Regulation of VDR by ΔNp63α is associated with inhibition of cell invasion
Ramakrishna Kommagani
1
Mary K. Leonard
1
Stefanie Lewis
1
Rose-Anne Romano
0
Satrajit Sinha
0
Madhavi P. Kadakia
()
1
0
Department of Biochemistry, State University of New York at Buffalo
,
NY 14203
,
USA
1
Department of Biochemistry and Molecular Biology, Boonshoft School of Medicine, Wright State University
,
Dayton, OH 45435
,
USA
Summary The p63 transcription factor has a pivotal role in epithelial morphogenesis. Multiple transcripts of the TP63 gene are generated because of alternative promoter usage and splicing. Np63 is the predominant isoform of p63 observed during epithelial morphogenesis and in human cancers. Loss of Np63 expression has been shown to promote invasiveness in a subset of human cancer cell lines. Here, we studied whether the regulation of VDR by Np63 controls the invasiveness of an ce epidermoid cancer cell line. We demonstrate that VDR ne expression is induced by all p63 isoforms, including Np63. ic Endogenous Np63 protein was observed to bind to the VDR S promoter, and silencing of endogenous Np63 resulted in diminished VDR expression. Although silencing of p63 inhibits
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Jo (Osada et al., 1998; Shimada et al., 1999; Yang et al., 1999). p63
contains three functional domains, an N-terminal transactivation
(TA), a central DNA-binding domain and an oligomerization
domain. A high degree of conservation is observed within the
DNAbinding domains of p63 and p53, therefore p63 transactivates several
p53-responsive genes (Shimada et al., 1999). The TP63 gene
generates six different isoforms: three TA isoforms (TAp63,
TAp63 and TAp63) and three N isoforms (Np63, Np63
and Np63) because of the differential promoter usage and
alternative splicing. Although p63 is not mutated in human cancers,
and unlike p53 is not considered to be a tumor suppressor, TP63
mutations have been observed in several human developmental
syndromes (Barrow et al., 2002; van Bokhoven et al., 2001; van
Bokhoven and McKeon, 2002).
p63 has a major role in development, particularly in epithelial
morphogenesis during embryonic development (Mills et al., 1999;
Yang et al., 1999). p63, in particular Np63, is highly expressed
in basal layers of stratified epithelium and is essential for
maintenance of epithelial tissue integrity. p63-knockout mice exhibit
severe developmental defects, including defects in limbs, hair
follicles, teeth and epidermal development (Mills et al., 1999; Yang
et al., 1999). The developmental abnormalities observed in p63/
mice were mainly attributed to defects in stratified epithelial
maintenance and differentiation. Additionally, although TAp63
initiates the epithelial stratification program, Np63 is indispensable
for the maintenance of epithelial stem cell proliferation and
differentiation, thus making Np63 the most physiologically
VDR expression leading to an increase in cell migration,
overexpression of p63 or VDR results in reduced cell migration
as a result of increased VDR expression. Therefore, it is
conceivable that p63 inhibits cell invasion by regulating VDR
expression. Finally, we observed that expression of p63 and VDR
overlaps in the wild-type mouse skin, but a reduced or complete
absence of VDR expression was observed in skin from p63-null
mice and in p63-null mouse embryonic fibroblasts. In
conclusion, we demonstrate a direct transcriptional regulation
of VDR by Np63. Our results highlight a crucial role for VDR
in p63-mediated biological functions.
relevant isoform to study in most epithelial systems (Koster et al.,
2004).
The loss of p63 expression is correlated with cancer progression
in various cancers, including prostate and bladder cancers (Park et
al., 2004; Parsons et al., 2001; Urist et al., 2002). An amplified
level of the Np63 isoform, which promotes proliferation by
inducing the pro-survival proteins, has been observed in squamous
cell carcinoma (Hu et al., 2002; Senoo et al., 2002; Sniezek et al.,
2004; Wu et al., 2005). Moreover, it has been shown that TAp63
isoforms promote growth arrest and apoptosis in several cancer cell
lines by inducing anti-proliferative genes (Kommagani et al., 2006;
Shimada et al., 1999; Spiesbach et al., 2005), and by inhibiting the
pro-proliferative genes (Senoo et al., 2002; Wu et al., 2005).
Interestingly, downregulation of Np63 expression leads to an
increase in cell motility and invasiveness of squamous cell
carcinoma cells (Higashikawa et al., 2007). Altogether, the above
studies suggest isoform specific functions of p63 and therefore
delineating the role of specific p63 isoforms is necessary to
understand the overall biology of p63.
Recently, we have demonstrated the transcriptional activation of
vitamin D receptor (VDR) by the TAp63 isoform (Kommagani et
al., 2006). Vitamin D receptor is a ligand-dependent transcription
factor, and is a natural receptor for the secosteroid hormone vitamin
D (...truncated)