Identification of genes that synergize with Cbfb-MYH11 in the pathogenesis of acute myeloid leukemia

Acute myeloid leukemia subtype M4 with eosinophilia is associated with a chromosome 16 inversion that creates a fusion gene CBFB-MYH11. We have previously shown that CBFB-MYH11 is necessary but not sufficient for leukemogenesis. Here, we report the identification of genes that specifically cooperate with CBFB-MYH11 in leukemogenesis. Neonatal injection of Cbfb-MYH11 knock-in chimeric mice with retrovirus 4070A led to the development of acute myeloid leukemia in 2-5 months. Each leukemia sample contained one or a few viral insertions, suggesting that alteration of one gene could be sufficient to synergize with Cbfb-MYH11. The chromosomal position of 67 independent retroviral insertion sites (RISs) was determined, and 90% of the RISs mapped within 10 kb of a flanking gene. In total, 54 candidate genes were identified; six of them were common insertion sites (CISs). CIS genes included members of a zinc finger transcription factors family, Plag1 and Plagl2, with eight and two independent insertions, respectively. CIS genes also included Runx2, Myb, H2T24, and D6Mm5e. Comparison of the remaining 48 genes with single insertion sites with known leukemia-associated RISs indicated that 18 coincide with known RISs. To our knowledge, this retroviral genetic screen is the first to identify genes that cooperate with a fusion gene important for human myeloid leukemia.

Long-range effects of retroviral insertion on c-myb: overexpression may be obscured by silencing during tumor growth in vitro

The c-myb oncogene is a frequent target for retroviral activation in hemopoietic tumors of avian and mammalian species. While insertions can target the gene directly, numerous clusters of retroviral insertion sites have been identified which map close to c-myb and outside the transcription unit in T-lymphomas (Ahi-1, fit-1, and Mis-2) and monocytic and myeloid leukemias (Mml1, Mml2, Mml3, and Epi-1). Previous analyses showed no consistent effect of these insertions on c-myb expression, raising the possibility that other nearby genes were the true targets. In contrast, our analysis of four cell lines established from lymphomas bearing insertions at fit-1 (fti-1) (feline leukemia virus) and Ahi-1 (Moloney murine leukemia virus) shows that these display higher expression levels of c-myb RNA and protein compared to a panel of phenotypically similar cell lines lacking such insertions. An interesting feature of the cell lines with long-range c-myb insertions was that each also carried an activated Myc allele. The potential for oncogenic synergy between Myb and Myc in T-cell lymphoma was confirmed in transgenic mice overexpressing alleles of both genes in the T-cell compartment, lending further credence to the case for c-myb as the major target for long-range activation. In contrast, mapping and analysis of c-myb neighboring genes (HBS1 and FLJ20069) showed that the expression of these genes did not correlate well with the presence of proviral insertions. A possible explanation for the paradoxical behavior of c-myb was provided by one of the murine T-lymphoma lines bearing an insertion at Ahi-1 (p/m16i) that reproducibly down-regulated c-myb RNA and protein to very low levels or undetectable levels on prolonged culture. Our observations implicate c-myb as a key target of upstream and downstream retroviral insertions. However, overexpression may become dispensable during outgrowth in vitro, and perhaps during tumor progression in vivo, providing a potential rationale for the previously observed discordance between retroviral insertion and c-myb expression levels.

Prognostic variables in newly diagnosed children and adolescents with acute myeloid leukemia: Children's Cancer Group Study 213

The objective of this study was to identify biologic parameters that were associated with either exceptionally good or poor outcome in childhood acute myeloid leukemia (AML). Among the children with AML who entered Children's Cancer Group trial 213, 498 patients without Down syndrome or acute promyelocytic leukemia (APL) comprise the basis for this report. Univariate comparisons of the proportion of patients attaining complete remission after induction (CR) indicate that, at diagnosis, male gender, low platelet count (< or =20 000/microl), hepatomegaly, myelodysplastic syndrome (MDS), French-American- British (FAB) category M5, high (>15%) bone marrow (BM) blasts on day 14 of the first course of induction, and +8 are associated with lower CR rates, while abnormal 16 is associated with a higher CR rate. Multivariate analysis suggests high platelet count at diagnosis (>20 000/microl), absence of hepatomegaly, < or =15% day 14 BM blast percentage, and abnormal 16 are independent prognostic factors associated with better CR. Univariate analysis demonstrated a significant favorable relationship between platelet count at diagnosis (>20 000/microl), absence of hepatomegaly, low percentage of BM blasts (< or =15%), and abnormal 16 with overall survival. Absence of hepatomegaly, < or =15% day 14 BM blast percentage, and abnormal 16 were determined to be independent prognostic factors associated with better survival.

Molecular characterization of the mouse Tem1/endosialin gene regulated by cell density in vitro and expressed in normal tissues in vivo

Human tumor endothelial marker 1/endosialin (TEM1/endosialin) was recently identified as a novel tumor endothelial cell surface marker potentially involved in angiogenesis, although no specific function for this novel gene has been assigned so far. It was reported to be expressed in tumor endothelium but not in normal endothelium with the exception of perhaps the corpus luteum. Here we describe the cDNA and genomic sequences for the mouse Tem1/endosialin homolog, the identification and characterization of its promoter region, and an extensive characterization of its expression pattern in murine and human tissues and murine cell lines in vitro. The single copy gene that was mapped to chromosome 19 is intronless and encodes a 92-kDa protein that has 77.5% overall homology to the human protein. The remarkable findings are 1) this gene is ubiquitously expressed in normal human and mouse somatic tissues and during development, and 2) its expression at the mRNA level is density-dependent and up-regulated in serum-starved cells. In vitro, its expression is limited to cells of embryonic, endothelial, and preadipocyte origin, suggesting that the wide distribution of its expression in vivo is due to the presence of vascular endothelial cells in all the tissues. The ubiquitous expression in vivo is in contrast to previously reported expression limited to corpus luteum and highly angiogenic tissues such as tumors and wound tissue.

Deregulated c-Myb expression in murine myeloid leukemias prevents the up-regulation of p15(INK4b) normally associated with differentiation

Deregulated expression of the proto-oncogene c-myb, which results from provirus integration, is thought to be responsible for transformation in a set of murine leukemia virus (MuLV)-induced myeloid leukemias (MML). We reported recently that this transcription factor promotes proliferation by directly transactivating c-myc and inhibits cell death through its up-regulation of Bcl-2 (Schmidt et al., 2000). To understand more about how these cells become transformed we looked at how they deal with cellular pathways inducing growth arrest. Specifically, we were interested in the expression of the tumor suppressor gene Cdkn2b (p15(INK4b)) in MML because this gene is expressed during myeloid differentiation and its inactivation by methylation has been shown to be important for the development of human acute myeloid leukemia. mRNA levels for p15(INK4b) and another INK4 gene p16(INK4a) were examined in monocytic Myb tumors and were compared with expression of the same genes in c-myc transformed monocytic tumors that do not express c-Myb. The Cdkn2a (p16(INK4a)) gene was generally not expressed in either tumor type, an observation explained by methylation or deletion in the promoter region. Although Cdkn2b (p15(INK4b)) mRNA was expressed in the Myc tumors, many transcripts were aberrant in size and contained only exon 1. Surprisingly, in the majority of the Myb tumors there was no p15(INK4b) transcription and neither deletion nor methylation could explain this result. Additional experiments demonstrated that, in the presence of constitutive c-Myb expression, the induction of p15(INK4b) mRNA that accompanies differentiation of M1 cells to monocytes does not occur. Therefore, the transcriptional regulator c-Myb appears to prevent activation of a growth arrest pathway that normally accompanies monocyte maturation.

Quality improvement within Independent Practitioner Associations: lessons from New Zealand

AIMS

To ascertain what quality improvement activities are being performed by associations of general practitioners (GPs) in New Zealand, to find out how they are supporting these activities, and learn about their experience of the process.

METHOD

A cross sectional questionnaire study of 25 independent practitioner associations (IPAs) in New Zealand.

RESULTS

All respondents (n=25) believed quality improvement was a responsibility of their organization, and for 48% it was their highest priority. All organizations carried out and supported a range of quality improvement activities. The major perceived barriers to quality improvement were negative attitudes and lack of time and money to support the process. Strategies to overcome these barriers included providing comparative data to staff in a peer group setting and providing financial incentives, management support and education.

CONCLUSIONS

Considerable quality improvement activity is occurring in primary care in New Zealand. A variety of barriers to the process and methods of overcoming them have been identified by some, but not all IPAs.

Cigarette smoking, salivary/gingival crevicular fluid cotinine and periodontal status. A 10-year longitudinal study

BACKGROUND, AIMS

The primary purpose of this study was to determine the association of salivary and gingival crevicular fluid (GCF) cotinine levels with periodontal disease status in smokers and non-smokers.

METHODS

147 male smokers and 30 male non-smokers were included in the current longitudinal study. The 177 individuals were part of a group of 200 subjects (89%) seen 10 years previously for a baseline survey. Oral hygiene indices, probing depth and attachment loss were recorded. Salivary and GCF cotinine levels of 58 smokers were determined by means of ELISA.

RESULTS

Results indicated that no significant difference was found in subjects who smoked, when compared to subjects who did not smoke with respect to plaque accumulation and calculus deposits. Smokers, however, had fewer gingival bleeding sites. Cigarette smoking was associated with a greater increase in probing depth and attachment loss, as well as greater tooth loss at an earlier age. There was greater tooth loss in smokers than non-smokers (p < 0.001). 11 smokers became edentulous, while only 1 non-smoker lost all his teeth within 10 years. The degree of periodontal tissue breakdown was different in each age group with greater periodontal deterioration as age increased. All smokers had detectable salivary and GCF cotinine. Mean GCF cotinine was about 4x higher than mean salivary cotinine levels. Individuals who smoked > or = 20 pack years when compared to <20 pack years, had significantly higher saliva and GCF cotinine levels (p < or = 0.05).

CONCLUSION

Neither salivary cotinine nor GCF cotinine was significantly correlated with probing depth, attachment loss and tooth loss (p > 0.05).

Phosphorylation-dependent conformation and proteolytic stability of c-Myb

The c-Myb oncoprotein is a critical regulator of hematopoietic cell proliferation and differentiation. Normal c-Myb is rapidly degraded by the ubiquitin-26S proteasome pathway, and instability determinants have been localized within the negative regulatory domain in the carboxyl terminus. Our recent work has shown that, in myeloid cells, inhibition of cellular Ser/Thr protein phosphatases with okadaic acid (OA) causes a rapid increase in c-Myb phosphorylation and 26S proteasome-dependent breakdown [J. Bies, S. Feikova, D. P. Bottaro, and L. Wolff (2000) Oncogene 19, 2846-2854]. Furthermore, phosphoamino acid analyses revealed that the increase in phosphorylation was mainly on threonine residues. Here we investigated the ability of c-Myb to bind DNA following phosphorylation. Our results suggest that the hyperphosphorylated form of c-Myb binds to DNA with affinity very similar to the hypophosphorylated form. Therefore, the increased proteolytic instability of the former cannot be explained by a difference in DNA-binding capacity. Conformational changes in the carboxyl terminus were proposed previously to be a consequence of phosphorylation because we observed phosphorylation-induced alterations in gel electrophoresis mobilities and alterations in recognition by specific monoclonal antibodies. Further support for this notion has come from this study, in which we have detected new degradation products in electrophoretic mobility shift assays, as well as an increased rate of in vitro proteolysis, following OA treatment. We speculate that these alterations in the conformation of the negative regulatory domain expose epitopes on the surface of c-Myb, which in turn can serve as recognition signal(s) for ubiquitin-26S proteasome proteolytic machinery.

Three genes with different functions in transformation are regulated by c-Myb in myeloid cells

The proto-oncogene c-myb is constitutively expressed in murine leukemia virus-induced myeloid leukemia (MML) due to the integration of virus at this locus. Our recent focus has been the determination of genes regulated by this transcription factor that may be involved in transformation. Data presented here, using conditional expression of Myb in myeloid cells, show that c-Myb directly transactivates the endogenous c-myc and Bcl-2 genes, which explains at least in part how c-Myb regulates proliferation and survival. In addition, c-Myb prevents expression at the RNA level of the tumor suppressor INK4b gene. This gene encodes a cyclin-dependent kinase inhibitor, p15INK4b, that is normally upregulated at the mRNA level during myeloid differentiation and promotes growth arrest. The MMLs are generally characterized as differentiated monocytic tumors and possess the phenotype that is normally associated with p15INK4b expression. c-Myb inhibits expression of this gene, however, and therefore acts to promote a pathway which is abnormal in mature cells. This activity of c-Myb collaborates with its maintenance of c-myc expression to promote growth.

Constitutive ubiquitination and degradation of c-myb by the 26S proteasome during proliferation and differentiation of myeloid cells

Steady state levels of transcription factors play an important role in proliferation and differentiation of hematopoietic cells. The transcription factor c-Myb is frequently activated by retrovirus integration in murine and avian leukemias. Its deregulation has been also implicated in human acute and chronic leukemias and some other nonhematopoietic tumors. It is a short-lived protein, which is rapidly degraded by the 26S proteasome. Truncation at the carboxyl (COOH) terminus, which has occurred in some oncogenic forms ofc-Myb, results in the increased resistance to proteolysis. This stabilization correlates in vitro with less efficient ubiquitination. Here, we report the first evidence of post-translational modification of c-Myb by ubiquitin in vivo using HA-labeled ubiquitin. We also show that, in contrast to the unstable wild type or amino (NH2)-terminally truncated c-Myb form, stable carboxyl (COOH)-terminally truncated c-Myb is not targeted to degradation by covalent attachment of ubiquitin in vivo. In addition, following an analysis of subcellular fractionation of proteins from cells treated with a 26S proteasome inhibitor we were able to localize c-Myb exclusively in the nuclear compartment, suggesting the absence of a requirement for export to cytoplasm prior proteolytic processing. Furthermore, pulse-chase experiments of c-Myb protein isolated from interphase cells or cells synchronized in the G2/M or G1 phases of cell cycle did not reveal substantial cell cycle dependent differences in proteolytic processing by the 26S proteasome. Also, the demonstration that the half-life of c-Myb in myeloid progenitor M1 cells induced to differentiate along the monocytic pathway is the same as in undifferentiated cells suggested that proteolytic breakdown of c-Myb is a constitutive process during proliferation and differentiation.

Tax oncoprotein trans-represses endogenous B-myb promoter activity in human T cells

The B-myb gene was identified on the basis of its homology with the protooncogene c-myb, homolog of the avian myeloblastosis virus (AMV) and avian leukemia virus (E26) transforming genes. Several studies using antisense constructs or antisense oligonucleotides as well as overexpression experiments suggest that B-Myb plays an important role in the transition from G(1) to S phase of the cell cycle and that B-Myb expression is cell cycle regulated. We have previously demonstrated that the human T cell lymphotropic virus type 1 (HTLV1) trans-activator Tax is able to repress transcription from c-myb promoter reporter constructs as well as from the endogenous c-myb promoter in human T cells and that this effect is mediated through inhibition of the c-Myb trans-activating functions. Here we report that both HTLV-1 as well as HTLV-2 Tax proteins inhibit c-Myb trans-activation in mouse embryo fibroblasts (MEFs). In addition to c-Myb, B-Myb expression is also markedly downregulated in HTLV-1-transformed cells at both RNA and protein levels. Furthermore, by using a Jurkat T cell line stably transfected with a tax gene driven by a cadmium-inducible promoter (JPX9), we were able to demonstrate that Tax directly represses the endogenous B-myb promoter in T cells. Because c-Myb and B-Myb have been involved in cell cycle progression, our results suggest that Tax, by repressing both c-Myb and B-Myb endogenous promoters, may bypass their requirement for cell cycle progression in HTLV-1-transformed T cells.

Hyperphosphorylation and increased proteolytic breakdown of c-Myb induced by the inhibition of Ser/Thr protein phosphatases

The c-myb proto-oncogene encodes a nuclear phosphoprotein that plays a crucial role in normal hematopoiesis. It is a short-lived transcription factor rapidly degraded by the 26S proteasome. Although it has been shown that instability determinants reside in its carboxyl terminus, the molecular mechanism of c-Myb degradation is unknown. Here, we report the first evidence that phosphorylation plays a role in targeting the protein to the proteasome. Inhibition of cellular serine/threonine protein phosphatase activity by okadaic acid resulted in hyperphosphorylation of c-Myb and extremely rapid turnover. The hyperphosphorylation resulted in a protein with altered properties that was indicative of conformational changes. Its mobility on gel electrophoresis was altered as well as its recognition by specific monoclonal antibody. The altered hyperphosphorylated protein still bound to DNA with an affinity similar to that of the hypophosphorylated form. Phosphorylation of three previously identified sites, serines 11, 12, and 528, does not appear to be involved in the proposed changes in conformation or stability. However, phosphoamino acid analyses of the hyperphosphorylated form of c-Myb revealed increased c-Myb phosphorylation mainly on threonine residues that correlated with other okadaic acid-induced alterations of c-Myb. These findings indicate that Ser/Thr phosphatases prevent conformational changes that may play an important role in controlled degradation of c-Myb. Oncogene (2000) 19, 2846 - 2854

HTLV-I Tax transrepresses the human c-Myb promoter independently of its interaction with CBP or p300

The c-Myb proto-oncogene is preferentially expressed in hematopoietic lineages, and highly expressed in several leukemia types. The Human T-cell Leukemia Virus Type I (HTLV-I) is the etiological agent of Adult T-cell Leukemia/Lymphoma (ATLL). A previous report suggested that Tax, the viral transactivator, is able to suppress the transactivation potential of c-Myb protein by competing for recruitment of CBP. We tested whether such a competition could affect transcription from the c-Myb promoter in Tax expressing T-cells. Using several c-Myb promoter reporter constructs carrying mutations in various regions, we demonstrate that Tax suppression of c-Myb transactivation results in transrepression of the c-Myb promoter through the Myb responsive elements in Jurkat T-cells. The ability of Tax mutants M22, M47 and V89A to interact with the full-length CBP and p300 proteins in vitro, and their ability to repress the c-Myb promoter, was then evaluated. Although both M47 and M22 bind to CBP and p300 to a similar extent, only M47 was able to repress the c-Myb promoter, suggesting that competition for CBP/p300 binding was not the mechanism underlying Tax's effect. This concept was further supported by the fact that the Tax mutant V89A transrepresses the c-Myb promoter efficiently in spite of an impaired binding to CBP and p300. Therefore, Tax-mediated repression of the c-Myb promoter appears to be independent from a direct competition between c-Myb and Tax for recruitment of CBP/p300. Interestingly, a decreased transcription from the endogenous c-Myb promoter was observed in several HTLV-I transformed T-cell lines. Finally, the ability of Tax to directly repress the endogenous c-Myb promoter was demonstrated in a Jurkat cell line stably transfected with a tax gene driven by a cadmium-inducible promoter.

Regulation of the resident chromosomal copy of c-myc by c-Myb is involved in myeloid leukemogenesis

c-myb is a frequent target of retroviral insertional mutagenesis in murine leukemia virus-induced myeloid leukemia. Induction of the leukemogenic phenotype is generally associated with inappropriate expression of this transcriptional regulator. Despite intensive investigations, the target genes of c-myb that are specifically involved in development of these myeloid lineage neoplasms are still unknown. In vitro assays have indicated that c-myc may be a target gene of c-Myb; however, regulation of the resident chromosomal gene has not yet been demonstrated. To address this question further, we analyzed the expression of c-myc in a myeloblastic cell line, M1, expressing a conditionally active c-Myb-estrogen receptor fusion protein (MybER). Activation of MybER both prevented the growth arrest induced by interleukin-6 (IL-6) and rapidly restored c-myc expression in nearly terminal differentiated cells that had been exposed to IL-6 for 3 days. Restoration occurred in the presence of a protein synthesis inhibitor but not after a transcriptional block, indicating that c-myc is a direct, transcriptionally regulated target of c-Myb. c-myc is a major target that transduces Myb's proliferative signal, as shown by the ability of a c-Myc-estrogen receptor fusion protein alone to also reverse growth arrest in this system. To investigate the possibility that this regulatory connection contributes to Myb's oncogenicity, we expressed a dominant negative Myb in the myeloid leukemic cell line RI-4-11. In this cell line, c-myb is activated by insertional mutagenesis and cannot be effectively down regulated by cytokine. Myb's ability to regulate c-myc's expression was also demonstrated in these cells, showing a mechanism through which the proto-oncogene c-myb can exert its oncogenic potential in myeloid lineage hematopoietic cells.

Identification of protein instability determinants in the carboxy-terminal region of c-Myb removed as a result of retroviral integration in murine monocytic leukemias

The c-myb oncogene has been a target of retroviral insertional mutagenesis in murine monocytic leukemias. One mechanism by which c-myb can be activated is through the integration of a retroviral provirus into the central portion of the locus, causing premature termination of c-myb transcription and translation. We had previously shown that a leukemia-specific c-Myb protein, truncated at the site of proviral integration by 248 amino acids, had approximately a fourfold-increased half-life compared to the normal c-Myb protein, due to its ability to escape rapid degradation by the ubiquitin-26S proteasome pathway. Here we provide evidence for the existence of more than one instability determinant in the carboxy-terminal region of the wild-type protein, which appear to act independently of each other. The data were derived from examination of premature termination mutants and deletion mutants of the normal protein, as well as analysis of another carboxy-terminally truncated protein expressed in leukemia. Evidence is provided that one instability determinant is located in the terminal 87 amino acids of the protein and another is located in the vicinity of the internal region that has leucine zipper homology. In leukemias, different degrees of protein stability are attained following proviral integration depending upon how many determinants are removed. Interestingly, although PEST sequences (rich in proline, glutamine, serine, and threonine), often associated with degradation, are found in c-Myb, deletion of PEST-containing regions had no effect on protein turnover. This study provides further insight into how inappropriate expression of c-Myb may contribute to leukemogenesis. In addition, it will facilitate further studies aimed at characterizing the specific role of individual regions of the normal protein in targeting to the 26S proteasome.

In vitro suppression of programmed cell death of B cells by tissue inhibitor of metalloproteinases-1

Cellular pathways for induction of programmed cell death (PCD) have been identified, but little is known about specific extracellular matrix processes that may affect apoptosis along those pathways. In this study, a series of Burkitt's lymphoma (BL) cell lines were assayed for their expression of tissue inhibitor of metalloproteinases (TIMP)-1. Results indicate that TIMP-1-positive BL lines show resistance to cold-shock-induced apoptosis. Furthermore, recombinant TIMP-1, but not TIMP-2 or a synthetic metalloproteinase inhibitor (BB-94), confers resistance to apoptosis induced by both CD95-dependent and -independent (cold shock, serum deprivation, and gamma-radiation) pathways in TIMP-1-negative BL lines. TIMP-1 suppression of PCD is not due to metalloproteinase inhibition, as reduction and alkylation of the TIMP-1 did not abolish this activity. Retroviral induction of TIMP-1 not only resulted in cell survival but also in continued DNA synthesis for up to 5 d in the absence of serum, while controls underwent apoptosis. This resistance to apoptosis is reversed by anti-TIMP-1 antibodies, demonstrating that secreted TIMP-1 is active in blocking apoptosis. Furthermore, TIMP-1 upregulation induced expression of Bcl-XL but not Bcl-2 as well as decreased NF-kappaB activity as compared with controls. These results demonstrate that TIMP-1 suppresses apoptosis in B cells and suggests a novel activity for TIMP-1 in tissue homeostasis.

Effectiveness of a sonic toothbrush in maintenance of dental implants. A prospective study

This study assessed the efficacy of a sonic and a manual toothbrush in reducing plaque and gingivitis around dental implants. Subjects were randomly assigned to either sonic (n = 16) or manual (n = 15) study groups. Groups were balanced according to baseline levels of plaque and gingivitis. The plaque (PI), gingival (GI), and bleeding (BI) indices as well as probing depths were determined at baseline, and at 4, 8, 12, and 24 week follow-up visits. Mean scores per person were calculated for each clinical parameter. Oral hygiene habits, compliance and acceptance were also evaluated over the study period. Within group comparisons from baseline throughout the study, as well as between group comparisons (i.e., sonic versus manual), were determined. Overall, plaque, gingival, and bleeding indices in both groups were lower at each follow-up visit when compared to the baseline. Within group comparisons demonstrated that both the sonic toothbrush subjects and the manual toothbrush subjects had significantly lower PI, GI, and BI scores at each post-baseline visit (4, 8, 12, and 24 weeks) than at baseline (p<0.005). In addition, the sonic toothbrush subjects also had significantly lower probing depths at each post-baseline visit than at baseline (p < 0.005). Between group comparisons demonstrated that the sonic toothbrush subjects over time had significantly lower PI and BI scores around dental implants than the manual toothbrush subjects (Repeated measures MANOVA; PI, p = 0.01; BI, p = 0.017). The sonic toothbrush subjects had lower GI scores and reduced probing depths over time when compared to manual toothbrush subjects but these scores were not statistically significant (GI; probing depth, p > 0.05). No implant problems (e.g., loose screws) were attributable to the sonic toothbrush. Relevant to oral hygiene habits, subjects in both groups demonstrated a high level of compliance with their assigned toothbrush. Overall, the results of this study demonstrated that sonic toothbrushing significantly reduced plaque, gingival inflammation and bleeding, and probing pocket depths around implants over the 6-month trial period. It is concluded that sonic brushing is an effective means of dental implant maintenance.

Augmented post-induction therapy for children with high-risk acute lymphoblastic leukemia and a slow response to initial therapy

BACKGROUND

Children with high-risk acute lymphoblastic leukemia (ALL) who have a slow response to initial chemotherapy (more than 25 percent blasts in the bone marrow on day 7) have a poor outcome despite intensive therapy. We conducted a randomized trial in which such patients were treated with either an augmented intensive regimen of post-induction chemotherapy or a standard regimen of intensive post-induction chemotherapy.

METHODS

Between January 1991 and June 1995, 311 children with newly diagnosed ALL who were either 1 to 9 years of age with white-cell counts of at least 50,000 per cubic millimeter or 10 years of age or older, had a slow response to initial therapy, and entered remission at the end of induction chemotherapy were randomly assigned to receive standard therapy (156 children) or augmented therapy (155). Those with lymphomatous features were excluded. Event-free survival and overall survival were assessed from the end of induction treatment.

RESULTS

The outcome at five years was significantly better in the augmented-therapy group than in the standard-therapy group (Kaplan-Meier estimate of event-free survival [+/-SD]: 75.0+/-3.8 vs. 55.0+/-4.5 percent, P<0.001; overall survival: 78.4+/-3.7 vs. 66.7+/-4.2 percent, P=0.02). The difference between treatments was most pronounced among patients one to nine years of age, all of whom had white-cell counts of at least 50,000 per cubic millimeter (P<0.001). Risk factors for an adverse event in the entire cohort included a white-cell count of 200,000 per cubic millimeter or higher (P=0.004), race other than black or white (P<0.001), and the presence of a t(9;22) translocation (P=0.007). The toxic effects of augmented therapy were considerable but manageable.

CONCLUSIONS

Augmented post-induction chemotherapy results in an excellent outcome for most patients with high-risk ALL and a slow response to initial therapy.

Activation of bcl-2 suppressible 40 and 44 kDa p38-like kinases during apoptosis of early and late B lymphocytic cell lines

Activation of several different kinases characterizes the induction of apoptosis. Abelson virus transformed pre-B lymphocytes undergo apoptosis within 24 h of serum deprivation, PKA activation or gamma-irradiation, and the activity of two kinases of ca. 40 and 44 kDa is specifically induced during this apoptotic process. Bcl-2 expression prevents both apoptosis and the induction of these kinases. Immunologic and substrate similarities indicate that these kinases are related to the p38 family of MAP kinases. More mature cells of the B lymphocytic lineage, plasmacytomas, also exhibit induction of these kinases when apoptosis is induced by withdrawal of serum or IL-6. Treatment of the pre-B cells with ICE protease inhibitors when apoptotic stimuli are delivered prevents induction of the kinase activity, and partially inhibits apoptosis. These findings indicate that the induction of these 40 and 44 kDa p38 related kinases is a common feature of apoptosis in mouse B lymphocytic cells and may represent a step downstream of ICE proteases in the signal cascade that leads to programmed cell death.

Response of children with high-risk acute lymphoblastic leukemia treated with and without cranial irradiation: a report from the Children's Cancer Group

PURPOSE

Intensified intrathecal (i.t.) chemotherapy without cranial radiation therapy (CRT) prevents CNS relapse in children with low-risk and intermediate-risk acute lymphoblastic leukemia (ALL). In the current study, high-risk ALL patients who achieved a rapid early response (RER) to induction chemotherapy were randomized to receive intensive systemic chemotherapy and presymptomatic CNS therapy that consisted of either i.t. methotrexate (MTX) and CRT or intensified i.t. MTX alone.

PATIENTS AND METHODS

Children (n = 636) with high-risk ALL (aged 1 to 9 years and WBC count > or = 50,000/microL or age > or = 10 years, excluding those with lymphomatous features) who achieved an RER (< or = 25% marrow blasts on day 7) to induction therapy and lacked CNS disease at diagnosis were randomized to receive systemic therapy with either i.t. MTX and CRT (regimen A, n = 317) or intensified i.t. MTX alone (regimen B, n = 319).

RESULTS

Interim analysis in July 1993 revealed 3-year event-free survival (EFS) estimates of 82.1% +/- 4.0% (SD)and 70.4% +/- 4.2% for patients treated on regimens A and B, respectively (P = .004). As of January 1996, outcome had changed: 5-year EFS estimates were 69.1% +/- 3.4% and 75.0% +/- 2.7% for regimens A and B, respectively (P = 0.50). Marrow relapses comprised 57 events on regimen A and 43 events on regimen B. Fewer late events occurred on regimen B.

CONCLUSION

For high-risk pediatric ALL patients who show an RER to induction therapy and are treated with systemic Children's Cancer Group (CCG)-modified Berlin-Frankfurt-Munster (BFM) chemotherapy, presymptomatic CNS therapy that consists of either i.t. MTX plus CRT or intensified i.t. MTX alone results in a similar 5-year EFS outcome. Furthermore, intensified i.t. MTX may protect against late bone marrow relapse.

Augmented Berlin-Frankfurt-Munster therapy abrogates the adverse prognostic significance of slow early response to induction chemotherapy for children and adolescents with acute lymphoblastic leukemia and unfavorable presenting features: a report from the Children's Cancer Group

PURPOSE

Compared with previous Children's Cancer Group (CCG) acute lymphoblastic leukemia (ALL) trials, therapy based on the Berlin-Frankfurt-Munster (BFM) 76 trial has effected an improvement in event-free survival (EFS). In an attempt to improve EFS further, CCG investigators formulated an augmented BFM (A-BFM) regimen that provides prolonged, intensified postinduction chemotherapy relative to the CCG-modified BFM regimen.

PATIENTS AND METHODS

We tested A-BFM in 101 patients with ALL and unfavorable presenting features that showed slow early response (SER) to induction therapy who attained remission on day 28. Their outcome was compared with that of 251 concurrent patients with unfavorable presenting features, a rapid early response to therapy (RER), and remission by day 28, treated with CCG-BFM with or without cranial radiation (CRT).

RESULTS

The 4-year EFS rate from the end of induction for SER patients treated with A-BFM was 70.8% +/- 4.6%. Seventeen patients remain in continuous remission beyond 5 years. Vincristine (VCR) neurotoxicity developed in 50% of patients, but was rarely debilitating. Allergies to Escherichia coli L-asparaginase (L-ASP) occurred in 35% of patients. Avascular necrosis of bone (AVN) developed in 9% of patients. In comparison, a concurrent RER group treated with standard BFM +/- CRT had a 4-year EFS rate of 73.1% +/- 4.6%.

CONCLUSION

The toxicity of A-BFM is significant, but acceptable. Compared with historical control SER patients treated with CCG-modified BFM, A-BFM therapy appears to produce a significant improvement in EFS. This is the first study to show that intensive chemotherapy, as given in the A-BFM regimen, can abrogate the adverse prognostic significance of SER.

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.

Oncogenic activation of c-Myb by carboxyl-terminal truncation leads to decreased proteolysis by the ubiquitin-26S proteasome pathway

c-myb activation by insertional mutagenesis in murine myeloid leukemias can lead to amino (NH2)-terminal or carboxyl (COOH)-terminal truncation of its protein product. We observed that in these leukemias, the steady state level of the protein truncated at the COOH terminus was remarkably higher than that of the protein truncated at the NH2-terminus or full length wild-type protein. To examine the rate of proteolysis of different forms of Myb in a uniform cellular background, the proteins were constitutively expressed in the myeloblast cell line M1, using the retrovirus vector LXSN. In pulse chase experiments, using metabolically 35S-labeled proteins, it was determined that COOH-terminal truncation of c-Myb by 248 aa (CT-c-Myb) substantially increases protein stability, resulting in a t1/2 of about 140 min, as compared to 50 min for full length c-Myb (FL-c-Myb). In an investigation of the mechanism involved in the in vivo degradation of this short lived transcription factor, inhibitors of the lysosomal (chloroquine), proteasomal (ALLM, ALLN, lactacystin) and calpains (EGTA, E-64d, BAPTA/AM) pathways were utilized. Results of this experiment identified the 26S proteasome as a major pathway responsible for rapid breakdown of the protein in hematopoietic cells. Further experiments carried out in vitro demonstrated that c-Myb can be ubiquitinated, suggesting that this process may be involved in the targeting of wild-type c-Myb to degradation by the 26S proteasome. In addition, it was demonstrated that CT-c-Myb was less efficiently ubiquitinated than wild-type protein indicating that defects in modification account for its escape from rapid turnover. We speculate that the increased half-life of c-Myb resulting from truncation could contribute to its transforming potential.