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Biomedical subjects

D A Liebermann

Publications and source records attributed to D A Liebermann.

54 records · Page 3Linked to original sources
PubMed1994

Induction of bax by genotoxic stress in human cells correlates with normal p53 status and apoptosis.

DNA-damaging agents such as ionizing radiation (IR) activate the tumor suppressor p53 and in some cases can cause apoptosis. M1 cells, which do not express the endogenous tumor suppressor gene p53, undergo apoptosis following activation of a temperature sensitive p53 transgene, where it has been shown that bax, an important mediator of apoptosis, is a p53 target gene (Selvakumaran et al, Oncogene 9, 1791-8, 1994). Since p53 can function as a transcription factor after activation by IR, the genetic response to this stress was examined in a panel of human cells with defined p53 status. Like the p53-regulated gene gadd45, bax was rapidly induced, as measured by increased mRNA levels, in the p53 wt (wild type) human myeloid line ML-1, and it was not induced in cells lacking functional p53. However, unlike other p53-regulated genes, bax was only induced in p53 wt cells in which IR also triggered apoptosis. In the case of bcl2, which opposes bax function, mRNA levels were reduced in ML-1 cells after IR. Thus, bax appears to be an unique p53-regulated gene in that its induction by IR not only requires functional p53 but also requires that the cells be apoptosis "proficient."

Apoptosis↗
PubMed1994

Tumor suppressor p53 is a regulator of bcl-2 and bax gene expression in vitro and in vivo.

The p53 tumor suppressor gene product can induce apoptotic cell death through an unknown mechanism. Here we demonstrate that a temperature-sensitive p53 induces temperature-dependent decreases in the expression of the apoptosis-suppressing gene bcl-2 in the murine leukemia cell M1, while simultaneously stimulating increases in the expression of bax, a gene which encodes a dominant-inhibitor of the Bcl-2 protein. Mice deficient in p53 exhibit increases in Bcl-2 and decreases in Bax protein levels in several tissues as determined by immunohistochemical and immunoblot methods. The findings suggest a potential mechanism by which p53 regulates apoptosis, as well as responses to radiation and chemotherapeutic drugs in cancer.

Animals↗
PubMed1994

Genetic programs of myeloid cell differentiation.

A great body of evidence indicates that hematopoietic cytokines and the availability of their cognate receptors at the cell membrane surface of myeloid progenitors play crucial roles in lineage commitment and differentiation. Little is known of how these receptors couple to downstream signal transduction pathways to convert the extracellular signal into a change in the genetic program. Lineage switching of myeloid progenitors suggests that a limited number of key regulatory genes govern lineage commitment. Several transcription factors have been implicated as key regulators, positive or negative, of myeloid lineage commitment and terminal differentiation. Evidence for an autocrine mechanism involving interleukin-6 in coupling late stages of myeloid cell proliferation to cell maturation is presented. Elucidation of molecular events that take place in cell cycle control associated with growth arrest and differentiation would further enhance the understanding of the genetic programs that govern myeloid cell development.

Animals↗
PubMed1993

The zinc finger transcription factor Egr-1 is essential for and restricts differentiation along the macrophage lineage.

We have isolated cDNA clones of myeloid differentiation primary response (MyD) genes, activated in the absence of de novo protein synthesis following induction for differentiation along either the macrophage or granulocyte lineage in human myeloblastic leukemia HL-60 cells. One cDNA clone of a primary response gene, expressed upon macrophage differentiation, encoded for Egr-1, a zinc finger transcription factor. The Egr-1 gene was observed to be transcriptionally silent in HL-60 cells, but active in U-937 and M1 cells, the latter two being predetermined for macrophage differentiation. Egr-1 antisense oligomers in the culture media blocked macrophage differentiation in both myeloid leukemia cell lines and normal myeloblasts. HL-60 cells constitutively expressing an Egr-1 transgene (HL-60Egr-1) could be induced for macrophage, but not granulocyte, differentiation. These observations indicate that expression of Egr-1 is essential for and restricts differentiation of myeloblasts along the macrophage lineage.

Animals↗
PubMed1993

Proto-oncogenes of the fos/jun family of transcription factors are positive regulators of myeloid differentiation.

The proto-oncogenes c-jun, junB, junD, and c-fos recently have been shown to encode for transcription factors with a leucine zipper that mediates dimerization to constitute active transcription factors; juns were shown to dimerize with each other and with c-fos, whereas fos was shown to dimerize only with juns. After birth, hematopoietic cells of the myeloid lineage, and some other terminally differentiated cell types, express high levels of c-fos. Still, the role of fos/jun transcription factors in normal myelopoiesis or in leukemogenesis has not been established. Recently, c-jun, junB, and junD were identified as myeloid differentiation primary response genes stably expressed following induction of terminal differentiation of myeloblastic leukemia M1 cells. Intriguingly, c-fos, though induced during normal myelopoiesis, was not induced upon M1 differentiation. To gain further insights into the role of fos/jun in normal myelopoiesis and leukemogenicity, M1fos and M1junB cell lines, which constitutively express c-fos and junB, respectively, were established. It was shown that enforced expression of c-fos, and to a lesser extent junB, in M1 cells results in both an increased propensity to differentiate and a reduction in the aggressiveness of the M1 leukemic phenotype. M1fos cells constitutively expressed immediate-early and late genetic markers of differentiated M1 cells. The in vitro differentiation of normal myeloblasts into mature macrophages and granulocytes, as well as the increased propensity of M1fos leukemic myeloblasts to be induced for terminal differentiation, was dramatically impaired with use of c-fos antisense oligomers in the culture media. Taken together, these observations show that the proto-oncogenes which encode for fos/jun transcription factors play important roles in promoting myeloid differentiation. The ability of the M1 leukemic myeloblasts to be induced for terminal differentiation in the absence of apparent fos expression indicates that there is some redundancy among the fos/jun family of transcription factors in promoting myeloid differentiation; however, juns alone cannot completely compensate for the lack of fos. Thus, genetic lesions affecting fos/jun expression may play a role in the development of "preleukemic" myelodysplastic syndromes and their further progression to leukemias.

Animals↗
PubMed1992

Genotoxic-stress-response genes and growth-arrest genes. gadd, MyD, and other genes induced by treatments eliciting growth arrest.

As discussed throughout this paper, many mammalian DDI genes are associated with growth responses, including both positive responses to growth stimulation and negative responses involving transient growth arrest and terminal differentiation. It is interesting that several immediate-early genes encoding transcription factors, the jun genes, are DDI, are induced by terminal differentiation, and also are associated with positive growth responses. In negative growth-response genes, their control is complex and almost certainly involves multiple regulatory mechanisms. The role of growth-arrest genes after exposure to DNA-damaging agents is currently not known, but as growth arrest can have a protective effect on cells exposed to DNA-damaging agents in both bacteria and eukaryotes, some protective role(s) for the gadd genes may exist. Whatever the roles are for the individual gadd genes, the response of the gadd genes to DNA-damaging agents and other growth-arrest signals has been highly conserved during mammalian evolution, and it is likely that this stress response, as reflected by induction of one or more gadd genes, is present in most or perhaps all mammalian cells. Our findings that the gadd group overlaps with another group of growth-arrest genes, the MyD, indicate that these two groups combined define a new class of genes whose protein products are likely to play a role in cell growth cessation.

Aging↗
PubMed1992

Deregulated c-myb disrupts interleukin-6- or leukemia inhibitory factor-induced myeloid differentiation prior to c-myc: role in leukemogenesis.

The c-myb proto-oncogene is abundantly expressed in tissues of hematopoietic origin, and changes in endogenous c-myb genes have been implicated in both human and murine hematopoietic tumors. c-myb encodes a DNA-binding protein capable of trans-activating the c-myc promoter. Suppression of both of these proto-oncogenes was shown to occur upon induction of terminal differentiation but not upon induction of growth inhibition in myeloid leukemia cells. Myeloblastic leukemia M1 cells that can be induced for terminal differentiation with the physiological hematopoietic inducers interleukin-6 and leukemia inhibitory factor were genetically manipulated to constitutively express a c-myb transgene. By using immediate-early to late genetic and morphological markers, it was shown that continuous expression of c-myb disrupts the genetic program of myeloid differentiation at a very early stage, which precedes the block previously shown to be exerted by deregulated c-myc, thereby indicating that the c-myb block is not mediated via deregulation of c-myc. Enforced c-myb expression also prevents the loss in leukemogenicity of M1 cells normally induced by interleukin-6 or leukemia inhibitory factor. Any changes which have taken place, including induction of myeloid differentiation primary response genes, eventually are reversed. Also, it was shown that suppression of c-myb, essential for terminal differentiation, is not intrinsic to growth inhibition. Taken together, these findings show that c-myb plays a key regulatory role in myeloid differentiation and substantiate the notion that deregulated expression of c-myb can play an important role in leukemogenicity.

Animals↗
PubMed1991

Interleukin-6- and leukemia inhibitory factor-induced terminal differentiation of myeloid leukemia cells is blocked at an intermediate stage by constitutive c-myc.

Interleukin-6 (IL-6) and leukemia inhibitory factor (LIF), two multifunctional cytokines, recently have been identified as physiological inducers of hematopoietic cell differentiation which also induce terminal differentiation and growth arrest of the myeloblastic leukemic M1 cell line. In this work, it is shown that c-myc exhibited a unique pattern of expression upon induction of M1 terminal differentiation by LIF or IL-6, with an early transient increase followed by a decrease to control levels by 12 h and no detectable c-myc mRNA by 1 day; in contrast, c-myb expression was rapidly suppressed, with no detectable c-myb mRNA by 12 h. Vectors containing the c-myc gene under control of the beta-actin gene promoter were transfected into M1 cells to obtain M1myc cell lines which constitutively synthesized c-myc. Deregulated and continued expression of c-myc blocked terminal differentiation induced by IL-6 or LIF at an intermediate stage in the progression from immature blasts to mature macrophages, precisely at the point in time when c-myc is normally suppressed, leading to intermediate-stage myeloid cells which continued to proliferate in the absence of c-myb expression.

Animals↗
PubMed1991

Leukemia inhibitory factor and interleukin-6 trigger the same immediate early response, including tyrosine phosphorylation, upon induction of myeloid leukemia differentiation.

Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6), two multifunctional cytokines lacking structural homology and binding to distinct receptors, share interesting functional similarities, which include induction of hematopoietic differentiation in normal and myeloid leukemia cells, induction of neuronal cell differentiation, and stimulation of acute-phase protein synthesis in hepatocytes. Structural information on the LIF receptor is not yet available, whereas recent cloning of the IL-6 receptor has shown it to be bipartite, with a signal-transducing subunit that lacks sequence homology to known protein kinases and produces second messengers of unknown nature. The molecular nature of the mechanisms which LIF and IL-6 use to induce cell differentiation is not known. To address this issue, we took advantage of a clone of M1 myeloblastic leukemia cells capable of being induced for terminal differentiation by both LIF and IL-6 directly activate the same set of immediate early response genes upon induction of M1 myeloid differentiation. At least two mechanisms of gene activation, one transcriptional and the other posttranscriptional, are shown to be involved. It is also shown that the LIF and IL-6 immediate early response, at suboptimal cytokine concentrations, is additive. Using a variety of protein kinase activators and inhibitors, we have shown that the intracellular signalling pathways for both LIF and IL-6 are distinct from those of known second messengers and involve protein phosphorylation, notably tyrosine phosphorylation of a 160-kDa protein, as an essential step(s) in the immediate early activation of MyD gene expression. These observations indicate that the functional similarities of LIF and IL-6 as inducers of cell differentiation prevail at the level of the complex differentiation immediate early response and implicate common mechanisms of signal transduction for LIF- and IL-6-induced differentiation.

Cell Differentiation↗
PubMed1991

Interferon regulatory factor 1 is a myeloid differentiation primary response gene induced by interleukin 6 and leukemia inhibitory factor: role in growth inhibition.

To better understand the immediate early genetic response of myeloid cells to terminal differentiation and growth inhibitory stimuli, we have recently isolated complementary DNA clones of myeloid differentiation primary response (MyD) genes, activated in the absence of protein synthesis in M1 myeloid precursor cells following induction for terminal differentiation and growth arrest by conditioned media of mouse lungs, a potent physiological source of hemopoietic differentiation inducers. In this study, it is shown that one particular MyD complementary DNA clone, expressed highly in normal precursor enriched bone marrow cells, encodes for interferon regulatory factor 1 (IRF-1), a positive transcription factor for expression of the beta-interferon (IFN-beta) gene. Using a clone of M1 cells inducible for terminal differentiation by both interleukin 6 (IL-6) and leukemia inhibitory factor (LIF), two multifunctional cytokines recently identified as physiological inducers of hemopoietic cell differentiation, it has been shown that IRF-1 expression is rapidly induced by IL-6 and LIF in the absence of protein synthesis and is followed by a later increase in the levels of IFN-beta mRNA, observed to be largely dependent on protein synthesis. Also, it is shown that the growth inhibition associated with IL-6 or LIF induced terminal differentiation could be partially abrogated via the use of IRF-1 antisense oligomers or IFN-beta antiserum. Taken together, these findings imply a regulatory cascade, where induction of terminal myeloid differentiation by IL-6 or LIF triggers the immediate early activation of IRF-1, leading to the later induction of IFN-beta, in turn playing an autocrine role in growth inhibition.

Animals↗
PubMed1991

Sequence and expression of a cDNA encoding MyD118: a novel myeloid differentiation primary response gene induced by multiple cytokines.

We report here the full length cDNA sequence and the deduced amino acid sequence of MyD118, a novel myeloid differentiation primary response gene transiently expressed in M1D+ myeloid precursors following induction of terminal differentiation and growth arrest by IL6. MyD118 expression was observed to be induced also in the absence of protein synthesis, following stimulation of M1D+ cells by IL1, LPS and Leukemia Inhibitory Factor (LIF). Detectable levels of MyD118 RNA were observed in myeloid precursor enriched murine bone marrow, but not in several other nonmyeloid murine tissues.

Amino Acid Sequence↗
PubMed1991

Suppression of c-myc and c-myb is tightly linked to terminal differentiation induced by IL6 or LIF and not growth inhibition in myeloid leukemia cells.

Cell proliferation and differentiation are intimately related processes where the proto-oncogenes c-myc and c-myb have been implicated to play a role. Previously, we have shown that both c-myc and c-myb were induced in normal myeloid precursors when the cells were stimulated for growth, were expressed in the autonomously proliferating myeloid leukemic M1 cell line and were rapidly suppressed in both normal and M1 cells following induction of terminal differentiation associated with growth arrest. In order to distinguish molecular events associated with terminal differentiation versus those due to growth inhibition, as well as to increase our understanding of the role of the proto-oncogenes c-myc and c-myb in both of these cellular processes, in this work we have studied the expression of c-myc and c-myb in M1 cells induced for growth inhibition associated with terminal differentiation (via treatment with the physiological inducers IL6 or leukemia inhibitory factor mean value of LIF), partial differentiation (using IL1 or LPS) or no detectable differentiation properties (using IFN beta or IFN gamma). We show that, for all the treatments used in this study, down regulation of the proto-oncogenes c-myc and c-myb occurred only when M1 cells were stimulated to undergo terminal differentiation. In addition, we transfected the M1 cell line with a vector containing the c-myc gene under control of the beta-actin promoter, so that c-myc was no longer down regulated by IL6 or LIF. Previously, we have shown that in the presence of the myeloid differentiation inducers IL6 or LIF, these M1myc cells were blocked at an intermediate stage of myeloid differentiation and continued to proliferate. In sharp contrast to their altered response to IL6 or LIF, M1myc cells were as responsive as the parental M1 cells to growth suppression by the different antiproliferative compounds which do not induce terminal differentiation. Thus, continued expression of c-myc had no effect on growth suppression induced by IL1, IFN beta, IFN gamma and LPS. Taken together, these results indicate that c-myc and c-myb down regulation is not necessary for growth suppression, but down regulation of c-myc is, and c-myb may be, essential for terminal differentiation.

Animals↗
PubMed1990

Complexity of the immediate early response of myeloid cells to terminal differentiation and growth arrest includes ICAM-1, Jun-B and histone variants.

Differentiation inducible leukemic as well as normal myeloid precursors treated with physiological myeloid differentiation inducer have been used to explore the immediate early genetic response of cells to terminal differentiation and growth arrest stimuli. cDNA clones of 12 distinct genes, referred to as MyD genes, which are activated in the absence of protein synthesis following induction of myeloid differentiation and growth arrest have been isolated. Sequence analysis of both ends of MyD cDNA clones, and analysis of MyD gene expression following induced differentiation of M1D+ and normal myeloid precursors, has shown that the immediate early genetic response of myeloid cells to the induction of terminal differentiation is complex. This complex response involves a variety of genes, some of which are known and others unknown, including: transient induction of ICAM-1, a gene encoding for a ligand to a cell surface adhesion receptor; stable induction of Jun-B, a gene encoding for a nuclear transcription factor; and increased expression of histone genes which encode for terminal differentiation histone variants. These findings demonstrate that terminal differentiation and growth arrest immediate early response genes encode for at least three distinct types of gene products, which may play a role to reprogram the transcriptional activity of proliferating and non-differentiated cells towards their conversion into terminally differentiated nonproliferating cells.

Amino Acid Sequence↗
PubMed1990

Dissection of the immediate early response of myeloid leukemia cells to terminal differentiation and growth inhibitory stimuli.

To better understand the immediate early genetic response of myeloid cells to terminal differentiation and growth inhibitory stimuli, complementary DNA clones of myeloid differentiation primary response (MyD) genes have recently been isolated. In this study, a set of known (junB, c-jun, ICAM-1, H1(0), and H3.3 histone variants) and novel (MyD88, MyD116) MyD genes were used as immediate early molecular markers to further dissect the primary genetic response of myeloid cells to various differentiation and growth inhibitory stimuli. Expression of all of these MyD genes was highly induced in autonomously replicating differentiation inducible M1D+ myeloblasts following induction of terminal differentiation and growth inhibition by interleukin 6. Expression of all MyD genes except MyD88 was induced upon inhibition of M1D+ cell growth and induction of early, but not late, differentiation markers by interleukin 1 and lipopolysaccharide. In sharp contrast, only expression of H1(0) and H3.3 histone variants was increased following inhibition of M1D+ cell growth by interferon beta or gamma, which did not induce any differentiation associated properties. No increase in the expression of any of these MyD genes was seen in a clone of WEHI-3B D- myelomonocytic cells following stimulation with interleukin 6, which neither induced it for differentiation nor inhibited its growth. 12-O-Tetradecanoylphorbol-13-acetate, known to be a potent inducer of jun expression in many cell types, failed to induce high or stable expression of junB and c-jun in M1D+ cells, where it did not induce differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Nucleotide sequence and expression of a cDNA encoding MyD88, a novel myeloid differentiation primary response gene induced by IL6.

We report here the full length cDNA sequence and the deduced amino-acid sequence of MyD88, a novel myeloid differentiation primary response gene activated in M1D+ myeloid precursors, following induction of terminal differentiation and growth arrest by IL6. Detectable levels of MyD88 RNA were observed in myeloid precursor enriched murine bone-marrow, but not in several other non-myeloid murine tissues.

Adaptor Proteins, Signal Transducing↗
PubMed1989

Proto-oncogene expression and dissection of the myeloid growth to differentiation developmental cascade.

Physiological inducers of myeloid cell growth and differentiation were used to simultaneously analyze the expression of the proto-oncogenes c-myc, c-myb, c-fos, c-fes and c-fms during normal myelopoiesis, where growth is coupled to differentiation, as compared with that in leukemia, where growth has been uncoupled from differentiation as well as upon suppression of the leukemic phenotype via induction of differentiation and growth arrest. Proto-oncogene expression was also used as a tool to dissect the growth to differentiation developmental cascade. Myeloid cell growth was correlated with high c-myc and c-myb RNA levels, decreasing to undetectable levels in terminally differentiated cells. No c-myc RNA was detected in normal myeloid progenitors induced for differentiation without growth, using media conditioned by mouse granulocytes (GCM), indicating that c-myc may play either no role or an inhibitory one in differentiation. RNA levels of the proto-oncogenes c-fos, c-fes and c-fms were undetectable in normal or M1 differentiation inducible (D+) leukemic myeloblasts, and were stably induced upon stimulation of the normal precursors for growth and differentiation, with highest levels at the time when most of the cells had undergone terminal differentiation. Only c-fes RNA was induced upon M1D+ differentiation. It was also shown to be induced upon induction of differentiation without growth in normal myeloid precursors. Using c-myc and c-myb RNA suppression as molecular markers for induction of M1D+ differentiation, the existence of myeloid differentiation factor(s), distinct from myeloid growth factors, has been demonstrated. Such differentiation inducing activity was found in media conditioned by mouse lungs or granulocytes, and was induced in normal myeloid precursors by the myelopoietic growth factors IL3, GM-CSF, G-CSF, and M-CSF. Taken together, the results of this study enhance and add to previous work to better correlate the expression of the proto-oncogenes myc, myb, fes, fos and fms with several parameters of normal and abnormal myeloid cell growth and differentiation. The results indicate that the normal myeloid growth to differentiation developmental cascade entails a mechanism whereby myeloid growth factors induce myeloid differentiation factors, subsequently suppressing c-myc and c-myb RNA expression, leading to the induction of differentiation and growth arrest, including early accumulation of c-fes RNA followed by accumulation of c-fos and c-fms RNAs. It was also indicated that this cascade is impaired in leukemia.

Animals↗