Inhibition of CCAAT/Enhancer Binding Protein Family DNA Binding in Mouse Epidermis Prevents and Regresses Papillomas

Won Jun Oh,Michael J Gerdes,Vikas Rishi,Andras Orosz,Charles Vinson

doi:10.1158/0008-5472.can-06-2746

Won Jun Oh, Michael J Gerdes + Show 3 more

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https://doi.org/10.1158/0008-5472.can-06-2746

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Abstract

The CCAAT/enhancer binding proteins (C/EBP) are a family of B-ZIP DNA binding proteins that act as transcription factors to regulate growth and differentiation of many cell types, including keratinocytes. To examine the consequences of inhibiting the C/EBP family of transcription factors in skin, we generated transgenic mice that use the tetracycline system to conditionally express A-C/EBP, a dominant negative that inhibits the DNA binding of C/EBP family members. We expressed A-C/EBP in the basal layer of the skin epidermis during a two-step skin carcinogenesis protocol. A-C/EBP expression caused hyperplasia of the basal epidermis and increased apoptosis in the suprabasal epidermis. The mice developed fewer papillomas and had systemic hair loss. A-C/EBP expression caused C/EBPbeta protein to disappear whereas C/EBPalpha, p53, Bax, and caspase-3 protein levels were dramatically up-regulated in the suprabasal layer. Primary keratinocytes recapitulate the A-C/EBP induction of cell growth and increase in p53 protein. A-C/EBP expression after papilloma development caused the papillomas to regress with an associated increase in apoptosis and up-regulation of p53 protein. Furthermore, A-C/EBP-expressing mice heterozygous for p53 were more susceptible to papilloma formation, suggesting that the suppression of papilloma formation has a p53-dependent mechanism. These results implicate DNA binding of C/EBP family members as a potential molecular therapeutic target.

Highlights

The CCAAT/enhancer binding protein (C/EBP) family of basic leucine zipper (B-ZIP) transcription factors are involved in many aspects of cell growth and differentiation in a variety of cell types [1,2,3]
To express A-C/EBP in the skin, tetracycline operon (TetO)-A-C/EBP mice were crossed with a second transgenic mouse (K5-tTA) that expresses the tTA using the keratin 5 (K5) promoter [31] that is expressed in the basal epidermis
Examination of adult skin by reverse transcription-PCR (RT-PCR) indicates that A-C/EBP is tightly regulated and expression only occurs in K5:A-C/EBP mice in the absence of doxycycline (Fig. 1B)

Summary

Introduction

The CCAAT/enhancer binding protein (C/EBP) family of basic leucine zipper (B-ZIP) transcription factors are involved in many aspects of cell growth and differentiation in a variety of cell types [1,2,3]. The six C/EBP family members are similar in the B-ZIP domain and can homodimerize and/or heterodimerize with each other to bind specific DNA sequences [4,5,6,7,8,9]. The two most studied family members are C/EBPa and C/EBPh, which have contrasting roles in cell growth, differentiation, and oncogenesis. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). C/EBPh is expressed in the undifferentiated growing basal epidermis whereas C/EBPa is expressed in the more quiescent differentiating suprabasal epidermis [21]

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