Novel Interleukin-2 Receptor Subunit Detected by Cross-Linking Under High-Affinity Conditions

Abstract

Interleukin-2 (IL-2) binds to both high- and low-affinity classes of IL-2 receptors on activated T lymphocytes. Only the high-affinity receptors are involved in receptor-mediated endocytosis and normally transduce the mitogenic signals of IL-2; however, the structural features distinguishing the high- and low-affinity receptors are unknown. When 125I-labeled IL-2 was chemically cross-linked to activated human T lymphocytes, two major bands were identified. First, as predicted, a 68- to 72-kilodalton band, consisting of IL-2 (15.5 kilodaltons) cross-linked to the IL-2 receptor (55 kilodaltons), was observed. Second, an unpredicted 85- to 92-kilodalton moiety was detected. This band was not present when IL-2 was cross-linked to transfected C127 cells, which exclusively express low-affinity receptors. The data presented are most consistent with the existence of a 70- to 77-kilodalton glycoprotein subunit (p70) which, upon associating with the 55-kilodalton low-affinity receptor (p55), transforms it into a high-affinity site. It is proposed that p55 and p70 be referred to as the alpha and beta subunits, respectively, of the high-affinity IL-2 receptor.

Expression of functional human interleukin‐2 receptors in murine interleukin‐3‐dependent cells

“…This variation in receptor endocytosis mediated by two affinity forms of the IL2 receptor must result from a structural difference between the receptor complexes. The recent description of^ a second IL2-binding protein has led to the suggestion that the high-affinity IL2 receptor is composed of al least two polypeptides, p55 and p70, each of which is capable of independently binding IL2 with low or intermediate affinity (12)(13)(14)(15)(16). The associated binding of one molecule of IL2 by both the p55 and p70 chains has been suggested to result in the high-affinity binding state (15,16).…”

Murine interleukin‐2 receptor subunits differentially detected with anti‐interleukin‐2 monoclonal antibodies

“…The 105 kDa complex has not been described for human cell lines, but was recently found in other mouse cell lines as a complex of IL-2 and p90 IL-2R [11,12]. The bands of much higher molecular mass may be aggregates or complexes of receptor subunits as has been suggested for human [8] and mouse cell lines [11,12]. Since the human low-affinity IL-2R, p55 has been reported to be quantitatively cleaved into two fragments by trypsin [15], I tested mouse IL-2R subunits for their sensitivity to trypsin.…”

“…The gels were dried and autoradiographed at -80°C for 3-21 days on Fuji HR-A film with a Fuji Grenex G-12 intensifying screen. been ascribed to complexes of a single 15 kDa IL-2 molecule with p55 and p70/75 IL-2R subunit, respectively [8,9], it is very likely that the 65-70 kDa and 80-85 kDa complexes observed in the murine cell system were also complexes between IL-2 with the p50/55 or the p65/70 IL-2R subunit. The 105 kDa complex has not been described for human cell lines, but was recently found in other mouse cell lines as a complex of IL-2 and p90 IL-2R [11,12].…”

“…In addition, non-lymphoid cells transfected with p55 cDNA expressed only lowaffinity IL-2R and failed to transduce the signal of IL-2 [7]. Using radioiodinated IL-2 and chemical cross-linking methodology, a non-Tac IL-2 binding protein of 70/75 kDa has been identified [8,9]. The p70/75 IL-2R expressed on LGL cells has an intermediate affinity for IL-2 in itself but is capable of transducing the signal of IL-2 [10].…”

Daclizumab (anti-Tac, Zenapax) in the treatment of leukemia/lymphoma

“…Furthermore, there was the issue of the structural explanation for the great difference in affinity between high-(10 À11 M) and low-10 À8 M) affinity receptors. We resolved these issues in parallel with investigators in the laboratory of Warren Leonard by co-discovering a novel non-Tac 70 kDa IL-2 binding protein, IL-2R beta, that is shared with IL-15 (Sharon et al, 1986;Tsudo et al, 1986). Subsequently, the high-affinity IL-2 receptor was shown to also include the 64 kDa IL-2R g chain (or gc) shared by IL-4, IL-7, IL-9, IL-15 and IL-21 (Sugamura et al, 1996)).…”