IL-7 induces rapid internalization of CD127 by clathrin mediated endocytosis, leading to subsequent degradation by the proteasome. (174.1)

Abstract

Abstract IL-7, a potent immunomodulatory cytokine, is currently being investigated as a potential therapy and vaccine adjuvant in the treatment of HIV infection. In order to maximize these therapeutic strategies, we must first understand how the IL-7 receptor is regulated. We show here that in pimary human CD8 T cells, IL-7 decreases surface CD127 expression on CD8 T-cells in a dose- and time-dependent manner with initial suppression as early as 20 minutes and maximal suppression at 12 hours. This decrease at the cell surface is followed by loss of total CD127 protein within the cell as demonstrated by western blot. IL-7 induces internalization of surface CD127 through endocytic vesicles. The endocytosis inhibitors Filipin, and Dynasore both prevent IL-7 induced down regulation of CD127 at the cell membrane. Consistent with this we have shown by confocal microscopy that in resting CD8 T-cells CD127 is distributed evenly throughout the cell. After treatment with IL-7, CD127 forms multiple intracellular punctae with increased co-localization with clathrin by 5 minutes followed by co-localization with the early endosomal marker EEA1 after 30 minutes. By 2 hours CD127 staining associates with the late endosome marker RAB7 and the proteasomal 20S subunit, while at the same time showing decreased colocalization with the lysosomal marker LAMP1. Interestingly, the proteasome inhibitors lactacystin and MG132 both blocked IL-7’s ability to down regulate CD127.