Investigations into the cross-reactivity of rabbit antibodies raised against nonhomologous pairs of synthetic peptides derived from HIV-1 gp120 proteins

The immunological cross-reactivity of several peptides with specific pattern-property characteristics related to the epitopes of human immunodeficiency virus type 1 (HIV-1) gp160/ 120 envelope proteins has been investigated. Proteins with similar primary structures can be expected to show functional or topographic similarities, such as specific epitopes which may cross-react with antibodies derived from the immunisation of animals with other members of the same protein family. These structure-function characteristics may be revealed as periodicities derived from presentations based on the discrete Fourier transformation of the distributions of various physico-chemical amino acid descriptors, constituting the polypeptide backbone and amino acid side-chains of the protein molecule. Such approaches, for example, have permitted prediction of periodicities corresponding to secondary structural motifs, including amphipathic alpha-helices and beta-sheets, within protein sequences, and have helped to clarify potential binding sites for ligands, substrates or cofactors with interacting macromolecules. Based on this approach, characteristic periodicities have been identified which represent common Fourier transform spectral properties of the envelope (ENV) gp160/120 glycoproteins from a range of HIV-1 isolates. In addition, similar periodicities have been detected as components of the discrete Fourier transform representation of the corresponding amino acid descriptors of the CD4 binding domain of gp120. Accordingly, we have synthesised several peptides having periodic characteristics in their discrete Fourier transform representations similar to these HIV-1 proteins. These nonhomologous synthetic peptides induced cross-reactive antibodies in New Zealand White rabbits. Polyclonal antibodies raised to one of these peptides reacted with HIV-1 ENV gp120-related proteins, as determined by enzyme-linked immunosorbent assay and Western blotting techniques. These findings provide further evidence for a role of immunological cross-reactivity and molecular biomimicry in the development of peptide-based vaccines directed against viral or bacterial pathogens.

Evidence that a novel human differentiation-inhibiting protein blocks the dimethyl sulfoxide-induced differentiation of erythroleukemia cells by inhibiting the activation of membrane protein kinase C

We have previously reported (J. P. Durkin et al., Blood, 79: 1161-1171, 1992) the isolation of a human differentiation-inhibiting protein (DIP) which selectively inhibits and blocks the differentiation of erythroid burst-forming unit progenitor cells in bone marrow colony assay, and the dimethyl sulfoxide (DMSO)-induced differentiation of cultured murine erythroleukemia (MEL) cells. DIP blocks MEL cell differentiation directly, without affecting the ability of the cells to proliferate. In the present study, DIP (at < 1 ng/ml) inhibited MEL cell differentiation only when added to the culture medium within 1 h after DMSO induction, indicating that it blocked an early, critical step in erythroleukemia cell differentiation. The protein kinase C (PKC) inhibitor H-7 also maximally inhibited the differentiation of MEL cells during this same period following induction, suggesting that DIP may have blocked an early PKC-dependent process. Indeed, DIP was found to abolish a transient increase in membrane PKC activity which was triggered in MEL cells within 10-30 min after DMSO addition. This increase in membrane PKC activity resulted from the activation of an inactive pool of PKC residing on membranes, and not from the translocation of cytosolic PKC to membranes. DMSO also stimulated membrane PKC activity and differentiation in human erythroleukemia cells and HL-60 myeloid leukemia cells. As was the case with MEL cells, DIP prevented the early activation of PKC and the differentiation of human erythroleukemia cells. However, it did not inhibit the early increase in PKC activity in HL-60 cells or the subsequent differentiation of these cells. These results suggest that DIP blocks erythroleukemia cell differentiation by inhibiting an early and critical activation of inactive membrane PKC.

The identification and characterization of a novel human differentiation-inhibiting protein that selectively blocks erythroid differentiation

We have isolated a novel inhibitor of erythropoietic differentiation from the plasma of a patient suffering from idiopathic pure red cell aplasia. This differentiation-inhibiting protein (DIP) specifically blocked the differentiation of human burst-forming unit-erythroid (BFU-E), but not colony-forming unit-erythroid (CFU-E) cells. DIP also blocked the maturation of murine BFU-E cells, but not CFU-E or CFU-granulocyte-macrophage cells, and it inhibited the dimethyl sulfoxide (DMSO)-induced differentiation of Friend murine erythroleukemia cells (FLC) at levels between 10(-10) and 10(-12) mol/L. DIP activity was not detectable in the plasma of normal, healthy subjects. Unlike other known inhibitors of hematopoiesis, DIP appears to directly inhibit erythropoietic differentiation, because it did not affect the proliferation of untreated FLC and it effectively blocked FLC hemoglobinization without affecting the ability of the blocked cells to proliferate. DIP blocked FLC differentiation only when added to the culture medium within 1 hour of inducing the cells with DMSO, suggesting that the protein inhibited an early, but critical, DMSO-induced cellular process. DIP appears to be at least partially responsible for the patient's anemia, and its unique activity suggests a role in the early development of some erythroleukemias.

Characterization of a novel erythropoiesis-inhibiting human protein

We have isolated an erythropoiesis-inhibiting protein, DIP (differentiation-inhibiting protein), from the blood of a 60-year-old woman suffering from pure red cell aplasia. This protein inhibits the growth and differentiation of normal human and murine BFU-E, but not CFU-E, cells as well as dimethyl sulfoxide-induced hemoglobin synthesis by Friend murine erythroleukemia cells. It appears that DIP primarily affects differentiation rather than proliferation, because it does not inhibit the proliferation of untreated Friend erythroleukemia cells. DIP seems to function like a recently described 45-kDa autocrine differentiation-inhibiting protein factor (ADIF) which is secreted by tsAEV-transformed chicken erythroleukemia cells. Both proteins selectively block the differentiation of normal human and murine BFU-E cells as well as the differentiation (but not the proliferation) of Friend murine erythroleukemia cells. However, the human DIP is not an autocrine product of the patient's bone marrow cells, nor does it affect chicken erythroid cells.

Purification and characterization of proteins with associated tyrosine protein kinase activity from human B lymphocytes

Burkitt lymphoma cells and their counterpart of normal origin contain proteins with associated tyrosine protein, kinase activity. These proteins were isolated by affinity chromatography and Fast Pressure Liquid Chromatography. Proteins with enzyme activity had an app. M. W. of 47 KDa. This protein in extracts of Burkitt lymphoma cells differed by overall charge and phosphorylation from the 47 KDa protein isolated from B lymphocytes of normal origin. Before and after purification the 47 KDa protein of Burkitt lymphoma cells reacted with an antibody directed against the dodecapeptide Arg-Arg-Leu-Ile-Glu-Asp-Asn-Glu-Tyr-Thr-Ala-Arg (conserved region of pp60src), the 47 KDa protein from B cells of normal origin did not; the same protein from both cell lines reacted with anti-pp60src antibody. These results suggest that a tyrosine protein kinase, related to the products of the src family of oncogenes, is modified in Burkitt lymphoma cells.

Differentiation of Burkitt lymphoma cells by hexamethylenbisacetamide

Hexamethylenbisacetamide (HMBA) can induce the Burkitt lymphoma Raji cells to enter the differentiation process as evidenced by the decrease of HLA-DR antigens. This event is preceded by a decrease of c-myc expression and of the phosphorylation of cellular proteins, due to either a decrease of tyrosine protein kinase activity or an increase of tyrosine phosphatase activity. These three events form a sequence and are part of the genetic program for differentiation and growth though they may not be causally related.

Autocrine differentiation-inhibiting factor (ADIF) from chicken erythroleukemia cells acts on human and mouse early BFU-E erythroid progenitors

tsAEV-LSCC HD3 chicken erythroid cells transformed by the avian erythroblastosis virus (AEV) secrete an autocrine differentiation-inhibiting factor, ADIF, which blocks differentiation without affecting proliferation of the chicken erythroid cells that synthesize and secrete it into the culture medium. The chicken erythroleukemia cell ADIF activity is not restricted to avians. It prevents dimethylsulfoxide (DMSO) from stimulating murine Friend erythroleukemia cells to synthesize hemoglobin. ADIF also blocks erythroid differentiation in normal human and murine bone marrow where it selectively targets the early BFU-E (burst-forming) erythroid precursor cells without affecting the more advanced CFU-E erythroid precursor cells or cells of the different granulocyte-macrophage lineage.

Viral products in cells infected with vesicular stomatitis virus and superinfected with Rous sarcoma virus

In cells infected with Vesicular Stomatitis virus (VSV) ts 1026 and superinfected with Rous Sarcoma virus (RSV) synthesis of vsrc mRNA and RSV env mRNA decreases. In these cells post-translational processing of RSV precursor proteins is impaired and small amounts of VSV antigens are detected.

AEV-transformed erythroleukemia cell induced differentiation: expression of specific cell membrane antigenic molecules

A simultaneous decay of the expression of Im 140 kDa, Im 150 kDa and Im 160 kDa high MW membrane antigens, concomitant with the cell proliferation arrest, was observed during erythropoietin induced differentiation of ts 34 AEV-transformed erythroid cells cultivated at the restrictive temperature. Expression of embryo-immature antigens was maintained during induced differentiation of erythroleukemia cells, but their MW shifted from 50 to 48 kDa, which corresponds to the MW of embryo-immature antigens detected on normal erythroid cells. In the absence of erythropoietin at the restrictive temperature, conditions under which the ts 34 AEV-transformed erythroid cells fail to differentiate and maintain their capacity to proliferate, the expression of high MW antigens as well as the expression of embryo-immature antigens remained unaffected. Therefore, it is shown that the expression of specific membrane antigens is modulated under conditions rendering the erythroleukemia cell differentiation process possible.

Binding of proteins, including pp60src, to activated CH-sepharose 4B

Activated CH-Sepharose 4B and protein A Sepharose CL-4B can bind, selectively and non-specifically, polypeptides from chick embryo cells. The major polypeptides bound have apparent molecular masses of 57-60 kDa and 47-49 kDa and cannot be eluted by extensive washing with buffers containing detergents. One of the 57-60 kDa polypeptides was identified by immunoblotting as the transforming protein of Rous Sarcoma Virus (RSV), pp60src. This polypeptide could be removed from the solid phase immunoabsorbent with 60% dimethylsulfoxide, but not with 2% SDS, 5% beta-mercaptoethanol, 1 M NaCl or 0.1% Tween 20.

Isolation of proteins with kinase activity and related to pp60 src from human cells

A protein kinase activity (PK) was associated with immunoprecipitates between polypeptides of human lymphoblastoid cells of malignant origin (Raji cell line) or of their normal counterparts ( Priess cell line) and antibodies directed against avian pp60 src or against the carboxyterminal hexapeptide of pp60 src. Therefore, these human cells and Rous Sarcoma Virus (RSV) transformed avian cells share antigenic determinants of pp60 src and, in particular, its carboxyterminal sequence, as well as one of its functions, a protein kinase activity. The protein kinase from Raji cells phosphorylated predominantly tyrosine residues, that from Priess cells threonine residues.

Immunological study of a cellular 35K phosphorylated polypeptide detected in Rous sarcoma virus transformed cells

We have immunoprecipitated a phosphoprotein of 35K daltons (35K) common to RSV-transformed chick embryo fibroblasts (CEF) and rodent cells. The phosphorylation of this antigen depends on the expression of the v-src gene and contains phosphotyrosine. The pre-existing 35K protein, of CEF infected de novo, was further shown to become phosphorylated shortly after the appearance of active pp60v-src, and about 1 day before morphological transformation. The experiments with RSV-transformed rodent cells have shown that the 35K phosphoprotein is associated with the cellular framework. Another phosphoprotein of 37K was found in the RSV-transformed rodent cells, but not in the transformed CEF. However, this protein was not phosphorylated at tyrosine residues and its phosphorylation persisted, at the restrictive temperature, in cells transformed by a ts mutant of RSV.

Normal or retrovirus-infected cultured chicken embryo cells express the 48,000 D age-related antigen characteristic of embryonic chicken erythrocytes

The surface of normal or retrovirus-infected chick embryo cells was labelled with 125I using lactoperoxidase. The solubilized membrane material was allowed to react with antisera raised in rabbits to cultured chick embryo cells or to the membranes of embryonic or adult chicken erythrocytes. Analysis of the immunoprecipitates shows that chicken embryo cells not of erythropoietic origin express on their surface membrane an antigenic polypeptide of mol. wt. 48,000 daltons (D), which appears to be identical with that expressed on embryonic chicken erythrocytes.

[5-Bromodeoxyuridine augmentation of the expression, on chick embryo fibroblasts of a cellular antigen present on avian oncoviruses]

Treatment of Chick embryo fibroblasts (CEF) with 5-bromodeoxyuridine considerably increases the expression on the cell membrane of a cellular antigen related to an antigen specific to Chick embryo erythrocytes, present on the envelope of avian sarcoma oncoviruses produced by CEF.

A structural change of the plasma membrane induced by oncogenic viruses: quantitative studies with the freeze-fracture technique

In BHK21 hamster cells a significant increase in density of intramembranous particles occurs in freeze-fractured plasma membranes after transformation by hamster sarcoma and polyoma viruses. A similar change has been observed in chick embryo cells infected and transformed by a mutant of Rous sarcoma virus thermosensitive for transformation, at both permissive and nonpermissive temperatures. There is also an increase in particle density in chick cells infected with the Rous-associated avian leukosis virus type 1. The newly appeared particles may represent the insertion of new proteins in hydrophobic regions of plasma membrane, in response to the action of oncogenic viruses.