Transforming growth factor-beta and breast cancer: Tumor promoting effects of transforming growth factor-beta

Activated Abl kinase inhibits oncogenic transforming growth factor-beta signaling and tumorigenesis in mammary tumors

Transforming growth factor-beta (TGF-beta) is a ubiquitous cytokine with dual roles in tumor suppression and promotion, and these dichotomous functions have frustrated the development of therapies targeting oncogenic signaling by TGF-beta. In comparison, Abl is well established as an initiator of hematopoietic cancers; however, a clear role for Abl in regulating solid tumor development remains elusive. Here, we investigated the role of Abl in TGF-beta-mediated epithelial-mesenchymal transition (EMT) in normal and metastatic mammary epithelial cells (MECs). In doing so, we identified Abl as an essential regulator of MEC morphology and showed that Abl inactivation was sufficient to induce phenotypic and transcriptional EMT in normal MECs. Increasing Abl activity in metastatic MECs resulted in their complete morphological reversion, restored their cytostatic response to TGF-beta, and blocked their secretion of matrix metalloproteinases induced by TGF-beta. Constitutively active Abl expression blocked TGF-beta-responsive mammary tumor growth in mice, while Imatinib therapy afforded no clinical benefit in mice bearing mammary tumors. Collectively, this investigation establishes Abl as a potent mediator of MEC identity, and as a suppressor of oncogenic TGF-beta signaling during mammary tumorigenesis. Notably, our findings strongly caution against the use of pharmacological Abl antagonists in the treatment of developing and progressing mammary tumors.

TGF-beta3 and cancer: a review

With the development of growth factors and growth factor modulators as therapeutics for a range of disorders, it is prudent to consider whether modulating the growth factor profile in a tissue can influence tumour initiation or progression. As recombinant human TGF-beta3 (avotermin) is being developed for the improvement of scarring in the skin it is important to understand the role, if any, of this cytokine in tumour progression. Elevated levels of TGF-beta3 expression detected in late-stage tumours have linked this cytokine with tumourigenesis, although functional data to support a causative role are lacking. While it has proved tempting for researchers to interpret a 'correlation' as a 'cause' of disease, what has often been overlooked is the normal biological role of TGF-beta3 in processes that are often subverted in tumourigenesis. Clarifying the role of this cytokine is complicated by inappropriate extrapolation of the data relating to TGF-beta1 in tumourigenesis, despite marked differences in biology between the TGF-beta isoforms. Indeed, published studies have indicated that TGF-beta3 may actually play a protective role against tumourigenesis in a range of tissues including the skin, breast, oral and gastric mucosa. Based on currently available data it is reasonable to hypothesize that administration of acute low doses of exogenous TGF-beta3 is unlikely to influence tumour initiation or progression.

TGF-beta receptor levels regulate the specificity of signaling pathway activation and biological effects of TGF-beta

TGF-beta is a pluripotent cytokine that mediates its effects through a receptor composed of TGF-beta receptor type II (TGFBR2) and type I (TGFBR1). The TGF-beta receptor can regulate Smad and nonSmad signaling pathways, which then ultimately dictate TGF-beta's biological effects. We postulated that control of the level of TGFBR2 is a mechanism for regulating the specificity of TGF-beta signaling pathway activation and TGF-beta's biological effects. We used a precisely regulatable TGFBR2 expression system to assess the effects of TGFBR2 expression levels on signaling and TGF-beta mediated apoptosis. We found Smad signaling and MAPK-ERK signaling activation levels correlate directly with TGFBR2 expression levels. Furthermore, p21 levels and TGF-beta induced apoptosis appear to depend on relatively high TGFBR2 expression and on the activation of the MAPK-ERK and Smad pathways. Thus, control of TGFBR2 expression and the differential activation of TGF-beta signaling pathways appears to be a mechanism for regulating the specificity of the biological effects of TGF-beta.

An orally active small molecule TGF-beta receptor I antagonist inhibits the growth of metastatic murine breast cancer

BACKGROUND

Transforming growth factor beta (TGF-beta) plays a complex role in breast carcinogenesis. Initially functioning as a tumor suppressor, this cytokine later contributes to the progression of malignant cells by enhancing their invasive and metastatic potential as well as suppressing antitumor immunity. The purpose of this study was to investigate the efficacy of SM16, a novel small molecule ALK5 kinase inhibitor, to treat a highly metastatic, TGF-beta-producing murine mammary carcinoma (4T1).

MATERIALS AND METHODS

Mice bearing established 4T1 tumors were treated with SM16 intraperitoneally (i.p.) or orally, and primary and metastatic tumor growth was assessed.

RESULTS

SM16 inhibited Smad2 phosphorylation in cultured 4T1 tumor cells as well as primary and metastatic 4T1 tumor tissue. Blockade of TGF-beta signal transduction in 4T1 tumor cells by SM16 prevented TGF-beta-induced morphological changes and inhibited TGF-beta-induced invasion in vitro. When delivered via daily i.p. injection or orally through mouse chow, SM16 inhibited the growth of primary and metastatic 4T1 tumors. Splenocytes isolated from mice on the SM16 diet displayed enhanced IFN-gamma production and antitumor CTL activity. Furthermore, SM16 failed to inhibit the growth and metastasis of established 4T1 tumors in immunodeficient SCID mice.

CONCLUSION

Taken together, the data indicate that the antitumor efficacy of SM16 is dependent on an immune-mediated mechanism and that SM16 may represent a safe and effective treatment for metastatic breast cancer.

Integrating biological knowledge with gene expression profiles for survival prediction of cancer

Due to the large variability in survival times between cancer patients and the plethora of genes on microarrays unrelated to outcome, building accurate prediction models that are easy to interpret remains a challenge. In this paper, we propose a general strategy for improving performance and interpretability of prediction models by integrating gene expression data with prior biological knowledge. First, we link gene identifiers in expression dataset with gene annotation databases such as Gene Ontology (GO). Then we construct "supergenes" for each gene category by summarizing information from genes related to outcome using a modified principal component analysis (PCA) method. Finally, instead of using genes as predictors, we use these supergenes representing information from each gene category as predictors to predict survival outcome. In addition to identifying gene categories associated with outcome, the proposed approach also carries out additional within-category selection to select important genes within each gene set. We show, using two real breast cancer microarray datasets, that the prediction models constructed based on gene sets (or pathway) information outperform the prediction models based on expression values of single genes, with improved prediction accuracy and interpretability.

Transforming growth factor-beta signaling: emerging stem cell target in metastatic breast cancer?

In most human breast cancers, lowering of TGFbeta receptor- or Smad gene expression combined with increased levels of TGFbetas in the tumor microenvironment is sufficient to abrogate TGFbetas tumor suppressive effects and to induce a mesenchymal, motile and invasive phenotype. In genetic mouse models, TGFbeta signaling suppresses de novo mammary cancer formation but promotes metastasis of tumors that have broken through TGFbeta tumor suppression. In mouse models of "triple-negative" or basal-like breast cancer, treatment with TGFbeta neutralizing antibodies or receptor kinase inhibitors strongly inhibits development of lung- and bone metastases. These TGFbeta antagonists do not significantly affect tumor cell proliferation or apoptosis. Rather, they de-repress anti-tumor immunity, inhibit angiogenesis and reverse the mesenchymal, motile, invasive phenotype characteristic of basal-like and HER2-positive breast cancer cells. Patterns of TGFbeta target genes upregulation in human breast cancers suggest that TGFbeta may drive tumor progression in estrogen-independent cancer, while it mediates a suppressive host cell response in estrogen-dependent luminal cancers. In addition, TGFbeta appears to play a key role in maintaining the mammary epithelial (cancer) stem cell pool, in part by inducing a mesenchymal phenotype, while differentiated, estrogen receptor-positive, luminal cells are unresponsive to TGFbeta because the TGFBR2 receptor gene is transcriptionally silent. These same cells respond to estrogen by downregulating TGFbeta, while antiestrogens act by upregulating TGFbeta. This model predicts that inhibiting TGFbeta signaling should drive the differentiation of mammary stem cells into ductal cells. Consequently, TGFbeta antagonists may convert basal-like or HER2-positive cancers to a more epithelioid, non-proliferating (and, perhaps, non-metastatic) phenotype. Conversely, these agents might antagonize the therapeutic effects of anti-estrogens in estrogen-dependent luminal cancers. These predictions need to be addressed prospectively in clinical trials and should inform the selection of patient populations most likely to benefit from this novel anti-metastatic therapeutic approach.

TGF-beta1 genotype and phenotype in breast cancer and their associations with IGFs and patient survival

Transforming growth factor-beta (TGF-beta)-mediated signals play complicated roles in the development and progression of breast tumour. The purposes of this study were to analyse the genotype of TGF-beta1 at T29C and TGF-beta1 phenotype in breast tumours, and to evaluate their associations with IGFs and clinical characteristics of breast cancer. Fresh tumour samples were collected from 348 breast cancer patients. TGF-beta1 genotype and phenotype were analysed with TaqMan and ELISA, respectively. Members of the IGF family in tumour tissue were measured with ELISA. Cox proportional hazards regression analysis was performed to assess the association of TGF-beta1 and disease outcomes. Patients with the T/T (29%) genotype at T29C had the highest TGF-beta1, 707.9 pg mg(-1), followed by the T/C (49%), 657.8 pg mg(-1), and C/C (22%) genotypes, 640.8 pg mg(-1), (P=0.210, T/T vs C/C and C/T). TGF-beta1 concentrations were positively correlated with levels of oestrogen receptor, IGF-I, IGF-II and IGFBP-3. Survival analysis showed TGF-beta1 associated with disease progression, but the association differed by disease stage. For early-stage disease, patients with the T/T genotype or high TGF-beta1 had shorter overall survival compared to those without T/T or with low TGF-beta1; the hazard ratios (HR) were 3.54 (95% CI: 1.21-10.40) for genotype and 2.54 (95% CI: 1.10-5.89) for phenotype after adjusting for age, grade, histotype and receptor status. For late-stage disease, however, the association was different. The T/T genotype was associated with lower risk of disease recurrence (HR=0.13, 95% CI: 0.02-1.00), whereas no association was found between TGF-beta1 phenotype and survival outcomes. The study suggests a complex role of TGF-beta1 in breast cancer progression, which supports the finding of in vitro studies that TGF-beta1 has conflicting effects on tumour growth and metastasis.

Consortium analysis of 7 candidate SNPs for ovarian cancer

The Ovarian Cancer Association Consortium selected 7 candidate single nucleotide polymorphisms (SNPs), for which there is evidence from previous studies of an association with variation in ovarian cancer or breast cancer risks. The SNPs selected for analysis were F31I (rs2273535) in AURKA, N372H (rs144848) in BRCA2, rs2854344 in intron 17 of RB1, rs2811712 5' flanking CDKN2A, rs523349 in the 3' UTR of SRD5A2, D302H (rs1045485) in CASP8 and L10P (rs1982073) in TGFB1. Fourteen studies genotyped 4,624 invasive epithelial ovarian cancer cases and 8,113 controls of white non-Hispanic origin. A marginally significant association was found for RB1 when all studies were included [ordinal odds ratio (OR) 0.88 (95% confidence interval (CI) 0.79-1.00) p = 0.041 and dominant OR 0.87 (95% CI 0.76-0.98) p = 0.025]; when the studies that originally suggested an association were excluded, the result was suggestive although no longer statistically significant (ordinal OR 0.92, 95% CI 0.79-1.06). This SNP has also been shown to have an association with decreased risk in breast cancer. There was a suggestion of an association for AURKA, when one study that caused significant study heterogeneity was excluded [ordinal OR 1.10 (95% CI 1.01-1.20) p = 0.027; dominant OR 1.12 (95% CI 1.01-1.24) p = 0.03]. The other 5 SNPs in BRCA2, CDKN2A, SRD5A2, CASP8 and TGFB1 showed no association with ovarian cancer risk; given the large sample size, these results can also be considered to be informative. These null results for SNPs identified from relatively large initial studies shows the importance of replicating associations by a consortium approach.

TGF-beta signalling-related markers in cancer patients with bone metastasis

We measured transforming growth factor (TGF)-beta-dependent biomarkers in plasma and in peripheral blood mononuclear cells (PBMCs) to identify suitable pharmacodynamic markers for future clinical trials with TGF-beta inhibitors. Forty-nine patients with bone metastasis were enrolled in the study, including patients with breast (n=23) and prostate cancer (n=15). Plasma TGF-beta1 levels were elevated in more than half of the cancer patients (geometric mean 2.63 ng ml(-1)) and positively correlated with increased platelet factor 4 (PF4) levels, parathyroid-related protein (PTHrP), von Willebrand Factor (vWF) and interleukin (IL)-10. PBMC were stimulated ex vivo to determine the individual biological variability of an ex vivo assay measuring pSMAD expression. This assay performed sufficiently well to allow its future use in a clinical trial of a TGF-beta inhibitor.

Transforming growth factor-beta and the immune response to malignant disease

Transforming growth factor-beta (TGF-beta) is a key player in malignant disease through its actions on host tissues and cells. Malignant cells often secrete large amounts of TGF-beta that act on nontransformed cells present in the tumor mass as well as distal cells in the host to suppress antitumor immune responses creating an environment of immune tolerance, augmenting angiogenesis, invasion and metastasis, and increasing tumor extracellular matrix deposition. Cells of the innate immune system contribute to the high concentrations of TGF-beta found in tumor masses. In addition, dendritic cell subpopulations secreting TGF-beta contribute to the generation of regulatory T cells that actively inhibit the activity of other T cells. Elevated levels of plasma TGF-beta are associated with advanced stage disease and may separate patients into prognostically high-risk populations. Anti-TGF-beta therapy could reverse the immunosuppressive effects of this cytokine on the host as well as decrease extracellular matrix formation, decrease angiogenesis, decrease osteolytic activity, and increase the sensitivity of the malignant cells to cytotoxic therapies and immunotherapies. Phase I clinical trials of an inhibitor of TGF-beta receptor type I kinase activity and a TGF-beta neutralizing antibody are under way.

Antisense therapeutics for tumor treatment: the TGF-beta2 inhibitor AP 12009 in clinical development against malignant tumors

Overexpression of the cytokine transforming growth factor-beta 2 (TGF-beta2) is a hallmark of various malignant tumors including pancreatic carcinoma, malignant glioma, metastasizing melanoma, and metastatic colorectal carcinoma. This is due to the pivotal role of TGF-beta2 as it regulates key mechanisms of tumor development, namely immunosuppression, metastasis, angiogenesis, and proliferation. The antisense technology is an innovative technique offering a targeted approach for the treatment of different highly aggressive tumors and other diseases. Antisense oligonucleotides are being developed to inhibit the production of disease-causing proteins at the molecular level. The immunotherapeutic approach with the phosphorothioate oligodeoxynucleotide AP 12009 for the treatment of malignant tumors is based on the specific inhibition of TGF-beta2. After providing preclinical proof of concept, the safety and efficacy of AP 12009 were assessed in clinical phase I/II open-label dose-escalation studies in recurrent or refractory high-grade glioma patients. Median survival time after recurrence exceeded the current literature data for chemotherapy. Currently, phase I/II study in advanced pancreatic carcinoma, metastatic melanoma, and metastatic colorectal carcinoma and a phase IIb study in recurrent or refractory high-grade glioma are ongoing. The preclinical as well as the clinical results implicate targeted TGF-beta2 suppression as a promising therapeutic approach for malignant tumor therapy.

Cancer associated fibroblasts stimulated by transforming growth factor beta1 (TGF-beta 1) increase invasion rate of tumor cells: a population study

Cancer associated fibroblasts (CAFs) are believed to promote tumor growth and progression. Our objective was to measure the effect of TGF-beta1 on fibroblasts isolated from invasive breast cancer patients. Fibroblasts were isolated from tissue obtained at surgery from patients with invasive breast cancer (CAF; n = 28) or normal reduction mammoplasty patients (normal; n = 10). Myofibroblast activation was measured by counting cells immunostained for smooth muscle alpha actin (ACTA2) in cultures +/- TGF-beta 1. Conditioned media (CM) was collected for invasion assays and RNA was isolated from cultures incubated in media +/- TGF-beta1 for 24 h. Q-PCR was used to measure expression of cyclin D1, fibronectin, laminin, collagen I, urokinase, stromelysin-1, and ACTA2 genes. Invasion rate was measured in chambers plated with MDA-MB-231 cells and exposed to CM in the bottom chamber; the number of cells that invaded into the bottom chamber was counted. Wilcox Rank Sum tests were used to evaluate differences in CAFs and normal fibroblasts and the effect of TGF-beta 1. There was no difference in percent myofibroblasts or invasion rate between normal and CAF cultures. However, TGF-beta1 significantly increased the percent of myofibroblasts (P < 0.01) and invasion rate (P = 0.02) in CAF cultures. Stromelysin-1 expression was significantly higher in normal versus CAF cultures (P < 0.01). TGF-beta 1 significantly increased ACTA2 expression in both normal and CAF cultures (P < 0.01). Expression of fibronectin and laminin was significantly increased by TGF-beta in CAF cultures (P < 0.01). CAFs were measurably different from normal fibroblasts in response to TGF-beta 1, suggesting that TGF-beta stimulates changes in CAFs that foster tumor invasion.

Src phosphorylates Tyr284 in TGF-beta type II receptor and regulates TGF-beta stimulation of p38 MAPK during breast cancer cell proliferation and invasion

Genetic and epigenetic events often negate the cytostatic function of transforming growth factor-beta (TGF-beta) in mammary epithelial cells (MEC), which ultimately enables malignant MECs to proliferate, invade, and metastasize when stimulated by TGF-beta. The molecular mechanisms underlying this phenotypic conversion of TGF-beta function during mammary tumorigenesis remain poorly defined. We previously established alpha(v)beta(3) integrin and Src as essential mediators of mitogen-activated protein kinase (MAPK) activation, invasion, and epithelial-to-mesenchymal transition stimulated by TGF-beta in normal and malignant MECs. Mechanistically, beta(3) integrin interacted physically with the TGF-beta type II receptor (TbetaR-II), leading to its tyrosine phosphorylation by Src and the initiation of oncogenic signaling by TGF-beta. We now show herein that Src phosphorylated TbetaR-II on Y284 both in vitro and in vivo. Interestingly, although the expression of Y284F-TbetaR-II mutants in breast cancer cells had no effect on TGF-beta stimulation of Smad2/3, this TbetaR-II mutant completely abrogated p38 MAPK activation by TGF-beta. Accordingly, Src-mediated phosphorylation of Y284 coordinated the docking of the SH2 domains of growth factor receptor binding protein 2 (Grb2) and Src homology domain 2 containing (Shc) TbetaR-II, thereby associating these adapter proteins to MAPK activation by TGF-beta. Importantly, Y284F-TbetaR-II mutants also abrogated breast cancer cell invasion induced by alpha(v)beta(3) integrin and TGF-beta as well as partially restored their cytostatic response to TGF-beta. Our findings have identified a novel alpha(v)beta(3) integrin/Src/Y284/TbetaR-II signaling axis that promotes oncogenic signaling by TGF-beta in malignant MECs and suggest that antagonizing this signaling axis may one day prove beneficial in treating patients with metastatic breast cancers.

Microenvironment of the involuting mammary gland mediates mammary cancer progression

Breast cancer diagnosed after a completed pregnancy has higher metastatic potential and therefore a much poorer prognosis. We hypothesize that following pregnancy the process of mammary gland involution, which returns the gland to its pre-pregnant state, co-opts some of the programs of wound healing. The pro-inflammatory milieu that results, while physiologically normal, promotes tumor progression. In this review, the similarities between mammary gland involution after cessation of milk-production and pathological tissue remodeling are discussed in light of emerging data demonstrating a role for pathological tissue remodeling in cancer.

Transforming growth factor-[beta]1 -509T reduces risk of colorectal cancer, but not adenoma in Koreans

The proliferation of colorectal epithelial cells is regulated by various stimuli including cytokines and growth factors, thus the variants of those genes can modify the colorectal cancer risk. TGF-[beta]1 can act as both a tumor suppressor and a stimulator of tumor progression. TGF-[beta]1 C-509T polymorphism in the promoter sequence has been associated with increased levels of plasma TGF-[beta]1 in individuals with T allele. To evaluate the potential influences of this polymorphism on colorectal adenoma and cancer risk, a case-control study was conducted in Korea. A total of 646 subjects were prospectively enrolled in Seoul National University Hospital. Risk of colorectal neoplasms was evaluated separately for 244 patients with colorectal adenoma, 152 patients with colorectal cancer relative to 250 healthy controls. Genotypes were determined by the PCR-RFLP method. ORs and 95% CIs were calculated by a multivariate logistic regression analysis. The TGF-[beta]1 -509T allele containing genotypes posed a reduced risk of colorectal cancer (adjusted OR = 0.59, 95% CI = 0.28-0.92). But there was no association between this polymorphism and colorectal adenoma. Our results suggest that the TGF-[beta]1 -509T allele may have a protective role in the development of colorectal cancer, possibly consistent with its role as an inhibitor of epithelial malignant transformation.

Associations of breast cancer development in patients with systemic sclerosis: an exploratory study

The goal of this study was to describe the clinical characteristics of patients with a diagnosis of systemic sclerosis who develop breast cancer and to identify associations for this relationship. From 769 patients followed at the scleroderma center of our institution over the past 16 years, 24 patients developed a diagnosis of breast cancer. The demographics and clinical characteristics of these patients will be compared to those of a randomly selected group of scleroderma patients without a diagnosis of cancer. A further analysis will compare the patients who developed their breast cancer before the diagnosis of systemic sclerosis to those diagnosed after. Twenty-four patients developed 25 breast cancers with 13 patients diagnosed before the diagnosis of systemic sclerosis and 11 after. Compared to 48 randomly selected systemic sclerosis patients without a diagnosis of cancer, the patients with breast cancer were diagnosed with systemic sclerosis at an older age (53.5 +/- 15.2) as compared to those without (42.4 +/- 12.5) (p = 0.002). A relatively equal amount of patients had the diffuse and limited form of systemic sclerosis, while pulmonary fibrosis (p = 0.015) and the lack of antinuclear antibody (ANA) positivity (p = 0.02) were more commonly seen in patients with breast cancer. Patients who developed breast cancer before the diagnosis of systemic sclerosis were older at systemic sclerosis diagnosis (61.6 +/- 11.3) compared to those after (43.9 +/- 13.5) (p = 0.03). An older age at diagnosis of systemic sclerosis, a lack of ANA positivity, and the presence of pulmonary fibrosis were more commonly seen in patients with systemic sclerosis who have a diagnosis of breast cancer.

Effect of the different phosphorylated Smad2 protein localizations on the invasive breast carcinoma phenotype

Smad2 participates in the TGF-beta signaling pathway, where it cooperates with transcription factors to regulate expression of defined genes. The purpose of this study was to investigate the expression pattern of phosphorylated Smad2 (pSmad2) in association with clinicopathological parameters and biological markers of proliferation and invasion. Immunohistochemistry was applied on paraffin-embedded sections from 164 patients with invasive breast carcinomas to detect the expression of the proteins pSmad2, ER, PR, Ki67, topoisomerase IIa, ERK2, catenin-p120, MMP-14 and TIMP-2. pSmad2 protein was detected in the nuclei of the malignant cells (68.1%) and in the tumor fibroblasts (55.2%). Nuclear pSmad2 was inversely correlated with histological grade and LN (p=0.047 and p=0.05) as well as with Ki67 and topoIIa (p=0.003 and p=0.021, respectively). There was also an inverse relation between nuclear pSmad2 and normal immunoexpression of the adhesion molecule catenin-p120 (p=0.028). Both nuclear and stromal pSmad2 were positively correlated with ERK2 of tumor fibroblasts (p=0.008 and p=0.0001, respectively), while stromal pSmad2 was furthermore related to stromal MMP-14 and tumor TIMP-2 (p=0.006 and p=0.022, respectively). Patients with high expression of cancerous pSmad2 tended to have a better prognosis, although statistic significance was never reached. pSmad2 was found to play a dual role, according to its distribution. Nuclear localization was thus found to be related to a less aggressive tumor phenotype, whereas stromal location was associated with an invasive phenotype.

ALK5 promotes tumor angiogenesis by upregulating matrix metalloproteinase-9 in tumor cells

Transforming growth factor beta 1 (TGF-beta1) is a potent tumor suppressor but, paradoxically, TGF-beta1 enhances tumor growth and metastasis in the late stages of cancer progression. This study investigated the role of TGF-beta type I receptor, ALK5, and three mitogen-activated protein kinases (MAPKs) in metastasis by breast cancer cell line MDA-MB-231. We show that autocrine TGF-beta signaling in MDA-MB-231 cells is required for tumor cell invasion and tumor angiogenesis. Expression of kinase-inactive ALK5 reduces tumor invasion and formation of new blood vessels within the tumor orthotopic xenografts in severe combined immunodeficiency (SCID) mice. In contrast, constitutively active ALK5-T204D enhances tumor invasion and angiogenesis by stimulating expression of matrix metalloproteinase MMP-9/gelatinase-B. Ablation of MMP-9 in ALK5-T204D cells by RNA interference (RNAi) reduces tumor invasion and tumor growth. Importantly, RNAi-MMP-9 reduces tumor neovasculature and increases tumor cell death. Induction of MMP-9 by TGF-beta-ALK5 signaling requires MEK-ERK but not JNK, p38 MAPK or Smad4. Dominant-negative MEK blocks and constitutively active MEK1 enhances MMP-9 expression. However, all three MAPK cascades (ERK, JNK and p38 MAPK) are required for TGF-beta-mediated cell migration. Collectively, our results show that TGF-beta-ALK5-MAPK signaling in tumor cells promotes tumor angiogenesis and MMP-9 is an important component of this program.

A novel functional polymorphism in the transforming growth factor-beta2 gene promoter and tumor progression in breast cancer

Transforming growth factor-beta (TGF-beta), a multifunctional growth factor, plays an important role in breast cancer. There is increasing evidence that enhanced expression of TGF-beta promotes breast cancer progression contributing to metastasis and invasiveness of the tumor. We identified a functional polymorphism in the TGFB2 promoter, a 4-bp insertion at position -246 relative to the transcriptional start site (-246ins). Transient transfection experiments showed that the -246ins polymorphism significantly increased TGFB2 promoter activity in breast cancer cells. Electrophoretic mobility shift assays revealed binding of the transcription factor Sp1 to the -246ins allele. Overexpression of Sp1 enhanced promoter activity of the -246ins allele, demonstrating that Sp1 mediates transcriptional activation. Furthermore, the -246ins allele was associated with enhanced TGF-beta(2) expression in breast cancer tissue (P = 0.0005). To evaluate the role of the polymorphism in breast cancer, frequency of the -246ins allele was determined in breast cancer patients (n = 78) and healthy female controls (n = 143). No significant differences were found. However, the presence of the -246ins allele was associated with lymph node metastasis (P = 0.003). The -246ins allele was a significant predictor for lymph node metastasis independent of estrogen and progesterone receptor status in a multivariate logistic regression analysis (P = 0.0118, odds ratio, 5.18; 95% confidence interval, 1.44-18.62). We provide evidence that the TGFB2 -246ins polymorphism leads to enhanced TGF-beta(2) expression levels in vivo and might thereby contribute to tumor progression and development of metastases.

Autocrine PDGFR signaling promotes mammary cancer metastasis

Metastasis is the major cause of cancer morbidity, but strategies for direct interference with invasion processes are lacking. Dedifferentiated, late-stage tumor cells secrete multiple factors that represent attractive targets for therapeutic intervention. Here we show that metastatic potential of oncogenic mammary epithelial cells requires an autocrine PDGF/PDGFR loop, which is established as a consequence of TGF-beta-induced epithelial-mesenchymal transition (EMT), a faithful in vitro correlate of metastasis. The cooperation of autocrine PDGFR signaling with oncogenic Ras hyperactivates PI3K and is required for survival during EMT. Autocrine PDGFR signaling also contributes to maintenance of EMT, possibly through activation of STAT1 and other distinct pathways. Inhibition of PDGFR signaling interfered with EMT and caused apoptosis in murine and human mammary carcinoma cell lines. Consequently, overexpression of a dominant-negative PDGFR or application of the established cancer drug STI571 interfered with experimental metastasis in mice. Similarly, in mouse mammary tumor virus-Neu (MMTV-Neu) transgenic mice, TGF-beta enhanced metastasis of mammary tumors, induced EMT, and elevated PDGFR signaling. Finally, expression of PDGFRalpha and -beta correlated with invasive behavior in human mammary carcinomas. Thus, autocrine PDGFR signaling plays an essential role during cancer progression, suggesting a novel application of STI571 to therapeutically interfere with metastasis.

Post-transcriptional Control of Cited2 by Transforming Growth Factor β

Cited2 is a transcription factor without typical DNA binding domains. Cited2 interacts with cAMP-responsive element-binding protein-binding protein (CBP)/p300, TFAP2, Lhx2, and nuclear receptors, such as peroxisome proliferator-activated receptor and estrogen receptor to function as a transcriptional modulator. Overexpression of Cited2 in Rat1 cells leads to tumor formation in nude mice, suggesting that Cited2 is a transforming gene. Through microarray analysis, Cited2 was found to be down-regulated by transforming growth factor beta1 (TGF-beta) in various cell lines. In this study, we confirmed that both mRNA and protein levels of Cited2 are down-regulated in MDA-MB-231 breast cancer cells. Overexpression of Smad7 or knockdown of Smad4 in MDA-MB-231 cells showed that the Smad pathway is involved in the down-regulation of Cited2. Based on nuclear run-on analysis and Cited2 promoter/reporter assay, Cited2 transcription was not affected by TGF-beta, supporting that down-regulation of Cited2 by TGF-beta is most likely through post-transcriptional regulation. By using transcriptional inhibitors, we demonstrated that the turnover of Cited2 transcripts appears to be accelerated during TGF-beta stimulation. Pharmacologic inhibition of translation with cycloheximide attenuated Cited2 down-regulation by TGF-beta. We examined the expression of recombinant Cited2 gene introduced into MDA-MB-231 cells by stable transfection, and we found that mRNA containing the Cited2 protein-coding region controlled by a heterologous promoter indeed responds to TGF-beta-mediated down-regulation. Study from Cited2 deletion mutants showed that the C-terminal conserved region of Cited2 coding sequence is essential for the down-regulation. This is the first demonstration that TGF-beta-mediated down-regulation of Cited2 is post-transcriptional, through the Smad pathway, and requires the presence of its coding sequence.

A crucial function of PDGF in TGF-beta-mediated cancer progression of hepatocytes

Polarized hepatocytes expressing hyperactive Ha-Ras adopt an invasive and metastatic phenotype in cooperation with transforming growth factor (TGF)-beta. This dramatic increase in malignancy is displayed by an epithelial to mesenchymal transition (EMT), which mimics the TGF-beta-mediated progression of human hepatocellular carcinomas. In culture, hepatocellular EMT occurs highly synchronously, facilitating the analysis of molecular events underlying the various stages of this process. Here, we show that in response to TGF-beta, phosphorylated Smads rapidly translocated into the nucleus and activated transcription of target genes such as E-cadherin repressors of the Snail superfamily, causing loss of cell adhesion. Within the TGF-beta superfamily of cytokines, TGF-beta1, -beta2 and -beta3 were specific for the induction of hepatocellular EMT. Expression profiling of EMT kinetics revealed 78 up- and 235 downregulated genes, which preferentially modulate metabolic activities, extracellular matrix composition, transcriptional activities and cell survival. Independent of the genetic background, platelet-derived growth factor (PDGF)-A ligand and both PDGF receptor subunits were highly elevated, together with autocrine secretion of bioactive PDGF. Interference with PDGF signalling by employing hepatocytes expressing the dominant-negative PDGF-alpha receptor revealed decreased TGF-beta-induced migration in vitro and efficient suppression of tumour growth in vivo. In conclusion, these results provide evidence for a crucial role of PDGF in TGF-beta-mediated tumour progression of hepatocytes and suggest PDGF as a target for therapeutic intervention in liver cancer.

Serum levels of transforming growth factor beta1 are significantly correlated with venous invasion in patients with gastric cancer

BACKGROUND AND AIM

The significance of serum levels of transforming growth factor (TGF)-beta1 in the development of gastric cancer is unclear. The purpose of this study is to determine whether serum TGF-beta1 correlated with the clinicopathological findings of patients with gastric cancer.

METHODS

Transforming growth factor-beta1 levels in the serum of 275 gastric cancer patients and 275 gender- and age-matched healthy controls were measured with enzyme-linked immunosorbent assay (ELISA) using a commercially available kit.

RESULTS

The mean level of serum TGF-beta1 of gastric cancer patients (15.9 +/- 5.9 ng/mL) was significantly higher than that (13.9 +/- 7.4 ng/mL) of healthy controls (P < 0.01). The odds ratio for the subjects in the highest quartile (16.7 ng/mL or more) was 4.03 (95% confidence interval, 2.14-7.58), as compared with that for the subjects in the lowest quartile (0-9.5 ng/mL). Patients with venous invasion compared to those without venous invasion had significantly elevated serum TGF-beta1 (17.3 +/- 7.2 vs 15.0 +/- 5.1 ng/mL; P = 0.04). There were no statistically significant differences between the two groups categorized by histological type, lymph node metastasis and distant metastasis. Logistical regression analysis showed that venous invasion was significantly correlated with elevated serum TGF-beta1 levels (P = 0.02).

CONCLUSIONS

The present study showed that an elevated serum TGF-beta1 level may be significantly correlated with venous invasion in gastric cancer patients.

A New IκB Kinase β Inhibitor Prevents Human Breast Cancer Progression through Negative Regulation of Cell Cycle Transition

Constitutive nuclear factor-kappaB (NF-kappaB) activity plays a crucial role in the development and progression of lymphoma, leukemia, and some epithelial cancers. Given the contribution of NF-kappaB in carcinogenesis, a novel approach that interferes with its activity might have therapeutic potential against cancers that respond poorly to conventional treatments. Here, we have shown that a new IkappaB kinase beta inhibitor, IMD-0354, suppressed the growth of human breast cancer cells, MDA-MB-231, HMC1-8, and MCF-7, by arresting cell cycle and inducing apoptosis. In an electrophoretic mobility shift assay and a reporter assay, IMD-0354 abolished the NF-kappaB activity in MDA-MB-231 cells in a dose-dependent manner. In the cells incubated with IMD-0354, cell cycle arrested at the G0-G1 phase and apoptotic cells were increased. The expression of some cell cycle regulatory molecules and antiapoptotic molecules was suppressed in cells treated with IMD-0354. On the other hand, cyclin-dependent kinase suppressor p27Kip1 was up-regulated by the addition of IMD-0354. Daily administration of IMD-0354 inhibited tumor expansion in immunodeficient mice into which MDA-MB-231 cells were transplanted. These results indicate that NF-kappaB may contribute to cell proliferation through up-regulation of cell cycle progression; accordingly, inhibition of NF-kappaB activity might have a therapeutic ability in the treatment of human breast cancers.

TGF-beta 1 could be a missing link in the interplay between ER and HER-2 in breast cancer

Breast cancer is a very heterogeneous disease considering a number of biomarkers which are under investigation. However, most important biomarkers in a clinical setting are ER (estrogen receptors) and HER-2 (human epidermal growth factor receptor 2), but still only as predictive markers for tamoxifen and trastuzumab therapy. Their prognostic role is still subject of investigation. On the other hand, although, TGF-beta1 is known as marker of invasiveness and metastatic capacity of breast cancer cells, this marker has never been considered to be introduced in routine clinical setting. TGF-beta1 is ER regulated biomarker which act synergistically with HER-2. Aim of this study is to show that clinical significance of determination ER and HER-2 status could be improved, when they are related with TGF-beta1 as additional biomarker. It seems that TGF-beta1 could make a difference regarding prognosis and prediction in breast cancer patients. This hypothesis could be easily verified in corresponding clinical research.

RNF11 is a multifunctional modulator of growth factor receptor signalling and transcriptional regulation

Our laboratory has found that the 154aa RING finger protein 11 (RNF11), has modular domains and motifs including a RING-H2 finger domain, a PY motif, an ubiquitin interacting motif (UIM), a 14-3-3 binding sequence and an AKT phosphorylation site. RNF11 represents a unique protein with no other known immediate family members yet described. Comparative genetic analysis has shown that RNF11 is highly conserved throughout evolution. This may indicate a conserved and non-redundant role for the RNF11 protein. Molecular binding assays using RNF11 have shown that RNF11 has important roles in growth factor signalling, ubiquitination and transcriptional regulation. RNF11 has been shown to interact with HECT-type E3 ubiquitin ligases Nedd4, AIP4, Smurf1 and Smurf2, as well as with Cullin1, the core protein in the multi-subunit SCF E3 ubiquitin ligase complex. Work done in our laboratory has shown that RNF11 is capable of antagonizing Smurf2-mediated inhibition of TGFbeta signalling. Furthermore, RNF11 is capable of degrading AMSH, a positive regulator of both TGFbeta and EGFR signalling pathways. Recently, we have found that RNF11 can directly enhance TGFbeta signalling through a direct association with Smad4, the common signal transducer and transcription factor in the TGFbeta, BMP, and Activin pathways. Through its association with Smad4 and other transcription factors, RNF11 may have a role in direct transcriptional regulation. Our laboratory and others have found nearly 80 protein interactions for RNF11, placing RNF11 at the cross-roads of cell signalling and transcriptional regulation. RNF11 is highly expressed in breast tumours. Deregulation of RNF11 function may prove to be harmful to patient therapeutic outcomes. RNF11 may therefore provide a novel target for cancer therapeutics. The purpose of this review is to discuss the role of RNF11 in cell signalling and transcription factor modulation with special attention given to the ubiquitin-proteasomal pathway, TGFbeta pathway and EGFR pathway.

Tumor-stroma interactions

The importance of stromal cells and the factors that they express during cancer initiation and progression has been highlighted by recent literature. The cellular components of the stroma of epithelial tissues are well-recognized as having a supportive role in carcinogenesis, where the initiating mutations of a tumor originate in the epithelial cells. The use of mouse models and xenografts suggests that mutations in the stromal fibroblasts can also initiate epithelial tumors. Many of these tumors result from the alteration of paracrine growth factor pathways that act on the epithelia. However, the tissue specificity of the responses to the growth factors is a mystery not yet solved.

Effect of conditional knockout of the type II TGF-beta receptor gene in mammary epithelia on mammary gland development and polyomavirus middle T antigen induced tumor formation and metastasis

Transforming growth factor-beta (TGF-beta) isoforms are growth factors that function physiologically to regulate development, cellular proliferation, and immune responses. The role of TGF-beta signaling in mammary tumorigenesis is complex, as TGF-beta has been reported to function as both a tumor suppressor and tumor promoter. To elucidate the role of TGF-beta signaling in mammary gland development, tumorigenesis, and metastasis, the gene encoding type II TGF-beta receptor, Tgfbr2, was conditionally deleted in the mammary epithelium (Tgfbr2MGKO). Loss of Tgfbr2 in the mammary epithelium results in lobular-alveolar hyperplasia in the developing mammary gland and increased apoptosis. Tgfbr2MGKO mice were mated to the mouse mammary tumor virus-polyomavirus middle T antigen (PyVmT) transgenic mouse model of metastatic breast cancer. Loss of Tgfbr2 in the context of PyVmT expression results in a shortened median tumor latency and an increased formation of pulmonary metastases. Thus, our studies support a tumor-suppressive role for epithelial TGF-beta signaling in mammary gland tumorigenesis and show that pulmonary metastases can occur and are even enhanced in the absence of TGF-beta signaling in the carcinoma cells.

Cancer progression: is inhibin alpha from Venus or Mars?

The inhibin field has been perplexed by the information that inhibin alpha is a tumour suppressor in mice yet is elevated in women with ovarian cancer. Furthermore, we have consistently observed a down-regulation or loss of inhibin alpha in prostate cancer patient samples and cell lines. However, our latest data have prompted us to re-evaluate the role of inhibin alpha in prostate and other cancers. Using the analogy of TGF-beta as a springboard for our hypothesis, we offer a unifying model whereby the previously conflicting observations in mice, men and women can be explained. We propose that initially inhibin alpha is tumour-suppressive and is expressed in benign and early-stage primary cancers. Tumour-suppressive inhibin alpha is then silenced as the tumour progresses but is reactivated as a pro-metastatic factor in advanced, aggressive cancers.

Conditional overexpression of active transforming growth factor beta1 in vivo accelerates metastases of transgenic mammary tumors

To address the role of transforming growth factor (TGF) beta in the progression of established tumors while avoiding the confounding inhibitory effects of TGF-beta on early transformation, we generated doxycycline (DOX)-inducible triple transgenic mice in which active TGF-beta1 expression could be conditionally regulated in mouse mammary tumor cells transformed by the polyomavirus middle T antigen. DOX-mediated induction of TGF-beta1 for as little as 2 weeks increased lung metastases >10-fold without a detectable effect on primary tumor cell proliferation or tumor size. DOX-induced active TGF-beta1 protein and nuclear Smad2 were restricted to cancer cells, suggesting a causal association between autocrine TGF-beta and increased metastases. Antisense-mediated inhibition of TGF-beta1 in polyomavirus middle T antigen-expressing tumor cells also reduced basal cell motility, survival, anchorage-independent growth, tumorigenicity, and metastases. Therefore, induction and/or activation of TGF-beta in hosts with established TGF-beta-responsive cancers can rapidly accelerate metastatic progression.

Dual Role of Transforming Growth Factor β in Mammary Tumorigenesis and Metastatic Progression

It is generally accepted that transforming growth factor β (TGFβ) is both a tumor suppressor and tumor promoter. Whereas loss or attenuation of TGFβ signal transduction is permissive for transformation, introduction of dominant-negative TGFβ receptors into metastatic breast cancer cells has been shown to inhibit epithelial-to-mesenchymal transition, motility, invasiveness, survival, and metastases. In addition, there is evidence that excess production and/or activation of TGFβ by cancer cells can contribute to tumor progression by paracrine mechanisms involving neoangiogenesis, production of stroma and proteases, and subversion of immune surveillance mechanisms in tumor hosts. These data provide a rationale in favor of blockade of autocrine/paracrine TGFβ signaling in human mammary tumors with therapeutic intent. Several treatment approaches are currently in early clinical development and have been the focus of our laboratory. These include (1) ligand antibodies or receptor-containing fusion proteins aimed at blocking ligand binding to cognate receptors and (2) small-molecule inhibitors of the type I TGFβ receptor serine/threonine kinase. Many questions remain about the viability of anti-TGFβ treatment strategies, the best molecular approach (or combinations) for inhibition of TGFβ function in vivo, the biochemical surrogate markers of tumor response, the molecular profiles in tumors for selection into clinical trials, and potential toxicities, among others.

Tumour-Stromal Interactions in Breast Cancer: The Role of Stroma in Tumourigenesis

Mammary stromal tissue has a major role in the control and regulation of physiological processes in the breast. Recently, the function of stroma in supporting the tumourigenic process as well as responding to the oncogenic lesion has become clearer. This review differs from the conventional view in that it focuses on and discusses the newly available evidence that points to the fact that mammary stroma has a significant contribution in actively generating transformed lesions and tumours. As such, the oncogenic signals can be dependent or independent of genetic mutations in mammary stromal cells. As a supportive and responsive agent in tumourigenesis, the stroma is induced by tumour cells to express critical signals that drive proliferation, angiogenesis, and motility while suppressing cell death. As an oncogenic agent in tumourigenesis, the stroma can provoke tumourigenicity in adjacent cells in the absence of pre-existing tumour cells leading to the acquisition of genomic changes. Investigating the mechanism by which the tumourigenic cues of the stroma facilitate the generation of malignant epithelial cells will provide invaluable insights into the oncogenic process.

Tumour-stroma interaction: cancer-associated fibroblasts as novel targets in anti-cancer therapy?

Stroma cells, together with extracellular matrix components, provide the microenvironment that is pivotal for cancer cell growth, invasion and metastatic progression. Characteristic stroma alterations accompany or even precede the malignant conversion of epithelial cells. Crucial in this process are fibroblasts, also termed myofibroblasts or cancer-associated fibroblasts (CAFs) that are located in the vicinity of the neoplastic epithelial cells. They are able to modify the phenotype of the epithelial cells by direct cell-to-cell contacts, through soluble factors or by modification of extracellular matrix components. Seminal functional studies in various cancer types, including breast, colon, prostate and lung cancer, have confirmed the concept that fibroblasts can determine the fate of the epithelial cell, since they are able to promote malignant conversion as well as to revert tumour cells to a normal phenotype. This review focuses on characteristic changes of fibroblasts in cancer and provides the experimental background elucidating functional properties of CAFs in the carcinogenic process. A possible implication in lung carcinogenesis is emphasised. Finally, a laser-capture- and microarray-based approach is presented, which comprehensively characterises carcinoma-associated fibroblasts in their in vivo environment for the identification of potential targets for anti-cancer therapy.

Disruption of LTBP-4 function reduces TGF-beta activation and enhances BMP-4 signaling in the lung

Disruption of latent TGF-β binding protein (LTBP)–4 expression in the mouse leads to abnormal lung development and colorectal cancer. Lung fibroblasts from these mice produced decreased amounts of active TGF-β, whereas secretion of latent TGF-β was significantly increased. Expression and secretion of TGF-β2 and -β3 increased considerably. These results suggested that TGF-β activation but not secretion would be severely impaired in LTBP-4 −/− fibroblasts. Microarrays revealed increased expression of bone morphogenic protein (BMP)–4 and decreased expression of its inhibitor gremlin. This finding was accompanied by enhanced expression of BMP-4 target genes, inhibitors of differentiation 1 and 2, and increased deposition of fibronectin-rich extracellular matrix. Accordingly, increased expression of BMP-4 and decreased expression of gremlin were observed in mouse lung. Transfection of LTBP-4 rescued the −/− fibroblast phenotype, while LTBP-1 was inefficient. Treatment with active TGF-β1 rescued BMP-4 and gremlin expression to wild-type levels. Our results indicate that the lack of LTBP-4–mediated targeting and activation of TGF-β1 leads to enhanced BMP-4 signaling in mouse lung.

α2HS-glycoprotein, an Antagonist of Transforming Growth Factor β In vivo, Inhibits Intestinal Tumor Progression

Transforming growth factor (TGF)-beta1 is associated with tumor progression and resistance to chemotherapy in established cancers, as well as host immune suppression. Here, we show that the serum glycoprotein alpha2-HS-glycoprotein (AHSG) blocks TGF-beta1 binding to cell surface receptors, suppresses TGF-beta signal transduction, and inhibits TGF-beta-induced epithelial-mesenchymal transition, suggesting that AHSG may play a role in tumor progression. In 66 consecutive sporadic human colorectal cancer specimens, we observed a 3-fold depletion of ASHG in tumor compared with normal tissue, whereas levels of other abundant plasma proteins, albumin and transferrin, were equivalent. Using the Multiple intestinal neoplasia/+ (Min/+) mouse model of intestinal tumorigenesis, we found twice as many intestinal polyps overall, twice as many large polyps (>3 mm diameter), and more progression to invasive adenocarcinoma in Min/+ Ahsg-/- mice than in littermates expressing Ahsg. Phosphorylated Smad2 was more abundant in the intestinal mucosa and tumors of Min/+ mice lacking Ahsg, demonstrating increased TGF-beta signaling in vivo. Furthermore, TGF-beta-mediated suppression of immune cell function was exaggerated in Ahsg-/- animals, as shown by inhibition of macrophage activation and reduction in 12-O-tetradecanoylphorbol 13-acetate-induced cutaneous inflammation. Reconstitution of Ahsg-/- mice with bovine Ahsg suppressed endogenous TGF-beta-dependent signaling to wild-type levels, suggesting that therapeutic enhancement of AHSG levels may benefit patients whose tumors are driven by TGF-beta.

Investigation of three new mouse mammary tumor cell lines as models for transforming growth factor (TGF)-beta and Neu pathway signaling studies: identification of a novel model for TGF-beta-induced epithelial-to-mesenchymal transition

Introduction

This report describes the isolation and characterization of three new murine mammary epithelial cell lines derived from mammary tumors from MMTV (mouse mammary tumor virus)/activated Neu + TβRII-AS (transforming growth factor [TGF]-β type II receptor antisense RNA) bigenic mice (BRI-JM01 and BRI-JM05 cell lines) and MMTV/activated Neu transgenic mice (BRI-JM04 cell line).

Methods

The BRI-JM01, BRI-JM04, and BRI-JM05 cell lines were analyzed for transgene expression, their general growth characteristics, and their sensitivities to several growth factors from the epidermal growth factor (EGF) and TGF-β families (recombinant human EGF, heregulin-β₁ and TGF-β₁). The BRI-JM01 cells were observed to undergo a striking morphologic change in response to TGF-β₁, and they were therefore further investigated for their ability to undergo a TGF-β-induced epithelial-to-mesenchymal transition (EMT) using motility assays and immunofluorescence microscopy.

Results

We found that two of the three cell lines (BRI-JM04 and BRI-JM05) express the Neu transgene, whereas, unexpectedly, both of the cell lines that were established from MMTV/activated Neu + TβRII-AS bigenic tumors (BRI-JM01 and BRI-JM05) do not express the TβRII-AS transgene. The cuboidal BRI-JM01 cells exhibit a short doubling time and are able to form confluent monolayers. The BRI-JM04 and BRI-JM05 cell lines are morphologically much less uniform, grow at a much slower rate, and do not form confluent monolayers. Only the BRI-JM05 cells can form colonies in soft agar. In contrast, all three cell lines form colonies in Matrigel, although the BRI-JM04 and BRI-JM05 cell lines do so more efficiently than the BRI-JM01 cell line. All three cell lines express the cell surface marker E-cadherin, confirming their epithelial character. Proliferation assays showed that the three cell lines respond differently to recombinant human EGF and heregulin-β₁, and that all are growth inhibited by TGF-β₁, but that only the BRI-JM01 cell line undergoes an EMT and exhibits increased motility upon TGF-β₁ treatment.

Conclusion

We suggest that the BRI-JM04 and BRI-JM05 cell lines can be used to investigate Neu oncogene driven mammary tumorigenesis, whereas the BRI-JM01 cell line will be useful for studying TGF-β₁-induced EMT.

Overexpression of HER2 (erbB2) in Human Breast Epithelial Cells Unmasks Transforming Growth Factor β-induced Cell Motility

We have examined overexpression of the human epidermal growth factor receptor 2 (HER2) to determine if it modifies the anti-proliferative effect of transforming growth factor (TGF)-beta against MCF-10A human mammary epithelial cells. Exogenous TGF-beta inhibited cell proliferation and induced Smad-dependent transcriptional reporter activity in both MCF-10A/HER2 and MCF-10A/vector control cells. Ligand-induced reporter activity was 7-fold higher in HER2-overexpressing cells. In wound closure and transwell assays, TGF-beta induced motility of HER2-transduced, but not control cells. The HER2-blocking antibody trastuzumab (Herceptin) prevented TGF-beta-induced cell motility. Expression of a constitutively active TGF-beta type I receptor (ALK5(T204D)) induced motility of MCF-10A/HER2 but not MCF-10A/vector cells. TGF-beta-induced motility was blocked by coincubation with either the phosphatidylinositol 3-kinase inhibitor LY294002, the mitogen-activated protein kinase (MAPK) inhibitor U0126, the p38 MAPK inhibitor SB202190, and an integrin beta(1) blocking antibody. Rac1 activity was higher in HER2-overexpressing cells, where both Rac1 and Pak1 proteins were constitutively associated with HER2. Both exogenous TGF-beta and transduction with constitutively active ALK5 enhanced this association. TGF-beta induced actin stress fibers as well as lamellipodia within the leading edge of wounds. Herceptin blocked basal and TGF-beta-stimulated Rac1 activity but did not repress TGF-beta-stimulated transcriptional reporter activity. These data suggest that 1) overexpression of HER2 in nontumorigenic mammary epithelial is permissive for the ability of TGF-beta to induce cell motility and Rac1 activity, and 2) HER2 and TGF-beta signaling cooperate in the induction of cellular events associated with tumor progression.

Enhanced tumor formation in cyclin D1 x transforming growth factor beta1 double transgenic mice with characterization by magnetic resonance imaging

Transgenic mice that overexpress cyclin D1 protein in the liver develop liver carcinomas with high penetrance. Transforming growth factor beta (TGF-beta) serves as either an epithelial cell growth inhibitor or a tumor promoter, depending on the cellular context. We interbred LFABP-cyclin D1 and Alb-TGF-beta1 transgenic mice to produce cyclin D1/TGF-beta1 double transgenic mice and followed the development of liver tumors over time, characterizing cellular and molecular changes, tumor incidence, tumor burden, and tumor physiology noninvasively by magnetic resonance imaging. Compared with age-matched LFABP-cyclin D1 single transgenic littermates, cyclin D1/TGF-beta1 mice exhibited a significant increase in tumor incidence. Tumor multiplicity, tumor burden, and tumor heterogeneity were higher in cyclin D1/TGF-beta1 mice compared with single transgenic littermates. Characteristics of cyclin D1/TGF-beta1 livers correlated with a marked induction of the peripheral periductal oval cell/stem cell compartment of the liver. A number of cancerous lesions from cyclin D1/TGF-beta1 mice exhibited unique features such as ductal plate malformations and hemorrhagic nodules. Some lesions were contiguous with the severely diseased background liver and, in some cases, replaced the normal architecture of the entire organ. Cyclin D1/TGF-beta1 lesions, in particular, were associated with malignant features such as areas of vascular invasion by hepatocytes and heterogeneous hyperintensity of signal on T2-weighted magnetic resonance imaging. These findings demonstrate that TGF-beta1 promotes stem cell activation and tumor progression in the context of cyclin D1 overexpression in the liver.

Role of transforming growth factor β in breast carcinogenesis

Transforming growth factor (TGF) beta is a pre-eminent negative growth regulator that has antiproliferative effects on a range of epithelial cells. This ability has evoked interest in this growth factor as a tumour suppressor with potential clinical significance. In the early stages of breast carcinogenesis, a growth-inhibitory response to TGFbeta is maintained, which depends on an intact TGFbeta signalling pathway. Tumour development and progression of cells along a neoplastic continuum is accompanied by loss of this growth-inhibitory response to TGFbeta, which might instead promote tumour growth indirectly through a combination of permissive effects on stromal tissue, angiogenesis, and the immune system. This review discusses the complexity of functional pleiotropy and the continually changing roles of TGFbeta as a tumour evolves, along with competing therapeutic strategies. The boosting of local endogenous amounts of TGFbeta in conjunction with enhancement of cellular responsiveness might be appropriate in early malignant disease, and anti-TGFbeta approaches could yield a therapeutic gain in metastatic states.

T29C Polymorphism in the Transforming Growth Factor β1 Gene and Postmenopausal Breast Cancer Risk: The Multiethnic Cohort Study

Laboratory studies suggest a dual role for the transforming growth factor-β (TGF-β) signaling pathway in breast cancer. The normal antiproliferative activity of TGF-β in early breast tumor development is replaced by a promoting effect in later stages. A T29C transition polymorphism in the TGFB1 gene has been associated with higher circulating TGF-β1 levels, and inconsistently with breast cancer risk in three recent studies. We tested the association of this variant with invasive breast cancer in a case-control study of 1123 cases and 2314 controls nested in the Multiethnic Cohort (MEC) Study. This study is a large prospective study being conducted in Hawaii and Los Angeles that includes Japanese, white, African American, Latino, and Native Hawaiian women who were predominantly postmenopausal at baseline. After adjustment for breast cancer risk factors, the odds ratio (OR) and 95% confidence interval (95% CI) for the TGFB1 29 CC genotype was 0.95 (95% confidence interval: 0.76–1.18), compared to the TT genotype. Analyses stratified by race/ethnicity, stage, or age category did not reveal any association of this variant with breast cancer. Given the strong biological rationale and the scarce and divergent epidemiologic data to date, additional investigations of the relationship between breast cancer and genetic variants in the TGF-β signaling pathway appear warranted.

Breast cancer biomarkers and molecular medicine

The first part of this two-part review of established and emerging breast cancer biomarkers and molecular diagnostics considers breast cancer predisposition, screening tests for diagnosis, diagnosis using small specimens and metastatic lesions, micrometastatic disease and breast cancer prognosis assessment. Prognostic factors covered in this review include: cytogenetic markers, DNA ploidy and S phase determination, cell proliferation markers, cell cycle regulators and growth factor measurements including epithelial growth factor receptor, HER-2/neu and a variety of other relevant molecules controlling proliferation, differentiation and angiogenesis. The first section of part two will continue the consideration of breast cancer prognostic factors including oncogenes, tumor suppressor genes, cell adhesion molecules, invasion-associated proteins and proteases, hormone receptor proteins, drug resistance proteins, apoptosis regulators, transcription factors, telomerase, DNA repair and methylation and transcriptional profiling using high-density genomic microarrays. The second section of part two will consider the prediction of therapy response using the techniques of pharmacogenetics and pharmacogenomics.

Genetic Polymorphisms in the TGF-β1 Gene and Breast Cancer Survival

The effect of genetic polymorphisms in the TGF-beta1 gene at codon 10 (T+29C), codon 25 (G+74C), and the promoter region [C --> T at -509 from the transcription site, (C-509T)] on breast cancer survival was evaluated among a cohort of 1111 patients. The median follow-up time for the cohort was 5.17 years after cancer diagnosis. No DNA sequence variation at codon 25 of the TGF-beta1 gene was found, whereas polymorphisms in C-509T and T+29C were in strong linkage disequilibrium. Patients who carried the C allele of T+29C polymorphism had a reduced 5-year disease-free survival rate (75.6% for T/C, and 78.2% for C/C) compared with the T/T genotype (85.1%; P, 0.04); the age-adjusted hazard ratio was 1.5 (95% confidence interval, 1.1-2.2). Adjustment for clinical prognostic factors slightly attenuated the association (hazard ratio, 1.4, 95% confidence interval, 1.0-1.9). Our study suggests that genetic polymorphisms in the TGF-beta1 gene may play a role in breast cancer progression.

Cooperation of the ErbB2 receptor and transforming growth factor beta in induction of migration and invasion in mammary epithelial cells

MCF10A mammary epithelial cells form growth-arrested structures when cultured in three-dimensional basement membrane gels. Activation of the receptor tyrosine kinase ErbB2 induces formation of proliferative structures that share properties with noninvasive early stage lesions. We conducted a genetic screen to identify cDNAs that can cooperate with ErbB2 to induce migration in these cells, with the hypothesis that they would represent candidate "second hits" in the development of invasive breast carcinomas. We found that expression of transforming growth factor (TGF)beta1 and TGFbeta3 in cells expressing activated ErbB2 induces migration in transwell chambers and invasive behavior in both basement membrane cultures and invasion chambers. The ability of ErbB2 to cooperate with TGFbeta correlated with sustained, elevated activation of extracellular signal-regulated kinase (Erk)-mitogen-activated protein kinase. Pharmacological reduction of Erk activity inhibited the cooperative effect of TGFbeta and ErbB2 on migration and expression of activated Erk kinase was sufficient to cooperate with TGFbeta to induce migration and invasion, suggesting that sustained Erk activation is critical for ErbB2/TGFbeta cooperation. In addition, we show that costimulation of ErbB2 and TGFbeta induces autocrine secretion of factors that are sufficient to induce migration, but not invasion, by means of both epidermal growth factor receptor-dependent and -independent processes. These results support the role of TGFbeta as a pro-invasion factor in the progression of breast cancers with activated ErbB2 and suggest that activation of the Erk and epidermal growth factor receptor pathways are key in mediating these events.

Involvement of TGF-beta(s)/T(beta)Rs system in tumor progression of murine mammary adenocarcinomas

We studied the expression of TGF-beta/T(beta)R system and its biological role in tumor development, in M3 and MM3 murine mammary adenocarcinomas with different metastasizing capability and in LM3 and LMM3 derived cell lines. All the studied cells secreted TGF-beta(s) and expressed T(beta)Rs. While the proliferation of the poorly metastatic M3 cells was significantly inhibited by 4 ng/ml TGF-beta(s), the highly metastatic MM3 cells were only slightly inhibited in response to the highest dose used. LM3 and LMM3 cells, highly invasive and metastatic, were totally refractory to TGF-beta antiproliferative effect. The role of TGF-beta in modulating key proteolytic cascades in tumor progression was also studied. TGF-beta(s) enhanced metalloproteinases production in all the studied cells while induced a stimulatory net effect on plasmin system activity only in the more metastatic cells. Our results in this murine mammary tumor lineage support the concept that dissociation of TGF-beta regulated growth control versus proteolytic enzyme pathways promotes tumor dissemination.

Increased malignancy of Neu-induced mammary tumors overexpressing active transforming growth factor beta1

To determine if Neu is dominant over transforming growth factor beta (TGF-beta), we crossed mouse mammary tumor virus (MMTV)-Neu mice with MMTV-TGF-beta1(S223/225) mice expressing active TGF-beta1 in the mammary gland. Bigenic (NT) and Neu-induced mammary tumors developed with a similar latency. The bigenic tumors and their metastases were less proliferative than those occurring in MMTV-Neu mice. However, NT tumors exhibited less apoptosis and were more locally invasive and of higher histological grade. NT mice exhibited more circulating tumor cells and lung metastases than Neu mice, while NT tumors contained higher levels of phosphorylated (active) Smad2, Akt, mitogen-activated protein kinase (MAPK), and p38, as well as vimentin content and Rac1 activity in situ than tumors expressing Neu alone. Ex vivo, NT cells exhibited higher levels of P-Akt and P-MAPK than Neu cells. These were inhibited by the TGF-beta inhibitor-soluble TGF-beta type II receptor (TbetaRII:Fc), suggesting they were activated by autocrine TGF-beta. TGF-beta stimulated migration of Neu cells into surrounding matrix, while the soluble TGF-beta inhibitor abrogated motility and invasiveness of NT cells. These data suggest that (i) the antimitogenic and prometastatic effects of TGF-beta can exist simultaneously and (ii) Neu does not abrogate TGF-beta-mediated antiproliferative action but can synergize with TGF-beta in accelerating metastatic tumor progression.

The L10P polymorphism of the transforming growth factor-beta 1 gene is not associated with breast cancer risk

Transforming growth factor-beta 1 (TGF-beta1) is a potent inhibitor of proliferation of epithelial, endothelial and hematopoietic cells and acts as a tumor suppressor. The gene for TGF-beta1, TGFB1, carries a common T/C variation of nucleotide 29, resulting in a leucine (L) to proline (P) polymorphism at codon 10 (TGFB1 L10P). The less common 10P allele has repeatedly been linked to higher TGF-beta1 levels and in at least one study to a lower incidence of breast cancer. To further analyze the role of this polymorphism for breast cancer risk, 500 patients with histologically confirmed breast cancer and 500 sex-and age-matched healthy control subjects were genotyped for the TGFB1 L10P polymorphism by an allele-specific polymerase chain reaction assay. TGFB1 LL, LP and PP genotype frequencies were not significantly different for patients (39.6, 44.2, 16.2%) and controls (36.5, 45.9, 17.6%). We conclude that the TGFB1 L10P polymorphism is not associated with breast cancer risk.