Cyclin T1-Dependent Genes in Activated CD4+ T and Macrophage Cell Lines Appear Enriched in HIV-1 Co-Factors

HIV-1 is dependent upon cellular co-factors to mediate its replication cycle in CD4+ T cells and macrophages, the two major cell types infected by the virus in vivo. One critical co-factor is Cyclin T1, a subunit of a general RNA polymerase II elongation factor known as P-TEFb. Cyclin T1 is targeted directly by the viral Tat protein to activate proviral transcription. Cyclin T1 is up-regulated when resting CD4+ T cells are activated and during macrophage differentiation or activation, conditions that are also necessary for high levels of HIV-1 replication. Because Cyclin T1 is a subunit of a transcription factor, the up-regulation of Cyclin T1 in these cells results in the induction of cellular genes, some of which might be HIV-1 co-factors. Using shRNA depletions of Cyclin T1 and transcriptional profiling, we identified 54 cellular mRNAs that appear to be Cyclin T1-dependent for their induction in activated CD4+ T Jurkat T cells and during differentiation and activation of MM6 cells, a human monocytic cell line. The promoters for these Cyclin T1-dependent genes (CTDGs) are over-represented in two transcription factor binding sites, SREBP1 and ARP1. Notably, 10 of these CTDGs have been reported to be involved in HIV-1 replication, a significant over-representation of such genes when compared to randomly generated lists of 54 genes (p value<0.00021). The results of siRNA depletion and dominant-negative protein experiments with two CTDGs identified here, CDK11 and Casein kinase 1 gamma 1, suggest that these genes are involved either directly or indirectly in HIV-1 replication. It is likely that the 54 CTDGs identified here include novel HIV-1 co-factors. The presence of CTDGs in the protein space that was available for HIV-1 to sample during its evolution and acquisition of Tat function may provide an explanation for why CTDGs are enriched in viral co-factors

Formation of Trans-Activation Competent HIV-1 Rev:RRE Complexes Requires the Recruitment of Multiple Protein Activation Domains

The HIV-1 Rev trans-activator is a nucleocytoplasmic shuttle protein that is essential for virus replication. Rev directly binds to unspliced and incompletely spliced viral RNA via the cis-acting Rev Response Element (RRE) sequence. Subsequently, Rev oligomerizes cooperatively and interacts with the cellular nuclear export receptor CRM1. In addition to mediating nuclear RNA export, Rev also affects the stability, translation and packaging of Rev-bound viral transcripts. Although it is established that Rev function requires the multimeric assembly of Rev molecules on the RRE, relatively little is known about how many Rev monomers are sufficient to form a trans-activation competent Rev:RRE complex, or which specific activity of Rev is affected by its oligomerization. We here analyzed by functional studies how homooligomer formation of Rev affects the trans-activation capacity of this essential HIV-1 regulatory protein. In a gain-of-function approach, we fused various heterologous dimerization domains to an otherwise oligomerization-defective Rev mutant and were able to demonstrate that oligomerization of Rev is not required per se for the nuclear export of this viral trans-activator. In contrast, however, the formation of Rev oligomers on the RRE is a precondition to trans-activation by directly affecting the nuclear export of Rev-regulated mRNA. Moreover, experimental evidence is provided showing that at least two protein activation domains are required for the formation of trans-activation competent Rev:RRE complexes. The presented data further refine the model of Rev trans-activation by directly demonstrating that Rev oligomerization on the RRE, thereby recruiting at least two protein activation domains, is required for nuclear export of unspliced and incompletely spliced viral RNA

Polyamines and cancer: old molecules, new understanding

The amino-acid-derived polyamines have long been associated with cell growth and cancer, and specific oncogenes and tumour-suppressor genes regulate polyamine metabolism. Inhibition of polyamine synthesis has proven to be generally ineffective as an anticancer strategy in clinical trials, but it is a potent cancer chemoprevention strategy in preclinical studies. Clinical trials, with well-defined goals, are now underway to evaluate the chemopreventive efficacy of inhibitors of polyamine synthesis in a range of tissues

TGF-beta 1 is a potent inducer of human effector T cells.

Abstract TGF-beta 1 is known to modulate lymphocyte activation affecting cell proliferation and the production of cytokines and Igs. Little is known about the characteristics of T cells grown in the presence of TGF-beta 1. We have stimulated human T cells with PHA in the presence of TGF-beta 1 under serum-free conditions for 7 days and characterized the resulting cell population. TGF-beta 1 (0.0032 to 10 ng/ml) affected neither [3H]thymidine incorporation (day 4) nor cell yield (day 7) in these cultures. However, cells activated in the presence of TGF-beta 1 proliferated vigorously in secondary cultures and produced highly elevated amounts of IL-2 (12 +/- 3-fold enhancement of IL-2 production in response to CD2 plus CD28 stimulation compared with control cells, mean +/- SEM; n = 10). The enhancing effects of TGF-beta 1 were demonstrable over a wide range of concentrations (0.4 to 10 ng/ml). The increased IL-2 protein production was paralleled by a dramatic up-regulation of IL-2 mRNA. In addition, cells precultured with TGF-beta 1 responded with enhanced cluster formation in the secondary cultures. With regard to their phenotype, we observed an increased expression of the alpha E beta 7-integrin human mucosal lymphocyte-1 and of the CD2-restricted epitope CD2R, whereas the expression of CD11a was slightly decreased. In contrast, TGF-beta 1 did not influence the constitutive or activation-induced expression of CD4, CD8, CD45RA, CD45RO, CD25, CD71, CD54, CD58, CD59, and B7. We conclude that TGF-beta 1 supports the generation of human effector cells with a strongly enhanced capacity to respond to subsequent restimulation.</jats:p