethylatable talin1 variants, we demonstrate that methylation of talin1 at Lys2454 is important for integrin-dependent neutrophil infiltration into the peritoneal cavity. Furthermore, we show that treatment with an Ezh2 inhibitor or reconstitution of talin1-deficient myeloid cells with unmethylatable talin1 significantly reduces the number of organ-infiltrating neutrophils and protects mice from LPS-induced mortality.

Ezh2 restrains macrophage inflammatory responses, and is critical for neutrophil migration in response to pulmonary infection

“…A likely explanation for this is due to protein methyltrasferase-mediated activity of EZH2 on talin-1 cleavage, which disrupts binding to F-actin, leading to disrupted adhesion complex formation and aberrant cell migration (19). This is also consistent with more recent studies showing that disruption of talin1 methylation sites impairs transmigration of neutrophils across the peritoneal vascular epithelium during inflammation, an effect also mimicked by treatment with an EZH2 inhibitor (25).…”

The functional significance of Talin1 in dendritic cells

“…Despite the loss of the integrin activator talin1, immature B cells are able to migrate into the splenic white pulp in an integrin-dependent manner to further their maturation 273,274 . This could be due to the accumulation of a reservoir of talin1 molecules in the peri-nuclear region of the cell 124,275,276,282 . In addition, the loss of talin1 in B cells could also be partially compensated by paxillin, a regulator of VLA-4 (integrin α4b1) whereby it promotes the anchorage of VLA-4 to its ligand VCAM-1 independent of chemokine signaling-mediated integrin inside-out signaling to enhance both integrin binding affinity and avidity to its respective ligand 272,277,278,279,280 , under shear flow.…”

“…The retention of MZ B cells in the spleen is compromised in the absence of talin1 272 or in the presence of blocking antibodies against integrins VLA-4 and LFA-1 273,274 . Integrins are required to anchor B cells in the MZ, a region of the spleen that lies between the white pulp and the vast splenic circulatory network (red pulp), so as to resist the shear flow of blood through the spleen 273,274 , a process similar to the integrindependent extravasation of neutrophils into the peritoneal cavity 282 . Furthermore, talin1deficient mature B cells are also unable to enter the LNs from the blood and the lymphatic vascular network 272 , suggesting that integrin inside-out signaling mediated by talin1 and the CXCR4/CXCL12, CCR7/CCL19 and CCR7/CCL21 chemokine axes 283 are necessary for the homing process.…”

“…Recently, our lab described the significance of talin1 methylation in the integrindependent migration of DC 73,124 and neutrophils 282 , whereby the tri-methylation of talin1…”

“…Besides, mice with talin1-deficient neutrophils or neutrophils expressing unmethylatable talin1 (K2454A and K2454Q) variants are less susceptible to LPS endotoxemia-induced mortality compared to mice with wildtype neutrophils or neutrophils expressing methyl-mimicking talin1 (K2454F) 282 . Enhanced survivability of mice can be explained by the diminished infiltration of talin1-deficient neutrophils or neutrophils with un-methylatable talin1 variants into organs such as the kidneys, liver and lungs, protecting these mice from the cytotoxic effects of neutrophils and multiorgan damage 282 . However, with the present data at hand, it is possible that the TLR4 signal transduction cascade in talin1-deficient neutrophils, similar to talin1-deficient DCs are also compromised by the depletion of talin1.…”