title: E2F7 can regulate proliferation, differentiation, and apoptotic responses in human keratinocytes: implications for cutaneous squamous cell carcinoma formation.
abstract: The E2F family of transcription factors plays a crucial role in the regulation of genes involved in cell proliferation, differentiation, and apoptosis. In keratinocytes, the inhibition of E2F is a key step in the control and initiation of squamous differentiation. Because the product of the recently identified E2F7a/E2F7b gene has been shown to repress E2F-regulated promoters, and to be abundant in skin, we examined its role in the epidermis. Our results indicate that E2F7b mRNA expression is selectively associated with proliferation-competent keratinocytes. Moreover, E2F7 was able to antagonize E2F1-induced proliferation and apoptosis. In contrast, although E2F7 was able to inhibit proliferation and initiate differentiation, it was unable to antagonize the differentiation suppression induced by E2F1. These data indicate that E2F7-mediated suppression of proliferation and apoptosis acts through E2F1-dependent pathways, whereas E2F7-induced differentiation acts through an E2F1-independent pathway. These data also suggest that proliferation, differentiation, and survival of primary human keratinocytes can be controlled by the relative ratio of E2F1 to E2F7. Because deregulated proliferation, differentiation, and apoptosis are hallmarks of cancer, we examined the expression levels of E2F1 and E2F7 in cutaneous squamous cell carcinomas (CSCC). We found that both genes were overexpressed in CSCCs compared with normal epidermis. Furthermore, inhibition of E2F7 in a SCC cell line sensitized the cells to UV-induced apoptosis and doxorubicin-induced apoptosis. Combined, these data suggest that the selected disruption of E2F1 and E2F7 in keratinocytes is likely to contribute to CSCC formation and may prove to be a viable therapeutic target.
authors.affiliation: Translational Research Unit, Cancer Collaborative Group, Princess Alexandra Hospital, Wooloongabba, Queensland 4102, Australia.
authors.forename: Liliana
authors.initials: L
authors.lastname: Endo-Munoz
authors.forename: Alison
authors.initials: A
authors.lastname: Dahler
authors.forename: Ngari
authors.initials: N
authors.lastname: Teakle
authors.forename: Danny
authors.initials: D
authors.lastname: Rickwood
authors.forename: Mehlika
authors.initials: M
authors.lastname: Hazar-Rethinam
authors.forename: Ibtissam
authors.initials: I
authors.lastname: Abdul-Jabbar
authors.forename: Scott
authors.initials: S
authors.lastname: Sommerville
authors.forename: Ian
authors.initials: I
authors.lastname: Dickinson
authors.forename: Pritinder
authors.initials: P
authors.lastname: Kaur
authors.forename: Sophie
authors.initials: S
authors.lastname: Paquet-Fifield
authors.forename: Nicholas
authors.initials: N
authors.lastname: Saunders
mesh_terms: D017209:Apoptosis; D002294:Carcinoma, Squamous Cell / Q000209:etiology*; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D050687:E2F1 Transcription Factor / Q000037:antagonists & inhibitors; D050702:E2F7 Transcription Factor / Q000032:analysis / Q000502:physiology*; D006801:Humans; D015603:Keratinocytes / Q000166:cytology*; D012878:Skin Neoplasms / Q000209:etiology*
chemical_list: D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050702:E2F7 Transcription Factor; C481054:E2F7 protein, human