Recombinant interleukin 2 regulates levels of c-myc mRNA in a cloned murine T lymphocyte.

The cellular oncogene c-myc has been implicated in the regulation of growth of normal and neoplastic cells. Recently, it was suggested that c-myc gene expression may control the G0----G1-phase transition in normal lymphocytes that were stimulated to enter the cell cycle by the lectin concanavalin A (ConA). Here we describe the effects of purified recombinant interleukin 2 (rIL2) and of ConA on levels of c-myc mRNA in the noncytolytic murine T-cell clone L2. In contrast to resting (G0) primary cultures of lymphocytes, quiescent L2 cells have a higher RNA content than resting splenocytes and express receptors for interleukin 2 (IL2). Resting L2 cells are therefore best regarded as early G1-phase cells. Purified rIL2 was found to stimulate the rapid accumulation of c-myc mRNA in L2 cells. Levels of c-myc mRNA became maximal within 1 h and declined gradually thereafter. In contrast, ConA induced slower accumulation of c-myc mRNA in L2 cells, with increased levels of c-myc mRNA becoming detectable 4 to 8 h after stimulation. Experiments with the protein synthesis inhibitor cycloheximide demonstrated that the increase in levels of c-myc mRNA that were induced by ConA was a direct effect of this lectin and not secondary to IL2 production. Cyclosporin A, an immunosuppressive agent, markedly reduced the accumulation of c-myc mRNA that was induced by ConA but only slightly diminished the accumulation of c-myc mRNA that was induced by rIL2. Taken together, these data provide evidence that (i) c-myc gene expression can be regulated by at least two distinct pathways in T lymphocytes, only one of which is sensitive to cyclosporine A, and (ii) the accumulation of c-myc mRNA can be induced in T cells by IL2 during the G1 phase of the cell cycle.     

人绒毛膜癌细胞Jar卵泡抑素基因表达的调控

用逆转录-多聚酶链聚合反应(RT-PCR)方法证实, 表皮生长因子(EGF)可刺激人绒癌细胞株Jar卵泡抑素mRNA的表达, 并呈剂量依赖效应, 最大效应剂量为1.0 nmol/L, 半数有效剂量为0.3 nmol/L.GM-CSF虽然单独对人绒癌细胞株Jar卵泡抑素mRNA表达无任何影响, 但却能显著抑制EGF刺激后的人绒癌细胞株Jar卵泡抑素mRNA的表达,并有剂量依赖关系,最大效应剂量为10 nmol/L, 抑制率达62.3%, 半数有效剂量为3.0 nmol/L.提示胎盘组织卵泡抑素基因除受多种激素调控外, 还受一些生长因子内分泌和旁分泌的调控.     

In vivo and in vitro structural analysis of the rplJ mRNA leader of Escherichia coli. Protection by bound L10-L7/L12

The rplJL-rpoBC operon of Escherichia coli is regulated in part at the level of translation by an autogenous mechanism (feedback regulation) that involves ribosomal protein L10-L7/L12. Feedback regulation occurs as the result of L10-L7/L12 binding to a site on the untranslated leader region of the rplJ mRNA that is located more than 100 nucleotides upstream from the translation start site. Previous studies have indicated that the secondary structure of the rplJ leader region is important for efficient translation and feedback regulation. We have done chemical modification experiments to examine the secondary structure of approximately 200 nucleotides of the rplJ leader region, and we propose a secondary structure that is consistent with the experimental data. RNA structure was probed in vitro by treating samples of total cellular RNA with diethyl pyrocarbonate and in vivo by treating log-phase cultures with dimethyl sulfate. Modified bases were detected by primer extension using three different oligonucleotide primers. The proposed structure includes five double-stranded regions designated I to V, separated by single-stranded segments numbered 1 to 5. We have also identified specific nucleotides in the rplJ mRNA leader that are protected by purified L10-L7/L12 from methylation by dimethyl sulfate in vitro. The protected bases are located within a bulge-loop of region IV, a portion of the mRNA that has been shown genetically to be necessary for feedback regulation.     

Unusual regulation of expression of the herpes simplex virus DNA polymerase gene.

During herpes simplex virus infection, expression of the viral DNA polymerase (pol) gene is regulated temporally as an early (beta) gene and is additionally down-regulated at late times at the level of translation (D. R. Yager, A. I. Marcy, and D. M. Coen, J. Virol. 64:2217-2225, 1990). To examine the role of viral DNA synthesis in pol regulation, we studied pol expression during infections in which viral DNA synthesis was blocked, either by using drugs that inhibit Pol or ribonucleotide reductase or by using viral mutants with lesions in either the pol or a primase-helicase subunit gene. Under any of these conditions, the level of cytoplasmic pol mRNA was reduced. This reduction was first seen at approximately the time DNA synthesis begins and, when normalized to levels of other early mRNAs, became as great as 20-fold late in infection. The reduction was also observed in the absence of the adjacent origin of replication, oriL. Thus, although pol mRNA accumulated as expected for an early gene in terms of temporal regulation, it behaved more like that of a late (gamma) gene in its response to DNA synthesis inhibition. Surprisingly, despite the marked decrease in pol mRNA in the absence of DNA synthesis, the accumulation of Pol polypeptide was unaffected. This was accompanied by loss of the normal down-regulation of translation of pol mRNA at late times. We suggest a model to explain these findings.