title: E2F modulates keratinocyte squamous differentiation: implications for E2F inhibition in squamous cell carcinoma.
abstract: E2F regulation is essential for normal cell cycle progression. Therefore, it is not surprising that squamous cell carcinoma cell lines (SCC) overexpress E2F1 and exhibit deregulated E2F activity when compared with normal keratinocytes. Indeed, deliberate E2F1 deregulation has been shown to induce hyperplasia and skin tumor formation. In this study, we report on a dual role for E2F as a mediator of keratinocyte proliferation and modulator of squamous differentiation. Overexpression of E2F isoforms in confluent primary keratinocyte cultures resulted in suppression of differentiation-associated markers. Moreover, we found that the DNA binding domain and the trans-activation domain of E2F1 are important in mediating suppression of differentiation. Use of a dominant/negative form of E2F1 (E2F d/n) found that E2F inhibition alone is sufficient to suppress the activity of proliferation-associated markers but is not capable of inducing differentiation markers. However, if the E2F d/n is expressed in differentiated keratinocytes, differentiation marker activity is further induced, suggesting that E2F may act as a modulator of squamous differentiation. We therefore examined the effects of E2F d/n in a differentiation-insensitive SCC cell line. We found that treatment with the differentiating agent, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), or expression of E2F d/n alone had no effect on differentiation markers. However, a combination of E2F d/n + TPA induced the expression of differentiation markers. Combined, these data indicate that E2F may play a key role in keratinocyte differentiation. These data also illustrate the unique potential of anti-E2F therapies in arresting proliferation and inducing differentiation of SCCs.
authors.affiliation: Epithelial Pathobiology Group, Cancer Biology Programme, Centre for Immunology and Cancer Research, University of Queensland, Princess Alexandra Hospital, Woolloongabba, Australia 4102.
authors.forename: Chung Fai
authors.initials: CF
authors.lastname: Wong
authors.forename: Liam M
authors.initials: LM
authors.lastname: Barnes
authors.forename: Alison L
authors.initials: AL
authors.lastname: Dahler
authors.forename: Louise
authors.initials: L
authors.lastname: Smith
authors.forename: Magdalena M
authors.initials: MM
authors.lastname: Serewko-Auret
authors.forename: Claudia
authors.initials: C
authors.lastname: Popa
authors.forename: Ibtissam
authors.initials: I
authors.lastname: Abdul-Jabbar
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Saunders
mesh_terms: D001665:Binding Sites; D015415:Biomarkers / Q000032:analysis; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D004817:Epidermis; D016368:Frameshift Mutation; D015870:Gene Expression; D006801:Humans; D015603:Keratinocytes / Q000166:cytology*; D017354:Point Mutation; D020033:Protein Isoforms / Q000235:genetics; D013329:Structure-Activity Relationship; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D015415:Biomarkers; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D020033:Protein Isoforms; D014157:Transcription Factors; D004247:DNA; D013755:Tetradecanoylphorbol Acetate