A c-myc antisense oligodeoxynucleotide inhibits entry into S phase but not progress from G₀ to G₁

Abstract

Initiation of T-lymphocyte proliferation by mitogen or antigen involves a cascade of gene activation events. Thus, by the time mitogen-activated T cells have reached the G₁/S interface, many genes that are transcriptionally silent in G_O, like the c-myc, IL-2, IL-2 receptor (IL-2R) and transferrin receptor (TfR) genes, have been transcriptionally activated^1–4. To understand the role of the individual genes in the activation process, one must be able to interfere specifically with the expression or function of each particular gene product. In this way, by blocking the IL-2R with an antibody, it has been demonstrated that IL-2/IL-2R interaction is required to induce TfR expression in activated T cells³. When the function or expression of intracellular proteins is to be blocked, however, the need to introduce antibodies into the cytoplasm of viable cells, although possible^5–7, is a limiting factor. We have taken another approach, namely the exogenous addition to bulk cell cultures of small antisense oligomers. Sequence-specific anti-sense oligodeoxyribonucleotides have been reported to inhibit intracellular viral replication without interfering with cellular protein synthesis^8,9. Similarly, rabbit globin mRNA translation in a cell-free system and in rabbit reticulocytes has been inhibited by oligomers complementary to the globin mRNA initiation codon region¹⁰. Recently, a pentadecadeoxyribonucleotide complementary to the initiation codon and four downstream codons of human c-myc mRNA was reported to inhibit the proliferation of the human leukaemic cell line HL-60 specifically¹¹. We report here that the same c-myc complementary oligonuelectide inhibits mitogen-induced c-myc protein expression in human T lymphocytes and prevents S phase entry. Interestingly, c-myc antisense treatment did not inhibit G₀ to G₁ traversal as assessed by morphologic blast transformation, transcriptional activation of the IL-2R and TfR genes, or induction of ³H-uridine incorporation.