Neoplastic transformation of human epidermal keratinocytes by AD12-SV40 and Kirsten sarcoma viruses

Cancer cells arise from bacteria

Background

The origin of cancer cells is the most fundamental yet unresolved problem in cancer research. Cancer cells are thought to be transformed from the normal cells. However, recent studies reveal that the primary cancer cells (PCCs) for cancer initiation and secondary cancer cells (SCCs) for cancer progression are formed in but not transformed from the senescent normal and cancer cells, respectively. Nevertheless, the cellular mechanism of PCCs/SCCs formation is unclear. Here, based on the evidences (1) the nascent PCCs/SCCs are small and organelle-less resembling bacteria; (2) our finding that the cyanobacterium TDX16 acquires its algal host DNA and turns into a new alga TDX16-DE by de novo organelle biogenesis, and (3) PCCs/SCCs formations share striking similarities with TDX16 development and transition, we propose the bacterial origin of cancer cells (BOCC).

Presentation of the hypothesis

The intracellular bacteria take up the DNAs of the senescent/necrotic normal cells/PCCs and then develop into PCCs/SCCs by hybridizing the acquired DNAs with their own ones and expressing the hybrid genomes.

Testing the hypothesis

BOCC can be confirmed by testing BOCC-based predictions, such as normal cells with no intracellular bacteria can not "transform" into cancer cells in any conditions.

Implications of the hypothesis

According to BOCC theory: (1) cancer cells are new single-celled eukaryotes, which is why the hallmarks of cancer are mostly the characteristics of protists; (2) genetic changes and instabilities are not the causes, but the consequences of cancer cell formation; and (3) the common role of carcinogens, infectious agents and relating factors is inducing or related to cellular senescence rather than mutations. Therefore, BOCC theory provides new rationale and direction for cancer research, prevention and therapy.

Upregulation of endocan by Epstein-Barr virus latent membrane protein 1 and its clinical significance in nasopharyngeal carcinoma

Endocan (or called Esm-1) has been shown to have tumorigenic activities and its expression is associated with poor prognosis in various cancers. Latent membrane protein 1 (LMP1) is an Epstein-Barr virus (EBV)-encoded oncoprotein and has been shown to play an important role in the pathogenesis of EBV-associated nasopharyngeal carcinoma (NPC). To further understand the role of LMP1 in the pathogenesis of NPC, microarray analysis of LMP1-regulated genes in epithelial cells was performed. We found that endocan was one of the major cellular genes upregulated by LMP1. This induction of endocan by LMP1 was confirmed in several epithelial cell lines including an NPC cell line. Upregulation of endocan by LMP1 was found to be mediated through the CTAR1 and CTAR2 domains of LMP1 and through the LMP1-activated NF-κB, MEK-ERK and JNK signaling pathways. To study whether endocan was expressed in NPC and whether endocan expression was associated with LMP1 expression in NPC, the expression of endocan and LMP1 in tumor tissues from 42 NPC patients was evaluated by immunohistochemistry. Expression of endocan was found in 52% of NPC specimens. Significant correlation between LMP1 and endocan expression was observed (p<0.0001). Moreover, NPC patients with endocan expression were found to have a shorter survival than NPC patients without endocan expression (p=0.0104, log-rank test). Univariate and Multivariate analyses revealed that endocan was a potential prognostic factor for NPC. Finally, we demonstrated that endocan could stimulate the migration and invasion ability of endothelial cells and this activity of endocan was dependent on the glycan moiety and the phenylalanine-rich region of endocan. Together, these studies not only identify a new molecular marker that may predict the survival of NPC patients but also provide a new insight to the pathogenesis of NPC.

Id2 regulates the proliferation of squamous cell carcinoma in vitro via the NF-κB/Cyclin D1 pathway

Squamous cell carcinoma (SCC) is a significant cause of cancer morbidity and mortality worldwide, with an incidence of up to 166 cases per 100 000 population. It arises in the skin, upper aerodigestive tract, lung, and cervix and affects more than 200 000 Americans each year. We report here that a microarray experiment comparing 41 SCC and 13 normal tissue specimens showed that Id2, a gene that controls the cell cycle, was significantly up-regulated in SCC. Enforced expression of Id2 in vitro stimulated the proliferation of SCC cells and up-regulated the transcription of nuclear factor kappa B (NF-κB) and cyclin D1. Enhancement of the NF-κB activity with p65 significantly increased the cell proliferation and the transcription of cyclin D1, whereas inhibition of the NF-κB activity with I kappa B alpha mutant (IκBα M) and pyrroline dithiocarbamate (PDTC) abrogated cell proliferation and transcription of cyclin D1. Furthermore, a mutated NF-κB binding site in the cyclin D1 promoter fully abrogated the Id2-induced transcription of cyclin D1. Taken together, these data indicate that Id2 induces SCC tumor growth and proliferation through the NF-κB/cyclin D1 pathway.

Inhibitor of differentiation 1 contributes to head and neck squamous cell carcinoma survival via the NF-kappaB/survivin and phosphoinositide 3-kinase/Akt signaling pathways

PURPOSE

A key issue in cancer is apoptosis resistance. However, little is known about the transcription factors that contribute to cellular survival of head and neck squamous cell carcinoma (HNSCC).

EXPERIMENTAL DESIGN

Three batches (54, 64, and 38) of HNSCC specimens were used for cellular and molecular analyses to determine the major molecular signaling pathways for cellular survival in HNSCC. Animal models (cell culture and xenografts) were used to verify the importance of apoptosis resistance in HNSCC.

RESULTS

Inhibitor of differentiation (Id) family member, Id1, was significantly upregulated in clinical HNSCC specimens and acted to protect keratinocytes from apoptosis. Transfection of HNSCC cells with Id1 in vitro induced the phosphorylation of Akt (p-Akt) via phosphoinositide 3-kinase and increased the expression of survivin via NF-kappaB. Blockage of both pathways by specific inhibitors (LY294002 and IkappaBalphaM, respectively) abrogated Id1-induced cell survival of keratinocytes. In vivo studies showed that increased expression of Id1 allowed nontumorigenic keratinocytes (Rhek-1A) to become tumorigenic in nude mice by increased expression of survival genes such as p-Akt and survivin. More importantly, short interfering RNA for Id1 significantly reduced HNSCC tumor volume of HNSCC in xenograft studies. Analysis of clinical data verified the importance of the Id1 downstream molecule, survivin, in the prognosis of HNSCC patients.

CONCLUSIONS

The above data, taken together, suggest that Id1 and its downstream effectors are potential targets for treatment of HNSCC because of their contribution to apoptosis resistance.

Human papillomavirus type 16 E5 protein inhibits hydrogen-peroxide-induced apoptosis by stimulating ubiquitin-proteasome-mediated degradation of Bax in human cervical cancer cells

To investigate the mechanism by which the human papillomavirus (HPV) E5 protein contributes to the carcinogenesis of uterine cervical cancer, we studied the effect of HPV E5 on apoptosis of cervical cancer cells and its underlying mechanism. Expression of HPV16 E5 protein inhibited hydrogen peroxide-induced apoptosis in C-33A cervical cancer cells. E5 decreased the expression of Bax protein, and exogenous expression of Bax abolished the anti-apoptotic effect of E5. Knockdown of E5 by small interfering RNA sensitized CaSki cervical cancer cells to hydrogen peroxide-induced apoptosis with concurrent increase in Bax expression. Transient expression of E5 significantly increased the degradation rate of Bax protein by inducing the ubiquitination. The E5-induced decrease in Bax expression was inhibited by a cyclooxygenase-2 (COX-2) inhibitor, prostaglandin E2 (PGE(2)) receptor antagonists and cyclic adenosine monophosphate-dependent protein kinase (PKA) inhibitor. Treatment with PGE(2) decreased the expression of Bax and inhibited hydrogen peroxide-induced apoptosis of C-33A cells. We concluded that HPV16 E5 protein inhibits hydrogen peroxide-induced apoptosis of cervical cancer cells by stimulating the ubiquitin-proteasome-mediated degradation of Bax protein, and the pathway involves COX-2, PGE(2) and PKA. This finding suggests the possibility that HPV 16 E5 protein contributes to cervical carcinogenesis by inhibiting apoptosis of transformed cervical epithelial cells.

TNF-alpha drives matrix metalloproteinase-9 in squamous oral carcinogenesis

OBJECTIVES/HYPOTHESIS

It is well known that invasion is a seminal event in the progression of oral and other head and neck carcinoma sites. We have previously demonstrated tumor necrosis factor (TNF)-alpha and its dependent cytokines are upregulated in saliva during oral carcinogenesis. TNF-dependent events stimulate nuclear factor (NF)-kappaB and many NF-kappaB-dependent genes are associated with cancer progression.

MATERIALS AND METHODS

In the present study, we examined NF-kappaB stimulation of matrix metalloproteinase (MMP)-9 in a precancerous keratinocyte cell line that models leukoplakia (Rhek cells). We stimulated Rhek cells with both TNF-alpha and phorbol myristate acetate, known stimulants of NF-kappaB. We then assayed MMP-9 transcription and secretion by luciferase reporter genes, quantitative real-time polymerase chain reaction, and fluorometric enzyme-linked immunosorbent serologic assay.

RESULTS

We discovered that the MMP-9 promoter was significantly stimulated by phorbol myristate acetate and TNF-alpha on luciferase reporter gene assays. Further, we uncovered that functional MMP-9 promoter activation was accompanied by significant increases in MMP-9 gene expression, as judged by quantitative real-time polymerase chain reaction. Functional activation of the MMP-9 protein was stimulated by TNF-alpha and PMA on a fluorescent enzyme-linked immunosorbent serologic assay. Finally, we searched our salivary proteomic database for increases in MMP-9 and discovered it was the third most significant protein in salivas of oral cavity cancer patients over normal controls.

CONCLUSIONS

We conclude the milieu cytokine, TNF-alpha, has the capacity to provide stimulation of events related to early invasion of oral cavity cancer, as judged by its ability to stimulate MMP-9.

Development of human dermal epithelial cell-based bioassay for the dioxins

None of bioassays is complete for assessing biological impact in humans upon the xenobiotic exposure due to species and organ-specific responsiveness. Thus, it is speculated that the human cell-based bioassay may be more appropriate system because of its direct relevance to humans. Here, we have developed a human epidermal cell-based bioassay for the dioxins and related compounds. The AD12-SV40-immortalized human keratinocyte cell line was stably transfected with a recombinant expression vector which contains the luciferase gene under dioxin-inducible control of four DREs. The tansfectants showed a consistent dose-response of luciferase activity upon dioxin exposure even after 120 passages. The maximal half effective dose (EC50) was 200 pM with a maximum of 32-fold induction of luciferase activity at 5 nM. The minimum detection limit was 10 pM. Optimal exposure time for the assay was 24h. When cells were treated with aryl hydrocarbon receptor agonists of different toxic equivalent factor (TEF) values, the shape of the dose-response curve for each compound was parallel to that of TCDD and the maximum response was similar, indicating that this bioassay system can be applied to generate the total toxic equivalency (TEQ) estimate from the samples. When relative induction potency of luciferase activities for each compound was calculated, it was similar to WHO-TEF values within an order of magnitude. This human cell system can be used as an efficient screening tool to quantify the TEQ values of dioxin-like chemicals in the samples and may help understand the interspecies difference between humans and animals.

Ras oncogenes: split personalities

Extensive research on the Ras proteins and their functions in cell physiology over the past 30 years has led to numerous insights that have revealed the involvement of Ras not only in tumorigenesis but also in many developmental disorders. Despite great strides in our understanding of the molecular and cellular mechanisms of action of the Ras proteins, the expanding roster of their downstream effectors and the complexity of the signalling cascades that they regulate indicate that much remains to be learnt.

A genetic basis for tumour suppression

The technique of somatic cell hybridization has established the phenomenon of tumour suppression and provided evidence for a genetic basis for suppression. Further refinements aimed at eventually identifying 'tumour suppressor' genes include the use of monochromosome transfer via microcell hybridization. The application of this technique to the study of tumour suppression in tumorigenic HeLa cell x fibroblast hybrids, Wilms' tumour, retinoblastoma and osteosarcoma cells is described. The issue of whether tumour suppression involves a direct effect on expression of activated oncogenes is discussed. Transformation of normal human cells in culture by activated cellular oncogenes is an extremely rare event. This may be due to a relatively greater genomic stability of human cells compared to rodent cells. We describe the use of a spontaneously immortalized human keratinocyte cell line, HaCaT, for studies of the effects of introduction of activated c-Ha-ras oncogene into these cells, with particular reference to tumorigenic conversion.

Characterization of rat spiral ligament cell line immortalized by adenovirus 12-simian virus 40 hybrid virus

OBJECTIVES

Spiral ligament fibrocytes play an important role in inner ear ion homeostasis and are classified into several subtypes according to expression of specific enzymes such as Na+, K+ -ATPase, Ca++ -ATPase, and carbonic anhydrase. Although our understanding of the cell and molecular biology of spiral ligament fibrocytes has increased over time, access to these cells still remains a significant hurdle hindering future studies. In this study, we aimed to establish a rat spiral ligament cell line with minimal disruption of the original characteristics.

METHODS

The primary spiral ligament fibrocytes were exposed to adenovirus 12-simian virus 40 hybrid virus for immortalization. Karyotypic analysis was performed after stabilization of the infected cells, and the population doubling time was compared to that of the primary cell. The cell line was characterized by immunolabeling and electron microscopy.

RESULTS

We describe the establishment and characterization of a line of type I spiral ligament fibrocytes immortalized with an adenovirus 12-simian virus 40 hybrid virus.

CONCLUSIONS

This cell line can be a useful research tool for investigating the role of spiral ligament fibrocytes in homeostasis and inflammation of the inner ear.

Expression of the serine protease DESC1 correlates directly with normal keratinocyte differentiation and inversely with head and neck squamous cell carcinoma progression

BACKGROUND

As part of ongoing studies aimed at identifying the molecular events involved in head and neck squamous cell carcinoma progression, we recently isolated a novel serine protease, DESC1. This study was conducted to further characterize DESC1.

METHODS

Specimens of normal, dysplastic, and carcinomatous oropharyngeal mucosa (n = 31) were evaluated for DESC1 immunoreactivity using standard streptavidin-biotin immunoperoxidase techniques. Between-lesion stain intensity values were analyzed using multiple Wilcoxon tests. DESC1 expression was also evaluated in cultured human keratinocytes after induction of differentiation by calcium challenge, with subsequent real-time reverse transcriptase-polymerase chain reaction quantification.

RESULTS

DESC1 immunoreactivity decreased as lesions approached a malignant phenotype. Post hoc testing comparing the different lesion types and DESC1 staining values showed significance between "normal" and "carcinoma" (p = .0017) groups. Induction of normal keratinocyte differentiation by calcium challenge was accompanied by an increase in DESC1 expression (p = .002).

CONCLUSIONS

These results suggest downregulation of DESC1 during squamous cell carcinoma progression and upregulation during normal epithelial differentiation.

Oncogenic activity of Epstein-Barr virus latent membrane protein 1 (LMP-1) is down-regulated by lytic LMP-1

The Epstein-Barr virus (EBV) is an oncogenic human herpesvirus. EBV latent membrane protein 1 (LMP-1) is a viral oncogene that manifests its oncogenic phenotype through activation of cellular signaling pathways involved in cell growth, survival, differentiation, and transformation. Lytic LMP-1 (lyLMP-1) is a related EBV gene without oncogenic properties. The lyLMP-1 gene is found in 60% of the EBV strains circulating in nature, but it is not found in EBV strains associated with nasopharyngeal carcinoma. We recently demonstrated that lyLMP-1 down-regulates the half-life of LMP-1 in epithelial cells. Therefore in this study, we tested the hypothesis that lyLMP-1 concomitantly down-regulates LMP-1 oncogenic activity. The results demonstrated that lyLMP-1 inhibits LMP-1-mediated intracellular signaling activation, epithelial cell growth and survival, and fibroblast cell transformation in a dose-dependent manner. Lytic LMP-1 manifested this effect through the promotion of LMP-1 degradation and a reduction in the expressed quantity of LMP-1. Thus, lyLMP-1 functions as a posttranslational negative regulator of LMP-1 oncogenesis. These results support a model of EBV-associated epithelial oncogenesis in which lyLMP-1 may act in vivo to reduce the risk of LMP-1-mediated transformation and is therefore subjected to negative selection in nasopharyngeal carcinoma pathogenesis.

Evidence for alternative candidate genes near RB1 involved in clonal expansion of in situ urothelial neoplasia

In this paper, we present whole-organ histologic and genetic mapping studies using hypervariable DNA markers on chromosome 13 and then integrate the recombination- and single-nucleotide polymorphic sites (SNPs)-based deletion maps with the annotated genome sequence. Using bladders resected from patients with invasive urothelial carcinoma, we studied allelic patterns of 40 microsatellite markers mapping to all regions of chromosome 13 and 79 SNPs located within the 13q14 region containing the RB1 gene. A whole-organ histologic and genetic mapping strategy was used to identify the evolution of allelic losses on chromosome 13 during the progression of bladder neoplasia. Markers mapping to chromosomal regions involved in clonal expansion of preneoplastic intraurothelial lesions were subsequently tested in 25 tumors and 21 voided urine samples of patients with bladder cancer. Four clusters of allelic losses mapping to distinct regions of chromosome 13 were identified. Markers mapping to the 13q14 region that is flanked by D13S263 and D13S276, which contains the RB1 gene, showed allelic losses associated with early clonal expansion of intraurothelial neoplasia. Such losses could be identified in approximately 32% bladder tumor tissue samples and 38% of voided urines from patients with bladder cancer. The integration of distribution patterns of clonal allelic losses revealed by the microsatellite markers with those obtained by genotyping of SNPs disclosed that the loss within an approximately 4-Mb segment centered around RB1 may represent an incipient event in bladder neoplasia. However, the inactivation of RB1 occurred later and was associated with the onset of severe dysplasia/carcinoma in situ. Our studies provide evidence for the presence of critical alternative candidate genes mapping to the 13q14 region that are involved in clonal expansion of neoplasia within the bladder antecedent to the inactivation of the RB1 gene.

Pseudomonas aeruginosa Lipopolysaccharide Induction of Keratinocyte Proliferation, NF-κB, and Cyclin D1 Is Inhibited by Indomethacin

NF-kappaB is activated during acute inflammatory states as well as in other injury response disease states. Several pathologic states in squamous tissue injury response are characterized by increased squamous proliferation. This study was performed to investigate the hypothesis that Pseudomonas aeruginosa LPS is able to activate a proliferative phenotype in squamous cells via NF-kappaB induction and that this NF-kappaB-mediated response may be abrogated with the classic anti-inflammatory agent indomethacin. EMSA, luciferase reporter gene experiments, Western blots, and cellular proliferation assays were performed in normal and transformed human keratinocytes after stimulation with P. aeruginosa LPS. EMSA and luciferase reporter gene assays showed a 3- to 5-fold induction of active NF-kappaB in human keratinocyte cell lines after stimulation with P. aeruginosa LPS. The stimulation correlated with significantly increased cellular proliferation. As one potential mechanism for this increase in proliferation, an NF-kappaB-specific activation of cyclin D1 was observed. Both the NF-kappaB induction and proliferation response were inhibited with indomethacin and in dominant negative stable transfection clones. P. aeruginosa LPS activates proliferation of human keratinocytes, potentially through the induction of NF-kappaB and cyclin D1. These findings suggest that bacterial components can contribute to proliferative disease states in squamous epithelium through NF-kappaB activation.

Cre-mediated reversible immortalization of human renal proximal tubular epithelial cells

Primary human renal proximal tubule epithelial cells (RPTECs) are of limited use for basic research and for clinical applications due to their limited lifespan in culture. Here we used two lentivirus vectors carrying the human telomerase (hTERT) and the SV40T antigen (Tag) flanked by loxP sites to reversibly immortalize RPTECs. Transduced RPTEC clones continued to proliferate while retaining biochemical and functional characteristics of primary cells. The clones exhibited contact-inhibited, anchorage- and growth factor-dependent growth and did not form tumors in nude mice, suggesting that the cells were not transformed. Transient Cre expression in these cells led to efficient proviral deletion, upregulation of some renal specific activities, and decreased growth rates. Ultimately, the cells underwent replicative senescence, indicating intact cell cycle control. Thus, reversible immortalization allows the expansion of human RPTECs, leading to large production of RPTECs that retain most tissue-specific properties.

Functional genetics and experimental models of human cancer

Abundant evidence supports the hypothesis that cancer arises from normal cells through the stepwise accumulation of genetic mutations. The study of cells obtained from patients with cancer has identified numerous molecules and pathways that fundamentally contribute to malignant transformation; however, cancer cell lines are often difficult to isolate or maintain, and the cell lines that are available for experimentation represent only a small subset of late-stage human cancers. Recent work has elucidated the role of telomerase in regulating human cell lifespan and has enabled the development of new experimental systems to study human cancer. This review highlights the recent progress in combining genetic methods and primary human cells to understand the role of specific genes and pathways in cancer pathogenesis.

Epstein–Barr virus latent membrane protein 1 induces micronucleus formation, represses DNA repair and enhances sensitivity to DNA-damaging agents in human epithelial cells

The latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV) is a viral oncogene and it is essential for the transformation of resting B cells by the virus. The protein acts as a ligand-less membrane receptor and triggers numerous cellular signaling pathways. Cellular transformation frequently has been associated with genomic instability. To investigate whether EBV LMP1 induces chromosomal aberrations, micronucleus (MN) formation was examined in LMP1-expressing epithelial cells. The expression of wild-type LMP1 enhanced both spontaneous and bleomycin-induced MN formation. MN formation may be induced by inactivation of DNA repair and, therefore, we investigated the effect of LMP1 on DNA repair, using a host cell reactivation (HCR) assay. In the HCR assay, LMP1 reduced the capacity for DNA repair of both NPC-TW01 (p53-wild-type) and H1299 (p53-deficient) cells. As reduction of DNA repair by LMP1 occurs in p53-wild-type and p53-deficient cells, it seems that LMP1 can repress DNA repair in a p53-independent manner. Inactivation of DNA repair may render cells sensitive to DNA-damaging agents. In this study, H1299 cells harboring LMP1 were shown to be more sensitive to UV and bleomycin than those with a vector control. Using various deletion mutants of EBV LMP1 to determine the regions of LMP1 required to enhance MN formation, inhibit DNA repair and sensitize cells to DNA-damaging agents, we found that the region a. a. 189-222 (located within the CTAR1 domain) was responsible for sensitizing cells to UV and bleomycin, as well as for enhancing MN formation and repressing DNA repair. Based on these results, we suggest that disruption of DNA repair by LMP-1 results in an accumulation of unrepaired DNA and consequent genomic instability, which may contribute to the oncogenesis of LMP1 in human epithelial cells.

Hyperproliferation and p53 status of lens epithelial cells derived from alphaB-crystallin knockout mice

alphaB-Crystallin, a major protein of lens fiber cells, is a stress-induced chaperone expressed at low levels in the lens epithelium and numerous other tissues, and its expression is enhanced in certain pathological conditions. However, the function of alphaB in these tissues is not known. Lenses of alphaB-/- mice develop degeneration of specific skeletal muscles but do not develop cataracts. Recent work in our laboratory indicates that primary cultures of alphaB-/- lens epithelial cells demonstrate genomic instability and undergo hyperproliferation at a frequency 4 orders of magnitude greater than that predicted by spontaneous immortalization of rodent cells. We now demonstrate that the hyperproliferative alphaB-/- lens epithelial cells undergo phenotypic changes that include the appearance of the p53 protein as shown by immunoblot analysis. Sequence analysis showed a lack of mutations in the p53 coding region of hyperproliferative alphaB-/- cells. However, the reentry of hyperproliferative alphaB-/- cells into S phase and mitosis after DNA damage by gamma-irradiation were consistent with impaired p53 checkpoint function in these cells. The results demonstrate that expression of functionally impaired p53 is one of the factors that promote immortalization of lens epithelial cells derived from alphaB-/- mice. Fluorescence in situ hybridization using probes prepared from centromere-specific mouse P1 clones of chromosomes 1 and 9 demonstrated that the hyperproliferative alphaB-/- cells were 30% diploid and 70% tetraploid, whereas wild type cells were 83% diploid. Further evidence of genomic instability was obtained when the hyperproliferative alphaB-/- cells were labeled with anti-beta-tubulin antibodies. Examination of the hyperproliferative alphaB-/- mitotic profiles revealed the presence of cells that failed to round up for mitosis, or arrested in cytokinesis, and binucleated cells in which nuclear division had occurred without cell division. These results suggest that the stress protein and molecular chaperone alphaB-crystallin protects cells from acquiring impaired p53 protein and genomic instability.

Immortalization of rat eustachian tube epithelial cells by adenovirus 12-simian virus 40 hybrid virus

The eustachian tube epithelial cells play an important role in the initial pathogenesis of otitis media. In order to study the role of the eustachian tube epithelial cells in the pathogenesis of otitis media, we have established a rat eustachian tube epithelial cell line. The cell line was derived by infecting primary cultures of eustachian tube epithelial cells with the adenovirus 12-simian virus 40 (Adl2-SV40) hybrid virus. The immortalized cells have retained the morphological characteristics of the parental cells and show positive staining with anti-cytokeratin antibodies (a marker for epithelial cells), but not with anti-vimentin antibodies (a fibroblast marker). The cells have been in continuous culture for more than 10 months and have undergone 38 passages. Western blotting and cell staining have confirmed the expression of the SV40 T antigen and p53. Chromosomal analysis indicates that the cell line is aneuploid and derived from male rat epithelial cells. Together, our results suggest that the cell line originated from eustachian tube epithelial cells from a male rat and was successfully immortalized by the Ad12-SV40 virus.

Immortalization and transformation of primary human airway epithelial cells by gene transfer

One critical step in the development of a cancerous cell is its acquisition of an unlimited replicative lifespan, the process termed immortalization. Experimental model systems designed to study cellular transformation ex vivo have relied to date on the in vitro selection of a subpopulation of cells that have become immortalized through treatment with chemical or physical mutagens and the selection of rare clonal variants. In this study, we describe the direct immortalization of primary human airway epithelial cells through the successive introduction of the Simian Virus 40 Early Region and the telomerase catalytic subunit hTERT. Cells immortalized in this way are now responsive to malignant transformation by an introduced H-ras or K-ras oncogene. These immortalized human airway epithelial cells, which have been created through the stepwise introduction of genetic alterations, provide a novel experimental model system with which to study further the biology of the airway epithelial cell and to dissect the molecular basis of lung cancer pathogenesis.

In vitro response of human gingival epithelioid S-G cells to minocycline

Minocycline, a broad-spectrum antibiotic used in the treatment of acne and periodontal disease and to control inflammatory diseases such as rheumatoid arthritis, has recently been shown to induce a spectrum of adverse health effects. In the light of these contradictory data, this research was directed to provide basic information on the toxicology of minocycline, using in vitro cell culture models, and to evaluate its efficacy in periodontal therapies, particularly for wound healing. The human gingival epithelioid S-G cell line was used as the bioindicator. The greater toxicity of minocycline over doxycycline and tetracycline, related antimicrobial agents, probably correlated with its higher lipophilicity. The cytotoxicity of minocycline was unaffected by an S9 hepatic microsomal fraction, indicating that it is a direct-acting, rather than a metabolism-mediated, cytotoxicant. In comparative toxicity studies, much variation in the degree of sensitivity to minocycline was noted for different cell types. No correlation in the extent of sensitivity to minocycline and the physiologic state of the bioindicator cell (normal, transformed or malignant) was noted. The toxicity of minocycline to the S-G cells was dependent on its concentration and length of exposure. For a continuous 3-day exposure of the S-G cells to minocycline, the midpoint cytotoxicity (or, NR(50)) value, as quantified in the neutral red (NR) assay, was 204 microg/ml on day 1, 84 microg/ml on day 2, and 59 microg/ml on day 3. For a 1-h exposure of the S-G cells in phosphate buffered saline (PBS), the NR(50) value was 780 microg/ml minocycline. Although a 1-h exposure in PBS to 200 microg/ml minocycline exerted some toxicity, the S-G cells recovered on exposure to growth medium; irreversible, progressive damage occurred at 400 microg/ml minocycline and greater. Minocycline, at 50 microg/ml, enhanced attachment of the S-G cells to a gelatin-coated surface and cell migration towards an immobilized fibronectin gradient, both biologic parameters important in periodontal wound healing. Minocycline generally had little or no effect on production of the pro-inflammatory cytokines, interleukin-6 (IL-6) and interleukin-8 (IL-8), by non-activated S-G cells, the exception being stimulation of IL-6 at 48 h. IL-1beta, however, greatly stimulated IL-6 and IL-8 production, which was further increased by concurrent exposure to minocycline. This suggested that minocycline may enhance the ability of gingival epithelial cells to participate in the early, inflammatory phase of periodontal wound healing. The limitation of minocycline efficacy to a rather narrow window of concentration, centering about 50 microg/ml, and primarily for short-term exposures may possibly explain, in part, the contradictory clinical data on the health effects of this drug.

Microtubule disruption in keratinocytes induces cell-cell adhesion through activation of endogenous E-cadherin

The association of the cytoskeleton with the cadherin--catenin complex is essential for strong cell-cell adhesion in epithelial cells. In this study, we have investigated the effect of microtubule organization on cell-cell adhesion in differentiating keratinocytes. When microtubules of normal human epidermal keratinocytes (NHEKs) grown in low calcium media (0.05 mM) were disrupted with nocodazole or colcemid, cell-cell adhesion was induced through relocalization of the E-cadherin-catenin-actin complex to the cell periphery. This was accompanied by actin polymerization. Also, it was found that microtubule disruption-induced cell-cell adhesion was significantly reduced in more advanced differentiated keratinocytes. For example, when NHEK cells cultured under high calcium (1.2 mM) for 8 d and then in low calcium for 1 d were treated with nocodazole, there was no induction of cell-cell adhesion. Also long-term treatment of a phorbol ester for 48 h inhibited nocodazole-induced cell-cell adhesion of NHEK. Furthermore, this nocodazole-induced cell-cell adhesion could be observed in squamous cancer cell lines (A431 and SCC-5, -9, and -25) under low calcium condition, but not in the keratinocyte cell lines derived from normal epidermis (HaCaT, RHEK). On the other hand, HaCaT cells continuously cultivated in low calcium media regained a less differentiated phenotype such as decreased expression of cytokeratin 10, and increased K5; these changes were accompanied with inducibility of cell-cell adhesion by nocodazole. Together, our results suggest that microtubule disruption can induce the cell-cell adhesion via activation of endogenous E-cadherin in non- or early differentiating keratinocytes. However, this is no longer possible in advanced terminally differentiating keratinocytes, possibly due to irreversible changes effected by cell envelope barrier formation.

Sequencing and characterization of the human thiazide-sensitive Na-Cl cotransporter (SLC12A3) gene promoter

The thiazide-sensitive Na-Cl cotransporter SLC12A3 displays expression restricted to distal convoluted tubule cells where it catalyzes the uptake of sodium and chloride through the apical membrane. We sequenced 1959 bp of the 5' flanking region of human SLC12A3, located the area of transcription initiation, and used deletion constructs of the flanking region to determine areas that affect reporter gene expression in two cell lines, MDCT and CHO. Amplification of the 5' end of SLC12A3 cDNA from an adapter-ligated human kidney cDNA library demonstrated that transcription initiation is confined to an area from -18 to -6 bp upstream of the translation start codon. Maximum promoter activity (9.815 +/- 0.864 times control) was observed in MDCT cells using a promoter containing 1019 bp of the 5' flanking region. A promoter containing only 134 bp of the 5' flanking region upstream of the translation initiation codon maintained reporter gene expression at levels equal to 75% of that maximally observed (7.375 +/- 0.533 times control). Sequence analysis of this minimal promoter responsible for most of the SLC12A3 promoter activity revealed a TATA element, two Sp binding sites, a potential E box, and a potential binding site for NF-1/CTF or NY-I/CP-I. This promoter, and all other promoter constructs from SLC12A3, displayed repressor activity in CHO cells. A construct containing sequence 94 bp upstream of the initiation codon with two potential Sp binding sites was required for this repression. Protein-DNA interactions between the 182 bp region immediately upstream of the start codon and the nuclear proteins from rat kidney cortex and HeLa cells were examined to further clarify the role of the putative binding sites for SLC12A3 expression. Physiological studies investigating the effects of osmolarity, pH, and mineralocorticoid steroid on promoter activity demonstrated that the promoter activity was repressed by acidification, whereas no effects of increased osmolarity or deoxycorticosterone acetate addition were observed.

Development of human cell lines from multiple organs

While the majority of carcinogenesis studies have relied on the use of rodent cells in culture, experimental models to define the role of carcinogenic agents in the development of cancers must be established by using a variety of human cells. Unlike rodent cells, normal human cells in culture rarely undergo spontaneous transformation and have generally proven to be resistant to neoplastic transformation by carcinogens. Remarkable progress has been made during the past decade in human cell transformation systems. Malignant transformation of human cells in culture has been achieved by a stepwise process: immortalization and conversion of the immortalized cells to tumorigenic cells. One of the critical initial events in the progression of normal human cells to tumor cells is the escape from cellular senescence, with few exceptions; normal human cells require immortalization to provide a practical system for carcinogenesis studies. Different cell types require different conditions and transforming agents to achieve a useful cell line. The current state of the art in immortalization of human cells will be presented.

Immortalization of rat middle ear epithelial cells by adeno 12-SV40 hybrid virus

Rat middle ear epithelial cells were infected with the adeno 12-SV40 hybrid virus. The cell line thus obtained displays features of primary cultured epithelial cells in both light microscopic and ultrastructural examinations. The immortalized cells have been in continuous proliferation for 40 passages and more than 17 months. Immunohistochemical analysis of the immortalized cells was positive for the SV40 T antigen and the tumor suppressor protein p53. The cells also stained positive for cytokeratin, an epithelial cell marker, and negative for vimentin, a fibroblast marker. These results, together with karyotype analysis, indicate that this cell line originated from rat middle ear epithelial cells and retains the characteristics of epithelial cells. This cell line will be useful for studying the normal cellular biology of middle ear epithelial cells, as well as the cellular and molecular mechanisms involved in the bacteria-middle ear epithelial cell interaction.

Promotion of S-phase entry and cell growth under serum starvation by SAG/ROC2/Rbx2/Hrt2, an E3 ubiquitin ligase component: association with inhibition of p27 accumulation

The sensitive-to-apoptosis gene (SAG) was initially identified as a redox-inducible, apoptosis-protective protein and subsequently found to be the second family member of regulator of cullins (ROC)/RING box protein (Rbx)/Hrt, which acts as a component of E3 ubiquitin ligase. We report here that SAG promoted cell growth under serum starvation. Microinjection of SAG mRNA into quiescent NIH/3T3 cells induced S-phase entry as determined by [(3)H]-thymidine incorporation. Likewise, overexpression of SAG by either adenovirus infection of immortalized human epidermal keratinocytes (Rhek-1) or DNA transfection of SY5Y human neuroblastoma cells induced cell proliferation under serum starvation. Because cyclin-dependent kinase inhibitors (CKIs), including p21, p27, and p57, are degraded through the ubiquitin pathway, we tested whether SAG-induced cell growth is associated with CKI degradation. Although there was no significant difference in the levels of p21 and p57 between the vector controls and SAG-overexpressing cells, serum starvation induced 10- to 18-fold accumulation of p27 in control Rhek-1 cells. Accumulation of p27 was remarkably inhibited (only 2 to 5-fold) in SAG-infected cells. Inhibition of p27 accumulation was also observed in stably SAG-overexpressing SY5Y cells. Significantly, SAG-associated inhibition of p27 accumulation was largely abolished by the treatment with a proteasome inhibitor. In vivo binding of SAG and Skp2, an F-box protein that promotes p27 ubiquitination, was detected, and the binding was enhanced in SAG-overexpressing cells grown under serum starvation. Thus, SAG-induced growth with serum withdrawal appears to be associated with SAG-mediated p27 degradation. Mol. Carcinog. 30:37-46, 2001.

Angiogenesis modulators expression in culture cell lines positives for HPV-16 oncoproteins

Altered angiogenesis response is observed in patients with cervical cancer. In this study we examined whether Human Papilloma Virus (HPV) positive epithelial cells are able to produce angiogenic modulators. When added to human umbilical vein endothelial cells (HUVEC) the media conditioned by HPV-16 positive cells was able to induce proliferation, whereas a contrary effect was observed for media derived from non-tumorigenic keratinocytes. The analyses of angiogenesis modulator's mRNA levels result in a decrease of the antiangiogenic factors TSP-1 and 2 in HPV-16 positive cells. In contrast the expression of the pro-angiogenic molecules: bFGF, IL-8, TGF-beta, TNFalpha, and VEGF were higher in these cells as compared to control keratinocytes. Furthermore the pattern of VEGF isoforms observed in the cells positive for the viral genome point to a preferential induction of the VEGF(189) isoform. We therefore conclude that cervical cancer cells expressing HPV-16 genome are able to contribute to the pro-angiogenic response that might support tumor growth and invasion of the surrounding tissues.

Radiation-induced carcinogenesis: studies using human epithelial cell lines

It has proved difficult to develop suitable models to study radiation-induced carcinogenesis by using human epithelial cells. However, immortalised human epithelial cell lines have proved useful. Unirradiated cells from the human keratinocyte cell line (HPV-G) and the human embryonic lung cell line (L132) were found to be tumourigenic in T-cell-deficient mice; thus, they are not suitable for transformation studies. Human urothelial cell lines (SV-HUC-1, NT11, BC16) and the human thyroid epithelial cell line (HTori-3) were nontumourigenic. The urothelial cell lines were refractory to radiation-induced carcinogenesis, and only one small tumour was observed in 57 mice that received irradiated cells. Whereas tumours were not produced following irradiation of these urothelial cells, changes in anchorage-independent growth were observed after a single dose of 8 Gy gamma-irradiation but not after 2 or 4 Gy. Irradiation of the human thyroid epithelial cell line (HTori-3) in vitro resulted in tumour formation. Passaging of the cells in vitro before injection did not seem to be critical. Some of the cell lines derived from the primary thyroid tumours exhibited p53 mutations in exons 5, 6, 7, and 8, as detected by single-stranded conformational polymorphism (SSCP) analysis. Thus, the human thyroid epithelial cell line (HTori-3) looks promising as a model for investigating the molecular events in radiation-induced carcinogenesis.

In vitro response of human gingival epithelial S-G cells to resveratrol

WST-1 (mitochondrial dehydrogenase activities). Arrest of cell growth, due to inhibition of DNA synthesis, may explain the leveling of toxicity between day 2 and 3 for a 3-day continuous exposure to resveratrol. Irreversible damage to cell proliferation was noted in S-G cells exposed to 75-150 microM resveratrol for 2 days and then subsequently maintained for another 3 days in resveratrol-free medium. The cytotoxicity of resveratrol was neither potentiated nor ameliorated in the presence of an hepatic S9 microsomal fraction. The cytotoxicity of hydrogen peroxide to S-G cells was lessened by N-acetyl-L-cysteine and quercetin, but not by resveratrol. For nitric oxide, only N-acetyl-L-cysteine reduced toxicity. The ability of resveratrol to function as an antioxidant was, therefore, not noted under these test conditions.

Transfer of SV40 temperature-sensitive early gene into human epidermal keratinocytes by the recombinant adenovirus vector

We constructed a recombinant adenovirus vector that contained the origin-defective SV40 early gene, coding temperature-sensitive T antigen. This vector transferred the SV40 early gene into human epidermal keratinocytes with high efficiency. T antigen conferred the ability of keratinocytes to grow with limited differentiation in the presence of serum and high calcium concentration at the permissive temperature (34 degrees C), although normal keratinocytes were induced to differentiate and stop growing under the same conditions. The serum/Ca++-resistant cells did not proliferate at the nonpermissive temperature (40 degrees C), indicating that they depended on T antigen for their proliferation. The temperature-sensitive T antigen dissociated from the tumor suppressor gene products, p53, at 40 degrees C. The serum/Ca++-resistant cells still had the ability to proceed to terminal differentiation when injected into SCID mice as cultured keratinocytes. However, they did not form an apparent basal layer. This indicated that the tissue remodeling process in the serum/Ca++-resistant keratinocytes was abnormal. All of these epidermoid cysts disappeared within 8 wk and no tumor developed for 6 mo. We consider that deltaE1/SVtsT is a useful tool to examine multistep carcinogenesis of human epithelial cells in vitro.

Constitutive activation of transcription factors NF-(kappa)B, AP-1, and NF-IL6 in human head and neck squamous cell carcinoma cell lines that express pro-inflammatory and pro-angiogenic cytokines

We previously reported that human head and neck squamous cell carcinomas (HNSCCs) express the pro-inflammatory and pro-angiogenic cytokines interleukin (IL)-1alpha, IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor in vitro and in vivo. The promoter region of the genes encoding these cytokines include binding sites for the transcription factors nuclear factor (NF) kappaB/Rel A, activator protein-1 (AP-1), and CCAAT enhancer-binding protein beta (C/EBPbeta, or NF-IL6), which have been reported to contribute to activation of these cytokine genes. In the study presented here, we examined the activation, composition, and function of these transcription factors in HNSCC cell lines that express pro-inflammatory cytokines, by using electrophoretic mobility shift and reporter-gene assays. Constitutive activation of NF-kappaB, AP-1, and NF-IL6 DNA-binding proteins was detected. Supershift analysis with antibodies specific for NF-kappaB, AP-1, and NF-IL6 binding proteins showed that the NF-kappaB-binding protein included p65/Rel A and p50; AP-1 activity included c-jun, junB, junD, and Fra-1; and NF-IL6 included C/EBPbeta. Mutational analysis of the NF-kappaB, AP-1, and NF-IL6 sites in the IL-8 promoter region showed that NF-kappaB and AP-1 sites contributed to constitutive IL-8 reporter activity in HNSCC. HNSCC lines that exhibited increased IL-8 secretion relative to simian virus 40-immortalized and primary keratinocyte cell lines also demonstrated a concordant increase in NF-kappaB reporter activity relative to nonmalignant keratinocytes. We concluded that the early transcription factors NF-kappaB, AP-1, and NF-IL6 are constitutively activated in human HNSCC cell lines and that NF-kappaB and AP-1 promote expression of the pro-inflammatory and pro-angiogenic cytokine IL-8 in HNSCC. The demonstration of the activation of these transcription factors will be helpful in defining the identity and role of these and other early gene products that contribute to pathogenesis of the malignant phenotype in HNSCC and in defining potential targets for pharmacologic and molecular therapy of HNSCC. Mol. Carcinog. 26:119-129, 1999. Published 1999 Wiley-Liss, Inc.

Immortalization of chinchilla middle ear epithelial cells by adenovirus 12-simian virus 40 hybrid virus

In order to study the cellular and molecular mechanisms of the pathogenesis of otitis media, a chinchilla middle ear epithelial cell line (CMEE-1) with differentiated cell characteristics was established by infection of a primary culture with the adenovirus 12-simian virus 40 (Ad12-SV40) hybrid. This cell line has been in continuous culture for 42 passages, whereas the parent cells underwent senescence and died at the 8th passage. The cell line also retains epithelial morphology and expresses cytokeratin polypeptides 4, 7, and 18, characteristic markers for epithelia. In Western blots of cell proteins, bands at 94 and 53 kd were labeled after binding antibodies against SV40 large T antigen and p53, respectively. Karyotype analysis showed that the cell line is derived from chinchilla epithelial cells. These findings confirm that the cell line is a chinchilla epithelial cell immortalized by the hybrid virus.

Creation of human tumour cells with defined genetic elements

During malignant transformation, cancer cells acquire genetic mutations that override the normal mechanisms controlling cellular proliferation. Primary rodent cells are efficiently converted into tumorigenic cells by the coexpression of cooperating oncogenes. However, similar experiments with human cells have consistently failed to yield tumorigenic transformants, indicating a fundamental difference in the biology of human and rodent cells. The few reported successes in the creation of human tumour cells have depended on the use of chemical or physical agents to achieve immortalization, the selection of rare, spontaneously arising immortalized cells, or the use of an entire viral genome. We show here that the ectopic expression of the telomerase catalytic subunit (hTERT) in combination with two oncogenes (the simian virus 40 large-T oncoprotein and an oncogenic allele of H-ras) results in direct tumorigenic conversion of normal human epithelial and fibroblast cells. These results demonstrate that disruption of the intracellular pathways regulated by large-T, oncogenic ras and telomerase suffices to create a human tumor cell.

Establishment and characterization of normal and initiated hamster tracheal epithelial cell system

The development and characterization of normal hamster tracheal epithelial (HTE) cell system and its initiated subline is described in the present study. Normal HTE cells grew in a monolayer, had a stable diploid karyotype, were anchorage dependent and non-tumorigenic. The presence of desmosomal attachments and keratin filaments confirmed the epithelial nature of these cells. An initiated subline DTC8 was isolated after treatment of HTE cells with a suboptimal dose of 9,10-dimethyl-1,2-benz[a]anthracene (DMBA). These DTC8 cells grew in a monolayer, had a higher growth rate and saturation density, were weakly anchorage independent and non-tumorigenic. Treatment of DTC8 cells with 100 ng 12-O-tetradecanoyl phorbol-13-acetate (TPA), resulted in transformation of these cells which then showed anchorage independent growth on semisolid agar and formed tumours in 85% animals. As DTC8 cells showed heterogeneity in chromosome number, they were further cloned by the limiting dilution method using gamma-irradiated hamster embryonic fibroblasts as a feeder layer. The clone H7I, isolated among these clones had all the properties of initiated cells.

CD21-Dependent infection of an epithelial cell line, 293, by Epstein-Barr virus

Epstein-Barr virus (EBV) is invariably present in undifferentiated nasopharyngeal carcinomas, is found sporadically in other carcinomas, and replicates in the differentiated layer of the tongue epithelium in lesions of oral hairy leukoplakia. However, it is not clear how frequently or by what mechanism EBV infects epithelial cells normally. Here, we report that a human epithelial cell line, 293, can be stably infected by EBV that has been genetically marked with a selectable gene. We show that 293 cells express a relatively low level of CD21, that binding of fluorescein-labeled EBV to 293 cells can be detected, and that both the binding of virus to cells and infection can be blocked with antibodies specific for CD21. Two proteins known to form complexes with CD21 on the surface of lymphoid cells, CD35 and CD19, could not be detected at the surface of 293 cells. All infected clones of 293 cells exhibited tight latency with a pattern of gene expression similar to that of type II latency, but productive EBV replication and release of infectious virus could be induced inefficiently by forced expression of the lytic transactivators, R and Z. Low levels of mRNA specific for the transforming membrane protein of EBV, LMP-1, as well as for LMP-2, were detected; however, LMP-1 protein was either undetectable or near the limit of detection at less than 5% of the level typical of EBV-transformed B cells. A slight increase in expression of the receptor for epidermal growth factor, which can be induced in epithelial cells by LMP-1, was detected at the cell surface with two EBV-infected 293 cell clones. These results show that low levels of surface CD21 can support infection of an epithelial cell line by EBV. The results also raise the possibility that in a normal infection of epithelial cells by EBV, the LMP-1 protein is not expressed at levels that are high enough to be oncogenic and that there might be differences in the cells of EBV-associated epithelial cancers that have arisen to allow for elevated expression of LMP-1.

A malignant transformation of human cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin exhibits altered expressions of growth regulatory factors

The neoplastic transformation of human cells in culture with exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has recently been reported. In this study, expressions of growth regulatory factors were analyzed to examine their possible roles in TCDD-induced malignant transformation of human cells. Reverse transcription-polymerase chain reaction (RT-PCR) and immunoblot analysis were performed to detect altered expressions of genes associated with dioxin responses. The RT-PCR analysis showed that expressions of the growth regulatory factors, such as transforming growth factor-beta1 (TGF-beta1), plasminogen activator inhibitor-2 (PAI-2) and tumor necrosis factor-alpha (TNF-alpha), were significantly changed in the transformed cells as compared with the parental cells. Whereas parental cells showed a dose-dependent increase of PAI-2 mRNA levels following TCDD exposure, the transformed cells did not show any significant induction. In addition, constitutive levels of PAI-2 mRNA were 25 times lower in the transformed cells than in the parental cells. The mRNA stability assay suggests that downregulation of PAI-2 mRNA in the transformed cells may be associated with the posttranscriptional control. Expression of TGF-beta1 mRNA in the transformed cells was also four times lower than the parental cells. However, levels of TNF-alpha mRNA in the transformed cells were increased 3-fold. These results suggest that dysregulation of growth regulatory factors may be involved in TCDD-induced cellular transformation. Whereas plenty of studies demonstrated a number of immediate toxic effects by TCDD, this study revealed an initial evidence that altered expression of growth regulatory genes, such as PAI-2, TGF-beta1 or TNF-alpha, are some of the genetic events fixed in the genome following the successive cell divisions of TCDD-damaged cells. It is suggested that these changes may be associated with TCDD-induced malignant transformation of human cells.

Approaches to developing alternative and predictive toxicology based on PBPK/PD and QSAR modeling

Systematic toxicity testing, using conventional toxicology methodologies, of single chemicals and chemical mixtures is highly impractical because of the immense numbers of chemicals and chemical mixtures involved and the limited scientific resources. Therefore, the development of unconventional, efficient, and predictive toxicology methods is imperative. Using carcinogenicity as an end point, we present approaches for developing predictive tools for toxicologic evaluation of chemicals and chemical mixtures relevant to environmental contamination. Central to the approaches presented is the integration of physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) and quantitative structure--activity relationship (QSAR) modeling with focused mechanistically based experimental toxicology. In this development, molecular and cellular biomarkers critical to the carcinogenesis process are evaluated quantitatively between different chemicals and/or chemical mixtures. Examples presented include the integration of PBPK/PD and QSAR modeling with a time-course medium-term liver foci assay, molecular biology and cell proliferation studies. Fourier transform infrared spectroscopic analyses of DNA changes, and cancer modeling to assess and attempt to predict the carcinogenicity of the series of 12 chlorobenzene isomers. Also presented is an ongoing effort to develop and apply a similar approach to chemical mixtures using in vitro cell culture (Syrian hamster embryo cell transformation assay and human keratinocytes) methodologies and in vivo studies. The promise and pitfalls of these developments are elaborated. When successfully applied, these approaches may greatly reduce animal usage, personnel, resources, and time required to evaluate the carcinogenicity of chemicals and chemical mixtures.

Alterations of signal transduction pathways involved in 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced malignant transformation of human cells in culture

Effects of signal transduction pathways in TCDD-induced neoplastic transformation of human cells were assessed with respect to PLC-coupled signaling pathways, adenylyl cyclase-mediated responses and PKC isozyme expressions. A lower stimulation of the intracellular free calcium levels with exposure to extracellular ATP or histamine was observed in the transformed cells, as compared to the parental cells. While the steady-state level of IP3 was higher in the transformed cells, the magnitude of stimulation of IP3 generation by ATP or histamine was significantly lower in the transformed cells than the parental cells. These results indicate that a downregulation PLC-coupled signaling pathways may be involved in the TCDD-induced transformation of human cells. While the steady-state levels of cAMP accumulation were similar between the two cell lines, treatment of PGE2, a potent differentiation inducer, stimulated a higher accumulation of cAMP in the parental cells but isoproterenol, a typical beta-adrenergic agonist, did not induce a significant difference between the two cell lines. These results suggest that desensitization of cAMP-mediated response to extracellular signals including differentiation signals may be associated with a possible mechanism of the carcinogenesis. Elevated expression of PKC-alpha, -gamma, -zeta, -epsilon, -lambda, and -tau were observed in TCDD-transformed cells, indicating a possible association of altered expression of PKC isozymes with TCDD-induced transformation of human cells. The present study demonstrates that alterations of signal transduction pathways are involved in the TCDD-induced transformation of human cells and provides a valuable basis to investigate effects of signaling pathway as a possible mechanism of TCDD-induced carcinogenesis in human cells.

Nephrotoxicity testing in vitro--what we know and what we need to know

The kidney is affected by many chemicals. Some of the chemicals may even contribute to end-stage renal disease and thus contribute considerably to health care costs. Because of the large functional reserve of the kidney, which masks signs of dysfunction, early diagnosis of renal disease is often difficult. Although numerous studies aimed at understanding the mechanisms underlying chemicals and drugs that target various renal cell types have delivered enough understanding for a reasonable risk assessment, there is still an urgent need to better understand the mechanisms leading to renal cell injury and organ dysfunction. The increasing use of in vitro techniques using isolated renal cells, nephron fragments, or cell cultures derived from specific renal cell types has improved our insight into the molecular mechanisms involved in nephrotoxicity. A short overview is given on the various in vitro systems currently used to clarify mechanistic aspects leading to sublethal or lethal injury of the functionally most important nephron epithelial cells derived from various species. Whereas freshly isolated cells and nephron fragments appear to represent a sufficient basis to study acute effects (hours) of nephrotoxins, e.g., on cell metabolism, primary cultures of these cells are more appropriate to study long-term effects. In contrast to isolated cells and fragments, however, primary cultures tend to first lose several of their in vivo metabolic properties during culture, and second to have only a limited life span (days to weeks). Moreover, establishing such primary cultures is a time-consuming and laborious procedure. For that reason many studies have been carried out on renal cell lines, which are easy to cultivate in large quantities and which have an unlimited life span. Unfortunately, none of the lines display a state of differentiation comparable to that of freshly isolated cells or their primary cultures. Most often they lack expression of key functions (e.g., gluconeogenesis or organic anion transport) of their in vivo correspondents. Therefore, the use of cell lines for assessment of nephrotoxic mechanisms will be limited to those functions the lines express. Upcoming molecular biology approaches such as the transduction of immortalizing genes into primary cultures and the utilization of cells from transgenic animals may in the near future result in the availability of highly differentiated renal cells with markedly extended life spans and near in vivo characteristics that may facilitate the use of renal cell culture for routine screening of nephrotoxins.

Cell lines with extended in vitro growth potential from human renal proximal tubule: characterization, response to inducers, and comparison with established cell lines

Few model systems exist for the study of injury to human renal proximal tubule epithelium. Optimized differentiated human renal epithelial cell lines with extended in vitro growth potential would provide an alternative model system to primary culture or other available non-human mammalian kidney cell lines. For this purpose, human renal tubule epithelial cells were isolated from normal kidney cortex and exposed in culture to a hybrid immortalizing virus, adenovirus 12-SV40. Cell lines were developed by limiting dilution, and three selected cell lines were screened for growth pattern, production of immortalizing virus, tumorigenicity, and ploidy. Cell lines were also monitored for response to inducer agents and matrix factors and were screened for expression of biochemical properties and differentiation markers of renal epithelium. All three are nonproducers of the immortalizing virus and are nontumorigenic. They grow in monolayer, have intermediate growth kinetics, and express markers of renal proximal tubular epithelium by immunohistochemistry. They also express biochemical properties comparable to other widely used proximal tubular cell lines including LLC-RK1, OK, and HK-2 and comparable to human tubular cells in stable culture. Growth medium containing low levels of fetal calf serum, or epidermal growth factor combined with parathyroid hormone, produced optimal growth characteristics, brush border enzyme expression, biochemical properties, and glucose transport in a selected cell line. The addition of dimethyl sulfoxide allows maintenance in morphologically intact monolayers for prolonged periods. These cell lines should be useful model systems for the study of human renal proximal tubular injury or disease.

Chromosomal changes observed in immortalized human keratinocytes transformed by ionizing radiation

Human epithelial cancer cells were induced by concerted action of DNA tumor virus and X-ray radiation. Treatment of nontumorigenic early passage AD12-SV40 immortalized epithelial cells (RHEK-1) at passage 23 with radiation, resulted in further changes in their growth properties. One day old cultures of these RHEK-1 cells were irradiated with graded doses of X-rays (0, 2, 4, 6, and 8 Gy i.e. RHEK-1, RHEK-1/200R, RHEK-1/400R, RHEK-1/600R, and RHEK-1/800R). Morphologic alterations, the ability to grow in soft agar, and to form rapidly-growing squamous cell carcinomas in nude mice were concomitantly acquired properties of the radiation transformed cell lines RHEK-1/200R and RHEK-1/ 400R. On the basis of commonality in having addition of some extra material in chromosome 11 in the region between q14/q22 in all tumorigenic cell lines RHEK-1/200R and RHEK-1/400R, and deletion of the same region in nontumorigenic irradiated cell lines-RHEK-1/600R and RHEK-1/800R, it is deduced this region may have some important oncogene/s or other gene/s that play an important role in tumorigenesis. When compared to squamous cell carcinoma data, the duplication observed in the present study is also observed in 28 to 38% of head and neck and also in 25% of cases of untreated malignant lesions of oral squamous cell carcinoma. Thus, this study shows the correlation between in vitro induced squamous cell carcinoma to in vivo tumors.

Effects of the calcium influx inhibitor carboxyamido-triazole on the proliferation and invasiveness of human prostate tumor cell lines

Aberrant cellular signaling is a central feature of malignant cells and a potential target for anti-cancer therapy. Carboxyamido-triazole (CAI) is a calcium influx inhibitor that alters calcium-sensitive signal transduction pathways and suppresses the proliferative and metastatic potential of malignant cells. We have examined the effects of CAI on several tumor-associated parameters in human prostate cancer cell lines to evaluate the potential of CAI as a signal-transduction therapy agent for advanced-stage prostate cancer. Measuring anchorage-dependent cell growth, continuous application of CAI inhibited the growth of DU-145, PPC-1, PC3 and LNCaP tumor cells with 50% inhibitory concentrations ranging 10-30 microM. Direct cell enumeration assays revealed that the growth-suppressing activity of CAI toward DU-145 cells was reversible, indicating a cytostatic effect of the drug on tumor cells. The drug also inhibited the proliferation of several immortalized human prostatic epithelial cell lines. The proliferation of HaCaT- and RHEK-1-immortalized keratinocyte cell lines was relatively insensitive to CAI. Additionally, invasion by DU-145, PC3 and PPC-1 cells through Matrigel in vitro was reduced approximately 60-70% by 10 microM CAI. Other cellular effects of CAI included an attenuation of the elevation of intracellular free calcium in response to bombesin and carbachol in PC3 cells and a marked dose-dependent inhibition of prostate-specific antigen secretion in LNCaP cell cultures.