The primary interest of our research is to understand the pathogenic mechanisms of tumor viruses with the goal to identify targets for effective therapeutic and preventive applications. We currently use Kaposi’s sarcoma-associated herpesvirus (KSHV) and its associated cancer, Kaposi’s sarcoma (KS), as a model system to study how an oncogenic virus modulates cellular pathways and host environments to facilitate its infection and replication, and causes cancer.

KS is an inflammatory vascular spindle cell cancer of proliferative endothelial cells commonly found in AIDS patients. In some African regions, KS has become the dominant cancer in both adult and pediatric patients with or without HIV infection. In addition to its importance as an emerging pathogen of major human diseases, KSHV is an excellent model for studying inflammation and angiogenesis, and interactions of virus-host and virus-virus.

KSHV is a gammaherpesvirus encoding close to 100 genes and 12 microRNAs. We have developed an efficient bacteria-mammalian shuttle system for the genetic manipulation of KSHV by cloning the 170 kb KSHV genome as a bacteria artificial chromosome, and a highly efficient infection system of primary human umbilical vein endothelial cells, in which KSHV transforms the infected cells into angiogenic proliferative spindle phenotypes closely resembling KS tumor cells. We employ comprehensive genetic, genomic, molecular, cellular, and biochemical approaches to define the molecular basis of the sophisticated interplays of virus-cell interactions. To this end, we have examined the viral transcriptional and replication programs, and the altered cellular pathways following KSHV infection. KSHV infection modulates multiple cellular pathways such as mitogen-activated protein kinase (MAPK) pathways to facilitate its infection and replication. KSHV activation of MAPK pathways leads to malignant cellular proliferation by accelerating cell cycle progression, cell invasion by inducing matrix metalloproteinases, and neoangiogenesis by inducing inflammatory and angiogenic cytokines. KSHV infection also induces chromosome instability, which predisposes the infected cells to cellular transformation. These works have identified MAPK pathways and other angiogenic pathways as potential therapeutic and preventive targets. Ongoing experiments are testing inhibitors of these pathways in animal models with the hope that some of them can be taken into clinical trials in the near future. In the same time, we are also conducting translational clinical projects to validate these laboratory findings with the emphasis on the KSHV-host and KSHV-HIV interactions.

To identify KSHV genes that are essential for malignant cellular transformation, we have generated mutagenesis library that contains mutants of all known KSHV genes and microRNAs. We currently focus on KSHV latent genes, microRNAs, genes that induce angiogenesis, and genes that regulate KSHV latency and reactivation.

We initially identified and characterized the KSHV immunodominant major latent protein, LNA (LANA). LNA has since been shown to be a multi-functional viral protein that maintains the stability of viral episomes and targets multiple cellular pathways. We demonstrated that LNA is essential for KSHV episome persistence and represses viral lytic transcriptional program in the context viral infection. In addition, we have identified a novel nuclear protein KLIP1 that interacts with LNA, and shown that KLIP1 is a cell cycle-dependent potent transcriptional repressor manipulated by LNA in KSHV latent infection. Recent studies have shown that KLIP1 interacts with myeloid leukemia factor 1 (MLF1), and possibly has a role in the genesis of erythroleukemias. KLIP1 is also a component of centromere, and regulates cytokinesis

We were the first to identify and characterize the first KSHV oncogene viral interferon regulatory factor (vIRF). vIRF is the first viral protein identified to have sequence homology to cellular IRFs, a family of transcriptional factors that are involved in a variety of functions including but not limiting to oncogenesis, cell proliferation, differentiation, apoptosis, and host defense. We have defined the transcriptional mechanism controlling vIRF expression and identified a novel transcriptional silencer, which could have implication for the transcriptional repression of other KSHV lytic genes in KSHV latency.

KSHV encodes a replication and transcription activator, RTA (ORF50). The expression of RAT is sufficient and necessary for activating for KSHV lytic replication. RTA targets both viral and cellular genes to achieve its functions. We are currently mapping the viral and cellular targets and promoter binding sites of RTA in the whole-genome scale. These works should provide insights into the mechanisms of KSHV replication.

Key Words
KSHV/HHV8, Kaposi's sarcoma, AIDS-related malignancies, Angiogenesis, Inflammation, microRNA, Herpesvirus, Latency and Reactivation