ABSTRACT
The mechanism by which transforming growth factor-ß (TGFß) regulates differentiation in human epidermal keratinocytes is still poorly understood. To assess the role of Smad signaling, we engineered human HaCaT keratinocytes either expressing small interfering RNA against Smads2, 3, and 4 or overexpressing Smad7 and verified impaired Smad signaling as decreased Smad phosphorylation, aberrant nuclear translocation, and altered target gene expression. Besides abrogation of TGFß-dependent growth inhibition in conventional cultures, epidermal morphogenesis and differentiation in organotypic cultures were disturbed, resulting in altered tissue homeostasis with suprabasal proliferation and hyperplasia upon TGFß treatment. Neutralizing antibodies against TGFß, similar to blocking the actions of EGF-receptor or keratinocyte growth factor, caused significant growth reduction of Smad7-overexpressing cells, thereby demonstrating that epithelial hyperplasia was attributed to TGFß-induced "dermis"-derived growth promoting factors. Furthermore impaired Smad signaling not only blocked the epidermal differentiation process or caused epidermal-to-mesenchymal transition but induced a switch to a complex alternative differentiation program, best characterized as mucous/intestinal-type epithelial differentiation. As the same alternative phenotype evolved from both modes of Smad-pathway interference, and reduction of Smad7-overexpression caused reversion to epidermal differentiation, our data suggest that functional TGFß/Smad signaling, besides regulating epidermal tissue homeostasis, is not only essential for terminal epidermal differentiation but crucial in programming different epithelial differentiation routes.
Subject(s)
Cell Differentiation/physiology , Keratinocytes/physiology , Morphogenesis/physiology , Signal Transduction/physiology , Smad Proteins/metabolism , Transforming Growth Factor beta1/metabolism , Animals , Cells, Cultured , Epidermal Cells , Epidermis/physiology , Homeostasis , Humans , Keratinocytes/cytology , Kruppel-Like Factor 4 , Kruppel-Like Transcription Factors/genetics , Kruppel-Like Transcription Factors/metabolism , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolism , Smad Proteins/geneticsABSTRACT
Many regenerative cells are label-retaining cells (LRCs) due to their ability to keep a DNA label over a prolonged time. Until recently, isolation of vital LRCs was hampered due to the necessary use of fixation methods. To circumvent this, we generated a lentiviral-(HIV-1) based vector expressing a Tet-Off controlled histone 2B-GFP (Tet-Off-H2B-GFP) reporter gene for the detection and isolation of viable LRCs. In initial experiments, the vector was successfully used to infect 2- and 3-dimensional tissue culture models. Infected cultures from skin and pancreatic cells showed a very tight regulation of H2B-GFP, were sensitive to minimal amounts of doxycycline (Dox) and had a stable transgenic expression over the time of this study. Our lentiviral vector represents a reliable and easy to handle system for the successful infection, detection and isolation of LRCs from various tissues in vitro, in vivo and ex vivo.
