Anti-IgM-mediated Regulation of c-myc and Its Possible Relationship to Apoptosis

• Published in: The Journal of biological chemistry Vol. 271; no. 31; pp. 18875 - 18884
• Main Authors: Kaptein, John S., Lin, Ching-Kow E., Wang, C. Linzhi, Nguyen, Tam Thuan, Kalunta, Cosmas I., Park, Eunhee, Chen, Fun-Shan, Lad, Pramod M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02-08-1996; American Society for Biochemistry and Molecular Biology
• Subjects: Antibodies, Anti-Idiotypic - metabolism; Apoptosis - genetics; Apoptosis - immunology; Base Sequence; Burkitt Lymphoma - genetics; Burkitt Lymphoma - immunology; Burkitt Lymphoma - pathology; CD40 Antigens - metabolism; Cell Division - genetics; Cell Division - immunology; Cell Line; Epstein-Barr virus; Genes, myc; Herpesvirus 4, Human - physiology; Humans; Immunoglobulin M - metabolism; Molecular Sequence Data; Oligonucleotides, Antisense - genetics; Oligonucleotides, Antisense - pharmacology; Proto-Oncogene Proteins c-myc - biosynthesis; Proto-Oncogene Proteins c-myc - genetics; Proto-Oncogene Proteins c-myc - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Neoplasm - genetics; RNA, Neoplasm - metabolism; Tumor Cells, Cultured; Viral Proteins - physiology
• DOI: 10.1074/jbc.271.31.18875
• EISSN: 1083-351X
• ISSN: 0021-9258

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.