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Sox17 promotes cell cycle progression and inhibits TGF-beta/Smad3 signaling to initiate progenitor cell behavior in the respiratory epithelium.

Lange AW, Keiser AR, Wells JM, Zorn AM, Whitsett JA - PLoS ONE (2009)

Bottom Line: Notably, Sox17 enhanced cyclin D1 expression in vivo and activated cyclin D1 promoter activity in vitro.Sox17 decreased the expression of transforming growth factor-beta (TGF-beta)-responsive cell cycle inhibitors in the adult mouse lung, including p15, p21, and p57, and inhibited TGF-beta1-mediated transcriptional responses in vitro.Further, Sox17 interacted with Smad3 and blocked Smad3 DNA binding and transcriptional activity.

View Article: PubMed Central - PubMed

Affiliation: Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center and the University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America.

ABSTRACT
The Sry-related high mobility group box transcription factor Sox17 is required for diverse developmental processes including endoderm formation, vascular development, and fetal hematopoietic stem cell maintenance. Expression of Sox17 in mature respiratory epithelial cells causes proliferation and lineage respecification, suggesting that Sox17 can alter adult lung progenitor cell fate. In this paper, we identify mechanisms by which Sox17 influences lung epithelial progenitor cell behavior and reprograms cell fate in the mature respiratory epithelium. Conditional expression of Sox17 in epithelial cells of the adult mouse lung demonstrated that cell cluster formation and respecification of alveolar progenitor cells toward proximal airway lineages were rapidly reversible processes. Prolonged expression of Sox17 caused the ectopic formation of bronchiolar-like structures with diverse respiratory epithelial cell characteristics in alveolar regions of lung. During initiation of progenitor cell behavior, Sox17 induced proliferation and increased the expression of the progenitor cell marker Sca-1 and genes involved in cell cycle progression. Notably, Sox17 enhanced cyclin D1 expression in vivo and activated cyclin D1 promoter activity in vitro. Sox17 decreased the expression of transforming growth factor-beta (TGF-beta)-responsive cell cycle inhibitors in the adult mouse lung, including p15, p21, and p57, and inhibited TGF-beta1-mediated transcriptional responses in vitro. Further, Sox17 interacted with Smad3 and blocked Smad3 DNA binding and transcriptional activity. Together, these data show that a subset of mature respiratory epithelial cells retains remarkable phenotypic plasticity and that Sox17, a gene required for early endoderm formation, activates the cell cycle and reinitiates multipotent progenitor cell behavior in mature lung cells.

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Cyclin D1 expression is induced by Sox17.(A–B) Immunohistochemistry for cyclin D1 was performed on lung sections from adult CCSPrtTA (A) and CCSPrtTA/tetO-Sox17 (B) transgenic mice treated with Dox for 2 d. Cyclin D1 staining was increased in bronchioles and type II cells after Sox17 expression. Scale bars, 50 µm. (C) The regulatory region of cyclin D1 contains a conserved Sox binding site (boxed). MLE-15 cells were transiently transfected with human cyclin D1-luciferase reporter constructs and empty vector, t-Sox17, or full length Sox17. While the −47/+187 cyclin D1-luciferase reporter was moderately responsive to Sox17 (2.6-fold), Sox17 strongly activated the cyclin D1 promoter constructs containing the conserved Sox binding site (arrowheads; −96/+187; 6.4-fold and −944/+187; 5.9-fold). Experiments were performed three times in triplicate and representative results are shown±the standard deviation of the mean. Asterisks indicate statistical significance determined by Student's t-test (p<0.05).
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pone-0005711-g006: Cyclin D1 expression is induced by Sox17.(A–B) Immunohistochemistry for cyclin D1 was performed on lung sections from adult CCSPrtTA (A) and CCSPrtTA/tetO-Sox17 (B) transgenic mice treated with Dox for 2 d. Cyclin D1 staining was increased in bronchioles and type II cells after Sox17 expression. Scale bars, 50 µm. (C) The regulatory region of cyclin D1 contains a conserved Sox binding site (boxed). MLE-15 cells were transiently transfected with human cyclin D1-luciferase reporter constructs and empty vector, t-Sox17, or full length Sox17. While the −47/+187 cyclin D1-luciferase reporter was moderately responsive to Sox17 (2.6-fold), Sox17 strongly activated the cyclin D1 promoter constructs containing the conserved Sox binding site (arrowheads; −96/+187; 6.4-fold and −944/+187; 5.9-fold). Experiments were performed three times in triplicate and representative results are shown±the standard deviation of the mean. Asterisks indicate statistical significance determined by Student's t-test (p<0.05).

Mentions: Since cyclin D1 is a key regulator of progression through the G1 phase of the cell cycle and was increased in lungs from CCSPrtTA/tetO-Sox17 mice, we sought to determine if it was a direct downstream target of Sox17 during induction of respiratory epithelial cell proliferation. Quantitative real time RT-PCR performed using total RNA isolated from whole left lobes demonstrated that cyclin D1 mRNA was increased 1.3-fold in lungs from adult CCSPrtTA/tetO-Sox17 mice exposed to Dox for 1 day (data not shown). Staining for cyclin D1 was markedly increased in bronchioles and alveolar type II cells of CCSPrtTA/tetO-Sox17 mice following 2 days exposure to Dox (Fig. 6A–B). Thus, cyclin D1 mRNA and protein levels were significantly increased in lungs from CCSPrtTA/tetO-Sox17 mice just prior to the onset of proliferation, consistent with the concept that cyclin D1 contributes to the cell cycle reentry of mature respiratory epithelial cells following expression of Sox17.


Sox17 promotes cell cycle progression and inhibits TGF-beta/Smad3 signaling to initiate progenitor cell behavior in the respiratory epithelium.

Lange AW, Keiser AR, Wells JM, Zorn AM, Whitsett JA - PLoS ONE (2009)

Cyclin D1 expression is induced by Sox17.(A–B) Immunohistochemistry for cyclin D1 was performed on lung sections from adult CCSPrtTA (A) and CCSPrtTA/tetO-Sox17 (B) transgenic mice treated with Dox for 2 d. Cyclin D1 staining was increased in bronchioles and type II cells after Sox17 expression. Scale bars, 50 µm. (C) The regulatory region of cyclin D1 contains a conserved Sox binding site (boxed). MLE-15 cells were transiently transfected with human cyclin D1-luciferase reporter constructs and empty vector, t-Sox17, or full length Sox17. While the −47/+187 cyclin D1-luciferase reporter was moderately responsive to Sox17 (2.6-fold), Sox17 strongly activated the cyclin D1 promoter constructs containing the conserved Sox binding site (arrowheads; −96/+187; 6.4-fold and −944/+187; 5.9-fold). Experiments were performed three times in triplicate and representative results are shown±the standard deviation of the mean. Asterisks indicate statistical significance determined by Student's t-test (p<0.05).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2682659&req=5

pone-0005711-g006: Cyclin D1 expression is induced by Sox17.(A–B) Immunohistochemistry for cyclin D1 was performed on lung sections from adult CCSPrtTA (A) and CCSPrtTA/tetO-Sox17 (B) transgenic mice treated with Dox for 2 d. Cyclin D1 staining was increased in bronchioles and type II cells after Sox17 expression. Scale bars, 50 µm. (C) The regulatory region of cyclin D1 contains a conserved Sox binding site (boxed). MLE-15 cells were transiently transfected with human cyclin D1-luciferase reporter constructs and empty vector, t-Sox17, or full length Sox17. While the −47/+187 cyclin D1-luciferase reporter was moderately responsive to Sox17 (2.6-fold), Sox17 strongly activated the cyclin D1 promoter constructs containing the conserved Sox binding site (arrowheads; −96/+187; 6.4-fold and −944/+187; 5.9-fold). Experiments were performed three times in triplicate and representative results are shown±the standard deviation of the mean. Asterisks indicate statistical significance determined by Student's t-test (p<0.05).
Mentions: Since cyclin D1 is a key regulator of progression through the G1 phase of the cell cycle and was increased in lungs from CCSPrtTA/tetO-Sox17 mice, we sought to determine if it was a direct downstream target of Sox17 during induction of respiratory epithelial cell proliferation. Quantitative real time RT-PCR performed using total RNA isolated from whole left lobes demonstrated that cyclin D1 mRNA was increased 1.3-fold in lungs from adult CCSPrtTA/tetO-Sox17 mice exposed to Dox for 1 day (data not shown). Staining for cyclin D1 was markedly increased in bronchioles and alveolar type II cells of CCSPrtTA/tetO-Sox17 mice following 2 days exposure to Dox (Fig. 6A–B). Thus, cyclin D1 mRNA and protein levels were significantly increased in lungs from CCSPrtTA/tetO-Sox17 mice just prior to the onset of proliferation, consistent with the concept that cyclin D1 contributes to the cell cycle reentry of mature respiratory epithelial cells following expression of Sox17.

Bottom Line: Notably, Sox17 enhanced cyclin D1 expression in vivo and activated cyclin D1 promoter activity in vitro.Sox17 decreased the expression of transforming growth factor-beta (TGF-beta)-responsive cell cycle inhibitors in the adult mouse lung, including p15, p21, and p57, and inhibited TGF-beta1-mediated transcriptional responses in vitro.Further, Sox17 interacted with Smad3 and blocked Smad3 DNA binding and transcriptional activity.

View Article: PubMed Central - PubMed

Affiliation: Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center and the University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America.

ABSTRACT
The Sry-related high mobility group box transcription factor Sox17 is required for diverse developmental processes including endoderm formation, vascular development, and fetal hematopoietic stem cell maintenance. Expression of Sox17 in mature respiratory epithelial cells causes proliferation and lineage respecification, suggesting that Sox17 can alter adult lung progenitor cell fate. In this paper, we identify mechanisms by which Sox17 influences lung epithelial progenitor cell behavior and reprograms cell fate in the mature respiratory epithelium. Conditional expression of Sox17 in epithelial cells of the adult mouse lung demonstrated that cell cluster formation and respecification of alveolar progenitor cells toward proximal airway lineages were rapidly reversible processes. Prolonged expression of Sox17 caused the ectopic formation of bronchiolar-like structures with diverse respiratory epithelial cell characteristics in alveolar regions of lung. During initiation of progenitor cell behavior, Sox17 induced proliferation and increased the expression of the progenitor cell marker Sca-1 and genes involved in cell cycle progression. Notably, Sox17 enhanced cyclin D1 expression in vivo and activated cyclin D1 promoter activity in vitro. Sox17 decreased the expression of transforming growth factor-beta (TGF-beta)-responsive cell cycle inhibitors in the adult mouse lung, including p15, p21, and p57, and inhibited TGF-beta1-mediated transcriptional responses in vitro. Further, Sox17 interacted with Smad3 and blocked Smad3 DNA binding and transcriptional activity. Together, these data show that a subset of mature respiratory epithelial cells retains remarkable phenotypic plasticity and that Sox17, a gene required for early endoderm formation, activates the cell cycle and reinitiates multipotent progenitor cell behavior in mature lung cells.

Show MeSH
Related in: MedlinePlus