Research

My laboratory's research interests are in two areas: mechanism of regulation and functions of viral stress-inducible genes (VSIG) and tissue specific functions of angiotensin-converting enzyme (ACE).

Transcription of a group of mammalian genes is strongly induced by a variety of stimuli related to virus infection such as double-stranded (ds) RNA, interferons (IFN) and viral proteins. We are identifying these genes (VSIG) by microarray analyses and delineating the distinct signaling pathways used for inducing these genes. For Toll-like receptor 3-mediated dsRNA signaling, we have demonstrated critical roles of receptor Tyr phosphorylation and PI3 kinase. Moreover, we have shown that IRF-3, the critical transcription factor, is activated by two-step phosphorylation.

The most prominent VSIG products are members of the P56 family. They interact specifically with different subunits of the translation initiation factor, eIF-3, and inhibit protein synthesis Thus, a new IFN, dsRNA and virus-mediated pathway of translational regulation has been discovered. Human P56 also inhibits human papilloma virus DNA replication by binding to the viral E1 protein.

Another family of VSIG-encoded proteins is the 2-5(A) synthetase family of enzymes which, when activated by dsRNA, polymerize ATP into a series of 2',5'-linked oligoadenylates. Using a combination of genetic and biochemical approaches, we have identified the acceptor binding, the donor binding, the catalytic and the dimerization sites of a OAS2 isozyme and determined that the two subunits participate in criss-cross catalytic actions. Recently, in collaboration with Vivien Yee, we have obtained the crystal structure of a OAS1 isozyme and determined the basis for its activation by dsRNA.

We are interested in identifying cellular dsRNA-binding proteins and determining their physiological functions. The IFN-induced protein kinase, PKR and its activator, PACT, are two such proteins. We discovered PACT and identified a small domain of PACT that binds to the kinase domain of PKR and activates the enzyme. We have generated PACT knockout mice; these mice have specific developmental defects indicating important physiological functions of PACT.

The most well known physiological property of ACE is its pivotal role in blood pressure regulation. Recent studies, however, indicate a much broader activity of ACE in renal, immunological and male reproductive functions. For understanding the full repertoire of ACE actions, we have used a combination of gene knockout and tissue-specific transgene expression to conclude that expression of the germinal isozyme of ACE in sperm is sufficient for maintaining male fertility, but the somatic isozyme cannot substitute for this function of the germinal isozyme. Using a similar approach, we have shown that regulation of blood pressure and maintenance of normal kidney functions are two separable properties of the somatic isozyme. Further studies are in progress to delineate additional physiological functions of ACE.