Biosynthetic Processing of Human Interleukin‐2 Receptor (Tac Antigen)

Abstract

Biosynthetic processing of the T-cell surface receptor for interleukin-2 was investigated in a cultured human T-cell line MT-1 by means of metabolic and cell surface radiolabeling followed by immunoprecipitation with a monoclonal antireceptor antibody (anti-Tac) and analysis by one-and two-dimensional polyacrylamide gel electrophoresis.The nascent precursor of the receptor (Mr= about 40,000, pI=6.2-6.5) underwent a post-translational modification giving rise to the mature receptor (IL-2R; Mr=60,000-65,000, pI = 4.2-4.7) within 2-4 hr. The post-translational processing of IL-2R caused a 20,000-25,000 increase in apparent molecular weight and a 2.0-2.5 acidic shift in the isoelectric point. The increase in molecular weight was attributable mainly to addition of sugar residues including glucosamine and galactose, and the charge shift to the addition of sialic acids. A carboxylic ionophore monensin completely blocked the maturation of IL-2R at the mid-stage of the processing. Fatty acid attachment appeared to comprise one of the steps of the post-translational modification.Two-dimensional analyses of IL-2R biosynthesis enabled identification of the precursor of IL-2R and its intermediate forms, from which it was partially possible to estimate reactions involved in the maturation of the precursor molecule.

Metabolism of Tac (IL2Ralpha): physiology of cell surface shedding and renal catabolism, and suppression of catabolism by antibody binding.

“…Tac has O-glycosylation sites in proximity to the Cys192-Leu 193 cleavage site (46), and glycosylation patterns for Tac in normal and ma- (43) and suggests the sequence is crucial to Tac shedding. lignant T cells show variation by gel mobilities of extracted proteins (28,47). Whether this pattern also changes during T cell activation and downregulation of Tac is, to our knowledge, unknown.…”

Biophysical Characterization of a Recombinant Soluble Interleukin 2 Receptor (Tac)

“…Derivation of Molecular Mass by Ultracentrifugation-Tac 224 was calculated to have a protein mass of 25,253 daltons (9, 20). The protein is substituted with N-and O-linked sugars and, from pI shift analysis, contains approximately 10 sialic acid residues (21)(22)(23). In a separate article, 4 we demonstrate a nondenaturing method to derive glycoprotein molecular weights when only the mass of the protein component is known.…”

IL-2 receptor gene regulation by cytokines ; Role of ATL-derived factor(s) (ADFs) in ATL.

“…The lack of the antibody-induced down-regulation of IL-2-R (25) in these cells first suggested to us the presence of an abnormality in either regulation or the structure of IL-2-R in ATL. Therefore, we have studied the structure of IL-2-R (29,30) and the mechanism of abnormal regulation of IL-2-R, to clarify whether or not IL-2/IL-2-R system is involved in the leukemogenic process in ATL. It has become clear that in many HTLV-I(+) T-cells is there a continuous activation of normal IL-2-R gene (10,14) associated with the production of ADF (ATL-derived factor) (23,34), which is an IL-2-R inducing factor without IL-2 activity.…”