Genetic integrity of transforming growth factor beta (TGF-beta) receptors in cervical carcinoma cell lines: loss of growth sensitivity but conserved transcriptional response to TGF-beta

Transforming growth factor-β1 in carcinogenesis, progression, and therapy in cervical cancer

Transforming growth factor β1 (TGF-β1) is a multifunctional cytokine that plays important roles in cervical tumor formation, invasion, progression, and metastasis. TGF-β1 functions as a tumor inhibitor in precancerous lesions and early stage cancers of cervix whereas as a tumor promoter in later stage. This switch from a tumor inhibitor to a tumor promoter might be due to various alterations in TGF-β signaling pathway, such as mutations or loss of expression of TGF-β receptors and SMAD proteins. Additionally, the oncoproteins of human papillomaviruses have been shown to stimulate TGF-β1 expression, which in turn suppresses host immune surveillance. Thus, in addition to driving tumor cell migration and metastasis, TGF-β1 is believed to play a key role in promoting human papillomavirus infection by weakening host immune defense. In this article, we will discuss the role of TGF-β1 in the expression, carcinogenesis, progression, and therapy in cervical cancers. A better understanding of this cytokine in cervical carcinogenesis is essential for critical evaluation of this cytokine as a potential prognostic marker and therapeutic target.

Transforming Growth Factor β Signaling in Colorectal Cancer Cells With Microsatellite Instability Despite Biallelic Mutations in TGFBR2

BACKGROUND & AIMS

Most colorectal cancer (CRC) cells with high levels of microsatellite instability (MSI-H) accumulate mutations at a microsatellite sequence in the gene encoding transforming growth factor β receptor II (TGFBR2). TGFβ signaling therefore is believed to be defective in these tumors, although CRC cells with TGFBR2 mutations have been reported to remain sensitive to TGFβ. We investigated how TGFβ signaling might continue in MSI-H CRC cells.

METHODS

We sequenced the 10-adenines microsatellite sequence in the TGFBR2 gene of 32 MSI-H colon cancer tissues and 6 cell lines (HCT116, LS180, LS411N, RKO, SW48, and SW837). Activation of TGFβ signaling was detected by SMAD2 phosphorylation and through use of a TGFβ-responsive reporter construct in all CRC cell lines. Transcripts of TGFBR2 were knocked-down in CRC cells using short hairpin RNA. Full-length and mutant forms of TGFBR2 were expressed in LS411N cells, which do not respond to TGFβ, and their activities were measured.

RESULTS

SMAD2 was phosphorylated in most MSI-H CRC tissues (strong detection in 44% and weak detection in 34% of MSI-H tumors). Phosphorylation of SMAD2 in MSI-H cells required TGFBR2—even the form encoding a frameshift mutation. Transcription and translation of TGFBR2 with a 1-nucleotide deletion at its microsatellite sequence still produced a full-length TGFBR2 protein. However, protein expression required preservation of the TGFBR2 microsatellite sequence; cells in which this sequence was replaced with a synonymous nonmicrosatellite sequence did not produce functional TGFBR2 protein.

CONCLUSION

TGFβ signaling remains active in some MSI-H CRC cells despite the presence of frameshift mutations in the TGFBR2 gene because the mutated gene still expresses a functional protein. Strategies to reactivate TGFβ signaling in colorectal tumors might not be warranted, and the functional effects of mutations at other regions of microsatellite instability should be evaluated.

Nimesulide inhibits the proliferation of HepG2 by up-regulation of Smad4

Objectives:

Hepatocellular carcinoma (HCC) is receiving increased attention. This study was designed to investigate the effect of selective Cyclooxygenase-2 (COX-2) inhibitor, nimesulide, on the expression of Smad4 in human hepatocellular carcinoma HepG2.

Materials and Methods:

HepG2 cells were incubated in various concentrations of nimesulide (25, 50, 100, 200, 400 μmol/L) to detect the effect of proliferation by MTS. The apoptosis of HepG2 was determined by TUNEL; fluorescence microscope was used to observe the expression of Smad4.

Results:

The result showed that nimesulide inhibited the proliferation of HepG2 cell in a concentrations-dependent manner, and promoted the karyopyknosis and fragmentation of HepG2 cell nucleus, induced its apoptosis, the number of fluorescence labeling of Smad4 in Nimesulide group was higher than control group (P<0.05).

Conclusions:

Nimesulide inhibits the proliferation and promotes apoptosis of HepG2 by up-regulation of Smad4 in HepG2.

Hesperetin: an inhibitor of the transforming growth factor-β (TGF-β) signaling pathway

We have identified a previously unknown function of the natural compound, hesperetin. Here, we demonstrate that this small molecular agent is able to inhibit the transforming growth factor-β (TGF-β) signaling pathway. Single-molecule force measurements and single-molecule fluorescence imaging show that hesperetin interferes with ligand-receptor interactions. Furthermore, by Western blot analysis, it was confirmed that hesperetin also inhibits the phosphorylation of Smad3, a down-stream target of the TGF-β pathway. In addition we demonstrated that this compound hinders TGF-β1-induced cancer cell migration and invasion. These results suggest a potential future application for hesperetin as a TGF-β inhibitor in cancer therapy.

Tissue expression of TGF-β1 in uterine cervical samples from HIV/AIDS patients

Case-control study based on the immunohistochemistry for TGF-β1 evaluation of cervical samples obtained from two groups of women: CIN/HIV- and CIN/HIV+. Eleven women infected with HIV and with a histopathological diagnosis of CIN were included. The control group consisted of 12 patients with CIN. Cervical tissue samples obtained from all patients were submitted to histopathology and semiquantitative analysis of immunostaining for TGF-β1 protein. In addition, the peripheral CD4+ cell count and viral load were evaluated in HIV + patients. Tissue expression of the cytokine was higher in the CIN/HIV+ group compared to control (p = 0.0023). In addition, higher TGF-β1 expression was observed in higher grade cervical lesions in the two groups. There was a trend toward a direct correlation between peripheral CD4+ T cell count and tissue TGF-β1, and toward an inverse correlation between viral load and cytokine expression. Thus, TGF-β1 was more marked in situations in which cervical lesions are known to present a more aggressive behavior, suggesting that this cytokine is involved in the pathogenesis of tumor growth in these lesions. Tissue expression of TGF-β1 is increased in cervical samples from HIV-infected women with CIN.

Expression of Müllerian inhibiting substance type II receptor and antiproliferative effects of MIS on human cervical cancer

This study aimed to analyze expression of Müllerian inhibiting substance type II receptor (MISRII) protein and mRNA in cervical neoplasia, to demonstrate the growth inhibition of cervical cancer cells by administration of highly purified recombinant human Müllerian inhibiting substance (MIS) and, furthermore, to evaluate the clinical significance of MIS as a biological modifier for MIS receptor expressing tumors. Reverse transcriptase polymerase chain reaction (RT-PCR) was used for MISRII mRNA expression, and in situ hybridization and immunohistochemistry were used to observe expression, location of MISRII mRNA and protein, respectively. To demonstrate the effect of MIS on the viability of cervical cancer cells, methyl thiazole tetrazolium (MTT) assay was performed. Flow cytometry was used to evaluate the cell cycle distribution after exposure to MIS in cervical cancer cells, and the annexin-V-FITC staining method was performed to demonstrate apoptosis by MIS in cervical cancer cells. Expression of MISRII protein and mRNA were observed in all normal cervical and cervical carcinoma tissues. There was no significant difference in expression of MISRII protein and MISRII mRNA between normal cervical and cervical carcinoma tissues. MTT assay showed negative correlation between MIS exposure time and the viability of cervical cells (P=0.008). The changes in cell cycle distribution after MIS exposure suggest that MIS plays an important role in inducing cellular apoptosis by causing arrest at the G1 phase and increasing cells at sub-G0G1 phase. Annexin-V-FITC staining methods showed that cellular apoptosis was, respectively, 10.44 and 12.89% after 24 and 48 h of MIS exposure in cervical carcinoma cells. There was a negative correlation between cellular survival and MIS exposure time. This study demonstrates that MISRII is present on normal cervical and cervical carcinoma tissues, and MIS shows receptor-mediated antiproliferative effect on cervical cells in vitro. These data suggest that MIS may be used as a biological modifier or therapeutic modulator on MISRII-expressing tumors in the future.

Expression and mutational analysis of TGF-beta/Smads signaling in human cervical cancers

OBJECTIVE

To define the molecular basis of TGF-beta1 function in cervical carcinogenesis, we explored the expression and mutational status of TGF-beta1, TGF-beta1 receptors, and Smads, the regulators of the TGF-beta1 signaling pathway, in human cervical cancers.

METHODS

Expression of TGF-beta1, TGF-beta1 receptors, and Smads transcripts were determined by quantitative reverse transcription-polymerase chain reaction (RT-PCR), and sequence alteration was analyzed using RT-PCR-single-strand conformation polymorphism (SSCP) analysis. Genomic levels of TGF-beta1, TGF-beta1 receptors and Smads was also measured by quantitative genomic PCR.

RESULTS

Abnormal overexpression of TGF-beta1 and abnormal reduction of type II TGF-beta1 receptor were identified in 36% (18 of 50) and 20% (10 of 50) of cervical cancer tissues, respectively. 22% (11 of 50) in Smad2 and 14% (7 of 50) in Smad4 revealed tumor specific mRNA reduction less than a half of normal means. In addition, no evidence for sequence alterations of the gene was found by RT-PCR-SSCP analysis.

CONCLUSION

Our study demonstrates that disruption of TGF-beta/Smad signaling pathway exist in human cervical cancer, suggesting that abnormal expressions of the member of TGF-beta/Smad signaling pathway might contribute to the malignant progression of human cervical tumors via suppressing the tumor suppression function of TGF-beta1 1's tumor suppression function.

Mechanisms of decreased expression of transforming growth factor-beta receptor type I at late stages of HPV16-mediated transformation

Transforming growth factor-beta (TGF-beta) signaling is disrupted in many cancers, including cervical cancer, leading to TGF-beta resistance. Although initially sensitive, human papillomavirus type 16 (HPV16) immortalized human keratinocytes (HKc/HPV16) become increasingly resistant to the growth inhibitory effects of TGF-beta during in vitro progression to a differentiation resistant phenotype (HKc/DR). We have previously shown that loss of TGF-beta sensitivity in HKc/DR is attributed to decreased expression of TGF-beta receptor type I (TGF-beta RI), while the levels of TGF-beta receptor type II (TGF-beta RII) remain unchanged. The present study explored molecular mechanisms leading to reduced TGF-beta RI expression in HKc/DR. Using TGF-beta RI and TGF-beta RII promoter reporter constructs, we determined that acute expression of the HPV16 oncogenes E6 and E7 decreased the promoter activity of TGF-beta RI and TGF-beta RII by about 50%. However, promoter activity of TGF-beta RI is decreased to a greater extent than TGF-beta RII as HKc/HPV16 progress to HKc/DR. Reduced TGF-beta RI expression in HKc/DR was found not to be linked to mutations within the TGF-beta RI promoter or to promoter methylation. Electrophoretic mobility shift and supershift assays using probes encompassing Sp1 binding sites in the TGF-beta RI promoter found no changes between HKc/HPV16 and HKc/DR in binding of the transcription factors Sp1 or Sp3 to the probes. Also, Western blots determined that protein levels of Sp1 and Sp3 remain relatively unchanged between HKc/HPV16 and HKc/DR. Overall, these results demonstrate that mutations in or hypermethylation of the TGF-beta RI promoter, along with altered levels of Sp1 or Sp3, are not responsible for the reduced expression of TGF-beta RI we observe in HKc/DR. Rather the HPV16 oncogenes E6 and E7 themselves exhibit an inhibitory effect on TGF-beta receptor promoter activity.

Expression of Smad2 and Smad4 in cervical cancer: absent nuclear Smad4 expression correlates with poor survival

Alterations in transforming growth factor-beta signaling, due to a decrease in Smad2 and especially Smad4 expression, has primarily been reported in pancreatic and colorectal cancers, although loss of the chromosomal region 18q21.1, containing the loci of Smad2 and Smad4, is among the most frequent molecular alterations in cervical cancer. The aim of our study was to investigate whether decreased Smad2 and Smad4 protein expression in primary cervical cancers is associated with molecular alterations at 18q21.1, mutations in the functional domains of Smad2 and Smad4 or hypermethylation, and to assess the biological relevance of decreased Smad2 and Smad4 expression. Subsequently, Smad2, Smad4 and p21 protein expression was determined by immunohistochemistry in 117 primary cervical carcinomas, assembled in a tissue array. Smad signaling was shown to be associated with p21 mRNA expression. All the tumors expressed Smad2 or Smad4. Weak cytoplasmic Smad2 or weak cytoplasmic Smad4 expression could not be attributed to loss of heterozygosity at 18q21.1. Despite weak/moderate Smad2 expression and absent nuclear Smad4 expression, the coding regions of the functional MH1 and MH2 domains of Smad2 and Smad4 were unchanged, as assessed by sequence analysis. The Smad4 promoter region was unmethylated in tumor samples with weak/moderate cytoplasmic Smad4 expression. Remarkably, both weak cytoplasmic Smad4 expression and absent nuclear Smad4 expression significantly correlated with poor disease-free (P=0.003 and P=0.003, respectively) and overall 5-year survival (P=0.003 and P=0.010, respectively). Our findings support the hypothesis that Smad4 is a target molecule for functional inactivation in cervical cancer.

Down-regulation of transforming growth factor-beta type II receptor (TGF-betaRII) protein and mRNA expression in cervical cancer

BACKGROUND

Cervical carcinogenesis is a multistep process initiated by "high risk" human papillomaviruses (HR-HPV), most commonly HPV16. The infection per se is, however, not sufficient to induce malignant conversion. Transforming Growth Factor beta (TGF-beta) inhibits epithelial proliferation and altered expression of TGF-beta or its receptors may be important in carcinogenesis. One cofactor candidate to initiate neoplasia in cervical cancer is the prolonged exposure to sex hormones. Interestingly, previous studies demonstrated that estrogens suppress TGF-beta induced gene expression. To examine the expression of TGF-beta2, TGF-betaRII, p15 and c-myc we used in situ RT-PCR, real-time PCR and immunohistochemistry in transgenic mice expressing the oncogene E7 of HPV16 under control of the human Keratin-14 promoter (K14-E7 transgenic mice) and nontransgenic control mice treated for 6 months with slow release pellets of 17beta-estradiol.

RESULTS

Estrogen-induced carcinogenesis was accompanied by an increase in the incidence and distribution of proliferating cells solely within the cervical and vaginal squamous epithelium of K14-E7 mice. TGF-beta2 mRNA and protein levels increased in K14-E7 transgenic mice as compared with nontransgenic mice and further increased after hormone-treatment in both nontransgenic and transgenic mice. In contrast, TGF-betaRII mRNA and protein levels were decreased in K14-E7 transgenic mice compared to nontransgenic mice and these levels were further decreased after hormone treatment in transgenic mice. We also observed that c-myc mRNA levels were high in K14-E7 mice irrespective of estrogen treatment and were increased in estrogen-treated nontransgenic mice. Finally we found that p15 mRNA levels were not increased in K14-E7 mice.

CONCLUSION

These results suggest that the synergy between estrogen and E7 in inducing cervical cancer may in part reflect the ability of both factors to modulate TGF-beta signal transduction.

Elevated Expression of the Oncogene c-fms and Its Ligand, the Macrophage Colony-Stimulating Factor-1, in Cervical Cancer and the Role of Transforming Growth Factor-β1 in Inducing c-fms Expression

Cervical cancer is the third most common gynecologic cancer in the United States. The presence and possible involvement of several cytokines have been studied in cervical cancer; however, very little data, if any, are available on whether cervical tumors are responsive to stimulation by the macrophage colony-stimulating factor-1 (CSF-1). Given the involvement of c-fms and its ligand CSF-1 in gynecologic cancers, such as that of the uterus and the ovaries, we have examined the expression of c-fms and CSF-1 in cervical tumor (n = 17) and normal cervix (n = 8) samples. The data show that c-fms and its ligand are significantly higher in cervical carcinomas compared with normal samples. Immunohistochemistry not only showed that tumor cells expressed significantly higher levels of c-fms but also c-fms levels were markedly higher in tumor cells than tumor-associated stromal cells. Blocking c-fms activity in cervical cancer cells, which express CSF-1 and c-fms, resulted in increased apoptosis and decreased motility compared with control, suggesting that CSF-1/c-fms signaling may be involved in enhanced survival and possibly invasion by cervical cancer cells via an autocrine mechanism. Combined, the data show for the first time the induction of CSF-1 and c-fms in cervical carcinomas and suggest that c-fms activation may play a role in cervical carcinogenesis. Additionally, our data suggest that transforming growth factor-beta1 may be a factor in inducing the expression of c-fms in cervical cancer cells. The data suggest that c-fms may be a valuable therapeutic target in cervical cancer.

A cell-based high-throughput assay for screening inhibitors of human papillomavirus-16 long control region activity

Cervical carcinomas express human papillomavirus (HPV) E6 and E7 oncoproteins, which are required to maintain the proliferative state of cancer cells. Repression of E6 and E7 expression results in acquisition of senescent phenotype and in the rescue of functional p53 and p105(Rb) pathways; therefore, therapies directed against either viral protein may be beneficial. However, the systems to study HPV in vitro are technically difficult and not convenient for screening of antiviral compounds. This has hampered the discovery of drugs against HPV. Here we describe the generation and use of a high-throughput screening system based on keratinocytes stably transfected with a reporter construct containing the regulatory sequence of E6 and E7 gene transcription (LCR) that allows easy detection of inhibitors of E6 and E7 expression in libraries of synthetic or biological compounds. The assay was used to screen a wide panel of cytokines: among them, IL-4, IL-13, TGF-beta1, TGF-beta2, TGF-beta3, TNF-alpha, IFN-alpha, and IFN-beta were found to induce a strong inhibition of the LCR activity. Our assay provides a validated tool in the search for drugs against HPV-associated cervical carcinomas and allowed the first systematic analysis of the effect of cytokines on the HPV-16 LCR transcriptional activity.

Differences in Smad4 expression in human papillomavirus type 16-positive and human papillomavirus type 16-negative head and neck squamous cell carcinoma

The SMADs are a group of interrelated proteins that mediate transforming growth factor beta (TGF-beta) signaling. Upon TGF-beta binding the TGF-beta type I receptor phosphorylates Smad2 and Smad3, which then complex with Smad4 and translocate to the nucleus, with subsequent activation of target genes. Disruption of TGF-beta signaling is thought to contribute to the development of head and neck squamous cell carcinomas (HNSCC). Alterations in the function of the DPC4/Smad4 tumor suppressor gene have been found to inactivate TGF-beta signaling in several tumor types. For example, DPC4/Smad4 is lost or mutated in colorectal, pancreatic, and esophageal cancers. In addition, DPC4/Smad4 transcriptional activity and TGF-beta ability to inhibit DNA synthesis is blocked by the E7 protein of the human papillomavirus type 16 (HPV16) in cervical carcinoma cell lines. HPV16 infection is a risk factor for the development of a subset of HNSCC. This study was undertaken to investigate a potential correlation between expression of components of the TGF-beta signaling pathway and HPV16 status in HNSCC tumors. We examined the expression of TGF-beta signaling proteins Smad2, Smad2-P, and Smad4 by immunohistochemistry in 27 HPV16-negative and 16 HPV16-positive HNSCCs. We compared the expression patterns and assessed their relationship to HPV16 status. No significant differences were detected between HPV16-positive and HPV16-negative tumors in the expression of Smad2 and Smad2-P. Smad4 expression, however, was decreased in 56% of the HPV16-positive tumors and in 39% of HPV16-negative tumors. This difference was statistically significant (P = 0.01) suggesting that loss of Smad4 expression may be involved in HPV16-induced carcinogenesis of HNSCC.

Substantial changes in gene expression of Wnt, MAPK and TNFalpha pathways induced by TGF-beta1 in cervical cancer cell lines

Transforming growth factor-beta 1 (TGF-beta1) is a potent inhibitor of epithelial cell proliferation. During the development of cervical carcinoma however, an increase in production of TGF-beta1 is accompanied by decreased sensitivity for the growth-limiting effect of TGF-beta1. TGF-beta1 has an anti-proliferative effect on cells of the immune system and thus can be advantageous for tumor progression. The aim of the present study was to determine the effect of TGF-beta1 on mRNA expression profile of genes in pathways involved in cell growth and cell death, in cervical carcinoma cell lines with different sensitivity to TGF-beta1. For this purpose, we have investigated changes in gene expression in TGF-beta1 stimulated cervical cancer cell lines with high (CC10B), intermediate (SiHa) and low (HeLa) sensitivity to the anti-proliferative effect of TGF-beta1, at timepoints 0, 6, 12 and 24 h. Microarray analysis, using Affymetrics focus arrays, representing 8973 genes, was used to measure gene expression. In our study novel target genes involved in tumor necrosis factor alpha (TNFalpha), mitogen-activated protein kinase (MAPK) and wingless type (Wnt) pathways in response to TGF-beta1 were found. Substantial differences in gene expression between TGF-beta1 sensitive and insensitive cell lines were observed involving genes in TNFalpha, MAPK, Wnt and Smad pathways. Since these pathways are implicated in cell proliferation and cell death, these pathways may play a role in determining the overall sensitivity of a cell to TGF-beta1 induced cell growth inhibition. The results were subsequently validated by quantitative real-time PCR. Increased resistance to TGF-beta1 induced cell growth inhibition was correlated with an elevated production of TGF-beta1 by the cell lines, as measured by enzyme linked immunosorbent assay. TGF-beta1 production did not inhibit cell growth, since blocking TGF-beta1 protein by anti-TGF-beta had no effect on cell proliferation. TGF-beta1 excretion by tumor cells more likely contributes to paracrine stimulation of tumor development.

Smad4 deficiency in cervical carcinoma cells

Squamous cell carcinoma of the uterine cervix is one of the most frequent cancers affecting women worldwide. Carcinomas arise from cervical intraepithelial lesions, in which infection with high-risk human papillomavirus types has led to deregulated growth control through the actions of the viral E6 and E7 oncoproteins. The molecular mechanisms underlying progression to invasive tumor growth are poorly understood. One important feature, however, is the escape from growth inhibition by transforming growth factor beta (TGF-beta). Loss of chromosomal arm 18q is among the most frequent cytogenetic alterations in cervical cancers and has been associated with poor prognosis. Since the TGF-beta response is mediated by Smad proteins and the tumor suppressor gene Smad4 resides at 18q21, we have analysed the Smad4 gene for cervical cancer-associated alterations in cell lines and primary carcinomas. Here, we report Smad4 deficiency in four out of 13 cervical cancer cell lines which is due to an intronic rearrangement or deletions of 3' exons. All cell lines, however, showed either absent or moderate responsiveness to TGF-beta irrespective of their Smad4 status. In 41 primary squamous cervical carcinomas analysed, 10 samples showed loss of Smad4 protein expression and 26 samples a reduced expression. Altogether, our results strongly suggest that Smad4 gene alterations are involved in cervical carcinogenesis.

Prognostic relevance of TGF-beta1 and PAI-1 in cervical cancer

Cervical carcinoma is a human papilloma virus (HPV)-related immunogenic type of malignancy, in which escape of the tumor from the hosts' immune response is thought to play an important role in carcinogenesis. The multifunctional cytokine transforming growth factor-beta(1) (TGF-beta(1)) is involved in immunosuppression, stroma and extracellular matrix formation and controlling (epithelial) cell growth. The plasminogen activating (PA) system plays a key role in the cascade of tumor-associated proteolysis leading to extracellular matrix degradation and stromal invasion. Changes in expression of components of this system, including plasminogen activator inhibitor-1 (PAI-1), have been associated with poor prognosis in a variety of solid tumors. The present study was undertaken to assess the role of both components on relapse, survival and other clinicopathologic parameters in cervical cancer. The expression of TGF-beta(1) mRNA in 108 paraffin-embedded cervical carcinomas was detected by mRNA in situ hybridization. Immunohistochemistry was used to investigate the expression of PAI-1 protein. The presence of cytoplasmatic TGF-beta(1) mRNA in tumor cells was not significantly correlated with the other clinicopathologic parameters investigated or with a worse (disease-free) survival. Expression of the PAI-1 protein in tumor cells was strongly correlated with worse overall and disease-free survival, in addition to well-known prognostic parameters such as lymph node metastasis, depth of tumor infiltration, tumor size and vasoinvasion. In the multivariate analysis, PAI-1 turned out to be a strong independent prognostic factor. In a subgroup of patients without lymph node metastases, PAI-1 was predictive for worse survival and relapse of disease, too. Our results show that the (enhanced) expression of PAI-1 by carcinoma cells is correlated with worse (overall and disease-free) survival of patients with cancer of the uterine cervix. The expression of TGF-beta(1) in itself is not associated with worse survival in these patients. Although simultaneous presence of the 2 factors was observed in all tumors, induction of PAI-1 by TGF-beta(1) could not be demonstrated in our group of cervical carcinomas.

Differential Activation of Smads in HeLa and SiHa Cells That Differ in Their Response to Transforming Growth Factor-β

We assessed the responsiveness of six human cervical cancer cell lines to transforming growth factor (TGF)-beta with p3TP-lux reporter assay and found that HeLa and SiHa cells were highly responsive to TGF-beta. However, when pSBE4-BV/Luc reporter with four Smad binding elements was used, only the SiHa, not the HeLa, cells showed Smad activation. Smad DNA binding activity was relatively more in SiHa than in HeLa cells upon TGF-beta treatment, and the active complex contained Smad 2 and Smad 4. In 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays, HeLa cells treated with 5 ng/ml of TGF-beta for 24 h showed proliferation, whereas SiHa cells showed growth inhibition under the same conditions. TGF-beta treatment resulted in G(0)/G(1) arrest with a reduction in S-phase only in SiHa cells. A chemical inhibitor of Smad activation (SB203580) blocked the growth inhibitory effect of TGF-beta in SiHa, whereas the proliferative response in HeLa was unaffected. TGF-beta-induced translocation of phospho-Smad 2 was relatively less in HeLa than in SiHa cells. MAPK activation occurred within 5 min and persisted up to 15 min upon TGF-beta treatment in HeLa but was negligible in SiHa cells. TGF-beta activated JNK in HeLa, but SiHa cells showed a down-regulation of its activity. When an inhibitor of MAPK (U0126) was used, the TGF-beta-mediated proliferative response in HeLa cells was completely abolished. SB203580 did not affect MAPK activation induced by TGF-beta in HeLa cells. We report for the first time an activation, presumably independent of Smad activation, of TGF-beta-dependent MAPK within 5 min of treatment that resulted in cell cycle progression in a cervical adenocarcinoma cell line, HeLa.

Aberrant methylation of the specific CpG island portion regulates cyclooxygenase-2 gene expression in human gastric carcinomas

Although it has been well established that overexpression of cyclooxygenase-2 (Cox-2) favors tumorigenesis and metastasis, the molecular mechanism that regulates Cox-2 expression has not been well defined in gastric carcinoma. Aberrant methylation of the CpG island is known to be one of the powerful mechanisms for the suppression of gene expression, and usually, CpG islands are very rich in promoter region and exon-1 region. But, it is controversial whether Cox-2 gene expression is regulated by methylation of promoter region or exon-1 region. In this study, we examined whether the hyper-methylation mediated transcriptional silencing of Cox-2 also occurred in human gastric carcinoma tissues and which portion of CpG island methylation is important in Cox-2 gene expression. Genomic DNAs from human gastric carcinoma tissues were treated with three methylation-sensitive restriction enzymes and then Southern blot analysis was performed. Out of 30 primary gastric tumor samples, 26 cases (86.6%) showed overexpression of Cox-2. Four cases (13.3%) with relatively decreased Cox-2 gene expression were associated with the presence of aberrant methylation of Cox-2 CpG island. We also found that methylation of promoter region and not exon-1 region is related with the transcriptional silencing of Cox-2 in gastric carcinoma cancer by detailed methylation mapping using bisulfite sequencing analysis. Our results suggest that the DNA methylation-mediated transcriptional silencing of Cox-2 is a predominant mechanism for the down-regulation of Cox-2 expression in human gastric carcinoma. Furthermore, the results suggest that methylation of not exon-1 region but promoter region is important to regulation of Cox-2 gene expression.

Decreased expression of human papillomavirus E2 protein and transforming growth factor-beta1 in human cervical neoplasia as an early marker in carcinogenesis

BACKGROUND AND OBJECTIVES

Human papillomavirus (HPV) is thought to be one of the possible causative factors in cervical carcinogenesis, and cervical carcinoma cells are refractory to tumor transforming growth factor (TGF)-beta1. The purpose of this study is to investigate the possible cause-effect association between HPV and TGF-beta1 during cervical tumorigenesis.

METHODS

We assessed the expression of HPV capsid proteins, HPV-16 E7, HPV-16 E2 (C and N terminals), TGF-beta1, and their receptors TGF-beta RI and RII by immunohistochemistry in 48 paraffin-embedded blocks of tumor tissue derived from patients of cervical neoplasia.

RESULTS

Expression of TGF-beta1 decreased as tumor cells progressed from cervical intraepithelial neoplasia (CIN)1, CIN2, CIN3, to microinvasive carcinoma (P < 0.05). Levels of TGF-betaRI and TGFbeta-RII stayed the same in all cases. HPV was found in 89.6% of the studied sections, and cervical lesions without HPV infection expressed significantly less TGF-beta1 (P < 0.05). By comparing the expression pattern of TGF-beta1 and HPV in the neoplastic cells with that of normal cervical epithelium in each section, we found loss of HPV-16 E2 higher in CIN3 (15/24) than in CIN1 or CIN2 (3/7), and there is a significant trend that loss of HPV-16 E2 expression correlated with a >50% loss of TGF-beta1 at the lesion site (P < 0.05).

CONCLUSIONS

Our result showed co-suppression of HPV and TGF-beta1 expression during progression of cervical squamous cell cancer. Using antibody against HPV-16 E2 may be an auxiliary tool for the investigation of cervical tumor progression.

Loss of expression, and mutations of Smad 2 and Smad 4 in human cervical cancer

Mutations in Smads, intermediates of transforming growth factor-beta signaling, are known to contribute to the loss of sensitivity to transforming growth factor-beta, a common feature of many neoplastic cells. However, not much information is available on Smad alterations in cervical cancer and so we probed, for the first time, for alterations in Smad 2 and Smad 4 genes using human cervical cancer cell lines and human cervical tissue samples. Using PCR/reverse transcription-PCR, single-stranded conformation polymorphism analysis and DNA sequencing, we observed a deletion of 'G' in the L3 loop (crucial in Smad-receptor interaction) in C-33A cells, and an insertion of 'A' in codon 122 (loss of MH2 domain) from a cervical tumor sample, both of which caused frame shift and pretermination in Smad 2. In addition, a G/A transition at 31 bp upstream-nontranslated regions of exon 8 of Smad 4 was found in Bu 25TK cells. Smad 2 expression was less in some of the cervical tumor samples than that of nonmalignant samples and six cancer samples showed C-terminal deletions that abolish Smad 2 phosphorylation sites. The loss of expression of Smad 4 found in some cervical tumor samples was due to transcription loss rather than deletion of the gene. Our results highlight an important role for Smad 2 and Smad 4 in human cervical tumors.

Transforming growth factor-beta1 induces tumor stroma and reduces tumor infiltrate in cervical cancer

Cervical carcinomas consist of tumor cell nests surrounded by varying amounts of intratumoral stroma containing different quantities and types of immune cells. Besides controlling (epithelial) cell growth, the multifunctional cytokine transforming growth factor-beta(1) (TGF-beta(1)) is involved in the formation of stroma and extracellular matrix (ECM) and in immunosuppression. Several malignancies are known to be associated with enhanced production of TGF-beta(1), repression or mutation of TGF-beta transmembrane receptors, or mutations at the postreceptor intracellular signaling pathway. The aim of our study was to investigate the role of tumor cell-derived TGF-beta(1) on the amount of intratumoral stroma; the deposition of collagen IV, fibronectin, and laminin; and the tumor infiltrate in cervical carcinoma. The expression of TGF-beta(1) mRNA in 108 paraffin-embedded cervical carcinomas was detected by mRNA in situ hybridization. Immunohistochemistry was used to investigate the amount of tumor stroma and ECM proteins and the extent of the tumor infiltrate. Plasminogen activator inhibitor-1 (PAI-1) protein expression in tumor cells was determined to verify the biological activity of TGF-beta(1.) Cytoplasmatic TGF-beta(1) mRNA expression in tumor cells was significantly correlated with the amount of intratumoral stroma and the deposition of collagen IV. TGF-beta(1) mRNA expression in every tumor was accompanied by PAI-1 expression, indicating biological activity of TGF-beta(1). An inverse relationship between TGF-beta(1) mRNA expression in tumor cells and the extent of the tumor infiltrate was demonstrated. Our results indicate that cervical cancer cells affect the amount and the composition of the intratumoral stroma and the tumor infiltrate by the production and secretion of TGF-beta(1).

Polymorphism in codons 10 and 25 of the transforming growth factor-beta 1 (TGF-beta1) gene in patients with invasive squamous cell carcinoma of the uterine cervix

Transforming growth factor-beta 1 (TGF-beta1) has a multifactorial role in the development of cervical cancer. It potently inhibits the growth of epithelial cells that harbour oncogenic human papilloma viruses (HPVs). TGF-beta1 also inhibits the expression of the early viral transforming regions E6 and E7, which appear to be the key oncoproteins. It has been suggested that squamous cell carcinomas are devoid of TGF-beta1, raising the possibility that elevated levels of this growth factor could protect against cervical cancer. It is also recognized that the production and levels of TGF-beta1 are genetically predetermined and individually variable. Two genetic polymorphisms in the DNA encoding the leader sequence of the TGF-beta1 gene have been described and shown to be associated with the production of high or low TGF-beta1 levels in vivo and in vitro. We hypothesized that the inheritance of these polymorphisms could influence the development of invasive cervical cancer. This hypothesis was investigated by studying polymorphism in codons 10 and 25 of the TGF-beta1 gene. We studied 97 patients with invasive cervical cancer and 73 healthy controls and found that the distributions of alleles T (Leu) and/or C (Pro) and alleles G (Arg) and/or C (Pro) in codons 10 and 25, respectively, were similar. There was no significant association between the alleles and the histological degree of cancer differentiation. It appears that the role of this growth factor in cervical oncogenesis is not related to the point mutations that we examined in codons 10 and 25 of the TGF-beta1 gene. We speculate that other factors, including additional polymorphisms of the TGF-beta1 gene, the status of TGF-beta1 receptors, the complex cytokine network, differential responsiveness of cells to the stimuli, and the status of the precancer/cancer genome, may play a role in development of invasive cervical cancer.

p130 mediates TGF-beta-induced cell-cycle arrest in Rb mutant HT-3 cells

OBJECTIVE

The retinoblastoma proteins include Rb and the functionally and structurally related proteins p107 and p130. It has been reported that HT-3 cells are sensitive to TGF-beta growth inhibition, despite the Rb mutation. The purpose of this study was to elucidate the growth-inhibitory mechanism of TGF-beta in Rb mutant HT-3 cells.

METHODS

Growth inhibition by TGF-beta in cervical carcinoma cell lines was evaluated by counting cell numbers. Cell-cycle distribution was determined by staining DNA with propidium iodide (PI) and measured using a flow cytometer. The level of each protein expression was determined by Western blot analysis. To evaluate the assembly of cdk2/p21, cdk2/cyclin E, and E2F-4/p130 complexes by TGF-beta, immunoprecipitation was performed.

RESULTS

TGF-beta inhibited the proliferation of HT-3 cells expressing mutant Rb protein and efficiently induced cell-cycle arrest at G(1) phase. p21 protein level was elevated in TGF-beta-treated HT-3 cells, while other G(1) regulatory protein levels were unaltered. TGF-beta markedly enhanced the binding of p21 with cdk2 but decreased that of cdk2 with cyclin E and inhibited the phosphorylation of p130 but did not change Rb and p107 protein status. We also found that E2F-1 protein level was lower in TGF-beta-treated cells and suggest that this might be the result of enhanced binding between E2F-4 and p130.

CONCLUSIONS

Our results demonstrate that p130, instead of Rb, can mediate growth inhibition by TGF-beta in Rb mutant HT-3 cells.

Attenuation of transforming growth factor beta-induced growth inhibition in human hepatocellular carcinoma cell lines by cyclin D1 overexpression

Transforming growth factor-beta1 (TGF-beta1) causes growth inhibition in many cell types. Since its role in the outgrowth of human hepatocellular carcinoma (HCC) is not clearly understood, we investigated the growth inhibitory effects of TGF-beta1, the genetic and molecular integrity of TGF-beta receptors, and the expression levels of cell cycle regulating proteins in 11 human HCC cell lines. Of 11 cell lines, 3 (27%) showed growth inhibition to TGF-beta1, whereas the other 8 cell lines did not. We performed Southern and Northern analysis of TGF-beta type I and II receptors and examined poly-adenine track mutation of the TGF-beta type II receptor, but failed to find any genetic mutation. The transcriptional induction of plasminogen activator inhibitor-1 and p21(WAF1/CIP1) by TGF-beta were detected in all HCC cell lines, implying that the molecular integrity of the TGF-beta receptors might be intact. The amplification and overexpression of cyclin D1 gene was detected in 4 (50%) of 8 HCC cells that showed resistance to TGF-beta1. The suppression of cyclin D1 expression with antisense cyclin D1 facilitated the TGF-beta1-triggered growth inhibition in a TGF-beta1 resistant HCC cell line containing amplified cyclin D1 gene. In conclusion, the overexpression of cyclin D1 may be responsible for the attenuation of TGF-beta1 induced growth inhibition in some HCC cells.

Cytokine profile of cervical cancer cells

OBJECTIVE

In patients with cervical carcinoma, the presence of cytokines produced by T(H)2 cells, and the presence of an eosinophilic inflammatory infiltrate, has been associated with a less effective immune response and tumor progression. In the present study, we have investigated the cytokine profile of cervical carcinoma cells. In addition, we have measured whether differences in cytokine profiles between normal and malignant cervical epithelial cells are present.

METHODS

For this purpose we have determined the mRNA expression patterns of 20 relevant cytokines by RT-PCR and Southern blotting in 3 normal primary cervical epithelial cell cultures (NPE) and 10 cervical cancer cell lines (CCCL).

RESULTS

TGF-beta(1), IL-4, IL-12p35, and IL-15 were produced by all CCCL and NPE. TNF-alpha, IL-10, IL-5, and RANTES were present in most NPE, but not in any of the CCCL. MCP-1 was expressed in all CCCL but in only one NPE. The presence of the anti-inflammatory cytokine TGF-beta(1) in cervical carcinomas was confirmed by RNA in situ hybridization on tissue sections of carcinomas from which the CCCL originated.

CONCLUSIONS

Our results suggest that cervical carcinoma cells produce immunomodulatory cytokines and that cytokine expression patterns change after malignant transformation. The implications of locally produced cytokines by cervical cancer cells are further discussed.

Transforming growth factor beta1, urokinase-type plasminogen activator and plasminogen activator inhibitor-1 mRNA expression in head and neck squamous carcinoma and normal adjacent mucosa

BACKGROUND

A balance between urokinase-type plasminogen activator (uPA) and its main inhibitor type-1 (PAI-1) appears to be important for cancer invasive behavior. Since uPA/PAI-1 system seems to be regulated by transforming growth factor beta1 (TGFbeta1) in different cell types, our aim was to investigate the relationship between the expression of the three genes and lymph node status in head and neck squamous cell carcinomas (HNSCC) at specific sites.

MATERIALS AND METHODS

uPA, PAI-1, and TGFbeta1 mRNAs were determined by Northern analysis in tumor, and paired normal mucosa samples were obtained from 91 operable HNSCC patients.

RESULTS

In oral cavity, excluding tongue, TGFbeta1, PAI-1, and uPA mRNAs values were consistently lower in the normal tissues than in tumors. In larynx tumors, TGFbeta1 expression was increased, but no statistically significant differences were found for uPA or PAI-1 mRNAs as compared with normal tissues. Tongue tumors overexpressed only uPA mRNA, and uPA levels showed significant parallel variations with TGFbeta1 and PAI-1 mRNAs mainly in pN+ tumors. In oral cavity tumors, an inverse correlation between TGFbeta1 and uPA was observed in pN0 subgroup, elevated uPA mRNA was counterbalanced by high PAI-1 mRNA TGFbeta1, and PAI-1 were not coordinately expressed. Correlations between the three markers were not found in larynx. Hypopharynx tumors, all staged as pN+, expressed the lowest TGFbeta1 mRNA mean values.

CONCLUSIONS

Combined information about TGFbeta1, uPA, and PAI-1 mRNAs may add some clues to the understanding of the pathophysiological role of uPA system in head and neck squamous cell carcinoma.

Divergence and convergence of TGF-beta/BMP signaling

The transforming growth factor-beta (TGF-beta) superfamily includes more than 30 members which have a broad array of biological activities. TGF-beta superfamily ligands bind to type II and type I serine/threonine kinase receptors and transduce signals via Smad proteins. Receptor-regulated Smads (R-Smads) can be classified into two subclasses, i.e. those activated by activin and TGF-beta signaling pathways (AR-Smads), and those activated by bone morphogenetic protein (BMP) pathways (BR-Smads). The numbers of type II and type I receptors and Smad proteins are limited. Thus, signaling of the TGF-beta superfamily converges at the receptor and Smad levels. In the intracellular signaling pathways, Smads interact with various partner proteins and thereby exhibit a wide variety of biological activities. Moreover, signaling by Smads is modulated by various other signaling pathways allowing TGF-beta superfamily ligands to elicit diverse effects on target cells. Perturbations of the TGF-beta/BMP signaling pathways result in various clinical disorders including cancers, vascular diseases, and bone disorders.

Chromosome 3p tumor-suppressor gene alterations in cervical carcinomas

Loss of heterozygosity (LOH) on chromosome 3p is a common event in cervical cancer and typically occurs in a dispersed pattern involving several loci. This implies that more than one resident tumor-suppressor gene is involved in the genesis of these tumors; however, specific targets remain to be identified. The region of 3p14.2-pter encompasses a region of frequent loss and contains at least three tumor-suppressor genes: fragile histidine triad (FHIT), transforming growth factor-beta receptor II (T beta R-II), and Von Hippel-Lindau. To identify those loci within 3p14.2-pter that are important in cervical cancer, invasive tumors were first subjected to high-density LOH analysis. With 25 microsatellite markers, LOH was detected in seven of 15 cervical carcinomas (47%). Losses always included markers mapping to 3p22, and markers at this location were exclusively lost in two tumors, implicating this as a site of a cervical tumor-suppressor gene. Because it is a known tumor-suppressor gene located at 3p22 and thus a potential target for inactivation in these tumors, the T beta R-II gene was subsequently screened for mutation and altered expression levels. Whereas no tumor-derived mutations were detected in any of the tumors, six of ten tumors showed T beta R-II transcript levels reduced by > or = 50% when compared with normal cervical epithelium. Nine of 15 (60%) tumors exhibited LOH at 3p22 or reduced expression of T beta R-II, suggesting that reduced T beta R-II levels contribute to cervical tumorigenesis. Two cases exhibited silent germline polymorphisms of T beta R-II: one corresponding to a C1167T transversion and the other to an A1266G transition. The FHIT gene, which is located at 3p14.2, also frequently incurred LOH and abnormal transcription in these tumors. LOH of FHIT was observed in five of the 15 tumors analyzed. Neither mutations nor homozygous deletions of FHIT were detected in the tumors. However, aberrantly short transcripts of the FHIT gene were evident in six of nine (67%) tumors. Only one of these also displayed LOH, indicating that this gene was altered in at least 10 of 15 (67%) tumors. These results provide evidence that the inactivation of two known tumor-suppressor genes, TbetaR-II and FHIT, on chromosome 3p is involved in cervical carcinogenesis. Mol. Carcinog. 30:159--168, 2001.

Invasion and metastasis of a mammary tumor involves TGF-beta signaling

Several studies have correlated escape from TGF-beta-mediated cell cycle arrest with the tumorigenic phenotype. Most often, this escape from growth control has been linked to dysfunctional TGF-beta receptors or defects in the TGF-beta-mediated SMAD signaling pathway. In this report, we found that highly metastatic 4T1 mammary carcinoma cells express functional TGF-beta receptors capable of initiating SMAD-mediated transcription, yet are not growth inhibited by TGF-beta1. We further observed that TGF-beta directly contributes to the metastatic behavior of this cell line. Exposure to TGF-beta caused 4T1 cells to undergo morphological changes associated with the metastatic phenotype and invade more readily through collagen coated matrices. Furthermore, expression of a dominant negative truncated type II receptor diminished TGF-beta signaling and significantly restricted the ability of 4T1 cells to establish distant metastases. Our results suggest that regardless of 4T1 resistance to TGF-beta-mediated growth inhibition, TGF-beta signaling is required for tumor invasion and metastases formation.

TGF-beta-mediated cell cycle arrest of HPV16-immortalized human ectocervical cells correlates with decreased E6/E7 mRNA and increased p53 and p21(WAF-1) expression

Transforming growth factor beta (TGF-beta) suppresses proliferation and potentiates apoptosis of HPV16-immortalized human cervical epithelial cells (ECE16-1). Exposure of ECE16-1 to TGF-beta1 increased expression of p53 and induced cell cycle arrest. We examined, by Western blotting, expression of p53 and related cell cycle regulatory proteins after treatment. p53 levels increased as a function of time and dose. Increased p53 appeared to be active, since TGF-beta1 treatment increased the activity of a p53 transcriptional response element in a luciferase reporter plasmid. Additionally, the proteins of the p53-regulated genes, p21(WAF1), mdm2, and Bax, were increased with similar time and dose responses. We did not observe consistent changes in protein levels of cyclin D, cyclin E, CDK4, CDK6, CDK2, p27(Kip1), p16(INK4a), or RNA levels of p15(INK4b). Activity of CDK4 or 6, measured by phosphorylation of an Rb fragment, remained constant during the response period; however, activity of CDK2 (phosphorylation of histone H1) decreased. Concordantly, increased levels of p21(WAF1) were immunoprecipitated with anti-CDK2 antibodies. During treatment, the phosphorylation state of Rb shifted to a hypophosphorylated form. mRNA for the HPV E6/E7 genes decreased; however, significant changes in the E7 protein were not observed, while increased levels of Rb immunoprecipitated with anti-E7 antibodies were observed. These data are consistent with the following model. In ECE16-1 cells, there exists a fine balance between inhibitory levels of p53 and Rb and the antagonists, E6 and E7. TGF-beta1 treatment decreases steady-state levels of E6/E7 mRNA, which results in a shifted balance (lowered activity of E6) in favor of increased p53 expression, resulting in activation of the cell cycle inhibitory gene, p21(WAF1). This protein binds the cyclin E/CDK2 complex that maintains Rb in a phosphorylated state. Rb shifts to a hypophosphorylated state, resulting in G1 arrest, presumably by binding E2F transcription factors.

Loss of transforming growth factor-beta (TGF-beta) receptor type I mediates TGF-beta resistance in human papillomavirus type 16-transformed human keratinocytes at late stages of in vitro progression

Human keratinocytes (HKc) immortalized by human papillomavirus type 16 DNA (HKc/HPV16) progress toward malignancy through growth factor-independent (HKc/GFI) and differentiation-resistant stages (HKc/DR). This progression is associated with a loss of sensitivity to growth inhibition by both all-trans-retinoic acid (RA) and transforming growth factor-beta (TGF-beta). In the accompanying article (Borger et al., 2000, Virology 270, 397-407), we demonstrate that RA resistance in HKc/HPV16 arises despite functional nuclear retinoid receptors and that TGF-beta mediates growth inhibition by RA. To investigate the basis for the loss of TGF-beta sensitivity during in vitro progression of HKc/HPV16, we explored the expression of TGF-beta receptors type I and type II in independently derived HKc/HPV16 lines and their corresponding HKc/GFI and HKc/DR derivatives. While TGF-beta receptor type II mRNA levels were unchanged during progression, mRNA levels for TGF-beta receptor type I decreased dramatically as the cells became TGF-beta resistant. At the HKc/DR stage, loss of TGF-beta receptor type I mRNA, compared to low-passage cells, ranged from 55 to 87% in four HKc/HPV16 lines examined. Immunohistochemistry, using anti-TGF-beta receptor type I antibodies, confirmed a loss of TGF-beta receptor type I expression in HKc/DR. Reintroduction of the TGF-beta-receptor type I into TGF-beta-resistant HKc/DR completely restored growth inhibition by TGF-beta. Southern blot analysis of DNA extracted from normal HKc, HKc/HPV16, and HKc/DR ruled out any gross changes in the TGF-beta receptor type I gene. The activity of the TGF-beta receptor type I promoter, cloned upstream of a luciferase reporter gene, was decreased in HKc/DR, to an extent comparable to the decrease in mRNA levels for the TGF-beta receptor type I. Thus, TGF-beta resistance at late stages of HPV16-mediated transformation of HKc is the result of a loss of expression of TGF-beta receptor type I.

Defects in TGF-beta signaling overcome senescence of mouse keratinocytes expressing v-Ha-ras

Previous studies have shown that TGFbeta1 expression is upregulated in mouse keratinocytes infected with a v-rasHa retrovirus, although the functional significance of this has not been clear. Here we show that v-rasHa retrovirus transduced primary mouse keratinocytes undergo hyperproliferation followed by a TGFbeta1 dependent G1 growth arrest and senescence. The growth arrest is accompanied by a 15-fold increase in total TGFbeta1 secreted and a fourfold increase in secreted active TGFbeta1. When cultured in the presence of a neutralizing antibody to TGFbeta1, the senescence response is suppressed. Levels of the TGFbeta1 target p15ink4b increase during senescence as does association of this kinase inhibitor with cyclinD/cdk4 complexes. However, p16ink4a, p53 and p19ARF expression also increase during senescence. Genetic analysis shows that TGFbeta1 null and dominant negative TbetaBRII expressing v-rasHa keratinocytes resist the G1 growth arrest and do not senescence. This resistance is associated with low expression of p15ink4b and p16ink4a, constitutive Rb phosphorylation and high levels of cdk4 and cdk2 kinase activity. In contrast, inactivation of TGFbetabeta1 secretion or response does not block the induction of p53 and p19ARF, but the level of p21waf1, a p53 target gene, is reduced in cyclin D/cdk4 and cyclin E/cdk2 complexes. Thus, although multiple senescence pathways are activated in response to a ras oncogene, inactivation of TGFbeta1 secretion or response is sufficient to block the senescence program. Since v-rasHa transduced TGFbeta1-/- keratinocytes form squamous cell carcinomas following skin grafting, these results suggest that in mouse keratinocytes, defects in TGFbeta1 signaling accelerate malignant progression by overcoming oncogene induced replicative senescence.

Molecular mechanisms of inactivation of TGF-beta receptors during carcinogenesis

Signals from the TGF-betas are mediated by the TGF-beta receptors and their substrates, the Smad proteins. Inactivation of either of the two transmembrane serine/threonine kinases called the TGF-beta type I and type II receptors is now known to underlie a wide variety of human pathologies including, especially carcinogenesis. Numerous studies have now demonstrated that the TGF-beta receptor complex and its downstream signaling intermediates constitute a tumor suppressor pathway. We review here a specific pathway of mutational inactivation of the TGF-beta type II receptor resulting from microsatellite instability and demonstrate that, by contrast, the most common mechanism of loss of expression of the TGF-beta type II receptor involves transcriptional repression. This provides a new target for therapeutic intervention.

Structural alterations of transforming growth factor-beta receptor genes in human cervical carcinoma

The development and progression of invasive uterine cervical carcinomas appear to be associated with the progressive loss of sensitivity to transforming growth factor-beta (TGFbeta)-mediated cell cycle arrest. In order to identify possible molecular mechanisms responsible for TGFbeta resistance, we screened the 7 exons of the type II (TbetaR-II) TGFbeta receptor and the 9 exons of the type I (TbetaR-I) TGFbeta receptor genes for mutations in 16 paraffin-embedded primary invasive cervical carcinoma specimens. In one of these carcinomas, we found a novel G-->T transversion in exon 3 of TbetaR-II that introduces a premature stop codon (E142Stop) and presumably results in the synthesis of a truncated soluble exoreceptor. In one tumor, a silent A-->C transversion mutation that may affect mRNA splicing was present in exon 6 of TbetaR-I. In addition, 7 of 16 cases were heterozygous for a G-->A polymorphism in intron 7 of TbetaR-I. Finally, we identified a 9 base pair in-frame germline deletion in exon 1 of TbetaR-I resulting in loss of 3 of 9 sequential alanine residues at the N-terminus in 6 of 16 cases. Analysis of specimens from case-control studies indicated that carriers of this del(GGC)3 TbetaR-I variant allele may be at a increased risk for the development of cervical carcinoma (p=0.22). Furthermore, the response of cells expressing the variant receptor to TGFbeta was diminished. Our results support the notion that diverse alterations in the TGFbeta signaling pathway may play a role in the development of cervical cancer.