Anti-IgM-mediated regulation of c-myc and its possible relationship to apoptosis.
Anti-IgM treatment of Burkitt's lymphoma cells is followed by either growth arrest or induction of apoptosis. In this study we have explored the role of c-myc in these events. Our results in Ramos cells indicate the following. (a) The decline in c-myc mRNA occurs at about 4 h; inhibition of about 80% being observed. (b) The stability of c-myc message is involved since the half-life of c-myc mRNA is decreased from about 30 min in untreated cells to about 15 min following treatment with anti-IgM. In the presence of cycloheximide, a protein synthesis inhibitor, the half-life is increased to about 50 min and was unaltered by treatment with anti-IgM. (c) By contrast, nuclear run-on experiments indicated no change in transcription rates for c-myc message due to treatment with anti-IgM. (d) A decrease in c-myc causes apoptosis since specific repression of c-myc with antisense oligonucleotides decreases the levels of c-Myc, inhibits growth rate, decreases viability, and induces apoptosis. (e) Anti-CD40 inhibition of apoptosis occurs without alteration in anti-IgM-induced down-regulation of c-myc mRNA, suggesting that it acts distally to c-myc down-regulation. Other cell lines were also investigated. In Epstein-Barr virus (EBV)-positive cell lines (Daudi, Raji, and Namalwa), anti-IgM treatment for 24 h results in growth inhibition without induction of apoptosis. In EBV-negative cell lines (ST486 and CA46, as well as Ramos), a more heterogeneous pattern of responses to anti-IgM are observed. Ramos and ST486 cells both show growth inhibition and apoptosis upon anti-IgM treatment; CA46 cells shown only growth inhibition but not apoptosis. Anti-IgM causes a decline in c-myc mRNA levels in all of these lines, as well as in c-Myc protein level in the two lines investigated, Daudi and Ramos, regardless of apoptosis. Addition of antisense c-myc oligonucleotides to the cells reduced growth in both Daudi and Ramos cells lines, however it resulted in substantial apoptosis only in Ramos cells. These results suggest that anti-IgM destabilizes c-myc mRNA by a process that involves mRNA turnover, rather than transcription rates. However anti-IgM exerts differential effects in EBV-positive and EBV-negative cell lines. EBV-positive cells are uniformly resistant to apoptosis, while EBV-negative cell lines show a tendency to apoptosis but with exceptions. Growth inhibition can be uncoupled from apoptosis in EBV-positive cell lines, but not in those EBV-negative cell lines prone to apoptosis. Furthermore, down-regulation of c-myc message correlates with growth inhibition in these cells, but is an insufficient link to apoptosis. By contrast inhibition of apoptosis by anti-CD40 occurs even though c-myc mRNA is decreased.
Kaptein
J S
JS
Regional Research Laboratory, Kaiser Foundation Hospitals, Los Angeles, California 90027, USA.
Lin
C K
CK
Wang
C L
CL
Nguyen
T T
TT
Kalunta
C I
CI
Park
E
E
Chen
F S
FS
Lad
P M
PM
D000888:Antibodies, Anti-Idiotypic / Q000378:metabolism*; D017209:Apoptosis / Q000235:genetics* / Q000276:immunology*; D001483:Base Sequence; D002051:Burkitt Lymphoma / Q000235:genetics / Q000276:immunology / Q000473:pathology; D019013:CD40 Antigens / Q000378:metabolism; D002455:Cell Division / Q000235:genetics / Q000276:immunology; D002460:Cell Line; D016259:Genes, myc; D004854:Herpesvirus 4, Human / Q000502:physiology; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism*; D008969:Molecular Sequence Data; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000494:pharmacology; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014764:Viral Proteins / Q000502:physiology
D000888:Antibodies, Anti-Idiotypic; D019013:CD40 Antigens; D007075:Immunoglobulin M; D016376:Oligonucleotides, Antisense; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D014764:Viral Proteins