4088

SMAD3

SMAD family member 3;SMAD3;SMAD family member 3

MAD homolog 3|MAD, mothers against decapentaplegic homolog 3|SMA- and MAD-related protein 3|SMAD, mothers against DPP homolog 3|hMAD-3|hSMAD3|mad homolog JV15-2|mad protein homolog|mad3|mothers against DPP homolog 3|mothers against decapentaplegic homolog

15q22.33

protein-coding

Transforming growth factor (TGF)-beta can suppress and promote breast cancer progression. How TGF-beta elicits these dichotomous functions and which roles the principle intracellular effector proteins Smad2 and Smad3 have therein, is unclear. Here, we investigated the specific functions of Smad2 and Smad3 in TGF-beta-induced responses in breast cancer cells in vitro and in a mouse model for breast cancer metastasis. We stably knocked down Smad2 or Smad3 expression in MDA-MB-231 breast cancer cells. The TGF-beta-induced Smad3-mediated transcriptional response was mitigated and enhanced by Smad3 and Smad2 knockdown, respectively. This response was also seen for TGF-beta-induced vascular endothelial growth factor (VEGF) expression. TGF-beta induction of key target genes involved in bone metastasis, were found to be dependent on Smad3 but not Smad2. Strikingly, whereas knockdown of Smad3 in MDA-MB-231 resulted in prolonged latency and delayed growth of bone metastasis, Smad2 knockdown resulted in a more aggressive phenotype compared with control MDA-MB-231 cells. Consistent with differential effects of Smad knockdown on TGF-beta-induced VEGF expression, these opposing effects of Smad2 versus Smad3 could be directly correlated with divergence in the regulation of tumor angiogenesis in vivo. Thus, Smad2 and Smad3 differentially affect breast cancer bone metastasis formation in vivo.

A key feature of TGF-beta signaling activation in cancer cells is the sustained activation of SMAD complexes in the nucleus; however, the drivers of SMAD activation are poorly defined. Here, using human and mouse breast cancer cell lines, we found that oncogene forkhead box M1 (FOXM1) interacts with SMAD3 to sustain activation of the SMAD3/SMAD4 complex in the nucleus. FOXM1 prevented the E3 ubiquitin-protein ligase transcriptional intermediary factor 1 gamma (TIF1gamma) from binding SMAD3 and monoubiquitinating SMAD4, which stabilized the SMAD3/SMAD4 complex. Loss of FOXM1 abolished TGF-beta-induced SMAD3/SMAD4 formation. Moreover, the interaction of FOXM1 and SMAD3 promoted TGF-beta/SMAD3-mediated transcriptional activity and target gene expression. We found that FOXM1/SMAD3 interaction was required for TGF-beta-induced breast cancer invasion, which was the result of SMAD3/SMAD4-dependent upregulation of the transcription factor SLUG. Importantly, the function of FOXM1 in TGF-beta-induced invasion was not dependent on FOXM1's transcriptional activity. Knockdown of SMAD3 diminished FOXM1-induced metastasis. Furthermore, FOXM1 levels correlated with activated TGF-beta signaling and metastasis in human breast cancer specimens. Together, our data indicate that FOXM1 promotes breast cancer metastasis by increasing nuclear retention of SMAD3 and identify crosstalk between FOXM1 and TGF-beta/SMAD3 pathways. This study highlights the critical interaction of FOXM1 and SMAD3 for controlling TGF-beta signaling during metastasis.

Smad3, a major intracellular mediator of TGFbeta signaling, functions as both a positive and negative regulator in carcinogenesis. In response to TGFbeta, the TGFbeta receptor phosphorylates serine residues at the Smad3 C-tail. cancer cells often contain high levels of the MAPK and CDK activities, which can lead to the Smad3 linker region becoming highly phosphorylated. Here, we report, for the first time, that mutation of the Smad3 linker phosphorylation sites markedly inhibited primary tumor growth, but significantly increased lung metastasis of breast cancer cell lines. In contrast, mutation of the Smad3 C-tail phosphorylation sites had the opposite effect. We show that mutation of the Smad3 linker phosphorylation sites greatly intensifies all TGFbeta-induced responses, including growth arrest, apoptosis, reduction in the size of putative cancer stem cell population, epithelial-mesenchymal transition, and invasive activity. Moreover, all TGFbeta responses were completely lost on mutation of the Smad3 C-tail phosphorylation sites. Our results demonstrate a critical role of the counterbalance between the Smad3 C-tail and linker phosphorylation in tumorigenesis and metastasis. Our findings have important implications for therapeutic intervention of breast cancer.

The transforming growth factor beta (TGF-beta) signaling pathway has been considered both a tumor suppressor and a cancer promoter. Additionally, downregulation of cell adhesion molecules such as E-cadherin plays an important role in the metastatic potential of colorectal cancer (CRC). The aim of the present study was to evaluate TGF-beta, TGF-beta type I receptor (TGF-betaR1), TGF-beta type II receptor (TGF-betaR2), Smad4, pSmad2/3, and E-cadherin expression in colorectal carcinoma and to correlate the obtained data with other standard prognostic parameters, such as disease stage, metastases, and patient survival. TGF-beta, TGF-betaR1, TGF-betaR2, Smad4, pSmad2/3, and E-cadherin expression was evaluated immunohistochemically in 195 unrelated CRC specimens and the results subjected to various statistical analyses. TGF-beta was expressed in 71.28%, TGF-betaR1 in 61.0%, TGF-betaR2 in 54.4%, Smad4 in 61.5%, pSmad2/3 in 71.3%, and E-cadherin in 50.26% of the colorectal carcinoma samples tested. The correlation of immunoexpression with the clinicopathological parameters of CRC revealed that the high expression of TGF-beta and low expression of TGF-betaR1, TGF-betaR2, Smad4, pSmad2/3, and E-cadherin were correlated with tumor-node-metastasis (TNM) stage of disease. High TGF-beta expression and low TGF-betaR1, TGF-betaR2, Smad4, and pSmad2/3 expression were also correlated with lymph node metastasis. The Kaplan-Meier survival curves demonstrated a clear association of cancer-specific overall survival with high TGF-beta, as well as low TGF-betaR1, TGF-betaR2, Smad4, pSmad2/3, and E-cadherin expression. Our results suggest that TGF-beta, TGF-betaR1, TGF-betaR2, Smad4, pSmad2/3, and E-cadherin are closely related to TNM stage of CRC. Moreover, TGF-beta, TGF-betaR2, Smad4, pSmad2/3, and E-cadherin emerge as valuable independent biomarkers of prognosis in CRC patients.

Epithelial-mesenchymal transition (EMT) was shown to confer tumor cells with abilities essential for metastasis, including migratory phenotype, invasiveness, resistance to apoptosis, evading immune surveillance, and tumor stem cell traits. Therefore, inhibition of EMT can be an important therapeutic strategy to inhibit tumor metastasis. Here, we show that activation of peroxisome proliferator-activated receptor gamma (PPAR-gamma) inhibits transforming growth factor beta (TGF-beta)-induced EMT in lung cancer cells and prevents metastasis by antagonizing Smad3 function. Activation of PPAR-gamma by synthetic ligands (troglitazone and rosiglitazone) or by a constitutively active form of PPAR-gamma prevents TGF-beta-induced loss of E-cadherin expression and inhibits the induction of mesenchymal markers (vimentin, N-cadherin, fibronectin) and matrix metalloproteases. Consistently, activation of PPAR-gamma also inhibited EMT-induced migration and invasion of lung cancer cells. Furthermore, effects of PPAR-gamma ligands were attenuated by siRNA-mediated knockdown of PPAR-gamma, indicating that the ligand-induced responses are PPAR-gamma dependent. Selective knockdown of Smad2 and Smad3 by siRNA showed that TGF-beta-induced EMT is Smad3 dependent in lung cancer cells. Activation of PPAR-gamma inhibits TGF-beta-induced Smad transcriptional activity but had no effect on the phosphorylation or nuclear translocation of Smads. Consistently, PPAR-gamma activation prevented TGF-beta-induced transcriptional repression of E-cadherin promoter and inhibited transcriptional activation of N-cadherin promoter. Finally, treatment of mice with troglitazone or knockdown of Smad3 in tumor cells significantly inhibited TGF-beta-induced experimental metastasis in SCID-Beige mice. Together, with the low toxicity profile of PPAR-gamma ligands, our data show that these ligands may serve as potential therapeutic agents to inhibit metastasis.

Aberrant histone methylation is a frequent event during tumor development and progression. KMT1E (also known as SETDB1) is a histone H3K9 methyltransferase that contributes to epigenetic silencing of both oncogenes and tumor suppressor genes in cancer cells. In this report, we demonstrate that KMT1E acts as a metastasis suppressor that is strongly downregulated in highly metastatic lung cancer cells. Restoring KMT1E expression in this setting suppressed filopodia formation, migration, and invasive behavior. Conversely, loss of KMT1E in lung cancer cells with limited metastatic potential promoted migration in vitro and restored metastatic prowess in vivo. Mechanistic investigations indicated that KMT1E cooperates with the TGFbeta-regulated complex SMAD2/3 to repress metastasis through ANXA2. Together, our findings defined an essential role for the KMT1E/SMAD2/3 repressor complex in TGFbeta-mediated lung cancer metastasis.

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Very little is known about aggressive forms of this disease, such as metastatic or recurrent MBs. In order to identify pathways involved in aggressive MB pathophysiology, we performed unbiased, whole genome microarrays on MB tumors at both the human and murine levels. Primary human MBs were compared, transcriptomically, to their patient-matched recurrent or metastatic tumors. expression profiling was also performed on murine tumors from two spontaneously developing MB mouse models (Ptch+/- and Smo/Smo) that present with differing clinical severities. At both the human and murine levels we identified transforming growth factor-beta (TGF-beta) as a potential contributor to MB progression/metastasis. Smad3, a major downstream component of the TGF-beta pathway, was also evaluated using immunohistochemistry in malignant human tissues and was shown to correlate with MB metastasis and survival. Similarly, Smad3 expression during development identified a subset of cerebellar neuronal precursors as putative cells of origin for the Smad3-positive MBs. To our knowledge, this is the first study that links TGF-beta to MB pathogenesis. Our research suggests that canonical activation of this pathway leads to better prognosis for patients.

Transforming growth factor-beta (TGF-beta) is thought to play a role in the pathobiological progression of ovarian cancer because this peptide hormone is overexpressed in cancer tissue, plasma, and peritoneal fluid. In the current study, we investigated the role of the TGF-beta/Smad3 pathway in ovarian cancer metastasis by regulation of an epithelial-to-mesenchymal transition. When cancer cells were cultured on plastic, TGF-beta1, TGF-beta2, and TGF-beta3 induced pro-matrix metalloproteinase (MMP) secretion, loss of cell-cell junctions, down-regulation of E-cadherin, up-regulation of N-cadherin, and acquisition of a fibroblastoid phenotype, consistent with an epithelial-to-mesenchymal transition. Furthermore, Smad3 small interfering RNA transfection inhibited TGF-beta-mediated changes to a fibroblastic morphology, but not MMP secretion. When cancer cells were cultured on a three-dimensional collagen matrix, TGF-beta1, TGF-beta2, and TGF-beta3 stimulated both pro-MMP and active MMP secretion and invasion. Smad3 small interfering RNA transfection of cells cultured on a collagen matrix abrogated TGF-beta-stimulated invasion and MMP secretion. Analysis of Smad3 nuclear expression in microarrays of serous benign tumors, borderline tumors, and cystadenocarcinoma revealed that Smad3 expression could be used to distinguish benign and borderline tumors from carcinoma (P = 0.006). Higher Smad3 expression also correlated with poor survival (P = 0.031). Furthermore, a direct relationship exists between Smad3 nuclear expression and expression of the mesenchymal marker N-cadherin in cancer patients (P = 0.0057). Collectively, these results implicate an important role for the TGF-beta/Smad3 pathway in mediating ovarian oncogenesis by enhancing metastatic potential.