The two nuclear proteins NF-kappa B (consisting of subunits p50 an dp65) and the DNA-binding subunit of NF-kappa B (p50) by itself, also called KBF1, are constitutively expressed and localized in the nucleus of the human T-cell line IARC 301.5. In order to define the roles of these two factors, which bind to the same kappa B enhancers, in transcription activation we have prepared somatic cell hybrids between IARC 301.5 and a murine myeloma. Most hybrids express both KBF1 and NF-kappa B in their nuclei, but one hybrid expresses only KBF1. The kappa B enhancer of the gene encoding the interleukin-2 (IL-2) receptor alpha chain (IL-2R alpha) is functional only in the hybrids expressing nuclear NF-kappa B. These findings show that nuclear NF-kappa B is necessary to activate the kappa B enhancer, while KBF1 by itself is not sufficient. We propose that KBF1 is a competitive inhibitor of NF-kappa B and discuss how these factors may be involved in the transient expression of IL-2 and IL-2R alpha genes during the immune response.
High-affinity interleukin 2 (IL2) receptors on humanT lymphocytes are multimeric complexes containing two IL2-binding polypeptides, a and @ chains of 50-55 and 70-75 kDa, respectively, associated by noncovalent bonds.IL2 binds to high-affinity IL2 receptors on the surface of T lymphocytes, mediates cell growth, and is internalized.In this paper, we used a biochemical method to directly identify the receptors components internalized together with the ligand.12'I-IL2receptor complexes were solubilized with the detergent 3-[(3-cholamidopropyI)dimethylammonio]-l-propanesulfonate, and IL2-binding polypeptides were identified by cross-linking with disuccinimidyl suberate.Under such conditions, the noncovalent association between a and @ is maintained.After IL2 internalization, two complexes of about 70 and 90 kDa, IL2 crosslinked to a and B, respectively, were found inside the cells.Both components were immunoprecipitated with either anti-a or anti-@ monoclonal antibodies.This shows that the a and @ chains are found in an intracellular compartment after IL2 endocytosis, and remain associated as a ternary complex with IL2.Interleukin 2 (IL2),' a growth factor for T lymphocytes, transduces the growth signal through a specific receptor complex that binds IL2 with high affinity ( K d , 10-100 PM) (1-3).The high-affinity receptor complex consists of at least two distinct receptor components, the a chain of 50-55 kDa (4-8), and the p chain of 70-75 kDa (9-13).a and p polypeptides, when expressed on the cell surface without / 3 and a , respectively, bind IL2 with a lower affinity.They form low and intermediate affinity receptors, with dissociation constants of 10 and 1 nM, respectively.The very high affinity of functional receptors for the ligand is due to the combination of two properties of individual chains, the high association rate of IL2 to a chains, and the slow dissociation of IL2 to ( 3 chains (14, 15). a and ( I subunits are bound by noncovalent association to form high-affinity receptors (16), the structure of which has not been further determined.In addition to a and p, the ~5 6 ' ' ~ tyrosine kinase is associated to the p chain and
The growth factor interleukin 2 (IL2) binds to and is internalized together with high-affinity surface receptors present on lymphoid cells. This endocytosis thus results in down-regulation of the receptors. However, it is not known if the internalization is relevant to the induction of cell growth. In the present study a rat monoclonal antibody to the P55 chain of the IL2 receptor was used to examine the role of receptor internalization in the IL2-dependent autocrine human tumor T cell line IARC 301. When given alone, this antibody did not inhibit IL2 binding, internalization, or IL2-dependent cell proliferation. However, crosslinking by anti-rat immunoglobulins, which did not affect binding of the growth factor, inhibited both IL2 internalization and cell proliferation. Besides offering a novel means for the specific inhibition of the uptake of IL2 bound to IL2 high-affinity receptors, the results are compatible with the association of this receptor-ligand uptake to the growth stimulation by IL2.
