[Percutaneous dilatational tracheostomy]

BACKGROUND

Tracheostomy provides a method for long-term ventilation in intensive care, which reduces the risk of necrotizing lesions of the pharyngeal and laryngeal mucosa. Since the introduction of the percutaneous dilatational tracheostomy, experienced physicians are able to perform bedside tracheostomies. This presentation reviews the complication rate and long-term outcome of percutaneous dilatational tracheostomy.

PATIENTS AND METHOD

The method was applied in 57 patients following previous orotracheal intubation averaging 7.8 days (3 to 15 days). Underlying diseases were sepsis/SIRS in 29, stroke in 7, cerebral hypoxemia after cardiopulmonary resuscitation in 10, trauma in 7, prolonged weaning in 2, primary neurological diseases in 2.

RESULTS

The following complications occurred during the procedure: 1 major and 7 minor bleedings. 2 subcutaneous emphysemas, 1 mediastinal emphysema following tracheal injury. No complication required surgical intervention. In the follow-up 17 patients (30%) died from their underlying disease, none from complications of the tracheostomy. After removed of the tracheal tube, in 39 patients the stoma closed spontaneously within 7 to 14 days. In 8 patients the tracheostoma persisted for more than 3 months, but no clinically relevant tracheal stenosis was found.

CONCLUSION

Percutaneous dilatational tracheostomy is a safe procedure easy to perform in intensive care units. Bronchoscopic control is necessary to avoid complications.

Traction and television for reduction of unilateral childhood rotatory atlanto-axial subluxation

We report the use of television in maintaining unilateral rotation of the head in a child being treated conservatively for a delayed rotatory atlanto-axial subluxation.

Pancreatic imaging

Pancreatic cancer has traditionally been difficult to diagnose. There are now numerous diagnostic tests that can visualize these tumors early when they are small and determine which cases are the most likely to be unresectable. The principal tests, including spiral CT, MR imaging, endoscopic ultrasound, and laparoscopy, have advantages and disadvantages. The purpose of this article is to review each technique, and try to come up with a recommended approach to evaluating the patient with pancreatic malignancy.

The proto-oncogene c-myc and apoptosis

Deregulated expression of c-Myc not only promotes proliferation, but also can either induce or sensitize cells to apoptosis. Inappropriate expression of c-Myc under conditions which inhibit growth and down-regulate endogenous c-Myc expression, including serum deprivation and exposure to cytotoxic agents including the anticancer agents vinblastine, etoposide, Ara-C, and nocodazole, usually results in programmed cell death in many different cell types. Also, inappropriate Myc expression is associated with an apoptotic response elicited by induction of differentiation. The proapoptotic property of c-Myc requires an intact N-terminal transactivation domain and bHLHZip domain, as well as interaction with Max, thereby implicating c-Myc target genes in this apoptotic process. Although some target genes, namely cdc25A and ODC, have been shown to participate in Myc-mediated apoptosis, no target gene has yet been identified which is essential for this apoptotic response. It is possible that the response of cells inappropriately expressing c-Myc is due not only to the growth arrest signals per se, but also to signals elicited by specific growth inhibitors in the context of a particular biological setting. Also regulating the response of the cells is expression of other oncogenes and tumor suppressor genes, as well as paracrine and autocrine survival factors. Apoptosis associated with inappropriate Myc expression limits the tumorigenic effect of the c-myc proto-oncogene. Mechanisms which inhibit apoptosis should enhance or promote tumorigenesis.

MyD genes in negative growth control

Two interrelated cellular processes are invoked simultaneously upon induction of differentiation, the regulated progression of cells through successive stages of cell differentiation and growth inhibition which ultimately leads to growth arrest. In tissues with rapid cell turnover terminally differentiated cells undergo programmed cell death. Terminal differentiation, thus, represents one form of negative growth control. It was surmised that the molecular engine which drives the differentiation process forward requires induction of positive regulators of terminal cell differentiation, to be found among differentiation primary response genes, as well as suppression of negative regulators, which correspond to genes which control cellular growth. This line of thought has prompted the isolation of myeloid differentiation primary response (MyD) genes activated in the absence of de novo protein synthesis, upon IL-6 induced terminal differentiation of murine M1 myeloblastic leukemia cells, where the cells growth arrest and ultimately undergo programmed cell death. As delineated in this review many of the genes identified as MyD genes, including both known genes [IRF-1, (AP-1)Fos/Jun.EGR-1] and novel ones (MyD88, MyD116, MyD118), turned out to play a role in negative growth control, including growth suppression and apoptosis, in many cell types, of both hematopoietic and non hematopoietic origins.

Clinical implications of endoluminal ultrasonography using through-the-scope catheter probes

BACKGROUND

Ultrasound catheter probe-assisted endosonography is a relatively new technique. The aim of this prospective multicenter study was to determine its potential clinical impact by assessing changes in diagnostic and therapeutic management affected by catheter probes compared with ultrasound endoscopes.

METHODS

Endosonographers at three centers selected theoretic diagnostic and therapeutic plans that would be followed if neither catheter probes nor ultrasound endoscopes were available. Patients with suitable lesions underwent endosonography with catheter probes followed by an ultrasound endoscope. Diagnostic and therapeutic plans were noted after each examination.

RESULTS

Sixty-six patients, of whom 15 had a stenotic esophageal cancer, 39 had a mucosal or submucosal lesion, and 12 had a stricture of the pancreaticobiliary system or the gastrointestinal tract, were enrolled. If neither form of endosonography were available, invasive or surgical diagnostic procedures would have been performed on 23 (35%) patients and surgical therapy would have been planned in 31 (47%) patients. Catheter probe-assisted ultrasonography and endoscopic ultrasonography led to a less invasive diagnostic plan in 11 (16%) and 12 (18%) patients and a less invasive therapeutic plan in 10 (15%) and 14 (21%) patients, respectively (p > 0.1 for differences).

CONCLUSIONS

Catheter probe-assisted endosonography has a modest effect on diagnostic and therapeutic management, comparable with endoscopic ultrasonography in the same patients. The vast majority of effected changes are toward less invasive management.

The zinc finger transcription factor Egr-1 activates macrophage differentiation in M1 myeloblastic leukemia cells

We previously have shown that the zinc finger transcription factor Egr-1 blocked granulocytic differentiation of HL-60 cells, restricting differentiation along the monocytic lineage. Egr-1 also was observed to block granulocyte colony-stimulating factor (G-CSF)-induced differentiation of interleukin-3 (IL-3)-dependent 32Dcl3 hematopoietic precursor cells, endowing the cells with the ability to be induced by granulocyte-macrophage colony-stimulating factor (GM-CSF) for terminal differentiation along the macrophage lineage. To better understand the function of Egr-1 as a positive modulator of monocytic differentiation, in this work we have studied the effect of ectopic expression of Egr-1 on the murine myeloblastic leukemic cell line M1, which is induced for differentiation by the physiological inducer IL-6. It is shown that, unlike in HL-60 and 32Dcl3 cells, ectopic expression of Egr-1 in M1 cells resulted in activation of the macrophage differentiation program in the absence of differentiation inducer. This included the appearance of morphologically differentiated cells, decreased growth rate in mass culture, and cloning efficiency in soft agar, and expression of endogenous c-myb and c-myc mRNAs was markedly downregulated. Untreated M1Egr-1 cells also exhibited cell adherence, expression of Fc and C3 receptors, and upregulation of the myeloid differentiation primary response genes c-Jun, junD, and junB and the late genetic markers ferritin light-chain and lysozyme. Ectopic expression of Egr-1 in M1 cells also dramatically increased the sensitivity of the cells for IL-6-induced differentiation, allowed a higher proportion of M1 cells to become terminally differentiated under conditions of optimal stimulation for differentiation, and decreased M1 leukemogenicity in vivo. These findings demonstrate that the functions of Egr-1 as a positive modulator of macrophage differentiation vary, depending on the state of lineage commitment for differentiation of the hematopoietic cell type.

Role of a mutant p53 protein in apoptosis: characterization of a function independent of transcriptional trans-activation

Wild-type (wt) tumor suppressor p53 has been implicated in cellular radiosensitivity, mediated by its role in apoptosis and growth arrest. Intriguingly, it was observed that the temperature sensitive (ts) mutant p53val135 protein functions as a positive modulator of cellular radiosensitivity, as evident from acceleration of irradiation-induced apoptosis of M1p53ts (p53val135) cells at the non-permissive temperature; this effect was correlated with acceleration of exit from the G2 checkpoint of the cell cycle. In this work it is shown that the ability of mutant p53val135 to accelerate irradiation-induced apoptosis, at the non-permissive temperature, was devoid of transcriptional trans-activation of p53 target genes. In contrast, the apoptotic function of wt p53val135 was observed to include components which are both dependent and independent of transcriptional trans-activation. Taken together, these observations suggest that mutant p53val135 protein retains the apoptotic component of wt p53 that is devoid of transcriptional trans-activation, and that, although this activity is insufficient to induce apoptosis on its own, it can cooperate to accelerate DNA damage-induced cell death. The results of this work contribute to a better understanding of the complexity of the apoptotic response elicited by wt p53, and highlight the potential role of mutant p53 proteins, as well as trans-activation independent apoptosis, in tumor suppression by irradiation therapy.

Defining the physician's duty to warn: consensus statement of Ontario's Medical Expert Panel on Duty to Inform

Ontario's Medical Expert Panel on Duty to Inform was formed to consider the duty of Ontario physicians in circumstances where a patient threatens to kill or cause serious bodily harm to a third party. The panel was concerned about the implications of any duty to inform on the integrity of the physician-patient relationship, particularly with respect to confidentiality. The panel agreed that regulations safeguarding the confidentiality of patient information ought to be changed only if there is a critical reason for doing so, but, after deliberation, the panel members concluded that the need to protect the public from serious risk of harm is a paramount concern that should supersede the duty of confidentiality. The recommendations reported here were endorsed in principle by the panelists and the groups they represented (the Royal College of Physicians and Surgeons of Canada, the Canadian Medical Protective Association, the College of Physicians and Surgeons of Ontario, the Ontario College of Family Physicians and the Ontario Medical Association) and are being implemented by the College of Physicians and Surgeons of Ontario.

AP-1 (Fos/Jun) transcription factors in hematopoietic differentiation and apoptosis

A combination of in vitro and in vivo molecular genetic approaches have provided evidence to suggest that AP-1 (Fos/Jun) transcription factors play multiple roles in functional development of hematopoietic precursor cells into mature blood cells along most, if not all, of the hematopoietic cell lineages. This includes the monocyte/macrophage, granulocyte, megakaryocyte, mastocyte and erythroid lineages. In addition, studies using c-fos knockout mice have established a unique role for Fos, as a member of the AP-1 transcription factor complex, in determining the differentiation and activity of progenitors of the osteoclast lineage, a population of bone-forming cells which are of hematopoietic origin as well. Evidence has also accumulated to implicate AP-1 (Fos/Jun) transcription factor complexes as both positive and negative modulators of distinct apoptotic pathways in many cell types, including cells of hematopoietic origin. Fos/Jun have been implicated as positive modulators of apoptosis induced in hematopoietic progenitor cells of the myeloid lineage, a function that may relate to the control of blood cell homeostasis, as well as in programmed cell death associated with terminal differentiation of many other cell types, and apoptosis associated with withdrawal of growth/survival factors. On the other hand, the study of apoptosis induced in mammalian cells has implicated AP-1 in the protection against apoptosis induced by DNA-damaging agents. However, evidence to the contrary has been obtained as well, suggesting that AP-1 may function to modulate stress-induced apoptosis either positively or negatively, depending on the microenvironment and the cell type in which the stress stimulus is induced.

Risk assessments for acute violence to third parties: a review of the literature

OBJECTIVES

To provide an overview of risk assessments for acute violence to third parties by combining a clinical and research focus and to offer guidelines to physicians conducting clinical assessments.

METHOD

A computerized literature search of the MEDLINE and PSYCHINFO data bases from 1967 to 1996 was completed using the key words violence, aggression, dangerous behaviour, risk, risk assessment, risk factors, and practice guidelines. The search yielded 116 relevant references, 26 of which were original research articles on risk factor identification. A secondary search, based on the citations from the primary search, yielded an additional 8 general discussion articles.

RESULTS

Risk assessments may be conducted using different methods, although all methods should be systematic and comprehensive. Research shows that risk assessments do have validity for use in short-term prediction and that it is possible to develop clinical guidelines in this area. A combined clinical and research approach holds the most promise for improving the accuracy of probability estimates, and most published guides and tools rely on such a combination.

CONCLUSIONS

Risk assessments are an important and necessary part of the clinical examination. Because this field has sufficiently evolved, there is abundant literature to refer to when determining what constitutes an acceptable assessment for risk of violence to third parties and when it is appropriate to conduct such an examination.

Lineage-specific regulation of hematopoiesis by HOX-B8 (HOX-2.4): inhibition of granulocytic differentiation and potentiation of monocytic differentiation

Homeobox proteins comprise a major class of transcription factors, which have been implicated in normal hematopoiesis and leukemogenesis. Notable in this context is the homeobox gene HOX-B8 (formerly known as HOX-2.4), which was shown to cooperate with hematokines to induce leukemia, and to enhance self-renewal of immature myeloid progenitors when expressed alone. How HOX-B8 may affect lineage specific development of hematopoietic progenitor cells is unknown. Here it is shown that ectopic expression of HOX-B8 specifically inhibited dimethyl sulfoxide (DMSO)-induced granulocytic differentiation of autonomously proliferating HL-60 myeloid progenitor cells. HOX-B8 also inhibited the granulocyte colony-stimulating factor (G-CSF)-induced granulocytic developmental program of factor dependent 32Dcl3 hematopoietic progenitors, including survival, proliferation, and differentiation, as evident by rapid apoptosis of the cells following removal of interleukin-3 (IL-3) and addition of G-CSF. In sharp contrast, HOX-B8 had no effect on macrophage differentiation of M1 and HL-60 cells induced by IL-6 and phorbol-12-myristate-13-acetate, respectively. Moreover, HOX-B8 expression endowed the 32Dcl3 cells with the ability to be induced by granulocyte-macrophage colony-stimulating factor (GM-CSF) for terminal differentiation exclusively along the macrophage lineage; this effect was at least partially mediated via expression of the zinc finger transcription factor Egr-1. Thus, ectopic expression of HOX-B8 in hematopoietic progenitor cells appears to differentially affect lineage specific development, negatively regulating granulocyte development and positively regulating macrophage development.

Tyrosine hydroxylase assay for detection of low levels of enzyme activity in peripheral tissues

A nonisotopic assay for tyrosine hydroxylase, with optimized signal-to-noise ratios, enables determination of low levels of enzyme activity in peripheral tissues. DOPA produced by the enzyme is measured using HPLC with electrochemical detection. Increased signal-to-noise ratios are obtained by including in the reaction mixture glycerol for reduction of blank values and dihydropteridine reductase and NADPH for regeneration of the tetrahydropteridine cofactor. With this method, tyrosine hydroxylase activity can be detected in as few as 200 PC12 cells and in peripheral tissues at levels as low as 4.5 fmol/min/mg wet weight. The assay permits activity to be assessed in a variety of peripheral tissues.

Sphincter of Oddi dysfunction is associated with chronic pancreatitis

OBJECTIVES

Chronic pancreatitis can be caused by ductal obstruction resulting from cicatricial papillary stenosis, but sphincter of Oddi motility studies have been inconclusive in patients with established chronic pancreatitis. We sought to determine whether there is an association between papillary sphincter dysfunction and changes of early chronic pancreatitis.

METHODS

Consecutive patients who underwent sphincter of Oddi manometry to investigate unexplained upper abdominal pain (n = 104) were assessed for evidence of chronic pancreatitis by pancreatic ductography, endoscopic ultrasound, and pancreatic fluid bicarbonate concentration.

RESULTS

Sphincter of Oddi dysfunction patients were four times more likely (odds ratio = 4.6) to have evidence of chronic pancreatitis than were those without sphincter dysfunction (p = 0.01). Of 68 patients with sphincter of Oddi dysfunction, 20 (29%) had structural evidence of chronic pancreatitis. Twenty of 23 (87%) patients with chronic pancreatitis had sphincter of Oddi dysfunction.

CONCLUSIONS

Sphincter of Oddi dysfunction is associated with changes of chronic pancreatitis in patients with unexplained pancreaticobiliary pain. Longitudinal follow-up is required to confirm these preliminary findings.

Pancreatic sphincter hypertension increases the risk of post-ERCP pancreatitis

BACKGROUND AND STUDY AIMS

The reason for the increased risk of pancreatitis after endoscopic retrograde cholangiopancreatography (ERCP) in patients with sphincter of Oddi dysfunction is not known. This study sought to determine whether pancreatic sphincter hypertension might explain some of the increased risk.

PATIENTS AND METHODS

The incidence of pancreatitis was determined from a cohort of patients who underwent pancreatic sphincter manometry. Additional data collected included: pancreatic and biliary sphincter manometry results, distal bile duct diameter, chronic pancreatitis grade by pancreatography, and endoscopic treatments.

RESULTS

Ten of 32 patients (31%) with pancreatic sphincter hypertension developed post-ERCP pancreatitis, compared to one of 33 (3%) with normal pancreatic manometry (P = 0.002). Patients with pancreatic sphincter hypertension were more likely to undergo endoscopic treatments (88%) compared to those with normal manometry (27%) (P = 0.001). The distal bile duct diameter was significantly smaller (4.5 +/- 0.5 mm) in patients who developed post-ERCP pancreatitis than in those who did not (6.2 +/- 0.3) (P = 0.025). Patients with small distal bile duct diameters (< 5 mm) were three times more likely to develop post-ERCP pancreatitis than those with larger ducts (relative risk [RR] 3.1, 95% confidence interval [CI] 0.9, 10.7). Patients with pancreatic sphincter hypertension were ten times more likely to develop post-ERCP pancreatitis than those with normal pancreatic manometry (RR 10.3, 95% CI 1.5, 76.0). In patients with a small bile duct size, pancreatic sphincter hypertension substantially increased the risk compared to those with normal manometry (RR 18.1, 95% CI 1.1, 287.6).

CONCLUSIONS

Pancreatic sphincter hypertension greatly increases the risk of post-ERCP pancreatitis in patients undergoing treatment or evaluation, or both, for sphincter of Oddi dysfunction.

MuLV-insertional mutagenesis of c-myb and Mml1 in a murine model for promonocytic leukemia

Analysis of retroviral integration sites in MuLV-induced promonocytic leukemias has determined that two genetic loci, c-myb and Mml1, can contribute to disease development but not in the same leukemia. Recent studies aimed at understanding the function of Myb in leukemia development have focused on the consequences of ectopic Myb expression on monocytic and granulocytic differentiation in vitro. In all instances Myb was shown to block growth arrest but not commitment to differentiation, a result which is consistent with observed effects of Myb in leukemia development. No effect of Myb protein truncation was observed in these studies although similar truncations are produced as a result of insertional mutagenesis. Common integration site, Mml1, was recently identified and mapped to mouse chromosome 10 within 1cM of c-myb. Despite its linkage to c-myb, Myb mRNA and protein expression appear to be unaffected in leukemias with Mml1 integrations.

Clinical implications of endoscopic ultrasound: the American Endosonography Club Study

BACKGROUND

Despite increased clinical use of endoscopic ultrasound (EUS), there are little data regarding complications of EUS or its impact on patient management.

METHODS

A prospective multicenter study was completed to evaluate clinical outcomes of EUS. Before each EUS examination the endosonographer recorded further theoretical patient management plans as if EUS was unavailable. After the EUS, endosonographers recorded actual management plans based on EUS results. The actual management plan after EUS was compared to the theoretical management before EUS. Complications were assessed in short-term follow-up.

RESULTS

Four hundred twenty-eight subjects were enrolled. Of subjects able to be evaluated, EUS changed the treatment plan in 74%. Management changes of major importance occurred in 120 patients (31% of subjects able to be evaluated) and included decisions regarding surgery (62 patients), decisions regarding nonsurgical invasive management (36 patients), and decisions regarding further follow-up (22 patients). When there was a change in management, the change was to less costly, risky, or invasive management in 55%, to more costly/risky/invasive in 37%, and to equally costly/risky/invasive in 8%. Short-term follow-up was completed in 81% of subjects, with six complications identified (1.7%). Three complications were mild, two were moderate, one severe, and none fatal.

CONCLUSIONS

(1) Changes in management plan may occur in the majority of patients based on EUS results. (2) The management changes are often of major importance with regard to health care costs and safety, and are more often in the direction of less costly, risky, and invasive management. (3) EUS is safe in experienced hands.

The proto-oncogene c-myc blocks myeloid differentiation independently of its target gene ornithine decarboxylase

Ornithine decarboxylase (ODC), a rate-limiting enzyme of polyamine biosynthesis, has been shown to be required for entry into and progression through the cell cycle and to be a transcriptional target of the proto-oncogene, c-myc. We show that ODC transcripts and enzyme activity are down-regulated following induction of myeloid differentiation, using M1 myeloblastic leukemic cells and normal cells from bone marrow (BM), and fail to be suppressed when c-myc expression is deregulated. In M1mycer cells, when endogenous c-myc expression has been suppressed following stimulation by interleukin-6 (IL-60), treatment with estrogen and cycloheximide results in induction of ODC transcripts. These data demonstrate that ODC is a c-myc target gene in M1 cells. It was of interest to determine whether deregulated ODC expression would alter the myeloid differentiation program. To answer this question, M1-ODC cell lines constitutively expressing ODC were established. These cells can undergo terminal differentiation and growth arrest following IL-6 stimulation, exactly like parental M1 cells, demonstrating that deregulated ODC expression is not sufficient to block myeloid differentiation. Another question to be answered was whether ODC expression is necessary for the c-myc-mediated block in differentiation. The use of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC enzyme activity, indicates that ODC is not necessary for the c-myc-mediated differentiation block.

The differentiation primary response gene MyD118, related to GADD45, encodes for a nuclear protein which interacts with PCNA and p21WAF1/CIP1

Towards dissecting the regulation of terminal differentiation, including growth arrest and apoptosis, myeloid differentiation primary response (MyD) genes, induced in the absence of de novo protein synthesis following induction of M1 myeloblastic leukemia cells for terminal differentiation have been isolated. MyD118 was one of the novel MyD genes cloned, subsequently observed also to be a primary response gene to TGF-beta, which induces M1 cells for growth arrest and apoptosis uncoupled from differentiation. The MyD118 encoded protein was observed to be remarkably similar to the protein encoded by Gadd45, a growth arrest and DNA damage induced gene, regulated in part by the tumor suppressor p53. Though evidence has accumulated that MyD118 functions as an important modulator of negative growth control both in hematopoietic and non-hematopoietic cells, its mechanism of action is unknown. To better understand the role(s) of MyD118 in negative growth control, we have analysed the expression and biological characteristics of the MyD118 protein, compared to the Gadd45 protein, in distinct pathways of growth arrest and apoptosis, including p53 dependent and independent pathways either coupled or uncoupled from differentiation. It is shown that MyD118 and Gadd45 differentially accumulated upon induction of distinct pathways of growth arrest and apoptosis; notably, MyD118, but not Gadd45, was induced by TGF-beta, whereas Gadd45, but not MyD118, was induced by activating wild type (wt) p53 function. It is also shown that MyD118 is a nuclear protein, which regardless of the pathway induced, predominantly localized within the cell nucleus, and interacted with the DNA replication and repair protein PCNA and the cyclin dependent kinase inhibitor P21WAF1/CIP1. MyD118 also modestly stimulated DNA repair in vitro. All of these characteristics were shared with Gadd45. Finally, it is demonstrated that MyD118, Gadd45 and p21 synergized in the suppression of colony formation by NIH3T3 cells. Taken together, these findings demonstrate that MyD118 and Gadd45 are representative of a new protein family that share remarkable functional similarities in the control of distinct pathways of negative growth, including the suppression of cellular growth and programmed cell death.

Activated abl oncogenes and apoptosis: differing responses of transformed myeloid progenitor cell lines

Activation of the c-abl protooncogene occurs during the generation of both the Abelson murine leukemia virus and the bcrabl fusion gene. To further dissect the biological properties of these proteins, we studied their effect on apoptosis. Using dimethyl sulfoxide (DMSO) to induce apoptosis in the murine myeloid progenitor cell line 32Dcl3, we examined the effect of expression of both v-abl and bcrabl transgenes on apoptosis. v-abl expressing 32Dcl3 cells are sensitive to apoptosis induction, similar to parental 32Dcl3 cells. In contrast, bcrabl expression 32Dcl3 cells are protected from the apoptotic stimulus resulting from DMSO exposure. Analyzing the expression patterns for Bcl-2 and Bax, two proteins known to modulate the apoptotic response, we found a downregulation of Bcl-2 and enhanced expression of Bax in 32Dcl3 cells. In 32Dcl3/v-Abl cells, Bcl-2 expression remained constant while Bax was upregulated, whereas in 32Dcl3 cells expressing bcrabl, there was continuous expression of Bcl-2 at a level greater than observed in v-abl transformed cells. Taken together, our data demonstrate that although both activated abl gene products promote overlapping effects of some biological responses (i.e., factor-independent proliferation) they diverge in their effect on apoptotic signaling pathways.

B-Myb prevents growth arrest associated with terminal differentiation of monocytic cells

B-Myb is a transcriptional regulator of gene expression and is highly homologous to c-Myb in its N-terminal DNA binding domain. However, unlike c-myb, whose expression is restricted largely to immature hematopoietic cells, B-myb mRNA has been found to be expressed in all proliferating mammalian cell lines and is clearly regulated in a cell cycle dependent manner. That c-Myb and B-Myb proteins perform different roles in proliferation and/or differentiation is suggested by the redundancy of their expression. It was previously shown that degenerated c-Myb expression can inhibit IL-6 induced terminal differentiation of the leukemia cell line M1. We found that, unlike the downregulation of c-Myb protein which is an early response of progenitor M1 cells to IL-6 treatment, the downregulation of B-Myb occurs late, just prior to terminal differentiation and growth arrest. It was, therefore, of interest to examine the role of the murine B-Myb protein in the proliferation and differentiation of the M1 cells and to compare these effects to those of c-Myb in the same system. Clones ectopically producing B-Myb, like those ectopically expressing c-Myb, proliferated in the presence of the differentiation-inducing agent and did not undergo the programmed cell death which normally follows terminal macrophage differentiation. In addition, the cell-cycle distribution of M1/B-Myb cells was comparable to untreated cells. Although M1/B-Myb and M1/c-Myb clones treated with IL-6 appeared quite immature, differentiation markers were demonstrated to be maintained at near normal levels (e.g. MyD88, Mac-2), or be partially reduced in expression (C3, Fc and Mac-1 receptors) suggesting that the cells had undergone commitment to maturation, but were unable to terminally differentiate.

Retroviral insertional mutagenesis in murine promonocytic leukemias: c-myb and Mml1

Studies have focused on two genetic loci, c-myb and Mml1, whose activation by retroviral insertional mutagenesis contribute to promonocytic leukemia in our acute monocytic leukemia (AMoL) model. Multiple mechanisms of activation of c-myb by retroviral insertional mutagenesis implicate both transcriptional deregulation and protein truncation in conversion of this proto-oncogene to an oncogene. Because transformation by c-Myb can be viewed as a block to differentiation our studies moved into two in vitro systems to evaluate effects of truncated forms of c-Myb on cytokine induced maturation of myeloid progenitors to the granulocyte and macrophage lineages. Deregulated expression of truncated and full length c-Myb did not result in maintenance of the myelomonocytic progenitor state but rather a block in differentiation at intermediate to late steps in the maturation processes of myelomonocytic cells. Our results argue that inhibition of differentiation is due to c-Myb's ability to maintain the proliferative state of cells. Interestingly, the phenotype of continuously proliferating monocytic cells resembles that of the tumor cell phenotype. Recently we identified a new target of integration, Mml1, which is rearranged in ten promonocytic leukemias that do not have c-myb rearrangements. This locus which was mapped to chromosome 10 is presently being characterized.

The carboxyl terminus of the murine MyD116 gene substitutes for the corresponding domain of the gamma(1)34.5 gene of herpes simplex virus to preclude the premature shutoff of total protein synthesis in infected human cells

The herpes simplex virus 1 mutants from which both copies of the gamma(1)34.5 gene had been deleted trigger total shutoff of protein synthesis in human neuroblastoma cells and human foreskin fibroblasts but not in African green monkey (Vero) cells. The carboxyl-terminal 64 amino acids of gamma(1)34.5 are homologous to the corresponding domain of MyD116, a murine myeloid differentiation primary responsive gene. The carboxyl-terminal domain of gamma(1)34.5 is required to preclude the shutoff of protein synthesis (J. Chou and B. Roizman, Proc. Natl. Acad. Sci. USA 91:5247-5251, 1994). We report that in-frame substitution of the carboxyl terminus of gamma(1)34.5 with the corresponding domain of MyD116 in the context of the viral genome restored the ability of gamma(1)34.5 to preclude premature shutoff of protein synthesis in both neuroblastoma cells and in human foreskin fibroblasts. The results suggest that (i) in the course of its evolution, the virus "borrowed" a gene fragment to preclude a cell response to infection and (ii) the carboxyl terminus of MyD116 and its family of genes known as GADD34 may have a similar function(s) in cells stressed by growth arrest, DNA damage, and differentiation and in herpes simplex virus infection.