PDE8 controls CD4+ T cell motility through the PDE8A-Raf-1 kinase signaling complex

Abstract
cAMP levels are regulated by phosphodiesterase enzymes (PDEs), which are potential targets for treating inflammatory disorders. We have previously demonstrated that PDE8 influences T cell motility. In this study, we reveal for the first time that PDE8A regulates T cell function through the V-raf-1 murine leukemia viral oncogene homolog 1 (Raf-1) kinase signaling pathway. To explore T cell motility under physiological conditions, we analyzed T cell interactions with endothelial cells and ligands using flow assays. The PDE8-selective enzymatic inhibitor PF-04957325 inhibits the adhesion of in vivo myelin oligodendrocyte glycoprotein (MOG)-activated inflammatory CD4+ T effector (Teff) cells to brain endothelial cells under shear stress. Recent findings show that PDE8A associates with Raf-1, creating a compartment of low cAMP around Raf-1, which protects it from protein kinase A (PKA)-mediated inhibitory phosphorylation. To assess the role of this complex in Teff cells, we employed a cell-permeable peptide that selectively disrupts the PDE8A-Raf-1 interaction. This disruptor peptide is more effective than the enzymatic inhibitor in inhibiting Teff-endothelial cell interactions. Moreover, the disruptor peptide specifically targets the LFA-1/ICAM-1 interaction, reducing adhesion, spreading, and locomotion of Teff cells under flow conditions. Mechanistically, disruption of the PDE8A-Raf-1 complex significantly alters Raf-1 signaling in Teff cells. Our findings indicate that inhibiting PDE8A with enzymatic inhibitors or disrupting the PDE8A-Raf-1 kinase complex reduces Teff cell adhesion and migration under flow, offering a novel approach to target T cells in inflammatory PF-04957325 conditions.