The biological function of naturally occurring DOCK2 inhibitor in tissue-specific immune evasion

Abstract

Abstract Study objection DOCK2 is a Rac-specific guanine nucleotide exchange factor (GEF) predominantly expressed in hematopoietic cells. DOCK2 is essential for migration and activation of leukocytes, and its mutations in humans cause severe immunodeficiency, thereby indicating that DOCK2 plays a key role in immune surveillance. Interestingly, however, we found that a naturally occurring DOCK2 inhibitor exists in our body and named this molecule DOCK2 inhibitory metabolite (D2IM). In this study, we aimed to reveal biological functions of D2IM. Method The specificity of D2IM was examined with Rac GEF assay and binding assay. T cells and neutrophils from WT mouse were treated with D2IM and subjected to Rac activation assay and chemotaxis assay. D2IM production in various tissues was monitored with mass spectrometry. In addition, influence of the lack of CS on ultraviolet- and antigen-induced ocular inflammationwas analyzed using KO mice lacking D2IM synthase. Result CS inhibited the Rac GEF activity of murine DOCK2 protein in vitro with a IC50 value of 2.0 mM. When leukocytes were treated with D2IM, chemoattractant-induced Rac activation was severely impaired, resulting in a marked reduction of migratory response of lymphocytes and neutrophils. D2IM most abundantly existed in the Harderian gland, which produces lipids to form the oily layer of the tear film, and its production was completely lost in mice lacking D2IM synthase. We found that the lack of D2IM augmented ultraviolet- and antigen-induced ocular inflammation in mice, which was suppressed by administration of eye drops containing D2IM. Conclusion D2IM is a naturally occurring DOCK2 inhibitor that contributes to create immune evasive microenvironment in the eye.