Expression of c-myc proto-oncogene in normal human lymphocytes. Regulation by transcriptional and posttranscriptional mechanisms.

Abstract

Aberrant expression of the c-myc gene results from nonrandom chromosomal translocations involving the transcriptionally active antigen receptor gene loci, in particular lymphocytic leukemias and lymphomas, and is believed to contribute to the etiology of these neoplasms. In addition to its expression in abnormal lymphocytes, increased accumulation of c-myc mRNA occurs rapidly in normal B-and T-lymphocytes after stimulation with appropriate mitogens. The mechanisms that mediate these mitogeninduced elevations in c-myc mRNA levels, however, have not been determined for normal B and T cells. By using enriched populations of B-and T-lymphocytes obtained from freshly isolated human tonsils and stimulated with Staphylococcus-A or with phytohemagglutinin, respectively, we observed marked elevations (20-40-fold) in the steady state levels of accumulated cmyc messenger RNA (mRNA) within I h of exposure of cells to mitogens; modest increases (three-to fivefold) in the relative rate of transcription of the c-myc gene through protein synthesisindependent (cycloheximide-insensitive) mechanisms; and rapid rates of degradation of mature c-myc mRNAs through protein synthesis-dependent (cycloheximide-sensitive) mechanisms. These findings corroborate previous studies in other cell types and provide evidence for both transcriptional and posttranscriptional control of c-myc proto-oncogene expression in normal human lymphocytes.

Macrophage- and astrocyte-derived transforming growth factor beta as a mediator of central nervous system dysfunction in acquired immune deficiency syndrome.

“…For Northern blots, 5 Ag RNA was fractionated on 1.0% agarose gels containing formaldehyde and transferred to nitrocellulose filters. The blots were prehybridized and then sequentially hybridized with the "P-labeled cDNA probes : HIV-1 (a 6.5kb segment of HIV-1 encoding gag/pol/env), human TGF-01 (provided by Dr. R. Derynck, Genentech Inc., South San Francisco, CA) (32), and He7 (provided by Dr. J. Reed, University of Pennsylvania School of Medicine, Philadelphia, PA) (36). The blots were washed twicein 2x SSC, 0.1% SDS for 15 min at room temperature and for 30 min at 65°C in 0.1x SSC, 0.1% SDS.…”

MYC expression and distribution in normal mature lymphoid cells

“…Contrary to highly proliferating cell lines and tissues, MYC RNA levels in purified tonsil T and B lymphocytes are barely detectable and steady‐state rates of transcription are extremely low . Not surprisingly, in situ hybridization studies in normal lymphoid tissue have not been reported.…”

Single cell tuning of Myc expression by antigen receptor signal strength and interleukin‐2 in T lymphocytes

“…It was recognised many years ago that upregulation of Myc mRNA accompanied T cell activation (Reed et al , 1987 ; Kelly & Siebenlist, 1988 ; Wang et al , 2011a ). More recently, the Immunological Genome Project has mapped the transcriptional profiles of multiple T cell populations and reported high levels of Myc mRNA in immune-activated effector T cells (Best et al , 2013 ).…”

“…The relevance of understanding the control of Myc protein levels in T cells was highlighted recently: immune-activated T cells lacking the system L amino acid transporter Slc7a5 upregulate Myc mRNA but fail to express Myc protein and hence have global metabolic defects (Sinclair et al , 2013 ). In this context, many experiments have analysed Myc mRNA in T cells activated pharmacologically with phorbol esters, calcium ionophores and plant lectins (Kelly et al , 1983 ; Reed et al , 1987 , 1988 ; Kelly & Siebenlist, 1988 ), but there is almost no detailed analysis of Myc protein in T cells responding to physiological stimuli. Accordingly, the present study has explored how engagement of the T cell antigen receptor (TCR) with peptide/major histocompatibility complexes (p/MHC) controls Myc expression.…”