Research Interest

HIV-1-induced neurological dysfunctions represent a complex series of events, which result from direct and indirect communication between virus and host cells in the brain. The direct mechanism includes replication of HIV-1 in microglia, and to a lesser degree in astrocytes, whereas the indirect pathway involves viral and cellular secretory factors that impact upon neurons and other brain cells. In both events, a cascade of regulatory reactions including signal transduction plays a pivotal role in derailing cell functions that are manifested by pathological features such as apoptosis of neuronal and astrocytic cells; demyelination; and abnormal morphological appearance of various cells within the central nervous system (CNS). In one of the major research projects in my lab, I focus my attention on signal transduction pathways that have a potential in modulating direct and indirect pathways involved in the genesis of neuropathology in AIDS brain. We perform experiments to investigate the effect of viral regulatory protein, Tat and cellular modulators secreted by the infected cells upon NGF and its downstream effectors in neuronal cells. More specifically, experiments are aimed to investigate functional and physical interactions of factors within MAP kinase pathway with cdK5/p35, the important regulator of neuronal cell differentiation and apoptosis. In a related set of studies, we are investigating the role of Wnt and TGF- signal transduction pathways in control of HIV-1 gene expression and replication in microglia and astrocytes. More specifically, the cooperative interaction of Tat with the key components of Wnt pathway, which includes TCF-4 and -Catenin, and the functional interaction of Smads, the critical downstream regulators of TGF-, and C/EBP, a transcription factor that bridges both Wnt and TGF- regulatory function, are explored. Our observations are then confirmed using clinical samples, by examining the various components of the signal transduction pathways, which are subject for deregulation by HIV-1 in brain. These studies will ultimately emphasize/ determine the biological relevance of our findings. We anticipate that our data will provide important information to understand the basic mechanisms that dictate neuronal cell differentiation and death, and our goal is to utilize the outcome of these studies for devising molecular therapeutic strategies to block viral replication, and improve neuronal vitality during the course of the disease.

In a second main project, I am investigating the regulation of cytokines including TGF, TNF, and several chemokines in brain cells upon expression of the HIV-1 gene. More specifically, we are investigating the mechanism by which the HIV-1 regulatory protein Tat can regulate the genes responsible for the expression of these cytokines. Earlier studies have demonstrated that activation of the HIV-1 LTR by Tat may require several cellular proteins including cyclin T1 and its partner cdk9, which associate with Tat and TAR, and are positioned near the viral transcription start site. The interaction of these proteins allows for the phosphorylation of RNA polymerase II, an event that increases the enzymatic activity of this protein and augments transcriptional activity. Tat also stimulates transcription of several immunomodulators and cytokines in CNS cells. In fact, it is now believed that some of the injury seen in AIDS brain is induced by soluble factors such as TNF, TGF-1, and IL-1, etc. As these genes lack the TAR RNA sequence, one can anticipate the participation of an alternative pathway in Tat-mediated transcription of genes in a TAR-independent manner. More recently, we have identified a cellular protein, Pur, which exhibits the unique ability to bind to Tat and to interact with the GC/GA DNA sequence positioned upstream of a variety of cellular genes including TNF and TGF1. As such, one can speculate that the association of Pur with Tat alone or in combination with cyclin T1/cdk9 results in the activation of TGF1 and TNF by Tat in CNS cells. In this research project we are investigating the effect of Tat on the expression of TNF and TGF-1 in primary CNS cultures and to examine the effect of cyclin T1/cdk9 and/or Pur in Tat-mediated transcriptional activation of these cytokines in primary cultures of human microglia and astrocytes. Moreover, studies are in progress to investigate the structural and functional interplay between Tat, cyclin T1/cdk9 and Pur in CNS cells, and by creating mutant proteins based on cyclin T1/cdk9 and Pur, develop therapeutic molecules that bind to Tat and sequester its activity. Results from these molecular studies will provide comprehensive information on the mechanism of cellular gene activation by Tat in the CNS and may serve as an initial step toward the development of targeted and effective therapeutic compounds against HIV-1 Tat in the CNS.

Gene Therapy:

The use of retroviruses and adenoviruses as vectors for high efficiency delivery system of foreign genes and for the correction of some genetic defects has been my long-term interest. Strategies are being designed for tissue/cell-targeted delivery of therapeutic genes to the brain using these vectors to control expression of inflammatory cytokines and viral replication in brain.