Mutation of Asp20 of human interleukin-2 reveals a dual role of the p55 alpha chain of the interleukin-2 receptor.
Mutation of Asp20 in human interleukin-2 (IL-2) to Lys is known to result in an IL-2 molecule with unchanged binding to the p55 subunit of the IL-2 receptor, but with greatly decreased affinity for the p75 subunit (Collins, L., Tsien, W.-H., Seals, C. et al. Proc. Natl. Acad. Sci USA 1988. 85: 7709). Here we demonstrate that Lys20 IL-2 competed with a reduced (10-fold) affinity for high-affinity IL-2 receptors on two murine cell lines HT2 and CTLL. In parallel with this difference in receptor interaction, Lys20 IL-2 stimulated half-maximal HT2 cell proliferation at a 10-fold higher concentration than wild-type IL-2. However, half-maximal stimulation of CTLL cells required a 100-fold higher concentration of Lys20 IL-2. A similar 100-fold reduction in bioactivity of Lys20 IL-2 was observed for primary, activated, human or murine lymphocytes. Anti-p55 antibodies increased the concentration of Lys20 IL-2 required to stimulate HT2 cells to that required for CTLL cells. These data suggest that CTLL cells, while able to bind Lys20 IL-2 with high affinity, are lacking a p55-dependent function necessary for optimal stimulation. Therefore, p55 has a dual role, being important both for high-affinity IL-2 binding and for optimal cell triggering.
Flemming
C L
CL
Chester Beatty Laboratories, Institute of Cancer Research, London.
Russell
S J
SJ
Collins
M K
MK
D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry; D002460:Cell Line; D004252:DNA Mutational Analysis; D006801:Humans; D066298:In Vitro Techniques; D007376:Interleukin-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008213:Lymphocyte Activation; D051379:Mice; D015375:Receptors, Interleukin-2 / Q000737:chemistry* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000276:immunology*
D007376:Interleukin-2; D015375:Receptors, Interleukin-2; D001224:Aspartic Acid