Our Science – Ruscetti Website
Sandra K. Ruscetti, Ph.D.
The focus of our research is devoted to understanding the molecular basis for the pathogenesis of retrovirus-induced diseases. We have been studying retroviruses that cause leukemia or neurological disease in rodents to obtain basic information on how molecular changes in normal cells can result in pathological consequences. We hope to use the information gained from our studies to design and test rational strategies to counteract the retrovirus-induced molecular events that are responsible for these diseases.
Erythroleukemia Induced by the Friend Spleen Focus-Forming Virus
Friend spleen focus-forming virus (SFFV) causes a rapid, multi-stage leukemia and provides an important model for understanding the molecular changes that result in various phases of leukemia and for testing therapeutic strategies to block each stage. While normal erythroid cells require the erythroid hormone erythropoietin (Epo), SFFV-infected erythroid cells in the first stage of disease proliferate and differentiate in the absence of Epo, leading to erythroid hyperplasia and polycythemia. This is due to interaction of the SFFV envelope protein with a unique receptor tyrosine kinase, sf-Stk, which is preferentially expressed in erythroid cells. This interaction results in activation of the kinase and various components of the Epo signal transduction pathway. The second stage of disease is characterized by the outgrowth of a rare, malignant erythroid cell in which SFFV has activated the transcription factor PU.1 to block erythroid cell differentiation. We demonstrated that activation of PU.1 in erythroid cells results in high expression of the hematopoietic phosphatase SHP-1 and subsequently to a specific block in the phosphorylation of STAT1, a transcription factor important for erythroid cell differentiation. More recently we demonstrated that SFFV-transformed erythroleukemia cells can metastasize to the bone marrow, where they are retained and subsequently cause meningeal leukemia, a common neurological complication of human leukemia. Future work is aimed at better understanding the molecular basis for Friend SFFV-induced meningeal leukemia and testing specific therapeutic strategies to block multi-stage leukemia using our retrovirus-induced mouse model. In collaboration with Larry Keefer and members of his laboratory, we have shown that SFFV-induced erythroleukemia cells, but not normal hematopoietic cells, are killed by the nitric oxide prodrug JS-K, and studies are in progress to determine the target of NO in these cells and to test JS-K for its efficacy in treating the various stages of SFFV-induced erythroleukemia.
Several years ago we made the novel observation that sf-Stk, the tyrosine kinase activated by SFFV in erythroid cells, can also be activated by the virus when it is expressed in non-erythroid cells, resulting in transformation of fibroblasts in vitro and non-erythroid malignancies in mice. All of the signal transducing molecules activated by SFFV in erythroid cells were also activated in SFFV/sf-Stk-transformed fibroblasts except for STATs 1 and 5, whose activation appears to require the Epo receptor. We showed that PU.1 is not involved in the transformation of non-erythroid cells, but that activated sf-Stk is absolutely required for this process. Since our studies on sf-Stk indicate that its activation can lead to transformation of various cell types, we are extending our studies to determine if the human counterpart of sf-Stk, sf-RON, is activated in any human malignancies and whether it contributes to transformation.
Neurological Disease Induced by a Variant of Friend Murine Leukemia Virus
As a second retroviral model system, we have been studying PVC-211 murine leukemia virus (MuLV), a variant of the erythroleukemia-inducing Friend MuLV that causes a rapid neurodegenerative disease in rodents. PVC-211 MuLV-infected diseased brain and spinal cord exhibit the spongiform pathology characteristic of some human neurodegenerative diseases such as HTLV-1-associated myelopathy/tropical spastic paraparesis and transmissible spongiform encephalopathy. We previously demonstrated that subtle changes in the envelope gene of the virus altered its host range from that of its leukemia-inducing parent Friend MuLV, enabling it to gain access to the central nervous system by infecting brain capillary endothelial cells (BCEC). By comparing BCEC from uninfected and PVC MuLV-infected rats, we found that virus-infected BCEC express high levels of inducible nitric oxide synthase and show evidence of NO production. We recently demonstrated that PVC-211 MuLV infection of BCEC in vivo results in the production of vascular endothelial cell growth factor and the chemokine MIP-1α, leading to vascular leakage and activation of microglia, the resident macrophages of the central nervous system. Further studies demonstrated that depletion of microglia from rat brains blocks neurodegeneration induced by PVC-211 MuLV and that treatment with antiserum to MIP-1α or splenectomy, both of which reduce the number of activated microglia in the brain, can delay disease, clearly demonstrating the importance of activated microglia in the development of PVC-211 MuLV-induced neurodegeneration. Current studies are focused on using pharmacological interventions to block or mitigate PVC-211 MuLV-induced neurodegeneration.
Collaborators on this research are Dr. Larry Keefer, Laboratory of Comparative Carcinogenesis, CCR, NCI; Drs. Candace Pert and Michael Ruff, RAPID Pharmaceuticals; Dr. Kazuo Nishigaki, Yamaguchi University.
This page was last updated on 5/7/2012.