https://www.cell.com/cell/pdf/S0092-8674(03)00432-X.pdf

Mechanisms of TGF-β Signaling from Cell Membrane to the Nucleus

The basic elements of the transforming growth factor-β (TGFβ) pathway were revealed more than a decade ago. Since then, the concept of how the TGFβ signal travels from the membrane to the nucleus has been enriched with additional findings, and its multifunctional nature and medical relevance have relentlessly come to light. However, an old mystery has endured: how does the context determine the cellular response to TGFβ? Solving this question is key to understanding TGFβ biology and its many malfunctions. Recent progress is pointing at answers.

/pdf/tgfb-signalling-in-context-56apiue88r.pdf

TGFβ signalling in context.

The specification and proper arrangements of new cell types during tissue differentiation require the coordinated regulation of gene expression and precise interactions between neighboring cells. Of the many growth factors involved in these events, Wnts are particularly interesting regulators, because a key component of their signaling pathway, β-catenin, also functions as a component of the cadherin complex, which controls cell-cell adhesion and influences cell migration. Here, we assemble evidence of possible interrelations between Wnt and other growth factor signaling, β-catenin functions, and cadherin-mediated adhesion.

/pdf/convergence-of-wnt-s-catenin-and-cadherin-pathways-34ya7ckl0m.pdf

Convergence of Wnt, ß-Catenin, and Cadherin Pathways

Tgfbeta signaling in growth control, cancer, and heritable disorders

Epithelial and hematopoietic cells have a high turnover and their progenitor cells divide continuously, making them prime targets for genetic and epigenetic changes that lead to cell transformation and tumorigenesis. The consequent changes in cell behavior and responsiveness result not only from genetic alterations such as activation of oncogenes or inactivation of tumor suppressor genes, but also from altered production of, or responsiveness to, stimulatory or inhibitory growth and differentiation factors. Among these, transforming growth factor β (TGF-β) and its signaling effectors act as key determinants of carcinoma cell behavior. The autocrine and paracrine effects of TGF-β on tumor cells and the tumor micro-environment exert both positive and negative influences on cancer development. Accordingly, the TGF-β signaling pathway has been considered as both a tumor suppressor pathway and a promoter of tumor progression and invasion. Here we evaluate the role of TGF-β in tumor development and attempt to reconcile the positive and negative effects of TGF-β in carcinogenesis.

TGF-beta signaling in tumor suppression and cancer progression.

Smad2 and Smad3 Positively and Negatively Regulate TGFβ-Dependent Transcription through the Forkhead DNA-Binding Protein FAST2

The transforming growth factor-β (TGFβ) and Wnt/wingless pathways play pivotal roles in tissue specification during development. Activation of Smads, the effectors of TGFβ superfamily signals, results in Smad translocation from the cytoplasm into the nucleus where they act as transcriptional comodulators to regulate target gene expression. Wnt/wingless signals are mediated by the DNA-binding HMG box transcription factors lymphoid enhancer binding factor 1/T cell-specific factor (LEF1/TCF) and their coactivator β-catenin. Herein, we show that Smad3 physically interacts with the HMG box domain of LEF1 and that TGFβ and Wnt pathways synergize to activate transcription of the Xenopus homeobox gene twin (Xtwn). Disruption of specific Smad and LEF1/TCF DNA-binding sites in the promoter abrogates synergistic activation of the promoter. Consistent with this observation, introduction of Smad sites into a TGFβ-insensitive LEF1/TCF target gene confers cooperative TGFβ and Wnt responsiveness to the promoter. Furthermore, we demonstrate that TGFβ-dependent activation of LEF1/TCF target genes can occur in the absence of β-catenin binding to LEF1/TCF and requires both Smad and LEF1/TCF DNA-binding sites in the Xtwn promoter. Thus, our results show that TGFβ and Wnt signaling pathways can independently or cooperatively regulate LEF1/TCF target genes and suggest a model for how these pathways can synergistically activate target genes.

https://www.pnas.org/content/pnas/97/15/8358.full.pdf

Association of Smads with lymphoid enhancer binding factor 1/T cell-specific factor mediates cooperative signaling by the transforming growth factor-β and Wnt pathways

The node and the anterior visceral endoderm (AVE) are important organizing centers that pattern the mouse embryo by establishing the anterior–posterior (A–P), dorsal–ventral (D–V), and left–right (L–R) axes. Activin/nodal signaling through the Smad2 pathway has been implicated in AVE formation and in morphogenesis of the primitive streak, the anterior end of which gives rise to the node. The forkhead DNA-binding protein, FoxH1 (or Fast), functions as a Smad DNA-binding partner to regulate transcription in response to activin signaling. Here, we show that deletion of FoxH1 in mice results in failure to pattern the anterior primitive streak (APS) and form node, prechordal mesoderm, notochord, and definitive endoderm. In contrast, formation of the AVE can occur in the absence of FoxH1. The FoxH1 mutant phenotype is remarkably similar to that of mice deficient in the forkhead protein Foxa2 (HNF3β), and we show that Foxa2 expression is dependent on FoxH1 function. These results show that FoxH1 functions in an activin/nodal–Smad signaling pathway that acts upstream of Foxa2 and is required specifically for patterning the APS and node in the mouse.

/pdf/foxh1-fast-functions-to-specify-the-anterior-primitive-22u9t3jfwc.pdf

FoxH1 (Fast) functions to specify the anterior primitive streak in the mouse

Transforming growth factor-beta (TGF-beta) and Wnt ligands function in numerous developmental processes, and alterations of both signaling pathways are associated with common pathologic conditions, including cancer. To obtain insight into the extent of interdependence of the two signaling cascades in regulating biological responses, we used an oligonucleotide microarray approach to identify Wnt and TGF-beta target genes using normal murine mammary gland epithelial cells as a model. Combination treatment of TGF-beta and Wnt revealed a novel transcriptional program that could not have been predicted from single ligand treatments and included a cohort of genes that were cooperatively induced by both pathways. These included both novel and known components or modulators of TGF-beta and Wnt pathways, suggesting that mutual feedback is a feature of the coordinated activities of the ligands. The majority of the cooperative targets display increased expression in tumors derived from either Min (many intestinal neoplasia) or mouse mammary tumor virus (MMTV)-Wnt1 mice, two models of Wnt-induced tumors, with nine of these genes (Ankrd1, Ccnd1, Ctgf, Gpc1, Hs6st2, IL11, Inhba, Mmp14, and Robo1) showing increases in both. Reduction of TGF-beta signaling by expression of a dominant-negative TGF-beta type II receptor in bigenic MMTV-Wnt1/DNIIR mice increased mammary tumor latency and was correlated with a decrease in expression of Gpc1, Inhba, and Robo1, three of the TGF-beta/Wnt cooperative targets. Our results indicate that the TGF-beta and Wnt/beta-catenin pathways are firmly intertwined and generate a unique gene expression pattern that can contribute to tumor progression.

https://cancerres.aacrjournals.org/content/canres/67/1/75.full.pdf

Transcriptional Cooperation between the Transforming Growth Factor-β and Wnt Pathways in Mammary and Intestinal Tumorigenesis

Background: Several studies have shown that cooperation between transforming growth factor beta (TGF-β) and Wnt/wingless signaling pathways plays a role in controlling certain developmental events. These factors elicit their biological effects through distinct pathways in which TGF-β and Wnt signaling induce activation of the transcriptional regulators Smads and lymphoid enhancer binding factor/T-cell-specific factor (LEF/TCF), respectively. To understand the mechanism for cooperativity between these pathways, we have investigated the molecular mechanism for this synergistic effect.

Methods: Transcriptional assays were conducted by transient transfection of HepG2 cells with use of luciferase reporter constructs. Protein/protein interaction studies were conducted in vitro with the use of glutathione-S-transferase pull-down assays and in intact cells by immunoprecipitation and immunoblotting.

Results: We show that Smads physically interact with LEF1/TCF transcription factors and that specific DNA binding sites in the Xenopus twin promoter are required for synergistic activation by TGF-β and Wnt pathways. In addition, we demonstrate that TGF-β-dependent activation of LEF1/TCF target genes can occur independently of β-catenin, an essential component of the Wnt signaling pathway.

Conclusions: TGF-β and Wnt signaling pathways can independently or cooperatively regulate LEF1/TCF target genes. This suggests that the cooperation between these pathways may be important for the specification of cell fates during development.

Etienne Labbé

Papers

Smad2 and Smad3 Positively and Negatively Regulate TGFβ-Dependent Transcription through the Forkhead DNA-Binding Protein FAST2

Association of Smads with lymphoid enhancer binding factor 1/T cell-specific factor mediates cooperative signaling by the transforming growth factor-β and Wnt pathways

FoxH1 (Fast) functions to specify the anterior primitive streak in the mouse

Transcriptional Cooperation between the Transforming Growth Factor-β and Wnt Pathways in Mammary and Intestinal Tumorigenesis

Transcriptional regulation by Smads: crosstalk between the TGF-beta and Wnt pathways.