Volume 19, No 3, Mar 2009
ISSN: 1001-0602
EISSN: 1748-7838 2018
impact factor 17.848*
(Clarivate Analytics, 2019)
Volume 19 Issue 3, March 2009: 328-339
ORIGINAL ARTICLES
PI3-kinase-dependent activation of apoptotic machinery occurs on commitment of epidermal keratinocytes to terminal differentiation
Sam M Janes1, Tyler A Ofstad2, Douglas H Campbell3, Ayad Eddaoudi4, Gary Warnes5, Derek Davies6 and Fiona M Watt7
1Centre for Respiratory Research, Rayne Institute, University College London, 5 University Street, London WC1E 6BT, UK
2Graduate Program in Neurosciences, University of California, San Diego, CA 92093-0662, USA
3Immune System Therapeutics Ltd, 235 Jones Street, Ultimo, NSW 2007, Australia
4Molecular Immunology Unit, Institute of Child Health, University College London, 30 Guilford Street, London WC1N 1EH, UK
5Institute of Cell and Molecular Science, Barts and The London School of Medicine and Dentistry, 4 Newark Street, London E1 2AT, UK
6Cancer Research UK London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, UK
7Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
Correspondence: Fiona M Watt,(fiona.watt@cancer.org.uk)
We have investigated the earliest events in commitment of human epidermal keratinocytes to terminal differentiation. Phosphorylated Akt and caspase activation were detected in cells exiting the basal layer of the epidermis. Activation of Akt by retroviral transduction of primary cultures of human keratinocytes resulted in an increase in abortive clones founded by transit amplifying cells, while inhibition of the upstream kinase, PI3-kinase, inhibited suspension-induced terminal differentiation. Caspase inhibition also blocked differentiation, the primary mediator being caspase 8. Caspase activation was initiated by 2 h in suspension, preceding the onset of expression of the terminal differentiation marker involucrin by several hours. Incubation of suspended cells with fibronectin or inhibition of PI3-kinase prevented caspase induction. At 2 h in suspension, keratinocytes that had become committed to terminal differentiation had increased side scatter, were 7-aminoactinomycin D (7-AAD) positive and annexin V negative; they exhibited loss of mitochondrial membrane potential and increased cardiolipin oxidation, but with no increase in reactive oxygen species. These properties indicate that the onset of terminal differentiation, while regulated by PI3-kinase and caspases, is not a classical apoptotic process.
Cell Research (2009) 19:328-339. doi: 10.1038/cr.2008.281; published online 2 September 2008
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