Biological activity of analogs of the peptide hormone luliberin in the regulation of the immune response of T cells

Abstract

The ability of the antitumor analogs of luliberin (LH-RH), a hypothalamic peptide hormone, to stimulate the immune function of T cells is examined in experiments with the gone coding for interleukin-2 (IL-2). Recombinant MIL2C or 4xPu DNA containing the marker gene of chloramphenicol acetyltransferase (CAT) under the control of a 2.2 kb promoter of murine IL-2 gene or four copies of purine-rich element (from -292 to -246 base pairs), respectively, is injected in Xenopus laevis oocytes. The promoter activity is blocked by inoculation of the protein fraction of nuclear extracts from resting mouse splenic T cells. The IL-2 gene promoter is dereppressed after injection of the short LH-RH analog L1 (7 amino acid residues) into the oocyte nucleus or cytoplasm. The addition of L1 or L2 (an LH-RH analog consisting of 10 amino acid residues) to the incubation medium activates mouse splenic T ceils and stimulates the synthesis of IL-2 mRNA 2-to 3-fold more intensely than ConA+rlL-2, judging from dot-blot and in situ hybridization data. Cytological analysis of cell culture shows that the presence of L1 and L2 peptides in the culture medium promotes differentiation of T cells. It is hypothesized that the antitumor activity of these peptides is associated with the stimulation of IL-2 synthesis. Key Words: luliberin; interleukin-2 gene; mRNA synthesisIt was hypothesized that protein molecules have biologically active sites responsible for binding to cell receptors, protein-protein recognition, and formation of complexes activating gene expression [4]. The gene coding for interleukin-2 (IL-2) is a convenient tool for the investigation of the role of peptides in the regulation of the expression of eukaryotic genes. Protein product of IL-2 gene plays the key role in the immune response of T cells.The aim of this study was to evaluate the ability of two analogs of the peptide hormone luliberin (LH-RH) to regulate the expression of IL-2 gene.Institute of Experimental Medicine, Russian Academy of Medical Sciences; "Institute of High Molecular Compounds, Russian Academy -of Sciences, St. Petersburg; "'St. Petersburg State University These analogs are peptides consisting of seven (L1) and ten (L2) amino acid residues. The choice of luliberin is based on the fact that it is synthesized not only in hypothalamus, but also in T cells [3]. Tests for antitumor activity showed that L1 and L2 peptides inhibit tumor growth by 40 and 80%, respectively.Previously, we showed that L1 specifically interacts in vitro with the promoter of bovine IL-2 gene and stimulates the production of IL-2-1ike growth factor in a culture of surviving mouse splenic T cells (lymphoblastic transformation data) [2]. The ability of L2 to interact with the promoter of human IL-2 gene was demonstrated by binding to the promoter of digoxin-labeled tL-2 DNA on a nitrocellulose membrane [ 1 ].