Peptide-based multi-agonists: a new paradigm in metabolic pharmacology.

Obesity and its comorbidities, such as type 2 diabetes, are pressing worldwide health concerns. Available anti-obesity treatments include weight loss pharmacotherapies and bariatric surgery. Whilst surgical interventions typically result in significant and sustained weight loss, available pharmacotherapies are far less effective, typically decreasing body weight by no more than 5-10%. An emerging class of multi-agonist drugs may eventually bridge this gap. This new class of specially tailored drugs hybridizes the amino acid sequences of key metabolic hormones into one single entity with enhanced potency and sustained action. Successful examples of this strategy include multi-agonist drugs targeting the receptors for glucagon-like peptide-1 (GLP-1), glucagon and the glucose-dependent insulinotropic polypeptide (GIP). Due to the simultaneous activity at several metabolically relevant receptors, these multi-agonists offer improved body weight loss and glucose tolerance relative to their constituent monotherapies. Further advancing this concept, chimeras were generated that covalently link nuclear acting hormones such as oestrogen, thyroid hormone (T3 ) or dexamethasone to peptide hormones such as GLP-1 or glucagon. The benefit of this strategy is to restrict the nuclear hormone action exclusively to cells expressing the peptide hormone receptor, thereby maximizing combinatorial metabolic efficacy of both drug constituents in the target cells whilst preventing the nuclear hormone cargo from entering and acting on cells devoid of the peptide hormone receptor, in which the nuclear hormone might have unwanted effects. Many of these multi-agonists are in preclinical and clinical development and may represent new and effective tools in the fight against obesity and its comorbidities.

Are peptide conjugates the golden therapy against obesity?

Obesity is a worldwide pandemic, which can be fatal for the most extremely affected individuals. Lifestyle interventions such as diet and exercise are largely ineffective and current anti-obesity medications offer little in the way of significant or sustained weight loss. Bariatric surgery is effective, but largely restricted to only a small subset of extremely obese patients. While the hormonal factors mediating sustained weight loss and remission of diabetes by bariatric surgery remain elusive, a new class of polypharmacological drugs shows potential to shrink the gap in efficacy between a surgery and pharmacology. In essence, this new class of drugs combines the beneficial effects of several independent hormones into a single entity, thereby combining their metabolic efficacy to improve systems metabolism. Such unimolecular drugs include single molecules with agonism at the receptors for glucagon, glucagon-like peptide 1 and the glucose-dependent insulinotropic polypeptide. In preclinical studies, these specially tailored multiagonists outperform both their mono-agonist components and current best in class anti-obesity medications. While clinical trials and vigorous safety analyses are ongoing, these drugs are poised to have a transformative effect in anti-obesity therapy and might hopefully lead the way to a new era in weight-loss pharmacology.

SSBP2 is an in vivo tumor suppressor and regulator of LDB1 stability.

SSBP proteins bind and stabilize transcriptional cofactor LIM domain-binding protein1 (LDB1) from proteosomal degradation to promote tissue-specific transcription through an evolutionarily conserved pathway. The human SSBP2 gene was isolated as a candidate tumor suppressor from a critical region of loss in chromosome 5q14.1. By gene targeting, we show increased predisposition to B-cell lymphomas and carcinomas in Ssbp2(-/-) mice. Remarkably, loss of Ssbp2 causes increased LDB1 turnover in the thymus, a pathway exploited in Trp53(-/-)Ssbp2(-/-) mice to develop highly aggressive, immature thymic lymphomas. Using T-cell differentiation as a model, we report a stage-specific upregulation of Ssbp2 expression, which in turn regulates LDB1 turnover under physiological conditions. Furthermore, transcript levels of pTalpha, a target of LDB1-containing complex, and a critical regulator T-cell differentiation are reduced in Ssbp2(-/-) immature thymocytes. Our findings suggest that disruption of the SSBP2-regulated pathways may be an infrequent but critical step in malignant transformation of multiple tissues.

Histone deacetylase inhibitors induce the degradation of the t(8;21) fusion oncoprotein.

The t(8;21) chromosomal translocation that generates the fusion oncoprotein RUNX1-ETO predominates in leukemia patients of the French-American-British (FAB) class M2 subtype. The oncoprotein has the capacity to promote expansion of hematopoietic stem/progenitor cells and induces leukemia in association with other genetic alterations. Here, we show that RUNX1-ETO undergoes degradation in response to treatment with histone deacetylase inhibitors, one of which, depsipeptide (DEP), is currently undergoing phase II clinical testing in a variety of malignancies. These compounds induce turnover of RUNX1-ETO without affecting the stability of RUNX1-ETO partner proteins. In addition, RUNX1-ETO physically interacts with heat shock protein 90 (HSP90). DEP treatment interrupts the association of RUNX1-ETO with HSP90 and induces proteasomal degradation of RUNX1-ETO. DEP and the HSP90 antagonist 17-allylamino-geldanamycin (17-AAG) both triggered RUNX1-ETO degradation, but without any additive or cooperative effects. These findings may stimulate the development of more rational and effective approaches for treating t(8;21) patients using histone deacetylase inhibitors or HSP90 inhibitors.

Expression of the TAL1/SCL transcription factor in physiological and pathological vascular processes.

The TAL1/SCL transcription factor is essential for haematopoietic commitment and vascular remodelling during embryonic development. To help clarify its role in postnatal vascular processes, we characterized the expression of mouse Tal1 protein by immunocytochemistry in several experimental models of blood vessel formation. In adult mice, Tal1 protein was expressed in rare microvascular endothelial cells and in extravascular cells provisionally identified as endothelial progenitors from their morphology, proximity to vessels and expression of vascular endothelial growth factor receptor-2. The number of Tal1-expressing endothelial cells increased significantly but transiently in all the models-hormone-induced ovulation, wound healing and tumour development. Finally, Tal1 protein was detected in the nuclei of newly formed lymphatic endothelial cells in tumour-bearing animals. These results show that TAL1 is expressed by vascular endothelial cells and endothelial progenitors at sites of physiological and pathological neovascularization and suggest a role for this transcription factor in adult vasculogenesis. This work also provides the first evidence for TAL1 expression in lymphangiogenesis.

RUNX1 associates with histone deacetylases and SUV39H1 to repress transcription.

RUNX1 (AML1) is a gene that is frequently disrupted by chromosomal translocations in acute leukemia. Like its Drosophila homolog Runt, RUNX1 both activates and represses transcription. Both Runt and RUNX1 are required for gene silencing during development and a central domain of RUNX1, termed repression domain 2 (RD2), was defined as being required for transcriptional repression and for the silencing of CD4 during T-cell maturation in thymic organ cultures. Although transcriptional co-repressors are known to contact other repression domains in RUNX1, the factors that bind to RD2 had not been defined. Therefore, we tested whether RD2 contacts histone-modifying enzymes that may mediate both repression and gene silencing. We found that RD2 contacts SUV39H1, a histone methyltransferase, via two motifs and that endogenous Suv39h1 associates with a Runx1-regulated repression element in murine erythroleukemia cells. In addition, one of these SUV39H1-binding motifs is also sufficient for binding to histone deacetylases 1 and 3, and both of these domains are required for full RUNX1-mediated transcriptional repression. The association between RUNX1, histone deacetylases and SUV39H1 provides a molecular mechanism for repression and possibly gene silencing mediated by RUNX1.

Age and cytogenetics as predictors of event free survival in patients with acute non-lymphocytic leukemia receiving high dose cytosine arabinoside and daunorubicin as consolidation chemotherapy.

Between 1991 and 1999, 67 patients with acute non-lymphocytic leukemia (ANLL) in complete remission received high dose cytarabine (HiDAC) 3 gm/m2 q12h x 12 doses followed by daunorubicin 45 mg/m2/day x 3 days as consolidation therapy. Five year actuarial event free survival (EFS) was 34% +/- 6%. Age was significantly associated with EFS. EFS was 60% +/- 15% in patients age 20 to 29, 48% +/- 16% in patients age 30 to 39, 23% +/- 10% in patients age 40 to 49, 31% +/- 11% in patients age 50 to 59, and 0% in patients age > or = 60. Contrary to other reports which have used different HiDAC regimens, we found no relationship between cytogenetics and EFS. Cytogenetics were defined as favorable risk: t(8;21), inv (16), and del (16); neutral risk: normal or t(15;17); and unfavorable risk: any abnormality not included in favorable risk or neutral risk. EFS was 29% +/- 17% in patients with favorable cytogenetics, 37% +/- 14% in patients with neutral cytogenetics, and 31% +/- 12% in patients with unfavorable cytogenetics. These differences were not statistically significant. Because of the successful use of allogeneic transplantation at relapse in patients with matched related donors, five year actuarial survival (S) in this series was 40% +/- 6%. Five year actuarial survival was 57% +/- 9% for patients age < or = 44 and 25% +/- 8% for patients age > or = 45. This difference is statistically significant, p < .025. Clinicians should be cautious about making clinical decisions regarding consolidation therapy of ANLL on the basis of the presence or absence of cytogenetic abnormalities as the importance of cytogenetics may depend on the specific therapy which is employed.

Valacyclovir for the prevention of cytomegalovirus infection after allogeneic stem cell transplantation: a single institution retrospective cohort analysis.

A retrospective single center study was performed to evaluate the safety and efficacy of valacyclovir for prevention of cytomegalovirus (CMV) infection (reactivation) after allogeneic stem cell transplantation (SCT). We compared a group of 31 patients at risk for CMV reactivation (donor, recipient or both seropositive for CMV) who received valacyclovir at an oral dose of 1 g three times a day for CMV prophylaxis with a matched cohort of 31 patients who did not receive the drug or any other form of CMV prophylaxis. Valacyclovir was used as primary prophylaxis in 12 patients and as secondary prophylaxis (after a prior CMV reactivation was effectively treated with either ganciclovir or foscarnet and without CMV antigenemia at the start of valacyclovir) in the remaining 19 patients. The two treatment groups were well matched for the donor-recipient CMV serological status and other pre-transplant characteristics. CMV reactivation was detected by blood antigenemia testing using a commercially available immunofluorescence assay for CMV lower matrix protein pp65 in circulating leukocytes. For primary prophylaxis, 3/12 patients who received valacyclovir reactivated CMV compared to 24/31 patients in the control group (P < 0.001). For secondary prophylaxis, 5/19 valacyclovir patients reactivated compared to 16/24 control patients (P < 0.05). Valacyclovir was well tolerated except for infrequent and mild gastrointestinal side-effects. There was no difference in the incidence of CMV disease in the two groups. Prophylaxis with valacyclovir appears to be safe and efficacious in preventing both primary and secondary CMV reactivation in at-risk patients after allogeneic SCT. Larger prospective randomized studies will be required to confirm these observations.

Limited efficacy of intensified preparative regimens and autologous transplantation as salvage therapy in high grade non-Hodgkin's lymphoma.

Between 9/86 and 6/98, 22 patients with relapsed or refractory high grade lymphoma received intensified preparative therapy and underwent autologous transplantation at a single institution. Two intensified preparative regimens were used--cyclophosphamide, etoposide, total body irradiation (CY-VP-TBI) (N=17) and cyclophosphamide, BCNU, etoposide (CBV) (N=5). For all patients undergoing autologous transplantation, 5 year actuarial survival (S) and 5 year event free survival (EFS) were only 18% +/- 8%. Treatment related mortality was 14% overall but only 8% in patients receiving G-CSF or GM-CSF. Survival was significantly inferior to the survival observed in a concurrent series of patients with intermediate grade lymphoma, 34% +/- 6%, p < .05. Using high dose therapy in conjunction with autologous transplantation at the time of relapse may not be as valuable a strategy in high-grade lymphoma as in intermediate grade lymphoma although most studies combine the two disorders. Alternative strategies for the use of transplantation in high grade lymphoma, such as the use of transplantation as consolidation therapy, need to be investigated.

Is total body irradiation a necessary component of preparative therapy for autologous transplantation in non-Hodgkin's lymphoma.

Between September 1986 and June 1998, 157 patients with low grade, intermediate grade, or high grade lymphoma underwent autologous transplantation at a single institution. Two preparative regimens were used: cyclophosphamide, etoposide, total body irradiation (CY-VP-TBI) (N=110) and cyclophosphamide, BCNU, etoposide (CBV) (N=47). The two groups were not significantly different with respect to source of stem cells, gender, stage at presentation, incidence of prior bone marrow involvement, sensitivity to salvage therapy, or histologic grade of lymphoma. The CBV group was significantly older, 49% of patients over age 50, as compared to 26% of patients over age 50 for the CY-VP-TBI group. Response rates and the incidence of fatal toxicity were similar for the two groups. Five year actuarial survival was 31% +/- 9% for CBV and 38% +/- 5% for CY-VP-TBI, p =.85. In a multivariate analysis, in which preparative regimen, age, histologic grade of lymphoma, and sensitivity to salvage therapy were the independent variables, TBI was not significantly associated with survival, and the direction of the trend was for TBI to be less effective than CBV. TBI does not appear to be an essential component of preparative therapy for autologous transplantation in patients with lymphoma.

Intensified preparative regimens and allogeneic transplantation in refractory or relapsed intermediate and high grade non-Hodgkin's lymphoma.

Between September 1986 and June 1998, 32 patients with relapsed or refractory intermediate or high grade lymphoma received intensified preparative therapy and underwent allogeneic transplantation at a single institution. Patients were considered for allogeneic transplantation if they failed to respond to initial therapy, failed to respond to salvage therapy, relapsed after autologous transplantation, had bone marrow involvement, or failed attempts to harvest autologous stem cells. Patients had a median age of 39 years and had generally received at least two chemotherapy regimens. Five year actuarial survival (S) was 16% +/- 6%; median survival was 4 months. Survival was significantly worse in patients who had received high intensity brief duration chemotherapy prior to transplantation and was also significantly worse in patients who did not receive total body irradiation (TBI). This likely reflects the fact that the patients with the most resistant disease had required local radiotherapy and could not receive TBI. While treatment related mortality played a major role in limiting the effectiveness of allogeneic transplantation, in this heavily pre-treated population of patients with resistant disease, only 39% of patients achieved a complete response following allogeneic transplantation, and in only 40% of that group was long term disease free survival achieved.

P/CAF-mediated acetylation regulates the function of the basic helix-loop-helix transcription factor TAL1/SCL.

The basic helix-loop-helix transcription factor TAL1 (or SCL) is a critical regulator of hematopoietic and vascular development and is misexpressed in the majority of patients with T-cell acute lymphoblastic leukemia. We found previously that TAL1 could interact with transcriptional co-activator and co-repressor complexes possessing histone acetyltransferase and deacetylase activities, respectively. Here, we report that TAL1 is subject to acetylation in vivo and can be acetylated by p300 and the p300/CBP-associated factor P/CAF in vitro. P/CAF-mediated acetylation, which mapped to a lysine-rich motif in the loop region, increased TAL1 binding to DNA while selectively inhibiting its interaction with the transcriptional co-repressor mSin3A. Furthermore, P/CAF protein, TAL1-P/CAF interaction and TAL1 acetylation increased significantly in murine erythroleukemia cells induced to differentiate in culture, while enforced expression of an acetylation-defective P/CAF mutant inhibited endogenous TAL1 acetylation, TAL1 DNA-binding activity, TAL1-directed transcription and terminal differentiation of these cells. These results reveal a novel mechanism by which TAL1 activity is regulated and implicate acetylation of this transcription factor in promotion of erythroid differentiation.

Donor origin of circulating endothelial progenitors after allogeneic bone marrow transplantation.

Endothelial cell precursors circulate in blood and express antigens found on hematopoietic stem cells, suggesting that such precursors might be subject to transplantation. To investigate, we obtained adherence-depleted peripheral blood mononuclear cells from 3 individuals who had received a sex-mismatched allogeneic bone marrow transplant (BMT) and cultured the cells on fibronectin-coated plates with endothelial growth factors. The phenotype of the spindle-shaped cells that emerged in culture was characterized by immunofluorescent staining, and the origin of the cells was determined using a polymerase chain reaction (PCR)-based assay for polymorphic short tandem repeats (STRs). The cells manifested a number of endothelial characteristics-such as von Wlllebrand factor, CD31, and Flk-1/KDR expression; Bandeiraea simplicifolia lectin 1 binding; and acetylated low-density lipoprotein uptake-but lacked expression of certain markers of activation or differentiation, including intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and the epitope for the anti-endothelial cell antibody P1H12. For each patient and at all time points studied (ranging from 5 to 52 months after transplantation), STR-PCR analysis showed that cultured cells and nucleated blood cells came exclusively from the bone marrow donor. These results demonstrate that circulating endothelial progenitors are both transplantable and capable of long-term repopulation of human allogeneic BMT recipients.

Intensified preparative regimens and autologous transplantation in refractory or relapsed intermediate grade non-Hodgkin's lymphoma.

Between September 1986 and June 1998, 99 patients with relapsed or refractory IGL received intensified preparative therapy and underwent autologous transplantation at a single institution. Two intensified preparative regimens were used: cyclophosphamide, etoposide, total body irradiation (CY-VP-TBI) (n = 66) and cyclophosphamide, BCNU, etoposide (CBV) (n = 33). As clinical features and results were not different for the two preparative regimens, results were combined. For all patients undergoing autologous transplantation, 5-year actuarial overall survival (OS) was 34% +/- 6%; 5-year event-free survival (EFS) was 26% +/- 5%. For patients who responded to primary therapy, salvage therapy, or both, OS was 42% +/- 7%; for non-responders to prior therapy, OS was 14% +/- 7%, P < 0.025. OS was better among patients responding to salvage therapy (50% +/- 9%), than among patients who had a complete response to initial therapy, but failed to respond or were untested/unevaluable with respect to salvage therapy (26% +/- 10%; P < 0.025). On multivariate analysis, response to salvage therapy was associated with survival following autologous transplantation (P < 0. 005). Treatment related mortality was 9% overall and only 6% after G-CSF and GM-CSF were introduced into routine clinical practice. High-intensity preparative therapy is highly effective, with acceptable treatment-related mortality, in patients with IGL who have responded to induction therapy, salvage therapy, or both. The best responses are observed in patients responding to salvage therapy. Randomized prospective studies will be needed to further define the role of intensified preparative regimens. Bone Marrow Transplantation (2000) 25, 257-262.

mSin3A regulates murine erythroleukemia cell differentiation through association with the TAL1 (or SCL) transcription factor.

Activation of the TAL1 (or SCL) gene is the most frequent gain-of-function mutation in T-cell acute lymphoblastic leukemia (T-ALL). TAL1 belongs to the basic helix-loop-helix (HLH) family of transcription factors that bind as heterodimers with the E2A and HEB/HTF4 gene products to a nucleotide sequence motif termed the E-box. Reported to act both as an activator and as a repressor of transcription, the mechanisms underlying TAL1-regulated gene expression are poorly understood. We report here that the corepressor mSin3A is associated with TAL1 in murine erythroleukemia (MEL) and human T-ALL cells. Interaction mapping showed that the basic-HLH domain of TAL1 was both necessary and sufficient for TAL1-mSin3A interaction. TAL1 was found, in addition, to interact with the histone deacetylase HDAC1 in vitro and in vivo, and a specific histone deacetylase inhibitor, trichostatin A (TSA), relieved TAL1-mediated repression of an E-box-containing promoter and a GAL4 reporter linked to a thymidine kinase minimal promoter. Further, TAL1 association with mSin3A and HDAC1 declined during dimethyl sulfoxide-induced differentiation of MEL cells in parallel with a decrease in mSin3A abundance. Finally, TSA had a synergistic effect with enforced TAL1 expression in stimulating MEL cells to differentiate, while constitutive expression of mSin3A inhibited MEL cell differentiation. These results demonstrate that a corepressor complex containing mSin3A and HDAC1 interacts with TAL1 and restricts its function in erythroid differentiation. This also has implications for this transcription factor's actions in leukemogenesis.

Mitogen-activated protein kinase mediates erythropoietin-induced phosphorylation of the TAL1/SCL transcription factor in murine proerythroblasts.

Ectopic expression of the basic helix-loop-helix transcription factor TAL1 (or SCL) is the most frequent gain-of-function mutation in T-cell acute lymphoblastic leukaemia. Gene-knockout studies in mice have demonstrated that TAL1 is required for embryonic and adult haematopoiesis, and considerable evidence suggests it also has important functions in terminal erythroid differentiation. We reported previously that TAL1 phosphorylation is stimulated by erythropoietin in splenic proerythroblasts isolated from mice infected with the anaemia-inducing strain of Friend virus and show here the signalling pathway responsible. Erythropoietin was found to stimulate nuclear mitogen-activated protein kinase activity in addition to TAL1 protein phosphorylation, both of which were quantitatively inhibited by the mitogen-activated protein kinase kinase inhibitor PD 098059 and the phosphatidylinositol 3-kinase inhibitor wortmannin. Tryptic phosphopeptide analysis of radiolabelled TAL1 immunoprecipitated from nuclear extracts of Friend virus-induced proerythroblasts revealed that phosphorylation of Ser(122), shown previously to be a substrate for the mitogen-activated protein kinase ERK1 (extracellular signal-regulated protein kinase) in vitro, was specifically, although not exclusively, increased by erythropoietin and inhibited by wortmannin and PD 098059. These results are consistent with an erythropoietin-stimulated signalling pathway in which there is direct activation of a mitogen-activated protein kinase kinase by phosphatidylinositol 3-kinase and identify TAL1 as one of its nuclear targets. These data suggest, in addition, a specific mechanism by which the principal regulator of erythroid differentiation could enhance TAL1 function, in addition to increasing its expression.

p300 functions as a transcriptional coactivator for the TAL1/SCL oncoprotein.

Activation of the TAL1 (or SCL) gene, originally identified through its involvement by a recurrent chromosomal translocation, is the most frequent gain-of-function mutation recognized in T-cell acute lymphoblastic leukemia (T-ALL). The TAL1 proteins contain a basic helix - loop - helix (bHLH) motif characteristic of a large family of transcription factors that control transcription from an E box target element as heterodimers with the E2A- and HEB-encoded gene products. Gene knockout studies in mice indicate that this transcription factor is required for embryonic and adult hematopoiesis, and considerable evidence suggests it has specific functions in terminal erythroid differentiation. We investigated whether the broadly expressed nuclear protein p300, known to function as a coactivator for other bHLH proteins involved in cellular differentiation, also interacts with TAL1. p300 was found to coimmunoprecipitate with Tal1 in extracts from murine erythroleukemia (MEL) cells induced to differentiate with dimethylsulfoxide (DMSO), and p300 and Tal1 were observed in a common E box DNA-binding complex in extracts from differentiating MEL cells. p300 also interacted with Tal1 in protein pulldown assays, suggesting this was a direct interaction. Finally, p300 augmented transcription by Tal1 from an E box-containing promoter and by a GAL4-Tal1 fusion from a promoter containing the GAL4 DNA-binding element. Deletion analysis identified the bHLH domain of Tal1 and amino-terminal sequences of p300 as necessary for p300-stimulated transactivation and Tal1-p300 interaction in vitro. These results indicate that recruitment of the transcriptional coactivator p300 can positively regulate TAL1-directed gene expression. The dependence of their interaction in MEL cells on addition of a differentiation inducer suggests, further, that this TAL1-p300 complex may have an important role in terminal erythroid differentiation.

Retroviral gene therapy in ApoE-deficient mice: ApoE expression in the artery wall reduces early foam cell lesion formation.

BACKGROUND: Apolipoprotein E (apoE) has long been known to play an important role in the clearance of plasma lipoproteins. More recently, a direct role for apoE in delaying atherogenesis has been proposed. Macrophage production of apoE in the artery wall has been demonstrated to provide protection against atherosclerotic lesion development independently from its role in lipoprotein clearance. However, whether macrophage apoE can affect lesion growth at all stages of atherogenesis remains to be established. METHODS AND RESULTS: To evaluate the role of macrophage apoE in different stages of atherogenesis, as well as to establish a novel gene therapy approach to atherosclerotic vascular disease, we used an apoE-expressing retrovirus to transduce apoE-deficient (-/-) bone marrow for transplantation into apoE(-/-) recipient mice. Three weeks after bone marrow transplantation, apoE was expressed from arterial macrophages and was detectable in plasma associated with lipoproteins at 0.5% to 1% of normal levels but did not affect plasma cholesterol levels. We used 2 groups of recipient mice: younger mice with lesions consisting primarily of foam cells and older mice with more advanced lesions. When either the mouse or human apoE transgenes were expressed in mice from 5 to 13 weeks of age, there was a significant reduction in lesion area, whereas no effects were detected in mice that expressed apoE from 10 to 26 weeks of age. CONCLUSIONS: We demonstrate that arterial macrophage apoE secretion can delay atherogenesis if expressed during foam cell formation but is not beneficial during the later stages of atherogenesis. These data also provide evidence that apoE transgene expression from arterial macrophages may have therapeutic applications.

Identification of mutations in two major mRNA isoforms of the Chediak-Higashi syndrome gene in human and mouse.

Chediak-Higashi syndrome is an autosomal recessive, immune deficiency disorder of human (CHS) and mouse (beige, bg) that is characterized by abnormal intracellular protein transport to, and from, the lysosome. Recent reports have described the identification of homologous genes that are mutated in human CHS and bg mice. Here we report the sequences of two major mRNA isoforms of the CHS gene in human and mouse. These isoforms differ both in size and in sequence at the 3' end of their coding domains, with the smaller isoform (approximately 5.8 kb) arising from incomplete splicing and reading through an intron. These mRNAs also differ in tissue distribution of transcription and in predicted biological properties. Novel mutations were identified within the region of the coding domain common to both isoforms in three CHS patients: C-->T transitions that generated stop codons (R50X and Q1029X) were found in two patients, and a novel frameshift mutation (deletion of nucleotides 3073 and 3074 of the coding domain) was found in a third. Northern blots of lymphoblastoid mRNA from CHS patients revealed loss of the largest transcript (approximately 13.5 kb) in two of seven CHS patients, while the small mRNA was undiminished in abundance. These results suggest that the small isoform alone cannot complement Chediak-Higashi syndrome.

Target-dependent effect of phosphorylation on the DNA binding activity of the TAL1/SCL oncoprotein.

Activation of the TAL1 (or SCL) gene, initially identified through its involvement by a recurrent chromosomal translocation, is the most frequent gain-of-function mutation recognized in T-cell acute lymphoblastic leukemia. The translational products of this gene contain the basic domain helix-loop-helix motif characteristic of a family of transcription factors that bind to a consensus nucleotide sequence termed the E-box. Previous work established that the TAL1 proteins are phosphorylated exclusively on serine and identified Ser122 as a substrate for the mitogen-activated protein kinase ERK-1. We provide evidence that an additional serine residue, Ser172, located in a conserved region proximal to the DNA binding domain and sharing homology with a similarly positioned sequence in the HLH oncoprotein LYL1, can be phosphorylated in vitro and in vivo by the catalytic subunit of cAMP-dependent protein kinase. Phosphorylation was found to alter TAL1 DNA binding activity in a target-dependent manner that was influenced by both the specific CANNTG E-box core motif and its flanking sequences. In contrast, the ability of TAL1 to interact with the E2A gene product E12 and its subcellular localization in transfected COS cells were unaffected by Ser172 phosphorylation. These results suggest this serine residue has a regulatory function and indicate a mechanism by which phosphorylation could affect DNA binding site discrimination.