Showing papers by "David Baltimore published in 1991"

Id proteins Id1 and Id2 selectively inhibit DNA binding by one class of helix-loop-helix proteins

Abstract: The DNA binding activities of some basic region and putative helix-loop-helix (bHLH)-containing transcriptional factors can be inhibited by the Id protein. Because Id contains the HLH motif for dimerization but not the basic amino acid region for DNA binding, heterodimers of Id with bHLH transcriptional factors may not bind to DNA. We have isolated and characterized the gene and cDNA clones for a new Id protein, designated Id2. The Id2 protein contains a helix-loop-helix motif similar to that of the previously described Id protein (referred to here as Id1), but the two proteins are different elsewhere. Id1 and Id2 are encoded by two unlinked genes, as shown by chromosome mapping. The two Id proteins have similar inhibitory activities. They selectively bind to and inhibit the function of one set of bHLH proteins, typified by E2A.E47 and E2B.m3, but not that of the other set, including TFE3, USF, and AP4. The Id proteins also homodimerize poorly. Expression of both Id genes is down-regulated during differentiation in a variety of cell types.

The role of Tat in the human immunodeficiency virus life cycle indicates a primary effect on transcriptional elongation.

Abstract: The mechanism of Tat transactivation was studied by treating cell lines containing Tat-defective viruses with purified Tat protein. These cell lines constitutively produce very low levels of virus in the absence of Tat, as measured by p24 antigen levels. Virus production can be increased greater than 30,000-fold by adding exogenous Tat. Tat addition increases mRNA levels early in the viral life cycle, and Tat is required for Rev function to become evident. There is no evidence for a translational effect of Tat. Nuclear run-on experiments show that the increase in mRNA levels is due to an increased efficiency of elongation of nascent transcripts. These results suggest that Tat may be a gene-specific elongation factor.

Virus-transformed pre-B cells show ordered activation but not inactivation of immunoglobulin gene rearrangement and transcription.

Abstract: Virus-transformed pre-B cells undergo ordered immunoglobulin (Ig) gene rearrangements during culture. We devised a series of highly sensitive polymerase chain reaction assays for Ig gene rearrangement and unrearranged Ig gene segment transcription to study both the possible relationship between these processes in cultured pre-B cells and the role played by heavy (H) chain (mu) protein in regulating gene rearrangement. Our analysis of pre-B cell cultures representing various stages of maturity revealed that transcription of each germline Ig locus precedes or is coincident with its rearrangement. Cell lines containing one functional rearranged H chain allele, however, continue to transcribe and to rearrange the allelic, unrearranged H chain locus. These cell lines appear to initiate but not terminate rearrangement events and therefore provide information about the requirements for activating rearrangement but not about allelic exclusion mechanisms.

Differentiation requires continuous regulation.

Abstract: Article de synthese traitant des mecanismes biochimiques et genetiques regulant le phenomene de differenciation cellulaire pour 2 especes d'insectes presentant ou non des mutations dans leur genome

Helix-loop-helix transcription factor E47 activates germ-line immunoglobulin heavy-chain gene transcription and rearrangement in a pre-T-cell line.

Abstract: E47 is a helix-loop-helix transcription factor that binds to sites in the immunoglobulin heavy-chain and K light-chain gene enhancers. Other proteins of this type are involved in cell-type determination. A possible role for E47 in B-cell development was tested by overexpressing a cDNA encoding E47 in the pre-T-cell line 2017. We found a dramatic activation of a germ-line heavy-chain gene transcript in these stable transfectants and an equally large induction of immunoglobulin D-to-J rearrangement, the first recognized step in B-cell development. Germ-line K light-chain gene transcription and rearrangement were unaffected, but transcription of the recombination-activating genes RAG-1 and RAG-2 and the lymphoid-specific transcription factor Oct-2 was increased. These T cells did not transcribe their rearranged DJ alleles, however, and failed to progress to the next stage of heavy-chain gene assembly, V-to-DJ rearrangement. Because transcription factor E47 can induce pre-T cells to carry out events of B-cell differentiation, it may be a crucial determinant of the earliest stages of B-cell development.

Rel-associated pp40: an inhibitor of the rel family of transcription factors.

Abstract: The Rel-associated protein pp40 is functionally related to I kappa B, an inhibitor of the transcription factor NF-kappa B. Purified pp40 inhibits the DNA binding activity of the NF-kappa B protein complex (p50:p65 heterodimers), p50:c-Rel heteromers, and c-Rel homodimers. The sequence of the complementary DNA encoding pp40 revealed similarity to the gene encoding MAD-3, a protein with mammalian I kappa B-like activity. Protein sequencing of I kappa B purified from rabbit lung confirmed that MAD-3 encodes a protein similar to I kappa B. The sequence similarity between MAD-3 and pp40 includes a casein kinase II and consensus tyrosine phosphorylation site, as well as five repeats of a sequence found in the human erythrocyte protein ankyrin. These results suggest that rel-related transcription factors, which are capable of cytosolic to nuclear translocation, may be held in the cytosol by interaction with related cytoplasmic anchor molecules.

The human t(1;19) translocation in pre-B ALL produces multiple nuclear E2A-Pbx1 fusion proteins with differing transforming potentials.

Abstract: The t(1;19) translocation that characterizes 25% of pediatric pre-B cell acute lymphoblastic leukemias (pre-B ALL) produces a chimeric gene, joining 5' sequences that encode a transcriptional activator domain of E2A with 3' sequences that, in part, encode a homeo box domain of a new gene called pbx1. Two E2A-pbx1 transcripts have been cloned. They encode the putative fusion proteins, p85(E2A-Pbx1) and p77(E2A-Pbx1), which differ in Pbx1 sequences alone, containing unique carboxyl termini whose sequences diverge after the Pbx1 homeo box. In this study, an antiserum to Pbx1 was used to investigate the identity and abundance of E2A-Pbx1 fusion proteins in both the pre-B ALL cell line, 697, and in cryopreserved leukemic bone marrow cells, obtained from six children with t(1;19)-positive pre-B ALL. Five species of E2A-Pbx1 proteins were identified in all cells containing t(1;19), two of which were indistinguishable from in vitro-translated p85(E2A-Pbx1) and p77(E2A-Pbx1). To assess the biological properties of p85(E2A-Pbx1) and p77(E2A-Pbx1) in fibroblasts, the cDNAs encoding these proteins were cloned into retroviral vectors, and each was introduced into NIH-3T3 cells. Both p85(E2A-Pbx1) and p77(E2A-Pbx1) are localized in the nucleus, and expression of either resulted in malignant conversion of NIH-3T3 cells as assayed by tumor formation in nude mice. When scored by focus formation, density-independent growth, and growth in agar assays, p77(E2A-Pbx1) was a much more potent transforming protein than was p85(E2A-Pbx1). Because subtle mutations in p85(E2A-Pbx1) converted its transforming activity into that of p77(E2A-Pbx1), we suggest that a sequence within the unique carboxyl terminus of p85(E2A-Pbx1) serves to negatively regulate its biochemical activity.

Kinetics of expression of multiply spliced RNA in early human immunodeficiency virus type 1 infection of lymphocytes and monocytes

Abstract: The genome of human immunodeficiency virus type 1 (HIV-1) encodes at least six proteins involved in regulation as well as the structural proteins Gag, Pol, and Env. The interplay of the various regulators generates early and late transcriptional phases in the HIV-1 life cycle; the earliest RNA is enriched in subgenomic species, and the genomic transcript appears at the later stage of infection. We investigated the nature of the mRNAs expressed in the early stages of infection when the 2 kilobase subgenomic species predominate. RNA was analyzed in the early phase of a one-step growth cycle of HIV-1 infection in T-lymphoid and monocytic cell lines by using PCR amplification of in vitro-synthesized viral cDNAs. In both cell lines, expression of Tat-, Rev-, and Nef-specific messages appeared simultaneously and could be detected within 8-12 hr of infection but in different amounts with a predominance of Nef-specific message. The Env-specific message could be detected as early as the Rev-specific message, indicating that expression of at least small amounts of the singly spliced message could occur before the accumulation of Rev.

Activation of phosphatidylinositol 3-kinase in cells expressing abl oncogene variants.

Abstract: A phosphoinositide kinase specific for the D-3 position of the inositol ring, phosphatidylinositol (PI) 3-kinase, associates with activated receptors for platelet-derived growth factor, insulin, and colony-stimulating factor 1, with products of the oncogenes src, fms, yes, crk, and with polyomavirus middle T antigen. Efficient fibroblast transformation by proteins of the abl and src oncogene families requires activation of their protein-tyrosine kinase activity and membrane association via an amino-terminal myristoylation. We have demonstrated that the PI 3-kinase directly associates with autophosphorylated, activated protein-tyrosine kinase variants of the abl protein. In vivo, this association leads to accumulation of the highly phosphorylated products of PI 3-kinase, PI-3,4-bisphosphate and PI-3,4,5-trisphosphate, only in myristoylated, transforming abl protein variants. Myristoylation thus appears to be required to recruit PI 3-kinase activity to the plasma membrane for in vivo activation and correlates with the mitogenicity of the abl protein variants.

The noncatalytic src homology region 2 segment of abl tyrosine kinase binds to tyrosine-phosphorylated cellular proteins with high affinity

Abstract: Several proteins implicated in the regulation of cell proliferation contain a common noncatalytic domain, src homology region 2 (SH2). We have used the bacterially expressed SH2 domain of abl protein-tyrosine kinase to evaluate the ability of this domain to bind to cellular proteins. ablSH2 specifically bound to a number of tyrosine-phosphorylated proteins from cells transformed by tyrosine kinase oncogenes in a filter-binding assay and to a subset of those proteins in solution. The SH2 probe bound almost exclusively to tyrosine-phosphorylated proteins, and binding was eliminated by dephosphorylation of cell proteins. Free phosphotyrosine could partially disrupt SH2 binding, suggesting that phosphotyrosine is directly involved in the binding interaction. These results demonstrate that an SH2 domain is sufficient to confer direct, high-affinity phosphotyrosine-dependent binding to proteins and suggest a general role for SH2 domains in cellular signaling pathways.

B-cell- and myocyte-specific E2-box-binding factors contain E12/E47-like subunits.

Abstract: Recent studies have identified a family of DNA-binding proteins that share a common DNA-binding and dimerization domain with the potential to form a helix-loop-helix (HLH) structure. Various HLH proteins can form heterodimers that bind to a common DNA sequence, termed the E2-box. We demonstrate here that E2-box-binding B-cell- and myocyte-specific nuclear factors contain subunits which are identical or closely related to ubiquitously expressed (E12/E47) HLH proteins. These biochemical function for E12/E47-like molecules in mammalian differentiation, similar to the genetically defined function of daughterless in Drosophila development.

Blast crisis in a murine model of chronic myelogenous leukemia.

Abstract: The P210bcr/abl protein is produced in cells from patients with Philadelphia chromosome-positive chronic myelogenous leukemia (CML). Retroviral transfer of the gene encoding P210bcr/abl into murine bone marrow induces a granulocytic leukemia that models the chronic phase of human CML. We have transferred the leukemic clone to syngeneic animals, albeit with surprising inefficiency, and have observed CML and clonally related acute leukemias of lymphoid or myeloid phenotype in some transplant recipients. These data show that murine CML can result from retroviral transfer of the bcr/abl gene into pluripotent hematopoietic stem cells, that infected clones repopulate poorly after adoptive transfer, and that these clones can give rise to acute leukemia, reflecting evolution to a phase resembling blast crisis in the human disease.

Mechanism of leukemogenesis induced by mink cell focus-forming murine leukemia viruses.

Abstract: The Friend or Moloney mink cell focus-forming (MCF) virus encodes a recombinant-type envelope glycoprotein, gp 70, that is closely related to the membrane glycoprotein, gp55, of Friend spleen focus-forming virus (SFFV). We have shown previously that gp55 has the ability to activate cell growth by binding to the cellular receptor for erythropoietin. Here we show that gp70 encoded by either the Friend of Moloney MCF virus also binds to the erythropoietin receptor and that coexpression of the receptor and gp70 in an interleukin-3 (IL-3)-dependent cell line can activate IL-3-independent growth. Furthermore, when the cDNA for the human IL-2 receptor beta chain, which is related by sequence to the erythropoietin receptor, was introduced into this cell line, it became growth factor independent after infection either with SFFV or with one of the two MCF viruses but not with an ecotropic virus. Based on these observations, we propose a mechanism for the early stage of luekemogenesis induced by the MCF-type murine leukemia viruses.

Silencing of the expression of the immunoglobulin kappa gene in non-B cells.

Abstract: Although the activating factor NF-_K B can be present in the nucleus of many cell types, transcription and rearrangement of the immunoglobulin kappa chain gene is restricted to cells of the B lineage. Part of this specificity is determined by sequences within the major intron of the kappa gene that specifically silence gene expression in non-B cells (T cells and HeLa cells). These sequences are found in a 232-bp fragment located 5' of the NF-K B binding sequence of the enhancer. When this fragment is added back upstream of an active NF-_K B site, it specifically decreases the expression of a linked gene by more than 10-fold in activated T cells but it has no effect on expression in B cells. The kappa silencer region acts in an orientation- and distance-independent manner and appears to be composed of multiple negative elements. The kappa silencer may act to restrict transcription and rearrangement of the C_K locus to cells of the B lineage.

v-abl causes hematopoietic disease distinct from that caused by bcr-abl.

Abstract: v-abl, the oncogene transduced by Abelson murine leukemia virus, was first characterized by its ability to transform lymphoid cells. bcr-abl, the oncogene formed by a t(9;22) translocation thought to occur in human hematopoietic stem cells, is detectable in almost all cases of chronic myelogenous leukemia (CML), a malignancy of granulocytic cells. bcr-abl also causes a CML-like syndrome in mice whose bone-marrow cells are infected with a retrovirus transducing the gene. More recent reports have suggested that v-abl can, however, cause a disease similar to CML. We demonstrate here that v-abl, when transduced in a helper virus-containing system, causes disease similar to, but distinct from, the CML-like syndrome induced by bcr-abl. Animals whose bone marrow has been infected by v-abl virus develop modest splenomegaly, marked granulocytosis, and malignant disease of several hematopoietic cell types. Unlike animals with CML-like disease resulting from bcr-abl, the polymorphonuclear leukocytes from animals infected with a v-abl construct do not contain the v-abl provirus at a significant frequency. Histopathologic analysis also shows significant differences between the diseases caused by v-abl and bcr-abl.

The long terminal repeat is not a major determinant of the cellular tropism of human immunodeficiency virus type 1.

Abstract: The long terminal repeats (LTRs) of human immunodeficiency virus type 1 (HIV-1) strains from the central nervous systems of four patients with AIDS and of an HIV-1 isolate which is highly macrophage-tropic were isolated by using the polymerase chain reaction. In transient transfection assays, these LTRs demonstrated no significant difference in basal or stimulated levels of transcription in any of a variety of cell lines tested, compared with expression directed from the LTR of a T-lymphocyte-tropic strain of HIV-1. Chimeric viruses were created with the LTRs of the macrophage-tropic and brain-derived viruses ligated to the viral backbone from a T-lymphocyte-tropic strain. No change in cellular tropism was demonstrated with these chimeric viruses. Thus, unlike the LTRs of some murine retroviruses, the LTR of HIV-1 does not appear to play a major role in determining cellular tropism.

v-abl causes hematopoietic disease distinct from that caused by bcr-abl. - eScholarship

Abstract: v-abl, the oncogene transduced by Abelson murine leukemia virus, was first characterized by its ability to transform lymphoid cells. bcr-abl, the oncogene formed by a t(9;22) translocation thought to occur in human hematopoietic stem cells, is detectable in almost all cases of chronic myelogenous leukemia (CML), a malignancy of granulocytic cells. bcr-abl also causes a CML-like syndrome in mice whose bone-marrow cells are infected with a retrovirus transducing the gene. More recent reports have suggested that v-abl can, however, cause a disease similar to CML. We demonstrate here that v-abl, when transduced in a helper virus-containing system, causes disease similar to, but distinct from, the CML-like syndrome induced by bcr-abl. Animals whose bone marrow has been infected by v-abl virus develop modest splenomegaly, marked granulocytosis, and malignant disease of several hematopoietic cell types. Unlike animals with CML-like disease resulting from bcr-abl, the polymorphonuclear leukocytes from animals infected with a v-abl construct do not contain the v-abl provirus at a significant frequency. Histopathologic analysis also shows significant differences between the diseases caused by v-abl and bcr-abl.

Transcription factors having a pathogenetic role in human neoplasias

Abstract: A method of detecting and/or quantitating either or both of the genes localized to the breakpoint of a consistently recurring chromosomal translocation present in a human neoplasm, the fusion DNA which crosses the breakpoint, or their encoded products, as well as reagents useful in the method. In particular, a method of detecting either or both of the genes localized to the t(1;19) breakpoint on chromosome 19 and chromosome 1 in human acute lymphoblastic leukemias, the fusion DNA which crosses the breakpoint or their encoded products.

Methods of detecting hepatitis A virus

Abstract: Methods for producing HAV cDNA, products thereof, and uses thereof, are described. HAV cDNA is produced, for example, by reverse transcribing HAV RNA and subsequently inserting the HAV cDNA into bacterial plasmids by genetic-engineering techniques. Transformed bacteria are then cloned and cultured to produce replicated chimetic plasmids containing the HAV cDNA. Such HAV cDNA is useful in assaying for the presence of HAV and in the production of HAV antigen and in the production of antibodies against HAV.

Dr Baltimore says "sorry".

Abstract: Dr David Baltimore says he had no knowledge of the fabrication of data in a paper in Cell of which he was a co-author, says he will work to develop new guidelines for misconduct and apologizes to Dr Margot O'Toole.

The Imanishi-Kari affair. Baltimore declares O'Toole mistaken.

Abstract: Dr Margot O'Toole's comment on the OSI draft report reproduced in Nature two weeks ago, has drawn the following reply from Dr David Baltimore, one of the authors of an article alleged to include fraudulent data.