Cell Adhesion Another important signaling axis under control
of p63 involves cell adhesion. Ablation of all p63 isoforms
in mammary epithelial MCF-10A cells causes a major
down-regulation of cell-to-matrix adhesive molecules, particularly
of integrins β1, β4 and α6, and of the matrix
protein Laminin-γ2, resulting in death by anoikis, which
can be completely prevented by expression of an shRNAinsensitive
ΔNp63α, but not by TAp63γ. Similarly, reintroduction
of integrin β4 into a p63-deficient background
can partially protect from anoikis, highlighting the importance
of cell-matrix adhesion for epithelial tissue integrity
and cell survival [37].
The transmembrane protein Perp facilitates cell-cell
adhesions by maintaining proper desmosome structure and
function. This protein, which had been previously shown to
be a p53 target, is also a direct p63 target in skin development.
Perp expression is absent in p63-null mice embryos.
Likewise, p63 ablation in mouse keratinocytes downregulates
Perp expression. Moreover, exogenous TAp63α,
TAp63γ, ΔNp63α, ΔNp63γ, and p53 are able to transactivate
Perp reporter expression, and endogenous p63 binds to a putative p53/p63 binding site in intron 1 on the
Perp gene. Of note, even though ΔNp63 isoforms are
expressed at much higher level than TAp63 isoforms, TAp63α
and TAp63γ are able to transactivate Perp expression
several folds higher than ΔNp63α and ΔNp63γ, as is
expected from their greater transactivation potential. Interestingly,
Perp-null mice develop dramatically blistering skin
and die shortly after birth, resembling some of the phenotypes
found in the p63-null mice [109].