Keratinocyte-specific Smad2 ablation results in increased epithelial-mesenchymal transition during skin cancer formation and progression
Kristina E. Hoot, … , Erwin Bottinger, Xiao-Jing Wang
Kristina E. Hoot, … , Erwin Bottinger, Xiao-Jing Wang
Published July 10, 2008
Citation Information: J Clin Invest. 2008;118(8):2722-2732. https://doi.org/10.1172/JCI33713.
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Research Article Oncology

Keratinocyte-specific Smad2 ablation results in increased epithelial-mesenchymal transition during skin cancer formation and progression

Abstract

TGF-β and its signaling mediators, Smad2, -3, and -4, are involved with tumor suppression and promotion functions. Smad4–/– mouse epidermis develops spontaneous skin squamous cell carcinomas (SCCs), and Smad3–/– mice are resistant to carcinogen-induced skin cancer; however, the role of Smad2 in skin carcinogenesis has not been explored. In the present study, we found that Smad2 and Smad4, but not Smad3, were frequently lost in human SCCs. Mice with keratinocyte-specific Smad2 deletion exhibited accelerated formation and malignant progression of chemically induced skin tumors compared with WT mice. Consistent with the loss of Smad2 in poorly differentiated human SCCs, Smad2–/– tumors were poorly differentiated and underwent epithelial-mesenchymal transition (EMT) prior to spontaneous Smad4 loss. Reduced E-cadherin and activation of its transcriptional repressor Snail were also found in Smad2–/– mouse epidermis and occurred more frequently in Smad2-negative human SCCs than in Smad2-positive SCCs. Knocking down Snail abrogated Smad2 loss–associated EMT, suggesting that Snail upregulation is a major mediator of Smad2 loss–associated EMT. Furthermore, Smad2 loss led to a significant increase in Smad4 binding to the Snail promoter, and knocking down either Smad3 or Smad4 in keratinocytes abrogated Smad2 loss–associated Snail overexpression. Our data suggest that enhanced Smad3/Smad4-mediated Snail transcription contributed to Smad2 loss–associated EMT during skin carcinogenesis.

Authors

Kristina E. Hoot, Jessyka Lighthall, Gangwen Han, Shi-Long Lu, Allen Li, Wenjun Ju, Molly Kulesz-Martin, Erwin Bottinger, Xiao-Jing Wang

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Figure 3

Snail activation and E-cadherin (ECad) loss in K5.Smad2–/– tissues.

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Altered gene expression associated with dedifferentiation and EMT in K5....
A K14 antibody was used for counterstain (red). (A) K5.Smad2–/– papillomas undergo EMT. When most of cells in Smad2+/+ papillomas or spontaneous Smad4–/– SCCs still retained E-cadherin staining (green), K5.Smad2–/– papillomas show significant loss of E-cadherin (green). Arrows in K5.Smad2+/+ image indicate patchy areas of E-cadherin loss, whereas arrows in K5.Smad2–/– tumors show patchy retention of E-cadherin (top row). At this stage, Snail staining (green) was primarily cytoplasmic in Smad2+/+ papillomas and spontaneous Smad4–/– SCCs, but K5.Smad2–/– tumors displayed nuclear Snail staining (bottom row). Scale bar: 100 μm. (B) K5.Smad2–/– pup skin 72 hours after Smad2 deletion demonstrated significant reduction of E-cadherin (green, upper row) with a concomitant increase in nuclear Snail (green, bottom row). K5.Smad4–/– pup skin 72 hours after Smad4 deletion showed no change in E-cadherin and Snail expression patterns from WT skin. Scale bar: 100 μm.