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L T Chow

Publications and source records attributed to L T Chow.

At least 19 recordsLinked to original sources
PubMed1992

Viral E1 and E2 proteins support replication of homologous and heterologous papillomaviral origins.

We have shown that E1 and E2 proteins of human papillomavirus type 11 (HPV-11) were essential to support the replication of the homologous viral origin (ori) in a transient replication assay, similar to reports on bovine papillomavirus type 1 (BPV-1). Unexpectedly, matched or even mixed combinations of E1 and E2 proteins from HPV-11 or BPV-1 replicated either ori in human, monkey, and rodent cell lines of epithelial or fibroblastic lineage, albeit with varied efficiencies. Either set of viral proteins was also able to initiate replication of ori-containing plasmids from many other human and animal papillomaviruses. Thus the interactions among the cis elements and trans factors of papillomaviruses are more conserved than expected from the other members of the papovavirus family, simian virus 40 and polyomavirus, for which large tumor antigen does not replicate a heterologous ori in either permissive or nonpermissive cells. We infer that the stringent species and tissue specificities observed for papillomaviruses in vivo are not entirely due to direct restrictions on viral DNA replication. Rather, transcriptional control of viral gene expression must play a dominant role.

3T3 Cells↗
PubMed1992

Expression of high-affinity laminin receptor mRNA correlates with cell proliferation rather than invasion in human papillomavirus-associated cervical neoplasms.

Induction of the expression of the Mr 67,000 high-affinity laminin receptor gene has been postulated as playing a role in the progression of human tumors to invasive cancers. We tested this hypothesis by examining histopathological sections of a large number of epithelial lesions of the genital tract associated with human papillomaviruses. In situ hybridization was performed with a riboprobe generated from a laminin receptor complementary DNA. Laminin receptor mRNA was expressed primarily in the less differentiated cells in normal squamous tissues and in a spectrum of squamous neoplasms. There was no net induction of mRNA per cell in intraepithelial or invasive squamous neoplasms relative to normal tissue. In contrast, laminin receptor mRNA was not expressed at a detectable level in normal glands of the uterine cervix but was dramatically induced in morphologically abnormal, human papillomavirus-positive glands, irrespective of the genotype of human papillomaviruses present. The induction occurred before any evidence of invasion, and there was no further increase during the transition from adenocarcinoma in situ to invasive carcinoma. We conclude that induction of high-affinity laminin receptor gene expression is associated with the development of malignancies of cervical glandular epithelia, but the increased expression appears to correlate with the proliferative rather than the invasive properties of these cells.

Blotting, Northern↗
PubMed1992

Intermolecular triplex formation distorts the DNA duplex in the regulatory region of human papillomavirus type-11.

A conformational distortion in the DNA duplex at the regulatory region of human papillomavirus type-11 next to an intermolecular triplex, formed with a synthetic oligonucleotide, was investigated with several chemical probes. The sequence targeted for triplex formation borders on the binding sites for the regulatory proteins encoded by the viral E2 open reading frame. Dimethyl sulfate, diethyl pyrocarbonate, and OsO4 all react to a greater extent with nucleotides in the duplex that are immediately adjacent to the triplex as compared to other bases throughout the duplex. This hypermodification was observed on both the polypurine and polypyrimidine strands of the duplex DNA. Similar hyperreactivity of bases flanking a triplex also was seen when the contiguous target polypurine tract was effectively extended by mutating interrupting pyrimidines in the human papillomavirus type-11 sequence to purines. We propose that this hyperreactivity is due to a structural distortion caused by the junction between the triplex and the duplex tracts.

Base Sequence↗
PubMed1992

Properties of bovine papillomavirus E1 mutants.

Ostensibly comparable mutants of bovine papillomavirus type 1 (BPV-1) affecting the E1 open reading frame that were constructed in several laboratories have been reported to exhibit either reduced or increased transformation efficiencies in established mouse cell lines relative to wild-type BPV-1 DNA. To resolve these discrepancies, we have reexamined many of the mutants in mouse C127 cells by using focus formation assays. Our primary conclusions are that all E1 mutants tested consistently generated reduced numbers of transformants and that the reduced transformation was not due to cell toxicity associated with E1 mutations, as had been proposed. Our results can best be explained by the inability of the E1 mutants to replicate extrachromosomally, therefore leading to a rapid loss of the BPV-1 DNA and consequently, reduced transformation. In support of this hypothesis, we demonstrated that the human papillomavirus type 11 E1 protein was able to suppress BPV-1 transformation, probably because of interference with BPV-1 replication. Therefore, we attribute the phenotypic disparities reported by the various laboratories to still undefined differences in assay conditions.

Animals↗
PubMed1992

Human papillomavirus type 16 and 18 gene expression in cervical neoplasias.

Human papillomavirus (HPV) types 16 and 18 are strongly implicated in the generation of progressive cervical neoplasms. The viruses produce complex families of overlapping messenger RNAs that are linked to differentiation, making it necessary to analyze gene expression in the context of morphology. We have developed HPV type 16 and type 18 subgenomic clones from which 3H-labeled riboprobes specific to individual mRNA families can be generated in vitro. Using these probes for in situ hybridization, we examined serial sections of archival biopsy specimens of the spectrum of genital lesions. In low-grade squamous lesions, all viral open reading frames were expressed, and the most abundant transcription spanned the E4 and E5 open reading frames at the 3' end of the E region. L region transcription coding for the capsid proteins was restricted to terminally differentiated keratinocytes. As the grade of neoplasia increased, cellular differentiation and overall viral transcription decreased and, with few exceptions, the L2 and L1 transcripts ceased to exist. The E6-E7 transforming region was invariably derepressed. Interestingly, the patterns of HPV-16 gene expression suggested the coexistence of episomal and integrated viral DNAs. In contrast, in HPV-18 lesions, all the viral template DNA appeared to have integrated. Integration was deduced to have occurred near the boundary of the E1 and E2 open reading frames. Viral transcription patterns were similar in carcinomas in situ and in invasive carcinomas, regardless of the histologic cell types or the associated virus types, consistent with the notion that additional host gene alterations were necessary for progression. On the basis of viral gene expression in vivo and the E6 promoter regulation previously characterized in vitro, we discuss a molecular mechanism for HPV-associated carcinogenesis.

Adenocarcinoma↗
PubMed1992

Extranodal Rosai-Dorfman disease: an uncommon cause of persistent nodule in the ear.

A 40-year-old woman presented with a nodule over the tragus of the right ear. A biopsy was initially reported as showing non-specific inflammation. In view of the persistence of the lesion, the histological material was reviewed, leading to revision of the diagnosis to Rosai-Dorfman disease, a diagnosis further confirmed by immunoreactivity of the histiocytes for S-100 protein. This case represented the extranodal form of Rosai-Dorfman disease in the absence of lymph node involvement.

Adult↗
PubMed1992

Epithelioid hemangioendothelioma of the brain.

Epithelioid hemangioendothelioma is a recently described vascular neoplasm characterized by epithelioid tumor cells and borderline biologic behavior. Its four principal sites of occurrence are the soft tissue, liver, lung, and bone. We report a case of primary cerebral epithelioid hemangioendothelioma in a 4-month-old male infant. The tumor consisted of loose aggregates of epithelioid cells with a focal cordlike or bridging-branching pattern, supported in a fibromyxoid stroma. The tumor cells displayed frequent intracytoplasmic vacuoles. Immunohistochemically, the tumor cells showed positive staining for Ulex europaeus agglutinin, vimentin, and cytokeratin. The tumor pursued an indolent clinical course. The patient was alive 28 months after initial presentation, but he was left with a severe neurological deficit because of the location and growth of the tumor.

Brain↗
PubMed1992

Perineurioma: an uncommon soft tissue neoplasm distinct from localized hypertrophic neuropathy and neurofibroma.

Perineurial cells, which normally surround the nerve fascicles within a nerve, can be distinguished from Schwann cells by their immunoreactivity for epithelial membrane antigen (EMA) and lack of reactivity for S-100 protein. We report two cases of perineurioma, a tumor composed exclusively of perineurial cells and distinct from other nerve sheath tumors. The first case involved a deep, soft-tissue mass of the neck, and the second involved a tumor located in the infraclavicular subcutaneous tissue. Both tumors were well circumscribed. Histologically, they were hypocellular and composed of spindle cells possessing elongated nuclei and bipolar, wavy, slender, strikingly elongated cytoplasmic processes, disposed in a background of collagen in the form of short bundles and whorls. In the first case, there were frequent calcospherites and remnants of a small nerve at the periphery. The spindle cells stained for EMA but not S-100 protein, chromogranin, neuron-specific enolase or Leu-7. Ultrastructurally, they possessed long cytoplasmic processes with incomplete basal lamina and occasional pinocytotic vesicles. Axons were not identified. Review of the literature shows that genuine perineuriomas are rare, and most cases reported as such are merely examples of localized hypertrophic neuropathy, a mononeuropathy characterized by fusiform swelling of a nerve, usually in the extremities. The involved segment in localized hypertrophic neuropathy contains distended fascicles composed of whorls of perineurial cells and fibrous tissue entrapping residual axons, probably representing a hyperplastic reaction to nerve damage. The term perineurioma should be reserved for the neoplasm composed only of perineurial cells and presenting as a soft tissue tumor.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Production of human papillomavirus and modulation of the infectious program in epithelial raft cultures. OFF.

Human papillomaviruses trophic for anogenital epithelia cause benign warts, and certain genotypes are closely associated with cervical neoplasia. By using our modifications of the epithelial raft culture system, we were able to recapitulate and modulate the infectious program of a papillomavirus in vitro for the first time. Small pieces of a condyloma containing human papillomavirus type 11 were explanted onto a dermal equivalent consisting of a collagen matrix with fibroblasts and were cultured at the medium-air interface. The infected stem cells proliferated rapidly across the matrix, stratified, and differentiated, as judged by histology. The results correlated with the state of epithelial differentiation, which, in turn, was dependent on the type of fibroblast in the matrix. Under conditions where the epithelial outgrowth underwent terminal differentiation, the entire productive program took place, leading to virion assembly. In contrast, using an alternative condition where the outgrowth failed to achieve terminal differentiation, only the E-region RNAs from the E1 promoter accumulated to any appreciable extent. The proliferating cell nuclear antigen was induced in the differentiated suprabasal cells in the productive cyst growth, which also exhibited high copy viral DNA and abundant E6-E7 RNAs. Comparable cells in the nonproductive cyst outgrowth were negative for all three. These results suggest that the E6 and E7 proteins may play a role in establishing a cellular environment conducive to vegetative viral replication. The culture conditions described should be useful for genetic analysis of this family of important human pathogens and for testing potential pharmacological agents.

3T3 Cells↗
PubMed1992

Control of human papillomavirus type 11 origin of replication by the E2 family of transcription regulatory proteins.

Replication of human papillomavirus type 11 (HPV-11) DNA requires the full-length viral E1 and E2 proteins (C.-M. Chiang, M. Ustav, A. Stenlund, T. F. Ho, T. R. Broker, and L. T. Chow, Proc. Natl. Acad. Sci. USA 89:5799-5803, 1992). Using transient transfection of subgenomic HPV DNA into hamster CHO and human 293 cells, we have localized an origin of replication (ori) to an 80-bp segment in the upstream regulatory region spanning nucleotide 1. It overlaps the E6 promoter region and contains a short A + T-rich segment and a sequence which is homologous to the binding site of the bovine papillomavirus type 1 (BPV-1) E1 protein in the BPV-1 ori. However, unlike the BPV-1 ori, for which half an E2-responsive sequence (E2-RS) or binding site suffices, an intact binding site is essential for the HPV-11 ori. Replication was more efficient when additional E2-RSs were present. The intact HPV-11 genome also replicated in both cell lines when supplied with E1 and E2 proteins. Expression vectors of transcription repressor proteins that lack the N-terminal domain essential for E2 transcriptional trans activation did not support replication in collaboration with the E1 expression vector. Rather, cotransfection with the repressor expression vectors inhibited ori replication by the E1 and E2 proteins. These results demonstrate the importance of the N-terminal domain of the E2 protein in DNA replication and indicate that the family of E2 proteins positively and negatively regulates both viral DNA replication and E6 promoter transcription.

Animals↗
PubMed1992

Solitary necrotic nodule of the liver: parasitic origin?

AIMS: To report further cases of solitary necrotic nodule of the liver and to study its nature. METHODS: Seven nodules were retrieved from 4000 necropsy and surgical liver specimens coming to light over the past five years. All of them satisfied the diagnostic criteria of solitary necrotic nodule: a solid lesion with a central necrotic core and a hyalinised fibrotic capsule containing elastic fibres. Their clinicopathological features were reviewed. RESULTS: The nodules were incidental findings at surgery or necropsy in four men and three women whose ages ranged from 48 to 79 years (mean 63.7 years). Four were found in the right lobe and three in the left. Six were subcapsular and only one deep in the parenchyma, with sizes ranging from 0.3-2.5 cm. Each of them was solitary, well demarcated, and round to oval with a firm, whitish rim and a core of yellowish white cheese-like to solid material. In addition to the basic architecture, there were a number of common and undescribed histological features: presence of varying numbers of small mural vessels with intimal fibrosis and obliteration, presence of cholesterol clefts and foamy cells among necrotic material, and sparsity of inflammatory cells. In the two cases where ghosts of degenerated cells and partially preserved liver reticulin pattern were noted, worms were identified, one being Clonorchis sinensis. CONCLUSIONS: The entity is believed to be a "burnt-out phase" of a variety of benign lesions. Parasitic infestation is another possible cause, and presence of ghosts of degenerate cells, partially preserved liver reticulin pattern, cholesterol clefts and foamy cells among necrotic material are auxiliary features pointing to such an aetiology. The variation in morphological fine details reflects both the lesion's diverse pathogenesis and the fact that it can be of varying duration.

Aged↗
PubMed1992

Recombinant retroviruses encoding human papillomavirus type 18 E6 and E7 genes stimulate proliferation and delay differentiation of human keratinocytes early after infection.

Human papillomavirus (HPV) DNAs are detected in most genital dysplasias and cancers, suggesting that these viruses perturb epithelial growth and differentiation. The E6 and E7 genes of HPV type 18 induce immortality in keratinocytes cultured from genital tract epithelia, and the immortal cell lines display aberrant squamous differentiation. To examine whether the E6 and E7 proteins directly alter keratinocyte growth and differentiation, high-titer recombinant retroviruses were constructed for efficient transfer and expression of HPV-18 genes E6, E6* and E7 in cultures of normal human keratinocytes. Infection with retroviruses encoding E6 and E7 stimulated cell proliferation, reduced the requirement for bovine pituitary extract and induced immortality. E6 and E7 also delayed but did not prevent the onset of terminal squamous differentiation. The magnitude of effects on growth and differentiation of cultured cells was directly related to levels of E7 protein expression. Thus, expression of the HPV-18 E6 and E7 genes stimulates cell proliferation and delays differentiation of keratinocytes in vitro.

Blotting, Southern↗