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Biomedical subjects

A W Harris

Publications and source records attributed to A W Harris.

At least 91 records · Page 5Linked to original sources
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.

Animals↗
PubMed1986

The c-myc oncogene perturbs B lymphocyte development in E-mu-myc transgenic mice.

Transgenic mice bearing a c-myc oncogene subjugated to the lymphoid-specific immunoglobulin heavy chain enhancer (E mu) develop clonal B lymphoid malignancies, but most young E mu-myc mice lack malignant clones. Their prelymphomatous state has allowed us to examine how constitutive c-myc expression influences B cell development. We find that early stages are overrepresented, even before birth. Pre-B cells of polyclonal origin increase greatly, while B cells develop in reduced number. Both the pre-B and the B cells appear to be in an active state, since they are larger than normal and a greater fraction are in the cell cycle. Enforced myc expression has thus favored proliferation over maturation. Hence, a normal function of c-myc may be to regulate differentiation as well as to promote cell cycling.

Animals↗
PubMed1985

beta-Adrenergic receptors and adenylate cyclase activity in murine lymphoid cell lines.

beta-Adrenergic receptors were determined in sixteen cultured tumor cell lines of T- and B-lymphoid derivation by the binding of the hydrophilic ligand [3H]CGP-12177. The number of receptors per cell varied from less than a hundred to over three thousand. Intracellular cAMP responses to isoproterenol and forskolin were measured for seven cell lines possessing a range of receptor numbers. No direct relationship was found between the isoproterenol-induced elevation of cAMP and the receptor number, and forskolin-induced increases in cAMP varied by more than 100-fold between cell lines. Adenylate cyclase activity was also measured in membrane preparations from the seven cell lines. The T-lymphoma line WEHI-22, the line with the highest receptor number (3700 per cell), showed very little response to any stimulatory agent. With the other four cell lines possessing receptors, the membrane-bound adenylate cyclase activity evoked by isoproterenol relative to that evoked by forskolin was found to be proportional to the number of receptors per cell. The number of receptors thus seems to determine the proportion of the inherent adenylate cyclase that can be activated by a beta-adrenergic agent. The levels of adenylate cyclase induced in membranes by GppNHp and by fluoride, relative to those induced by forskolin, were substantially higher with some cell lines than with others. These data and the results from WEHI-22 cells indicate that lymphoid cell lines differ in their content of functional C and N proteins.

Adenylyl Cyclase Inhibitors↗
PubMed1985

Activation of mouse lymphocytes inhibits induction of rapid cell death by x-irradiation.

A distinctive property of the resting lymphocyte is its ability to die rapidly in interphase after x-irradiation. Suspensions of thymocytes and peripheral lymphocytes from BALB/c mice were irradiated with doses ranging from 10 to 10,000 rad (0.1 to 100 Grays), and their viability was measured by eosin dye exclusion at intervals through 3 days of culture. After an initial latent period of a few hours, viability declined exponentially in a dose-dependent fashion. Doses as low as 20 rad caused some lymphocytes to die rapidly. After 1000 rad, 90% of the cells became nonviable in 15 to 20 hr and 99% in 25 to 35 hr. Peripheral lymphocytes showed a somewhat earlier loss of viability than did thymocytes, and were killed especially rapidly by 10,000 rad. Enriched T cells and B cells were killed by irradiation at equal rates, and medullary thymocytes were killed at the same rate as the whole thymocyte population. In contrast with resting cells, T and B lymphocytes activated by mitogens were not subject to such rapid induction of cell death. Irradiation with 1000 rad reduced the viability of activated cells by only 50% at a time when less than 1% of nonstimulated lymphocytes remained alive. Similarly, cloned lines of antigen-specific helper and cytotoxic T cells showed only a delayed and slow loss of viability after receiving 1000 rad. The state of activation can therefore be a significant determinant of the immunologic consequences of irradiation.

Animals↗
PubMed1984

Effect of cloned interferon-gamma on expression of H-2 and Ia antigens on cell lines of hemopoietic, lymphoid, epithelial, fibroblastic and neuronal origin.

Interferon-gamma (IFN-gamma), tested in the form of the product of a cloned murine IFN-gamma gene, was found to increase the expression of H-2 antigens on cultured cell lines of a wide variety of cell types including factor-dependent hemopoietic cells, pre-B and B cells, macrophages, T cells, mast cells and cell lines of epithelial, fibroblastic and neuronal origin. However, IFN-gamma induced Ia antigens on only B cells, macrophages and T-dependent mast cells or persisting cells. On the basis of these results, we suggest that a major function of IFN-gamma is to potentiate immune responses by enhancing the expression of H-2 and Ia antigens on a variety of cell types.

Animals↗