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Background: MicroRNA (MIR) is emerging as an important regulators of gene expression through post-transcriptional control.

Methods:  We have developed powerful bioinformatic tools for detecting new MIR in the whole human genome. These tools, together with powerful biologic methods, including a novel microarray for the detection of MIR, and direct cloning and sequencing of predicted MIR, were applied to the study of MIR in several viral species including HIV. The recent report on the presence of virally encoded MIR in Epstein Barr virus-infected cell lines lends support to our search and findings of MIR in a number of viral infections including HIV.

Results:  Comparing infected and non-infected cells, we have revealed differential expression of several host MIR, as well as the increased expression of some predicted viral MIR. We found that several of the up-regulated host MIR have binding sites on 3' UTR of mRNA that play a central role in HIV infection and its life cycle. Experiments are underway to determine the role of these MIR in the regulation of the predicted target genes and thus their involvement in viral infection. In parallel, some of the virally encoded MIR are associated with genes known to play a central role in viral replication and latency, and are therefore under intense study.

Conclusions:  HIV infection is associated with up-regulation of several host MIR and appearance of virally encoded MIR. At least some of the host and the virally encoded MIR may have a direct effect on viral replication and latency. Control of MIR expression or its modulation offers a novel approach for therapy of  HIV infection. The changed expression of host MIR with HIV infection, may also lend itself to new therapies affecting the host response and susceptibility to HIV infection.

Keywords: microRNA; HIV; host