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B Hoffman

Publications and source records attributed to B Hoffman.

At least 19 recordsLinked to original sources
PubMed1995

Molecular controls of growth arrest and apoptosis: p53-dependent and independent pathways.

Cell homeostasis is regulated by a balance between proliferation, growth arrest and programmed cell death (apoptosis). Until recently, studies on oncogenesis have focused on the regulation of cell proliferation. The recognition that negative growth control, including growth arrest and programmed cell death, must be understood to comprehend how appropriate cell numbers are maintained and how alterations in any part of the equation can contribute to malignancy has led to a burst of work in this field. This review focuses on what has been learned about distinct settings of negative growth control, analyzing p53-dependent and independent pathways of growth arrest and apoptosis either coupled or uncoupled from differentiation, with an emphasis on the use of hematopoietic cells. The importance of understanding the molecular biology of apoptotic and growth arrest pathways in cancer therapy, and future directions to study negative growth control are addressed as well.

Animals↗
PubMed1995

p53 involvement in control of G2 exit of the cell cycle: role in DNA damage-induced apoptosis.

DNA damage in proliferating mammalian cells induces a complex cellular response comprising perturbation of the cell cycle and programmed cell death. The relationship between p53-dependent and p53-independent apoptotic cell death, as well as the cell cycle checkpoints induced by DNA damaging agents were explored in hematopoietic cells, using M1 myeloblastic leukemia cells, which are null for p53 expression, genetically engineered M1 variants, expressing p53ts and bcl-2 transgenes, as well as myeloblast enriched bone-marrow cells obtained from wild type p53 (wt p53) and p53-deficient mice. It is shown that gamma-irradiation of M1p53ts cells activated a function of the temperature sensitive mutant transgene p53 (p53ts), promoting increased apoptosis relative to parental, null p53 M1 cells. It is also shown that the kinetics of apoptotic cell death induced by gamma-irradiation correlated with the rapidity of exit from gamma-ray-induced G2 arrest for all the different hematopoietic cell types indicated above. Finally, data has been obtained to demonstrate that, in addition to a role in apoptosis and G1 arrest, wild-type p53 positively modulated the exit from the gamma-ray-induced G2 checkpoint. Taken together, these findings indicate that this new function for p53 is a component of the physiological pathway by which p53 exerts its role in apoptosis.

Animals↗
PubMed1995

Dissection of the genetic programs of p53-mediated G1 growth arrest and apoptosis: blocking p53-induced apoptosis unmasks G1 arrest.

Employing the myeloblastic leukemia M1 cell line, which does not express endogenous p53, and genetically engineered variants, it was recently shown that activation of p53, using a p53 temperature-sensitive mutant transgene (p53ts), resulted in rapid apoptosis that was delayed by high level ectopic expression of bcl-2. In this report, advantage has been taken of these M1 variants to investigate the relationship between p53-mediated G1 arrest and apoptosis. Flow cytometric cell cycle analysis has provided evidence that activation of wild-type (wt) p53 function in M1 cells resulted in the induction of G1 growth arrest; this was clearly seen in the M1p53/bcl-2 cells because of the delay in apoptosis that unmasked p53-induced G1 growth arrest. This finding was further corroborated at the molecular level by analysis of the expression and function of key cell cycle regulatory genes in M1p53 versus M1p53/bcl-2 cells after the activation of wt p53 function; events that take place at early times during the p53-induced G1 arrest occur in both the M1p53 and the M1p53/bcl-2 cells, whereas later events occur only in the M1p53/bcl-2 cells, which undergo delayed apoptosis, thereby allowing the cells to complete G1 arrest. Finally, it was observed that a spectrum of p53 target genes implicated in p53-induced growth suppression and apoptosis were similarly regulated, either induced (gadd45, waf1, mdm2, and bax) or suppressed (c-myc and bcl-2), after activation of wt p53 function in M1p53 and M1p53/bcl-2 cells. Taken together, these findings show that wt p53 can simultaneously induce the genetic programs of both G1 growth arrest and apoptosis within the same cell type, in which the genetic program of cell death can proceed in either G1-arrested (M1p53/bcl-2) or cycling (M1p53) cells. These findings increase our understanding of the functions of p53 as a tumor suppressor and how alterations in these functions could contribute to malignancy.

Animals↗
PubMed1995

The zinc finger transcription factor Egr-1 potentiates macrophage differentiation of hematopoietic cells.

Previously we have shown that the zinc finger transcription factor Egr-1 is essential for and restricts differentiation of hematopoietic cells along the macrophage lineage, raising the possibility that Egr-1 actually plays a deterministic role in governing the development of hematopoietic precursor cells along the monocytic lineage. To test this hypothesis, we have taken advantage of interleukin-3-dependent 32Dcl3 hematopoietic precursor cells which, in addition to undergoing granulocytic differentiation in response to granulocyte colony-stimulating factor, were found to be induced for limited proliferation, but not differentiation, by granulocyte-macrophage colony-stimulating factor. It was shown that ectopic expression of Egr-1 blocked granulocyte colony-stimulating factor-induced terminal granulocytic differentiation, consistent with previous findings. In addition, ectopic expression of Egr-1 endowed 32Dcl3 cells with ability to be induced by granulocyte-macrophage colony-stimulating factor for terminal differentiation exclusively along the macrophage lineage. Thus, evidence that Egr-1 potentiates terminal macrophage differentiation has been obtained, suggesting that Egr-1 plays a deterministic role in governing the development of hematopoietic cells along the macrophage lineage.

Animals↗
PubMed1995

Effectiveness of a specialized asthma clinic in reducing asthma morbidity in an inner-city minority population.

Asthma is the most common chronic disease of childhood and a leading cause of morbidity in adults. Despite significant advances in medical therapy, asthma morbidity and mortality rates have risen dramatically over the past two decades, especially in minority and socioeconomically disadvantaged populations. Numerous intervention programs have been designed in an attempt to reduce asthma morbidity but few have targeted poor or minority populations. The purpose of this study was to assess whether an outpatient intervention program specifically targeted at a high-minority population in East Harlem, in New York City, was successful in reducing asthma morbidity. A retrospective chart review of 84 patient records was conducted. The patients were divided into two groups, an intervention group (n = 45), who were followed by an asthma specialist (allergist/immunologist), and a nonintervention group, followed by a general internist or pediatrician. Outcome variables including clinic walk-in visits, emergency room visits, and hospitalizations were determined and compared in the pre- and postintervention period in both groups. Patients in the intervention group had reduced total walk-in visits (73 vs. 27, p < 0.001), emergency room visits (30 vs. 5, p < 0.001), and hospitalizations (16 vs. 2, p < 0.001). In contrast, patients in the nonintervention group had no change in total walk-in visits (88 vs. 72), increased emergency visits (7 vs. 22, p < 0.05), and no change in hospitalizations (5 vs. 2), respectively. The outpatient intervention program has been successful in reducing asthma morbidity in the high-risk minority community of East Harlem. Future larger studies are warranted to extend this pilot program to other high-risk minority populations.

Adolescent↗
PubMed1994

Progression of the myeloid differentiation program is dominant to transforming growth factor-beta 1-induced apoptosis in M1 myeloid leukemic cells.

Hematopoiesis is a profound example of cell homeostasis that is regulated throughout life. This process requires the participation of many factors, including positive and negative regulators of growth and differentiation, that determine survival, growth stimulation, differentiation, functional activation, and programmed cell death. Understanding the effects of multiple stimuli on specific cells at the molecular and cellular level is crucial towards understanding how the population of blood cells maintains a homeostatic state. Two appropriate stimuli for analysis, both of which are found in bone marrow, are differentiation-inducing cytokines, which induce terminal differentiation associated with growth arrest, ultimately culminating in programmed cell death, and transforming growth factor-beta 1 (TGF-beta 1), which induces rapid growth arrest and apoptosis of hematopoietic cells. Previously, we have shown, using M1 myeloblastic leukemic cells as a model system, that differentiation-inducing cytokines induce terminal differentiation associated with growth arrest and, only after 5 to 7 days, apoptosis, whereas TGF-beta 1 induces rapid growth arrest and apoptosis. In this report, we show that M1 myeloid leukemic cells treated concomitantly with the differentiation inducer interleukin-6 and TGF-beta 1 undergo terminal differentiation, in which modulators of the MyD118 gene product, previously shown to be a positive regulator of TGF-beta 1-induced apoptosis, are implicated to play a role in protecting the cells from TGF-beta 1-induced apoptosis. Furthermore, using M1 cell variants blocked at different stages after induction of differentiation, including M1myb and M1myc, as well as conditionally blocked M1mycer, it has been shown that the dominance of interleukin-6 to TGF-beta 1-induced apoptosis is dependent on the progression of the differentiation program. Further studies with M1 and the genetically engineered M1 cell variants will be instrumental towards molecularly dissecting the interaction of hematopoietic differentiation with a variety of apoptotic pathways.

Animals↗
PubMed1994

Differentiation primary response genes and proto-oncogenes as positive and negative regulators of terminal hematopoietic cell differentiation.

By genetically manipulating hematopoietic cells of the myeloid lineage, including both normal cells and differentiation inducible leukemic cell lines, evidence was obtained to indicate that myeloid differentiation primary response (MyD) genes and proto-oncogenes, which are known to control cell growth, function as positive and negative regulators of terminal hematopoietic cell differentiation, which is associated with inhibition of cell growth, and, ultimately programmed cell death (apoptosis). Interferon regulatory factor-1 (IRF-1), an MyD gene induced by Interleukin 6 (IL-6) or Leukemia Inhibitory factor (LIF), plays a role in growth inhibition associated with terminal differentiation. Leucine zipper transcription factors of the fos/jun family, also identified as MyD genes, function as positive regulators of hematopoietic cell differentiation, increasing the propensity of myeloblastic leukemia cells to be induced for differentiation in vitro, and reducing the aggressiveness of their leukemic phenotype in vivo. The zinc finger transcription factor EGR-1, an MyD gene specifically induced upon macrophage differentiation, was shown to be essential for and to restrict differentiation along the macrophage lineage. Finally, evidence has been accumulating to indicate that the novel MyD genes--MyD116, MyD118 and gadd45 (a member in the MyD118 gene family)--play a role in growth arrest and apoptosis of hematopoietic cells, as well as other cell types. The proto-oncogenes c-myc and c-myb, known to regulate cellular growth, were shown to function as negative regulators of terminal differentiation. Both c-myc and c-myb are normally expressed in proliferating myeloblasts and suppressed following induction of differentiation. Deregulated and continuous expression of c-myc was shown to block terminal myeloid differentiation at an intermediate stage in the progression from immature blasts to mature macrophages, whereas deregulated and continuous expression of c-myb blocked the terminal differentiation program at the immature myeloblast stage. By manipulating myc function in conditional (differentiation inducible) mutant myeloblastic leukemia cell lines, expressing a chimeric mycer transgene, it was shown that there is a window during myeloid differentiation, after the addition of the differentiation inducer, when the terminal differentiation program switches from being dependent on c-myc suppression to becoming c-myc suppression independent, and where activation of c-myc has no apparent effect on mature macrophages. These myeloblastic leukemia cell lines provide a powerful tool to increase our understanding of the role of c-myc in normal hematopoiesis and in leukemogenesis, while also providing a strategy to clone myc target genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptor Proteins, Signal Transducing↗
PubMed1994

The novel primary response gene MyD118 and the proto-oncogenes myb, myc, and bcl-2 modulate transforming growth factor beta 1-induced apoptosis of myeloid leukemia cells.

Cell numbers are regulated by a balance among proliferation, growth arrest, and programmed cell death. A profound example of cell homeostasis, controlled throughout life, is the complex process of blood cell development, yet little is understood about the intracellular mechanisms that regulate blood cell growth arrest and programmed cell death. In this work, using transforming growth factor beta 1 (TGF beta 1)-treated M1 myeloid leukemia cells and genetically engineered M1 cell variants, the regulation of growth arrest and apoptosis was dissected. Blocking of early expression of MyD118, a novel differentiation primary response gene also shown to be a primary response gene induced by TGF beta 1, delayed TGF beta 1-induced apoptosis, demonstrating that MyD118 is a positive modulator of TGF beta 1-mediated cell death. Elevated expression of bcl-2 blocked the TGF beta 1-induced apoptotic pathway but not growth arrest induced by TGF beta 1. Deregulated expression of either c-myc or c-myb inhibited growth arrest and accelerated apoptosis, demonstrating for the first time that c-myb plays a role in regulating apoptosis. In all cases, the apoptotic response was correlated with the level of MyD118 expression. Taken together, these findings demonstrate that the primary response gene MyD118 and the c-myc, c-myb, and bcl-2 proto-oncogenes interact to modulate growth arrest and apoptosis of myeloid cells.

Animals↗
PubMed1994

The gadd and MyD genes define a novel set of mammalian genes encoding acidic proteins that synergistically suppress cell growth.

A remarkable overlap was observed between the gadd genes, a group of often coordinately expressed genes that are induced by genotoxic stress and certain other growth arrest signals, and the MyD genes, a set of myeloid differentiation primary response genes. The MyD116 gene was found to be the murine homolog of the hamster gadd34 gene, whereas MyD118 and gadd45 were found to represent two separate but closely related genes. Furthermore, gadd34/MyD116, gadd45, MyD118, and gadd153 encode acidic proteins with very similar and unusual charge characteristics; both this property and a similar pattern of induction are shared with mdm2, whic, like gadd45, has been shown previously to be regulated by the tumor suppressor p53. Expression analysis revealed that they are distinguished from other growth arrest genes in that they are DNA damage inducible and suggest a role for these genes in growth arrest and apoptosis either coupled with or uncoupled from terminal differentiation. Evidence is also presented for coordinate induction in vivo by stress. The use of a short-term transfection assay, in which expression vectors for one or a combination of these gadd/MyD genes were transfected with a selectable marker into several different human tumor cell lines, provided direct evidence for the growth-inhibitory functions of the products of these genes and their ability to synergistically suppress growth. Taken together, these observations indicate that these genes define a novel class of mammalian genes encoding acidic proteins involved in the control of cellular growth.

3T3 Cells↗
PubMed1994

Induction of p21 (WAF-1/CIP1) during differentiation.

The recently cloned protein, p21 (WAF1/CIP1) is a downstream effector of p53, and mediates growth arrest by inhibiting the action of G1 cyclin-dependent kinases. Since cellular differentiation is frequently characterized by G1 arrest, we examined whether p21 upregulation occurs in differentiation. We show that p21 expression is triggered by multiple differentiation-inducing agents in hematopoietic and hepatoma cells through a p53-independent pathway. The dramatic rise in p21 levels occurs as an immediate early response to differentiation inducers. The induction of p21 is coupled to the expression of early differentiation markers, and is uncoupled from apoptosis. Finally, evidence is presented that p21 expression is uncoupled from G1 arrest in the presence of deregulated c-myc.

Apoptosis↗
PubMed1994

Immediate early up-regulation of bax expression by p53 but not TGF beta 1: a paradigm for distinct apoptotic pathways.

Recently, both Bcl-2, which promotes cell survival, and Bax, which promotes cell death, have been implicated as major players in the control of apoptotic pathways, and it has been suggested that the ratio of Bcl-2 and Bax protein controls the relative susceptibility of cells to death stimuli. We have used M1 myeloid leukemia cells and genetically engineered M1 variants as a model system to study apoptosis induced by two distinct apoptotic stimuli. This includes apoptosis induced by activation of wild type p53 function of a temperature sensitive p53 transgene expressed in M1 cells, which do not express endogenous p53, and apoptosis induced by TGF beta 1. It is shown that the kinetics of apoptosis induced by p53 is more rapid than apoptosis induced by TGF beta 1. It is also shown that ectopic expression of Bcl-2, at levels which blocked TGF beta 1-induced apoptosis of M1 cells, delayed, but did not block, p53-induced apoptosis. Both p53 and TGF beta 1 down-regulated endogenous Bcl-2 expression, but only p53 up-regulated Bax expression, where bax has been identified as a p53 immediate early response gene. Thus, the p53-mediated up-regulation of Bax may provide at least a partial explanation for the more rapid rate of apoptosis induced by p53 compared to by TGF beta 1, as well as for the ineffectiveness of ectopoic Bcl-2 to abrogate p53-mediated apoptosis. These findings provide first insights to the molecular mechanisms which mediate p53-induced apoptosis, identifying bax and bcl-2 as p53 regulated genes, and serve as a paradigm of how the intracellular balance of Bcl-2 to Bax is differentially altered by distinct death stimuli.

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↗
PubMed1993

Mechanisms whereby lytic granules from cytotoxic T lymphocytes damage guinea pig ventricular myocytes.

During immunological rejection of the transplanted heart, cytotoxic T lymphocytes (CTL) infiltrate the myocardium and by damaging the myocytes contribute to loss of function. To address one important aspect of heart transplant rejection, we investigated in guinea pig ventricular myocytes how CTL-derived lytic granules containing the pore-forming protein perforin reduce the membrane potential (VM) and cause cell damage. The reduction in VM was biphasic; within 8.4 +/- 1.9 min VM was reduced from a control value of -78.4 +/- 1.9 mV to -69.9 +/- 3.5 mV. Subsequently, within 6.7 +/- 2.1 min VM declined to -3.4 +/- 1.2 mV, associated with a progressive contracture. Under whole cell voltage clamp, in myocytes held at their resting potential (VM = -76.2 +/- 0.9 mV), granules induced discrete inward current steps (resembling 'single channel' activity), with a mean amplitude of -86.8 +/- 1.4 pA and open times lasting from seconds up to several minutes. The mean conductance and reversal potential calculated from the linear regression analysis of the I-V relations were 1390 pS and -6.8 mV, respectively. The probable non-selectivity of these 'channels' and the resultant loss of membrane K+ selectivity can account for the reduction in VM. At the same time, opening of these pores leads to Ca2+ overload, resulting in contracture and cell damage.

Animals↗
PubMed1993

Lupus masquerading as CAPD peritonitis.

Abdominal serositis and mesenteric vasculitis are complications of SLE. We report a case of SLE presenting as abdominal pain in a CAPD patient. Lupus serositis/mesenteric vasculitis should be considered in the differential diagnosis of a CAPD patient with SLE who presents with abdominal pain but benign cell counts and cultures. This is especially important since untreated mesenteric vasculitis can lead to bowel perforation and death.

Abdominal Pain↗
PubMed1992

Analysis of effects of ultraviolet B radiation on induction of primary allergic reactions.

Acute, low-dose exposure to UVB light reveals a genetic polymorphism in humans with respect to the ability of irradiated skin to support the induction of contact hypersensitivity (CH) to dinitrochlorobenzene (DNCB). In healthy adult caucasians, as well as in humans with deeply pigmented skin, approximately 45% fail to develop CH when DNCB is painted on UVB-irradiated skin; these individuals are termed "UVB susceptible" (UVB-S), whereas those who develop CH at the challenge site are termed "UVB resistant" (UVB-R). The UVB-S trait is characteristic of virtually all patients with biopsy-proved basal/squamous cell cancer, and may therefore be a risk factor for this disease. We have investigated the effects of UVB on expression of primary allergic reactions (PAR) in healthy caucasian and black-skinned adults, as well as patients with skin cancer. Among UVB-R caucasians, very few (less than 25%) developed PAR at site exposed to UVB, whereas among black-skinned UVB-R subjects, all displayed a PAR at the UVB irradiated site. To determine whether the lack of PAR in UVB-R caucasian subjects was systemic or local in origin, DNCB was applied to UVB-exposed buttock skin, and each individual was then challenged with dilute DNCB on forearm skin twice: 11 and 30 d thereafter. When inflammatory responses were evaluated at the original hapten application site, as well as both challenge sites, complete concordance was observed between positive challenge reactions at 30 d (UVB-R) and positive challenge reactions at 11 d, whereas only one caucasian subject displayed a PAR at 12 d. Thus, UVB-R caucasians can display CH as early as 11 d following hapten application to UVB-treated skin, indicating that their failure to display PAR is a local, rather than a systemic, effect of UVB. Because UVB-induced phototoxicity was significantly greater in caucasian than in deeply pigmented skin, it is anticipated that phototoxicity leads to rapid hapten "washout" from UVB-exposed caucasian skin. We propose that PAR usually do not occur in UVB-treated caucasian skin because insufficient hapten remains at the site to trigger a spontaneous inflammation when systemic hapten-specific immunity emerges.

Adult↗