title: Signalling in the epidermis: the E2F cell cycle regulatory pathway in epidermal morphogenesis, regeneration and transformation.
abstract: The epidermis is the outermost layer in the skin, and it is the first line of defence against the environment. The epidermis also provides a barrier against loss of fluids and electrolytes, which is crucial for life. Essential in the maintenance of this tissue is its ability to continually self-renew and regenerate after injury. These two characteristics are critically dependent on the ability of the principal epidermal cell type, the keratinocyte, to proliferate and to respond to differentiation cues. Indeed, the epidermis is a multilayered tissue composed of keratinocyte stem cells and their differentiated progeny. Central for the control of cell proliferation is the E2F transcription factor regulatory network. This signaling network also includes cyclins, cdk, cdk inhibitors and the retinoblastoma (pRb) family of proteins. The biological importance of the E2F/pRb pathway is emphasized by the fact that a majority of human tumours exhibit alterations that disrupt the ability of pRb proteins to inhibit E2F, leading to permanent activation of the latter. Further, E2F is essential for normal epidermal regeneration after injury. Other member of the E2F signaling pathway are also involved in epidermal development and pathophysiology. Thus, whereas the pRb family of proteins is essential for epidermal morphogenesis, abnormal regulation of cyclins and E2F proteins results in tumorgenesis in this tissue. In this review, we discuss the role of each member of this important growth regulatory network in epidermal formation, homeostasis and carcinogenesis.
authors.affiliation: Dept. of Physiology & Pharmacology, University of Western Ontario, London, ON, Canada.
authors.forename: Iordanka A
authors.initials: IA
authors.lastname: Ivanova
authors.forename: Sudhir J A
authors.initials: SJ
authors.lastname: D'Souza
authors.forename: Lina
authors.initials: L
authors.lastname: Dagnino
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000502:physiology; D002471:Cell Transformation, Neoplastic; D016213:Cyclins / Q000502:physiology; D050684:E2F Transcription Factors / Q000502:physiology*; D000078404:Epidermal Cells; D004817:Epidermis / Q000196:embryology / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D008322:Mammals / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009024:Morphogenesis / Q000502:physiology; D009363:Neoplasm Proteins / Q000502:physiology; D012038:Regeneration / Q000502:physiology; D016160:Retinoblastoma Protein / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D012867:Skin / Q000293:injuries; D012878:Skin Neoplasms / Q000503:physiopathology*
chemical_list: D018797:Cell Cycle Proteins; D016213:Cyclins; D050684:E2F Transcription Factors; D009363:Neoplasm Proteins; D016160:Retinoblastoma Protein