Biomedical subjects

J Lotem

Publications and source records attributed to J Lotem.

At least 37 records · Page 2Linked to original sources

PubMed1995

A mutant p53 antagonizes the deregulated c-myc-mediated enhancement of apoptosis and decrease in leukemogenicity.

Myeloid leukemic M1 cells that do not express p53 and transfected M1 clones that constitutively express the [Val135]p53 mutant or deregulated c-myc or coexpressing both genes grew autonomously in culture with a similar growth rate and cloning efficiency. Expression of deregulated c-myc in M1 leukemic cells enhanced susceptibility to induction of apoptotic cell death and resulted in a reduced leukemogenicity when injected into isologous mice. Expression of the [Val135]p53 mutant did not change cell susceptibility to induction of apoptosis or leukemogenicity, but expression of this mutant p53 suppressed the effects of deregulated c-myc on these properties. The results indicate that the [Val135]p53 mutant can show a gain of function for susceptibility to apoptosis and leukemogenicity in leukemic cells with deregulated c-myc and, thus, enhance tumor development.

Animals↗

PubMed1995

Regulation of bcl-2, bcl-XL and bax in the control of apoptosis by hematopoietic cytokines and dexamethasone.

Treatment of M1 myeloid leukemic cells with interleukin 6 (IL-6) or dexamethasone (DEX), both of which induce differentiation in these cells, down-regulated expression of the apoptosis-suppressing gene bcl-2 and the apoptosis-promoting gene bax but up-regulated expression of the apoptosis-suppressing gene bcl-XL. There was a higher expression of bcl-XL in cells treated with DEX or DEX plus IL-6 compared to cells treated with IL-6 alone. The alternatively spliced bcl-X gene, bcl-Xs, which interferes with the action of bcl-2, was not expressed. Treatment with IL-6 increased the susceptibility of these cells to induction of apoptosis by Adriamycin or cycloheximide, but treatment with DEX or with IL-6 and DEX did not. Withdrawal of DEX after up-regulation of bcl-XL resulted in a decrease in bcl-XL expression and a concomitant increase in cell susceptibility to induction of apoptosis. Another myeloid leukemia that shows barely detectable expression of bcl-2 also showed up-regulated expression of bcl-XL but no change in bax after induction of differentiation with granulocyte-macrophage colony-stimulating factor, and this reduced cell susceptibility to induction of apoptosis by Adriamycin or cycloheximide. The results indicate that the related apoptosis-regulating genes bcl-2, bcl-XL, and bax are differently regulated and that up-regulation of bcl-XL expression may compensate for down-regulation of bcl-2 in the balance between genes that control apoptosis.

Animals↗

PubMed1995

Interferon-gamma inhibits apoptosis induced by wild-type p53, cytotoxic anti-cancer agents and viability factor deprivation in myeloid cells.

Different hematopoietic cytokines including colony-stimulating factors and interleukins can inhibit apoptotic cell death induced in myeloid cells by the tumor-suppressor gene wild-type 53 and a variety of cytotoxic anti-cancer agents. In this study we identity interferon-gamma as an anti-apoptotic cytokine for myeloid cells in which apoptosis was induced by wild-type p53, cytotoxic anti-cancer agents or viability factor deprivation. The inhibition of wild-type p53-mediated apoptosis in myeloid leukemic cells by interferon-gamma was not associated with downregulated expression of wild-type p53 or the p53-induced cyclin-dependent kinase inhibitor gene WAF-1, or with upregulated expression of the apoptosis-inhibiting gene bcl-2. Interferon-gamma also inhibited induction of apoptosis by a p53-independent pathway. Interferon-gamma inhibited apoptotic cell death caused by withdrawal of viability factors in normal myeloid precursor cells, the interleukin 3-dependent 32D cell line and differentiating myeloid leukemic cells. Interferon-alpha/beta did not inhibit apoptotic cell death in any of these systems. The results indicate that although interferon-gamma can inhibit cell multiplication and differentiation in myeloid cells, it shares with other hematopoietic cytokines the ability to protect normal and leukemic myeloid cells from induction of apoptosis.

Animals↗

PubMed1994

The network of hematopoietic cytokines.

Cell viability, multiplication, and differentiation to the various hematopoietic cell lineages are induced by a multigene cytokine family, and hematopoiesis is controlled by a network of interactions between these cytokines. This network includes positive regulators such as colony-stimulating factors and interleukins, and negative regulators such as transforming growth factor-beta and tumor necrosis factor. The functioning of the network requires an appropriate balance between positive and negative regulators, and the selective regulation of programmed cell death (apoptosis) by interaction of cytokines with their receptors. The cytokine network, which has arisen during evolution, allows considerable flexibility, depending on which part of the network is activated, and the ready amplification of response to a particular stimulus. This amplification occurs by autoregulation and transregulation of genes for the hematopoietic cytokines. There is also a transregulation by these cytokines of cytokine receptors. In addition to the flexibility of this network, both for response to present day infections and to infections that may develop in the future, a network may also be necessary to stabilize the whole system. The existence of a network and the cytokine-receptor regulation of apoptosis has to be taken into account in the clinical use of cytokines for therapy. Cytokines that regulate hematopoiesis induce the expression of genes for transcription factors. Cytokine signaling through transcription factors can thus ensure the autoregulation and transregulation of cytokine and receptor genes that occur in the network. Interactions between the cytokine network and transcription factors can also ensure production of specific cell types and stability of the differentiated state.

Biological Evolution↗

PubMed1994

Control of sensitivity to induction of apoptosis in myeloid leukemic cells by differentiation and bcl-2 dependent and independent pathways.

Induction of differentiation in M1 myeloid leukemic cells by the hematopoietic cytokines interleukin 6 and granulocyte-colony stimulating factor, or by the glucocorticoid dexamethasone, was associated with down-regulation of the apoptosis inhibiting gene bcl-2. The cytokine treated leukemic cells showed an increased sensitivity to induction of apoptotic cell death by the cancer chemotherapy compounds Adriamycin and cytosine arabinoside and by heat shock and cycloheximide. Dibutyryl cyclic AMP neither induced differentiation nor down-regulated bcl-2 expression, but it sensitized the cells to induction of apoptosis by some of these agents. Although dexamethasone induced differentiation and down-regulated bcl-2 expression, it did not sensitize the cells to induction of apoptosis and inhibited the apoptosis sensitizing effect of the cytokines and dibutyryl cyclic AMP. Dexamethasone did not inhibit induction of apoptosis by wild-type p53 or viability factor withdrawal. The apoptosis sensitizing effect of the cytokines and dibutyryl cyclic AMP was reversible upon their withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Apoptosis↗

PubMed1993

Hematopoietic cells from mice deficient in wild-type p53 are more resistant to induction of apoptosis by some agents.

Wild-type p53 is a tumor-suppressor gene that can induce cell death by apoptosis when expressed in myeloid leukemic and some other types of tumor cells. However, the question remained as to what extent wild-type p53 is a mediator of apoptosis in normal cells. We have used mice deficient in wild-type p53 to determine whether induction of apoptosis in hematopoietic cells from these p53 deficient mice is defective. We show here that bone marrow myeloid progenitor cells from p53-deficient mice are more resistant to induction of apoptosis when there was only a low concentration of the viability factors granulocyte-macrophage colony-stimulating factor; interleukins-1 alpha, -3, and -6; or stem cell factor; or when apoptosis was induced in these cells by irradiation or heat shock. The loss of one allele of wild-type p53 was sufficient for increased resistance. The higher resistance to apoptosis in p53-deficient mice was also found in irradiated thymocytes, but not in thymocytes treated with dexamethasone or in mature peritoneal granulocytes. The degree of resistance in irradiated myeloid progenitors and thymocytes showed a dosage effect of the number of wild-type p53 genes. The results show that wild-type p53 is involved in the induction of apoptosis by some agents in normal hematopoietic cells. Loss of wild-type p53 can, therefore, contribute to tumor development by decreasing cell death at low concentrations of viability factors and after exposure to a DNA-damaging agent. The results also show that there are wild-type p53-dependent and -independent pathways of normal cell apoptosis.

Animals↗

PubMed1993

Control of programmed cell death in normal and leukemic cells: new implications for therapy.

Programmed cell death (apoptosis) is a normal process by which cells are eliminated during normal embryonic development and in adult life. Disruption of this normal process resulting in illegitimate cell survival can cause developmental abnormalities and facilitate cancer development. Normal cells require certain viability factors and undergo programmed cell death when these factors are withdrawn. The viability factors are required throughout the differentiation process from immature to mature cells. Although many viability factors are also growth factors, viability and growth are separately regulated. Viability factors can have clinical value in decreasing the loss of normal cells including the loss that occurs after irradiation, exposure to other cytotoxic agents or virus infection including AIDS. There is no evidence that occurs after irradiation, exposure to other cytotoxic agents or virus infection including AIDS. There is no evidence that cancer cells are immortal. Programmed cell death can be induced in leukemic cells by removal of viability factors, by cytotoxic therapeutic agents, or by the tumor-suppressor gene wild-type p53. All these forms of induction of programmed cell death in leukemic cells can be suppressed by the same viability factors that suppress programmed cell death in normal cells. A tumor-promoting phorbol ester can also suppress this death program. The induction of programmed cell death can be enhanced by deregulated expression of the gene c-myc and suppressed by the gene bcl-2. Mutant p53 and bcl-2 suppress the enhancing effect on cell death of deregulated c-myc, and thus allow induction of cell proliferation and inhibition of differentiation which are other functions of deregulated c-myc. The suppression of cell death by mutant p53 and bcl-2 increases the probability of developing cancer. The suppression of programmed cell death in cancer cells by viability factors suggests that decreasing the level of these factors may increase the effectiveness of cytotoxic cancer therapy. Treatments that downregulate the expression or activity of mutant p53 and bcl-2 in cancer cells should also be useful for therapy.

Apoptosis↗

PubMed1993

Regulation by bcl-2, c-myc, and p53 of susceptibility to induction of apoptosis by heat shock and cancer chemotherapy compounds in differentiation-competent and -defective myeloid leukemic cells.

Myeloid leukemias that differ in their competence for induction of differentiation were analyzed for expression of bcl-2 and c-myc and for their sensitivity to induction of apoptosis by heat shock and cancer chemotherapy compounds. The M1 leukemia expressed a high level of bcl-2 and showed a much lower susceptibility to induction of apoptosis by heat shock, Adriamycin, 1-beta-D-arabinofuranosylcytosine, methotrexate, and cycloheximide, compared to five other leukemias which expressed a low level of bcl-2. There was no association between susceptibility to induction of apoptosis and competence for induction of differentiation. The difference in susceptibility to methotrexate, which is not regulated by the multidrug resistance (MDR) genes, and treatment with verapamil, which blocks MDR activity, have indicated that the higher resistance of the M1 leukemia to these agents was not due to MDR activity. The results indicate that the level of regulated bcl-2 expression in these myeloid leukemias was associated with cell susceptibility to induction of apoptosis by different apoptosis-inducing agents. Screening for expression of bcl-2 may thus be useful to characterize leukemias regarding susceptibility to induction of apoptosis by different agents. The level of regulated c-myc expressed in these leukemias was not associated with susceptibility to induction of apoptosis. Transfection with a deregulated mutant p53 into the M1 leukemia did not change susceptibility to apoptosis induction, but transfection with deregulated c-myc increased susceptibility to apoptosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Antineoplastic Agents↗

PubMed1992

Hematopoietic cytokines inhibit apoptosis induced by transforming growth factor beta 1 and cancer chemotherapy compounds in myeloid leukemic cells.

Transforming growth factor-beta 1 (TGF-beta 1) induces cell death in myeloid leukemia by apoptosis. In the M1 myeloid leukemia, this induction of apoptosis was inhibited by granulocyte colony-stimulating factor (G-CSF) or interleukin-6 (IL-6) and to a lesser extent by IL-1 alpha. IL-3 and stem cell factor/mast cell growth factor (SCF) showed only a marginal effect, and granulocyte-macrophage and macrophage CSFs (GM-CSF and M-CSF, respectively) were inactive. The induction of apoptosis by TGF-beta 1 in a different myeloid leukemia (7-M12) was inhibited by GM-CSF and IL-3 but not by the other cytokines. In the absence of TGF-beta 1, both M1 and 7-M12 leukemic cells were independent of hematopoietic cytokines for cell viability and growth. The cytotoxic compounds vincristine, vinblastine, adriamycin, cytosine arabinoside, cycloheximide, and sodium azide, some of which are used in cancer chemotherapy, induced cell death by apoptosis in both leukemias. As with TGF-beta 1, apoptosis induced by these cytotoxic compounds was inhibited by GM-CSF (7-M12 leukemia) and by G-CSF or IL-6 (M1 leukemia). Cyclosporine A decreased cell multiplication in M1 cells without inducing apoptosis, and G-CSF and IL-6 inhibited the cytostatic effect of cyclosporine A. It is suggested that the clinical use of cytokines to correct therapy-associated myelosuppression should be carefully timed to avoid protection of malignant cells from the cytotoxic action of the therapeutic compounds.

Animals↗

PubMed1992

Regulation of leukaemic cells by interleukin 6 and leukaemia inhibitory factor.

Interleukin 6 (IL-6) and leukaemia inhibitory factor (LIF) can have pleiotropic effects on different cell types. M1 myeloid leukaemic cells respond to IL-6 with activation of a terminal differentiation programme which includes activation of genes for certain haemopoietic regulatory proteins (IL-6, IL-1 alpha, IL-1 beta, granulocyte-macrophage colony-stimulating factor [GM-CSF], M-CSF, tumour necrosis factor and transforming growth factor [TGF] beta 1) and for receptors for some of these proteins, thus establishing a network of positive and negative regulatory cytokines. IL-6 and some other cytokines also induce during differentiation sustained levels of transcription factors that can regulate and maintain gene expression in the differentiation programme. M1 leukaemic cells induced to differentiate with IL-6 undergo programmed cell death (apoptosis) on withdrawal of IL-6, and can be rescued from apoptosis by IL-6, IL-3, M-CSF, G-CSF or IL-1, but not by GM-CSF. These differentiating leukaemic cells can also be rescued from apoptosis by the tumour promoter TPA (12-O-tetradecanoylphorbol-13-acetate) but not by the non-tumour-promoting isomer 4-alpha-TPA, and rescue from apoptosis can be achieved by different pathways. Apoptosis can also be induced in undifferentiated M1 leukaemic cells by expression of the wild-type form of the tumour suppressor p53 protein and IL-6 can rescue the cells from this wild-type p53-mediated apoptosis. There are clones of M1 cells that differentiate with IL-6 but not with LIF and another M1 clone that differentiates with either IL-6 or LIF. Differentiation induced by IL-6 or LIF is inhibited by TGF-beta 1. The pleiotropic effects of LIF, like those of IL-6, are presumably also in a network of interacting regulatory proteins.

Animals↗

PubMed1992

Inhibition of specific pathways of myeloid cell differentiation by an activated Hox-2.4 homeobox gene.

Abnormal expression of homeobox genes is one of the abnormalities associated with the development of murine and human leukemia. Myeloid leukemic cells that can be induced to differentiate to mature cells by interleukin 6 were stably transfected with an activated Hox-2.4 homeobox gene. Expression of the Hox-2.4 gene in the transfected clones inhibited specific pathways of the myeloid differentiation program induced by interleukin 6. The expression of some genes associated with differentiation was almost completely blocked, and the expression of other genes was either partially inhibited or not affected. The results support the hypothesis that abnormal expression of Hox-2.4 may contribute to the development of leukemia by interfering with the differentiation program.

Animals↗

PubMed1992

Selective regulation by hydrocortisone of induction of in vivo differentiation of myeloid leukemic cells with granulocyte-macrophage colony-stimulating factor, interleukin 6 and interleukin 1 alpha.

Clones of myeloid leukemic cells can differ in their ability to be induced to differentiate in vitro by different cytokines. Using such leukemic clones, we studied the regulation by hydrocortisone of induction of in vivo differentiation by injection of recombinant interleukin 6 (IL-6), interleukin 1 alpha (IL-1 alpha), and granulocyte-macrophage colony-stimulating factor (GM-CSF). Injection of IL-6 and IL-1 alpha induced in vivo differentiation of leukemic cells that were induced to differentiate by these cytokines in vitro, but not of leukemic cells that were not susceptible to these cytokines in vitro. In contrast, injection of GM-CSF induced in vivo differentiation both in leukemic cells that were susceptible or not susceptible to GM-CSF in vitro. The effect of GM-CSF, but not of IL-6 or IL-1 alpha, on inducing differentiation in vivo was inhibited by pretreatment with hydrocortisone. In leukemic cells that were not induced to differentiate with GM-CSF in vitro, this inhibition of differentiation by pretreatment with hydrocortisone was greater than inhibition of differentiation obtained by pretreatment with cyclophosphamide or irradiation or the use of nude mice. After hydrocortisone pretreatment, the number of peritoneal cells and their ability to produce GM-CSF and IL-6 were suppressed. It is suggested that hydrocortisone can inhibit the effect of an injected cytokine such as GM-CSF on induction of in vivo differentiation of leukemic cells by inhibiting the ability of host cells to produce cytokines to which the leukemic cells are susceptible.

Animals↗

PubMed1991

Rescue from programmed cell death in leukemic and normal myeloid cells.

Growth factor-independent clones of myeloid leukemic cells can regain a growth factor-dependent state during differentiation. Loss of viability in these differentiating leukemic cells in the absence of growth factor was associated with DNA fragmentation and morphologic changes typical of programmed cell death (apoptosis). The differentiating leukemic cells could be rescued from apoptosis by a hematopoietic growth factor such as interleukin-3 (IL-3) and by the tumor-promoting phorbol ester 12-O-tetra-decanoyl-phorbol-13-acetate (TPA), but not by the nonpromoting phorbol ester 4-alpha-TPA. IL-3 and TPA rescued differentiating myeloid leukemic cells by different pathways and also rescued normal myeloid precursor cells from apoptosis. The rescue of differentiating leukemic and normal myeloid cells by IL-3 or TPA was blocked by amiloride inhibitors of the Na+/H+ antiporter. We suggest that TPA may act as a tumor promoter by inhibiting programmed cell death.

Amiloride↗

PubMed1991

Wild-type p53 induces apoptosis of myeloid leukaemic cells that is inhibited by interleukin-6.

Wild-type p53 protein has many properties consistent with its being the product of a tumour suppressor gene. Although the normal roles of tumour suppressor genes are still largely unknown, it seems that they could be involved in promoting cell differentiation as well as in mediating growth arrest by growth-inhibitory cytokines. Hence, the abrogation of wild-type p53 expression, which is a common feature of many tumours, could eliminate these activities. We have now tested this notion by restoring the expression of p53 in a murine myeloid leukaemic cell line that normally lacks p53. The use of a temperature-sensitive p53 mutant allowed us to analyse cells in which the introduced p53 had either wild-type or mutant properties. Although there seemed to be no effect on differentiation, the introduction of wild-type p53 resulted in rapid loss of cell viability in a way characteristic of apoptosis (programmed cell death). The effect of wild-type p53 was counteracted by interleukin-6. Thus products of tumour suppressor genes could be involved in restricting precursor cell populations by mediating apoptosis.

Animals↗

PubMed1991

The network of hemopoietic regulatory proteins in myeloid cell differentiation.

There are clones of myeloid leukemic cells that can be induced to undergo terminal cell differentiation to macrophages by normal hemopoietic regulatory proteins. Induction of differentiation in two different clones of myeloid leukemic cells with interleukin 6 (IL-6) or granulocyte-macrophage colony-stimulating factor (GM-CSF) resulted in induction of mRNA for the hemopoietic regulatory proteins IL-6, GM-CSF, interleukin 1 alpha and interleukin 1 beta, tumor necrosis factor, and transforming growth factor beta 1. In one of these clones, induction of differentiation with GM-CSF was also associated with induction of mRNA for macrophage colony-stimulating factor (M-CSF) but not for the receptor for M-CSF (c-fms), whereas in the other clone, induction of differentiation with IL-6 was associated with induction of mRNA for both c-fms and M-CSF. The clones also differed in their responsiveness to these regulators. There was no induction of mRNA for granulocyte colony-stimulating factor or interleukin 3 during differentiation of either clone. The results indicate that the genes for a nearly normal network of positive and negative hemopoietic regulatory proteins are induced during differentiation of these myeloid leukemic cells and that there are leukemic clones with specific defects in this network.

Animals↗

PubMed1990

Selective regulation of the activity of different hematopoietic regulatory proteins by transforming growth factor beta 1 in normal and leukemic myeloid cells.

The viability of normal bone marrow myeloid precursor cells induced by interleukin-6 (IL-6) or IL-1 alpha and the ability of IL-6 and IL-1 alpha to induce the formation of colonies of granulocytes, macrophages, or megakaryocytes in densely seeded bone marrow cultures was suppressed by transforming growth factor-beta 1 (TGF-beta 1). Induction of normal bone marrow colony formation by IL-3 was much less sensitive to TGF-beta 1, and there was little or no effect of TGF-beta 1 on colony formation induced by macrophage colony-stimulating factor (M-CSF) or granulocyte-macrophage CSF (GM-CSF). In different clones of myeloid leukemic cells, TGF-beta 1 suppressed differentiation induced with IL-6, IL-1 alpha, or lipopolysaccharide (LPS), but did not suppress differentiation induced with IL-3 or GM-CSF. The effect of TGF-beta 1 on differentiation of the leukemic cells can be dissociated from its effect on cell growth. TGF-beta 1 suppressed the production of IL-6 in normal bone marrow cells cultured with IL-1 alpha and the production of IL-6 and GM-CSF in leukemic cells cultured with IL-1 alpha or LPS. The suppression of IL-6 production can explain the suppression by TGF-beta 1 of the effects of IL-1 alpha and LPS that are mediated by IL-6. TGF-beta 1 also suppressed differentiation in clones of myeloid leukemic cells induced with differentiation factor/leukemia inhibitory factor and tumor necrosis factor. In different leukemic clones TGF-beta 1 suppressed or enhanced induction of differentiation with dexamethasone. The results show that TGF-beta 1 can selectively control the activity of different molecular regulators of normal and leukemic hematopoiesis.

Animals↗

PubMed1990

Induction of genes for transcription factors by normal hematopoietic regulatory proteins in the differentiation of myeloid leukemic cells.

Induction of differentiation to macrophages in two different clones of myeloid leukemic cells by the hematopoietic regulatory proteins interleukin-6 (IL-6), or by granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3), is shown to be associated with sustained accumulation of c-jun, jun-B, and c-fos mRNA that code for proteins that form complexes that are transcription factors (AP-1). In one but not in the other of these leukemic clones, differentiation is also associated with sustained accumulation of mRNA for the putative transcription factor zif/268. The results indicate that differentiation of myeloid cells by normal hematopoietic regulatory proteins is associated with induction of sustained elevated levels of mRNA for transcription factors that can regulate and maintain gene expression in the differentiation program, and that zif/268 gene expression is not essential for differentiation to macrophages.

Animals↗

PubMed1989

Induction of dependence on hematopoietic proteins for viability and receptor upregulation in differentiating myeloid leukemic cells.

There are different types of myeloid leukemic cells that can be induced to differentiate to mature granulocytes or macrophages by different hematopoietic regulatory proteins. One type of leukemic clone can be induced to differentiate by recombinant macrophage and granulocyte differentiation-inducing protein-type 2 (MGI-2), which we have shown is Interleukin-6 (IL-6), and another type of leukemic clone can be differentiated by recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) or IL-3. There was no subpopulation of growth factor-responsive or differentiation-defective cells before induction of differentiation in either type of clone. In both clones, induction of differentiation-induced requirement for a hematopoietic protein for cell viability. Viability of the cells was maintained by IL-6, IL-3, or macrophage colony-stimulating factor (M-CSF) but not by GM-CSF in the cells differentiated by IL-6, and by GM-CSF or IL-3 but not by IL-6 or M-CSF in the cells differentiated by GM-CSF or IL-3. The viable cells with a differentiated phenotype continued to multiply. In undifferentiated leukemic cells with no or few surface receptors for some of these proteins, there was an upregulation of the number of receptors during differentiation for the proteins to which the cells responded. But there were also differentiating leukemic cells with an upregulation of GM-CSF receptors although GM-CSF could not maintain the viability of the differentiating cells. The results indicate that induction of hormone responsiveness and upregulation of the hormone receptors can both occur in differentiating leukemic cells, and that the regulation of these two events can be separated.

Animals↗