β2-Integrins regulate dendritic cells through nuclear deformation and activation of phospholipase A2 and DNA damage–inducible GADD34

Dendritic cells (DCs) reside in tissues and are activated by danger or pathogen-associated signals, leading to expression of costimulatory markers and cytokines, downregulation of β2-integrin-mediated adhesion, migration to lymph nodes, and activation of T cells. Conversely, β2-integrins are known to restrict DC activation and migration, but signaling pathways involved in this process remain poorly understood. Here, we show that β2-integrins regulate podosome formation as well as nuclear morphology of bone marrow-derived DCs (BMDCs) on both stiff and soft surfaces. Analysis of published gene expression data revealed that loss of β2-integrin adhesion and nuclear deformation both upregulate DC activation markers and cytokines, including Ccr7, Cd86, and Il12b. Growth arrest and DNA damage-inducible protein (GADD34; Ppp1r15) of the unfolded protein responses was also upregulated in both datasets. Utilizing a cytosolic phospholipase A2 (cPLA2) inhibitor, we show that the nuclear shape sensor cPLA2 controls interleukin-12 production and CD86 expression of β2-integrin adhesion-deficient BMDCs. We further show that the GADD34 pathway is activated in adhesion-deficient BMDCs, as eukaryotic translation initiation factor 2A (EIF2α) phosphorylation is reduced in these cells, whilst cPLA2 inhibition rescues EIF2α phosphorylation. Furthermore, GADD34 inhibition led to decreased interleukin-12 production and CD86 expression in β2-integrin-deficient BMDCs, whilst inhibition of protein kinase R-like endoplasmic reticulum kinase (the canonical EIF2α kinase) had no effect. Together, our results show that loss of β2-integrin adhesion leads to nuclear deformation and activation of a cPLA2-GADD34 pathway in BMDCs, which at least partly controls their activated phenotype. Our results therefore reveal how cell adhesion and nuclear deformation are connected to mechanically control DC activation.