PubMed Health⌕ Search

Biomedical subjects

M Dürst

Publications and source records attributed to M Dürst.

At least 19 recordsLinked to original sources
PubMed2006

Solution structure of the partially folded high-risk human papilloma virus 45 oncoprotein E7.

The oncoprotein E7 of human papilloma viruses (HPV) is involved in the pathogenesis and maintenance of human cervical cancers. The most prevalent HPV types found in cervix carcinomas are HPV16, 18 and 45. The structure of the E7 dimer from HPV45 (PDB 2F8B) was determined by nuclear magnetic resonance spectroscopy. Each monomer comprises an unfolded N-terminus and a well-structured C-terminal domain with a beta1beta2alpha1beta3alpha2 topology representing a unique zinc-binding fold found only for E7. Dimerization occurs through the alpha1/alpha1' helices and intermolecular beta-sheet formation but excludes the zinc-binding sites. E7 is reported to interact with a number of cellular proteins (e.g. pRb, p21(CIP1)). Binding of a peptide derived from the C-terminus of p21(CIP1) to the C-terminal domain of E7 was characterized by monitoring chemical shift perturbations of the amide groups of E7. This provides direct evidence that a shallow groove situated between alpha1 and beta1 of the E7 C-terminal domain is interacting with the C-terminus of p21(CIP1). Intriguingly, this binding site overlaps with the low-affinity binding site on E7 for the C-domain of pRb.

Amino Acid Sequence↗
PubMed2006

Aberrant methylation of the Wnt antagonist SFRP1 in breast cancer is associated with unfavourable prognosis.

The canonical Wnt signalling pathway plays a key role during embryogenesis and defects in this pathway have been implicated in the pathogenesis of various types of tumours, including breast cancer. The gene for secreted frizzled-related protein 1 (SFRP1) encodes a soluble Wnt antagonist and is located in a chromosomal region (8p22-p12) that is often deleted in breast cancer. In colon, lung, bladder and ovarian cancer SFRP1 expression is frequently inactivated by promoter methylation. We have previously shown that loss of SFRP1 protein expression is a common event in breast tumours that is associated with poor overall survival in patients with early breast cancer. To investigate the cause of SFRP1 loss in breast cancer, we performed mutation, methylation and expression analysis in human primary breast tumours and breast cell lines. No SFRP1 gene mutations were detected. However, promoter methylation of SFRP1 was frequently observed in both primary breast cancer (61%, n=130) and cell lines analysed by methylation-specific polymerase chain reaction (MSP). We found a tight correlation (P<0.001) between methylation and loss of SFRP1 expression in primary breast cancer tissue. SFRP1 expression was restored after treatment of tumour cell lines with the demethylating agent 5-aza-2'-deoxycytidine. Most interestingly, SFRP1 promoter methylation was an independent factor for adverse patient survival in Kaplan-Meier analysis. Our results indicate that promoter hypermethylation is the predominant mechanism of SFRP1 gene silencing in human breast cancer and that SFRP1 gene inactivation in breast cancer is associated with unfavourable prognosis.

Adult↗
PubMed2003

Establishment and characterisation of human papillomavirus type 16 DNA immortalised human tonsillar epithelial cell lines.

Oncogenic human papillomavirus (HPV) plays a possible aetiological role in a subset of head and neck cancers, particularly in tonsillar carcinomas. For establishing a model to study mechanisms involved in HPV-associated tonsillar carcinogenesis, normal human tonsillar epithelial (HTE) cells were transfected with full-length HPV-16 DNA. The transfections produced four immortalised cell lines, designated HTE-114/K1, HTE-114/K2, HTE-114/K3 and HTE-114/B. All transfected HTE cell lines were cytogenetically abnormal. They exhibited altered morphology and impaired expression of cytokeratins in organotypic cultures. They failed to form colonies in soft agarose and formed no tumours in nude mice within 6 months. Each of them contained integrated viral DNA in a distinctive pattern as shown by Southern blot hybridisation. Early viral transcripts containing the E7 gene were detected by northern blot hybridisation. In conclusion, primary HTE cells can be immortalised following transfection with full-length HPV-16 DNA; the immortalised cell lines had partially retained epithelial characteristics in their morphology and function. They seem to represent early stages of premalignant epithelial cells and thus provide a useful model for studying further the multistep molecular events of HPV-16-associated tonsillar carcinogenesis.

Animals↗
PubMed2002

HPV induced cervical carcinogenesis: molecular basis and vaccine development.

Association of infection with papillomavirus and dysplasia of the cervix uteri has been firmly established. There are only few cervical cancers where no HPV DNA is detectable. The mechanism of epithelial cell immortalization by interaction with tumour suppressor genes p53 and pRb by viral oncogenes E6 and E7 is elucidated. Progression of the HPV infected cell to a malignant phenotype involves further modification of host gene expression and/or mutations. The appearance of chromosomal aberrations can lead to mutational inactivation or loss of tumour suppressor genes (TSG), activation and amplification of oncogenes, with importance for the process of carcinogenesis. Oncogene amplification, with exception of few reports, seems not to be a major mechanism in cervical carcinogenesis. In contrast, cytogenetic and loss of heterozygosity (LOH) results from CIN and invasive cancer demonstrate alterations at specific chromosomal regions, pointing at localisation of TSG. Genetic alterations at chromosomes 3p, 6p, 1lq were frequently found early in tumour development Primary invasive carcinoma showed additional allelic losses at chromosome arms 6q, 17p and 18q. Useful biological diagnostic and prognostic markers for high-risk HPV infection and malignant progression may be p16NK4 p27Kip, and NET-I/C4.8. Putative senescence genes relevant for HPV-induced carcinogenesis are localized on chromosomes 2, 4 and 10. Genes for Telomerase suppression are presumably located on chromosomes 3, 4 and 6. Natural immune responses to HPV infection exist Therefore, immune therapy is an attractive possibility for prevention and therapy of HPV infection. To date, vaccine development has reached clinical evaluation. Prophylaxis aims at the induction of virus neutralizing antibodies to capsid proteins. Virus-like particle vaccines are currently tested in clinical trials. Due to the long lag period between infection and clinical manifestation trials will take a long time until conclusive results are obtained. Mandatory expression of viral and perhaps certain cellular genes in infected epithelial and tumour cells offers targets for therapeutic approaches. Since most dysplasia clears spontaneously the viral infection is immunogenic to some extent. However, in some individuals the immune response has to be stimulated by vaccination in order to be effective. Several strategies are being tested in clinical trials and others are in preclinical development The task will be to circumvent immunosuppressive features of the HPV infected cells.

Chromosome Mapping↗
PubMed2001

Evidence for a putative senescence gene locus within the chromosomal region 10p14-p15.

High-risk human papillomavirus (HPV) types 16 and 18 are involved in the multistep process of cervical cancer. Transfection of normal keratinocytes with high-risk HPV-DNA generally gives rise to immortal cultures. This may be explained by the loss of senescence genes as a consequence of HPV-induced genetic instability. On the basis of the dominance of cellular senescence over immortality, fusion of normal keratinocytes with HPV-immortalized cells results in complementation of these putative gene defects. In a previous study, we showed that underrepresentation of chromosome 10 is a characteristic phenomenon during the early phase of immortalization. Here we show that introduction of a normal copy of chromosome 10 into HPV16-immortalized cells (HPKII) by Microcell-mediated chromosome transfer resulted in senescence of a significant number of hybrids. By using several derivatives of chromosome 10 for further fusion experiments, the chromosomal region responsible for senescence could be assigned to 10p14-p15. The potential significance of loss of gene function in this region is underlined by the high frequency (38.7%) of loss of heterozygosity in cervical cancers including early stage tumors.

Carcinoma, Squamous Cell↗
PubMed2001

HPV16 L1E7 chimeric virus-like particles induce specific HLA-restricted T cells in humans after in vitro vaccination.

Cervical cancer has been shown to be highly associated with human papillomavirus (HPV) infection. The viral oncogenes E6 and E7 are constantly expressed by the tumor cells and are therefore targets for immunotherapy. In the present study we investigated the potential of HPV16 L1E7 chimeric virus-like particles (CVLP) to activate specific cytotoxic T lymphocytes in human blood donors. CVLP were expressed by recombinant baculovirus and purified. Direct incubation of freshly isolated peripheral blood lymphocytes (PBL) with CVLP resulted in induction of proliferation and growth of T cell lines. To enhance antigen presentation we also loaded dendritic cells with CVLP and used them to activate naive T cells. Growing cell lines were mainly CD3 positive (>95%) with a predominant CD4-positive and a minor CD8-positive component. Analysis of Tcell specificity was carried out by an interferon-gamma ELISpot assay. Dendritic cells pseudoinfected with CVLP or pulsed with human leukocyte antigen (HLA)-A*0201-restricted peptide E7(11-20) or with a newly identified HPV16 peptide L1(323-331) were used as stimulator cells. T cells responsive to CVLP were found in the cultures with frequencies of 0.5%-0.7%. Frequencies to peptides were around 0.1%. These T cells had cytolytic activity toward autologous B-lymphoblastic cell lines either pseudoinfected with CVLP or pulsed with HLA-A*0201-restricted peptides. They also lysed the HPV16- and HLA-A*0201-positive cervical cancer cell line CaSki, whereas HLA-A*0201-negative SiHa cells were not lysed. We conclude from our data that CVLP show promise for a therapeutic vaccine in patients with HPV16-positive cervical intraepithelial neoplasia lesions or cervical cancer.

Antigens, Viral↗
PubMed2001

Detection of integrated papillomavirus sequences by ligation-mediated PCR (DIPS-PCR) and molecular characterization in cervical cancer cells.

Human papillomavirus (HPV) genomes usually persist as episomal molecules in HPV associated preneoplastic lesions whereas they are frequently integrated into the host cell genome in HPV-related cancers cells. This suggests that malignant conversion of HPV-infected epithelia is linked to recombination of cellular and viral sequences. Due to technical limitations, precise sequence information on viral-cellular junctions were obtained only for few cell lines and primary lesions. In order to facilitate the molecular analysis of genomic HPV integration, we established a ligation-mediated PCR assay for the detection of integrated papillomavirus sequences (DIPS-PCR). DIPS-PCR was initially used to amplify genomic viral-cellular junctions from HPV-associated cervical cancer cell lines (C4-I, C4-II, SW756, and HeLa) and HPV-immortalized keratinocyte lines (HPKIA, HPKII). In addition to junctions already reported in public data bases, various new fusion fragments were identified. Subsequently, 22 different viral-cellular junctions were amplified from 17 cervical carcinomas and 1 vulval intraepithelial neoplasia (VIN III). Sequence analysis of each junction revealed that the viral E1 open reading frame (ORF) was fused to cellular sequences in 20 of 22 (91%) cases. Chromosomal integration loci mapped to chromosomes 1 (2n), 2 (3n), 7 (2n), 8 (3n), 10 (1n), 14 (5n), 16 (1n), 17 (2n), and mitochondrial DNA (1n), suggesting random distribution of chromosomal integration sites. Precise sequence information obtained by DIPS-PCR was further used to monitor the monoclonal origin of 4 cervical cancers, 1 case of recurrent premalignant lesions and 1 lymph node metastasis. Therefore, DIPS-PCR might allow efficient therapy control and prediction of relapse in patients with HPV-associated anogenital cancers.

Base Sequence↗
PubMed2001

Mass spectrometry meets chip technology: a new proteomic tool in cancer research?

DNA chip technologies are the most exiting genomic tools, which were developed within the last few years. It is, however, evident that knowledge of the gene sequence or the quantity of gene expression is not sufficient to predict the biological nature and function of a protein. This can be particularly important in cancer research where post-translational modifications of a protein can specifically contribute to the disease. To address this problem, several proteomic tools have been developed. Currently the most widely used proteomic tool is two-dimensional protein gel electrophoresis (2-DE), which can display protein expression patterns to a high degree of resolution. As an alternative to 2-DE, a preliminary study using a new technique was employed to generate protein expression patterns from whole tissue extracts. Surface-enhanced laser desorption/ionization (SELDI) allows the retention of proteins on a solid-phase chromatographic surface (ProteinChip Array) with direct detection of retained proteins by time of flight-mass spectrometry (TOF-MS). Using this system, we analyzed eight cases of renal cell carcinoma (RCC) including normal, peripheral and central tumor tissue as well as four microdissected cases of cervical intraepithelial neoplasia (CIN) and three microdissected cases of cervix uteri carcinoma. Differentially expressed proteins were found by comparing the protein expression patterns generated using SELDI-based TOF-MS of tumor tissue with normal and neoplastic tissue, respectively. By applying this fast and powerful ProteinChip array technology it becomes possible to investigate complex changes at the protein level in cancer associated with tumor development and progression.

Carcinoma, Renal Cell↗
PubMed2001

Microcell-mediated transfer of chromosome 4 into HeLa cells suppresses telomerase activity.

Telomerase activity can be detected in most human cancers and immortal cell lines. In contrast, the lack of telomerase activity in normal diploid fibroblasts has been correlated with progressive reduction of telomere lengths to critically short sizes followed by the cessation of cell division and the onset of senescence. Several investigators have provided evidence for the localization of a telomerase suppressor gene on chromosome 3. The aim of our study was to determine whether other chromosomes are involved in telomerase repression. Beside human chromosome 3 (serving as positive control), chromosomes 4, 6, and 11 were introduced into HeLa cells via microcell-mediated chromosome transfer. Telomerase activity from different hybrid cell lysates was determined at an early time point after fusion using a Telomerase ELISA kit. Strong repression of telomerase activity was only found in a subset of HeLa hybrids in which chromosome 3 or chromosome 4 had been introduced. Telomerase suppression induced by chromosome 3 or 4 transfer was paralleled by a high frequency (30% or 43%, respectively) of a senescent-like phenotype. Chromosomes 6 and 11, the functional loss of which is also implicated in cervical cancer, had no effect. These results indicate that normal human chromosomes 3 and 4 carry a gene or genes that suppress telomerase activity and induce cellular senescence in HeLa cells.

Cell Line, Transformed↗
PubMed2001

p53 mutations are rare events in recurrent cervical cancer.

Mutations of the p53 gene have been shown to be associated with aggressive growth behavior and increased recurrence rates for certain tumors. Primary cervical cancers contain oncogenic human papillomaviruses (HPV) in more than 90% of cases and usually possess wild-type p53 alleles. Cervical cancer cells contain detectable levels of functional p53 protein despite of the expression of the HPV E6 protein, which can induce p53 degradation. Thus, inactivation of p53 by somatic mutation should have functional consequences in HPV-positive cancers. We investigated whether p53 mutations play a role in the recurrence of the disease by analyzing p53 status in 18 biopsy specimens from recurrent cervical cancers. Only one of these (5.6%) contained a p53 mutation, as assessed by a sensitive yeast functional assay that detects mutations of the p53 mRNA between codons 52 and 364. These results indicate that p53 mutations are rare events in recurrent cervical carcinomas, and that somatic mutations of p53 do not provide cervical cancer cells with a selective growth advantage for recurrence.

Adult↗
PubMed2001

[HPV infection and cervical carcinoma--epidemiology, detection and immunology].

Certain molecularly defined types of human papillomaviruses (HPV) induce, by interaction with additional cofactors, cervical cancer. In comparison to infection with HPV, all risk factors identified to date are less important. In addition to HPV a not yet classified genetic predisposition is important. Identification of HPV in cervical smears is done by detection of viral DNA. PCR based methods have the highest specificity. Currently, first vaccination studies with therapeutic vaccines are performed and phase I/II trials for prophylactic vaccination show promising results.

Female↗
PubMed2000

Screening for high-grade cervical intra-epithelial neoplasia and cancer by testing for high-risk HPV, routine cytology or colposcopy.

The validity of testing for high-risk types of human papillomavirus (HPV) in cervical cancer prevention programs is undetermined. We compared the performance on primary screening of HPV DNA testing, cytology and colposcopy in detecting cervical intra-epithelial neoplasia (CIN) grade 2 or 3 or cancer. A cohort of 4,761 women, median age 35 years, was screened by routine cytology, routine colposcopy and testing for high-risk HPV by a PCR-based method. Within an 8-month period, women with abnormal findings on cytology or screening colposcopy or in whom high-risk HPV types were detected were referred for colposcopy and biopsy. Women negative on all initial screening tests were followed by a second screening examination. To correct for work-up bias, the true prevalence of CIN 2 or 3 or cancer was estimated by projection from histologically verified subgroups. Cervical biopsies were taken in 364 women (7.6%), of whom 114 (2.4%) showed CIN 2 (n = 34) or CIN 3 (n = 71) or cancer (n = 9). High-risk HPV testing achieved bias-corrected performance measures of 89.4% sensitivity, 93.9% specificity, 35.8% positive predictive value and 99.6% negative predictive value. Bias-corrected rates of true- and false-positives by high-risk HPV testing compared to cytology (colposcopy) were about 4.5 (6.7) and 19.1 (7.4) times higher, respectively. The quality of routine cytology was controlled by computer-assisted review, and the observed number of true-positives more than doubled after adding automated review results. In middle-aged women, testing for high-risk HPV types, particularly when negative, may be used to increase the screening interval in programs for secondary prevention of cervical cancer.

Adult↗
PubMed2000

Absence of antibody against human papillomavirus type 16 E6 and E7 in patients with cervical cancer is independent of sequence variations.

It is not known whether the lack of antibody response against human papillomavirus (HPV) type 16 E6 and E7 among some cervical cancer patients is due to naturally existing sequence variations. In this study, naturally occurring HPV-16 E6 and E7 variants (including the prototype) were cloned, antigens were expressed by in vitro transcription and translation, and the humoral immune response of 34 HPV-16-positive cervical cancer patients was analyzed by radioimmunoprecipitation assay (RIPA). In addition, the RIPA results were compared with those of a sandwich-protein ELISA, to further substantiate antibody status. Sera lacking E6 reactivity by RIPA remained negative by protein ELISA. All E6 antigens (the prototype and the variants 350G¿L83V, 131G¿R10G/350G¿L83V, 335T¿H78Y/350G¿L83V, 345G¿Y81C/350G¿L83V, and African 2 ¿Af2) showed cross-reactivity by RIPA. The lack of HPV-16 E6 or E7 antibodies is independent of naturally occurring variants in cervical cancer patients. Thus, testing for HPV-16 E6 or E7 prototype antigens seems to be sufficient in serological assays.

Amino Acid Substitution↗
PubMed2000

Differential cell cycle response of nontumorigenic and tumorigenic human papillomavirus-positive keratinocytes towards transforming growth factor-beta1.

Human papillomaviruses (HPVs) are causative agents of a number of malignancies in humans, including cervical cancer. Their tumorigenic potential is linked to expression of the viral E6/E7 genes which can interfere with normal cell cycle control by targeting p53, p21WAF1, p27KIP1, and pRb. We show here that nontumorigenic and tumorigenic HPV-positive keratinocytes (HPK) exhibit striking differences in the response of cell cycle regulatory genes towards transforming growth factor beta-beta1. Treatment with this agent led to an efficient induction of p53 and the growth-inhibitory p15INK4 and p21WAF1 genes only in nontumorigenic HPKs and was linked to an efficient reduction in viral E6/E7 oncogene expression. This was associated with increased pRb levels, exhibiting sustained hypophosphorylation, and a permanent growth arrest in the G1 phase of the cell cycle. In contrast, tumorigenic HPKs exhibited only a modest rise in p53 protein levels and a substantially reduced induction of the p15INK4 and p21WAF1 genes, which was linked to a lesser degree of viral oncogene repression. In addition, tumorigenic HPKs rapidly resumed cell growth after a transient G1 arrest, concomitantly with the reappearance of hyperphosphorylated pRb. These results support the notion that the progression of HPV-positive cells to a malignant phenotype is associated with increased resistance to growth inhibition by transforming growth factor-beta1. This is linked in the tumorigenic cells to a lack of persistent G1 arrest, inefficient induction of several cell cycle control genes involved in growth inhibition, and inefficient repression of the growth-promoting viral E6/E7 oncogenes.

Blotting, Northern↗
PubMed1999

Uniform distribution of HPV 16 E6 and E7 variants in patients with normal histology, cervical intra-epithelial neoplasia and cervical cancer.

High-risk human papillomaviruses (HPV), particularly HPV 16, are associated with invasive cervical cancer (ICC), and persistent high-risk HPV infection is considered to be a marker for progressive cervical intra-epithelial neoplasia (CIN). However, most high-risk, HPV-infected, pre-cancerous lesions will not progress to invasion. Several reports suggest that specific HPV 16 E6 and/or E7 sequence variations may be associated with a high risk for progression. No data from German patients have so far been reported. Therefore, we analyzed intra-type variations of these oncogenes in women with normal histology or CIN 1 (< or = CIN 1), CIN 2/3 or ICC. Cervical scrapes from 75 patients with normal histology or CIN and biopsies from 37 ICC patients all positive for HPV 16 were analyzed. The open reading frames of oncogenes HPV 16 E6 and E7 were amplified by nested PCR followed by primer cycle sequencing. From each cervical scrape, 2 independent PCR amplicons were generated and sequenced from both orientations. The prototype sequence of HPV 16 E6 and E7 was identified in 33% and 87% of < or = CIN 1, in 62% and 69% of CIN 2/3 and in 43% and 86% of ICC, respectively (not significant). Of all variants identified, the E6 variant 350G (L83V) and the E7 variant 822G were most frequently detected irrespective of histology and showed prevalence rates of 27% to 43% and 7% to 20%, respectively. No statistically significant differences in the prevalence of the E6 or E7 prototype sequences, any variants or multivariants in German women with < or = CIN 1, CIN 2/3 or ICC were found.

Adolescent↗
PubMed1999

Overriding of cyclin-dependent kinase inhibitors by high and low risk human papillomavirus types: evidence for an in vivo role in cervical lesions.

High risk types of human papillomavirus (HPV) are agents in the aetiology of cervical carcinoma. The products of two early genes, E6 and E7, appear to be the principal transforming proteins. Studies of various monolayer cell culture systems have shown that the E7 oncoprotein of human papillomavirus type 16 is able to neutralize or bypass the inhibitory effect of the cell cycle-dependent kinase (CDK) inhibitors (CKIs) p21WAF1/CIP1 and p27KIP1. To understand whether the p21WAF1/CIP1 or p27KIP1 neutralization also plays a role in vivo, we performed studies on clinical specimens. Forty-five cervical biopsies, including HPV-negative mucosa, HPV 16-positive preinvasive (low and high grade lesions) and invasive neoplasia as well as HPV 6-positive condyloma acuminatum were analysed by single and double immunohistology. We examined the positive cell cycle regulator cyclin A and the universal cell cycle marker Ki67 as well as the negative cell cycle regulators p21WAF1/CIP1 and p27KIP1. Here, we show that in a significant fraction of cells the G1 block can be overcome despite high levels of CKIs in HPV lesions. This phenomenon, which was more evident for p21WAF1/CIP1 than for p27KIP1 was most marked in low grade lesions and in condylomata acuminata, in which a high viral productivity is expected. These results indicate that the overriding of CKI inactivation by viral oncoproteins appears to be a conserved property between low and high risk HPV types. We conclude that the CKI neutralization by HPVs is likely to be required for viral DNA replication rather than for malignant transformation of the host cell.

Carcinoma, Squamous Cell↗
PubMed1998

Identification of novel molecular markers which correlate with HPV-induced tumor progression.

High risk HPVs (human papillomaviruses) are causally involved in the development of cervical cancer. However, other factors, such as somatic genetic alterations also play a decisive role in malignant conversion of cervical keratinocytes. Mutations and chromosomal aberrations are known to influence the pattern of gene expression. Therefore we used the recently developed RT-PCR based method of differential display of mRNAs to detect differences in gene expression which correlate with tumorigenicity. Non-tumorigenic HPV16-immortalized human foreskin keratinocytes (HPK IA) were compared with their tumorigenic counterparts and 49 different genes were identified which were either up- or downregulated. The identified genes encode proteins of the cytoskeleton and the extracellular matrix, the nuclear splicing apparatus, transcription regulators and membrane-associated proteins. The expression pattern of all genes was also examined by RNA-RNA in situ hybridization in biopsies of normal cervical epithelium, precancerous lesions and cancers. Two genes, C4.8 and C21.7, are of particular interest because their expression is upregulated in a subset of high grade precancerous lesions and in over 58% of cancers. These two genes may therefore be considered as putative progression markers. C4.8 is a new member of the transmembrane 4 (TM-4) protein family which includes tumor-associated antigens such as CD63 and TAPA-1, whereas C21.7 shows no significant homologies to any known genes or proteins.

Amino Acid Sequence↗