Modulation of the functional binding sites for TGF-β on the type II receptor leads to suppression of TGF-β signaling

Morin attenuates diethylnitrosamine-induced rat liver fibrosis and hepatic stellate cell activation by co-ordinated regulation of Hippo/Yap and TGF-β1/Smad signaling

Despite great progress in understanding the activation of hepatic stellate cells (HSCs) during liver fibrosis, therapeutic approaches to inhibit HSC activation remain very limited. Recent reports highlight Yes-associated protein (Yap) and transforming growth factor-β1 (TGF-β1) as critical regulators of HSC activation and henceforth a compound targeting Hippo/Yap and TGF-β1/Smad pathways would be a potential anti-fibrotic candidate. Morin, a dietary flavonoid, was earlier reported to inhibit HSC proliferation and induction of apoptosis of cultured HSCs, mainly by suppressing Wnt/β-catenin and NF-κB signaling, but its effect on Hippo/Yap and TGF-β1/Smad pathways was not determined. To address this concern, this study was carried out in cultured LX-2 cells and diethylnitrosamine-induced fibrotic rats. Morin activated hippo signaling through significantly increased expression of Mst1 and Lats1 with decreased expression of transcriptional effectors Yap/TAZ, thereby prevented HSC activation and also suppressed the expression of exacerbated TGF-β/Smad signaling molecules such as TGF-β1, p-Smad2/3, collagen-I, MMP-2, MMP-9 and TIMP-1 in cultured LX-2 and DEN induced fibrotic rats. Both the in vitro and in vivo results clearly showed that, morin by acting on Hippo/Yap and TGF-β1/Smad pathways, ameliorated experimental liver fibrosis, indicating that morin has potential for effective treatment of liver fibrosis.

Transforming growth factor beta receptor type III is a tumor promoter in mesenchymal-stem like triple negative breast cancer

Introduction

There is a major need to better understand the molecular basis of triple negative breast cancer (TNBC) in order to develop effective therapeutic strategies. Using gene expression data from 587 TNBC patients we previously identified six subtypes of the disease, among which a mesenchymal-stem like (MSL) subtype. The MSL subtype has significantly higher expression of the transforming growth factor beta (TGF-β) pathway-associated genes relative to other subtypes, including the TGF-β receptor type III (TβRIII). We hypothesize that TβRIII is tumor promoter in mesenchymal-stem like TNBC cells.

Methods

Representative MSL cell lines SUM159, MDA-MB-231 and MDA-MB-157 were used to study the roles of TβRIII in the MSL subtype. We stably expressed short hairpin RNAs specific to TβRIII (TβRIII-KD). These cells were then used for xenograft tumor studies in vivo; and migration, invasion, proliferation and three dimensional culture studies in vitro. Furthermore, we utilized human gene expression datasets to examine TβRIII expression patterns across all TNBC subtypes.

Results

TβRIII was the most differentially expressed TGF-β signaling gene in the MSL subtype. Silencing TβRIII expression in MSL cell lines significantly decreased cell motility and invasion. In addition, when TβRIII-KD cells were grown in a three dimensional (3D) culture system or nude mice, there was a loss of invasive protrusions and a significant decrease in xenograft tumor growth, respectively. In pursuit of the mechanistic underpinnings for the observed TβRIII-dependent phenotypes, we discovered that integrin-α2 was expressed at higher level in MSL cells after TβRIII-KD. Stable knockdown of integrin-α2 in TβRIII-KD MSL cells rescued the ability of the MSL cells to migrate and invade at the same level as MSL control cells.

Conclusions

We have found that TβRIII is required for migration and invasion in vitro and xenograft growth in vivo. We also show that TβRIII-KD elevates expression of integrin-α2, which is required for the reduced migration and invasion, as determined by siRNA knockdown studies of both TβRIII and integrin-α2. Overall, our results indicate a potential mechanism in which TβRIII modulates integrin-α2 expression to effect MSL cell migration, invasion, and tumorigenicity.

DW1029M, a novel botanical drug candidate, inhibits advanced glycation end-product formation, rat lens aldose reductase activity, and TGF-β1 signaling

DW1029M is a botanical extract consisting of Morus bark and Puerariae radix, produced by Dong-Wha Pharmaceutical, for nephroprotective drug development; it has been in phase II clinical trials in Korea. In our mechanistic investigations, we found that DW1029M inhibits advanced glycation end products (AGEs), rat lens aldose reductase (RLAR), and transforming growth factor (TGF)-β1 signaling, all of which are implicated in diabetic complications such as diabetic nephropathy and diabetic retinopathy. DW1029M inhibits AGE formation via Fe(2+) chelation. The extract contains 13 active constituents that inhibit AGE formation, 8 active constituents that inhibit RLAR activity, and 1 inhibitor of TGF-β1 signaling. Our results suggest DW1029M protects against diabetic nephropathy via blockade of AGE formation, RLAR activity, and TGF-β1 signaling.

TbetaR-II discriminates the high- and low-affinity TGF-beta isoforms via two hydrogen-bonded ion pairs

The TGF-beta isoforms, TGF-beta1, -beta2, and -beta3, share greater than 70% sequence identity and are almost structurally identical. TGF-beta2 differs from the others, however, in that it binds the TGF-beta type II receptor (TbetaR-II) with much lower affinity than either TGF-beta1 or -beta3. It has been previously shown that three conserved interfacial residues, Arg25, Val92, Arg94, in TGF-beta1 and -beta3 are responsible for their high-affinity interaction with TbetaR-II. In this study, the role of each of these residues was examined by creating single, double, and triple substitutions resulting in both TGF-beta3 loss-of-function and TGF-beta2 gain-of-function variants. One-dimensional 1H NMR spectra of the variants confirmed a lack of large structural perturbations. Affinities, kinetics, and thermodynamics for TbetaR-II binding were determined by surface plasmon resonance biosensor analysis. Double substitutions revealed that nearly all of the high-affinity binding is contributed by Arg25 and Arg94. Single site substitutions showed that Arg94 makes the greatest contribution. Substitution of Arg25 and Arg94 with alanine verified the requirement of the arginine guanidinium functional groups for the highly specific hydrogen-bonded ion pairs formed between Arg25 and Arg94 of TGF-beta1 and -beta3, and Glu119 and Asp32 of TbetaR-II. Further kinetic and thermodynamic analyses confirmed that Arg25 and Arg94 are primarily responsible for high-affinity binding and also revealed that noninterfacial longer range effects emanating from the TGF-beta structural framework contribute slightly to TbetaR-II binding. Growth inhibition assays showed that binding changes generally correlate directly with changes in function; however, a role Val92 in this cellular context was uncovered.

A forward chemical screen using zebrafish embryos with novel 2-substituted 2H-chromene derivatives

We synthesized 2-substituted 2H-chromene derivatives from salicylaldehyde using potassium vinylic borates in the presence of secondary amines. Our goal was to generate novel compounds that might modulate transforming growth factor-beta signaling, based on limited rational design. Potassium vinyl trifluoroborates react with salicylaldehydes at 80 degrees C in the presence of a secondary amine and produce 2-substituted 2H-chromene derivatives with a 70-90% yield. A small library of these compounds, predicted to potentially interact with transforming growth factor-beta receptors, was screened for bioactivity in living zebrafish embryos. We found that the related compounds differentially affect development, and demonstrate one compound that produces severe body axis alterations in early embryogenesis and at lower doses affects specifically cardiovascular development. This compound modulates specifically a Smad-independent transforming growth factor-beta-regulated mitogen-activated protein kinase pathway, namely p-SAPK/JNK. These compounds, as suggested by our biological assays, may prove useful to manipulate developmental programs and develop therapeutic tools.

TGF-beta has paradoxical and context dependent effects on proliferation and anoikis in human colorectal cancer cell lines

Transforming growth factor-beta (TGF-beta) is a pluripotent cytokine that can have both tumor suppressing and tumor promoting effects on epithelial cells. It is unclear what determines when TGF-beta and its signaling pathway act predominantly as a tumor suppressor pathway or as a tumor-promoter pathway and whether TGF-beta can have both classes of effects concurrently on a cell. We investigated the effect of TGF-beta on anoikis in colorectal cancer cell lines sensitive to TGF-beta-mediated growth inhibition to determine if the context of the cells could be one of the factors that would affect whether TGF-beta exerts tumor suppressor or oncogene activity on colon cancer cells. We observed variable effects of TGF-beta on anoikis in these cell lines, even though they all are growth-inhibited by TGF-beta. Thus, we show that TGF-beta has variable effects on anoikis in colon cancer cell lines that likely reflects the effects of concurrent gene mutations in the cancer cells and the activation state of the signaling pathways controlled by these genes.