Genetic Determinants of Feline Leukemia Virus-Induced Multicentric Lymphomas

AbstractThree discrete forms of feline leukemia virus (FeLV)-associated lymphoma have been described clinically: (1) thymic, (2) alimentary, and (3) multicentric. The most common and best-characterized lymphomas are of T-cell origin, generally occurring in the thymus. These tumors typically contain mature T-cells, involve the activation of a distinctive set of proto-oncogenes, and contain FeLV proviruses whose long terminal repeat (LTR) sequences contain tandemly repeated enhancers. Previous studies of a small group of extrathymic, multicentric lymphomas implicated a different set of genetic determinants. The present study expands those observations by examining the lineage of origin, the involvement of proto-oncogenes, and the structure of LTR andenvgene sequences in a set of 11 natural, extrathymic lymphomas of the multicentric type. A pattern of genetic events associated with FeLV-positive multicentric lymphomas emerges from this analysis that is clearly distinct from the pattern associated with thymic lymphomas. The tumors do not contain T-cells or B-cells, as evidenced by the germ line organization of TCRβ and IgH loci. Proto-oncogenes strongly implicated in T-cell lymphomagenesis are not involved in these tumors. Rather, a distinct set of proto-oncogenes may be involved. Most striking is the repeated occurrence of an FeLV isolate whose LTR andenvgene bear unique sequence elements

Distinctive receptor binding properties of the surface glycoprotein of a natural Feline Leukemia Virus isolate with unusual disease spectrum

<p>Abstract</p> <p>Background</p> <p>Feline leukemia virus (FeLV)-945, a member of the FeLV-A subgroup, was previously isolated from a cohort of naturally infected cats. An unusual multicentric lymphoma of non-T-cell origin was observed in natural and experimental infection with FeLV-945. Previous studies implicated the FeLV-945 surface glycoprotein (SU) as a determinant of disease outcome by an as yet unknown mechanism. The present studies demonstrate that FeLV-945 SU confers distinctive properties of binding to the cell surface receptor.</p> <p>Results</p> <p>Virions bearing the FeLV-945 Env protein were observed to bind the cell surface receptor with significantly increased efficiency, as was soluble FeLV-945 SU protein, as compared to the corresponding virions or soluble protein from a prototype FeLV-A isolate. SU proteins cloned from other cohort isolates exhibited increased binding efficiency comparable to or greater than FeLV-945 SU. Mutational analysis implicated a domain containing variable region B (VRB) to be the major determinant of increased receptor binding, and identified a single residue, valine 186, to be responsible for the effect.</p> <p>Conclusions</p> <p>The FeLV-945 SU protein binds its cell surface receptor, feTHTR1, with significantly greater efficiency than does that of prototype FeLV-A (FeLV-A/61E) when present on the surface of virus particles or in soluble form, demonstrating a 2-fold difference in the relative dissociation constant. The results implicate a single residue, valine 186, as the major determinant of increased binding affinity. Computational modeling suggests a molecular mechanism by which residue 186 interacts with the receptor-binding domain through residue glutamine 110 to effect increased binding affinity. Through its increased receptor binding affinity, FeLV-945 SU might function in pathogenesis by increasing the rate of virus entry and spread <it>in vivo</it>, or by facilitating entry into a novel target cell with a low receptor density.</p

Substitution of Feline Leukemia Virus Long Terminal Repeat Sequences into Murine Leukemia Virus Alters the Pattern of Insertional Activation and Identifies New Common Insertion Sites

The recombinant retrovirus, MoFe2-MuLV (MoFe2), was constructed by replacing the U3 region of Moloney murine leukemia virus (M-MuLV) with homologous sequences from the FeLV-945 LTR. NIH/Swiss mice neonatally inoculated with MoFe2 developed T-cell lymphomas of immature thymocyte surface phenotype. MoFe2 integrated infrequently (0 to 9%) near common insertion sites (CISs) previously identified for either parent virus. Using three different strategies, CISs in MoFe2-induced tumors were identified at six loci, none of which had been previously reported as CISs in tumors induced by either parent virus in wild-type animals. Two of the newly identified CISs had not previously been implicated in lymphoma in any retrovirus model. One of these, designated 3-19, encodes the p101 regulatory subunit of phosphoinositide-3-kinase-gamma. The other, designated Rw1, is predicted to encode a protein that functions in the immune response to virus infection. Thus, substitution of FeLV-945 U3 sequences into the M-MuLV long terminal repeat (LTR) did not alter the target tissue for M-MuLV transformation but significantly altered the pattern of CIS utilization in the induction of T-cell lymphoma. These observations support a growing body of evidence that the distinctive sequence and/or structure of the retroviral LTR determines its pattern of insertional activation. The findings also demonstrate the oligoclonal nature of retrovirus-induced lymphomas by demonstrating proviral insertions at CISs in subdominant populations in the tumor mass. Finally, the findings demonstrate the utility of novel recombinant retroviruses such as MoFe2 to contribute new genes potentially relevant to the induction of lymphoid malignancy

Coincident involvement of flvi-2, c-myc, and novel env genes in natural and experimental lymphosarcomas induced by feline leukemia virus

The flvi-2 locus is a target of insertional mutagenesis in thymic lymphosarcomas induced by feline leukemia virus (FeLV). flvi-2 encodes the gene bmi-1, whose product is implicated as a myc-collaborator in the induction of B- and T-cell lymphoma. We have examined the involvement of flvi -2 and myc in natural and experimentally induced FeLV-positive feline lymphosarcomas which are heterogeneous in anatomical origin, geographic origin, and strain of FeLV involved. We further compared these findings with previous reports of novel FeLV env genes in the same tumors. The results show that proviral insertion at flvi-2 occurs commonly in natural and experimental feline thymic lymphosarcomas of diverse origins [52% overall], and that alterations in c-myc commonly accompany insertional mutagenesis of flvi-2 [54% overall]. However, 46% of tumors with flvi-2 insertions apparently lack involvement of c-myc. These observations support the hypothesis that interruption of flvi-2 may be an early event in a multistep cascade, one possibility for completion of which is activation of c-myc. Interruption of flvi-2 was not observed in nonthymic lymphosarcomas of alimentary or multicentric origin, although c-myc may be involved. A proportion of both thymic and nonthymic tumors have been shown previously to contain FeLV proviruses with recombinant or mutant env genes. Our findings strongly implicate the insertional mutagenesis of flvi-2, the activation of c-myc, and the emergence of novel env genes in FeLV-mediated lymphomagenesis, particularly in the induction of thymic lymphosarcoma. The data show that these events may overlap, but do not necessarily occur concurrently