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D R Lowy

Publications and source records attributed to D R Lowy.

At least 55 records · Page 3Linked to original sources
PubMed1995

Divergent human papillomavirus type 16 variants are serologically cross-reactive.

It is not known whether DNA sequence variants of human papillomavirus type 16 (HPV-16) are distinct serotypes. To examine this question, the reactivities of women's sera from Zaire (n = 97) and Denmark (n = 123) were compared in IgG-specific ELISAs based on virus-like particles (VLPs) composed of the L1 major capsid protein derived from an HPV-16 variant common in central Africa (Z-1194) or one common in northern Europe (114K). These L1s differ in seven amino acids. There was a strong correlation between reactivity in the two assays for both sets of sera (correlation coefficients, 0.73 and 0.85 for Zairian and Danish sera, respectively). In only 1 serum was there evidence for a specific reaction to one but not the other VLP variant. The results support the conclusion that the virions of strains Z-1194 and 114K are serologically cross-reactive.

Cross Reactions↗
PubMed1995

Immunization with viruslike particles from cottontail rabbit papillomavirus (CRPV) can protect against experimental CRPV infection.

We tested the ability of vaccination with virus-like particles (VLPs) to protect domestic rabbits against papillomas induced by the cottontail rabbit papillomavirus (CRPV). A recombinant baculovirus system that expressed only the L1 major papillomavirus structural protein or L1 plus the minor L2 protein was used in insect cells as the source of VLPs. Groups of 10 rabbits were immunized with native or denatured VLPs from CRPV or type 1 bovine papillomavirus by using Freund's adjuvant. Alum was used as the adjuvant for an additional group immunized with CRPV L1-L2 VLPs. Animals were challenged with 5 x 10(10) and 2 x 10(11) particles on opposing flanks. No protection was seen in rabbits immunized with native or denatured bovine papillomavirus L1-L2 or with denatured CRPV L1-L2. In these groups, the lower and higher challenge doses resulted in 27 of 30 animals with extensive papillomas, with each of the remaining animals having a smaller number of persistent papillomas. Progression to carcinoma developed in 20 rabbits. Animals inoculated with native CRPV VLPs composed of L1 alone or L1-L2 developed many fewer lesions; the lower and higher challenge doses resulted in 17 of 29 and 5 of 29 rabbits, respectively, with no lesions, and the remainder developed only one to eight papillomas, which all regressed except for those on 1 rabbit. None developed cancer within 1 year of infection. Rabbits vaccinated with native CRPV VLPs developed high-titer antibodies in an enzyme-linked immunosorbent assay based on native VLPs, and passive transfer of serum or immunoglobulin G from rabbits immunized with CRPV VLPs protected against CRPV challenge. We conclude that native VLPs can induce antibody-mediated, type-specific protection against experimental papillomavirus infection.

Animals↗
PubMed1995

Papillomavirus L1 capsids agglutinate mouse erythrocytes through a proteinaceous receptor.

Virus-like particles (VLPs) composed of L1 derived from bovine papillomavirus type 1 (BPV-1), several human papillomavirus types, or cottontail rabbit papillomavirus (CRPV) agglutinated mouse but not human or rat erythrocytes. Treatment of mouse erythrocytes with trypsin prevented hemagglutination (HA) by BPV-1. Sera from rabbits immunized with native CRPV VLPs, which protect against experimental CRPV infection, exhibited high titers of antibodies that inhibited CRPV VLP HA activity, while sera from rabbits immunized with denatured CRPV VLPs or native BPV VLPs, which do not protect against CRPV infection, were not inhibitory. Testing for HA inhibition is a rapid and simple method for examining the serological relatedness of papillomaviruses and measuring protective antibody titers after VLP vaccination.

Animals↗
PubMed1994

A virus-like particle enzyme-linked immunosorbent assay detects serum antibodies in a majority of women infected with human papillomavirus type 16.

BACKGROUND: Previous studies have demonstrated that genital infection with high-risk types of human papillomavirus (HPV), most often HPV16, is the most significant risk factor for the development of cervical cancer. However, serologic assays that have been developed to identify high-risk HPV infection have either failed to associate serum reactivity with other indicators of HPV infection or have identified only a minority of HPV-infected individuals. PURPOSE: Our purpose was to determine whether a specifically developed enzyme-linked immunosorbent assay (ELISA) could detect IgG anti-HPV16 virion antibodies in the sera of women who had tested positive for genital HPV16 infection by DNA-based methods. METHODS: An ELISA was developed using newly developed HPV16 virus-like particles as antigens to detect anti-HPV16 virion IgG antibodies. These particles are comprised of HPV16 structural proteins that are self-assembled in insect cells after expression by recombinant baculoviruses. The sera of 122 women, whose HPV status had been previously evaluated by nucleic acid-based methods, were tested by this ELISA. RESULTS: The sera of 59% of women (32 of 54) positive for genital HPV16 DNA by polymerase chain reaction (PCR) were positive in the ELISA assay compared with sera from women who had tested negative for HPV DNA (P < .0005). In contrast, 6% of HPV DNA-negative women (two of 31) and 9% of women positive for low-risk HPV6/11 DNA (one of 11) were ELISA positive by this criterion. The sera of women who were DNA positive for two additional high-risk HPV types were evaluated; the sera of 31% of HPV18-positive (four of 13) and 38% of HPV31-positive women (five of 13) were positive in the HPV16 particle ELISA. The sera of 75% of HPV16 DNA-positive women with severe dysplasias (12 of 16) gave positive ELISA results. The sera of 67% of women (28 of 42) who tested positive for HPV16 DNA by both PCR and the less sensitive ViraType assay tested positive in the ELISA compared with 33% of women (four of 12) who were positive by PCR but negative by ViraType (P < .05). CONCLUSION: The majority of women with cervical HPV16 infection generate an IgG antibody response to conformationally dependent epitopes of HPV16 L1 that can be detected by ELISA. IMPLICATION: This particular ELISA, or a similar one incorporating virus-like particles of additional HPV types, may be useful in determining the natural history of high-risk HPV infection and perhaps help to identify women at risk for developing cervical cancer.

Adolescent↗
PubMed1994

Genital human papillomavirus infection.

Genital human papillomavirus (HPV) infection is a common sexually transmitted disease that at the present time is not effectively controlled or treated. Many infections are inapparent and transient. However, some HPV infections result in persistent lesions that in some cases undergo carcinogenic progression. A subset of genital HPVs, designated high-risk types, are preferentially associated with high-grade dysplasias and carcinomas. About 90% of cervical cancers contain high-risk HPV DNA, most often HPV16. Development of a subunit vaccine against high-risk genital HPVs is a desirable and, it appears, an increasingly feasible long-term goal. The viral E6 and E7 oncoproteins are selectively maintained and expressed in progressed HPV tumors and could potentially be targets for therapeutic vaccines. The L1 major virion structural proteins have recently been shown to self-assemble into virus-like particles when expressed in insect cells. These particles might serve as the basis for a prophylactic vaccine to prevent genital HPV infection.

Antibodies, Viral↗
PubMed1994

Interaction of papillomaviruses with the cell surface.

To initiate an investigation of the initial step in papillomavirus infection, we have examined the interaction of bovine papillomavirus type 1 (BPV) virions with C127 cells by two assays, binding of radioiodinated BPV virions to cell monolayers and BPV-induced focal transformation. Under physiological conditions, the labeled virions bound to the cell surface in a dose-dependent manner within 1 h. Antibody studies indicated that the interaction was specific and related to infectivity: polyclonal sera raised to BPV virions or to baculovirus-expressed BPV L1 virus-like particles (VLPs) inhibited BPV binding and focal transformation, while sera to denatured BPV virions, to denatured BPV L1, or to human papillomavirus type 16 (HPV-16) VLPs were not inhibitory. An exception was that antisera to BPV L2 were neutralizing but did not inhibit binding. Unlabeled BPV virions and BPV VLPs competed with binding to the cell surface in a concentration-dependent manner. Binding to the cell surface appeared to depend primarily on L1, since BPV VLPs composed of L1 alone or of L1/L2 were equally effective in inhibiting binding and focal transformation. VLPs of HPV-16 also inhibited BPV binding and BPV transformation of C127 cells, suggesting that they interact with the same cell surface molecule(s) as BPV virions. Radiolabeled BPV bound specifically to several mammalian cell lines of fibroblastic and epithelial origin, as well as to a human schwannoma and melanoma lines, although some lines bound up to 10 times as many counts as others. Radiolabeled HPV-16 VLPs bound to both human keratinocytes and mouse C127 cells. The results suggest that papillomaviruses bind a widely expressed and evolutionarily conserved cell surface receptor.

Animals↗
PubMed1994

Neutralization of bovine papillomavirus by antibodies to L1 and L2 capsid proteins.

We have generated four mouse monoclonal antibodies (MAbs) to bovine papillomavirus virions that bound type-specific, adjacent, and conformationally dependent epitopes on the L1 major capsid protein. All four MAbs were neutralizing at ratios of 1 MAb molecule per 5 to 25 L1 molecules, but only three effectively blocked binding of the virus to the cell surface. Therefore, antibodies can prevent papillomavirus infection by at least two mechanisms: inhibition of cell surface receptor binding and a subsequent step in the infectious pathway. The neutralizing epitopes of the bovine papillomavirus L2 minor capsid protein were mapped to the N-terminal half of L2 by blocking the neutralizing activity of full-length L2 antiserum with bacterially expressed peptides of L2. In addition, rabbit antiserum raised against amino acids 45 to 173 of L2 had a neutralizing titer of 1,000, confirming that at least part of the N terminus of L2 is exposed on the virion surface.

Animals↗
PubMed1994

Neurofibromin can inhibit Ras-dependent growth by a mechanism independent of its GTPase-accelerating function.

The NF1 gene, which is altered in patients with type 1 neurofibromatosis, has been postulated to function as a tumor suppressor gene. The NF1 protein product neurofibromin stimulates the intrinsic GTPase activity of active GTP-bound Ras, thereby inactivating it. Consistent with a tumor suppressor function, we have found that the introduction of NF1 in melanoma cell lines that are deficient in neurofibromin inhibited their growth and induced their differentiation. In addition, overexpression of neurofibromin in NIH 3T3 cells was growth inhibitory but did not alter the level of GTP.Ras in the cells. Transformation by v-ras, whose protein product is resistant to GTPase stimulation by neurofibromin, was inhibited in a cell line overexpressing neurofibromin, while transformation by v-raf was not altered. The results demonstrate that NF1 is a tumor suppressor gene that can inhibit Ras-dependent growth by a regulatory mechanism that is independent of neurofibromin's ability to stimulate Ras GTPase.

3T3 Cells↗
PubMed1994

Positive and negative regulation of cell proliferation by E2F-1: influence of protein level and human papillomavirus oncoproteins.

E2F-1 is a member of a family of transcription factors implicated in the activation of genes required for the progression through the S phase of the cell cycle. We have examined the biological activities of E2F-1 with short-term colony-forming assays and long-term immortalization assays. High levels of E2F-1, produced by transfection of the E2F-1 cDNA under the control of a strong promoter, reduced colony formation in normal human foreskin keratinocytes (NHFKs). This inhibition could not be overcome by wild-type human papillomavirus type 16 (HPV16) E6 and E7, two proteins which cooperate to immortalize NHFKs, or by a transdominant p53 mutant. High levels of E2F-1 also inhibited growth of primary and established fibroblasts. The growth-inhibitory activity required the DNA binding function of E2F-1 but not its transactivation or pRB binding activities. A positive role for lower levels of E2F-1 in NHFK immortalization was established by examining the ability of E2F-1 to complement HPV16 E7 mutants that were unable to cooperate with HPV16 E6 to immortalize NHFKs. Although E2F-1 was unable by itself to cooperate with E6, it did, in conjunction with E6, complement a p24GLY mutant of E7 that is defective for immortalization and binding of pRB and pRB-related proteins. By contrast, E2F-1 was unable to complement two other E7 mutants, p2PRO and p31/32ARG/PRO, which are also defective in the immortalization assay, although their proteins display wild-type binding of pRB in vitro. Since the binding of E7 to pRB results in disruption of pRB-E2F interaction and release of transcriptionally active E2F, the data support the hypothesis that binding of pRB by E7 and the consequence increase in E2F, the data support the hypothesis that binding of pRB by E7 and the consequence increase in E3F activity are important but not sufficient for E7-induced keratinocyte immortalization.

3T3 Cells↗
PubMed1993

Inactivation of the NF1 gene in human melanoma and neuroblastoma cell lines without impaired regulation of GTP.Ras.

The NF1 gene, which is altered in patients with type 1 neurofibromatosis, encodes neurofibromin, a protein whose GTPase-activating function can negatively regulate GTP-Ras by accelerating its conversion to inactive GDP-Ras. In schwannoma cell lines from patients with neurofibromatosis, loss of neurofibromin was previously shown to be associated with impaired regulation of GTP-Ras. Our analysis of other neural crest-derived tumor cell lines has shown that some melanoma and neuroblastoma cell lines established from tumors occurring in patients without neurofibromatosis contain reduced or undetectable levels of neurofibromin, with concomitant genetic abnormalities of the NF1 locus. In contrast to the schwannoma cell lines, GTP-Ras was appropriately regulated in the melanoma and neuroblastoma lines that were deficient in neurofibromin, even when c-H-ras was overexpressed in the lines. These results demonstrate that some neural crest tumors not associated with neurofibromatosis have acquired somatically inactivated NF1 genes and suggest a tumor-suppressor function for neurofibromin that is independent of Ras GTPase activation.

Blotting, Northern↗
PubMed1993

Cell transformation by ras and regulation of its protein product.

We are studying the biological activity and regulation of mammalian Ras protein in tumours and in physiological signalling. We have shown that GAP (the GTPase-activating protein) is a potent negative regulator of normal Ras in cells. Reduction or loss of the NF1 gene product neurofibromin, in association with genetic abnormalities of the NF1 locus, has been identified in schwannoma cell lines from patients with neurofibromatosis and in melanoma and neuroblastoma lines from patients without neurofibromatosis. Although loss of neurofibromin in the schwannoma lines was associated with a high proportion of normal Ras protein in the active GTP-bound state, Ras-GTP appeared to be appropriately regulated in the melanoma and neuroblastoma lines, which contain normal levels of GAP. Therefore the GTPase-activating activity of neurofibromin is not essential for negative regulation of Ras in some cell types and the putative tumour suppressor function of neurofibromin in such cell types is independent of its GTPase-activating activity. Mitogen activation of Ras in fibroblasts is mediated primarily by exchange factors, which probably interact with a region on the Ras protein distinct from the region required for interaction with GAP. Multiple full-length cDNAs have identified a mouse gene whose products are related to yeast CDC25 guanine nucleotide exchange factor.

Animals↗
PubMed1993

Efficient self-assembly of human papillomavirus type 16 L1 and L1-L2 into virus-like particles.

The L1 genes of two human papillomavirus type 16 (HPV16) isolates derived from condylomata acuminata were used to express the L1 major capsid protein in insect cells via recombinant baculoviruses. Both L1 major capsid proteins self-assembled into virus-like particles (VLP) with high efficiency and could be purified in preparative amounts on density gradients. The yield of VLP was 3 orders of magnitude higher than what has been obtained previously, using L1 derived from the prototype HPV16. DNA sequence comparison identified a single nonconserved amino acid change to be responsible for the inefficient self-assembly of the prototype L1. VLP were also obtained by expressing L1 of HPV6, HPV11, and cottontail rabbit papillomavirus, indicating that L1 from a variety of papillomaviruses has the intrinsic capacity to self-assemble into VLP. Coexpression of HPV16 L1 plus L2 by using a baculovirus double-expression vector also resulted in efficient self-assembly of VLP, and the average particle yield increased about fourfold in comparison to when L1 only was expressed. Coimmunoprecipitation of L1 and L2 and cosedimentation of the two proteins in a sucrose gradient demonstrated that L2 was incorporated into the particles. The ability to generate preparative amounts of HPV16 L1 and L1-L2 VLP may have implications for the development of a serological assay to detect anti-HPV16 virion immune responses to conformational epitopes and for immunoprophylaxis against HPV16 infection.

Animals↗
PubMed1993

Transformation-specific interaction of the bovine papillomavirus E5 oncoprotein with the platelet-derived growth factor receptor transmembrane domain and the epidermal growth factor receptor cytoplasmic domain.

The bovine papillomavirus E5 transforming protein appears to activate both the epidermal growth factor receptor (EGF-R) and the platelet-derived growth factor receptor (PDGF-R) by a ligand-independent mechanism. To further investigate the ability of E5 to activate receptors of different classes and to determine whether this stimulation occurs through the extracellular domain required for ligand activation, we constructed chimeric genes encoding PDGF-R and EGF-R by interchanging the extracellular, membrane, and cytoplasmic coding domains. Chimeras were transfected into NIH 3T3 and CHO(LR73) cells. All chimeras expressed stable protein which, upon addition of the appropriate ligand, could be activated as assayed by tyrosine autophosphorylation and biological transformation. Cotransfection of E5 with the wild-type and chimeric receptors resulted in the ligand-independent activation of receptors, provided that a receptor contained either the transmembrane domain of the PDGF-R or the cytoplasmic domain of the EGF-R. Chimeric receptors that contained both of these domains exhibited the highest level of E5-induced biochemical and biological stimulation. These results imply that E5 activates the PDGF-R and EGR-R by two distinct mechanisms, neither of which specifically involves the extracellular domain of the receptor. Consistent with the biochemical and biological activation data, coimmunoprecipitation studies demonstrated that E5 formed a complex with any chimera that contained a PDGF-R transmembrane domain or an EGF-R cytoplasmic domain, with those chimeras containing both domains demonstrating the greatest efficiency of complex formation. These results suggest that although different domains of the PDGF-R and EGF-R are required for E5 activation, both receptors are activated directly by formation of an E5-containing complex.

3T3 Cells↗
PubMed1993

The conserved C-terminal domain of the bovine papillomavirus E5 oncoprotein can associate with an alpha-adaptin-like molecule: a possible link between growth factor receptors and viral transformation.

The bovine papillomavirus E5 gene encodes an oncoprotein that can independently transform rodent fibroblasts. This small 44-amino-acid protein is thought to function through the activation of growth factor receptors. E5 activation of the epidermal growth factor receptor results in an increase in the number of activated receptors at the cell surface. This finding suggests that E5 may act by inhibiting the normal down regulation of activated epidermal growth factor receptor via coated pit-mediated endocytosis. We have constructed a fusion protein consisting of glutathione S-transferase and the conserved C-terminal domain of E5 (GST-E5) in order to identify E5-associated cellular proteins that may be involved in its transforming activity. We have identified a 125-kDa cellular protein with a strong associated serine kinase activity that specifically associated with GST-E5 in the reduced form but not with GST-E5 fusions that contained changes in several conserved amino acids. Microsequence and biochemical analyses suggest that p125 is a novel member of the alpha-adaptin family. Since alpha-adaptins have previously been shown to be involved in coated pit-mediated cell surface receptor endocytosis and down regulation, these results suggest that p125 may be an alpha-adaptin-like molecule involved in growth factor receptor down regulation and that E5 may act by inhibiting its activity.

3T3 Cells↗
PubMed1993

Functional role of GTPase-activating protein in cell transformation by pp60v-src.

Morphological transformation of NIH 3T3 cells was observed following coexpression of a portion of the ras GTPase-activating protein (GAP) comprising the amino terminus (GAP-N) and a mutant of v-src (MDSRC) lacking the membrane-localizing sequence. Cells expressing either of these genes alone remained nontransformed. Coexpression of GAP-N with MDSRC did not alter the subcellular localization, kinase activity, or pattern of cellular substrates phosphorylated by the MDSRC product. In contrast to SHC, phospholipase C-gamma 1, and the p85 alpha phosphatidylinositol 3'-kinase subunit, the endogenous GAP product (p120GAP) was highly tyrosine-phosphorylated only in cells transformed by wild-type v-src. Furthermore, for transformation induced by wild-type v-src as well as by coexpression of MDSRC and GAP-N, a strict correlation was observed between cell transformation, elevated tyrosine phosphorylation of p62, p190, and a novel protein of 150 kDa, and complex formation between these proteins and p120GAP. As with cells transformed by wild-type v-src, the MDSRC plus GAP-N transformants remained dependent on endogenous Ras. The results suggest that tyrosine phosphorylation and complex formation involving p120GAP represent critical elements of cell transformation by v-src and that complementation of the cytosolic v-src mutant by GAP-N results, at least in part, from the formation of these complexes.

3T3 Cells↗
PubMed1993

Regulated and constitutive activity by CDC25Mm (GRF), a Ras-specific exchange factor.

Serum stimulates cells to increase their proportion of Ras protein in the active GTP-bound state. We have recently identified four types (I to IV) of apparently full-length cDNAs from a single mammalian gene, called CDC25Mm or GRF, which is homologous to the Ras-specific exchange factor CDC25 of S. cerevisiae. The largest cDNA (type IV) is brain specific, with the other three classes, although they have distinct 5' ends, essentially representing progressive N-terminal deletions of this cDNA. When placed in a retroviral expression vector, all four types of cDNAs induced morphologic transformation of NIH 3T3 cells and an increase in the basal level of GTP.Ras. Serum stimulation of these transformants lead to a further increase in GTP.Ras only in cells expressing the type IV cDNA. Each type of GRF protein was found in cytosolic and membrane fractions, and the protein in each fraction could stimulate guanine nucleotide release from GDP.Ras in vitro. When NIH 3T3 cells and cells expressing the type IV protein were transfected with two versions of a mutant ras gene, one encoding membrane-associated Ras protein and the other encoding a cytosolic Ras protein, the basal levels of GTP bound to both forms of the mutant Ras protein were significantly higher in the cells expressing the type IV protein. However, serum increased the level of GTP bound to the membrane-associated mutant Ras protein in NIH 3T3 cells and in cells expressing the type IV protein but not in cells expressing the cytosolic version of the Ras protein. We conclude that each type of CDC25Mm induces cell transformation via the ability of its C terminus to stimulate guanine nucleotide exchange on Ras, the presence of N-terminal sequences is associated with a serum-dependent change in GTP.Ras, and the serum-dependent increase in GTP.Ras by exogenous CDC25Mm or by endogenous exchange factors probably requires membrane association of both Ras and the exchange factor.

3T3 Cells↗