title: AKT delays the early-activated apoptotic pathway in UVB-irradiated keratinocytes via BAD translocation.
abstract: Upon irradiation with a high dose of UVB, keratinocytes undergo apoptosis as a protective mechanism. In previous work, we demonstrated the existence of an early-activated UVB-induced apoptotic pathway in growth factor-depleted human keratinocytes, which can be substantially delayed by the exclusive supplementation of IGF-1. We now show that in human keratinocytes, IGF-1 inhibits the onset of UVB-triggered apoptosis through a transcriptional independent, AKT-mediated mechanism, involving BAD serine 136 phosphorylation. Our results show that the early UVB-induced apoptosis in growth factor-depleted human keratinocytes is exclusively triggered through the mitochondrial pathway. It is accompanied by BAX translocation, cytochrome c release, and procaspase-9 cleavage, but not by procaspase-8 or BID cleavage. In human keratinocytes, IGF-1 supplementation inhibits these events in a transcription-independent manner. Both IGF-1 supplementation and the transduction of a membrane-targeted form of AKT result in a shift of the BH3-only protein BAD from the mitochondria to the cytoplasm, paralleled by an increase of AKT-specific Ser136 phospho-BAD bound to 14-3-3zeta protein. These data indicate that AKT-induced BAD phosphorylation and its subsequent cytoplasmic sequestration by 14-3-3zeta is a major mechanism responsible for the postponement of UVB-induced apoptosis in human keratinocytes.
authors.affiliation: Laboratory of Dermatology, University of Leuven, Leuven, Belgium.
authors.forename: Sofie
authors.initials: S
authors.lastname: Claerhout
authors.forename: David
authors.initials: D
authors.lastname: Decraene
authors.forename: An
authors.initials: A
authors.lastname: Van Laethem
authors.forename: Sofie
authors.initials: S
authors.lastname: Van Kelst
authors.forename: Patrizia
authors.initials: P
authors.lastname: Agostinis
authors.forename: Marjan
authors.initials: M
authors.lastname: Garmyn
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001692:Biological Transport; D053453:Caspase 9 / Q000378:metabolism; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015603:Keratinocytes / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects*; D008928:Mitochondria / Q000502:physiology; D010766:Phosphorylation; D014176:Protein Biosynthesis; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051025:bcl-Associated Death Protein / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D007334:Insulin-Like Growth Factor I; D045304:Cytochromes c; D051057:Proto-Oncogene Proteins c-akt; D053453:Caspase 9