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Biomedical subjects

R D Burk

Publications and source records attributed to R D Burk.

At least 91 records · Page 5Linked to original sources
PubMed1994

Outcome of perinatal hepatitis B virus exposure is dependent on maternal virus load.

To evaluate the role of maternal hepatitis B virus (HBV) DNA levels in perinatal infection, two nested case-control studies were done within a cohort of 773 hepatitis B surface antigen (HBsAg)-positive Taiwanese women and their infants. As serum HBV DNA levels increased from < 0.005 to > or = 1.4 ng/mL among the hepatitis B e antigen (HBeAg)-positive mothers, the odds ratio (OR) for having a persistently infected infant increased from 1.0 to 147.0 (P for trend < .001). Among HBeAg-negative mothers, the OR for having a persistently infected infant was 19.2 (95% confidence interval, 2.3-176.6) in mothers with high versus low levels of serum HBV DNA. A logistic regression analysis identified maternal HBV DNA to be a stronger independent predictor of persistent infection than HBeAg status. Thus, perinatal exposure to high levels of maternal HBV DNA is the most important determinant of infection outcome in the infant.

Case-Control Studies↗
PubMed1994

Cell-mediated immune responses to E7 peptides of human papillomavirus (HPV) type 16 are dependent on the HPV type infecting the cervix whereas serological reactivity is not type-specific.

Forty-two women attending a colposcopy clinic for evaluation of abnormal cervical cytology and 13 normal controls were studied for the presence of lymphocyte proliferation (LP) cell-mediated immune (CMI) responses and serological reactivity to E7 peptides of human papillomavirus type 16 (HPV-16). HPV was typed by Southern blot hybridization of exfoliated cervicovaginal cell DNA. Positive LP responses (stimulation index > or = 5.0) to one or more E7 peptides were observed in 28.6% (12 of 42) of patients and 23.1% (three of 13) of controls. Of patients infected with HPV-16, -31 or -33, 63.6% (seven of 11) showed a positive LP response compared with 14.3% (two of 14) of women infected with other HPV types (P = 0.02), 17.6% (three of 17) negative for HPV (P = 0.02) and 23.1% (three of 13) of controls (HPV status unknown) (P = 0.05). C-terminal peptide 109 (amino acids 72 to 97) elicited positive LP responses in 45.4% (five of 11) of patients infected with HPV -16, -31 or -33 compared with 7.1% (one of 14) patients infected with other HPVs (P = 0.04), 5.9% (one of 17) of women negative for HPV (P = 0.02) and 7.7% (one of 13) of controls (P = 0.05). HPV-16 group-specific LP responses of borderline significance were also observed against E7 peptides 103, 105 and 108 (17-37, 37-54 and 62-80) (P = 0.07). ELISA reactivity (IgG) to E7 peptide 109 (72-97) was present in 7.7% (one of 13) of controls, 35.3% (six of 17) of HPV-negative patients, 42.9% (six of 14) of patients infected with other HPVs, and only 9.1% (one of 11) of patients infected with HPV-16, -31 or -33. CMI responses to C-terminal HPV-16 E7 peptide 109 (72-97) were thus significantly related to ongoing cervical infection with HPV-16 and closely related types, whereas serological reactivity to E7 peptides was not HPV type-specific.

Amino Acid Sequence↗
PubMed1994

Involvement of canine oral papillomavirus in generalized oral and cutaneous verrucosis in a Chinese Shar Pei dog.

Severe papillomatosis developed in the oral cavity and spread throughout the haired skin of the trunk and limbs of an 8-month-old female Chinese Shar Pei dog. The dog had received corticosteroids prior to referral, which was associated with the onset of demodecosis and papillomatosis. Papillomavirus structural antigens were detected in biopsies by immunohistochemistry using a panel of monoclonal and polyclonal antibodies. An 8.2-kilobase papillomavirus-specific DNA molecule was detected in the cutaneous lesions by high stringency Southern blot hybridization using a cloned canine oral papillomavirus DNA probe. Restriction enzyme analysis revealed that the virus in the cutaneous lesions was identical to the canine oral papillomavirus. Discontinuation of the steroids combined with the use of a mitocide, antibiotics, and an autogenous vaccine resolved the demodecosis and papillomatosis. This case report suggests that corticosteroid-induced immunosuppression can expand the tissue tropism of papillomaviruses.

Adrenal Cortex Hormones↗
PubMed1993

Identification of proximal and distal regulatory elements of the rat connexin32 gene.

We have investigated the genetic basis of the transcriptional regulation of the rat connexin32 gene which encodes the major gap junction protein in rat liver. Primer extension analysis of RNA isolated from adult rat liver identified multiple initiation sites clustered between -110 bp and -50 bp upstream from the translation start codon. An approx. 760 bp genomic DNA fragment upstream of the first exon which included the mRNA start sites was cloned 5' to the luciferase reporter cassette in p19LUC to yield pCx32-800/-33-LUC. Transfection of pCx32-800/-33-LUC resulted in a 200-fold increase in luciferase activity above p19LUC in the human hepatoma cell line HuH-7. Using a series of vectors containing 5' deletions of the 760 bp fragment, a basal promoter was localized between -179 bp and -134 bp. Three DNA:protein complexes were identified with the basal promoter fragment by DNA mobility shift assay using nuclear extracts from HuH-7 cells. Two of the DNA-binding complexes appeared to be related to the transcription factor Sp1. In addition, three DNase hypersensitive (HS) sites were identified within the genomic locus of connexin32 in adult rat liver. Two of the DNase HS regions behaved as silencer elements with both the native promoter and a heterologous promoter in HuH-7 cells. These data demonstrate that (1) the active promoter responsible for rat connexin32 mRNA transcription is located upstream of the first exon, (2) a basal promoter region was localized to a 50 bp region which formed multiple DNA:protein complexes, and (3) multiple proximal and distant regulatory elements are involved in the expression of connexin32.

Animals↗
PubMed1993

Characterization of the role of individual protein binding motifs within the hepatitis B virus enhancer I on X promoter activity using linker scanning mutagenesis.

A combination of linker scanning mutagenesis and deletional analyses has been used to determine the role of individual DNA-protein binding sites on expression from the hepatitis B virus (HBV) enhancer I-X promoter (map position (mp) 1042-1354, HBV adw2). Linker scanning mutation of the EF-C site caused a 67.5% drop in X promoter activity in HuH7 cells, but had no effect in HepG2 or HepSK cells. Mutation of the E element resulted in an approximately 50% reduction in X promoter activity in HuH7, HepG2, and HepSK cells. Deletional analysis showed that sequences upstream of the EF-C site (mp 1163) were required for full X promoter activity and implicated the NF-1a site as being sufficient for basal X promoter activity. However, PCR-directed linker scanning mutation of the NF-1a site did not cause a reduction in X promoter activity, indicating that this site was not an essential component of the X promoter. Taken together, these results indicated that multiple, partially redundant protein:DNA interactions in the enhancer I are essential for full X promoter activity. The lack of an essential basal promoter element supports the suggestion that the two separate HBV enhancer elements (enhI and enhII) were created by integration of the X gene into a primordial enhancer element.

Base Sequence↗
PubMed1993

The genetic drift of human papillomavirus type 16 is a means of reconstructing prehistoric viral spread and the movement of ancient human populations.

We have investigated the diversity of a hypervariable segment of the human papillomavirus type 16 (HPV-16) genome among 301 virus isolates that were collected from 25 different ethnic groups and geographic locations. Altogether, we distinguished 48 different variants that had diversified from one another along five phylogenetic branches. Variants from two of these branches were nearly completely confined to Africa. Variants from a third branch were the only variants identified in Europeans but occurred at lower frequency in all other ethnic groups. A fourth branch was specific for Japanese and Chinese isolates. A small fraction of all isolates from Asia and from indigenous as well as immigrant populations in the Americas formed a fifth branch. Important patterns of HPV-16 phylogeny suggested coevolution of the virus with people of the three major human races, namely, Africans, Caucasians, and East Asians. But several minor patterns are indicative of smaller bottlenecks of viral evolution and spread, which may correlate with the migration of ethnic groups in prehistoric times. The colonization of the Americas by Europeans and Africans is reflected in the composition of their HPV-16 variants. We discuss arguments that today's HPV-16 genomes represent a degree of diversity that evolved over a large time span, probably exceeding 200,000 years, from a precursor genome that may have originated in Africa. The identification of molecular variants is a powerful epidemiological and phylogenetic tool for revealing the ancient spread of papillomaviruses, whose trace through the world has not yet been completely lost.

Africa↗
PubMed1993

Hormonal regulation of hepatitis B virus gene expression: influence of androgen receptor.

Adult HBV-transgenic males produce more hepatitis B surface antigen (HBsAg) in serum than females. The difference decreases with castration and is restored with testosterone replacement. To investigate the contribution of the androgen receptor in this process, HBV-transgenic males were mated with females heterozygous for the testicular feminization mutation (Tfm), an X-linked gene with 90% reduced androgen receptor. A total of 19 phenotypic HBV-transgenic females were studied, of which eight XYTfm females were identified by the presence of Y-chromosome DNA using molecular hybridization. The 11 normal (XX) females had 11.7 +/- 3.5 micrograms/mL (mean +/- SD) of HBsAg in their serum, whereas the Tfm (XY) females had 17.1 +/- 5.9 micrograms/mL (p < 0.05). However, the Tfm (XY) females produced less HBsAg than 33 normal (XY) males (41 +/- 12 micrograms/mL), and the overall ratio of male/female HBsAg levels was reduced: XY/XX = 3 versus XYTfm/XX = 1.5. Although dexamethasone caused an increase in XYTfm and XX mice, testosterone did not increase HBsAg in XYTfm. These data indicate that hepatitis B expression as measured by HBsAg levels in this animal model is mediated through an androgen receptor.

Androgen-Insensitivity Syndrome↗
PubMed1993

Hepatocyte transplantation: an alternative system for evaluating cell survival and immunoisolation.

To evaluate systems for barrier immunoisolation of transplanted hepatocytes, we used transgenic mouse hepatocytes that secrete HBsAg. Hepatocytes were rapidly encapsulated in chitosan, a cationic polymer derived by deacetylation of chitin. Chitosan was allowed to electrostatically bond with anionic sodium alginate for creating an outer bipolymer membrane of the capsules. After encapsulation, hepatocyte viability remained unchanged for seven days in vitro with secretion of HBsAg into the culture medium throughout this period. Following intraperitoneal transplantation of encapsulated hepatocytes, HBsAg promptly appeared in blood of recipients. In congeneic recipients, serum HBsAg peaked at two weeks. Hepatocytes were present in recovered chitosan capsules and expressed HBsAg mRNA. In allogeneic recipients, however, serum HBsAg disappeared within one week and recovered chitosan capsules showed lymphomononuclear cells but not hepatocytes. Transplantation of chitosan encapsulated HbsAg secreting hepatocytes failed to induce an anti-HBs response, suggesting modulation of the host immune response. These results indicate that transplantation systems using genetically modified hepatocytes which secrete gene products in the blood of recipients should facilitate evaluation of hepatocyte encapsulation.

Animals↗
PubMed1993

Women with human immunodeficiency virus infection and abnormal Papanicolaou smears: a prospective study of colposcopy and clinical outcome.

OBJECTIVE: To determine the effect of human immunodeficiency virus (HIV) infection on colposcopic and histologic findings and clinical outcome in women who have abnormal Papanicolaou smears. METHODS: We conducted a prospective study of women with abnormal Papanicolaou smears from among those participating in a longitudinal study of HIV infection, human papillomavirus infection, and genital neoplasia. Women with squamous intraepithelial lesions (SIL) on blindly interpreted Papanicolaou smears were referred for colposcopy and standard gynecologic care. Colposcopic and histologic findings were correlated with cytology, and differences between HIV seropositives and seronegatives were analyzed. RESULTS: Thirty-eight of 48 women referred underwent colposcopy, of whom 36 (94.7%) had colposcopic or histologic findings no more severe than those suggested by Papanicolaou smear. Seventeen of 25 HIV seropositives (68%) had cervical or vaginal condyloma or neoplasia, compared with three of 13 seronegatives (23%) (odds ratio [OR] 7.1, 95% confidence interval [CI] 1.5-33.0). Among seropositives, seven (28%) had cervical intraepithelial neoplasia (CIN) grade II or III; ten (40%) had cervical or vaginal condyloma, CIN I, or both; and eight (32%) had no vaginal or cervical SIL. There was no case of invasive carcinoma. Seven seropositives (28%) had or developed multicentric disease, compared with no seronegatives (P = .07). Follow-up ranged at 3-37 months and showed that all three treated seronegative women and five of ten treated seropositive women had normal examinations. Three seropositive patients had persistent disease without progression, and two had progression of condyloma. No CIN II, CIN III, or invasive carcinoma was seen during follow-up. CONCLUSIONS: Among women seropositive for HIV who had SIL on a Papanicolaou smear, colposcopic and histologic findings were predicted reliably by the cytologic smear. Rapid progression of CIN after standard gynecologic care for early genital lesions was not seen.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Loss of heterozygosity on chromosome 17p and mutant p53 in HPV-negative cervical carcinomas.

Inactivation of the protein product of the wild-type tumour suppressor gene p53 through complexing of the protein with the E6 oncoprotein of human papillomaviruses (HPV) in HPV-infected cells is thought to be important in the aetiology of cervical carcinoma. Mutations of p53 have also been reported in HPV-negative carcinomas, and we now demonstrate loss of heterozygosity (LOH) of chromosome region 17p13 (in which p53 is located) in such tumours. Immunocytochemical staining with monoclonal antimutant-p53 antibody revealed that the carcinomas with LOH on 17p and completely lacking HPV DNA sequences had mutant p53. Thus the LOH had apparently resulted in the loss of the wild-type allele. Consequently, in both HPV-positive and HPV-negative tumours there is loss of function of wild-type p53, in the former because the protein product of the p53 gene complexes with that of the viral E6 gene, in the latter because the protein is altered, presumably as a result of a direct alteration of the p53 gene but possibly because of other post-translational changes. That this mutant allele of the tumour suppressor gene may sometimes behave like an oncogene is suggested by the presence of more than the expected number of copies of the remaining chromosome 17 homologue in some carcinomas.

Chromosome Aberrations↗
PubMed1992

Human papillomavirus type 13 and pygmy chimpanzee papillomavirus type 1: comparison of the genome organizations.

Human papillomavirus type 13(HPV-13) is associated with oral focal epithelial hyperplasia (FEH) in humans. A recent epidemic of a FEH-like disease in a pygmy chimpanzee (Pan paniscus) colony allowed us to clone a novel papillomavirus genome. To assess the homology between HPV-13 and the pygmy chimpanzee papillomavirus type 1 (PCPV-1), the complete nucleotide sequences of both FEH-related viruses were determined. In both viruses, all eight major open reading frames were located on one strand and the genomic organization was similar to that of other mucosal papillomaviruses. The genomes of PCPV-1 and HPV-13 showed extensive overall sequence homology (85%). They could be classified, using phylogenetic analysis, together with HPV types 6, 11, 43, and 44 in a group associated with benign orogenital lesions. These data indicate that two phylogenetically related papillomaviruses can elicit similar pathology in different primate host species, reflecting viral genomic similarities.

Animals↗
PubMed1992

Biologic characteristics of specific human papillomavirus types predicted from morphology of cervical lesions.

Human papillomavirus (HPV) DNA was detected by Southern blot hybridization in cervicovaginal lavage samples from 199 of 329 (60.5%) women attending a municipal hospital colposcopy clinic. Human papillomavirus was identified in 195 of 264 (73.9%) patients with a squamous intraepithelial lesion or cancer on biopsy or Papanicolaou smear (Bethesda system) compared with 11 of 65 (16.9%) without squamous intraepithelial lesion (P < .0001). The most common HPV type identified was HPV 16 (20.6% of positive samples), and 36.7% of isolates contained uncharacterized HPVs. Of women with cervical intraepithelial neoplasia (CIN) grade III or cancer, 23.4% were infected with HPV 16 compared with less than 4% with any other single HPV type. Based on biopsy diagnosis in patients infected with specific HPV types, HPVs 6 and 11 had low oncogenic potential; HPVs 18, 31, 35, and 45 had intermediate oncogenic potential; and HPVs 16 and 33 had high oncogenic potential. Hyperchromatic, unusually enlarged nuclei ("meganuclei"), and/or abnormal mitoses were found significantly more often in lesions infected with HPVs 16, 33, and 35 than in those infected with HPVs 6, 11, 18, 31, and 45, even in low-grade lesions, and may represent a histologic marker for HPVs with significant oncogenic potential. Human papillomavirus capsid protein was detected significantly less often by immunocytochemical staining in CIN I and CIN II lesions infected with HPVs 16 and 33 (8.3%) than in those infected with HPVs 6, 11, 18, and 31 (60%; P = .007), suggesting early abnormalities in cellular differentiation in lesions infected with highly oncogenic HPVs.

Antigens, Viral↗