Mutant p63 causes defective expansion of ectodermal progenitor cells and impaired FGF signalling in AEC syndrome.
Bottom Line: The AEC mutation exerts a selective dominant-negative function on wild-type p63 by affecting progenitor cell expansion during ectodermal development leading to a defective epidermal stem cell compartment.These phenotypes are associated with impairment of fibroblast growth factor (FGF) signalling resulting from reduced expression of Fgfr2 and Fgfr3, direct p63 target genes.Restoring Fgfr2b expression in p63(+/L514F) epithelial cells by treatment with FGF7 reactivates downstream mitogen-activated protein kinase signalling and cell proliferation.
Affiliation: Fondazione IRCCS SDN, Napoli, Italy.Show MeSH
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Mentions: To determine the contribution of Fgfr2b and Fgfr3b downregulation to FGF signalling and cell proliferation, we measured the levels of FGFR substrate 2α (FRS2α) tyrosine phosphorylation. In p63+/L514F primary keratinocytes, a strong reduction of Fgfr2b and Fgfr3b proteins was accompanied with a significant decrease in FRS2α phosphorylation (Fig 5A) indicating impaired activation of FGF signalling. FGF signalling leads to induction of the classical Ras/extracellular signal regulated kinase (ERK) pathway. In spite of impaired FGF receptor activity, ERK phosphorylation was unaffected in p63+/L514F keratinocytes. The presence of several other growth factors in the fully supplemented medium in which cells were grown may compensate for the impaired FGF receptor activity. In contrast, treatment of starved wild-type cells with KGF (keratinocyte growth factor or FGF-7), the Fgfr2b-specific ligand, resulted in ERK phosphorylation, whereas in mutant keratinocytes, ERK phosphorylation was impaired (Fig 5B). Restoring Fgfr2b expression by retroviral Fgfr2b transfer rescued ERK activation upon KGF treatment. As expected, EGF treatment elicited a similar induction in ERK phosphorylation in both wild-type and mutant keratinocytes, and exogenous Fgfr2b expression had no effect on EGF-induced ERK phosphorylation (Supporting Information Fig S9A) indicating a specific impairment of FGF/Ras/ERK pathway activation in mutant cells.