Date of Award

1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Since 1957, Friend erythroleukemia has been a model for studying mouse genes controlling susceptibility to cancer. The Friend virus complex contains a replication-competent helper virus (F-MuLV) and a replication-defective spleen focus-forming virus (F-SFFV). Friend erythroleukemia is a two-stage disease characterized by erythroid cell hyperplasia in the first stage and erythroid cell transformation in the second. The first stage is due to the interaction between the envelope ( env ) glycoprotein, gp55, of F-SFFV and the erythropoietin receptor (Epo-R) on the target cell surface. The second stage of the disease is due to transformation of one or a few infected cells by insertional activation of oncogenes or insertional inactivation of tumor suppressor genes. Several mouse genes control susceptibility to this disease. The Fv-2 gene prevents interaction between gP55 and Epo-R (reviewed by Hoatlin and Kabat, 1995). Variants of F-SFFV with the ability to overcome Fv-2 -mediated resistance have been isolated. They show deletions in the extra-cytoplasmic domain of the gp55 protein. The objective of this research is to test the hypothesis that deletions in the extracytoplasmic domain of the envelope glycoprotein of the F-SFFV enable it to overcome Fv-2 mediated resistance and to further localize the region(s) within this domain that are critical for its ability to overcome host resistance. Using the BB6 and RBV deletions as a starting point to determine the boundaries, a series of deletions were introduced into the wild-type env gene of F-SFFV. The env genes with deletions were sub-cloned into the expression vector pSFF. Sub-clones were transfected into NIH 3T3 fibroblasts infected with helper virus to generate recombinant virions expressing env glycoproteins with the in vitro -generated deletions. Recombinant virions; were injected into mice to assess the ability of the recombinant virions to overcome Fv-2 -mediated resistance. Sensitive mice showed characteristic sips of Friend viral erythroleukemia—altered hematocrits and splenomegaly—in all deletion mutants studied. However, resistant mice have not revealed signs of disease, and are being regularly monitored. Probable reasons for this prolonged latency of the deletion mutants in resistant mice are discussed.

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