Nancy J. Peffer

The v-rel oncogene encodes a κB enhancer binding protein that inhibits NF-κB function

Abstract Studies of NF-κB suggest that this enhancer binding activity corresponds to a family of at least four proteins (p50, p55, p75, and p85) differentially induced with biphasic kinetics during T cell activation. While p55 and p50 are closely related to the 50 kd DNA binding subunit of NF-κB, p75 and p85 exhibit DNA binding properties that distinguish them from this 50 kd poly-peptide and its regulatory subunits IκB and p65. All four members of this κB-specific protein family are structurally related to the v-Rel oncoprotein and one, p85, appears identical to human c-Rel. v-Rel, but not nontransforming v-Rel mutants, binds to the κB enhancer and inhibits NF-κB-activated transcription from the IL-2 receptor α promoter and HIV-1 LTR. These findings suggest a Rel-related family of κB enhancer binding proteins and raise the possibility that the transforming activity of v-Rel is Iinked to its inhibitory action on cellular genes under NF-κB control.

Lymphocytes isolated from the intestinal lamina propria of normal nonhuman primates have increased expression of genes associated with T-cell activation.

Synthesis of interleukin-2 (IL-2) and expression of interleukin-2 receptors play central roles in T-cell activation, proliferation, and differentiation. The state of activation of T lymphocytes in the intestinal lamina propria was compared with that of circulating lymphocytes and lymphocytes isolated from the spleen or mesenteric lymph nodes of normal nonhuman primates. Lamina propria lymphocytes (LPL) had significantly higher proliferation in response to recombinant IL-2 compared with the other populations. In agreement with this finding, LPL had a significantly higher percentage of interleukin-2 receptor-positive (IL-2R+) cells as determined by staining with fluoresceinated monoclonal anti-IL-2R antibody. Two-color immunofluorescence staining showed that both CD4+ and CD8+ lamina propria T cells were IL-2R+. It was also found that the percentage of major histocompatibility complex class II-positive T cells was higher in the lamina propria. Northern blot analysis with a cDNA specific for the IL-2R showed that unstimulated LPL had easily detectable IL-2R mRNA, whereas no IL-2R mRNA was found in unstimulated lymphocyte populations from other sites. The activation of the IL-2R gene in LPL was not associated with the activation of other cellular genes (actin, major histocompatibility complex class I). Although no IL-2 bioactivity was measured in culture supernatants of unstimulated lymphocytes, concanavalin A-stimulated LPL produced significantly more IL-2 than other lymphocytes. This finding was confirmed at the molecular level as IL-2 mRNA was not detected in unstimulated LPL but was found in concanavalin A-stimulated LPL. Thus, normal lamina propria T lymphocytes have selective expression of genes associated with cell activation.

Molecular Analysis of the Human Interleukin-2 Receptor

Complete expression of the human immune response requires the generation of activated T cells1. This activation sequence is initiated by an interaction of antigen with specific receptors present on the membrane of resting T cells. This receptor-ligand interaction, in the presence of macrophage derived interleukin-1 (IL-1), then triggers the production of interleukin-2 (IL-2, previously designated T cell growth factor)2,3. IL-2 is a well-characterized 14,500 dalton glycoprotein which promotes T cell proliferation following binding to specific high affinity IL-2 membrane receptors4–6. However, unlike receptors for antigen, IL-2 receptors are not expressed by resting T cells, but like IL-2, are synthesized following antigen activation. The interaction of IL-2 with its inducible receptor results in T cell proliferation and expansion of the antigen reactive T cell clone and culminates in the emergence of T cells mediating helper, suppressor, and cytotoxic T cell function. Thus, both the specificity and magnitude of the T cell immune response is in large measure controlled at the level of IL-2 receptor expression.

Molecular Cloning of cDNA for the Human Interleukin-2 Receptor

Interleukin-2 (IL-2 or T cell growth factor) is a 14,500 daltons glycoprotein critically involved in the development of a normal human immune response [1, 2]. Recently, cDNA for this lymphokine has been isolated and expressed in both prokaryotic and eukaryotic cells [3–5]. Further, the human IL-2 gene has been cloned, sequenced [6], and localized to chromosome 4. As with other polypeptide hormones, IL-2 exerts its biologic effects through binding to specific high affinity membrane receptors [7]. However, neither IL-2 nor IL-2 receptors are produced by resting T cells [7, 8]. Following exposure to antigen, T cells binding antigen enter a program of cellular activation leading to de novo synthesis and secretion of IL-2 and expression of IL-2 receptors. The interaction of IL-2 with its cellular receptor then triggers cellular proliferation, resulting in the growth and development of helper, suppressor, and cytotoxic T cells.