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Biomedical subjects

A W Harris

Publications and source records attributed to A W Harris.

At least 19 recordsLinked to original sources
PubMed1992

Retroviral infection accelerates T lymphomagenesis in E mu-N-ras transgenic mice by activating c-myc or N-myc.

Transgenic mice bearing a mutant, activated N-ras oncogene directed to express within hematopoietic cells by an immunoglobulin enhancer (E mu) sporadically develop T-cell lymphomas and non-lymphoid tumors that may be of macrophage origin. To identify genes that can collaborate with N-ras in hematopoietic neoplasia, Moloney murine leukemia virus was used as an insertional mutagen. Infection of newborn E mu-N-ras mice with the virus greatly accelerated tumorigenesis, and nearly all the tumors proved to be T-cell lymphomas. Their variable surface phenotype (CD4+CD8-, CD4+CD8+ and CD4-CD8-) suggested that cells at several stages of T-cell development were susceptible to tumorigenesis. Southern blot analysis revealed that 68% of the tumors bore a proviral insert 5' to the c-myc gene, while 13% had an insert within the 3' untranslated region of the N-myc gene. Insertion was associated with elevated expression of these genes. Hence, activation of a myc gene appears to be the dominant pathway to tumorigenesis by insertional mutagenesis in lymphoid cells expressing a mutant ras gene. However, since many of the tumors were not transplantable, even the partnership of myc and ras may not suffice for full lymphoid malignancy.

Animals↗
PubMed1991

bcl-2 transgene inhibits T cell death and perturbs thymic self-censorship.

Early death is the fate of most developing T lymphocytes. Because bcl-2 can promote cell survival, we tested its impact in mice expressing an E mu-bcl-2 transgene within the T lymphoid compartment. The T cells showed remarkably sustained viability and some spontaneous differentiation in vitro. They also resisted killing by lymphotoxic agents. Although total T cell numbers and the rate of thymic involution were unaltered, the response to immunization was enhanced, consistent with reduced death of activated T cells. No T cells reactive with self-superantigens appeared in the lymph nodes, but an excess was found in the thymus. These observations, together with previous findings on B cells, suggest that modulated bcl-2 expression is a determinant of life and death in normal lymphocytes.

Animals↗
PubMed1991

Enforced BCL2 expression in B-lymphoid cells prolongs antibody responses and elicits autoimmune disease.

The biological functions of the BCL2 gene were investigated in transgenic mice harboring human BCL2 cDNA under the control of an immunoglobulin heavy chain enhancer (E mu). Mice of a representative transgenic strain, E mu-bcl-2-22, had a great excess of B lymphocytes, immunoglobulin-secreting cells, and serum immunoglobulins, attributable to increased longevity of B-lineage cells. Pre-B and plasma cells as well as B cells exhibited prolonged survival in culture. Immunized animals produced an amplified and protracted antibody response. Within the first year of life, most mice spontaneously produced antibodies to nuclear antigens, and 60% developed kidney disease, diagnosed as immune complex glomerulonephritis. Thus E mu-bcl-2-22 mice constitute a transgenic model for a systemic autoimmune disease resembling the human disorder systemic lupus erythematosus.

Animals↗
PubMed1990

Novel primitive lymphoid tumours induced in transgenic mice by cooperation between myc and bcl-2.

The putative oncogene bcl-2 is juxtaposed to the immunoglobulin heavy chain (Igh) locus by the t(14;18) chromosomal translocation typical of human follicular B-cell lymphomas. The bcl-2 gene product is not altered by the translocation, but its expression is deregulated, presumably by the Igh enhancer E mu. Constitutive bcl-2 expression seems to augment cell survival, as infection with a bcl-2 retrovirus enables certain growth factor-dependent mouse cell lines to maintain viability when deprived of factor. Furthermore, high levels of the bcl-2 product can protect human B and T lymphoblasts under stress and thereby confer a growth advantage. Mice expressing a bcl-2 transgene controlled by the Igh enhancer accumulate small non-cycling B cells which survive unusually well in vitro but do not show a propensity for spontaneous tumorigenesis. In contrast, an analogous myc transgene, designed to mimic the myc-Igh translocation product typical of Burkitt's lymphoma and rodent plasmacytoma, promotes B lymphoid cell proliferation and predisposes mice to malignancy in pre-B and B lymphoid cells. Previous experiments have suggested that bcl-2 can cooperate with deregulated myc to improve in vitro growth of pre-B and B cells. Here we describe a marked synergy between bcl-2 and myc in doubly transgenic mice. E mu-bcl-2/myc mice show hyperproliferation of pre-B and B cells and develop tumours much faster than E mu-myc mice. Suprisingly, the tumours derive from a cell with the hallmarks of a primitive haemopoietic cell, perhaps a lymphoid-committed stem cell.

Animals↗
PubMed1990

An E mu-v-abl transgene elicits plasmacytomas in concert with an activated myc gene.

To clarify how the v-abl oncogene of Abelson murine leukemia virus contributes to lymphoid tumorigenesis, we introduced the gene linked to an immunoglobulin heavy chain enhancer (E mu) into the mouse germline. Although lymphoid development was not detectably affected in young E mu-v-abl mice, three transgenic lines shared a high predisposition to develop clonal plasmacytomas that secreted IgA or IgG. The unexpected absence of pre-B lymphomas suggests that Abelson virus generates such tumors by infecting an early lymphoid progenitor cell that has not yet activated the heavy chain enhancer. Most plasmacytomas bore a rearranged c-myc gene, apparently as a result of spontaneous translocation to the Igh locus. Moreover, progeny of a cross with analogous E mu-myc mice rapidly developed oligoclonal plasmacytomas. Thus, the collusion of v-abl with c-myc is stage specific, efficiently transforming plasma cells but not pre-B cells or B cells.

Abelson murine leukemia virus↗
PubMed1989

Lymphoid neoplasia and the control of haemopoietic differentiation.

Our broad aims are to delineate oncogenic events in lymphoid neoplasia and to search for genes that control haemopoietic differentiation. To explore lymphoid neoplasia, we have constructed transgenic mice bearing different oncogenes coupled to the immunoglobulin heavy chain enhancer (E mu), to force expression within lymphocytes. The prototype E mu-myc mice are highly prone to lymphomagenesis, generating pre-B and B cell lymphomas. In their pre-neoplastic phase, E mu-myc expression perturbs B cell development, accelerating the accumulation of pre-B cells. Lymphomagenesis requires additional oncogenic events, such as ras activation, and can be reconstructed in vitro. Transgenic mice bearing the N-myc, N-ras, v-abl and bcr-v-abl oncogenes are also prone to tumours. A striking demonstration that oncogenes can perturb lineage commitment has emerged. Introduction of the v-raf gene into cloned E mu-myc transgenic B cells frequently led to a switch in haemopoietic lineage: the cells became macrophages. Two clues to this remarkable metamorphosis are that the macrophage lines produce a myeloid growth factor and most bear marked karyotypic alterations, perhaps indicating that the balance between a few critical lineage control genes has been disturbed. To explore the hypothesis that genes encoding the DNA-binding homeo box domain participate in haemopoiesis, cDNA libraries from haemopoietic sources were screened, and several distinct homeo box cDNAs were isolated. They revealed a complex pattern of expression among haemopoietic cell lines. These genes are attractive candidates for regulators of haemopoietic differentiation.

Animals↗
PubMed1989

N-myc transgene promotes B lymphoid proliferation, elicits lymphomas and reveals cross-regulation with c-myc.

To assess the impact of constitutive N-myc expression on lymphocytes, we generated lines of transgenic mice bearing the murine N-myc oncogene coupled to the immunoglobulin heavy chain enhancer (E mu). As in mice carrying an analogous c-myc construct, E mu-N-myc mice exhibit a limited overgrowth of cycling pre-B cells and eventually succumb to clonal B lymphoid tumours. The endogenous N-myc and c-myc alleles are silent in both E mu-N-myc and E mu-myc lymphomas, suggesting that these genes are subject to auto- and cross-regulation. The regulatory interaction and the similar biological effects of N-myc and c-myc imply that the two genes perform interchangeable functions in the promotion of cell proliferation.

Animals↗
PubMed1989

A bcr-v-abl oncogene induces lymphomas in transgenic mice.

In chronic myeloid leukemia and some cases of acute lymphoblastic leukemia, a 9;22 chromosome translocation has fused most of the c-abl oncogene to a gene designated bcr. To explore in vivo the biological effects of the chimeric gene, we introduced a facsimile of the translocation product, a bcr-v-abl gene, into the mouse germ line under the control of the immunoglobulin heavy-chain enhancer or a retroviral long terminal repeat. Some transgenic mice bearing either construct developed clonal lymphoid tumors. T lymphomas predominated, but some pre-B lymphomas developed. The transgenes were expressed in the tumors but not detectably in the lymphoid tissues of nontumorous transgenic animals, implying that transcription is activated by a low-frequency somatic event. These results demonstrate that bcr-v-abl is tumorigenic in vivo and provide a new animal model for lymphomagenesis.

Animals↗
PubMed1989

The transgenic window on lymphoid malignancy.

Transgenic mice bearing an oncogene targetted for expression in a specific tissue can reveal how that oncogene influences differentiation and help to delineate the pathways to malignancy. To explore lymphoid neoplasia, we have made strains of transgenic mice bearing different oncogenes driven by the immunoglobulin heavy chain enhancer (E mu), which promotes expression within lymphocytes and certain myeloid cells. The prototype E mu-myc mice succumb to pre-B and B cell lymphomas, following a preneoplastic phase in which cycling pre-B cells are overproduced. The similar fate of E mu-N-myc mice suggests that N-myc and myc have overlapping functions. Surprisingly, E mu-N-ras mice develop T lymphomas and macrophage tumours but no B lineage tumours; thus the ability of ras to initiate tumorigenesis may be lineage specific. Similarly, the high predisposition of E mu-v-abl mice to develop plasmacytomas may indicate that v-abl is oncogenic only at certain stages of B cell maturation. The bcl-2 gene promotes cell survival rather than proliferation, and E mu-bcl-2 mice produce copious resting B lymphocytes. The random onset and monoclonality of tumours in the transgenic strains argues for spontaneous genetic alterations that cooperate with the trans-oncogene. Indeed, most plasmacytomas of E mu-v-abl mice bear spontaneous myc rearrangements. Moreover, a minority of E mu-myc B lymphomas exhibit ras mutation, and the tumorigenesis can be reconstructed by crossing E mu-myc and E mu-ras mice, or by retroviral delivery of v-ras or v-raf, either in vitro or in vivo. To access novel cooperating oncogenes, we are using a retrovirus lacking an oncogene as an insertional mutagen. This approach should be applicable to any trans-oncogenic strain and help to delineate the genetic events that trigger malignant clones.

Animals↗
PubMed1989

Acceleration of B-lymphoid tumorigenesis in E mu-myc transgenic mice by v-H-ras and v-raf but not v-abl.

Emu-myc transgenic mice constitutively express the c-myc oncogene from before birth, but their inexorable development of B-lymphoid tumors appears to require rare spontaneous alterations within B-lineage cells. To determine whether other oncogenes can cooperate with myc to induce B-lymphoid transformation, we infected neonatal Emu-myc mice and normal littermates with helper-free retroviruses bearing the v-H-ras, v-raf, or v-abl oncogene. The v-H-ras and the v-raf oncogene dramatically accelerated Emu-myc pre-B-lymphoma onset, whereas v-abl did not, despite the increased numbers of presumptive target pre-B cells in Emu-myc mice. These results imply that v-H-ras and v-raf synergize with deregulated myc expression to transform pre-B cells, while v-abl apparently does not.

Animals↗
PubMed1988

The E mu-myc transgenic mouse. A model for high-incidence spontaneous lymphoma and leukemia of early B cells.

Mice transgenic for a c-myc gene driven by the IgH enhancer (E mu-myc) were shown to almost invariably develop lymphomas, 90% succumbing in the first 5 mo of life. The tumors typically presented as rapidly progressive lymphadenopathy with thymic involvement and were highly malignant by transplantation assay. Morphologically, they were lymphoblastic lymphomas, usually accompanied by lymphoid leukemia and granulocytosis, and were distinct from the tumors that arose much later in 37% of nontransgenic mice of the same (C57BL/6 x SJL)F2 genetic background. Cell-surface markers on 31 E mu-myc tumors identified 52% as pre-B lymphomas, 29% as mixed pre-B and B lymphomas, and 19% as B lymphomas. The tumors appeared to arise at random from a population of pre-B cells expanded by constitutive expression of the myc transgene. A majority of the animals initiated malignancy at the rate of 17% per week. The rate at which the cycling, benign pre-B cells spontaneously convert to malignancy was estimated to about 10(-10) per cell per generation. A transient leukocytosis identified in young E mu-myc mice was developed into a rapid assay for inheritance of the transgene.

Animals↗
PubMed1988

Growth of E mu-myc transgenic B-lymphoid cells in vitro and their evolution toward autonomy.

Constitutive expression of the c-myc oncogene in the B lymphoid cells of E mu-myc transgenic mice promotes cellular proliferation and predisposes to lymphomagenesis. To delineate further how the pre-B cells of prelymphomatous mice have been altered, we have investigated their growth in vitro. They were not autonomous, since they died rapidly when cultured without feeder cells. When cultured on bone marrow stromal cells, E mu-myc cells initially grew to only slightly higher densities than B lineage cells from normal mice, but were larger and showed more cell cycle activity. After 14 weeks, all cultures appeared oligo- or monoclonal, as judged by analysis of Ig gene rearrangements. While the growth of the normal cells was constant, the E mu-myc cells started to grow to 10-fold higher densities after 14-20 weeks, implying a reduced requirement for growth factors. They remained dependent on feeder cells and were non-tumorigenic. By 25 weeks, however, the one remaining culture had become feeder-independent and tumorigenic. We suggest that deregulated c-myc expression in B cell precursors increases the rate of cell turnover, thereby increasing the frequency of genetic changes conductive to autonomous growth.

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