Sequential combined tumorigenic effect of HPV-16 and chemical carcinogens.

We immortalized oral keratinocytes by transfection with recombinant human papillomavirus type 16 (HPV-16) DNA and established two cell lines, human oral keratinocytes-16A (HOK-16A) and -16B (HOK-16B). These cell lines were morphologically different from the normal counterpart, contained HPV-16 DNA as integrated form and expressed numerous viral genes. However, these cells proliferated only in culture medium containing low calcium (0.15 mM) and are not tumorigenic in nude mice. To test the hypothesis that tumors can be developed by sequential combined effect of human papillomavirus and chemical carcinogens in the oral cavity, these immortalized cell lines were chemically transformed by exposure to either benzo[a]pyrene or methanesulfonic acid ethyl ester. Such transformants proliferated in medium containing physiological calcium levels (1.5 mM) and demonstrated enhanced growth potential in nude mice, whereas primary human oral keratinocytes treated with these chemical carcinogens failed to show any evidence of transformation. Chemically transformed cells contained integrated, intact HPV-16 sequences and transcribed significantly higher amount of HPV-16 E6/E7 messages and transforming growth factor-alpha (TGF-alpha) compared with the immortalized oral keratinocytes. Like the HPV-immortalized cell lines, the chemically transformed oral keratinocytes contained lower levels of newly synthesized, wild-type p53 proteins compared to normal cells, and expressed wild-type c-Ha-ras. These results indicate that this in vitro system is useful for investigating the mechanisms of multistep oral carcinogenesis.     

Immortalization of normal human oral keratinocytes with type 16 human papillomavirus.

Primary human oral keratinocytes were transformed by transfection with recombinant human papillomavirus type 16 (HPV-16) DNA, and two transformed cell lines named human oral keratinocytes-16A and -16B (HOK-16A and HOK-16B) were established. While normal cells and cells transfected with vector only exhibited a limited lifespan, the HOK-16A and HOK-16B lines demonstrated immortality and altered morphology from their normal counterpart. The HOK-16A and HOK-16B lines contained approximately 40 and approximately 25 copies of intact HPV-16 DNA as integrated form per cell respectively, and both cell lines expressed several viral specific poly(A+) RNAs. Notably these cell lines also overexpressed cellular myc proto-oncogene in comparison with the normal counterpart. However, the immortalized cell lines were not able to produce tumors in nude mice, indicating that the cells are partially transformed. The HOK-16A and HOK-16B lines are, therefore, useful for investigating the multistep molecular events of oral carcinogenesis.     

Combined effects of human papillomavirus-18 and n-methyl-n-nitro-n-nitrosoguanidine on the transformation of normal human oral keratinocytes

We immortalized oral keratinocytes by transfecting them with recombinant human papillomavirus (HPV) type 18 DNA and established three cell lines. These lines were morphologically different from their normal counterpart, contained integrated entire HPV-18 DNA, and expressed the viral E6/E7 genes. The cells contained less p53 protein and more c-myc mRNA than normal cells. However, they proliferated only in keratinocyte growth medium (KGM) containing low calcium and were not tumorigenic in nude mice. To test the hypothesis that tumors result from the combined effect of a “high-risk” HPV and chemical carcinogens in the human oral cavity, we exposed the immortalized cells to the chemical carcinogen N-methyl-N′-nitro-N-nitrosoguanidine. Three chemically transformed cell colonies were isolated. These cells (a) proliferated well in both KGM and Dulbecco′s modified minimum essential medium containing physiological levels of calcium; (b) were capable of proliferating in nude mice; (c) contained intact, integrated HPV-18 sequences; (d) transcribed substantially more HPV-18 E6/E7, transforming growth factor-α, and c-myc than the immortalized counterpart; and (e) contained, like the immortalized counterpart, less wild-type p53 protein and DCC message. These data indicate that human oral keratinocytes can be transformed by sequential exposure of normal keratinocytes to a “high-risk” HPV and chemical carcinogens. © 1994 Wiley-Liss, Inc.     

Differential effect of tumor necrosis factor on proliferation of primary human keratinocytes and cell lines containing human papillomavirus types 16 and 18.

Keratinocytes immortalized by human papillomaviruses (HPV) 16 and 18 are partially resistant to the inhibition of proliferation exerted by transforming growth factor-beta (TGF-beta). To determine if this finding reflects a generalized resistance to inhibitory cytokines, we studied the effect of tumor necrosis factor-alpha (TNF-alpha) on subconfluent cultures of both normal and HPV-immortalized human foreskin keratinocytes. Whereas primary and HPV-16-immortalized keratinocytes were sensitive to TNF-alpha, HPV-18-immortalized keratinocytes (and those immortalized by simian virus 40) were resistant to the inhibitory effects of this cytokine. The ability of HPV-18 to induce a more resistant phenotype correlated with its more potent in vitro transforming activity and its apparent association with more aggressive tumors. Interestingly, the state of TNF-induced growth inhibition in normal or HPV-16-immortalized keratinocytes was not accompanied by a reduction in the expression of c-myc RNA or protein. This contrasts sharply with the ability of TGF-beta to inhibit c-myc RNA expression in normal cells. Evidently, the resistance of HPV-immortalized keratinocytes to TNF-alpha and TGF-beta proceeds along different regulatory pathways.     

Both HPV and carcinogen contribute to the development of resistance to apoptosis during oral carcinogenesis

Oral carcinomas frequently contain human papilloma virus (HPV)-16/18. As p53 is degraded through interaction with HPV-16/18 products (E6/E7), p53 dysfunction may contribute to oral carcinogenesis. Furthermore, epidemiological studies suggest that smoking history may be critical for oral carcinogenesis. To delineate the involvement of HPV-16 infection and carcinogen in oral carcinogenesis, Park et al have established a multistep oral carcinogenesis model. Overexpression of p53 altered the expression of Fas antigen (Fas-R), Bax and Bcl-2; however, it remains unclear how the loss of p53 modifies the expression of these molecules. Using the multistep oral carcinogenesis model, we analyzed how the loss of p53 and carcinogen modified the expression of these molecules and their role in the development of resistance to apoptosis of oral carcinomas. The HOK-16B cell line was immortalized by HPV-16 transfection of normal human oral keratinocytes (NHOK). HOK-16B-BaP and HOK-16B-BaP-T1 were established from HOK-16B following short-term and long-term stimulation with the chemical carcinogen, benzo(a)pyrene, respectively. The malignant phenotype develops in sequence from HOK-16B, HOK-16B-BaP and HOK-16B-BaP-T1. The expression of apoptosis-related molecules was examined by Western blot analysis or by flow cytometry. Fas-mediated cytotoxicity was assessed using CH-11, an agonistic anti-Fas-R IgM monoclonal antibody. The apoptosis-related molecules examined were the Fas-R, Bcl-2, Bax, and Fas-associated phosphatase 1 (FAP-1). Downregulation of Fas-R and upregulation of Bcl-2 in HOK-16B-BaP were observed in HOK-16B-BaP and HOK-16B-BaPT1. Bax was downregulated in HOK-16B, HOK-16B-BaP and HOK-16B-BaP-T1. The expression of FAP-1 was increased with progression towards malignancy. NHOK and HOK-16B were relatively sensitive to CH-11, whereas HOK-BaP and HOK-BaP-T1 were resistant to CH-11. Treatment of HOK-16B-BaP with antisense bcl-2 oligonucleotide rendered the cells more sensitive to CH-11-induced apoptosis. These data demonstrate that both the loss of p53 and carcinogen stimulation are associated with altered expression of Fas-R, Bcl-2 and FAP-1, although the loss of p53 is sufficient for altered expression of Bax. Thus, both HPV infection and smoking contribute to acquisition of anti-apoptotic characteristics by oral carcinomas.     

HIV-1 Tat enhances replicative potential of human oral keratinocytes harboring HPV-16 genome

Introducing highly active antiretroviral therapy (HAART) has significantly decreased the morbidity and mortality in human immunodeficiency virus-positive (HIV+) individuals by decreasing the viral loads and increasing the CD4+ T-cell counts. Subsequently, the occurrence of many HIV-associated diseases has been dramatically declined except human papillomavirus (HPV)-associated lesions. Such notion suggests that immune response is not a major determinant, and that the direct interaction between HIV and HPV may be involved in the HPV-associated pathogenesis. In the current study, we investigated whether HIV plays a direct role in HPV-associated oral carcinogenesis by using HIV-1 transactivator protein (Tat), which is known to have oncogenic properties. We found that HIV-1 Tat not only increased the expression of HPV-16 E6 and E7 oncogenes in human oral keratinocytes harboring the HPV type-16 genome (HOK-16B), but also notably enhanced the proliferative capacity of the cells in vitro. Moreover, HOK-16B cells expressing HIV-1 Tat was capable of inducing cystic nodules in nude mice, while the control HOK-16B cells failed to produce nodules in the mice. Our results indicate that HIV could play a role in the HPV-associated pathogenesis by exerting oncogenic stimulus via Tat protein.     

Increased ICAM-1 expression in transformed human oral epithelial cells: molecular mechanism and functional role in peripheral blood mononuclear cell adhesion and lymphokine-activated-killer cell cytotoxicity

The intercellular adhesion molecule-1 (ICAM-1, CD54) serves as a counter-receptor for the beta2-integrins, LFA-1 and Mac-1, which are expressed on leukocytes. Although expression of ICAM-1 on tumor cells has a role in tumor progression and development, information on ICAM-1 expression and its role in oral cancer has not been established. Normal human oral keratinocytes (NHOK), human papilloma virus (HPV)-immortalized human oral keratinocyte lines (HOK-16B, HOK-18A, and HOK-18C), and six human oral neoplastic cell lines (HOK-16B-BaP-T1, SCC-4, SCC-9, HEp-2, Tu-177 and 1483) were used to study ICAM-1 expression and its functional role in vitro. Our results demonstrated that NHOK express negligible levels of ICAM-1, whereas immortalized human oral keratinocytes and cancer cells express significantly higher levels of ICAM-1, except for HOK-16B-BaP-T1 and HEp-2. Altered mRNA half-lives did not fully account for the increased accumulation of ICAM-1 mRNA. Adhesion of peripheral blood mononuclear cells (PBMC) to epithelial cells correlated with cell surface ICAM-1 expression levels. This adhesion was inhibited by antibodies specific for either ICAM-1 or LFA-1/Mac-1, suggesting a role for these molecules in adhesion. In contrast, lymphokine-activated-killer (LAK) cell cytotoxic killing of epithelial cells did not correlate with ICAM-1 levels or with adhesion. Nonetheless, within each cell line, blocking of ICAM-1 or LFA-1/Mac-1 reduced LAK cell killing, suggesting that ICAM-1 is involved in mediating this killing.     

Impaired nucleotide excision repair in UV-irradiated human oral keratinocytes immortalized with type 16 human papillomavirus genome

We previously reported that 'high risk' human papillomaviruses (HPV) induce genetic instability in human oral keratinocytes. To understand the mechanisms of HPV-induced genetic instability, we determined the nucleotide excision repair (NER) capacity of normal (NHOK) and human papillomavirus type-16 immortalized oral keratinocytes (HOK-16B) by strand-specific removal of UV-induced cyclobutane pyrimidine dimers (CPDs) from a 16 Kb fragment of the p53 gene. In NHOK the NER activity was initiated in both DNA strands immediately, although the process in the non-transcribed strand was notably slower than that of the transcribed strand. In HOK-16B cells the initiation of CPDs removal was delayed for at least 8 h in both DNA strands, and the process was significantly slower than that in NHOK. UV-irradiation enhanced the p53 protein level more than 30-fold in NHOK, but it did not significantly alter the protein level in the HOK-16B cells. UV-irradiation also increased the p21WAF1/CIP1 protein level only in NHOK. These data indicate that 'high risk' HPV induces genetic instability by impairing NER capacity of cells. Impaired NER activity of HOK-16B cells may be implicated with their inability to enhance active p53 when challenged by genotoxic stress.     

Effects of transforming growth factor beta-1 on growth-regulatory genes in tumour-derived human oral keratinocytes.

This study examined the effect of transforming growth factor beta-1 (TGF-beta 1) on c-myc, RB1, junB and p53 expression together with pRb phosphorylation, in carcinoma-derived and normal human oral keratinocytes with a range of inhibitory responses to this ligand. Amplification of c-myc was observed in eight of eight tumour-derived cell lines and resulted in corresponding mRNA expression. The down-regulation of c-myc expression by TGF-beta 1 predominantly reflected growth inhibition by TGF-beta 1, but in two of eight tumour-derived cell lines which were partially responsive to TGF-beta 1 c-myc expression was unaltered by this ligand. While RB1 mRNA levels were unaltered by TGF-beta 1, the ligand caused the accumulation of the underphosphorylated form of the Rb protein in all cells irrespective of TGF-beta 1-induced growth arrest. junB expression was up-regulated by TGF-beta 1 in cells with a range of growth inhibitory responses. All cells contained mutant p53. TGF-beta 1 did not affect p53 mRNA expression in both tumour-derived and normal keratinocytes and there was no alteration in p53 protein levels in keratinocytes expressing stable p53 protein following TGF-beta 1 treatment. The data indicate that TGF-beta-induced growth control can exist independently of the presence of mutant p53 and the control of Rb phosphorylation and c-myc down-regulation. It may be that TGF-beta growth inhibition occurs via multiple mechanisms and that the loss of one pathway during tumour progression does not necessarily result in the abrogation of TGF-beta-induced growth control.     

Comparative response of normal and of human papillomavirus-16 immortalized human epithelial cervical cells to benzo[a]pyrene.

Laboratory evidence suggests synergism of human papillomavirus (HPV) infection with cigarette smoking behaviors in enhancing the risk of cervical cancer. In this preliminary investigation, we tested the hypothesis that HPV infection may alter the metabolic activation of tobacco smoke carcinogens, such as benzo[a]pyrene (B[a]P), thereby playing a role in the etiology of cervical cancer. We examined in vitro the metabolism and DNA adduct formation of [3H]B[a]P in normal and HPV-16 immortalized human epithelial cervical cells in culture, and investigated the effect of [3H]B[a]P on growth of these cells. Cultures of normal human cervical cells and of HPV-16 immortalized cervical epithelial cells were exposed to 0.2 microM [3H]B[a]P for 24 and 48 h. [3H]B[a]P inhibited growth of both normal and HPV-16 immortalized cervical cells. However, the growth inhibition of normal cells was more profound than that of HPV-16 immortalized cells. Comparison of the metabolism of [3H]B[a]P in these cells indicated that they both metabolize [3H]B[a]P predominantly to [3H]trans-9,10-dihydroxy-9,10-dihydrobenzo[a]pyrene ([3H]B[a]P-9, 10-diol), [3H]r-7,t-8, 9,c-10-tetrahydroxy-7,8,9, 10-tetrahydrobenzo[a]pyrene ([3H]trans-anti-B[a]P-tetraol), and unknown polar products. Enzymatic hydrolysis of water-soluble metabolites indicated that the levels of glucuronide and sulfate conjugates in these cells are negligible. Similarly, both cell lines form similar [3H]B[a]P-DNA adducts. However, the level of the (+)[3H] anti-B[a]P diol epoxide (BPDE)-deoxyguanosine adduct in HPV-16 immortalized cells after 24 and 48 h exposures was 3.8 and 3. 1 pmol/mg DNA, respectively, which is 2.2-fold and 2.6-fold greater than the level of this adduct in normal cells. Under the conditions and within the time frame employed in these assays, both the cell growth and DNA damage induced by [3H]B[a]P appear to be higher in HPV-16 immortalized cells than those detected in normal cells. The results, although preliminary, suggest that HPV-16 immortalized cervical cells are more susceptible to DNA damage by BaP which, in part, may enhance their transformation to malignant cells.     

Abrogation of the retinoblastoma tumor suppressor checkpoint during keratinocyte immortalization is not sufficient for induction of centrosome-mediated genomic instability

Deregulation of the retinoblastoma (pRB) tumor suppressor pathway and telomerase activation have been identified as rate-limiting steps for immortalization of primary human epithelial cells. However, additional molecular aberrations including p53 inactivation, ras activation, and deregulation of protein phosphatase 2A activity are necessary for full transformation of immortalized epithelial cells. Genomic instability is observed in most human tumors and constitutes an important mechanism to allow emerging tumor cells to acquire additional mutations to efficiently overcome selection barriers during carcinogenic progression. In an attempt to model oral cancer in a human cell-based system, we analyzed normal oral epithelial keratinocytes with the pRB pathway dysregulated by loss of expression of the cyclin-dependent kinase (cdk) 4/cdk6 inhibitor p16(INK4A) and/or ectopic expression of cdk4 or expression of the human papillomavirus (HPV) type 16 E7 oncoprotein. Ectopic expression of cdk4 and HPV-16 E7 was equally efficient in extending the life span of normal oral keratinocytes, and each was able to cooperate with telomerase (hTERT) to immortalize these cells. HPV-16 E7/hTERT-immortalized normal oral keratinocytes showed centrosome abnormalities, whereas populations of cdk4/hTERT-immortalized cells or hTERT-immortalized cells that had lost expression of p16INK4A showed no such abnormalities. These results demonstrate that disruption of the p16INK4A/pRB checkpoint of epithelial cell immortalization does not necessarily lead to centrosome-associated genomic instability.     

Down-regulation of keratin 14 gene expression after v-Ha-ras transfection of human papillomavirus-immortalized human cervical epithelial cells.

Keratin expression in human cervical squamous cell carcinoma (SCC) lines differed significantly from both normal and human papillomavirus (HPV) immortalized exocervical cells. Keratin 14 (K14) expression, determined by protein synthesis and mRNA levels, was dramatically down-regulated in the cervical SCC lines while keratin 5 (K5) expression was not. K14 expression was similarly down-regulated in an HPV-16 immortalized cervical cell line after tumorigenic transformation with recombinant v-Ha-ras DNA. Cultures derived from nude mouse tumor explants also exhibited an altered keratin profile and the levels of K14 protein synthesis, as well as K14 mRNA, were not detectable. In both cases K5 protein synthesis was not significantly down-regulated. In addition, neoplastic cervical SCC lines exhibited up-regulation of keratins 7, 8, 13, and 19, combined with slight down-regulation of keratins 6 and 16. Epidermal keratinocytes responded in a different manner to exocervical cells. Transfection of human papillomavirus-immortalized epidermal keratinocytes with the BglII N fragment of herpes simplex virus 2 produced a neoplastic cell line, but K5 and K14 expression remained unchanged. Thus, neoplastic transformation of human exocervical cells, both in vivo (spontaneous cervical SCC) and in vitro (HPV-16- and v-Ha-ras-induced cervical SCC), is accompanied by characteristic changes in keratin expression. The specific down-regulation of K14 in these tumorigenic cervical cells, in the absence of significant changes in the expression of K5, implies that the normal coordinate regulation of K5 and K14 gene expression has been uncoupled.     

Elevated Bmi-1 expression is associated with dysplastic cell transformation during oral carcinogenesis and is required for cancer cell replication and survival

Bmi-1 is a polycomb group protein that was identified as c-myc cooperating oncogene in murine lymphomagenesis. The current study was undertaken to determine the role of Bmi-1 in human oral carcinogenesis. Bmi-1 protein and RNA expression levels were markedly enhanced in the cells of oral squamous cell carcinomas (OSCC) compared with that of normal human oral keratinocytes (NHOK). Enhanced-Bmi-1 expression was also detected in situ in the archived oral mucosal tissues with cancerous and precancerous histopathology, including that of mild epithelial dysplasia. Thus, Bmi-1 expression occurs at a very early stage in oral carcinogenesis. To determine the biological role of Bmi-1 in cell proliferation, endogenous Bmi-1 was knocked down in actively proliferating SCC4 cells and NHOK by RNA interference. After Bmi-1 knockdown, cell replication was severely retarded. However, the expression of p16(INK4A), a known cellular target of Bmi-1, was not changed in cells with or without Bmi-1 knockdown. Furthermore, Bmi-1 knockdown in HOK-16B-BaP-T cells, in which the p16(INK4A)/pRb pathway was abrogated, led to immediate arrest of replication and loss of viable cells. Thus, our data suggest that Bmi-1 may act through p16(INK4A)-independent pathways to regulate cellular proliferation during oral cancer progression.     

HPV-16 E7 protein bypasses keratinocyte growth inhibition by serum and calcium

The E6 and E7 genes of HPV-16 or HPV-18 both are necessary for effective immortalization of primary human genital keratinocytes. To analyse the individual role of E6 and E7 genes in dysregulating cell growth, we cloned the HPV-16 E6, E7 and E6/E7 genes into retroviruses. Primary human keratinocytes (PHK) were then infected with these retroviruses and selected in differentiation-inducing medium (high calcium and serum). The E6/E7 retroviruses were the most effective at inducing differentiation-resistant colonies. Intermediate numbers of colonies were induced by E6 and low numbers by E7. Interestingly, only cultures infected with E7 and E6/E7 retroviruses showed a significant proportion of cells progressing into the S phase, consistent with our earlier studies showing that E7 is required for the efficient immortalization of genital keratinocytes. Accompanying this entry into S phase, the E7 or E6/E7 transduced cells expressed high levels of cyclins A, B and E, but lower levels of cyclin D. In addition, cdc-2, cdk-2 and cdk-4 were also increased. No significant differences were detected in the expression of c-myc and c-fos between the vector and any of the transduced cells. Keratinocytes infected with the E7 retrovirus exhibited decreased levels of Rb protein and increased levels of p53, whereas cells infected with E6-expressing retroviruses displayed normal levels of Rb protein and decreased levels of p53. Finally, E7 induced a three-fold increase in bcl-2 expression. Our results indicate that the HPV-16 E7 gene alone is sufficient to bypass keratinoctye growth arrest induced by serum and calcium exposure and that the discordant expression of several cell regulatory proteins accompanies this unregulated proliferation.      

CANCER BIOLOGY: The human papillomavirus E6/E7 genes induce discordant changes in the expression of cell growth regulatory proteins

The E6/E7 oncoproteins of human papillomavirus (HPV) types 16and 18 are responsible for the efficient immortalization ofhuman genital keratinocytes and we have recently reported thatsuch immortalized cells display alterations in the expressionof cyclin A, cyclin B, and cdc-2. To determine whether thesealterations were the consequence of E6/E7 protein expressionor whether they resulted from the process of cellular immortalization,we multiply-infected primary genital keratinocytes with a retrovirusexpressing the HPV-18 E6/E7 genes and examined the cells foracute, pre-immortalization changes in several critical cellgrowth regulatory proteins including cyclin A, cyclin B, cdc-2,p53 and c-myc. In addition, we simultaneously evaluated theexpression of the E6/E7, bcl-2 and involucrin genes to determinewhether there were accompanying alterations in the expressionof viral genes or in cellular genes related to cell apoptosisand the state of keratinocyte differentiation. The cell cycleregulating proteins (cyclin A, cyclin B, cdc-2 and p53) changesignificantly within days after retroviral infection. CyclinB and cdc-2 increase over 4-fold by three passages and remainrelatively constant thereafter through passage 21, whereas thelevels of p53 protein decrease 25% by passage three. Increasesin the expression of cyclin A, cyclin B and cdc-2, and decreasesin p53 are therefore among the earliest observable changes incell regulatory proteins following E6/E7 gene expression andmay be important contributors to the development of cell immortalization.The expressions of viral E6/E7 genes, c-myc, bcl-2 and involucrinexhibit progressive changes with increased passage numbers untilpassage 21, presumably reflecting the selective outgrowth ofimmortalized cells.     

Combination therapy with podophyllin and vidarabine for human papillomavirus positive cervical intraepithelial neoplasia

Our aim was to establish an effective non-surgical treatment for cervical intraepithelial neoplasia (CIN) through inactivation of human papillomavirus (HPV), the major etiological agent for this disease. We show that vidarabine, a DNA polymerase inhibitor, suppressed growth and HPV gene expression in human cervical keratinocytes immortalized by HPV or in cervical cancer cell lines. Expression of HPV-16 E6 and E7 proteins in normal cervical keratinocytes sensitized cells to apoptosis in the presence of podophyllin or vidarabine. We applied vidarabine ointment and/or podophyllin to cervical epithelium in 28 cases of CIN I-II to evaluate the therapeutic effectiveness of these agents. Co-application of vidarabine and podophyllin in six treatments caused regression of lesions cytologically and histologically, and disappearance of HPV-16 or -18 DNA in 17 of 21 (81%) women. Our results suggest that the combination of vidarabine and podophyllin therapy is an effective non-surgical treatment for HPV-positive CIN.     

Characterization of novel cell lines established from three human oral squamous cell carcinomas

Human oral squamous cell carcinoma cell lines (KOSCC-11, -25A, -25B, -25C, -25D, -25E, -33A, and -33B) were established by explantation culture from these oral squamous cell carcinomas. The histopathology of the primary tumors, in vitro growth characteristics, epithelial origin, in vitro anchorage-independency, in vivo tumorigenicity, the frequency of human papillomavirus (HPV) infections, and the status of proto-oncogenes, tumor suppressor genes, DNA mismatch repair genes, and microsatellite instability were investigated in the cell lines. KOSCC-11 is a well-differentiated oral squamous cell carcinoma (OSCC) derived from mandibular gingiva. KOSCC-25A, -25B, -25C, -25D, and -25E cell lines were derived from the same OSCC. KOSCC-33A and -33B were established from the same tumor that originated from the maxillary sinus. All tumor lines studied grew as monolayers and showed: i) epithelial origin by the presence of desmosome and keratin; ii) in vitro anchorage-independent growth ability; and iii) tumorigenic potential in nude mice. The cancer cell lines did not contain HPV DNA and did not express viral genes. Northern blot analysis revealed: i) overexpression of EGFR in four cell lines, ii) overexpression of c-H-ras in four cell lines, iii) overexpression of c-myc in three cell lines, iv) decreased expression of TGF-alpha in seven cell lines, and v) decreased expression of c-jun in five cancer cell lines compared with normal human oral keratinocytes. In all KOSCC cell lines and their corresponding tumor tissues, mutations were identified in highly-conserved functional regions of the p53 gene. The KOSCC-11 cell line contained a frameshift mutation and the other cell lines harbored an identical p53 mutation at codon 175 from CGC (Arg) to CTC (Leu). In five cell lines, a significant reduction of p21WAF1/Cip1 protein was evident. Cancer cell lines expressed higher level of Rb protein than normal human oral keratinocytes. DCC, a tumor suppressor gene, was not detected in KOSCC-25C. The KOSCC-33A cell line displayed microsatellite instability and showed a loss of hMSH2 expression. These well-characterized human OSCC cell lines should serve as useful tools for understanding the biological characteristics of oral cancer.     

Induction of the neoplastic phenotype of EBV-established B lymphocytes by the human Ha-ras oncogene

We report on the use of human B lymphocytes immortalized by the Epstein-Barr virus (EBV) as targets for transformation by the c-Ha-ras oncogene of bladder carcinoma cells T24. Several stably transformed cell lines were obtained and their in vivo and in vitro growth properties as well as levels of expression of the ras gene were studied. The transformed phenotype in these cells was correlated to ras oncoprotein expression level; only the cell lines which overproduce p21 ras, by at least six-fold, were tumorigenic in nude mice. In this regard, our ras transformed cells behave as lymphoblastoid cells transformed by the c-myc oncogene, suggesting that c-myc and c-Ha-ras might act on the same regulatory level.