IL-7 induces endocytosis and degradation of IL-7 receptor-alpha chain in vitro.
Int Conf AIDS 2004 Jul 11-16; 15:(abstract no. MoOrA1046)
Zanetti G, Sasson SC, Zaunders JJ, Stanley KK, Kelleher AD University of New South Wales, Sydney, Australia
IL-7 serum levels are elevated in lymphopenic conditions including chronic HIV infection and inversely correlate with CD4 count. IL-7 plays a role in mediating CD4+T-cell homeostasis. It acts via IL-7 receptor, composed of gamma-chain CD132 and alpha-chain CD127, and expressed by most T-lymphocytes. Regulation of IL-7/IL-7R system is not fully understood, despite its potential relevance in T-cell homeostasis. PBMC were isolated by FICOLL density gradient centrifugation, and cultured in Iscove Modified Dulbecco Medium 10% AB serum at 37 or 15 deg C. Subcultures were treated with IL-7 (0-10ng/ml), cycloheximide (50muM), or tyrphostin (200muM). Cells were stained with CD3PerCP, CD4ECD, CD45ROFITC, CD127PE antibodies with or without permeabilisation and analysed by flow-cytometry. IL-7 caused down-regulation of CD127. Ex vivo 70-80% of CD4+ T-cells expressed CD127 on their surface, whereas less than 10% did after 4 hours with IL-7 (10ng/ml). The down-regulation was dose-dependent, and was reversed after removal of IL-7. When protein synthesis was inhibited with cycloheximide, re-expression of CD127 was blocked. Comparison between intra and extracellular staining revealed CD127 presence in the intracellular compartment at 30 and 60 min after addition of IL-7. Inhibition of membrane trafficking by conducting incubations at 15 deg C partially blocked this process, whereas incubation with the tyrosine analogue, tyrphostin, did not. Endogenous expression of CD127 was also dependent upon ongoing protein synthesis. Our data suggest that even in quiescent cells CD127 is turning over on the cell surface and stable expression relies on de novo protein synthesis. IL-7 induces temporary down-regulation of CD127 in a dose dependent manner, through internalisation followed by degradation. This pathway seems to be not mediated by tyrosine phosphorylation. The feedback effect of IL-7 on a component of its receptor could be relevant at tissue level in HIV infection, and requires further studies.
Keywords: AEGIS, Receptors, Interleukin-7, Interleukin-7, Antigens, CD4, Endocytosis, CD4 Lymphocyte Count, Down-Regulation, T-Lymphocytes, Protein Binding, HIV Infections, Cycloheximide, In Vitro, metabolism, immunology, genetics
