RORγt+ cells selectively express redundant cation channels linked to the Golgi apparatus

Abstract

Retinoid-related orphan receptor gamma t (RORγt) is a master transcription factor central to type 17 immunity involving cells such as T helper 17, group 3 innate lymphoid cells or IL-17-producing γδ T cells. Here we show that the intracellular ion channel TMEM176B and its homologue TMEM176A are strongly expressed in these RORγt+ cells. We demonstrate that TMEM176A and B exhibit a similar cation channel activity and mainly colocalise in close proximity to the trans-Golgi network. Strikingly, in the mouse, the loss of Tmem176b is systematically associated with a strong upregulation of Tmem176a. While Tmem176b single-deficiency has no effect on the course of experimental autoimmune encephalomyelitis, T cell or DSS-induced colitis, it significantly reduces imiquimod-induced psoriasis-like skin inflammation. These findings shed light on a potentially novel specific process linked to post-Golgi trafficking for modulating the function of RORγt+ cells and indicate that both homologues should be simultaneously targeted to clearly elucidate the role of this intracellular ion flow.

Dendritic cells require TMEM176A/B ion channels for optimal MHC II antigen presentation to naive CD4+ T cells

“…Confirming our previous hypothesis that TMEM176B traffics through but does not accumulate in the Golgi apparatus 6 Video 3). We then examined a variety of markers depicted in Figure 7G.…”

“…to as type 3 (or type 17) immune cells, producing the prototypical cytokines IL-17 and IL-22 and including Th17 CD4 + T cells, gdT17 cells, group 3 innate lymphoid cells (ILC3s) and NKT17 cells 6,[11][12][13][14] . Moreover, the Littman group included Tmem176a/b in the restricted group of 11 genes whose expression is directly dependent on RORγt in Th17 cells 15 .…”

“…Tmem176a and Tmem176b are homolog genes encoding structurally similar four-span transmembrane proteins 6,10,16 (Figure 1A). In the immune system, our previous studies 6,10,17 combined with the analysis of Immuno-Navigator 18 and Immgen 19 public databases (Figure S1) indicate that Tmem176a and Tmem176b are tightly co-regulated and highly expressed both in conventional DCs and in the RORgt + cell family (depicted in Figure 1B). Taken together, these observations along with reported evidence of genetic compensation in Tmem176b −/− single KO mice 6 strongly suggested the need to simultaneously target both genes to decipher their function.…”

“…To gain insight into the intracellular function of TMEM176A/B ion channels, we aimed to elucidate their subcellular localization that remains elusive as different studies reached different conclusions 5,6,32 . To this end, we used the Retention Using Selective Hooks (RUSH) system 33 , a two-state assay allowing fluorescence-based analysis of intracellular trafficking in living cells at physiological temperature (Figure 7A).…”

“…However, the function of this ion flux in the homeostasis and physiological response of conventional DCs has not been explored and is likely achieved by both TMEM176A and TMEM176B in a redundant fashion 6 .…”