Int J Stem Cells.  2018 Jun;11(1):111-120. 10.15283/ijsc17069.

TGF-β induces Smad2 Phosphorylation, ARE Induction, and Trophoblast Differentiation

Affiliations
  • 1Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine, Dayton, Ohio 45435, USA. Thomas.L.brown@wright.edu
  • 2Department of Reproductive Medicine, University of California-San Diego, San Diego, California 92093, USA.

Abstract

BACKGROUND
Transforming growth factor beta (TGF-β) signaling has been shown to control a large number of critical cellular actions such as cell death, differentiation, and development and has been implicated as a major regulator of placental function. SM10 cells are a mouse placental progenitor cell line, which has been previously shown to differentiate into nutrient transporting, labyrinthine-like cells upon treatment with TGF-β. However, the signal transduction pathway activated by TGF-β to induce SM10 progenitor differentiation has yet to be fully investigated.
MATERIALS AND METHODS
In this study the SM10 labyrinthine progenitor cell line was used to investigate TGF-β induced differentiation. Activation of the TGF-β pathway and the ability of TGF-β to induce differentiation were investigated by light microscopy, luciferase assays, and Western blot analysis.
RESULTS
AND CONCLUSIONS: In this report, we show that three isoforms of TGF-β have the ability to terminally differentiate SM10 cells, whereas other predominant members of the TGF-β superfamily, Nodal and Activin A, do not. Additionally, we have determined that TGF-β induced Smad2 phosphorylation can be mediated via the ALK-5 receptor with subsequent transactivation of the Activin response element. Our studies identify an important regulatory signaling pathway in SM10 progenitor cells that is involved in labyrinthine trophoblast differentiation.

Keyword

Placenta; Labyrinthine; TGF-β; Differentiation; Smad

MeSH Terms

Activins
Animals
Blotting, Western
Cell Death
Luciferases
Mice
Microscopy
Phosphorylation*
Placenta
Protein Isoforms
Response Elements
Signal Transduction
Stem Cells
Transcriptional Activation
Transforming Growth Factor beta
Trophoblasts*
Activins
Luciferases
Protein Isoforms
Transforming Growth Factor beta

Figure

  • Fig. 1 TGF-β isoforms induce trophoblast progenitor differentiation and Glut-1 transactivation. SM10 cells were treated for 72 hrs with (A) vehicle control, (B) 5 ng/ml TGF-β1, (C) 5 ng/ml TGF-β2, or (D) 2 ng/ml TGF-β3 to induce differentiation. (E) Glut-1 luciferase reporter activity in SM10s cells treated with vehicle control, TGF-β1, TGF-β2, or TGF-β3. Cells were transiently transfected with Glut1-lux and pRLSV40 using Metafectene. Twenty-four hours post-transfection, cells were treated with vehicle control, TGF-β1 (5 ng/ml), TGF-β2 (5 ng/ml), or TGF-β3 (2 ng/ml) for 24 or 72 hours. Luciferase activity was analyzed using the dual luciferase assay system. The Glut1-lux transactivation values were normalized to the constitutively active reporter, pRLSV40. Error bars represent standard error of the mean. (θ) indicates a significant increase in Glut1 luciferase transactivation compared to vehicle control at 24 hours and (*) indicates a significant increase from control at 72 hours. p<0.05.

  • Fig. 2 TGF-β induces SM10 cell differentiation and growth inhibition. SM10 cells were treated with (A) vehicle control, (B) TGF-β2 (5 ng/ml), (C) Activin A (5 ng/ml), or (D) Nodal (250 μg/ml) for 72 hrs to induce differentiation. (E) After 72 hours of treatment, cells were incubated with 1 μCi/ml 3H-Thymidine per well for 4 hours. Cells were then lysed and counted in scintillation fluid. Percent growth inhibition was determined as the amount of 3H-Thymidine incorporation compared to control. Percent growth inhibition is normalized to vehicle treated cells. Error bars represent standard error of the mean. *p<0.001.

  • Fig. 3 TGF-β induced differentiation can be mediated through the Alk-5 receptor. SM10 cells were treated without (A, B) or with (C, D) the Alk inhibitor SB431542 (10 μM) for 1 hour, followed by treatment without (A, C) or with (B, D) TGF-β 2 (5 ng/ml) for 48 hours.

  • Fig. 4 TGF-β triggers Smad2 phosphorylation and transactivation. (A) 3TP luciferase reporter activity in SM10s cells treated with vehicle control or TGF-β2. Cells were transiently transfected with 3TP-lux and pRLSV40 using Metafectene. Twenty-four hours post-transfection, cells were treated with vehicle or TGF-β2 (5 ng/ml) for 72 hours. Luciferase activity was analyzed using the dual luciferase assay system. The 3TP-lux transactivation values were normalized to the constitutively active reporter (pRLSV40). (B) Western blotting analysis of Smad2, Smad3, and Smad4 in TGF-β2 or vehicle-treated SM10 cells. COS-7 cells were used as a positive control. (C) Western blotting analysis of Phospho-Smad3 in TGF-β2 or vehicle-treated SM10 cells. COS-7 cells transiently transfected with the plasmid, pXIX-Smad3 and treated with TGF-β were used as a positive control. (D) Western blotting analysis of Phospho-Smad2 in the TGF-β2, Activin A, or vehicle-treated SM10 cells. (E) ARE luciferase reporter activity in SM10 cells transiently transfected with pCDNA3 control or pRK5-Smad2 and treated with vehicle control or TGF-β2. Cells were transiently transfected with ARE-lux, pLv-CMV-hFAST-1, and pRLSV40 using Metafectene. Twenty-four hours post-transfection, cells were treated with vehicle or TGF-β2 (5 ng/ml) for 72 hours. Luciferase activity was analyzed using the dual luciferase assay system. The ARE-lux transactivation values were normalized to the constitutively active reporter (pRLSV40). (F) ARE luciferase reporter activity in SM10 cells transiently transfected with pCDNA3 control or pRK5-Smad7 and treated with vehicle control or TGF-β2. Cells were transiently transfected with ARE-lux, pLv-CMV-hFAST-1, and pRLSV40 using Metafectene. Twenty-four hours post-transfection, cells were treated with vehicle or TGF-β2 (5 ng/ml) for 72 hours. Luciferase activity was analyzed using the dual luciferase assay system. The ARE-lux transactivation values were normalized to the constitutively active reporter (pRLSV40). Error bars represent standard error of the mean. *p<0.05.

  • Fig. 5 TGF-β induces Smad2 Phosphorylation, ARE Induction, and Trophoblast Differentiation Diagrammatic representation of the TGF-β signaling pathway in SM10 growth inhibition and trophoblast differentiation. The ligand, TGF-β, binds to cognate receptors and triggers activation via the TGF-β Type I receptor (ALK-5) to induce the phosphorylation of Smad2. Phospho-Smad2, via classically presumptive Smad 4 binding, triggers the transactivation of ARE response elements in target genes that inhibit cell growth and promote labyrinthine trophoblast differentiation. Smad 7 acts as a classical negative feedback inhibitor for the TGF-β signaling pathway.


Reference

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