Frequent aberration of the transforming growth factor-beta receptor II gene in cell lines but no apparent mutation in pre-invasive and invasive carcinomas of the uterine cervix

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.

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.

E6 and E7 oncoproteins from human papillomavirus type 16 induce activation of human transforming growth factor beta1 promoter throughout Sp1 recognition sequence

Human Papillomavirus (HPV) infection is the main etiologic agent of cervical cancer and HPV E6 and E7 oncogenes trans-regulate many cellular genes. An association between TGF-beta1 gene expression and cervical cancer development has been suggested; however, the mechanisms by which HPV influences TGF-beta1 expression remain unclear. In the present study we analyzed the mechanism through which HPV-16 E6 and E7 oncoproteins regulate the TGF-beta1 promoter in cervical tumor cells. Our results showed that E6 and E7 increased TGF-beta1 promoter activity. Furthermore, we identified a specific DNA sequence motif in the TGF-beta1 core promoter that is responsible for trans-activation and that corresponds to the Sp1e-binding site associated with HPV-16 E6 and E7 oncoproteins. Mutational analysis showed that the Sp1e recognition site abolished the trans-activation caused by E6 and E7. These results suggest a physical interaction and functional cooperation between viral oncoproteins and cellular regulatory elements of the TGF-beta1 promoter, and may explain the contribution of HPV-16 to TGF-beta1 gene expression in cervical cancer.

Transcriptional deregulation of VEGF, FGF2, TGF-beta1, 2, 3 and cognate receptors in breast tumorigenesis

Angiogenesis is an important event during the neoplastic process and is induced by the secretion of numerous growth factors from endothelial cells. Vascular endothelial growth factor (VEGF), basic fibroblastic growth factor (FGF2), and transforming growth factor-beta1, beta2, beta3 (TGF-beta1, 2, 3) and cognate receptors (TGF-betaRI, II, III) mRNA expression pattern was evaluated by RT-PCR in 25 breast cancer tissue samples and adjacent normal tissues, and correlated to clinicopathological features. Western blot analysis was performed to evaluate VEGF and TGF-beta1 protein levels. TGF-beta1 and TGF-beta3 mRNA levels were significantly different in breast cancer specimens of differing histology (ductal, lobular, other) (P=0.020 and P=0.043). No statistically significant difference was observed at the mRNA level of VEGF between normal and tumor tissues while elevated VEGF protein levels in tumors were associated with patients' menopausal status. A strong hormonal influence of ER and PR on TGF-beta mRNA expression was established. FGF2 transcript levels were substantially decreased in cancer compared to adjacent normal specimens (P=0.031). A disruption of mRNA co-expression patterns was observed in malignant breast tissues compared to controls. Western blot analysis revealed differences between VEGF and TGFbeta1 mRNA and their corresponding protein levels. A substantial negative correlation of TGF-beta1 protein and TGF-beta1 mRNA levels (P=0.016) was demonstrated by breast tissue-pair analysis. Summarizing, our findings suggest that transcript levels of the examined markers in breast cancer are associated with menopausal and hormonal status, while their co-expression pattern is altered in malignant tissues compared to controls. In addition the difference between VEGF and TGF-beta1 mRNA and protein levels observed, indicates that post-transcriptional mechanisms may regulate expression of these molecules in breast cancer.

VEGF, FGF2, TGFB1 and TGFBR1 mRNA expression levels correlate with the malignant transformation of the uterine cervix

Angiogenesis is a complex procedure induced by the secretion of numerous growth factors from endothelial cells. Vascular endothelial growth factor (VEGF), basic fibroblastic growth factor (FGF2), transforming growth factor-beta1, 2, 3 (TGFB1, 2, 3), and transforming growth factor-beta receptors (TGFBR1, 2, 3) mRNA expression pattern was evaluated in tissue samples with cervical intraepithelial neoplasia (CIN) and cervical cancer, compared to that of normal cervical tissues, and correlated to the clinical stage of the disease. Transcript levels of the above genes were assessed by RT-PCR analysis in a total of 44 cervical specimens. VEGF, TGFB1, TGFBR1, and FGF2 transcript levels were significantly different in the normal, CIN and cancer specimen groups (P=0.015, 0.001, 0.008, and 0.029, respectively). Higher TGFBR1 mRNA levels were observed in parallel with increased severity of the lesion, whereas FGF2 exhibited lower transcript levels. A highly significant increase of VEGF mRNA expression was found upon cervical neoplastic transformation (P<0.0001). High-grade squamous intraepithelial lesions exhibited higher VEGF mRNA levels than low-grade lesions (P=0.039). TGFBR1 and TGFBR3 receptors demonstrated significant co-expressions with TGFB2 (P<0.0001), and TGFB1 (P=0.005 and 0.002, respectively) in normal cervical specimens. However, a disruption of co-expression patterns was observed in the groups of CIN and cancer cases, compared to normal tissues. Our findings show that VEGF, FGF2, TGFB1 and TGFBR1 mRNA expression levels correlate with the malignant transformation of the uterine cervix. The involvement of the examined markers in cervical carcinogenesis is furthermore supported by the observed disruption of their mRNA co-expression patterns.

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.

Multiple epithelial and nonepithelial tumors in hereditary nonpolyposis colorectal cancer: characterization of germline and somatic mutations of the MSH2 gene and heterogeneity of replication error phenotypes

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal inherited cancer syndrome characterized by germline plus somatic mutations of DNA mismatch repair genes and familial clustering of cancers of colorectum and other visceral organs. So far, to our knowledge, there has been no proof of nonepithelial tumors in association with HNPCC. Here we report on a MSH2 frameshift HNPCC family with a carrier found to have multiple primary tumors, including endometrial hyperplasia, ovarian adenocarcinoma, skin cavernous hemangioma, and skin dermatofibrosarcoma protuberans (DFSP). We studied the replication error (RER) phenotype in noncoding (Bat-26, Bat-25, D2S123, D5S346, and D17S250) and coding (MSH3, MSH6, BAX, and TGFBR2 genes) DNA sequences, and characterized the germline and somatic mutations of the MSH2 gene in the tumors described above and in endometrial carcinomas from two of her affected siblings. RER was observed in an order of hyperplasic endometrium (6/10 markers), ovarian carcinoma (5/10 markers), endometrial carcinomas (4/9 and 3/10), DFSP (2/9 markers), and cavernous hemangioma (2/10 markers). All the tumors showed the same germline mutation of G5-->G6 frameshift at 183-187 and polymorphism of C1168T in a heterozygous pattern. In an endometrial carcinoma, deletion of the second allele of MSH2 was evident. Heterogeneous RER patterns were noted in multiple primary tumors of the same individual and in premalignant and malignant endometrial tumors from different individuals. The study demonstrated the two hits of the hMSH(2) gene as well as intra- and interindividual variations of RER phenotypes in HNPCC. The first characterized nonepithelial tumors in HNPCC seem to carry a limited panel of RER, including a framesift at the (A)(10) tract of TGFBR2.

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.

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).

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.

Role of transforming growth factor beta in cancer

Transforming growth factor beta (TGF-beta) is an effective and ubiquitous mediator of cell growth. The significance of this cytokine in cancer susceptibility, cancer development and progression has become apparent over the past few years. TGF-beta plays various roles in the process of malignant progression. It is a potent inhibitor of normal stromal, hematopoietic, and epithelial cell growth. However, at some point during cancer development the majority of transformed cells become either partly or completely resistant to TGF-beta growth inhibition. There is growing evidence that in the later stages of cancer development TGF-beta is actively secreted by tumor cells and not merely acts as a bystander but rather contributes to cell growth, invasion, and metastasis and decreases host-tumor immune responses. Subtle alteration of TGF-beta signaling may also contribute to the development of cancer. These various effects are tissue and tumor dependent. Identifying and understanding TGF-beta signaling pathway abnormalities in various malignancies is a promising avenue of study that may yield new modalities to both prevent and treat cancer. The nature, prevalence, and significance of TGF-beta signaling pathway alterations in various forms of human cancer as well as potential preventive and therapeutic interventions are discussed in this review.

Downregulation of transforming growth factor beta type II receptor in laryngeal carcinogenesis

AIMS

To investigate whether anomalies of transforming growth factor beta type II receptor (TGF-beta RII) expression occur in the early stages of laryngeal carcinogenesis and to assess their importance in the development of laryngeal squamous cell carcinoma. TGF-beta RII status was examined in laryngeal premalignant lesions coupled with malignant evolution and compared with a control group of similar lesions without progression to cancer.

METHODS

Immunohistochemical staining for TGF-beta RII was performed on 15 paraffin wax embedded biopsies from patients with precancerous laryngeal lesions who subsequently developed invasive squamous cell carcinoma of the larynx, and on 30 control biopsies from patients who did not develop cancer in a comparable follow up period. In addition, DNA extracted from 18 preneoplastic lesions and eight squamous cell carcinomas was amplified by the polymerase chain reaction at the poly A and the poly GT regions of the TGF-beta RII gene.

RESULTS

In the group of lesions with progression to carcinoma, 11 of 15 cases showed loss (< 20% of epithelial cells) of TGF-beta RII immunoreactivity, whereas among non-evolved lesions only five of 30 had similar altered expression of the receptor (p < 0.001, two tailed Fisher's exact test). All squamous cell carcinomas showed a degree of receptor expression comparable with that of the corresponding preneoplastic lesion, with the exception of one case, in which loss of the receptor was evident only in invasive cancer. Mutation of the poly A sequence of the TGF-beta RII gene was identified in only one precancerous lesion and in the subsequent squamous cell carcinoma.

CONCLUSIONS

These findings indicate that the downregulation of TGF-beta RII is an early event in laryngeal carcinogenesis, which may result in the loss of TGF-beta mediated growth inhibition, thereby facilitating the progression of laryngeal precancerous lesions to squamous cell carcinoma.

Transforming growth factor-beta signaling in cancer

Transforming growth factor (TGF-beta) is a multifunctional polypeptide implicated in the regulation of a variety of cellular processes including growth, differentiation, apoptosis, adhesion, and motility. Abnormal activation or inhibition of these TGF-beta regulated processes is implicated in many diseases, including cancer. Cancers can develop through selective exploitation of defects in TGF-beta signaling that occur at several different levels in the pathway. The TGF-beta signal transduction cascade is initiated when TGF-beta binds to transmembrane receptors. The TGF-beta receptors then phosphorylate and activate Smad proteins, which transduce the signal from the cytoplasm to the nucleus. In the nucleus, Smads can bind directly to DNA and cooperate with other transcription factors to induce transcription of TGF-beta target genes. Mutations in target genes, Smads, or the TGF-beta receptor are associated with certain human cancers.

Role of transforming growth factor beta in cancer

Transforming growth factor beta (TGF-beta) is an effective and ubiquitous mediator of cell growth. The significance of this cytokine in cancer susceptibility, cancer development and progression has become apparent over the past few years. TGF-beta plays various roles in the process of malignant progression. It is a potent inhibitor of normal stromal, hematopoietic, and epithelial cell growth. However, at some point during cancer development the majority of transformed cells become either partly or completely resistant to TGF-beta growth inhibition. There is growing evidence that in the later stages of cancer development TGF-beta is actively secreted by tumor cells and not merely acts as a bystander but rather contributes to cell growth, invasion, and metastasis and decreases host-tumor immune responses. Subtle alteration of TGF-beta signaling may also contribute to the development of cancer. These various effects are tissue and tumor dependent. Identifying and understanding TGF-beta signaling pathway abnormalities in various malignancies is a promising avenue of study that may yield new modalities to both prevent and treat cancer. The nature, prevalence, and significance of TGF-beta signaling pathway alterations in various forms of human cancer as well as potential preventive and therapeutic interventions are discussed in this review.

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.

Endocervical cancer is associated with an increase in the ligands and receptors for transforming growth factor-beta and a contrasting decrease in p27(Kip1)

OBJECTIVE

The aim of this study was to investigate the relationship between the expression of the TGF-beta ligands and TGF-beta receptors to the expression of p27(Kip1), a TGF-beta-regulated gene, in endocervical cancer.

METHODS

To examine the expression of TGF-beta and p27(Kip1) in malignant transformation of the uterine endocervix, a panel of 23 formalin-fixed and paraffin-embedded human cervical specimens, including 8 with benign endocervical glands, 8 with cervical adenocarcinoma in situ, and 7 with cervical adenocarcinomas, was used. Tissues were immunostained with polyclonal antibodies that react specifically with TGF-beta 1, TGF-beta 2, TGF-beta 3, TGF-beta RI, TGF-beta RII, and p27(Kip1).

RESULTS

Immunostaining for TGF-beta 1, TGF-beta 2, TGF-beta 3, TGF-beta RI, TGF-beta RII, and p27(Kip1) was detected in normal endocervix, with the TGF-betas showing weak cytoplasmic staining, while p27(Kip1) showed strong nuclear staining. Expression of TGF-beta increased significantly upon neoplastic transformation with the TGF-beta ligands and receptors showing strong cytoplasmic staining in adenocarcinoma in situ compared to normal endocervix. Interestingly, expression of TGF-beta was lower in adenocarcinoma than in adenocarcinoma in situ, but still significantly higher than in normal endocervix. TGF-beta 2 and TGF-beta 3 showed higher levels of immunostaining than TGF-beta 1 in adenocarcinomas. In contrast, p27(Kip1) protein expression decreased with progressive malignancy, with lower p27(Kip1) protein levels detected in adenocarcinoma than in adenocarcinoma in situ, while normal endocervix showed the highest level of p27(Kip1) protein expression.

CONCLUSION

Elevated expression of the TGF-beta ligands and receptors is found in both cervical adenocarcinoma in situ and adenocarcinoma compared to normal endocervix. In contrast, a progressive decrease in p27(Kip1) occurs upon neoplastic transformation of the normal endocervix to cervical adenocarcinoma. These results suggest that neoplastic transformation of the endocervix may be related to dysregulation of TGF-beta and p27(Kip1) seen as an elevation of TGF-beta and a reduction of p27(Kip1) expression that may lead to loss of cell cycle control.

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.