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 G0, like the c-myc, IL-2, IL-2 receptor (IL-2R) and transferrin receptor (TfR) genes, have been transcriptionally activated. 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 cells. 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, is a limiting factor. We have taken another approach, namely the exogenous addition to bulk cell cultures of small antisense oligomers. Sequence-specific antisense oligodeoxyribonucleotides have been reported to inhibit intracellular viral replication without interfering with cellular protein synthesis. 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 region. 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 specifically. We report here that the same c-myc complementary oligonucleotide 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.

Max and inhibitory c-Myc mutants induce erythroid differentiation and resistance to apoptosis in human myeloid leukemia cells

“…The expression of both mutants impaired K562 growth, as expected from the requirement of c-Myc in cell proliferation (Heikkila et al, 1987;Prochownik et al, 1988;Eilers et al, 1991;Evan et al, 1992;Nguyen et al, 1995). However, we wanted to isolate stable transfectants constitutively expressing the c-Myc inhibitory mutants so as to study their e ects on di erentiation and apoptosis of K562 cells.…”

Amino-terminal domains of c-myc and N-myc proteins mediate binding to the retinoblastoma gene product

“…In this regard it is noteworthy that either antisense c-myc oligonucleotides or pRb overexpression results in a block in cell cycle progression from GI to S phase (ref. 25, and S. Friend, personal communication). On the basis of our observations, it is tempting to speculate that dominant and recessive oncogenes can cooperate through direct binding to control progression through the cell cycle.…”

Cell cycle targets of Ras/Raf signalling

“…The gene is expressed throughout the whole cell cycle (Waters et al, 1991). The cMyc protein is a DNA binding protein, which is involved in transcriptional control of gene expression and has been shown to be essential for cell proliferation (Amati and Land, 1994;Heikkila et al, 1987). Overexpression of the c-Myc protein in arrested Rat1a cells leads to the activation of cyclinE/cdk2 complexes and subsequently to an entry into DNA replication (Steiner et al, 1995;Perez-Roger et al, 1997).…”