The biology and applications of small RNAs.

The Rossi lab has as its primary focus studies on the functions and therapeutic applications of small RNAs.  Within the past two decades there has been an explosion of new findings about roles that small RNAs play in biological processes.  Ribozymes are RNA molecules with enzymatic activities. There are many different types of ribozymes in nature but our lab has focused upon the hammerhead motif which is found as part of the self-cleaving domain of small plant viruses.  We have exploited these ribozymes for both basic studies of RNA catalysis and for therapeutic applications.  Ribozymes developed in our research program have been developed to target HIV and these have been inserted into human blood progenitor cells via a retroviral vector as part of a gene therapy program for the treatment of HIV infection.  To date 10 HIV positive patients have been treated with ribozymes developed in the lab.  Efforts to improve catalytic efficiency and co-localization of ribozymes with their targets in mammalian cells are still an ongoing effort in the lab.

The recent discovery of RNA interference in which long double stranded RNAs or RNA hairpins are processed in smaller 21 to 23 base duplexes called small interfering RNAs and micro RNAs has revolutionized mammalian cell genetics.  These small RNAs can be used to inhibit gene expression by targeting mRNAs with complementary sequences.  The lab has been studying the mechanism of RNAi at the biochemical level as well as exploiting this phenomenon for therapeutic applications in AIDS and cancer.  We have incorporated short hairpin RNA encoding genes into a lentiviral vector that can transduce hematopoietic progenitor cells and find that the expressed small interfering RNAs are potent inhibitors of HIV replication.  The goal of this research is to use combinations of shRNAs and other small RNA inhibitors of HIV replication to treat HIV patients combinatorially with gene therapy using their own hematopoietic stem cells to reconstitute their immune systems with HIV resistant lymphocytes and macrophages.  An important new finding in the lab is that small double stranded RNAs can trigger transcriptional gene silencing by directing histone methylation and DNA methylation in targeted promoter regions.  These small RNAs use components of the RNA interference machinery to target chromatin.  A major effort in the lab is to elucidate the active components of this process and to apply transcriptional gene silencing in a therapeutic setting.