Biomedical subjects

Jon C Aster

Publications and source records attributed to Jon C Aster.

At least 37 records · Page 2Linked to original sources

PubMed2005

Notch signaling controls the generation and differentiation of early T lineage progenitors.

Signaling by the transmembrane receptor Notch is critical for T lineage development, but progenitor subsets that first receive Notch signals have not been defined. Here we identify an immature subset of early T lineage progenitors (ETPs) in the thymus that expressed the tyrosine kinase receptor Flt3 and had preserved B lineage potential at low progenitor frequency. Notch signaling was active in ETPs and was required for generation of the ETP population. Additionally, Notch signals contributed to the subsequent differentiation of ETPs. In contrast, multipotent hematopoietic progenitors circulated in the blood even in the absence of Notch signaling, suggesting that critical Notch signals during early T lineage development are delivered early after thymic entry.

Animals↗

PubMed2005

NFkappaB activity, function, and target-gene signatures in primary mediastinal large B-cell lymphoma and diffuse large B-cell lymphoma subtypes.

Primary mediastinal large B-cell lymphoma (MLBCL) shares important clinical and molecular features with classic Hodgkin lymphoma, including nuclear localization of the nuclear factor kappaB (NFkappaB) subunit c-REL (reticuloendotheliosis viral oncogene homolog) in a pilot series. Herein, we analyzed c-REL subcellular localization in additional primary MLBCLs and characterized NFkappaB activity and function in a MLBCL cell line. The new primary MLBCLs had prominent c-REL nuclear staining, and the MLBCL cell line exhibited high levels of NFkappaB binding activity. MLBCL cells expressing a superrepressor form of inhibitor of kappa B alpha signaling (IkappaB alpha) had a markedly higher rate of apoptosis, implicating constitutive NFkappaB activity in MLBCL cell survival. The transcriptional profiles of newly diagnosed primary MLBCLs and diffuse large B-cell lymphomas (DLBCLs) were then used to characterize the NFkappaB target gene signatures of MLBCL and specific DLBCL subtypes. MLBCLs expressed increased levels of NFkappaB targets that promote cell survival and favor antiapoptotic tumor necrosis factor alpha (TNFalpha) signaling. In contrast, activated B cell (ABC)-like DLBCLs had a more restricted, potentially developmentally regulated, NFkappaB target gene signature. Of interest, the newly characterized host response DLBCL subtype had a robust NFkappaB target gene signature that partially overlapped that of primary MLBCL. In this large series of primary MLBCLs and DLBCLs, NFkappaB activation was not associated with amplification of the cREL locus, suggesting alternative pathogenetic mechanisms.

Apoptosis↗

PubMed2005

BRAF mutations are sufficient to promote nevi formation and cooperate with p53 in the genesis of melanoma.

Melanoma is the most lethal form of skin cancer, and the incidence and mortality rates are rapidly rising. Epidemiologically, high numbers of nevi (moles) are associated with higher risk of melanoma . The majority of melanomas exhibit activating mutations in the serine/threonine kinase BRAF . BRAF mutations may be critical for the initiation of melanoma ; however, the direct role of BRAF in nevi and melanoma has not been tested in an animal model. To directly test the role of activated BRAF in nevus and melanoma development, we have generated transgenic zebrafish expressing the most common BRAF mutant form (V600E) under the control of the melanocyte mitfa promoter. Expression of mutant, but not wild-type, BRAF led to dramatic patches of ectopic melanocytes, which we have termed fish (f)-nevi. Remarkably, in p53-deficient fish, activated BRAF induced formation of melanocyte lesions that rapidly developed into invasive melanomas, which resembled human melanomas and could be serially transplanted. These data provide direct evidence that BRAF activation is sufficient for f-nevus formation, that BRAF activation is among the primary events in melanoma development, and that the p53 and BRAF pathways interact genetically to produce melanoma.

Animals↗

PubMed2005

TRAF1 expression and c-Rel activation are useful adjuncts in distinguishing classical Hodgkin lymphoma from a subset of morphologically or immunophenotypically similar lymphomas.

We demonstrate that the expression of TRAF1 and activated c-Rel, two proteins that function in signaling events downstream of activated CD30 in Reed-Sternberg cells, reliably distinguish classical Hodgkin lymphoma from anaplastic large cell lymphoma, nodular lymphocyte predominant Hodgkin lymphoma, and nonmediastinal diffuse large B-cell lymphoma. By immunohistochemistry, we found strong TRAF1 staining in 21 of 25 cases of classical Hodgkin lymphoma. In contrast, strong TRAF1 staining was present in only 1 of 17 cases of anaplastic large cell lymphoma, 0 of 15 cases of lymphocyte predominant Hodgkin lymphoma, and 2 of 36 cases of nonmediastinal diffuse large B-cell lymphoma. Nuclear staining for c-Rel, a pattern consistent with NFkappaB activation, was observed in the Reed-Sternberg cells in 23 of 25 cases of classical Hodgkin lymphoma but only in 1 of 15 cases of anaplastic large cell lymphoma and 3 of 15 cases of nodular lymphocyte predominant Hodgkin lymphoma. A heterogeneous pattern of subcellular c-Rel localization was found in nonmediastinal diffuse large B-cell lymphoma. Taken together, the combination of strong cytoplasmic TRAF1 expression and nuclear c-Rel was present in 80% of cases of classical Hodgkin lymphoma (n = 25) but in only 3% of cases of the other malignant lymphomas tested (n = 62). Thus, the differential expression patterns of downstream components in the CD30 signaling pathway may prove a useful adjunct in distinguishing cases of classical Hodgkin lymphoma from other malignant lymphomas in routine clinical practice.

Biomarkers, Tumor↗

PubMed2005

Deregulated NOTCH signaling in acute T-cell lymphoblastic leukemia/lymphoma: new insights, questions, and opportunities.

Recent work has shown that the majority of human acute T-cell lymphoblastic leukemias and lymphomas (T-ALL) have gain-of-function mutations in NOTCH1, a type I transmembrane receptor that normally signals through a gamma-secretase-dependent mechanism that relies on ligand-induced regulated intramembranous proteolysis. Cleavage by gamma-secretase releases the intracellular domain of NOTCH1 (ICN1), permitting it to translocate to the nucleus and form a short-lived transcriptional activation complex that is essential for normal T-cell development. Two types of mutations are prevalent in human T-ALL: extracellular domain mutations that increase ICN1 production and C-terminal mutations that sustain ICN1 action. Inhibitors of ICN1 production and activity abrogate the growth of established T-ALL cell lines, and a clinical trial of a NOTCH pathway inhibitor in patients with refractory T-ALL has opened recently. These insights raise a number of new questions relevant to T-ALL pathogenesis and offer exciting opportunities for rational targeted therapy.

Dimerization↗

PubMed2004

Molecular profiling of diffuse large B-cell lymphoma identifies robust subtypes including one characterized by host inflammatory response.

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease with recognized variability in clinical outcome, genetic features, and cells of origin. To date, transcriptional profiling has been used to highlight similarities between DLBCL tumor cells and normal B-cell subtypes and associate genes and pathways with unfavorable outcome. To identify robust and highly reproducible DL-BCL subtypes with comprehensive transcriptional signatures, we used a large series of newly diagnosed DLBCLs, whole genome arrays, and multiple clustering methods. Tumors were also analyzed for known common genetic abnormalities in DLBCL. There were 3 discrete subsets of DLBCL-"oxidative phosphorylation," "B-cell receptor/proliferation," and "host response" (HR)-identified characterized using gene set enrichment analysis and confirmed in an independent series. HR tumors had increased expression of T/natural killer cell receptor and activation pathway components, complement cascade members, macrophage/dendritic cell markers, and inflammatory mediators. HR DLB-CLs also contained significantly higher numbers of morphologically distinct CD2+/CD3+ tumor-infiltrating lymphocytes and interdigitating S100+/gamma interferon-induced lysosomal transferase-positive (GILT+) CD1a-/CD123- dendritic cells. The HR cluster shared features of histologically defined T-cell/histiocyte-rich B-cell lymphoma, including fewer genetic abnormalities, younger age at presentation, and frequent splenic and bone marrow involvement. These studies identify tumor microenvironment and host inflammatory response as defining features in DLBCL and suggest rational treatment targets in specific DLBCL subsets.

Cluster Analysis↗

PubMed2004

Midline carcinoma of children and young adults with NUT rearrangement.

PURPOSE: A balanced chromosomal translocation, t(15;19), resulting in the BRD4-NUT oncogene, has been identified in a lethal carcinoma of young people, a disease described primarily in case reports. We sought to amass a more definitive series of tumors with NUT and/or BRD4 gene rearrangements and to determine distinct clinicopathologic features. PATIENTS AND METHODS: Carcinomas (N = 98) in young individuals (median age, 32.5 years) were screened for NUT and BRD4 rearrangements using dual-color fluorescence in situ hybridization. Four published carcinomas with BRD4 and NUT rearrangements were also evaluated. Immunophenotypic analyses were performed. RESULTS: Eleven tumors had NUT gene rearrangements, including eight with BRD4-NUT fusions and three with novel rearrangements, which were designated as NUT variant. All NUT-rearranged carcinomas (NRCs) arose from midline epithelial structures, including the first example arising below the diaphragm. Patients were young (median age, 17.6 years). Squamous differentiation (seen in 82% of NRCs) was particularly striking in NUT-variant cases. In this first description of NUT-variant carcinomas, the average survival (96 weeks, n = 3) was longer than for BRD4-NUT carcinomas (28 weeks, n = 8). Strong CD34 expression was found in six of 11 NRCs but in zero of 45 NUT wild-type carcinomas. CONCLUSION: NRCs arise from midline structures in young people, and NRCs with BRD4-NUT are highly lethal, despite intensive therapies. NUT-variant carcinomas might have a less fulminant clinical course than those with BRD4-NUT fusions. CD34 expression is characteristic in NRCs and, therefore, holds promise as a diagnostic test for this distinctive clinicopathologic entity.

Adolescent↗

PubMed2004

Activating mutations of NOTCH1 in human T cell acute lymphoblastic leukemia.

Very rare cases of human T cell acute lymphoblastic leukemia (T-ALL) harbor chromosomal translocations that involve NOTCH1, a gene encoding a transmembrane receptor that regulates normal T cell development. Here, we report that more than 50% of human T-ALLs, including tumors from all major molecular oncogenic subtypes, have activating mutations that involve the extracellular heterodimerization domain and/or the C-terminal PEST domain of NOTCH1. These findings greatly expand the role of activated NOTCH1 in the molecular pathogenesis of human T-ALL and provide a strong rationale for targeted therapies that interfere with NOTCH signaling.

Adolescent↗

PubMed2004

JAGGED1 expression is associated with prostate cancer metastasis and recurrence.

Recent studies suggest that NOTCH signaling can promote epithelial-mesenchymal transitions and augment signaling through AKT, an important growth and survival pathway in epithelial cells and prostate cancer in particular. Here we show that JAGGED1, a NOTCH receptor ligand, is significantly more highly expressed in metastatic prostate cancer as compared with localized prostate cancer or benign prostatic tissues, based on immunohistochemical analysis of JAGGED1 expression in human tumor samples from 154 men. Furthermore, high JAGGED1 expression in a subset of clinically localized tumors was significantly associated with recurrence, independent of other clinical parameters. These findings support a model in which dysregulation of JAGGED1 protein levels plays a role in prostate cancer progression and metastasis and suggest that JAGGED1 may be a useful marker in distinguishing indolent and aggressive prostate cancers.

Adult↗

PubMed2004

Mastermind critically regulates Notch-mediated lymphoid cell fate decisions.

During lymphoid development, Notch1 plays a critical role in the T-cell/B-cell lineage decision, while Notch2 is essential for marginal zone B-cell (MZB) development. Notch pathway activation induces translocation of intracellular Notch (ICN) to the nucleus, where it interacts with the transcription factor CSL (CBF1/RBP-Jk, Suppressor of Hairless, Lag-1). In vitro, ICN binds Mastermind-like proteins, which act as potent Notch coactivators. Three MAML family members (MAML1-3) have been identified in mammals, but their importance in vivo is unknown. To investigate the function of MAMLs in hematopoietic development, we introduced a dominant negative (DN) mutant of MAML1, capable of inhibiting Notch1-4, in murine hematopoietic stem cells. DNMAML1 resulted in early inhibition of T-cell development and the appearance of intrathymic B cells, phenotypes consistent with Notch1 inhibition. The T-cell differentiation block was as profound as that produced by enforced expression of the Notch modulator Deltex1. In DNMAML1-transduced spleen cells, a dramatic decrease in MZB cells was present, consistent with Notch2 inhibition. In contrast, Deltex1 did not decrease MZB cell numbers. These results suggest a critical role for MAMLs during Notch-mediated cell fate decisions in vivo and indicate that DNMAML1, but not Deltex1, can be used to interfere with the function of multiple Notch family members.

Animals↗

PubMed2004

Experimental rhesus lymphocryptovirus infection in immunosuppressed macaques: an animal model for Epstein-Barr virus pathogenesis in the immunosuppressed host.

To develop a model for Epstein-Barr virus (EBV) pathogenesis in immunosuppressed hosts, we studied experimental infections of immunocompetent versus SHIV 89.6P-infected, immunosuppressed rhesus macaques with the EBV-related rhesus lymphocryptovirus (LCV). Primary LCV infection after oral inoculation of 4 immunocompetent animals was characterized by an acute viremia and seroconversion followed by asymptomatic LCV persistence. Four immunosuppressed macaques infected orally with LCV failed to develop an LCV-specific humoral response and viremia was more pronounced, but there was no evidence of LCV-induced lymphoproliferative disease. A more aggressive primary challenge was administered by intravenous inoculation of 10(8) autologous, LCV-immortalized B cells in 4 additional immunosuppressed animals. Two animals with modest immunosuppression remained asymptomatic, and 1 of 2 severely immunosuppressed animals developed an aggressive, monoclonal LCV-positive lymphoma. These studies demonstrate the potential for lymphomagenesis in an experimental model system for EBV infection and underscore the strength and depth of immune control in limiting LCV-induced lymphoproliferative disease.

Animals↗

PubMed2004

Notch oncoproteins depend on gamma-secretase/presenilin activity for processing and function.

During normal development Notch receptor signaling is important in regulating numerous cell fate decisions. Mutations that truncate the extracellular domain of Notch receptors can cause aberrant signaling and promote unregulated cell growth. We have examined two types of truncated Notch oncoproteins that arise from proviral insertion into the Notch4 gene (Notch4/int-3) or a chromosomal translocation involving the Notch1 gene (TAN-1). Both Notch4/int-3 and TAN-1 oncoproteins lack most or all of their ectodomain. Normal Notch signaling requires gamma-secretase/presenilin-mediated proteolytic processing, but whether Notch oncoproteins are also dependent on gamma-secretase/presenilin activity is not known. We demonstrate that Notch4/int-3-induced activation of the downstream transcription factor, CSL, is abrogated in cells deficient in presenilins or treated with a pharmacological inhibitor of gamma-secretase/presenilins. Furthermore, we find that both Notch4/int-3 and TAN-1 accumulate at the cell surface, where presenilin-dependent cleavage occurs, when gamma-secretase/presenilin activity is inhibited. gamma-Secretase/presenilin inhibition effectively blocks cellular responses to Notch4/int-3, but not TAN-1, apparently because some TAN-1 polypeptides lack transmembrane domains and do not require gamma-secretase/presenilin activity for nuclear access. These studies highlight potential uses and limitations of gamma-secretase/presenilin inhibitors in targeted therapy of Notch-related neoplasms.

Adenoviridae↗

PubMed2004

Multiple niches for Notch in cancer: context is everything.

Notch receptor signaling has very distinctive roles in cancers originating from different types of cells that reflect its complex functions in normal tissue development and homeostasis. For example, recent studies have shown that Notch signals are oncogenic in pre-T cells but suppress tumor development in keratinocytes. Notch signaling contributes to pre-malignant metaplastic changes that precede pancreatic carcinoma, and it is also likely to be involved in other forms of metaplasia. In addition, several viral oncoproteins and chromosomal translocations target one or more components of a Notch transcriptional activation complex.

Humans↗

PubMed2004

T cell acute lymphoblastic leukemia/lymphoma: a human cancer commonly associated with aberrant NOTCH1 signaling.

PURPOSE OF REVIEW: Although constitutively activated forms of the NOTCH1 receptor are potent inducers of T cell acute lymphoblastic leukemia/lymphoma when expressed in the bone marrow stem cells of mice, the known involvement of NOTCH1 in human T cell acute lymphoblastic leukemia/lymphoma has been restricted to very rare tumors associated with a (7;9) chromosomal translocation involving the NOTCH1 gene. This picture has changed dramatically in the past year with the discovery of frequent mutations involving NOTCH1 in human T cell acute lymphoblastic leukemia/lymphoma. RECENT FINDINGS: NOTCH1 point mutations, insertions, and deletions producing aberrant increases in NOTCH1 signaling are frequently present in both childhood and adult T cell acute lymphoblastic leukemia/lymphoma and are detected in tumors from all major molecular subtypes. These observations are particularly important in the light of experiments using human and murine T cell acute lymphoblastic leukemia/lymphoma cell lines indicating that NOTCH1 signals are required for sustained growth and, in a subset of lines, survival. This inference is based in part on experiments conducted with small molecule inhibitors of gamma-secretase, a protease required for normal NOTCH signal transduction and the activity of the mutated forms of NOTCH1 found commonly in human T cell acute lymphoblastic leukemia/lymphoma. SUMMARY: These findings support a central role for aberrant NOTCH signaling in the pathogenesis of human T cell acute lymphoblastic leukemia/lymphoma, and they provide a rationale for trials of NOTCH inhibitors, such as gamma-secretase antagonists, in this aggressive human malignancy.

Amyloid Precursor Protein Secretases↗

PubMed2004

Molecular evidence for rhesus lymphocryptovirus infection of epithelial cells in immunosuppressed rhesus macaques.

Epstein-Barr virus (EBV) is a human oncogenic herpesvirus associated with epithelial cell and B-cell malignancies. EBV infection of B lymphocytes is essential for acute and persistent EBV infection in humans; however, the role of epithelial cell infection in the normal EBV life cycle remains controversial. The rhesus lymphocryptovirus (LCV) is an EBV-related herpesvirus that naturally infects rhesus macaques and can be used experimentally to model persistent B-cell infection and B-cell lymphomagenesis. We now show that the rhesus LCV can infect epithelial cells in immunosuppressed rhesus macaques and can induce epithelial cell lesions resembling oral hairy leukoplakia in AIDS patients. Electron microscopy, immunohistochemistry, and DNA-RNA in situ hybridization were used to identify the presence of a lytic rhesus LCV infection in these proliferative, hyperkeratotic, or parakeratotic epithelial cell lesions. These studies demonstrate that the rhesus LCV has tropism for epithelial cells, in addition to B cells, and is a relevant animal model system for studying the role of epithelial cell infection in EBV pathogenesis.

Animals↗

PubMed2004

Notch subunit heterodimerization and prevention of ligand-independent proteolytic activation depend, respectively, on a novel domain and the LNR repeats.

Notch proteins are transmembrane receptors that participate in a highly conserved signaling pathway that regulates morphogenesis in metazoans. Newly synthesized Notch receptors are proteolytically cleaved during transit to the cell surface, creating heterodimeric mature receptors comprising noncovalently associated extracellular (N(EC)) and transmembrane (N) subunits. Ligand binding activates Notch by inducing two successive proteolytic cleavages, catalyzed by metalloproteases and gamma-secretase, respectively, that permit the intracellular portion of N to translocate to the nucleus and activate transcription of target genes. Prior work has shown that the presence of N(EC) prevents ligand-independent activation of N, but the mechanisms involved are poorly understood. Here, we define the roles of two regions at the C-terminal end of N(EC) that participate in maintaining the integrity of resting Notch receptors through distinct mechanisms. The first region, a hydrophobic, previously uncharacterized portion of N(EC), is sufficient to form stable complexes with the extracellular portion of N. The second region, consisting of the three Lin12/Notch repeats, is not needed for heterodimerization but acts to protect N from ligand-independent cleavage by metalloproteases. Together, these two contiguous regions of N(EC) impose crucial restraints that prevent premature Notch receptor activation.

Amino Acid Motifs↗

PubMed2004

Functional diversity of notch family genes in fetal lung development.

In Drosophila, developmental signaling via the transmembrane Notch receptor modulates branching morphogenesis and neuronal differentiation. To determine whether the notch gene family can regulate mammalian organogenesis, including neuroendocrine cell differentiation, we evaluated developing murine lung. After demonstrating gene expression for notch-1, notch-2, notch-3, and the Notch ligands jagged-1 and jagged-2 in embryonic mouse lung, we tested whether altering expression of these genes can modulate branching morphogenesis. Branching of embryonic day (E) 11.5 lung buds increased when they were treated with notch-1 antisense oligodeoxynucleotides in culture compared with the corresponding sense controls, whereas notch-2, notch-3, jagged-1, or jagged-2 antisense oligos had no significant effect. To assess cell differentiation, we immunostained lung bud cultures for the neural/neuroendocrine marker PGP9.5. Antisense to notch-1 or jagged-1 markedly increased numbers of PGP9.5-positive neuroendocrine cells alone without affecting neural tissue, whereas only neural tissue was promoted by notch-3 antisense in culture. There was no significant effect on cell proliferation or apoptosis in these antisense experiments. Cumulatively, these observations suggest that interactions between distinct Notch family members can have diverse tissue-specific regulatory functions during development, arguing against simple functional redundancy.

Analysis of Variance↗

PubMed2003

F3/contactin acts as a functional ligand for Notch during oligodendrocyte maturation.

Axon-derived molecules are temporally and spatially required as positive or negative signals to coordinate oligodendrocyte differentiation. Increasing evidence suggests that, in addition to the inhibitory Jagged1/Notch1 signaling cascade, other pathways act via Notch to mediate oligodendrocyte differentiation. The GPI-linked neural cell recognition molecule F3/contactin is clustered during development at the paranodal region, a vital site for axoglial interaction. Here, we show that F3/contactin acts as a functional ligand of Notch. This trans-extracellular interaction triggers gamma-secretase-dependent nuclear translocation of the Notch intracellular domain. F3/Notch signaling promotes oligodendrocyte precursor cell differentiation and upregulates the myelin-related protein MAG in OLN-93 cells. This can be blocked by dominant negative Notch1, Notch2, and two Deltex1 mutants lacking the RING-H2 finger motif, but not by dominant-negative RBP-J or Hes1 antisense oligonucleotides. Expression of constitutively active Notch1 or Notch2 does not upregulate MAG. Thus, F3/contactin specifically initiates a Notch/Deltex1 signaling pathway that promotes oligodendrocyte maturation and myelination.

Animals↗