Nodal Morphogens

Nodal signals belong to the TGF-β superfamily and are essential for the induction of mesoderm and endoderm and the determination of the left–right axis. Nodal signals can act as morphogens—they have concentration-dependent effects and can act at a distance from their source of production. Nodal and its feedback inhibitor Lefty form an activator/inhibitor pair that behaves similarly to postulated reaction–diffusion models of tissue patterning. Nodal morphogen activity is also regulated by microRNAs, convertases, TGF-β signals, coreceptors, and trafficking factors. This article describes how Nodal morphogens pattern embryonic fields and discusses how Nodal morphogen signaling is modulated.In his 1901 book “Regeneration,” Thomas Hunt Morgan speculated that “if we suppose the materials or structures that are characteristic of the vegetative half are gradually distributed from the vegetative to the animal half in decreasing amounts, then any piece of the egg will contain more of these things at one pole than the other” and “gastrulation depends on the relative amounts of the materials in the different parts of the blastula” (Morgan 1901). Although Morgan’s speculations referred to the sea urchin embryo, they foretold our current understanding of morphogen gradients in frog and fish development. Morgan’s “materials,” “structures,” and “things” are the Nodal signals that create a vegetal-to-animal activity gradient to regulate germ layer formation and patterning. This article discusses how Nodal signaling provides positional information to fields of cells. I first portray the components of the signaling pathway and describe the role of Nodal signals in mesendoderm induction and left–right axis specification. I then discuss how Nodal morphogen gradients are thought to be generated, modulated, and interpreted.     

Genetic variants in TGF-β pathway are associated with ovarian cancer risk

The transforming growth factor-β (TGF-β) signaling pathway is involved in a diverse array of cellular processes responsible for tumorigenesis. In this case-control study, we applied a pathway-based approach to evaluate single-nucleotide polymorphisms (SNPs) in the TGF-β signaling pathway as predictors of ovarian cancer risk. We systematically genotyped 218 SNPs from 21 genes in the TGF-β signaling pathway in 417 ovarian cancer cases and 417 matched control subjects. We analyzed the associations of these SNPs with ovarian cancer risk, performed haplotype analysis and identified potential cumulative effects of genetic variants. We also performed analysis to identify higher-order gene-gene interactions influencing ovarian cancer risk. Individual SNP analysis showed that the most significant SNP was SMAD6: rs4147407, with an adjusted odds ratio (OR) of 1.60 (95% confidence interval [CI], 1.14–2.24, P = 0.0066). Cumulative genotype analysis of 13 SNPs with significant main effects exhibited a clear dose-response trend of escalating risk with increasing number of unfavorable genotypes. In gene-based analysis, SMAD6 was identified as the most significant gene associated with ovarian cancer risk. Haplotype analysis further revealed that two haplotype blocks within SMAD6 were significantly associated with decreased ovarian cancer risk, as compared to the most common haplotype. Gene-gene interaction analysis further categorized the study population into subgroups with different ovarian cancer risk. Our findings suggest that genetic variants in the TGF-β signaling pathway are associated with ovarian cancer risk and may facilitate the identification of high-risk subgroups in the general population.     

Murine CD4 T cells produce a new form of TGF-β as measured by a newly developed TGF-β bioassay

Background

It is generally assumed that T cells do not produce active TGF-β since active TGF-β as measured in supernatants by ELISA without acidification is usually not detectable. However, it is possible that active TGF-β from T cells may take a special form which is not detectable by ELISA.

Methodology/Principal Findings

We constructed a TGF-β bioassay which can detect both soluble and membrane-bound forms of TGF-β from T cells. For this bioassay, 293T cells were transduced with (caga)₁₂ Smad binding element-luciferase along with CD32 (Fc receptor) and CD86. The resulting cells act as artificial antigen presenting cells in the presence of anti-CD3 and produce luciferase in response to biologically active TGF-β. We co-cultured pre-activated murine CD4⁺CD25⁻ T cells or CD4⁺CD25⁺ T cells with the 293T-caga-Luc-CD32-CD86 reporter cells in the presence of anti-CD3 and IL-2. CD4⁺CD25⁻ T cells induced higher luciferase in the reporter cells than CD4⁺CD25⁺ T cells. This T cell-produced TGF-β is in a soluble form since T cell culture supernatants contained the TGF-β activity. The TGF-β activity was neutralized with an anti-mouse LAP mAb or an anti-latent TGF-β/pro-TGF-β mAb, but not with anti-active TGF-β Abs. An anti-mouse LAP mAb removed virtually all acid activatable latent TGF-β from the T cell culture supernatant, but not the ability to induce TGF-β signaling in the reporter cells. The induction of TGF-β signaling by T cell culture supernatants was cell type-specific.

Conclusions/Significance

A newly developed 293T-caga-Luc-CD32-CD86 reporter cell bioassay demonstrated that murine CD4 T cells produce an unconventional form of TGF-β which can induce TGF-β signaling. This new form of TGF-β contains LAP as a component. Our finding of a new form of T cell-produced TGF-β and the newly developed TGF-β bioassay system will provide a new avenue to investigate T cell function of the immune system.     

p130Cas Is Required for Mammary Tumor Growth and Transforming Growth Factor-��-mediated Metastasis through Regulation of Smad2/3 Activity

During breast cancer progression, transforming growth factor-β (TGF-β) switches from a tumor suppressor to a pro-metastatic molecule. Several recent studies suggest that this conversion in TGF-β function depends upon fundamental changes in the TGF-β signaling system. We show here that these changes in TGF-β signaling are concomitant with aberrant expression of the focal adhesion protein, p130Cas. Indeed, elevating expression of either the full-length (FL) or just the carboxyl terminus (CT) of p130Cas in mammary epithelial cells (MECs) diminished the ability of TGF-β1 to activate Smad2/3, but increased its coupling to p38 MAPK. This shift in TGF-β signaling evoked (i) resistance to TGF-β-induced growth arrest, and (ii) acinar filling upon three-dimensional organotypic cultures of p130Cas-FL or -CT expressing MECs. Furthermore, rendering metastatic MECs deficient in p130Cas enhanced TGF-β-stimulated Smad2/3 activity, which restored TGF-β-induced growth inhibition both in vitro and in mammary tumors produced in mice. Additionally, whereas elevating TβR-II expression in metastatic MECs had no affect on their phosphorylation of Smad2/3, this event markedly enhanced their activation of p38 MAPK, leading to increased MEC invasion and metastasis. Importantly, depleting p130Cas expression in TβR-II-expressing metastatic MECs significantly increased their activation of Smad2/3, which (i) reestablished the physiologic balance between canonical and noncanonical TGF-β signaling, and (ii) reversed cellular invasion and early mammary tumor cell dissemination stimulated by TGF-β. Collectively, our findings identify p130Cas as a molecular rheostat that regulates the delicate balance between canonical and noncanonical TGF-β signaling, a balance that is critical to maintaining the tumor suppressor function of TGF-β during breast cancer progression.     

The notch and TGF-β signaling pathways contribute to the aggressiveness of clear cell renal cell carcinoma

Background

Despite recent progress, therapy for metastatic clear cell renal cell carcinoma (CCRCC) is still inadequate. Dysregulated Notch signaling in CCRCC contributes to tumor growth, but the full spectrum of downstream processes regulated by Notch in this tumor form is unknown.

Methodology/Principal Findings

We show that inhibition of endogenous Notch signaling modulates TGF-β dependent gene regulation in CCRCC cells. Analysis of gene expression data representing 176 CCRCCs showed that elevated TGF-β pathway activity correlated significantly with shortened disease specific survival (log-rank test, p = 0.006) and patients with metastatic disease showed a significantly elevated TGF-β signaling activity (two-sided Student''s t-test, p = 0.044). Inhibition of Notch signaling led to attenuation of both basal and TGF-β1 induced TGF-β signaling in CCRCC cells, including an extensive set of genes known to be involved in migration and invasion. Functional analyses revealed that Notch inhibition decreased the migratory and invasive capacity of CCRCC cells.

Conclusion

An extensive cross-talk between the Notch and TGF-β signaling cascades is present in CCRCC and the functional properties of these two pathways are associated with the aggressiveness of this disease.     

Smad3 Prevents ��-Catenin Degradation and Facilitates ��-Catenin Nuclear Translocation in Chondrocytes

Our previous study demonstrated that transforming growth factor (TGF)-β activates β-catenin signaling through Smad3 interaction with β-catenin in chondrocytes. In the present studies, we further investigated the detailed molecular mechanism of the cross-talk between TGF-β/Smad3 and Wnt/β-catenin signaling pathways. We found that C-terminal Smad3 interacted with both the N-terminal region and the middle region of β-catenin protein in a TGF-β-dependent manner. Both Smad3 and Smad4 were required for the interaction with β-catenin and protected β-catenin from an ubiquitin-proteasome-dependent degradation. In addition, the formation of the Smad3-Smad4-β-catenin protein complex also mediated β-catenin nuclear translocation. This Smad3-mediated regulatory mechanism of β-catenin protein stability enhanced the activity of β-catenin to activate downstream target genes during chondrogenesis. Our findings demonstrate a novel mechanism between TGF-β and Wnt/β-catenin signaling pathways during chondrocyte development.