Association of p63 with proliferative potential in normal and neoplastic human keratinocytes

Correction of junctional epidermolysis bullosa by transplantation of genetically modified epidermal stem cells

The continuous renewal of human epidermis is sustained by stem cells contained in the epidermal basal layer and in hair follicles. Cultured keratinocyte stem cells, known as holoclones, generate sheets of epithelium used to restore severe skin, mucosal and corneal defects. Mutations in genes encoding the basement membrane component laminin 5 (LAM5) cause junctional epidermolysis bullosa (JEB), a devastating and often fatal skin adhesion disorder. Epidermal stem cells from an adult patient affected by LAM5-beta3-deficient JEB were transduced with a retroviral vector expressing LAMB3 cDNA (encoding LAM5-beta3), and used to prepare genetically corrected cultured epidermal grafts. Nine grafts were transplanted onto surgically prepared regions of the patient's legs. Engraftment was complete after 8 d. Synthesis and proper assembly of normal levels of functional LAM5 were observed, together with the development of a firmly adherent epidermis that remained stable for the duration of the follow-up (1 year) in the absence of blisters, infections, inflammation or immune response. Retroviral integration site analysis indicated that the regenerated epidermis is maintained by a defined repertoire of transduced stem cells. These data show that ex vivo gene therapy of JEB is feasible and leads to full functional correction of the disease.

Mesenchymal stem cell transplantation in a rabbit corneal alkali burn model: engraftment and involvement in wound healing

PURPOSE

To investigate whether systemically transplanted mesenchymal stem cells (MSCs) can home and engraft in tissue to promote cornea wound healing after alkali burn, as a new source for treatment.

METHODS

Corneal alkali burn was created in four group rabbits: Group I, normal bone marrow function, without MSCs transplantation; Group II, normal bone marrow function, with MSCs transplantation; Group III, bone marrow suppressed by cyclophosphamide, without MSCs; Group IV, bone marrow suppressed by cyclophosphamide, with MSCs. Clinical outcome was evaluated by cornea re-epithelization, cornea opacity, and neovascularization. Cell engraftment into bone marrow, circulation, and cornea was monitored. Immunohistochemistry, using proliferating cell nuclear antigen (PCNA), P63, vimentin, and alpha-smooth muscle actin (alpha-SMA) was carried out to assess the cell proliferative and differentiative ability.

RESULTS

At the time of 1-month follow-up, Group II rabbits showed the best clinical results with a clearer healed cornea compared with other groups. Well-formed neovascularization appeared on day 14 after alkali burn in Group II, that coincided with the maximum engraftment of MSCs. PCNA, P63, vimentin were more strongly expressed in Group II at multiple time points. DiI-labelled MSCs were differentiated into myofibroblast by the expression of alpha-SMA. Delayed and insufficient cell engraftment, with malformed neovascularization and retarded corneal wound healing was found in Groups III and IV.

CONCLUSIONS

Systemically transplanted MSCs can engraft to injured cornea to promote wound healing, by differentiation, proliferation, and synergizing with haemotopoietic stem cells.

E6/E7 expression of human papillomavirus type 20 (HPV-20) and HPV-27 influences proliferation and differentiation of the skin in UV-irradiated SKH-hr1 transgenic mice

The functional role of UV irradiation, in combination with the E6 and E7 proteins of the cutaneous human papillomavirus (HPV) types in the malignant conversion of benign papillomatous lesions, has not been elucidated. Transgenic SKH-hr1 hairless mice expressing HPV-20 and HPV-27 E6 and E7 proteins in the suprabasal compartment were generated and exposed to chronic UV irradiation. Histological and immunohistochemical examination of skin samples revealed enhanced proliferation of the epidermal layers and papilloma formation in both transgenic strains in comparison to what was observed with nontransgenic mice. Squamous cell carcinoma developed in the HPV-20 E6/E7 transgenic line as well as in the HPV-27 E6/E7 transgenic line. Several weeks after cessation of UV-B exposure, enhanced proliferation, as measured by BrdU incorporation, was maintained only in HPV-20 transgenic skin. Keratin 6 expression was increased in the transgenic mice throughout all cell layers. Expression of the differentiation markers involucrin and loricrin was reduced and disturbed. p63alpha expression was differentially regulated with high levels of cytoplasmic expression in clusters of cells in the granular layer of the skin in the transgenic lines 20 weeks after cessation of UV-B exposure, in contrast to uninterrupted staining in the nontransgenic lines. p53 was expressed in clusters of cells in nontransgenic and HPV-27 transgenic mice, in contrast to an even distribution in a higher number of cells in HPV-20 transgenic animals.

The E3 ubiquitin ligase Itch controls the protein stability of p63

p63, a member of the p53 family of transcription factors, plays an important role in epithelial development, regulating both cell cycle and apoptosis. Even though p63 activity is regulated mainly at the posttranslational level, the control of p63 protein stability is far from being fully understood. Here, we show that the Hect (homologous to the E6-associated protein C terminus)-containing Nedd4-like ubiquitin protein ligase Itch binds, ubiquitylates, and promotes the degradation of p63. The physical interaction occurs at the border between the PY and the SAM (sterile alpha motif) domains; a single Y504F mutation significantly affects p63 degradation. Itch and p63 are coexpressed in the epidermis and in primary keratinocytes where Itch controls the p63 protein steady-state level. Accordingly, p63 protein levels are significantly increased in Itch knockout keratinocytes. These data suggest that Itch has a fundamental role in the mechanism that controls endogenous p63 protein levels and therefore contributes to regulation of p63 in physiological conditions.

Cross-regulation between Notch and p63 in keratinocyte commitment to differentiation

Notch signaling promotes commitment of keratinocytes to differentiation and suppresses tumorigenesis. p63, a p53 family member, has been implicated in establishment of the keratinocyte cell fate and/or maintenance of epithelial self-renewal. Here we show that p63 expression is suppressed by Notch1 activation in both mouse and human keratinocytes through a mechanism independent of cell cycle withdrawal and requiring down-modulation of selected interferon-responsive genes, including IRF7 and/or IRF3. In turn, elevated p63 expression counteracts the ability of Notch1 to restrict growth and promote differentiation. p63 functions as a selective modulator of Notch1-dependent transcription and function, with the Hes-1 gene as one of its direct negative targets. Thus, a complex cross-talk between Notch and p63 is involved in the balance between keratinocyte self-renewal and differentiation.

The expression of p63 is associated with the differential stage in nasopharyngeal carcinoma and EBV infection

Background

Nasopharyngeal carcinoma (NPC) is common among Southern Chinese and the main histology is the undifferentiated carcinoma associated with Epstein-Barr virus (EBV) infection. p63 is a recently proved member of the p53 family based on the structural similarity to p53, but its function in NPC is still unknown. This study was aimed to investigate the association between p63 and NPC.

Results

p63 was expressed in 100%(202/202) of nasopharyngeal carcinoma (NPC) tissues but not in 29 nasopharynx inflammation and 17 non-cancerous nasopharyngeal epidermises on a tissue microarray by immunohistostaining. Further investigation suggested that the p63 expression was associated with the differential stage of NPC: p63 strong staining in Keratinizing squamous cell carcinoma, differentiated non-keratinizing NPC and undifferentiated non-keratinizing NPC presented the percentage of 5/8 (62.5%), 43/48 (92.5%) and 50/50 (100%), respectively. A significant difference (p = 0.001) existed between the keratinizing and non-keratinizing groups. No pathogenic mutations were detected in p63 gene in 12 primary NPC tissues and matched peripheral blood lymphocytes (PBL). Half-life measurement study revealed distinct stability of p63 protein in the different cell lines, especially between the carcinoma cell lines with EBV infection and the non-cancerous cell lines. The results of immunoprecipitation suggested a direct interaction between Epstein-Barr virus nuclear antigen 5 (EBNA-5) and p63 protein in NPC, and this binding would increase the stability of p63.

Conclusion

Our data suggested p63 might be used as an adjunct diagnostic marker of NPC and contributed a new way to understand the contribution of the EBV in the pathogenesis of NPC.

TA-p63-gamma regulates expression of DeltaN-p63 in a manner that is sensitive to p53

Genetic analysis indicates that TP63 is required for establishment and preservation of self-renewing progenitors within the basal layer of several epithelial structures, however, the specific contributions of transactivating (TA-p63) and dominant-negative (DeltaN-p63) isoforms remain largely undefined. Recent studies have suggested a model in which TA-p63 plays an important role in the establishment of progenitor populations in which expression of DeltaN-p63 contributes to the preservation of self-renewing capacity. Our previous studies indicate that DeltaN-p63 is a transcriptional target of p53, however, the absence of overt epithelial deficiencies in p53-/- mice and reports of increased expression of DeltaN-p63 in p53-/- mice suggest p53-independent mechanisms also contribute to expression of DeltaN-p63. Here, we present data indicating that, prolonged loss of p53 leads to the activation of a p53-independent mechanism for transcriptional regulation of DeltaN-p63. This p53-independent mechanism is sensitive to ectopic p53 but not to a p53 mutant that lacks the transactivation domain. We further show that in cells in which p53 is expressed TA-p63-gamma protein is destabilized in a manner that is p53 dependent and sensitive to pharmacologic inhibition of the 26S proteosome. Consistent with this observation, we demonstrate that loss of p53 leads to the stabilization of TA-p63-gamma that is reversible by ectopic p53. Finally, we present evidence that disruption of TA-p63-gamma expression leads to decreased expression of DeltaN-p63 and that overexpression of TA-p63-gamma was sufficient to enhance the activity of the DeltaN-p63 promoter. Taken together, our studies indicate that TA-p63-gamma is capable of activating expression of DeltaN-p63 and that this mechanism may account for p53-independent expression of DeltaN-p63.

Delineation of the ADULT syndrome phenotype due to arginine 298 mutations of the p63 gene

The ADULT syndrome (Acro-Dermato-Ungual-Lacrimal-Tooth, OMIM 103285) is a rare ectodermal dysplasia associated with limb malformations and caused by heterozygous mutations in p63. ADULT syndrome has clinical overlap with other p63 mutation syndromes, such as EEC (OMIM 604292), LMS (OMIM 603543), AEC (106260), RHS (129400) and SHFM4 (605289). ADULT syndrome characteristics are ectrodactyly, ectodermal dysplasia, mammary gland hypoplasia and normal lip and palate. The latter findings allow differentiation from EEC syndrome. LMS differs by milder ectodermal involvement. Here, we report three new unrelated ADULT syndrome families, all with mutations of arginine 298. On basis of 16 patients in five families with R298 mutation, we delineate the ADULT syndrome phenotype. In addition, we have documented a gain-of-function effect on the dNp63gamma isoform caused by this mutation. We discuss the possible relevance of oral squamous cell carcinoma in one patient, who carries this p63 germline mutation.

An autoregulatory loop directs the tissue-specific expression of p63 through a long-range evolutionarily conserved enhancer

p63, a p53 family member, is essential for the development of various stratified epithelia and is one of the earliest markers of many ectodermal structures, including the epidermis, oral mucosa, apical ectodermal ridge, and mammary gland. Genetic regulatory mechanisms controlling p63 spatial expression during development have not yet been defined. Using a genomic approach, we identified an evolutionarily conserved cis-regulatory element, located 160 kb downstream of the first p63 exon, which functions as a keratinocyte-specific enhancer and is sufficient to recapitulate expression of the endogenous gene during mouse embryogenesis. Dissection of the p63 enhancer activity revealed a positive autoregulatory loop in which the p63 proteins directly bind to and are essential regulators of the enhancer. Accordingly, transactivating p63 isoforms induce endogenous p63 expression in cells that do not normally express this gene, whereas dominant negative isoforms suppress p63 expression in keratinocytes. In addition the transcription factor AP-2 also binds to the enhancer and cooperates with p63 to induce its activity. These results demonstrate that a long-range autoregulatory loop is involved in the regulation of p63 expression during embryonic development and in adult cells.

Immunohistochemical expression of p16, p53, and p63 in colorectal adenomas and adenocarcinomas

PURPOSE

The aim of this study was to investigate the immunohistochemical expression of p16, p53, and p63 proteins according to some pathologic parameters related to colorectal adenomas and adenocarcinomas such as grade of dysplasia and histologic type.

METHODS

Immunohistochemistry with the antibodies p16, p53, and p63 was performed in tubular, tubular-villous, and villous adenomas (n = 30) and in well, moderately, and poorly differentiated adenocarcinomas (n = 30). The p63-positive cases were submitted to double immunolabeling with the cytokeratin 5 (CK5).

RESULTS

The p16 and p53 labelings were observed in some adenomas and adenocarcinomas but without any association with p63 expression, histologic type, or grade of differentiation of the neoplasm. P63 expression was found mainly in the villous adenomas and in the poorly differentiated adenocarcinomas. The poorly differentiated adenocarcinomas also exhibited coexpression of CK5 and p63.

CONCLUSIONS

Despite both p16 and p53 having been detected in colorectal neoplasms, they were not related to the different histologic variables nor to the expression of p63. However, p63 expression was closely associated with villous adenomas and poorly differentiated adenocarcinomas. Thus, p63 may represent a marker of poor differentiation in colorectal neoplasms. The coexpression of p63 and CK5 observed in this study could be related to divergent differentiation during the development of colorectal cancer, although further studies are warranted to refine the understanding of this process.

Defining the regulatory elements in the proximal promoter of DeltaNp63 in keratinocytes: Potential roles for Sp1/Sp3, NF-Y, and p63

p63, a homolog of the tumor suppressor p53, plays an important role in the formation of stratified epithelium such as those in the epidermis of the skin. The p63 gene gives rise to multiple functionally distinct protein isoforms, including the DeltaNp63 class of isoforms, which lacks the N-terminal transactivation domain and is synthesized from an internal promoter. DeltaNp63 proteins are the predominant isoforms expressed in keratinocytes and are thought to be important for maintenance of the proliferative capacity of these cells. Here, we have examined the transcriptional control mechanisms that govern the expression DeltaNp63 in keratinocytes. We first performed DNase I hypersensitive site mapping and demonstrated that the promoter region of DeltaNp63 is in open chromatin state in keratinocytes. To identify the cis-elements that regulate DeltaNp63, we have performed transient transfection assays in keratinocytes with several DeltaNp63 promoter constructs. This identified a short evolutionarily conserved fragment that harbors most of the transcriptional activity of the DeltaNp63 promoter. Biochemical studies of this element have revealed critical roles for CCAAT-box-binding factor (CBF/NF-Y) and Sp1/Sp3 family of proteins. In addition, our data suggest that DeltaNp63 is recruited to and can activate its own promoter, possibly through protein-protein interactions, thus providing an auto-regulatory loop of self-regulation. These studies support the notion that unique and distinct pathways control the expression of individual p53 family members and their various isoforms.

A dominant negative form of p63 inhibits apoptosis in a p53-independent manner

Stem cells are a source of differentiated cells in multiple tissues. If genetic alterations occur in stem cells, the problem persists and malignant cancers may arise. DeltaNp63alpha-a homologue of the tumor suppressor p53-is exclusively expressed in proliferating undifferentiated epithelial cells and cancer cells of epidermal origin. Here, we show that DeltaNp63alpha antagonizes DNA damage-induced apoptosis in a p53-independent manner. We found that upon cellular injury, DeltaNp63alpha must be downregulated before apoptotic program can be activated. The 5637 cell line has abundant levels of DeltaNp63alpha and mutant p53, and it is resistant to DNA damage-induced apoptosis. The knockdown of DeltaNp63alpha by RNA interference sensitized these cells to apoptosis upon genotoxic insult. This suggests that DeltaNp63alpha plays an anti-apoptotic role regardless of the p53 status. Considering the frequent mutations of p53 in tumor cells, our results provide important implications for the treatment of cancers in which p63 is amplified.

The expression of p63 in basal cell carcinomas and association with histological differentiation

BACKGROUND

We aim to examine p63 expression in basal cell carcinomas (BCCs) and to investigate association with their histopathological differentiation subtypes.

METHODS

Eighty-four BCCs were classified according to the histopathologic differentiation subtypes. Immunohistochemistry using monoclonal antibody against p63 was performed.

RESULTS

In nontumoral skin, p63 expression was consistently seen in basal/suprabasal cells of epidermis, hair matrix cells, and outer root sheath of the hair follicle. In BCCs, the cases were distributed as 47 undifferentiated, 28 differentiated (16 adenoid and 12 keratotic), and nine superficial. The nuclear p63 expression was negative in two cases, whereas 64 BCCs (76.2%) showed homogeneous p63 immunostaining. There was no statistically significant difference between p63 expression and histological differentiation subtypes (p > 0.05). The expression of p63 was found strongly and diffuse in 72.3% of solid undifferentiated and 82.1% differentiated and in 77.8% of superficial type BCCs.

CONCLUSIONS

p63 is consistently expressed in epidermal basal/suprabasal and adnexal basal cells. Most BCCs have higher homogeneous p63 expression than nontumoral epidermis, which is not changed according to histological differentiation subtypes. Thus, overexpression of p63 in all histological subtypes may confirm that basaloid progenitor cells are linked tumor-cell lineage and have a role in the tumorigenesis of BCC.

Expression of CD90 on keratinocyte stem/progenitor cells

BACKGROUND

The identification and purification of keratinocyte stem cells (KSCs) that are capable of self-renewal and maintenance of differentiating cell populations could contribute both to our understanding of the biology of these cells, and to significant clinical applications, such as the culturing of keratinocytes for transplantation to severe burn wounds. Here, we report the detection of CD90(+) cells in cultured normal human epidermal keratinocytes and adult skin.

OBJECTIVES

To investigate the biological function of CD90(+) and CD90(-) keratinocytes.

METHODS

CD90(+) and CD90(-) keratinocytes were purified from adult skin and cultured keratinocytes using fluorescent activated cell sorting, and their biological abilities were analysed using both in vitro and in vivo assays.

RESULTS

Flow cytometry (FCM) analysis identified approximately 18% of post-primary neonatal keratinocytes as CD90(+). However, during expansion of the culture, the expression level of CD90 rapidly decreased to about 2.5% at passage 10, while most of the keratinocytes maintained expression of alpha6 integrin. Purified CD90(+) keratinocytes demonstrated a sixfold higher cell growth rate than CD90(-) cells and the ability to form large (over 3 mm in diameter) colonies. We then quantitatively evaluated both populations using a previously described in vivo human epidermal cyst formation assay. Enhanced green fluorescent protein (EGFP)-labelled CD90(+) or CD90(-) keratinocytes were subcutaneously injected into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Six weeks after transplantation, EGFP(+) cell clusters in human epidermal cysts were evaluated using image analysis software. EGFP(+) cell cluster areas in the basal layer, derived from EGFP(+) CD90(+) cells, were eightfold larger than clusters of EGFP(+) CD90(-) cells. Furthermore, immunohistochemical staining and FCM analysis indicated that CD90 was expressed in most of the basal layer of the normal human epidermis.

CONCLUSIONS

These results indicated that CD90 is a useful marker for the detection of human KSC-enriched populations in cultured human keratinocytes.

Stem/progenitor and intermediate cell types and the origin of human prostate cancer

Theories of cell lineage in human prostatic epithelium, based on protein expression, propose that basal and luminal cells: 1) are either independently capable of self-renewal or 2) arise from stem cells expressing a full spectrum of proteins (p63, cytokeratins CK5/14, CK8/18, and glutathione-S-transferase-pi [GST-pi]) similar to cells of the embryonic urogenital sinus (UGS). Such embryonic-like stem cells are thought to give rise to mature basal cells and secretory luminal cells. By single cell cloning of an immortalized, normal human prostate-derived, non-tumorigenic RWPE-1 cell line, we isolated and characterized two epithelial cell types, WPE-stem and WPE-int. WPE-stem cells show: i) strong, sixfold greater nuclear expression of p63; ii) nearly twofold greater expression of CK14; iii) threefold less CK18, and iv) low androgen receptor (AR) expression as compared with WPE-int cells. WPE-stem cells are androgen-independent for growth and survival. WPE-int cells express very low p63 and CK5/14, and high CK18. WPE-int cells are androgen-independent for growth and survival but are highly responsive as shown by androgen induction of AR and prostate specific antigen (PSA). Compared with WPE-int cells, WPE-stem cells are smaller and show more rapid growth. WPE-stem cells can grow in an anchorage-independent manner in agar with 4.5-fold greater cloning efficiency and as free floating "prostaspheres" in liquid medium; and express over 40-fold higher matrix metalloproteinase-2 activity. These results indicate that WPE-stem cells express several features characteristic of stem/progenitor cells present in the UGS and in adult prostatic epithelium. In contrast, WPE-int cells have an intermediate, committed phenotype on the pathway to luminal cell differentiation. We propose that in normal prostatic epithelium, cells exist at many stages in a continuum of differentiation progressing from stem cells to definitive basal and luminal cells. Establishment and characterization of clones of human prostatic epithelial cells provide novel models for determining cell lineages, the origin of prostate cancer, and for developing new strategies for tumor prevention and treatment.

Cell size correlates with phenotype and proliferative capacity in human corneal epithelial cells

This study investigated whether cell size correlates with phenotype and proliferative capacity in human corneal epithelial cells. Primary cultured human corneal epithelial cells were sorted by flow cytometry based on forward scatter profile in comparison with the profile of beads of known size. Four fractions (A, B, C, and D) of cells ranging in size from 10 to 16, 17 to 23, 24 to 30, and >or=31 microm in diameter, respectively, were collected to evaluate their 5-bromo-2-deoxyuridine (BrdU) label retention properties, cell phenotype, and clonal growth capacity on a 3T3 fibroblast feeder layer. Among these four populations, cell size was shown to positively correlate with the expression of the differentiation markers keratin (K) 3, K12, and involucrin and inversely with the levels of stem cell-associated markers DeltaNp63 and ABCG2 and with colony-forming efficiency (CFE) and growth capacity. Population A with the smallest size, accounting for 11.0%+/-4.5% of the entire population, contained the greatest number of BrdU label-retaining slow-cycling cells, displayed the highest percentage of cells immunopositive to p63 and ABCG2 and negative to K3 and involucrin, expressed the highest levels of DeltaNp63 and ABCG2 mRNA and the lowest levels of K3, K12, and involucrin, and possessed the highest CFE and growth capacity. These findings suggest that cell size correlates with cell differentiation phenotypes and proliferative capacity in human corneal epithelial cells. The smallest cells in population A seem to be enriched for putative stem cells, and small cell size may represent one of the important properties of adult corneal epithelial stem cells.

The promyelocytic leukaemia protein tumour suppressor functions as a transcriptional regulator of p63

p63 plays unique developmental roles in epidermal morphogenesis, despite its structural similarity with p53. The p63 gene has two distinct promoters, coding for proteins containing an N-terminal transactivation domain (TA isoforms) and for proteins lacking this region (DeltaN isoforms). The full-length transcriptionally active TAp63 isoforms are capable of transactivating the majority of the p53 target promoters thus inducing cell cycle arrest and apoptosis. On the contrary, the DeltaNp63 isoforms seem to counteract the transactivation activities of p53 and TAp63 proteins, thus possibly conferring a proliferative advantage to cancer cells. However, the molecular mechanisms controlling the transcriptional activity of p63 remain largely unclear. Here we present data indicating that (i) the promyelocytic leukaemia protein (PML) physically interacts with p63, (ii) p63 is localized into the PML nuclear-bodies (PML-NBs) in vivo, and (iii) PML regulates p63 transcriptional activity. We show that the interaction of p63 with PML increases the levels of p63 in cultured cells as well as its ability to transactivate the p53-responsive elements of the GADD45, p21 and bax promoters. These data are consistent with a general role for PML as a functional modulator of all the p53 family members. Our findings strengthen the relevance of the cross talk between PML and the p53 family members, imply a new tumour suppressive function of PML and unveil a possible role for PML in epidermal morphogenesis and differentiation.

p63 and epithelial biology

The transcription factor p63 is a homologue of the tumor suppressor p53. Unlike p53, which is dispensable for normal development, p63 is critical for the development of stratified epithelial tissues such as epidermis, breast, and prostate. p63 encodes multiple protein isoforms with both transactivating and transcriptional repressor activities that can regulate a wide spectrum of target genes. p63 is also implicated in tumor formation and progression in stratified epithelia, with evidence for both tumor suppressive and oncogenic properties. This review will examine current data and hypotheses regarding the role of p63 in the development, maintenance, and tumorigenesis of stratified epithelium.

p63 mediates survival in squamous cell carcinoma by suppression of p73-dependent apoptosis

We demonstrate that deltaNp63alpha is an essential survival factor in head and neck squamous cell carcinoma (HNSCC) through its ability to suppress p73-dependent apoptosis. Inhibition of endogenous p63 expression by RNAi induces apoptosis selectively in HNSCC cells that overexpress deltaNp63alpha. Knockdown of p63 induces the proapoptotic bcl-2 family members Puma and Noxa, and both their induction and subsequent cell death are p53 independent but require transactivating isoforms of p73. Inhibition of p73-dependent transcription by deltaNp63alpha involves both direct promoter binding and physical interaction with p73. In HNSCC cells lacking endogenous deltaNp63alpha expression, bcl-2 is instead upregulated and can suppress p73-mediated death. Together, these data define a pathway whereby deltaNp63alpha promotes survival in squamous epithelial malignancy by repressing a p73-dependent proapoptotic transcriptional program.

Pathways involved in sunburn cell formation: deregulation in skin cancer

The incidence of squamous cell carcinoma of the skin is rising worldwide for decades. Chronic exposure to sunlight is the most important environmental risk factor for this type of skin cancer. This is predominantly due to the DNA damaging effect of ultraviolet-B (UVB) in sunlight. UVB induces also sunburn cells, i.e. apoptotic keratinocytes, which is a crucial protective mechanism against the carcinogenic effects of UVB irradiation. This process is regulated by a wide range of molecular determinants involved in the balance between pro- and anti-apoptotic pathways. Growing evidence suggests that the deregulation of this balance by chronic UVB irradiation, contributes to the development of skin cancer. This review gives a brief summary of major known pathways involved in the regulation of keratinocyte survival and cell death upon UVB damage and discusses the contribution of the deregulation of these cascades to photocarcinogenesis.

A lack of prognostic significance regarding DeltaNp63 immunoreactivity in lung cancer

DeltaNp63 is an isoform of the p53 homologue p63, which lacks an amino-terminal transactivation domain and antagonizes the induction of the gene expression by Deltap63. The aim of this study was to detect the DeltaNp63 expression in lung cancer using immunohistochemical (IHC) staining, and to evaluate the relationship between theDeltaNp63 expression level and the prognosis based on resected lung cancer tissues specimens from the of patients. We used immunohistochemistry to analyze the protein expression of DeltaNp63 in paraffin-embedded tumor samples from 161 well-characterized squamous cell carcinoma patients and compared the expression level of DeltaNp63, clinical variables and the survival outcome. Seventy-seven patients (47.8%) showed positive staining for DeltaNp63 in the nuclei of tumor cells. No significant difference was observed between the DeltaNp63 expression and the gender, age at operation, pathologic stage, pathologic T status, and pathologic N status. Based on the actuarial survival method, Kaplan-Meier method, and the log-rank test, the DeltaNp63 expression was not associated with survival for lung cancer. Differences in survival remained insignificant even after lung cancer patients were stratified according to stage or differentiation. The prognostic effects of DeltaNp63 expression do not appear to act as an important prognostic indicator in lung cancer. Our findings do not support that immunocytochemical markers demonstrate a relevant prognostic role in lung cancer.

Dlx genes, p63, and ectodermal dysplasias

Many events in vertebrate morphogenesis and organogenesis develop from epithelial/mesenchymal interactions. These processes involve a series of sequential and reciprocal interactions between the thickened epithelial sheets and underlying mesenchymal cells. Much has been learned from in vitro assays and knockout experiments in mice on the early signaling molecules that regulate the initial stages of the epithelial/mesenchymal interactions. In this review, we discuss effectors of these initial signals, specifically the p63 and Dlx families of transcription factors, that play central roles in embryonic patterning and regulation of different developmental processes, and provide a review of some of the mutations in these genes that have been associated with ectodermal dysplasias (EDs).

P63 deficiency: a failure of lineage commitment or stem cell maintenance?

A critical role for p63 in the development of stratified epithelia, such as the epidermis, has been recognized since the generation of mice lacking p63 expression. The molecular role of p63 in epidermal morphogenesis, however, remained controversial. The epidermal phenotype of p63-/- mice, which are born with a single-layered surface epithelium instead of a fully stratified epidermis, suggested that p63 could have a role in stem cell maintenance or in the commitment to stratification. In this review, we discuss evidence suggesting that p63 is required for the commitment to stratification, making p63 the earliest known gene expressed in the developing epidermis that is specific for the keratinocyte lineage.

Characterization of putative stem cell phenotype in human limbal epithelia

This study evaluated proposed molecular markers related to stem cell (SC) properties with the intention of characterizing a putative SC phenotype in human limbal epithelia. Human corneal and limbal tissues were cut in the vertical and horizontal meridians for histology, transmission electron microscopy (TEM), and immunostaining. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization were used to evaluate gene expression. TEM showed that the limbal basal cells were small primitive cells. Immunostaining disclosed that p63, ABCG2 and integrin alpha9 were primarily expressed by the basal epithelial cells of limbus. Antibodies against integrin beta1, epidermal growth factor receptor (EGFR), K19, enolase-alpha, and CD71 stained the basal cells of the limbus more brightly than the suprabasal epithelia. Integrin alpha6, nestin, E-cadherin and connexin 43 did not stain the limbal basal cells, but the suprabasal epithelia of the cornea and limbus showed strong immunoreactivity. K3 and involucrin stained only corneal and limbal superficial cells. RT-PCR showed higher levels of p63, ABCG2 and integrin alpha9 mRNA, but lower levels of K3, K12 and connexin 43 expressed in the limbal epithelia than the corneal epithelia. In situ hybridization showed that p63 transcripts were located in basal layer of the limbal epithelium. This work suggests that the basal epithelial cells of the limbus are p63, ABCG2 and integrin alpha9 positive, and nestin, E-cadherin, connexin 43, involucrin, K3, and K12 negative, with relatively higher expression of integrin beta1, EGFR, K19, and enolase-alpha. This putative SC phenotype may facilitate the identification and isolation of limbal epithelial SCs.

Expression of p63 in reactive hyperplasias and malignant lymphomas

p63 is a recently described p53 homologue. It is involved in survival and differentiation of reserve/stem cells in epithelia. To obtain new insights into the role of p63 in malignant lymphomas (MLs), immunohistochemical staining for p63 and p53 was performed in 126 cases of MLs. p63 was expressed in 38 cases of MLs (30.2%) including 32/61 cases (52.5%) of diffuse large B-cell lymphoma (DLBCL), 1/8 cases (12.5%) of precursor T-lymphoblastic lymphoma (T-LBL), 4/14 cases (28.6%) of follicular lymphoma, 1/6 cases (16.7%) of T/NK cell lymphoma. Among p63 positive cases, p63 was strongly expressed in 15/32 cases of DLBCL and 1/1 case of T-LBL. p63 was not expressed in mantle cell lymphomas, peripheral T-cell lymphomas, marginal zone B-cell lymphomas, plasma cell myelomas and Hodgkin's lymphomas. p63 was coexpressed with p53 in 18/38 p63 positive cases in which only 4 cases were strongly coexpressed. All p63+/p53+ cases were DLBCL. p63 overexpression (above 30%) cases showed significant poor survival (p=0.0228) in DLBCL. However, there was no statistically significant correlation between p63 expression and IPI score on Multivariate analysis. We could speculate that p63 could act indirectly as an oncogene by inhibiting p53 functions. Stage of differentiation of neoplastic lymphocytes appears to have a correlation with p63 expression in MLs.

Developmental and cellular factors underlying corneal epithelial dysgenesis in the Pax6+/- mouse model of aniridia

Heterozygosity for a PAX6 deficiency (PAX6+/-) results in low levels of the PAX6 transcription factor and causes aniridia. Corneal changes in aniridia-related keratopathy (ARK) include peripheral pannus and epithelial abnormalities, which eventually result in corneal opacity and contribute to visual loss. The corneal abnormalities of Pax6+/- mice provide an excellent model for the corneal changes seen in PAX6+/- humans. The aim of the present study was to investigate the contributions of different factors (including altered cell proliferation, abnormal epithelial differentiation and incursion of the conjunctival epithelium) that may underlie the pathogenesis of the corneal changes caused by low levels of Pax6 in heterozygous Pax6+/Sey-Neu (Pax6+/-) mice. BrdU incorporation showed enhanced proliferation of Pax6+/- corneal epithelium compared to wild-type controls and analysis of p63 (a marker of high proliferative potential) revealed a slight increase in frequency of p63-positive basal corneal epithelial cells in Pax6+/- mice. Immunohistochemical investigation of K12 (a Pax6-regulated marker of corneal epithelial differentiation) in 2-52-week-old mice showed that K12 expression was delayed and down-regulated in the Pax6+/- corneal epithelium, implying that differentiation of the Pax6+/- corneal epithelium was delayed and abnormal. Goblet cells were identified within the peripheral corneal epithelium of the Pax6+/- eyes, but some were surrounded by cells expressing K12, suggesting they may have arisen in situ in the corneal epithelium. These findings suggest that low levels of Pax6 may be directly responsible for failure or delay of proper differentiation of the corneal epithelial cells, but the proliferative component of the mutant epithelium is probably not impaired. This abnormal differentiation suggests that ARK is not entirely attributable to a limbal stem cell deficiency.

p63 expression in odontogenic cysts

A total of 123 cases of odontogenic cysts, distributed as follows: 30 follicular (FC), 35 radicular (RC), 53 keratocysts, 1 glandular odontogenic and 4 calcifying odontogenic cysts, were analysed by immunohistochemistry for expression of p63, a component of p53 protein family. In RCs p63 positivity was not only in basal and parabasal layers but also in the intermediate layer and about 1/3 of cases displayed a percentage of stained cells comprised between 0 and <5%, and about 2/3 between >5% and <50%. In FCs positivity was confined to basal and parabasal layers of the epithelium and in the majority of FCs the stained cells were comprised between 0 and <5%. OKCs displayed the most intense and diffuse p63 labeling. In conclusion, these data suggest that p63 expression may be useful to identify cysts type with more aggressive and invasive phenotype supporting the hypothesis of a suprabasal proliferative compartment in OKCs.

Expression of p63 in Diffuse Large B-Cell Lymphoma

The p63 gene, a homolog of the tumor suppressor gene TP53, maps to chromosome 3q27-28, a region frequently displaying genomic amplification in squamous cell carcinomas. p63 is expressed in a variety of epithelial tissues and has been reported to be critical for the normal development of stratified epithelia, including skin epidermis. In a previous study, the authors reported the expression of p63 in occasional cells in the germinal center of lymph nodes and also observed p63 expression in B-cell lymphomas, among other tumor types surveyed in that analysis. The present study was conducted to further analyze the potential clinical significance of identifying p63 expression, assessing a larger cohort of well-characterized patients with diffuse large B-cell lymphoma (DLBCL) (n = 172 cases) and a panel of established lymphoma cell lines. p63 expression at the microanatomic detail was examined by immunohistochemistry using a monoclonal antibody (clone 4A4), while distinction of p63 isoforms was analyzed by Western blotting and reverse transcription-polymerase chain reaction using isoform-specific primers. The authors found that a subset of DLBCL (32% of cases) expressed p63 in the nuclei of neoplastic lymphocytes. Examination of the different p63 isoforms revealed that the DeltaNp63 species was expressed by only one cell line, while the other p63 isoforms were found in most cell lines analyzed. The authors also observed that p63 expression correlated with high proliferative index, as assessed by Ki-67 immunostaining. Even though in univariate analysis p63 expression did not correlate with overall survival, the association of p63 with increased proliferative index suggests its involvement in DLBCL tumor progression.

The p53 Gene Family: Control of Cell Proliferation and Developmental Programs

For a quarter of a century the gene p53 has attracted close attention of scientists who deal with problems of carcinogenesis and maintenance of genetic stability. Multicellular organisms on our planet owe their rich evolution in many respects to the ability of this gene to protect cells from oncogenic transformation and harmful changes in DNA. A relatively recent discovery of structural p53 homologs, the genes p63 and p73, which seem to have more ancient roots, has roused keen interest in their function. Do they carry out oncosuppressor functions in partnership with p53 or do they possess their own specific functions? This review analyzes data on p53, p63, and p73 functional activity at the levels of the molecule, cell, and whole organism with the accent on examination of specific p63/p73 targets indicating a unique role of these genes in control of developmental processes.

DNA-binding and transactivation activities are essential for TAp63 protein degradation

The p53-related p63 gene encodes six isoforms with differing N and C termini. TAp63 isoforms possess a transactivation domain at the N terminus and are able to transactivate a set of genes, including some targets downstream of p53. Accumulating evidence indicates that TAp63 plays an important role in regulation of cell proliferation, differentiation, and apoptosis, whereas transactivation-inert deltaNp63 functions to inhibit p63 and other p53 family members. Mutations in the p63 gene that abolish p63 DNA-binding and transactivation activities cause human diseases, including ectrodactyly ectodermal dysplasia and facial clefting (EEC) syndrome. In this study, we show that mutant p63 proteins with a single amino acid substitution found in EEC syndrome are DNA binding deficient, transactivation inert, and highly stable. We demonstrate that TAp63 protein expression is tightly controlled by its specific DNA-binding and transactivation activities and that p63 is degraded in a proteasome-dependent, MDM2-independent pathway. In addition, the N-terminal transactivation domain of p63 is indispensable for its protein degradation. Furthermore, the wild-type TAp63gamma can act in trans to promote degradation of mutant TAp63gamma defective in DNA binding, and the TA domain deletion mutant of TAp63gamma inhibits transactivation activity and stabilizes the wild-type TAp63 protein. Taken together, these data suggest a feedback loop for p63 regulation, analogous to the p53-MDM2 feedback loop.

Expression of beta-catenin, p63 and CD34 in hair follicles during the course of androgenetic alopecia

During the hair growth cycle, the hair follicle appears to recapitulate part of its embryogenesis where both beta-catenin and p63 participate. The aim of the present study was to investigate the hypothesis that beta-catenin and p63 protein may be involved in the pathogenesis of androgenetic alopecia. Second, expression of CD34 protein was used to assess the capillary density of the affected skin. Cadavers were used as samples and the results showed that analysis of beta-catenin, p63 and CD34 expressions in human cadaverous scalp skin by immunohistochemical techniques were possible. We detected a higher expression of p63 in occipital skin in comparison to the affected frontal areas. However, we found only minimal changes in beta-catenin expression comparing frontal and occipital areas. A completely new finding was the expression of CD34 positive cells in the outer root sheath of hair follicles.

p63 deficiency activates a program of cellular senescence and leads to accelerated aging

The p53 tumor suppressor plays a key role in organismal aging. A cellular mechanism postulated to drive the aging process is cellular senescence, mediated in part by p53. Although senescent cells accumulate in elderly individuals, most studies have relied on correlating in vitro senescence assays with in vivo phenotypes of aging. Here, using two different mouse models in which the p53-related protein p63 is compromised, we demonstrate that cellular senescence and organismal aging are intimately linked and that these processes are mediated by p63 loss. We found that p63(+/-) mice have a shortened life span and display features of accelerated aging. Both germline and somatically induced p63 deficiency activates widespread cellular senescence with enhanced expression of senescent markers SA-beta-gal, PML, and p16(INK4a). Using an inducible tissue-specific p63 conditional model, we further show that p63 deficiency induces cellular senescence and causes accelerated aging phenotypes in the adult. Our results thus suggest a causative link between cellular senescence and aging in vivo, and demonstrate that p63 deficiency accelerates this process.

Unique domain functions of p63 isotypes that differentially regulate distinct aspects of epidermal homeostasis

p63 is critical for squamous development and exists as multiple isotypes of two subclasses, TA and DeltaN. DeltaNp63 isotypes can antagonize transcription by TAp63 and p53, and are highly expressed in squamous cell cancers. Using mouse keratinocytes as a biological model of squamous epithelium, we show that multiple p63 isotypes, DeltaN- and TA-containing, are expressed and differentially modulated during in vitro murine keratinocyte differentiation. DeltaNp63alpha declines with Ca2+-induced differentiation, while a smaller DeltaN-form, DeltaNp63s, persists, suggesting unique functions of the two DeltaN-forms. To investigate the impact of dysregulated p63 expression that is observed in cancers and to define the biological contribution of the different domains of the p63 isotypes, DeltaNp63alpha, DeltaNp63p40, TAp63alpha, TAp63gamma or beta-galactosidase were overexpressed in primary murine keratinocytes. Microarray, RT-PCR and western blot analyses revealed that overexpression of DeltaNp63p40, which lacks the entire alpha-tail present in DeltaNp63alpha, permits expression of a full panel of differentiation markers. This is in contrast to overexpression of the full-length DeltaNp63alpha, which blocks induction of keratin 10, loricrin and filaggrin. These findings support a role for the alpha-tail of DeltaNp63alpha in blocking differentiation-specific gene expression. Overexpression of either TAp63 isotype permits keratin 10 and loricrin expression, thus the alpha-terminus requires the cooperation of the DeltaN domain in blocking early differentiation. However, both TA isotypes block filaggrin induction. The DeltaN-terminus is sufficient to maintain keratinocytes in a proliferative state, as both DeltaN forms block Ca2+-mediated p21WAF1 induction and S-phase arrest, while sustaining elevated PCNA levels. No alteration in cell cycle regulation was observed in keratinocytes overexpressing TAp63alpha or TAp63gamma. Clarifying the functional distinctions between p63 isotypes and domains will help to elucidate how their dysregulation impacts tumor biology and may suggest novel therapeutic strategies for modulating behavior of tumor cells with altered expression of p53 family members.

Isoforms of DeltaNp63 and the migration of ocular limbal cells in human corneal regeneration

The p63 gene generates transactivating and N-terminally truncated transcripts (DeltaNp63) initiated by different promoters. Alternative splicing gives rise to three different C termini, designated alpha, beta, and gamma. In the ocular epithelium, the corneal stem cells, which are segregated in the basal layer of the limbus, contain the alpha isoform but not beta or gamma. Holoclones derived from the limbus are rich in alpha, meroclones contain little, and paraclones contain none. In normal resting corneal epithelium, p63 of all isoforms is absent. Upon corneal wounding, cells originating from the limbus and containing alpha migrate progressively through the epithelium of the peripheral and central cornea. In the absence of an attached limbus, no alpha isoform appears in the corneal epithelium. When migrating cells containing the alpha isoform appear in the wounded corneal epithelium, they are confined to the basal layer, but the suprabasal cells, not only of the cornea but of the limbus as well, contain mRNA encoding beta and gamma. These data support the concept that the alpha isoform of p63 is necessary for the maintenance of the proliferative potential of limbal stem cells and their ability to migrate over the cornea. The beta and gamma isoforms, being suprabasal and virtually absent from the resting limbus, are not stem cell markers but are likely to play a role in epithelial differentiation specifically during the process of corneal regeneration.

Molecular aetiology and pathogenesis of basal cell carcinoma

Recent insights into the cell biology of the epidermis and its appendages are transforming our understanding of the pathogenesis of basal cell carcinoma (BCC). The significant progress that has been made warrants a comprehensive review of the molecular and cellular pathology of BCC. The items addressed include environmental and genetic risk factors, the biology of the putative precursor cell(s), and the contribution of aberrations in processes such as apoptosis, cell proliferation, differentiation and signalling to carcinogenesis. Furthermore, established and novel treatment modalities are discussed with particular attention to future biological approaches.

p63 overexpression associates with poor prognosis in head and neck squamous cell carcinoma

p63 belongs to a protein family that includes 2 structurally related proteins, p53 and p73. The aim of this study was to investigate the biologic role of p63 in oral tumorigenesis and its possible role as prognostic marker in oral cancer. Ninety-four cases of oral squamous cell carcinoma and 10 cases of normal mucosa were analyzed for p63 expression by immunohistochemistry. Normal oral mucosa showed a basal and parabasal expression of p63. Five (5.3%) cases of oral cancer showed less than 10% of positive tumor cells; in 33 (35.1%) cases the positive tumor cells comprised between 10% and less than 30%, in 36 (38.3%) cases the positive tumor cells comprised between 30% and less than 50%, and in 20 (21.3%) cases the positive tumor cells were more than 50%. There was also a statistically significant correlation between p63 expression and tumor differentiation: p63 expression was amplified in poorly differentiated tumors (P < .05). When analyzed for prognostic significance, patients with perineural infiltration had poorer survival rates than the group with no perineural infiltration (P < .05) and patients with increased p63 expression had poorer survival rates than the group with reduced p63 expression (P < .05). The statistical analysis showed no significant correlation between p63 expression, sex, age, tumor size, staging, recurrence, and metastasis. Cases with diffuse p63 expression were more aggressive and poorly differentiated and related to a poorer prognosis. These data suggest that p63 expression may be useful to identify cases of oral squamous cell carcinoma with more aggressive and invasive phenotype providing novel diagnostic and prognostic information on individual patient survival with oral cancers.

Expression of p63 and p73 in ameloblastomas

BACKGROUND

To clarify the role of p53 homologs in oncogenesis and cytodifferentiation of odontogenic tumors, expression of p63 and p73 was analyzed in ameloblastomas as well as tooth germs.

METHODS

Tissue specimens of nine tooth germs and 48 benign and five malignant ameloblastomas were examined by immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) for the expression of p63 and p73.

RESULTS

Immunoreactivity for p63 and p73 was evident in epithelial cells neighboring the basement membrane in developing and neoplastic odontogenic tissues. p63 expression in desmoplastic ameloblastomas was significantly higher than in acanthomatous and granular cell ameloblastomas, and ameloblastic carcinomas showed higher p63 expression than metastasizing ameloblastomas. p73 expression was significantly higher in plexiform ameloblastomas than in follicular ameloblastomas, and basal cell ameloblastomas showed higher p73 expression than granular cell ameloblastomas. mRNA transcripts for Delta Np63 and TAp73 were detected in all developing and neoplastic odontogenic tissues. TAp63 mRNA was expressed in five of eight tooth germs, 16 of 34 ameloblastomas, and one of one malignant ameloblastoma, whereas Delta Np73 mRNA was recognized in one of eight tooth germs, nine of 34 ameloblastomas, and one of one malignant ameloblastoma.

CONCLUSION

The expression of p63 and p73 suggests that these p53 homologs play a role in differentiation and proliferation of odontogenic epithelial cells. Variations of predominantly expressed isoforms suggest that p63 and p73 might differentially function in odontogenic tissues.

Partial enrichment of a population of human limbal epithelial cells with putative stem cell properties based on collagen type IV adhesiveness

The concept that corneal epithelium stem cells reside in limbus has been recognized for more than a decade, but isolation of these stem cells has not been accomplished. This study was an initial attempt to isolate a population of human limbal epithelial cells enriched for certain putative stem cell properties based on their phenotype. Epithelial cells harvested from fresh human limbal rings and their primary cultures were allowed to adhere to collagen IV-coated dishes for 20 min and 2 hr, sequentially. The rapidly adherent cells (RAC), slowly adherent cells and non-adherent cells were evaluated for certain stem cell properties: (a) BrdU-label retention, (b) expression of basal cell (integrin beta1, p63, ABCG2) and differentiation (involucrin, keratin 12) markers, and (c) colony forming efficiency (CFE) and growth capacity on a 3T3 fibroblast feeder layer. Among unfractionated cells and the three selected populations, the RAC, accounting for about 10% of whole population, were enriched 5-fold in BrdU label-retaining cells, displayed the highest number of integrin beta1 and p63 positive and involucrin negative cells, expressed high levels of DeltaNp63 and ABCG2 mRNA, and lacked involucrin and K12 expression, and possessed the greatest CFE and growth capacity. These findings demonstrated for the first time that human limbal epithelial cells with stem cell properties can be partially enriched by their adhesiveness to collagen IV. The RAC population enriched for certain putative stem cell properties may prove useful in the future for transplantation to diseased and damaged corneas with limbal stem cell deficiency.

IGFBP-3 Is a Direct Target of Transcriptional Regulation by ΔNp63α in Squamous Epithelium

DeltaNp63alpha is a nuclear transcription factor that maintains epithelial progenitor cell populations, is overexpressed in several epithelial cancers, and can negatively regulate apoptosis. However, the mechanisms by which DeltaNp63alpha promotes cell survival are unclear. DeltaNp63alpha has been reported to act as a transcriptional repressor, but specific target genes directly repressed by DeltaNp63alpha remain unidentified. Here, we present evidence that DeltaNp63alpha functions to negatively regulate the proapoptotic protein IGFBP-3. Disruption of p63 expression in squamous epithelial cells increases IGFBP-3 expression, whereas ectopic expression of DeltaNp63alpha down-regulates IGFBP-3. DeltaNp63alpha binds to sites in the IGFBP-3 gene in vivo and can modulate transcription through these sites. Furthermore, DeltaNp63alpha and IGFBP-3 expression patterns are inversely correlated in normal squamous epithelium and squamous cell carcinomas. These data suggest that IGFBP-3 is a target of transcriptional repression by DeltaNp63alpha and that this repression represents a mechanism by which tumors that overexpress p63 may be protected from apoptosis.

Comparison of cell-suspension and explant culture of rabbit limbal epithelial cells

Currently, most investigators directly use limbal explants to culture corneal epithelial cells. However, it has not been identified that limbal stem cells do readily migrate from the limbal explants onto culture plate or amniotic membrane carrier. In this study a cell-suspension culture system for rabbit limbal stem cells was developed and compared with the direct explant method in the aspect of stem cells content in the culture system. Rabbit limbal epithelial cells were dissociated from rabbit eyes by dispase and single cell suspension was made for cell-suspension culture. DeltaNp63 expression of cultured rabbit limbal epithelial cells by cell-suspension technique and explant technique was detected. In cell-suspension culture, isolated cell-suspension was evaluated by flow cytometric analysis for vimentin expression and residual limbal tissue after dispase treatment was examined by scanning electron microscopy. In limbal epithelial cells suspension less than 5% cells were vimentin positive. Examination of residual limbal tissue confirmed that all the limbal epithelial cells had been removed. Histological examination revealed that with cell-suspension culture the cultured epithelial cells could differentiate better than with explant technique. In cells cultured with cell-suspension, there were much more cells expressing DeltaNp63 than in explant cultured cells. In cells cultured with explants, most of DeltaNp63 labelling cells mustered around the explants, and peripheral cells on the slides were DeltaNp63 negative. These results suggested that with pure limbal epithelial cells suspension including basal cells, which could directly enter into culture system, cell-suspension culture technique was significantly superior to explant culture technique in terms of stem cells content.

Cellular senescence induced loss of stem cell proportion in the skin in vitro

BACKGROUND

It is known that cellular senescence could affect culture results. A previous study on K19 found that the loss of stem cell proportion is the reason for difficulties experienced when culturing aged keratinocytes. But the situation is unclear, because K19 is not generally accepted as an epidermal stem cell marker.

OBJECTIVE

The aim of this study was to investigate the effects of cellular senescence caused by chronological aging or by repeated subcultures.

METHODS

The effects of cellular senescence were investigated using monolayer cultures of keratinocytes and reconstructed epidermis. We prepared keratinocytes from donors of different ages and by repeated subcultures. Flow cytometric analysis was performed using alpha6 integrin and CD71 antibodies, and candidate keratinocyte stem cell proportions were separated according to reactivities to these antibodies. Living skin equivalents (LSEs) were reconstructed using keratinocytes from child, adult and elderly donors.

RESULTS

Flow cytometric analysis showed a decrease in the candidate stem cell proportion in an age- or culture passage-dependent manner. LSE experiments showed that a reconstructed epidermis using child's keratinocytes was well formed compared to epidermis reconstructed using an elderly donor's keratinocytes. Different expression of proliferation markers was also observed according to donor age.

CONCLUSION

Our results showed that cellular senescence by chronological aging or repeated sub-culture induced the loss of candidate stem cell proportion in keratinocyte cultures. This seems to be the reason why it is difficult to culture keratinocytes from the elderly or by repeatedly culturing keratinocytes in vitro.

Expression of different p63 variants in healing skin wounds suggests a role of p63 in reepithelialization and muscle repair

Healing of skin wounds in mammals involves partial reconstruction of the dermis and coverage of the injured site by keratinocytes. The latter process is achieved by extensive migration and hyperproliferation of keratinocytes at the wound rim. Because the p53 protein family member p63 is expressed in human hyperproliferative epidermis, this study determined whether enhanced keratinocyte proliferation correlates with the expression of p63. Therefore, we investigated the temporal and spatial distribution of four major variants of the p63 transcription factor-TAp63alpha, TAp63gamma, DeltaNp63alpha and DeltaNp63gamma-during normal skin wound healing in mice. Transcripts encoding amino-terminally truncated DeltaNp63 variants were found at high levels in basal and suprabasal keratinocytes of the hyperproliferative wound epithelium. Interestingly, TAp63 variants, which include the conserved transactivation domain TA at their amino-terminus, were also expressed in wound keratinocytes as well as at the edge of the injured subcutaneous muscle panniculus carnosus. These findings suggest splice-variant specific functions of p63 in reepithelialization and muscle repair.

Expression of p63 in primary cutaneous adnexal neoplasms and adenocarcinoma metastatic to the skin

p63, a recently identified homologue of the p53 gene, has been reported to be essential in the development of epithelia and is mainly expressed by basal and myoepithelial cells. The purpose of this study was to investigate the pattern of p63 expression in cutaneous adnexal neoplasms and to assess its possible value in the differential diagnosis of primary cutaneous neoplasms vs adenocarcinomas metastatic to the skin. Immunohistochemical analysis for p63 was performed on formalin-fixed, paraffin-embedded archival tissue from 20 benign adnexal tumors, 10 malignant adnexal tumors and 14 adenocarcinomas metastatic to the skin. The expression of p63 was evaluated in epidermal cells, skin appendages and metastatic tumor cells. p63 was consistently expressed in the basal and suprabasal cells of epidermis and cutaneous appendages, including the basal/myoepithelial cells of sweat glands. Out of 20 benign adnexal tumors, 13 (65%) showed strong (score 3) p63 expression; the remaining seven (35%) cases had score 2. All primary cutaneous carcinomas, including adenocarcinomas, expressed p63. In contrast, none of the metastatic adenocarcinomas to the skin was positive for p63 (P<0.001). Based on our findings, analysis of p63 expression may help in the differential diagnosis of primary vs metastatic cutaneous adenocarcinomas.

Keratins of the Human Hair Follicle

Substantial progress has been made regarding the elucidation of differentiation processes of the human hair follicle. This review first describes the genomic organization of the human hair keratin gene family and the complex expression characteristics of hair keratins in the hair-forming compartment. Sections describe the role and fate of hair keratins in the diseased hair follicle, particularly hereditary disorders and hair follicle-derived tumors. Also included is a report on the actual state of knowledge concerning the regulation of hair keratin expression. In the second part of this review, essentially the same principles are applied to outline more recent and, thus, occasionally fewer data on specialized epithelial keratins expressed in various tissue constituents of the external sheaths and the companion layer of the follicle. A closing outlook highlights issues that need to be explored further to deepen our insight into the biology and genetics of the hair follicle.

Assessment of p63 expression in oral squamous cell carcinomas and dysplasias

OBJECTIVES

p63, a p53 homologue, may be associated with tumorigenesis in epithelial tissues through its inhibition of p53 transactivation functions. We sought to determine the pattern and levels of p63 expression in oral dysplasias and carcinomas using standard immunohistochemical staining. We also assessed and compared expression of p53 and a cell proliferation marker in these lesions.

STUDY DESIGN

This retrospective cross-sectional survey (n=67) included hyperkeratosis (10), mild dysplasia (9), moderate dysplasia (11), severe dysplasia/in situ carcinoma (10), squamous cell carcinoma (SCC) (22 [9 well differentiated, 7 moderately differentiated, 6 poor differentiated]), and normal mucosa (5). Serial sections were stained immunohistochemically with antibodies to p63 (4A4 recognizing all p63 isotypes), p53 (DO-7), and Ki-67 (MIB-1) proteins. In preinvasive lesions, both the percentage of positive cells and staining patterns (negative, basal, suprabasal) were assessed. In oral SCCs, the percentage of positive cells was assessed. Statistical analysis was done using the Tukey-Kramer multiple comparisons test.

RESULTS

A suprabasal p63 staining pattern was evident in keratinocyte nuclei in the entire range of noninvasive lesions studied, including normal mucosa. Most nuclei in invasive SCCs stained positive. When all grades of dysplasia were combined, the percent of p63 positive cells was significantly greater than hyperkeratosis (P < .01), and well-differentiated SCC (P < .001). Moderately differentiated SCC had statistically significant more positive cells than well-differentiated SSC (P < .01). Comparison of serial sections showed different p63 staining patterns compared to p53 or Ki-67 staining patterns.

CONCLUSIONS

We conclude that p63 is expressed in oral carcinomas and dysplasias, as determined by immunohistochemical staining with a primary antibody to all isotypes. Neither staining pattern nor percentage of stained cells could be used to differentiate the lesions studied. The statistically significant differences found between some groups are not likely to be of diagnostic value. p63 is not coexpressed with p53 expression or Ki-67 suggesting functional independence. When antibodies to the p63 isotypes become available, oral dysplasias and carcinomas should be reassessed.

The genetics of skin cancer

Recent advances in molecular genetics have led to a better understanding of the biological underpinnings of skin cancer formation. As with most cancers, the RB, p53, and RAS pathways appear to play prominent roles in the pathogenesis of several skin cancer types. Although various components of these pathways may be differentially altered in squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and cutaneous melanoma, the final biochemical expression of these defects may be the same. With the unraveling of these genetic mechanisms, a more targeted approach to diagnosis and treatment may be possible in the near future.

p63 and epithelial appendage development

Abstract Epithelial appendages share a common developmental program that relies on extensive interactions between epithelia and adjacent mesenchyme. The transcription factor p63 has a critical role in epithelial appendage development in both vertebrates and non-vertebrates. Both mice and zebrafish lacking p63 expression fail to develop epithelial appendages and other structures that develop as a result of epithelial-mesenchymal interactions. Furthermore, dominantly inherited mutations in p63 are the cause of a subset of human ectodermal dysplasias, which are characterized by developmental abnormalities in epithelia and epithelial appendages. While the importance of p63 for epithelial appendage development is evident, the molecular mechanisms by which p63 functions are largely unknown. In this review, we will discuss the current knowledge of the developmental role of p63 and the implications for epithelial appendage development.

The role of p63 in development and differentiation of the epidermis

Expression of p63, a transcription factor that is transcribed into six isoforms, is required for proper development of stratified epithelia, such as the epidermis. In the absence of p63, epithelia remain single-layered. The molecular role of p63 in development and differentiation of stratified epithelia, however, remains controversial. Based on recent studies, we now believe that p63 has a dual role and is essential for development as well as maintenance of the epidermis. During embryogenesis, p63 may be the molecular switch required for initiation of epithelial stratification. This is based on our recent data demonstrating that ectopic expression of a p63 isoform in single-layered epithelia results in the induction of a stratification program. Furthermore, in the mature epidermis, p63 may maintain the proliferative potential of basal keratinocytes. This is suggested by the observation that p63 is primarily expressed in the basal compartment of the epidermis, that p63 expression induces hyperproliferation, and that its expression needs to be downregulated for terminal differentiation to take place. In this review, we discuss recent evidence supporting this dual role for p63 and place it in the context of our increasing knowledge of epidermal development and differentiation.