title: Endocytic pathways and biological effects induced by UVB-dependent or ligand-dependent activation of the keratinocyte growth factor receptor.
abstract: UVB exposure of epidermal cells is known to trigger early and late molecular pathways dependent on receptor tyrosine kinases and reactive oxygen species (ROS). We have recently reported that UVB irradiation induces tyrosine phosphorylation, kinase activation, and internalization of the receptor for the keratinocyte growth factor (KGFR), a paracrine mediator of epithelial growth, differentiation, and survival. Here we analyzed in more detail the UVB-induced endocytic pathway of KGFR and the role of KGFR activation and internalization in regulating UVB-promoted apoptosis and cell cycle arrest. Immunogold electron microscopy and confocal analysis revealed that the UVB-induced endocytosis of KGFR occurs through clathrin-coated pits and that the internalized receptors are sorted to the degradative route and reach the lysosomal compartment with a timing similar to that induced by their ligand KGF. Treatment with the anti-oxidant N-acetylcysteine inhibited KGFR endocytosis, suggesting that the receptor internalization is mediated by the intracellular production of ROS. The ligand-independent KGFR endocytic pathway induced by UVB requires receptor kinase activity and tyrosine phosphorylation and involves transient receptor ubiquitination. Inhibition of KGFR activity reduces both the KGF-mediated proliferative response and the UVB-promoted apoptotic cell death, indicating a different effect of ligand-induced and UVB-induced KGFR triggering. In addition, receptor internalization leads to protection from apoptosis caused by UVB exposure. Finally, we compared directly the behavior of KGFR with that of the epidermal growth factor receptor (EGFR) upon UVB exposure. Surprisingly, biochemical and immunofluorescence analysis showed that EGFR, differently from KGFR, does not undergo UVB-induced tyrosine phosphorylation and internalization. Taken together, our results suggest a differential role of KGFR and EGFR in the response of epidermal cells to UVB possibly because KGFR endocytosis could be crucial for attenuation of survival signals in the suprabasal layers of human skin.
authors.affiliation: Dipartimento di Medicina Sperimentale e Patologia, Università di Roma La Sapienza, Rome, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Belleudi
authors.forename: Laura
authors.initials: L
authors.lastname: Leone
authors.forename: Laura
authors.initials: L
authors.lastname: Aimati
authors.forename: Maria Giovanna
authors.initials: MG
authors.lastname: Stirparo
authors.forename: Giorgia
authors.initials: G
authors.lastname: Cardinali
authors.forename: Cinzia
authors.initials: C
authors.lastname: Marchese
authors.forename: Luigi
authors.initials: L
authors.lastname: Frati
authors.forename: Mauro
authors.initials: M
authors.lastname: Picardo
authors.forename: Maria Rosaria
authors.initials: MR
authors.lastname: Torrisi
mesh_terms: D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle; D002966:Clathrin / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology* / Q000528:radiation effects*; D066246:ErbB Receptors / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D008024:Ligands; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D051497:Receptor, Fibroblast Growth Factor, Type 2 / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D002966:Clathrin; D008024:Ligands; D017382:Reactive Oxygen Species; D019000:Phosphotyrosine; D066246:ErbB Receptors; D051497:Receptor, Fibroblast Growth Factor, Type 2; C065104:keratinocyte growth factor receptor