T-cell restricted and unrestricted expression of transfected human interleukin-2 gene: phorbol ester- and calcium-inducible versus constitutive expression

Sequence of interleukin-2 isolated from human placental poly A+ RNA: possible role in maintenance of fetal allograft

There are several cell types within the placenta that produce cytokines which can contribute to the regulatory mechanisms that ensure normal pregnancy. The immunological milieu at the maternofetal interface is considered to be crucial for survival of the fetus. Interleukin-2 (IL-2) is expressed by the syncytiotrophoblast, the cell layer between the mother and the fetus. IL-2 appears to be a key factor in maintenance of pregnancy. Therefore, it was important to determine the sequence of human placental interleukin-2. Direct sequencing of human placental IL-2 cDNA was determined for the coding region. Subclone sequencing was carried out for the 5'- and 3'-untranslated regions (5'-UTR and 3'-UTR). The 5'-UTR for human placental IL-2 cDNA is 294 bp, which is 247 nucleotides longer than that reported for cDNA IL-2 derived from T cells. The sequence of the coding region is identical to that reported for T cell IL-2, while sequence analysis of the polymerase chain reaction (PCR) product showed that the cDNA from the 3' end was the same as that reported for cDNA from T cells. Human placental IL-2 cDNA is 1,028 base pairs (excluding the poly A tail), which is 247 bp longer at the 5' end than that reported for IL-2 T cell cDNA. Therefore, the extended 5'-UTR of the placental IL-2 cDNA may be a consequence of alternative promoter utilization in the placenta.

Delivery of interleukin 2 for immunotherapy

The local production of interleukin 2 (IL-2) by T lymphocytes acts to enhance the immune response by inducing growth and differentiation of a variety of immune cells. In clinical situations that require immunostimulation, such as vaccination and enhancement of tumor immunity, IL-2 therapy has been considered; however, the extraordinary toxicity of the drug inoculated systemically has greatly limited its application. Since the most serious toxic consequences of the drug are related to its systemic delivery, alternative strategies have been developed. Local delivery of the cytokine has been successfully used in some circumstances, and this form of delivery does not result in the life-threatening complications that limit systemic use. Liposome encapsulated IL-2 represents a mechanism to accentuate local delivery by causing a depot effect. Finally, the use of IL-2 has been predicated on the conception of the cytokine as an absolute monomer. Nevertheless, IL-2 spontaneously forms noncovalent and covalent self-associations. Because covalent dimers have been shown to initiate differential signalling in target cells, it is necessary to account for this property in devising and evaluating therapeutic protocols; moreover, it seems possible to use this property for modifying and regulating the therapeutic response.

Structure and analysis of the 5' flanking region of the human interleukin-2 gene

To investigate the structural and functional organization of the human interleukin-2 locus, the nucleotide sequence of 9339 bp of the 5' flanking region of this gene has been determined. Computer search analysis reveals five stretches with a high degree of homology between the human and mouse 5' flanking sequence, including a very distant 5' region. In this region additional binding sites for potential transcription factors were found that are identical to known regulatory sequences. The possible roles of these putative regulatory elements in the interleukin-2 gene regulation remain to be proven. The 5' end of the sequence contains almost full-length LINE element. LINE consensus open reading frames ORF1 and ORF2 in the reported sequence are interrupted by insertions, deletions or in-frame nonsense mutations. Comparative analysis of the ratio of codon changes that result in amino acid replacement to those that are silent revealed a high silent mutation frequency throughout the consensus ORF1 3' end, suggesting that this region is probably under selection for protein function.

Glucocorticoid receptor-mediated suppression of the interleukin 2 gene expression through impairment of the cooperativity between nuclear factor of activated T cells and AP-1 enhancer elements

The immunosuppressant hormone dexamethasone (Dex) interferes with T cell-specific signals activating the enhancer sequences directing interleukin 2 (IL-2) transcription. We report that the Dex-dependent downregulation of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and calcium ionophore-induced activity of the IL-2 enhancer are mediated by glucocorticoid receptor (GR) via a process that requires intact NH2- and COOH-terminal and DNA-binding domains. Functional analysis of chloramphenicol acetyltransferase (CAT) vectors containing internal deletions of the -317 to +47 bp IL-2 enhancer showed that the GR-responsive elements mapped to regions containing nuclear factor of activated T cells protein (NFAT) (-279 to -263 bp) and AP-1 (-160 to -150 bp) motifs. The AP-1 motif binds TPA and calcium ionophore-induced nuclear factor(s) containing fos protein. TPA and calcium ionophore-induced transcriptional activation of homo-oligomers of the NFAT element were not inhibited by Dex, while AP-1 motif concatemers were not stimulated by TPA and calcium ionophore. When combined, NFAT and AP-1 motifs significantly synergized in directing CAT transcription. Such a synergism was impaired by specific mutations affecting the trans-acting factor binding to either NFAT or AP-1 motifs. In spite of the lack of hormone regulation of isolated cis elements, TPA/calcium ionophore-mediated activation of CAT vectors containing a combination of the NFAT and the AP-1 motifs became suppressible by Dex. Our results show that the IL-2-AP-1 motif confers GR sensitivity to a flanking region containing a NFAT element and suggest that synergistic cooperativity between the NFAT and AP-1 sites allows GR to mediate the Dex inhibition of IL-2 gene transcription. Therefore, a Dex-modulated second level of IL-2 enhancer regulation, based on a combinatorial modular interplay, appears to be present.