Retinoic acid-induced upregulation of αE integrin (CD103) is TGFβ-dependent in human dendritic cells

Abstract CD103 (αE integrin) is thought to mediate the cross-talk between dendritic and epithelial cells. Based on a recent study showing retinoic acid (RA) may enhance CD103 expression at high concentrations (Hartog, Allergy and Immunology. 2013), we examined monocyte-derived dendritic cell (MoDC) CD103 expression levels with physiological concentrations of RA (100nM) under serum-free conditions. FACS analysis revealed that RA induced a significant increase of MoDCs positive for both extracellular and intracellular CD103 expression. Gene expression analysis corroborated these results with a 57-fold increase in ITGAE upon RA culture. Moreover, expression of β7, which forms the αEβ7 integrin heterodimer with CD103, was similarly upregulated by RA. We next evaluated the TGFβ-dependence of RA-induced CD103 regulation based on a study showing that itgαE gene expression in mice is regulated by TGFβ in T-cells (Robinson, Immunology. 2001). MoDCs were cultured with RA and SB431542, a TGFβR inhibitor that blocks SMAD phosphorylation. When MoDCs were cultured with RA and SB431542, CD103 expression was significantly reduced when compared to MoDCs cultured with RA alone (p<0.01). Similarly, qPCR analysis revealed RA-induced ITGAE gene expression was significantly decreased by 2.4-fold with SB431542 treatment. We also showed that TGFβ directly enhanced CD103 expression in human MoDCs. However, RA-treatment of the MoDCs did not result in enhanced secretion of TGFβ1/2/3 or enhanced expression of TGFβRI/II. Therefore, RA modulation of cellular TGFβ signaling pathways may be involved in the upregulation of CD103 expression. In summary, our studies reveal a TGFβ-dependent mechanism for RA-induced regulation of CD103 in human dendritic cells.