Biomedical subjects

M L Privalsky

Publications and source records attributed to M L Privalsky.

At least 55 records · Page 3Linked to original sources

PubMed1992

Retinoid and thyroid hormone receptors: ligand-regulated transcription factors as proto-oncogenes.

The retroviral v-erb A locus is derived from a cellular gene, c-erb A, encoding a thyroid hormone receptor. The v-erb A and c-erb A proteins are, in turn, members of a larger family of structurally and functionally interrelated polypeptides that includes the steroid, retinoic acid, and vitamin D3 receptors. These nuclear hormone receptors act by binding to specific sites on the cell genome and, in response to cognate hormone, modulating the transcription of adjacent 'target' genes. The expression, properties, and mechanisms of action of the thyroid hormone receptors (c-erb A proteins) and the closely related retinoic acid receptors are discussed.

Animals↗

PubMed1992

V-erbA and c-erbA proteins enhance transcriptional activation by c-jun.

The ability of different transcription factors to interact with one another is an important means by which the eucaryotic cell can integrate separate growth and differentiation signals into a coherent response. We report here an analysis of the interactions of transcription factors that are also the products of oncogenes: the erbA, jun and fos proteins. We demonstrate that the c-jun polypeptide can functionally interact with the c-erbA protein (thyroid hormone receptor) to yield an enhanced activity greater than that of either factor individually. Although the avian erythroblastosis v-erbA allele is generally thought to act as a transcriptional repressor in vertebrate cells, we also report the existence of promoter contexts where v-erbA, as well as c-erbA, can serve as 'co-activators' of c-jun function. V-erbA appears to augment retinoic acid receptor function in the same context. Our results suggest that v-erbA may have unanticipated positive effect on transcription in the neoplastic cell in addition to the repressor functions previously characterized.

Base Sequence↗

PubMed1992

Functional interaction between the two zinc finger domains of the v-erb A oncoprotein.

The v-erb A oncogene of avian erythroblastosis virus is a mutated and virally transduced copy of a host cell gene encoding a thyroid hormone receptor. The protein expressed by the v-erb A oncogene binds to DNA and acts as a dominant negative inhibitor of both the thyroid hormone receptor and the closely related retinoic acid receptor. The v-erb A protein has sustained two amino acid alterations within its DNA-binding domain relative to that of c-erb A, one of which, at serine 61, is known to be important for v-erb A function in the neoplastic cell. We report here that the second alteration, at threonine 78, also plays an important, although more indirect, role: alteration of the sequence at threonine 78 such that it resembles that of c-erb A can act as an intragenic suppressor and can partially restore function to a v-erb A protein rendered defective due to a mutation at position 61. Threonine 78 lies within the D-box of the v-erb A protein, a region thought to mediate receptor-receptor dimerizations, and is not in physical proximity to the serine at position 61. It therefore appears that an indirect interaction occurs between these two sites and that this interaction is crucial for v-erb A function.

Amino Acid Sequence↗

PubMed1991

v-erbA oncogene function in neoplasia correlates with its ability to repress retinoic acid receptor action.

The v-erbA oncoprotein of avian erythroblastosis virus is an aberrant version of a thyroid hormone receptor and functions in neoplasia by blocking erythroid differentiation and by modifying the growth properties of fibroblasts. v-erbA has been proposed to represent a novel dominant negative oncogene, acting in the cancer cell by interfering with the actions of its normal cell homologs, the thyroid hormone receptors. We report here that v-erbA can actually interfere with the actions of a variety of members of the steroid/retinoid receptor family and that the ability of v-erbA to act in neoplasia best correlates not with suppression of c-erbA action, but with interference with the retinoic acid receptor response. We suggest that v-erbA may act in neoplasia by promiscuously interfering with a retinoid-mediated differentiation process.

Alleles↗

PubMed1991

A subpopulation of the v-erb A oncogene protein, a derivative of a thyroid hormone receptor, associates with heat shock protein 90.

The v-erb A oncogene of avian erythroblastosis virus is derived from a host gene for a thyroid hormone receptor and is able to block differentiation of erythroid cells and modify the growth properties of fibroblasts. Unlike its host cell progenitor, the v-erb A protein is found in both cytoplasmic and nuclear fractions of the cell. I report here that the cytoplasmic form of the v-erb A protein is associated in a higher molecular weight complex with heat shock protein 90, the same polypeptide found in association with the unliganded steroid receptors and with the soluble forms of the src oncogene.

Animals↗

PubMed1991

Ontogeny of the v-erbA oncoprotein from the thyroid hormone receptor: an alteration in the DNA binding domain plays a role crucial for v-erbA function.

The avian erythroblastosis virus v-erbA oncogene is imprecisely derived from a cellular gene (c-erbA) encoding a thyroid hormone receptor: the v-erbA protein has sustained both small terminal deletions and internal amino acid sequence changes relative to c-erbA. We report here that one of these missense differences between v- and c-erbA proteins, located in a zinc finger DNA binding domain, has dramatic effects on the biological activities of the encoded protein. Back mutation of the viral coding sequence to resemble c-erbA at this site severely impairs erythroid transformation and produces subtle changes in DNA binding by the encoded protein, suggesting that differences in DNA binding by the viral and cellular proteins may be involved in the activation of v-erbA as an oncogene.

Amino Acid Sequence↗

PubMed1990

The viral erbA oncogene protein, a constitutive repressor in animal cells, is a hormone-regulated activator in yeast.

The v-erbA oncogene is a retrovirus-transduced and altered copy of a cellular gene for a thyroid hormone receptor. In animal cells, the v-erbA protein fails to respond to hormone and acts as a dominant negative allele, inhibiting gene activation normally conferred by the wild-type thyroid hormone receptor. We report here that, unexpectedly, the v-erbA protein acts as a hormone-regulated transcriptional activator in S. cerevisiae. We suggest that the ability of v-erbA protein to function as a transcriptional repressor or an activator is determined by interaction with, or modification by, other cellular factors, and that this phenomenon may be relevant to understanding ligand regulation of the normal thyroid and steroid hormone receptors.

Animals↗

PubMed1990

A subpopulation of the avian erythroblastosis virus v-erbA protein, a member of the nuclear hormone receptor family, is glycosylated.

The v-erbA oncogene of avian erythroblastosis virus is derived from a cellular gene for a thyroid hormone (T4/T3 thyronine) receptor and encodes a DNA-binding protein found principally in the nucleus of the infected cell. I report here that a subpopulation of the v-erbA protein is glycosylated. The v-erbA protein, therefore, is another member of the newly recognized family of eucaryotic transcription factors and related polypeptides which are glycoproteins.

Alpharetrovirus↗

PubMed1990

Sequence-specific DNA binding by the v-erbA oncogene protein of avian erythroblastosis virus.

The v-erbA oncogene, a transduced copy of a thyroid hormone receptor, plays an important role in establishment of the transformed cell phenotype induced by avian erythroblastosis virus. The ability of thyroid hormone receptors to bind to specific sites on chromatin and to thereby modify the expression of adjacent target genes is a crucial element in their mechanism of action in the normal cell. The v-erbA protein also bound at high affinity to a set of DNA fragments recognized by the rat thyroid hormone receptor, but the relative affinity of the v-erbA protein for the different binding sites was distinct from that previously reported for the thyroid hormone receptors.

Alpharetrovirus↗

PubMed1990

Mapping of functional domains within the v-erb A oncogene protein: the remnants of the hormone binding domain play multiple, vital roles in protein action.

The v-erb A oncogene represents a virally-transduced variant of a thyroid hormone receptor. Biochemical characterization of a series of mutant v-erb A proteins demonstrates that nuclear localization and DNA binding are both necessary for v-erb A function in the neoplastic cell and are mediated by multiple, overlapping domains within the v-erb A polypeptide. Domains of the v-erb A protein necessary for sequence-specific and sequence-independent DNA binding are distinguishable from one another, and encompass sequences projecting beyond the zinc-finger motifs themselves. Although unable to bind T3 thyroid hormone, the remnants of the hormone binding domain continue to play unanticipated essential roles in v-erb A protein function.

Cell Nucleus↗

PubMed1988

The avian erythroblastosis virus erbA oncogene encodes a DNA-binding protein exhibiting distinct nuclear and cytoplasmic subcellular localizations.

The protein product of the v-erbA oncogene of avian erythroblastosis virus was analyzed by use of site-specific antisera. The v-erbA protein was found to exist in distinct nuclear and cytoplasmic forms. Both nuclear and cytoplasmic species of the v-erbA protein were capable of binding to DNA, a property predicted based on the structural relatedness the v-erbA polypeptide shares with the thyroid and steroid hormone receptors. A mutation within the v-erbA coding region which inhibited DNA binding and nuclear localization also inhibited the ability of the v-erbA protein to potentiate erythroid transformation, consistent with a model of the v-erbA protein as a transcriptional regulator.

Alpharetrovirus↗

PubMed1988

Genetic dissection of functional domains within the avian erythroblastosis virus v-erbA oncogene.

The avian erythroblastosis virus v-erbA locus potentiates the oncogenic transformation of erythroid and fibroblast cells and is derived from a host cell gene encoding a thyroid hormone receptor. We report here the use of site-directed mutagenesis to identify and characterize functional domains within the v-erbA protein. Genetic lesions introduced into a putative hinge region or at the extreme C-terminus of the v-erbA coding domain had no significant effect on the biological activity of this polypeptide. In contrast, mutations introduced within the cysteine-lysine-arginine-rich center of the v-erbA coding region, a DNA-binding domain in the thyroid and steroid hormone receptors, abolished or severely compromised the ability of the viral protein to function. Our results suggest that the mechanism of action of the v-erbA protein in establishing the neoplastic phenotype is closely related to its ability to interact with DNA, presumably thereby altering expression of host target genes by either mimicking or interfering with the action of the normal c-erbA gene product.

Alpharetrovirus↗

PubMed1987

Transmembrane domain of the AEV erb B oncogene protein is not required for partial manifestation of the transformed phenotype.

The transmembrane domain was deleted from within the v-erb B protein coding region of avian erythroblastosis virus. The mutant oncogene encoded a shortened, apparently soluble form of the normally membrane bound v-erb B protein. Despite this alteration in subcellular distribution, the mutant polypeptide retained the ability to induce fibroblast transformation by several parameters, including the ability to display anchorage-independent growth. It appears that the transmembrane domain, although important for full manifestation of the transformed phenotype, is not essential for v-erb B-mediated oncogenic transformation.

Alpharetrovirus↗

PubMed1987

Creation of a chimeric oncogene: analysis of the biochemical and biological properties of v-erbB/src fusion polypeptide.

A novel gene was created that linked complementary portions of two different tyrosine kinase oncogenes: v-erB and v-src. The v-erbB/src chimera encoded a glycoprotein exhibiting the subcellular distribution of the v-erbB protein but containing the kinase catalytic domain of the v-src parent. Fibroblasts expressing the v-erbB/src gene product became transformed to an oncogenic state and closely resembled cells expressing the v-erbB parent oncogene. Our results indicated that v-erbB sequences can be functionally replaced by sequences derived from a different oncogene, v-src, and that important determinants of the transformed phenotype appear to be encoded in oncogene sequences distinct from those defining the kinase catalytic domain itself.

Animals↗

PubMed1986

Structural domains of the avian erythroblastosis virus erbB protein required for fibroblast transformation: dissection by in-frame insertional mutagenesis.

Avian erythroblastosis virus (AEV) induces erythroblastosis and fibrosarcomas. The viral erbB protein is required for AEV-mediated oncogenesis. To explore the structural aspects of the v-erbB polypeptide necessary for its oncogenic function, we created a series of small in-frame insertions in different domains of the v-erbB oncogene. AEV genomes bearing lesions within the v-erbB kinase domain demonstrated a drastically decreased ability to transform avian fibroblasts, establishing a functional role for this structurally conserved oncogene domain. In contrast, mutations in the extracellular domain, between the transmembrane region and the kinase domain, or at the extreme C terminus of the v-erbB protein had no effect on AEV-mediated fibroblast transformation. One lesion within the v-erbB kinase domain, a 10-amino acid insertion, produced a temperature-sensitive mutant capable of fibroblast transformation at 36 degrees C but not at 41 degrees C, suggesting that small in-frame insertions have general utility for the in vitro creation of conditional mutants.

Alpharetrovirus↗

PubMed1986

Mutagenesis of the avian erythroblastosis virus erbB coding region: an intact extracellular domain is not required for oncogenic transformation.

Avian erythroblastosis virus (AEV) is an oncogenic retrovirus of birds. The AEV-encoded erbB polypeptide, a transmembrane glycoprotein bearing an N-terminal domain exposed on the surface of virally transformed cells, plays a crucial role in AEV-mediated oncogenesis. We report here a characterization of a mutated form of the AEV erbB protein which lacks over two-thirds of the extracellular region of this oncogenic protein. This mutant v-erbB protein, although lacking the three possible extracellular sites of N-linked protein glycosylation, appears unimpaired in the ability to transform cells to an oncogenic phenotype.

Alpharetrovirus↗

PubMed1986

Orientation of the v-erb-B gene product in the plasma membrane.

The retroviral oncogene v-erb-B encodes a truncated version of the receptor for epidermal growth factor. To define the disposition of the v-erb-B protein within cells and across the plasma membrane, we raised antibodies against defined epitopes in the protein and used these in immunofluorescence to analyze cells transformed by v-erb-B. A small fraction of the v-erb-B protein was found on the plasma membrane in a clustered configuration. The bulk of the protein was located in the endoplasmic reticulum and Golgi apparatus. Epitopes near the amino terminus of the v-erb-B protein were displayed on the surface of the cell, whereas epitopes in the protein kinase domain were located exclusively within cells. We conclude that the v-erb-B protein spans the plasma membrane in a manner similar or identical to that of the epidermal growth factor receptor, even though the viral transforming protein does not possess the signal peptide that is thought to direct insertion of the receptor into the membrane.

Alpharetrovirus↗

PubMed1984

Subcellular localization of the v-erb-B protein, the product of a transforming gene of avian erythroblastosis virus.

Avian erythroblastosis virus (AEV) is an oncogenic retrovirus capable of transforming both fibroblasts and immature erythroid cells. The v-erb-B locus within the AEV genome encodes a glycosylated protein, expression of which is required for oncogenic transformation of either cell type. Subcellular localization of the v-erb-B glycoprotein in AEV-transformed cells is reported here. Results indicate that the v-erb-B protein is synthesized on dense membrane fractions and appears to possess the properties of an integral membrane protein. The bulk of the v-erb-B protein remains with dense membranes after synthesis, although a small quantity may slowly become associated with the plasma membrane. The biogenesis and subcellular location of the v-erb-B protein are thus quite different from those of the transforming proteins that display protein kinase activity. These differences are especially provocative because the amino acid sequences of the v-erb-B protein and the protein kinases are closely related to one another.

Alpharetrovirus↗