Our Science – Ruscetti Website

Sandra K. Ruscetti, Ph.D.

Laboratory of Cancer Prevention Head, Retroviral Pathogenesis Section Senior Investigator Building 469, Room 205 NCI-Frederick Frederick, MD 21702-1201 Phone:   301-846-5740 Fax:   301-846-6164 E-Mail:   ruscetti@ncifcrf.gov

Biography

Dr. Sandra Ruscetti Dr. Ruscetti is the head of the Retroviral Molecular Pathogenesis Section, Laboratory of Cancer Prevention. She received her Ph.D. from the University of Pittsburgh studying the genetic control of the immune response with Dr. Thomas Gill. In 1975, she joined the laboratories of Drs. Wade Parks and Edward Scolnick at NCI and began her work on the pathogenesis of mouse retroviruses.

Research

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 these studies to design rational strategies to counteract the molecular events that are responsible for the diseases induced and apply this to similar diseases in man.

Erythroleukemia Induced by the Friend Spleen Focus-Forming Virus

The major focus of our research is to gain a better understanding of the molecular basis for leukemia development by utilizing retrovirus-based mouse model systems. We are currently studying erythroleukemia induced by the Friend spleen focus-forming virus (SFFV), which provides an important model for understanding how deregulation of hematopoietic pathways can lead to leukemia. Although normal erythroid cells require erythropoietin (Epo) for proliferation and differentiation, those expressing the SFFV envelope protein proliferate and differentiate in the absence of Epo, resulting in acute erythroid hyperplasia and polycythemia. In addition, SFFV integration at the sfpi-1 locus results in expression of non-physiological levels of the myeloid transcription factor PU.1 in erythroid cells, causing a block in differentiation and the outgrowth of transformed cells. To understand how expression of the SFFV envelope protein in erythroid cells alters their growth and differentiation and how expression of PU.1 leads to their transformation, we have been studying signal transduction pathways known to be activated by Epo to determine if any of these are deregulated after SFFV infection. In non-transformed erythroid cells infected with SFFV, we have shown that most Epo-induced signal transducers, including Stat proteins, components of the Raf-1/MAP kinase pathway, PI 3-kinase, protein kinase C and Akt kinase, are constitutively activated through activation by the virus of a redundant signal transduction pathway involving insulin receptor substrate (IRS)-related adaptor proteins. Our recent studies indicate that a truncated form of the receptor tyrosine kinase Stk, which was recently implicated in susceptibility to SFFV-induced erythroleukemia, is activated and stabilized after covalent interaction with the SFFV envelope protein, suggesting that this kinase may be responsible for activating signal transducing molecules in SFFV-infected cells. Although Stat proteins are activated when SFFV infects erythroid cells, we observed that transformation of these cells was associated with a block in the activation of Stats 1 and 3 DNA-binding activity. This block is specific to Stat activation by Epo, not Stat activation by interferons in these cells. There is a direct correlation in SFFV-infected erythroid cells between expression of PU.1 and inhibition of Stat DNA-binding, suggesting that PU.1 may be involved in the block, perhaps by interfering with the interaction of certain Stat proteins with the promoters of genes required for erythroid cell differentiation. To date, our studies on SFFV-induced erythroleukemia have identified a number of molecular events associated with deregulation of cell growth and transformation that we can potentially target for therapeutic intervention.

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 provides an important model for understanding how retroviruses can undergo genetic changes that alter their interaction with cells in the host to cause novel biological effects. Using chimeric constructs between PVC-211 MuLV and its non-neuropathogenic parent Friend MuLV, we previously demonstrated that PVC-211 MuLV had undergone subtle changes in its envelope gene which allow it to efficiently infect brain capillary endothelial cells (BCEC), cells which are generally resistant to infection by MuLVs. This expanded host range allows PVC-211 MuLV to be expressed at high levels in the neonatal rodent brain and this results in a rapid neurodegenerative disease. Since viral infection of BCEC is crucial to the development of this neurological disease, we have concentrated our efforts on mapping changes in the envelope gene responsible for BCEC tropism and understanding the interaction of PVC-211 MuLV with its BCEC receptor. We demonstrated that the BCEC tropism of PVC-211 MuLV is the result of two amino acid changes in the region of the viral envelope glycoprotein that is thought to bind to CAT1, a cationic amino acid transporter that is the cellular receptor for ecotropic MuLVs. Recent studies indicate that one of these changes creates a unique heparin-binding site that may allow PVC-211 MuLV to bind to heparin-like molecules on the surface of BCEC to facilitate receptor binding. Although BCEC tropism is essential for the neuropathogenicity of PVC-211 MuLV, it is not sufficient. We are, therefore, carrying out studies to determine how expression of PVC-211 MuLV in BCEC leads to degeneration of neurons, which is indirect since the virus cannot be detected in neurons or significantly in any other cells in the central nervous system. Our recent studies indicate that infection of BCEC with PVC-211 MuLV leads to activation of inducible nitric oxide synthase and elevation of a 32kD cellular protein modified by tyrosine nitration, a hallmark of nitric oxide (NO)production. Thus, NO released from virus-infected BCEC could be responsible for neuronal damage in PVC-211 MuLV-infected rats. BCEC from rats infected with PVC-211 MuLV also express the chemokine LIX and studies are in progress to determine whether secretion of this chemokine may be responsible for the infiltration of neutrophils observed in the brains of virus-infected rats. Finally, our studies of PVC-211 MuLV demonstrate that the BCEC tropism of this virus can be further extended to capillary endothelial cells (CEC) from other organs, and we have initiated studies in an attempt to exploit this unique property of PVC-211 MuLV for use in gene transduction targeted to the proliferating endothelium associated with developing tumors.

Collaborators:

Collaborators on this research are Paul Hoffman, M.D., Dept. of Veterans Affairs Medical Center, Baltimore, MD, Michiaki Masuda, M.D., Ph.D., University of Tokyo, Japan, and Susan Wilt, Ph.D. Department of Veterans Affairs Medical Center, Bronx, NY.

This page was last updated on 6/12/2008.