MAF1, a novel plant protein interacting with matrix attachment region binding protein MFP1, is located at the nuclear envelope.

The interaction of chromatin with the nuclear matrix via matrix attachment region (MAR) DNA is considered to be of fundamental importance for chromatin organization in all eukaryotic cells. MAR binding filament-like protein 1 (MFP1) from tomato is a novel plant protein that specifically binds to MAR DNA. Its filament protein-like structure makes it a likely candidate for a structural component of the nuclear matrix. MFP1 is located at nuclear matrix-associated, specklelike structures at the nuclear envelope. Here, we report the identification of a novel protein that specifically interacts with MFP1 in yeast two-hybrid and in vitro binding assays. MFP1 associated factor 1 (MAF1) is a small, soluble, serine/threonine-rich protein that is ubiquitously expressed and has no similarity to known proteins. MAF1, like MFP1, is located at the nuclear periphery and is a component of the nuclear matrix. These data suggest that MFP1 and MAF1 are in vivo interaction partners and that both proteins are components of a nuclear substructure, previously undescribed in plants, that connects the nuclear envelope and the internal nuclear matrix.

The enhancer domain of the human cytomegalovirus major immediate-early promoter determines cell type-specific expression in transgenic mice.

The human cytomegalovirus (HCMV) major immediate-early promoter (MIEP) is one of the first promoters to activate upon infection. To examine HCMV MIEP tissue-specific expression, transgenic mice were established containing the lacZ gene regulated by the MIEP (nucleotides -670 to +54). In the transgenic mice, lacZ expression was demonstrated in 19 of 29 tissues tested by histochemical and immunochemical analyses. These tissues included brain, eye, spinal cord, esophagus, stomach, pancreas, kidney, bladder, testis, ovary, spleen, salivary gland, thymus, bone marrow, skin, cartilage, and cardiac, striated and smooth muscles. Although expression was observed in multiple organs, promoter activity was restricted to specific cell types. The cell types which demonstrated HCMV MIEP expression included retinal cells of the eye, ductile cells of the salivary gland, exocrine cells of the pancreas, mucosal cells of the stomach and intestine, neuronal cells of the brain, muscle fibers, thecal cells of the corpus luteum, and Leydig and sperm cells of the testis. These observations indicate that the HCMV MIEP is not a pan-specific promoter and that the majority of expressing tissues correlate with tissues naturally infected by the virus in the human host.

Strand-invasion of duplex DNA by peptide nucleic acid oligomers.

Polyamide oligomers, termed peptide nucleic acids (PNAs), bind with high affinity to both DNA and RNA and offer both antisense and antigene approaches for regulating gene expression. When a PNA binds to a complementary sequence in a double-stranded DNA, one strand of the duplex is displaced, and a stable D-loop is formed. Unlike oligodeoxynucleotides for which binding polarity is determined by the deoxyribose sugar, the unrestrained polyamide backbone of the PNA could permit binding to a DNA target in an orientation-independent manner. We now provide evidence that PNAs can, in fact, bind to their complementary sequence in DNA independent of the DNA-strand polarity--that is, a PNA binds to DNA in both "parallel" and "antiparallel" fashion. With a mixed-sequence 15-mer PNA, kinetic studies of PNA.DNA interactions revealed that D-loop formation was rapid and the complex was stable for several hours. However, when measured either by gel-mobility-shift analysis or RNA polymerase II-elongation termination, D-loop formation was salt dependent, but PNA-strand dissociation was not salt dependent. We observed that D-loop-containing DNA fragments had anomalous gel mobilities that varied as a function of the position of the D-loop relative to the DNA termini. On the basis of permutation analysis, the decreased mobility of the PNA.DNA complex was attributed to a bend in the DNA at or near the D-loop.

Antisense and antigene properties of peptide nucleic acids.

Peptide nucleic acids (PNAs) are polyamide oligomers that can strand invade duplex DNA, causing displacement of one DNA strand and formation of a D-loop. Binding of either a T10 PNA or a mixed sequence 15-mer PNA to the transcribed strand of a G-free transcription cassette caused 90 to 100 percent site-specific termination of pol II transcription elongation. When a T10 PNA was bound on the nontranscribed strand, site-specific inhibition never exceeded 50 percent. Binding of PNAs to RNA resulted in site-specific termination of both reverse transcription and in vitro translation, precisely at the position of the PNA.RNA heteroduplex. Nuclear microinjection of cells constitutively expressing SV40 large T antigen (T Ag) with either a 15-mer or 20-mer PNA targeted to the T Ag messenger RNA suppressed T Ag expression. This effect was specific in that there was no reduction in beta-galactosidase expression from a coinjected expression vector and no inhibition of T Ag expression after microinjection of a 10-mer PNA.

The 65-kDa subunit of human NF-kappa B functions as a potent transcriptional activator and a target for v-Rel-mediated repression.

Molecular cloning of the polypeptide component of the Rel-related human p75 nucleoprotein complex has revealed its identity with the 65-kDa (p65) subunit of NF-kappa B. Functional analyses of chimeric proteins composed of NF-kappa B p65 C-terminal sequences linked to the DNA-binding domain of the yeast GAL4 polypeptide have indicated that the final 101 amino acids of NF-kappa B p65 comprise a potent transcriptional activation domain. Transient transfection of human T cells with an expression vector encoding NF-kappa B p65, but not NF-kappa B p50, produced marked transcriptional activation of a basal promoter containing duplicated kappa B enhancer motifs from the long terminal repeat of type 1 human immunodeficiency virus. These stimulatory effects of NF-kappa B p65 were synergistically enhanced by coexpression of NF-kappa B p50 but were completely inhibited by coexpression of the v-rel oncogene product. Together, these functional studies demonstrate that NF-kappa B p65 is a transactivating subunit of the heterodimeric NF-kappa B complex and serves as one cellular target for v-Rel-mediated transcriptional repression.

A tyrosine kinase physically associates with the beta-subunit of the human IL-2 receptor.

Cell surface expression of the high affinity IL-2R regulates, in part, the proliferative response occurring in Ag- or mitogen-activated T cells. The functional high affinity IL-2R is composed of at least two distinct ligand-binding components, IL-2R alpha (Tac, p55) and IL-2R beta (p70/75). The IL-2R beta polypeptide appears to be essential for growth signal transduction, whereas the IL-2R alpha protein participates in the regulation of receptor affinity. We have prepared and characterized two mAb, DU-1 and DU-2, that specifically react with IL-2R beta. In vitro kinase assays performed with DU-2 immunoprecipitates, but not anti-IL-2R alpha or control antibody immunoprecipitates, have revealed co-precipitation of a tyrosine kinase enzymatic activity that mediates phosphorylation of IL-2R beta. Because both IL-2R alpha and IL-2R beta lack tyrosine kinase enzymatic domains, these findings strongly suggest that noncovalent association of a tyrosine kinase with the high affinity IL-2R complex. Deletion mutants of the intracellular region of IL-2R beta, lacking either a previously described "critical domain" between amino acids 267 and 322 or the carboxyl-terminal 198 residues (IL-2R beta 88), lacked the ability to co-precipitate this tyrosine kinase activity, as measured by phosphorylation of IL-2R beta in vitro. Both of these mutants also failed to transduce growth-promoting signals in response to IL-2 in vivo. Analysis of the IL-2R beta 88 mutant receptor suggested that a second protein kinase mediating phosphorylation on serine and threonine residues physically interacts with the carboxyl terminus of IL-2R beta. This kinase may be necessary but, alone, appears to be insufficient to support a full IL-2-induced proliferative response. These studies highlight the physical association of protein kinases with the cytoplasmic domain of IL-2R beta and their likely role in IL-2-induced growth signaling mediated through the multimeric high affinity IL-2R complex.

The v-rel oncogene encodes a kappa B enhancer binding protein that inhibits NF-kappa B function.

Studies of NF-kappa B suggest that this enhancer binding activity corresponds to a family of at least four proteins (p50, p55, p75, and p85) differentially induced with biphasic kinetics during T cell activation. While p55 and p50 are closely related to the 50 kd DNA binding subunit of NF-kappa B, p75 and p85 exhibit DNA binding properties that distinguish them from this 50 kd polypeptide and its regulatory subunits I kappa B and p65. All four members of this kappa B-specific protein family are structurally related to the v-Rel oncoprotein and one, p85, appears identical to human c-Rel. v-Rel, but not nontransforming v-Rel mutants, binds to the kappa B enhancer and inhibits NF-kappa B-activated transcription from the IL-2 receptor alpha promoter and HIV-1 LTR. These findings suggest a Rel-related family of kappa B enhancer binding proteins and raise the possibility that the transforming activity of v-Rel is linked to its inhibitory action on cellular genes under NF-kappa B control.

Induction of interleukin-2 receptor-alpha gene expression is regulated by post-translational activation of kappa B specific DNA binding proteins.

T cell mitogens induce the expression of specific trans-acting DNA binding proteins that in turn regulate the expression of the interleukin-2 receptor-alpha (IL-2R alpha) gene. To investigate whether de novo protein synthesis is required for the activation of these transacting factors and the induced expression of this receptor gene, Jurkat T cells were incubated with various inhibitors of protein synthesis prior to stimulation with phytohemagglutinin and phorbol 12-myristate 13-acetate (PMA). Despite the presence of cycloheximide or anisomycin at concentrations sufficient to block greater than 97% of cellular protein synthesis, phytohemagglutinin and phorbol 12-myristate 13-acetate effectively induced the expression of the IL-2R alpha gene as measured at the mRNA level. Similarly, gel retardation, DNA footprinting, and DNA-protein cross-linking studies revealed that these mitogens induced the activation of two predominant DNA binding proteins (50-55 and 80-90 kDa) in the presence or absence of cycloheximide and anisomycin. Both of these proteins specifically interacted with a kappa B-like binding site present in the IL-2R alpha promoter (-267 to -256) that is requisite for mitogen-induced expression of this receptor gene. These findings support a post-translational mechanism of induction of pre-existing, but inactive, DNA binding proteins which in turn bind to and activate the IL-2R alpha gene.

Sequence requirements for ligand binding and cell surface expression of the Tac antigen, a human interleukin-2 receptor.

Discrete peptide domains within the primary sequence of cell-surface receptor glycoproteins are believed to regulate not only their function but also their targeting to the cell membrane. To identify sequence elements required for intracellular transport and ligand binding by the human Tac interleukin-2 (IL-2) receptor, we prepared expression plasmids encoding a series of artificially mutated or naturally occurring variants of the Tac cDNA. In particular, we sought to further delineate the functional role of the sequences contributed by each of the eight exons that together encode the Tac protein. Deletion of exons 5 through 8 of the receptor had no detectable effect on IL-2 binding or intracellular transport of the Tac protein, and resulted in secreted forms of this IL-2-binding protein. Removal of sequences corresponding to all of exon 4 ablated IL-2 binding activity yet still permitted transport to the cell surface. In contrast, partial deletion of exon 4 sequences resulted in proteins that not only lacked IL-2 binding activity but also were sequestered within the endoplasmic reticulum. Removal of one or both of the N-linked glycosylation sites present in the Tac protein did not impair receptor transport or ligand binding. These results demonstrate that exon 4 of the Tac gene encodes amino acid residues that play an important role in regulating both the intracellular transport and function of this IL-2 receptor.

Lymphocytes isolated from the intestinal lamina propria of normal nonhuman primates have increased expression of genes associated with T-cell activation.

Synthesis of interleukin-2 (IL-2) and expression of interleukin-2 receptors play central roles in T-cell activation, proliferation, and differentiation. The state of activation of T lymphocytes in the intestinal lamina propria was compared with that of circulating lymphocytes and lymphocytes isolated from the spleen or mesenteric lymph nodes of normal nonhuman primates. Lamina propria lymphocytes (LPL) had significantly higher proliferation in response to recombinant IL-2 compared with the other populations. In agreement with this finding, LPL had a significantly higher percentage of interleukin-2 receptor-positive (IL-2R+) cells as determined by staining with fluoresceinated monoclonal anti-IL-2R antibody. Two-color immunofluorescence staining showed that both CD4+ and CD8+ lamina propria T cells were IL-2R+. It was also found that the percentage of major histocompatibility complex class II-positive T cells was higher in the lamina propria. Northern blot analysis with a cDNA specific for the IL-2R showed that unstimulated LPL had easily detectable IL-2R mRNA, whereas no IL-2R mRNA was found in unstimulated lymphocyte populations from other sites. The activation of the IL-2R gene in LPL was not associated with the activation of other cellular genes (actin, major histocompatibility complex class I). Although no IL-2 bioactivity was measured in culture supernatants of unstimulated lymphocytes, concanavalin A-stimulated LPL produced significantly more IL-2 than other lymphocytes. This finding was confirmed at the molecular level as IL-2 mRNA was not detected in unstimulated LPL but was found in concanavalin A-stimulated LPL. Thus, normal lamina propria T lymphocytes have selective expression of genes associated with cell activation.

Direct activation of human resting T cells by IL 2: the role of an IL 2 receptor distinct from the Tac protein.

High concentrations of interleukin 2 (IL 2) were shown to produce a delayed but pronounced proliferation of purified resting T cells in the apparent absence of other activation signals. Because these stimulatory effects of IL 2 occurred in the absence of detectable Tac+ cells, the possibility that IL 2 might be initially interacting with an IL 2 binding protein distinct from the Tac protein was studied. Chemical cross-linking studies with 125I-IL 2 revealed the presence of an IL 2 binding protein distinct from the Tac protein on the surface of these unstimulated T cells. This second IL 2 receptor has an estimated molecular size of 70,000 daltons, lacks reactivity with the anti-Tac antibody, and appears to be identical to the p70 protein recently proposed as a component of the high affinity IL 2 receptor. Scatchard analysis of IL 2 binding assays performed with the unactivated T cells revealed approximately 600 to 700 p70 sites per cell and an apparent Kd of 340 pM. These data indicate that the p70 protein present on resting T cells binds IL 2 with an intermediate affinity compared with the previously recognized high and low affinity forms of the receptor and may account for the high concentration of IL 2 needed to induce resting T cell proliferation. To investigate the early biologic consequences of IL 2 binding to the p70 protein, potential changes in the expression of genes involved in T cell activation were examined. Northern blotting revealed the rapid induction of c-myc, c-myb, and Tac mRNA after stimulation of resting T cells with a high concentration of IL 2. The anti-Tac antibody did not inhibit IL 2 induced expression of these genes, suggesting that the p70 protein rather than the Tac antigen or the high affinity IL 2 receptor complex mediated this signal. However, in contrast to these early activation events, the anti-Tac antibody significantly inhibited IL 2 induced T cell proliferation. This finding implicates the high affinity form of the IL 2 receptor in the proliferative response of the IL 2 activated T cells. Thus these data support a two step model for the induction of resting T cell proliferation by high doses of IL 2 involving the initial generation of an activation or "competence" signal through the p70 protein and a subsequent proliferation or "progression" signal through the high affinity form of the receptor.

Reconstitution of high affinity IL-2 receptor expression in a human T-cell line using a retroviral cDNA expression vector.

A recombinant amphotropic retrovirus was used to introduce the protein-coding region of the IL-2 receptor cDNA derived from HUT-102 cells into human CEM leukemic T-cells that lack these receptors. CEM T-cells that contained the virus expressed functional IL-2 receptors that transiently mediated five- to tenfold increases in [3H]thymidine incorporation following the addition of picomolar quantities of IL-2. Although IL-2 responsiveness was subsequently lost, it could be reinduced by cellular activation with the OKT11 monoclonal antibody. This phenotype also proved unstable with progressive time in culture. Despite the loss of IL-2 responsiveness, the infected CEM T-cells continued to express Tac antigen and displayed 50 to 200 high-affinity IL-2 receptors per cell that bound IL-2 with a dissociation constant of 4.3 pM. This affinity is fully equivalent to that detected on activated normal T-cells (2 to 50 pM). The apparent molecular size of the Tac antigen on these cells (55,000 to 60,000 daltons) was comparable to that on normal activated T-cells but 5000 daltons larger than the aberrant IL-2 receptors on HUT-102 cells. These data demonstrate that expression of a human IL-2 receptor cDNA in human T-cells results in high-affinity IL-2 receptor display that transiently imparts an IL-2 responsive state of growth. These results also raise the possibility that the T11 surface receptor may play an important regulatory role in high-affinity IL-2 receptor expression.

Trans-activator gene of HTLV-II induces IL-2 receptor and IL-2 cellular gene expression.

The human T-lymphotropic viruses types I and II (HTLV-I and -II) have been etiologically linked with certain T-cell leukemias and lymphomas that characteristically display membrane receptors for interleukin-2. The relation of these viruses to this growth factor receptor has remained unexplained. It is demonstrated here that introduction of the trans-activator (tat) gene of HTLV-II into the Jurkat T-lymphoid cell line results in the induction of both interleukin-2 receptor and interleukin-2 gene expression. The coexpression of these cellular genes may play a role in the altering T-cell growth following retroviral infection.

Structure of the human interleukin-2 receptor gene.

The gene encoding the human interleukin-2 (IL-2) receptor consists of 8 exons spanning more than 25 kilobases on chromosome 10. Exons 2 and 4 were derived from a gene duplication event and unexpectedly also are homologous to the recognition domain of human complement factor B. Alternative messenger RNA (mRNA) splicing may delete exon 4 sequences, resulting in a mRNA that does not encode a functional IL-2 receptor. Leukemic T cells infected with HTLV-I and normal activated T cells express IL-2 receptors with identical deduced protein sequences. Receptor gene transcription is initiated at two principal sites in normal activated T cells. Adult T cell leukemia cells infected with HTLV-I show activity at both of these sites, but also at a third transcription initiation site.

Interleukin 2 receptor gene expression in normal human T lymphocytes.

We have used cDNAs for the human interleukin 2 (IL-2) receptor to study IL-2 receptor gene expression in normal activated T cells. Resting T cells do not contain detectable IL-2 receptor mRNA. Within 1 hr after stimulation with phytohemagglutinin (PHA), a large, presumably nuclear precursor RNA species is seen, which then gradually disappears. Mature IL-2 receptor mRNA forms appear within 8 hr after stimulation, reach peak levels between 8 and 24 hr, and then decline. Thus, in PHA-activated lymphocytes the rise and fall in IL-2 receptor mRNA levels precede by more than 24 hr the peak and decline of IL-2 receptor protein expression occurring at the cell surface. 4 beta-Phorbol 12-myristate 13-acetate (PMA) also stimulates IL-2 receptor mRNA and protein expression by T cells. Combinations of optimal concentrations of PHA and PMA produce an additive effect on IL-2 receptor mRNA levels, suggesting that PHA and PMA may induce IL-2 receptor gene expression through different, complementary mechanisms. Nuclease S1-protection assays indicate that IL-2 receptor mRNAs may differ in length due to the use of three different polyadenylylation signals. Further, these assays demonstrate the presence of transcripts that lack a 216-base segment within the protein-coding region and thus do not encode a functional IL-2 receptor. Nuclear transcription assays indicate that the increase in IL-2 receptor mRNA is reflected at the level of transcription. Thus, IL-2 receptor gene regulation controls IL-2 receptor expression at the cell surface and is intimately linked to the control of T-cell proliferation.

Isolation and expression of complementary DNAs encoding the human interleukin 2 receptor.

Complementary DNAs corresponding to the human receptor for interleukin 2 (IL-2) have been molecularly cloned, sequenced, and expressed in COS-1 cells. The human genome appears to contain a single structural gene for this receptor; however, when transcribed at least two messenger RNAs (mRNAs) are produced which vary in length due to the use of different polyadenylation signals. Sequence analysis of the cloned complementary DNAs indicates an alternate pathway of mRNA processing for this receptor. Splicing of a 216 base pairs segment contained within the protein coding region results in an mRNA unable to code for the IL-2 receptor. In contact complementary DNAs corresponding to unspliced mRNA encode membrane receptors which bind both IL-2 and anti-Tac (monoclonal anti-IL-2 receptor antibody). Analysis of the deduced amino acid sequence reveals that the receptor is composed of 272 amino acids including a signal peptide 21 amino acids in length. Hydrophobicity analysis suggests a single 19 amino acid transmembrane domain. A short intracytoplasmic domain composed of 13 amino acids is present at the carboxy terminus and contains three potential phosphate acceptor sites (serine and threonine but not tyrosine) and typical positively charged amino acids presumably involved in cytoplasmic anchoring. Two sites for N-linked glycosylation sites and numerous extracytoplasmic O-linked glycosylation sites are present.

Molecular cloning and expression of cDNAs for the human interleukin-2 receptor.

We have purified the human T-cell growth factor (interleukin-2) receptor and have cloned, sequenced and expressed cDNAs corresponding to this receptor. We identify one gene, but two interleukin-2 receptor mRNAs which differ in their polyadenylation signals. We have isolated an additional cDNA that may correspond to an alternatively spliced mRNA that lacks a 216 base segment and appears to encode an altered membrane protein which cannot bind interleukin-2.