FGF8, c-Abl and p300 participate in a pathway that controls stability and function of the ΔNp63αprotein

Abstract

The p63 transcription factor, homolog to the p53 tumor suppressor gene, plays a crucial role in epidermal and limb development, as its mutations are associated to human congenital syndromes characterized by skin, craniofacial and limb defects. While limb and skin-specific p63 transcriptional targets are being discovered, little is known of the post-translation modifications controlling ΔNp63α functions. Here we show that the p300 acetyl-transferase physically interacts in vivo with ΔNp63α and catalyzes its acetylation on lysine 193 (K193) inducing ΔNp63α stabilization and activating specific transcriptional functions. Furthermore we show that Fibroblast Growth Factor-8 (FGF8), a morphogenetic signaling molecule essential for embryonic limb development, increases the binding of ΔNp63α to the tyrosine kinase c-Abl as well as the levels of ΔNp63α acetylation. Notably, the natural mutant ΔNp63α-K193E, associated to the Split-Hand/Foot Malformation-IV syndrome, cannot be acetylated by this pathway. This mutant ΔNp63α protein displays promoter-specific loss of DNA binding activity and consequent altered expression of development-associated ΔNp63α target genes. Our results link FGF8, c-Abl and p300 in a regulatory pathway that controls ΔNp63α protein stability and transcriptional activity. Hence, limb malformation-causing p63 mutations, such as the K193E mutation, are likely to result in aberrant limb development via the combined action of altered protein stability and altered promoter occupancy.

Genetic regulatory pathways of split‐hand/foot malformation

“…This is supported by the SHFM observed in Dlx2/5 −/− mice (Figure ) . The split hindlimbs in Dlx5/6 −/− mice are the result of a cell‐autonomous failure of the central AER to regulate p63 and to maintain and express morphogenetic signals (Figure ) . The degeneration of the AER in Dlx5/6 −/− mice led to SHFM phenotype which is similar to the phenotype of Dactylaplasia mice .…”

“…Fgf8 functions are to sustain epithelial‐mesenchymal signaling and assure the timely generation of the correct population of mesenchymal progenitors . It in turn regulates the function and stability of ΔNp63α by increasing the binding of ΔNp63α to the tyrosine kinase c‐Abl and the level of ΔNp63α acetylation . Aberration of Fgf8 expression is hypothesized to cause malfunction of ΔNp63α (Figure ).…”

“…In order for mice to have SHFM, alterations in Fgf8 expression need to accompany abnormal expression of other genes in AER as well. Loss of Fgf8 or mutations in Fgf8 leads to abnormal ΔNp63α protein stability, failure of AER stratification, and subsequent aberrant limb development (Figure ) …”

“…45 It in turn regulates the function and stability of ΔNp63α by increasing the binding of ΔNp63α to the tyrosine kinase c-Abl and the level of ΔNp63α acetylation. 25 Aberration of Fgf8 expression is hypothesized to cause malfunction of ΔNp63α (Figure 2). In order for a normal limb to develop, Fgf8 is crucial for the correct establishment of the signaling loop within the developing limb bud.…”

“…In order for mice to have SHFM, alterations in Fgf8 expression need to accompany abnormal expression of other genes in AER as well. Loss of Fgf8 or mutations in Fgf8 leads to abnormal ΔNp63α protein stability,24,25,44 failure of AER stratification, and subsequent aberrant limb development (Figure 2) 45. All lines of evidence suggest that abnormalities of TP63, WNT10B, DLX5, DLX6, FGF8, and FGFR1 lead to dysregulation of FGF8 in the central portion of the AER and subsequently lead to misexpression of a number of AER genes, failure of its stratification, and thus SHFM (Figure 2).…”