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Biomedical subjects

W G Nelson

Publications and source records attributed to W G Nelson.

69 records · Page 4Linked to original sources
PubMed1993

Human papillomavirus 16 E6 expression disrupts the p53-mediated cellular response to DNA damage.

Infection with certain types of human papillomaviruses (HPV) is highly associated with carcinomas of the human uterine cervix. However, HPV infection alone does not appear to be sufficient for the process of malignant transformation, suggesting the requirement of additional cellular events. After DNA damage, normal mammalian cells exhibit G1 cell-cycle arrest and inhibition of replicative DNA synthesis. This mechanism, which requires wild-type p53, presumably allows cells to undertake DNA repair and avoid the fixation of mutations. We directly tested whether the normal response of cervical epithelial cells to DNA damage may be undermined by interactions between the E6 protein expressed by oncogenic HPV types and wild-type p53. We treated primary keratinocytes with the DNA-damaging agent actinomycin D and demonstrated inhibition of replicative DNA synthesis and a significant increase in p53 protein levels. In contrast, inhibition of DNA synthesis and increases in p53 protein did not occur after actinomycin D treatment of keratinocytes immortalized with HPV16 E6/E7 or in cervical carcinoma cell lines containing HPV16, HPV18, or mutant p53 alone. To test the effects of E6 alone on the cellular response to DNA damage, HPV16 E6 was expressed in the carcinoma cell line RKO, resulting in undetectable baseline levels of p53 protein and loss of the G1 arrest that normally occurs in these cells after DNA damage. These findings demonstrate that oncogenic E6 can disrupt an important cellular response to DNA damage mediated by p53 and may contribute to the subsequent accumulation of genetic changes associated with cervical tumorigenesis.

Cell Cycle↗
PubMed1993

Nuclear events of apoptosis in vitro in cell-free mitotic extracts: a model system for analysis of the active phase of apoptosis.

We have developed a cell-free system that induces the morphological transformations characteristic of apoptosis in isolated nuclei. The system uses extracts prepared from mitotic chicken hepatoma cells following a sequential S phase/M phase synchronization. When nuclei are added to these extracts, the chromatin becomes highly condensed into spherical domains that ultimately extrude through the nuclear envelope, forming apoptotic bodies. The process is highly synchronous, and the structural changes are completed within 60 min. Coincident with these morphological changes, the nuclear DNA is cleaved into a nucleosomal ladder. Both processes are inhibited by Zn2+, an inhibitor of apoptosis in intact cells. Nuclear lamina disassembly accompanies these structural changes in added nuclei, and we show that lamina disassembly is a characteristic feature of apoptosis in intact cells of mouse, human and chicken. This system may provide a powerful means of dissecting the biochemical mechanisms underlying the final stages of apoptosis.

Animals↗
PubMed1987

Growth-related elevations of DNA topoisomerase II levels found in Dunning R3327 rat prostatic adenocarcinomas.

The relationship between DNA topoisomerase II expression and mammalian cell proliferation has been evaluated by determining enzyme levels in normal and neoplastic rat prostate tissues. By activity assay and by immunoblot analysis using anti-topoisomerase II antiserum, topoisomerase II levels were found to be elevated in both the Dunning R3327-H and the Dunning R3327-G rat prostatic adenocarcinomas over levels assayed in the normal rat dorsal prostate. Immunohistochemical studies using the antitopoisomerase II antiserum revealed that a greater fraction of nuclei contained detectable levels of topoisomerase II in tissue sections prepared from each of the Dunning tumors than in rat dorsal prostate tissue sections. The Dunning R3327-H and R3327-G tumors grow at different rates in vivo (J. T. Isaacs and D. S. Coffey, Clin. Oncol., 2: 479-498, 1983). When measured topoisomerase II levels were compared to known growth parameters for each of the tissues studied, topoisomerase II expression was found to be correlated with tissue growth rate.

Adenocarcinoma↗
PubMed1987

Synergistic enhancement by tumor necrosis factor of in vitro cytotoxicity from chemotherapeutic drugs targeted at DNA topoisomerase II.

Recombinant human tumor necrosis factor (rHTNF) alone had no effect on L929 tumor cells at 100 units/ml for 20 h of continuous exposure. However, under the same conditions, rHTNF markedly enhanced the cytotoxicity of Adriamycin, actinomycin D, 4'-(9-acridinylamino)-methanesulfon-m-anisidide, teniposide (VM 26), and etoposide (VP 16), all targeted at DNA topoisomerase II. The rHTNF had a minimally enhancing effect on the cytotoxicity of bleomycin, hydroxyurea, and 1-beta-D-arabinofuranosylcytosine and no effect on the cytotoxicity of cis-platinum, mitomycin C, vincristine, and vinblastine, all chemotherapeutic drugs with dose-related cytotoxic effects on L929 cells but mechanisms of action which do not appear to involve topoisomerase II. Treatment with rHTNF first and then topoisomerase-targeted drugs yielded no enhanced cytotoxicity, whereas pretreatment with drug followed by rHTNF yielded marked enhancement of cytotoxicity. Topoisomerases have previously been implicated in cell kill phenomena following treatment with certain chemotherapeutic agents [K.M. Tewey, et al., Science (Wash. DC), 226:466-468, 1984]. The data suggest that the lethality to the cell from topoisomerase-targeted drug treatment is increased by rHTNF in vitro. We suggest that rHTNF may be a useful adjuvant to this class of drugs which has well-known antitumor activity.

Animals↗
PubMed1987

Structural aspects of mammalian DNA replication: topoisomerase II.

The dynamic biology of mammalian DNA requires structural complexity. Previous studies on the structure and function of mammalian DNA have suggested that mammalian cell nuclei contain DNA organized into loop-domains by a nuclear structural subcomponent termed the nuclear matrix. The loop-domains, functioning as replicons during DNA synthesis, appear to be replicated by biosynthetic complexes located at fixed sites within the nuclear matrix milieu. Recently, we have found the mammalian DNA topoisomerase II enzyme to be associated with newly replicated DNA, and we speculate that the enzyme may be strategically positioned to untangle topologically intertwined daughter loop-domains before mitotic segregation. Further studies demonstrating growth-related elevations of DNA topoisomerase II levels in rat prostatic adenocarcinoma tissues support a role for the enzyme in cellular proliferation in vivo. The possible participation of DNA topoisomerase II in mammalian DNA replication and the proliferation-dependent appearance of the enzyme in neoplastic tissues may have important implications for therapeutic strategies directed at DNA topoisomerase II.

Animals↗
PubMed1984

Specific keratins as molecular markers for neoplasms with a stratified epithelial origin.

The expression of specific keratin polypeptides in human neoplasms was investigated by the immunoblot technique using monoclonal anti-keratin antibodies. Mr 50,000 and 58,000 keratins, recognized by AE1 and AE3 antibodies, respectively, were detected only in carcinomas of stratified epithelial origin, but not in carcinomas derived from simple epithelia. No keratin was detected in nonepithelial tumors including melanoma, lymphoma, neurofibroma, and sarcoma. The results suggest that the Mr 50,000 and 58,000 keratins provide useful molecular markers for identifying neoplasms of stratified squamous epithelial origin.

Antibodies, Monoclonal↗
PubMed1983

The 50- and 58-kdalton keratin classes as molecular markers for stratified squamous epithelia: cell culture studies.

The keratins are a highly heterogeneous group of proteins that form intermediate filaments in a wide variety of epithelial cells. These proteins can be divided into at least seven major classes according to their molecular weight and their immunological reactivity with monoclonal antibodies. Tissue-distribution studies have revealed a correlation between the expression of specific keratin classes and different morphological features of in vivo epithelial differentiation (simple vs. stratified; keratinized vs. nonkeratinized). Specifically, a 50,000- and a 58,000-dalton keratin class were found in all stratified epithelia but not in simple epithelia, and a 56,500- and a 65-67,000-dalton keratin class were found only in keratinized epidermis. To determine whether these keratin classes can serve as markers for identifying epithelial cells in culture, we analyzed cytoskeletal proteins from various cultured human cells by the immunoblot technique using AE1 and AE3 monoclonal antikeratin antibodies. The 56,500- and 65-67,000-dalton keratins were not expressed in any cultured epithelial cells examined so far, reflecting the fact that none of them underwent morphological keratinization. The 50,000- and 58,000-dalton keratin classes were detected in all cultured cells that originated from stratified squamous epithelia, but not in cells that originated from simple epithelia. Furthermore, human epidermal cells growing as a monolayer in low calcium medium continued to express the 50,000- and 58,000-dalton keratin classes. These findings suggest that the 50,000- and 58,000-dalton keratin classes may be regarded as "permanent" markers for stratified squamous epithelial cells (keratinocytes), and that the expression of these keratin markers does not depend on the process of cellular stratification. The selective expression of the 50,000- and 58,000-dalton keratin classes, which are synthesized in large quantities on a per cell basis, may explain the high keratin content of cultured keratinocytes.

Antibodies, Monoclonal↗
PubMed1983

Keratin classes: molecular markers for different types of epithelial differentiation.

Keratins are a group of water-insoluble proteins (molecular weight range 40-70 K) that form 10-nm tonofilaments in a wide variety of epithelial cells. The subunit composition of the keratin filaments varies with cell type, period of embryonic development, stage of histologic differentiation, cellular growth environment, and disease state. To better understand the functional significance of individual keratin species, we have generated three monoclonal antikeratin antibodies to different subsets of keratins and used these antibodies to localize specific keratins in normal human epidermis by a combination of immunohistochemical and biochemical techniques. The results indicate that the 50 K and 58 K keratins are present in all cell layers including the relatively undifferentiated basal layer, whereas the 56.5 K and 65-67 K keratins are associated only with the more differentiated cells above the basal layer. In a separate series of experiments, we used the monoclonal antibodies to survey the keratins expressed by various nonepidermal epithelia. The data show that keratins can be divided into at least seven major classes according to their immunologic reactivity and size. Among the keratin classes, the 50 K and 58 K classes appear to be characteristic of all stratified squamous epithelia, whereas the 56.5 K and 65-67 K classes are unique to the keratinized epidermis. These findings suggest that specific keratin classes, as defined by monoclonal antibodies, may serve as useful markers for different types of epithelial differentiation (simple versus stratified, keratinized versus nonkeratinized).

Animals↗
PubMed1983

Keratin expression during normal epidermal differentiation.

The four major epidermal keratins (65-67K, 58K, 56K, and 50K) have been localized in various cell layers of normal human epidermis. Guinea pig antisera and mouse monoclonal antibodies were prepared against human epidermal keratins and were characterized with respect to their specificity to individual keratin polypeptides by the immunoblot technique. These antibodies were used to stain vertical frozen sections of skin, and to identify keratins extracted from serial, horizontal skin sections. The results indicate that: (1) a 65-67K keratin component is limited to the suprabasal layers, (2) a 58K keratin is present throughout the epidermis, (3) a 56K keratin appears to be made only in cells above the basal layer, possibly in the upper spinous or granular layer, and (4) a 50K keratin is present in all living layers but is largely eliminated during stratum corneum formation. The 65-67K and 56K keratins, which are characteristic of suprabasal, terminally differentiated keratinocytes, may be regarded as molecular markers of keratinization.

Antibodies, Monoclonal↗
PubMed1982

Correlation of specific keratins with different types of epithelial differentiation: monoclonal antibody studies.

We have prepared three monoclonal antibodies against human epidermal keratins. These antibodies were highly specific for keratins and, in combination, recognized all major epidermal keratins of several mammalian species. We have used these antibodies to study the tissue distribution of epidermis-related keratins. In various mammalian epithelia, the antibodies recognized seven classes of keratins defined by their immunological reactivity and size. The 40, 46 and 52 kilodalton (kd) keratin classes were present in almost all epithelia; the 50 kd and 58 kd keratin classes were detected in all stratified squamous epithelia, but not in any simple epithelia; and the 56 kd and 65-67 kd keratin classes were unique to keratinized epidermis. Thus the expression of specific keratin classes appeared to correlate with different types of epithelial differentiation (simple versus stratified; keratinized versus nonkeratinized).

Animals↗
PubMed1982

Immunolocalization of keratin polypeptides in human epidermis using monoclonal antibodies.

Three monoclonal antibodies (AE1, AE2, and AE3) were prepared against human epidermal keratins and used to study keratin expression during normal epidermal differentiation. Immunofluorescence staining data suggested that the antibodies were specific for keratin-type intermediate filaments. The reactivity of these antibodies to individual human epidermal keratin polypeptides (65-67, 58, 56, and 50 kdaltons) was determined by the immunoblot technique. AE1 reacted with 56 and 50 kdalton keratins, AE2 with 65-67 and 56-kdalton keratins, and AE3 with 65-67 and 58 kdalton keratins. Thus all major epidermal keratins were recognized by at least one of the monoclonal antibodies. Moreover, common antigenic determinants were present in subsets of epidermal keratins. To correlate the expression of specific keratins with different stages of in vivo epidermal differentiation, the antibodies were used for immunohistochemical staining of frozen skin sections. AE1 reacted with epidermal basal cells, AE2 with cells above the basal layer, and AE3 with the entire epidermis. The observation that AE1 and AE2 antibodies (which recognized a common 56 kdalton keratin) stained mutually exclusive parts of the epidermis suggested that certain keratin antigens must be masked in situ. This was shown to be the case by direct analysis of keratins extracted from serial, horizontal skin sections using the immunoblot technique. The results from these immunohistochemical and biochemical approaches suggested that: (a) the 65- to 67-kdalton keratins were present only in cells above the basal layer, (b) the 58-kdalton keratin was detected throughout the entire epidermis including the basal layer, (c) the 56-kdalton keratin was absent in the basal layer and first appeared probably in the upper spinous layer, and (d) the 50-kdalton keratin was the only other major keratin detected in the basal layer and was normally eliminated during s. corneum formation. The 56 and 65-67-kdalton keratins, which are characteristic of epidermal cells undergoing terminal differentiation, may be regarded as molecular markers for keratinization.

Antibodies, Monoclonal↗
PubMedDate not supplied

Newly replicated DNA is associated with DNA topoisomerase II in cultured rat prostatic adenocarcinoma cells.

DNA topoisomerases have been proposed to function in a variety of genetic processes in both prokaryotes and eukaryotes. Here, we have assessed the role of DNA topoisomerase II in mammalian DNA replication by determining the proximity of newly synthesized DNA to covalent enzyme-DNA complexes generated by treating cultured rat prostatic adenocarcinoma cells with teniposide. Teniposide (VM-26), an epipodophyllotoxin, is known to interact with mammalian DNA topoisomerase II so as to trap the enzyme in a covalent complex with DNA. We have found that the teniposide-induced trapping of such complexes requires MgCl2, is stimulated by ATP and is inhibited by novobiocin. The formation of covalent complexes seems to be reversible on removal of teniposide. Furthermore, analysis of the covalent complexes formed between 3H-thymidine pulse-labelled DNA and topoisomerase II following teniposide treatment reveals a direct association of the enzyme with nascent DNA fragments. Our results suggest that DNA topoisomerase II may interact with newly replicated daughter DNA molecules near DNA replication forks in mammalian cells.

Adenocarcinoma↗