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

Alterations of the medullary epithelial compartment in the Aire-deficient thymus: implications for programs of thymic epithelial differentiation

A widely held model of thymic epithelial differentiation is based on patterns of keratin expression, where a K8(+)K5(+) progenitor gives rise to K8(+)K5/K14(-) cortical thymic epithelium (CTEC), and medullary thymic epithelium (MTEC) are K8(-)K5(+)K14(+). The thymic phenotype of p63-deficient mice indicates that p63 is an important regulator of proximal stages of thymic epithelial differentiation. In this study, we have examined several features of the thymic medullary compartment in wild-type and Aire-deficient thymi in an effort to integrate the proapoptotic activity of Aire with these different perspectives of TE differentiation. Patterns of keratin and p63 expression by MTEC described here are difficult to reconcile with postmitotic MTEC that express a K8(-)K14(+) phenotype and suggest that the patterns of p63 and keratin expression reflecting differentiation programs of other epithelial tissues provide a useful framework for revising models of TE differentiation. Alterations of the Aire(-/-) MTEC compartment included reduced expression of p63, increased frequency of MTEC expressing truncated Aire protein, and shifts in the pattern of keratin expression and epithelial morphology. These data suggest a scenario where cellular targets of Aire-mediated apoptosis are postmitotic MTEC that have not yet completed their terminal differentiation program. According to this view, the minor population of globular K8(+)K14(-/low) MTEC observed in the Aire(+/+) thymus and significantly expanded in the Aire(-/-) thymic medulla represent end-stage, terminally differentiated MTEC. These Aire-dependent alterations of the MTEC compartment suggest that the activity of Aire is not neutral with respect to the program of MTEC differentiation.

Impaired delta NP63 expression is associated with poor tumor development in transitional cell carcinoma of the bladder

The oncogenic isoform of the p63 protein, delta Np63 (delta Np63), plays an important role in the pathogenesis of many epithelial carcinomas, and emerging evidences suggest that delta Np63 is a promising drug target. However, the functions of delta Np63 in transitional cell carcinoma of bladder (TCCB) are poorly defined. In this study, a delta Np63 shRNA expression vector was transfected into TCCB cell line 5637 and cell cycling, cell proliferation and protein expression were assessed by flow cytometry and 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-dimethyl tetrazolium bromide (MTT) assay, and immunohistochemistry, respectively. The delta Np63 shRNA expression vector was also injected into 5637 cell xenograft tumors in nude mice, and tumor size was measured, tumor tissue morphology was assessed by immunohistopathology and transmission electron microscopy. In the in vitro study, delta Np63 shRNA transfection caused successful delta Np63 gene silencing and resulted in significant arrest of cell cycling and cellular proliferation (p<0.05) as well as cyclin D1 expression. In the nude mouse xenograft model, delta Np63 shRNA greatly inhibited tumor growth, induced tumor cell apoptosis (p<0.05) and resulted in cyclin D1 downregulation. Our data suggest that delta Np63 may play an oncogenic role in TCCB progression through promoting cell survival and proliferation. Intratumoral administration of delta Np63-specific shRNA suppressed tumor delta Np63 expression and cellular proliferation while promoted tumor cellular apoptosis, and therefore inhibited tumor growth and improved survival of xenograft-bearing mice, which was not accompanied by significant signs of systemic toxicity.

Notch tumor suppressor function

Cancer development results from deregulated control of stem cell populations and alterations in their surrounding environment. Notch signaling is an important form of direct cell-cell communication involved in cell fate determination, stem cell potential and lineage commitment. The biological function of this pathway is critically context dependent. Here we review the pro-differentiation role and tumor suppressing function of this pathway, as revealed by loss-of-function in keratinocytes and skin, downstream of p53 and in cross-connection with other determinants of stem cell potential and/or tumor formation, such as p63 and Rho/CDC42 effectors. The possibility that Notch signaling elicits a duality of signals, involved in growth/differentiation control and cell survival will be discussed, in the context of novel approaches for cancer therapy.

p53 family in development

The p53 family network is a unique cellular processor that integrates information from various pathways and determines cellular choices between proliferation, replication arrest/repair, differentiation, senescence, or apoptosis. The most studied role of the p53 family is the regulation of stress response and tumor suppression. By removing damaged cells from the proliferating pool, p53 family members preserve the integrity of the genome. In addition to this well recognized role, recent data implicate the p53 protein family in a broader role of controlling cell proliferation, differentiation and death. Members of the p53 protein family with opposing activity perform coordination of these processes. Imbalance of p53 protein family may contribute to a significant proportion of congenital developmental abnormalities in humans.

ATM kinase is a master switch for the Delta Np63 alpha phosphorylation/degradation in human head and neck squamous cell carcinoma cells upon DNA damage

We previously found that the pro-apoptotic DNA damaging agent, cisplatin, mediated the proteasome-dependent degradation of Delta Np63 alpha associated with its increased phosphorylated status. Since Delta Np63 alpha usually plays an opposite role to p53 and TAp63 in human cancers, we tested the notion that phosphorylation events induced by DNA damage would affect the protein degradation of Delta Np63 alpha in HNSCC cells upon cisplatin exposure. We found that Delta Np63 alpha is phosphorylated in the time-dependent fashion at the following positions: S385, T397 and S466, which were surrounded by recognition motifs for ATM, CDK2 and p70s6K kinases, respectively. We showed that chemical agents or siRNA inhibiting the activity of ATM, CDK2 and p70s6K kinases blocked degradation of Delta Np63 alpha in HNSCC cells after cisplatin exposure. Site-specific mutagenesis of Delta Np63 alpha residues targeted for phosphorylation by ATM, CDK2 or p70s6k led to dramatic modulation of Delta Np63 alpha degradation. Finally, we demonstrated that the Delta Np63 alpha protein is a target for direct in vitro phosphorylation by ATM, CDK2 or p70s6K. Our results implicate specific kinases, and target phosphorylation sites in the degradation of Delta Np63 alpha following DNA damage.

Enrichment of putative human epidermal stem cells based on cell size and collagen type IV adhesiveness

The enrichment and identification of human epidermal stem cells (EpSCs) are of paramount importance for both basic research and clinical application. Although several approaches for the enrichment of EpSCs have been established, enriching a pure population of viable EpSCs is still a challenging task. An improved approach is worth developing to enhance the purity and viability of EpSCs. Here we report that cell size combined with collagen type IV adhesiveness can be used in an improved approach to enrich pure and viable human EpSCs. We separated the rapidly adherent keratinocytes into three populations that range in size from 5-7 microm (population A), to 7-9 microm (population B), to > or =9 microm (population C) in diameter, and found that human putative EpSCs could be further enriched in population A with the smallest size. Among the three populations, population A displayed the highest density of beta1-integrin receptor, contained the highest percentage of cells in G0/G1 phase, showed the highest nucleus to cytoplasm ratio, and possessed the highest colony formation efficiency (CFE). When injected into murine blastocysts, these cells participated in multi-tissue formation. More significantly, compared with a previous approach that sorted putative EpSCs according to beta1-integrin antibody staining, the viability of the EpSCs enriched by the improved approach was significantly enhanced. Our results provide a putative strategy for the enrichment of human EpSCs, and encourage further study into the role of cell size in stem cell biology.

Differential expression of two new members of the p53 family, p63 and p73, in extramammary Paget's disease

BACKGROUND

The proteins p53, p63 and p73 are known to be overexpressed and to play important roles in the pathogenesis of many tumours, but the expression of p63 and p73 has not previously been investigated in extramammary Paget's disease (EMPD).

AIM

To investigate the potential contribution of p53, p63 and p73 in the pathogenesis of EMPD.

METHODS

In total, 35 paraffin wax-embedded tissue samples from patients with EMPD were examined using immunohistochemical staining for p53, p63 and p73.

RESULTS

All of the 35 EMPD specimens, including all 6 invasive EMPD and 2 metastatic lymph-node specimens, showed nuclear overexpression of both p53 and p73. The expression levels (percentage of positive cells) of p53 and p73 (90.66 +/- 12.53% and 80.20 +/- 13.07%) in EMPD were significantly higher than those of normal skin. There was a significant correlation between the expression levels of p53 and p73 in EMPD. In 29 of 35 EMPD specimens, there was no nuclear expression of p63, and weak or moderate staining was found in only 6 specimens. The expression level of p63 in EMPD was significantly less than that in normal skin.

CONCLUSIONS

Our study shows that the concordant overexpression of p53 and p73 and the decreased expression of p63 may play a pivotal role in the pathogenesis of EMPD. The decreased expression of p63 may play a more important role in the pathogenesis of EMPD than the overexpression of p53 and p73.

Expression of p63 and cyclooxygenase-2 and their correlation in skin tumors

To study the expression of p63 and cyclooxygenase-2 (cox-2) in skin tumors and evaluate the correlation between p63 and cox-2, the expressions of cox-2 and p63 were measured by streptavidin-peroxidase complex immunohistochemical technique in 17 cases of skin squamous cell carcinoma (SCC), 19 cases of Bowen's disease(Bowen), 11 cases of actinic keratosis(AK), 12 cases of seborreic keratosis(SK) and 13 specimens of normal skin. Our results showed that the expression of p63 in skin squamous cell carcinoma, Bowen's disease and actinic keratosis were significantly higher than that in seborreic keratosis, while the expression of p63 in seborreic keratosis was significantly higher than that in normal skin. The expression of cox-2 in skin squamous cell carcinoma, Bowen's disease and actinic keratosis were significantly higher than that in seborreic keratosis, while no statistical difference was noted in the expression of cox-2 between seborreic keratosis and normal skin. Cox-2 expression was positively correlated with the high p63 expression in malignant skin tumors. The increased expression of cox-2 and p63 may play an important role in the development of skin tumors and work synergetically in malignant skin tumors.

A skin microRNA promotes differentiation by repressing 'stemness'

In stratified epithelial tissues, homeostasis relies on the self-renewing capacity of stem cells located within the innermost basal layer. As basal cells become suprabasal, they lose proliferative potential and embark on a terminal differentiation programme. Here, we show that microRNA-203 is induced in the skin concomitantly with stratification and differentiation. By altering miR-203's spatiotemporal expression in vivo, we show that miR-203 promotes epidermal differentiation by restricting proliferative potential and inducing cell-cycle exit. We identify p63 as one of the conserved targets of miR-203 across vertebrates. Notably, p63 is an essential regulator of stem-cell maintenance in stratified epithelial tissues. We show that miR-203 directly represses the expression of p63: it fails to switch off suprabasally when either Dicer1 or miR-203 is absent and it becomes repressed basally when miR-203 is prematurely expressed. Our findings suggest that miR-203 defines a molecular boundary between proliferative basal progenitors and terminally differentiating suprabasal cells, ensuring proper identity of neighbouring layers.

Human VRK1 is an early response gene and its loss causes a block in cell cycle progression

Background

In mammalian cells regulatory proteins controlling the cell cycle are necessary due to the requirements of living in a heterogeneous environment of cell-interactions and growth factors. VRK1 is a novel serine-threonine kinase that phosphorylates several transcription factors and is associated with proliferation phenotypes.

Methodology/Principal Findings

In this report VRK1 has been identified as regulated in the cell cycle. VRK1 gene expression is activated by the addition of serum to starved cells, indicating it is required for the exit of G0 phase and entry in G1; a response that parallels the re-expression of MYC, FOS and CCND1 (cyclin D1) genes, suggesting that VRK1 is an early-response gene. VRK1 gene expression is also shutdown by serum withdrawal. The human VRK1 gene promoter cloned in a luciferase reporter responds similarly to serum. In response to serum, the level of VRK1 protein expression has a positive correlation with cell proliferation markers such as phosphorylated-Rb or PCNA, and is inversely correlated with cell cycle inhibitors such as p27. The elimination of VRK1 by siRNA results in a G1 block in cell division, and in loss of phosphorylated-Rb, cyclin D1, and other proliferation markers. Elimination of VRK1 by siRNA induces a reduction of cell proliferation. VRK1 colocalizes with p63 in proliferating areas of squamous epithelium, and identifies a subpopulation in the basal layer.

Conclusions/Significance

VRK1 is an immediate early response gene required for entry in G1, and due to its implication in normal cell proliferation and division, might be a new target for development of inhibitors of cellular proliferation.

U-box-type ubiquitin E4 ligase, UFD2a attenuates cisplatin mediated degradation of DeltaNp63alpha

DeltaNp63alpha, the dominant negative isoform of the p63 family is an essential survival factor in head and neck squamous cell carcinoma. This isoform has been shown to be down regulated in response to several DNA damaging agents, including cisplatin. But little is understood about the post-translational protein stability of DeltaNp63alpha. In this present study we demonstrate for the first time that DeltaNp63alpha physically interacts with U-box-type E4 ubiquitin ligase UFD2a. UFD2a stabilizes DeltaNp63alpha, and ubiquitylation of DeltaNp63alpha is attenuated by UFD2a both in the presence and absence of cisplatin. Ectopic expression of UFD2a increased the half-life of DeltaNp63alpha in association with a significant enhancement of the repressive transcriptional activity of DeltaNp63alpha. Downregulation of endogenous UFD2a by RNAi resulted in degradation of DeltaNp63alpha. Taken together, our current study provides an insight onto the regulation of DeltaNp63alpha protein levels in response to cisplatin and also suggests that UFD2a might play an important role in the regulation of cisplatin mediated cell death mediated by p63.

Tprg, a gene predominantly expressed in skin, is a direct target of the transcription factor p63

p63 and p73 are highly homologous members of the p53 family that originated by gene duplication at the invertebrate-to-vertebrate transition. We characterize here a previously unreported gene, Transformation-related protein 63 regulated (Tprg), located upstream of the p63 gene in the vertebrate genome, with striking similarity to Transformation related protein 63 regulated like (Tprgl), an uncharacterized gene located upstream of p73, suggesting that p63/Tprg and p73/Tprgl are embedded in a paralogue region originated from a single duplication event. Tprg is predominantly expressed in the epithelial compartment of the skin, more abundantly in differentiated cells. Consistent with its relative higher expression in differentiated keratinocytes, finely tuned p63 expression levels are required for optimal Tprg expression in primary keratinocytes. p63 is essential for Tprg expression as shown in p63-knockdown keratinocytes; however, high levels of p63 result in Tprg downregulation. p63 directly binds in vivo to a canonical p63-binding site in an evolutionary conserved genomic region located in Tprg intron 4. This genomic region is sufficient to function as a p63-inducible enhancer in promoter studies. Thus, we demonstrate that the Tprg gene is predominantly expressed in skin, is physically associated with the p63 gene during evolution, and directly regulated by p63 through a long-distance enhancer located within the Tprg locus.

Generation of human epidermal constructs on a collagen layer alone

Because engineered tissues are designed for clinical applications in humans, a major problem is the contamination of cocultures and tissues by allogenic molecules used to grow stem cells in vitro. The protocols that are commonly applied to generate epidermal equivalents in vitro require the use of irradiated murine fibroblasts as a feeder layer for keratinocytes. In this study, we report a simple procedure for growing human keratinocytes, isolated from adult skin, to generate an epidermal construct on a collagen layer alone. In this model, no human or murine feeder layers were used to amplify cell growth, and isolated keratinocytes were seeded directly at high cell density on the collagen-coated flasks or coverslips in an epithelial growth medium containing low calcium concentration. Morphological, immunochemical, and cytokinetic features of epithelial colonies grown on the collagen layer were typical of keratinocytes and were comparable with those reported for keratinocytes grown on a feeder layer. The stratification of keratinocytes generated 3-dimensional synthetic constructs displaying a tissue architecture comparable with that of natural epidermis. Epithelial cells expressed specific markers of keratinocyte terminal differentiation, including involucrin and filaggrin. Nevertheless, the number of cell layers was lower than in natural skin, and electron microscopical analysis revealed that the overall organization of these layers was poor compared with natural epidermis, including the formation of junctional complexes, basement membrane, and keratinization. The lack of epithelial-mesenchymal interactions that occur during skin histogenesis may account for such an incomplete maturation of epidermal constructs.

DeltaNp63 isoforms regulate CD44 and keratins 4, 6, 14 and 19 in squamous cell carcinoma of head and neck

The human p63 gene codes for multiple protein isoforms and is commonly over-expressed in squamous cell carcinoma of head and neck (SCCHN). This expression is predominantly of the DeltaN- and beta-isoforms, the former lacking the p53-related transactivation domain. p63 can activate or repress transcription of p53 and p73 target genes, but also has unique transcriptional targets and, unlike other p53 family members, is required for normal development and differentiation of squamous epithelia. We have identified novel targets of p63, using microarray analysis of SCCHN cells that stably over-express individual DeltaNp63 isoforms. All three isoforms induced expression of the cancer stem cell marker, CD44, with the DeltaNp63beta isoform showing strongest induction. Using chromatin immunoprecipitation, we were unable to show direct binding of p63 to the CD44 promoter, but found that p63 specifically increased expression of CD44 lacking variant exon 2. Each of the DeltaNp63 isoforms up-regulated expression of keratins 6A and 14 and down-regulated expression of keratins 4 and 19, in keeping with their expression patterns in SCCHN. The data strengthen the idea that p63 has key roles in regulating normal and abnormal differentiation processes through both induction and repression of genes with opposite functions. The identification of up-regulation and differential splicing of CD44 following p63 over-expression indicates roles in the regulation of adhesion, metastasis and the cancer stem cell phenotype.

p63 contributes to cell invasion and migration in squamous cell carcinoma of the head and neck

The transcription factor p63 is commonly over-expressed in squamous cell carcinomas of the head and neck (SCCHN). By microarray analysis of p63-siRNA-treated SCCHN cells we identified 127 genes whose expression relies on over-expression of p63. More than 20% of these genes are involved in cell motility. Chromatin immunoprecipitation and reporter assay revealed PAI-1 and AQP3 as direct p63 transcriptional targets. In addition to PAI-1, most of the key cell motility-related molecules are up-regulated by p63, such as MMP14 and LGALS1. Our findings indicate a contribution by p63 in cell invasion and migration, supporting an oncogenic role for p63 in SCCHN.

Characterization of DeltaNp63 isoforms in normal cornea and telomerase-immortalized human corneal epithelial cells

Previous reports have suggested that specific isoforms of the potential stem cell marker p63 may regulate corneal epithelial homeostatic renewal through control of cell proliferation. In this study, we characterized the presence of DeltaNp63 isoforms in telomerase-immortalized human corneal epithelial cells (hTCEpi) in comparison to normal human corneal epithelium to validate the hTCEpi cell line as a viable model for the study of p63 isoforms. We further examined roles for DeltaNp63 in proliferation and differentiation. For in vitro studies, hTCEpi cells were cultured in serum-free culture media and grown under 0.15 mM calcium or sequential 1.15 mM calcium/air-lifted culture. Fresh donor human corneal tissue was used to assess expression and localization in situ. mRNA and protein levels were assessed by real-time PCR, Immunofluorescence (IF) and Western blotting (WB). DeltaNp63 expression levels throughout the cell cycle were assessed by double-labeling with DeltaNp63 and Ki-67. In situ, DeltaNp63 localized to nuclei throughout the human corneal epithelium and was lost only in superficial cells. WB confirmed the presence of all three DeltaNp63 isoforms in the central corneal epithelium and in hTCEpi cells. DeltaNp63 mRNA levels decreased when grown on collagen substrate and under increased calcium/air-lifted culture. mRNA and protein levels increased as cells approached confluence, with a significant decrease in post-confluent culture. DeltaNp63 expression levels did not vary with the cell cycle, as assessed by Ki-67 labeling. Collectively, the presence of all three DeltaNp63 isoforms in hTCEpi cells and in intact cornea validates the use of this cell line for the study of individual isoforms in the corneal epithelium; and these data suggest that expression of DeltaNp63 isoforms are not altered as a function of the cell cycle or cell division in subconfluent hTCEpi cells cultured in serum-free media, but demonstrate reduced expression upon contact-inhibited growth down-regulation and differentiation. Significantly, the localization of DeltaNp63 in central corneal epithelial cells with a loss of expression in superficial cells suggests that DeltaNp63 may play a role in mediating desquamative events at the ocular surface.

p63 immunohistochemistry differentiates salivary gland oncocytoma and oncocytic carcinoma from metastatic renal cell carcinoma

Metastatic renal cell carcinoma (RCC) can pose diagnostic challenges in the head and neck often resembling benign and malignant oncocytic lesions. Immunohistochemical panels have been reported to help with this differential but are not entirely specific or sensitive. We have noticed that p63 routinely stains salivary gland oncocytomas but not metastatic RCC. Nineteen oncocytomas, 9 cases of oncocytosis, 9 oncocytic carcinomas and 16 head and neck metastatic RCC were studied. Morphologic features evaluated were cytoplasmic character (clear versus oncocytic), Fuhrman nuclear grade, mitotic rate, growth pattern, presence of lumens/blood lakes and stromal characteristics. Tumors were stained with antibodies to p63, renal cell carcinoma marker (RCCm), CD10, and vimentin. Eight benign oncocytic tumors (29%) had clear cell features while 6 metastatic RCC (37%) had oncocytic features. Median Fuhrman nuclear grade was 2 in oncocytoma and oncocytosis and 3 both oncocytic carcinoma and metastatic RCC. Mitotic rates were only significantly different between benign oncocytic tumors and metastatic RCC. All oncocytomas had lumina compared to half of metastatic RCC, all of which also demonstrated blood lakes. Seven benign oncocytic tumors (25%) and 5 oncocytic carcinomas (56%) had RCC-like vascular stroma. All primary salivary gland tumors were positive for p63, predominately in basal cell-type distribution. None of the metastatic RCC was positive. RCCm was entirely specific but lacked sensitivity for metastatic RCC while CD10 and vimentin showed variable sensitivity and specificity. While clinical history and morphology usually are adequate, demonstration of p63 staining can definitively exclude metastatic RCC from the differential diagnosis of similar appearing tumors in salivary glands, namely oncocytoma and oncocytic carcinoma, with 100% specificity and sensitivity. While RCCm, CD10, and vimentin performed adequately, they were significantly less reliable than p63 with both false positives and false negatives.

p73 expression modulates p63 and Mdm2 protein presence in complex with p53 family-specific DNA target sequence in squamous cell carcinogenesis

The expression of p73 and p63 isoforms is frequently deregulated in human epithelial tumors. We previously showed that loss of p73 protein expression associates with malignant conversion in vivo and ionizing radiation (IR) resistance in vitro in a clonal model of mouse epidermal carcinogenesis. Here we show that loss of endogenous p73 expression in squamous cell carcinoma (SCC) cells and tumors was concomitant with preferential DNA binding of the inhibitory DeltaNp63alpha isoform and reduction of transcriptionally active p63gamma isoforms binding to a p21 promoter sequence in vitro. Reconstitution of TAp73alpha in malignant cells increased the steady state DNA-binding capabilities of the endogenous transcriptionally active TAp63gamma and DeltaNp63gamma isoforms, correlating with restoration of tumor suppression but not IR sensitivity. Loss of p73 in malignant cells also coincided with increased presence of p53 family inhibitor Mdm2 in p53-specific DNA-bound complexes, whereas reconstitution of TAp73alpha expression resulted in exclusion of Mdm2 from these complexes. These results suggest a dual mechanism for TAp73alpha to foster tumor suppression through enhancement of the DNA-binding activity of p63gamma isoforms, and through inhibition of transcriptional repressors Mdm2 or DeltaNp63alpha.

Distinct epidermal stem cell compartments are maintained by independent niche microenvironments

The mammalian epidermis is a stratified, multilayered epithelium, consisting of the interfollicular epidermis and associated appendages, which extend into the dermis and include hair follicles, sebaceous glands, and sweat glands. Stem cells are essential for the maintenance of this tissue and are also potential sources of multipotent adult precursor cells. Stem cell populations occupying specific locations or niches have been identified in the interfollicular epidermis, the hair follicle and the sebaceous gland. Recent research has focused on how the stem cell niches provide specific sites where stem cells can reside indefinitely and undergo self-renewal or differentiation into specific cell lineages, as required for epidermal replenishment or hair follicle growth.

Differential p63 and p53 expression in human keloid fibroblasts and hypertrophic scar fibroblasts

The p63 gene belongs to the p53 gene family and encodes for sequence-specific transcription factors. p63 has been characterized primarily in the context of epidermis where is implicated in the establishment of keratinocyte cell fate and in maintenance of epithelial self-renewal. DeltaNp63 isoform has been showed to be involved in several kinds of human tumors of epidermal origin, even nonmalignant, for the neoplastic and proliferative potential. Here, we report the differential expression and the cellular localization of the DeltaNp63 isoform in fibroblasts isolated from human keloids and hypertrophic scars compared to normal skin. Differently from hypertrophic scar, our results show that DeltaNp63 has a nuclear localization and is overexpressed only in keloid fibroblasts, suggesting an essential role of DeltaNp63 in vivo in human keloids. Consistent with our results, we hypothesize that DeltaNp63 overexpression may be oncogenic because of its ability to block the activity of p53 since p53 is underexpressed in fibroblasts from keloids.

p63: defining roles in morphogenesis, homeostasis, and neoplasia of the epidermis

p63 is a member of a gene family also including the p53 tumor suppressor and p73. In contrast to p53, p63 is rarely mutated in human cancers. Rather, gene amplification and dysregulated expression of p63 protein have been observed, particularly in squamous cell carcinomas. p63 is essential for development of stratified squamous epithelium, including the epidermis. The p63 gene is expressed as multiple protein isoforms with different functional capacities, and the balance of these isoforms, along with the presence or absence of the other family members, p53 and p73, can impact biological outcome. Both gene silencing and overexpression approaches have been utilized to elucidate the contributions of specific p63 isoforms to normal epidermal morphogenesis and tissue maintenance. While numerous studies have established the essential nature of p63 in the epidermis, the basis of this requirement, and the unique, as well as, overlapping functions of the individual isoforms, remain controversial. In this review, we summarize the current understanding of roles played by specific p63 isoforms within the context of epidermal morphogenesis and homeostasis of the established epidermis, and the potential impact of p63 dysregulation on cancer development.

Immunohistochemical expression of p63 in endometrial polyps: evidence that a basal cell immunophenotype is maintained

OBJECTIVE

Although endometrial polyps likely originate from reserve cells in the basal layer, the underlying biology is not fully understood. One protein that plays an important role in regulating epithelial proliferation and differentiation is the 63-kd membrane protein (p63), which is also a marker of basal and reserve cells in the female genital tract. Our objective was to determine whether p63 is expressed differently in postmenopausal endometrial polyps than in the adjacent endometrium.

DESIGN

In this study, 36 specimens of endometrial polyps and 36 samples of the adjacent endometrium were obtained from postmenopausal women through hysteroscopic surgery performed in a tertiary-care university hospital. Immunohistochemistry was used to evaluate the expression of p63 in all samples.

RESULTS

The majority of endometrial polyp samples (94.4%) presented nuclear immunostaining for p63, whereas only 5.6% of adjacent endometrium samples were positive for p63 (P < 0.0001). Distribution of p63 immunostaining in the endometrial polyp samples was homogeneous.

CONCLUSIONS

Our results provide evidence that a basal cell immunophenotype is maintained in the endometrial polyps seen in postmenopausal women, suggesting that p63 plays a role in the pathogenesis of such polyps.

p63 in Primary Cutaneous Carcinosarcoma

Primary cutaneous carcinosarcomas (PCCs) are rare malignant neoplasms that are characterized by biphasic epithelial and mesenchymal differentiation. When the biphasic nature is not evident, immunohistochemical studies may be important in the diagnosis of PCCs. Although AE1/AE3 is frequently used to demonstrate the epithelial component, it may not be strongly expressed in epithelial cells that are not well-differentiated. p63 is a protein homologue of p53 that is expressed in poorly differentiated epithelial cells. We report 3 cases of PCC. The clearly epithelial areas of each tumor were frequently positive for both markers, whereas the sarcomatous areas were negative for both markers. Epithelial cells that were poorly differentiated and not easily identifiable were positive for p63 but negative for AE1/AE3. Of interest, transitional areas showed positivity for p63 alone. These 3 cases suggest that the use of both p63 and routine cytokeratin markers such as AE1/AE3 can increase the sensitivity for distinguishing epithelial cells over a range of differentiation states, which we propose will aid in the diagnosis of PCCs. In addition, the staining pattern of AE1/AE3 and p63 in these cases further supports the conversion theory of PCC.

Survival of cultured allogeneic limbal epithelial cells following corneal repair

In this study a technique for determining donor cell fate following corneal grafting was evaluated. Patients treated for limbal deficiency with allogeneic cultured corneal epithelial cells were studied to determine the fate of the grafted cells. The technique was evaluated initially through the use of donor eyes and then applied to the clinical analysis of 7 patients who had received a cultured corneal epithelial allograft. Cells removed from the cornea and any retrieved tissue were analyzed via polymerase chain reaction (PCR) genotyping to determine the origin of the cells populating the patients' healed cornea. A mixture of genotypes was detected in a cornea retrieved from a patient following a fully penetrating keratoplasty who had received a mixture of allogeneic tissue. Donor cells were no longer detected on the corneal surface of all 7 cases beyond 28 weeks postgraft. At these later time points, only patient genotype could be detected. These results demonstrate that PCR genotyping can be used to determine the origin of cells populating the surface of the cornea following the grafting of cultured allogeneic cells and demonstrates that transplanted cultured limbal epithelial cells do not persist on the surface of the host cornea for more than 28 weeks.

Cleft lip and palate repair in Hay-Wells/ankyloblepharon-ectodermal dysplasia-clefting syndrome

Hay-Wells/ankyloblepharon-ectodermal dysplasia-clefting syndrome is a rare autosomal dominant disorder characterized by ankyloblepharon, ectodermal dysplasia, and cleft lip and/or cleft palate. Mutations in the p63 gene recently have been shown to be etiologic in the majority of cases of ankyloblepharon-ectodermal dysplasia-clefting syndrome. To date, there have been no reports to document wound healing after cleft lip and/or palate repair in ankyloblepharon-ectodermal dysplasia-clefting patients. We describe two patients with ankyloblepharon-ectodermal dysplasia-clefting syndrome and provide a review of the literature. There have been no reported instances of wound healing complications in affected patients. Seventeen percent (3/18) of reported patients required revisions or repair of oronasal fistulae. Cleft lip and palate repair can be performed safely in patients with Hay-Wells syndrome.

C/EBPdelta regulates cell cycle and self-renewal of human limbal stem cells

Human limbal stem cells produce transit amplifying progenitors that migrate centripetally to regenerate the corneal epithelium. Coexpression of CCAAT enhancer binding protein δ (C/EBPδ), Bmi1, and ΔNp63α identifies mitotically quiescent limbal stem cells, which generate holoclones in culture. Upon corneal injury, a fraction of these cells switches off C/EBPδ and Bmi1, proliferates, and differentiates into mature corneal cells. Forced expression of C/EBPδ inhibits the growth of limbal colonies and increases the cell cycle length of primary limbal cells through the activity of p27^Kip1 and p57^Kip2. These effects are reversible; do not alter the limbal cell proliferative capacity; and are not due to apoptosis, senescence, or differentiation. C/EBPδ, but not ΔNp63α, indefinitely promotes holoclone self-renewal and prevents clonal evolution, suggesting that self-renewal and proliferation are distinct, albeit related, processes in limbal stem cells. C/EBPδ is recruited to the chromatin of positively (p27^Kip1 and p57^Kip2) and negatively (p16^INK4A and involucrin) regulated gene loci, suggesting a direct role of this transcription factor in determining limbal stem cell identity.

Ex vivo gene therapy cures a blistering skin disease

A recent publication that describes gene therapy treatment of a patient with an inherited blistering skin disease, epidermolysis bullosa, demonstrates for the first time that gene therapy can cure a disease of solid tissue. The treatment relies on ex vivo transduction of autologous epidermal stem cells with a normal copy of the defective gene, followed by reconstitution of the patient's skin with epithelial sheets that are grown from these genetically corrected cells. This approach holds promise for treatment not only of inherited disorders of the skin but also of other solid tissues that are becoming amenable to tissue engineering.

Regeneration of squamous epithelia from stem cells of cultured grafts

The only cultured cell types extensively used for tissue regeneration are the keratinocyte and the chondrocyte. Cultured autologous keratinocytes derived from the epidermis have been used for many years to produce grafts that regenerate an epidermis over a full-thickness wound, such as a third-degree burn. But there have been many failures of engraftment, and in the absence of criteria for the quality of the cultures, the causes of failure cannot be analyzed. It has become clear that the essential feature of the graft is the presence of an adequate number of stem cells. This article describes the criteria for estimating that number. Advances in graft preparation, combining better preservation of stem cells with ease of application of the graft, are also described. These improvements have been applied to cultures of ocular limbal cells, which contain the keratinocyte stem cells of the corneal epithelium. Cultures meeting the criteria of stem cell number have been grafted to 116 patients suffering from chemical destruction of the limbus. The procedure has been highly successful in the alleviation of suffering and the restoration of vision.

Mechanisms regulating epithelial stratification

The epidermis is a stratified epithelium that functions as a barrier protecting the organism from dehydration, mechanical trauma, and microbial insults. This barrier function is established during embryogenesis through a complex and tightly controlled stratification program. Whereas the morphological changes that occur during epidermal development have been extensively studied, the molecular mechanisms that govern this process remain poorly understood. In this review we summarize the current advances that have been made in understanding the molecular mechanisms that regulate epidermal morphogenesis.

DeltaNp63alpha promotes apoptosis of human epidermal keratinocytes

In this study we show that deltaNp63alpha overexpression in primary human epidermal keratinocytes causes decreased cell proliferation and increased apoptosis. These changes are associated with increased levels of p21 and p27, decreased cyclin D1 and cyclin E levels, reduced mitochondrial membrane potential, and enhanced procaspase and poly(ADP-ribose) polymerase cleavage. Bcl-xS and Bax levels are increased and Bcl-xL level is reduced. p53 levels are increased in the deltaNp63alpha-expressing cells and p53 overexpression reproduces features of the deltaNp63alpha phenotype. Increased p53 expression results in reduced deltaNp63alpha, suggesting that p53 may negatively regulate deltaNp63alpha level. DeltaNp63alpha also induces apoptosis in HaCaT and SCC-13 cells, which encode inactive p53 genes, suggesting that the response is p53 independent in these cell lines. Both deltaNp63alpha and TAp63alpha reduce SCC-13 cell survival. These studies indicate that both deltaNp63alpha and TAp63alpha can negatively regulate keratinocyte survival.

Prognostic impact of p53 and p63 immunoexpression in oral squamous cell carcinoma

BACKGROUND

The role of p53 and p63 proteins in the prognosis of oral squamous cell carcinoma (OSCC) is still debatable. Our aim here was to investigate the relationship between the immunoexpression of these proteins with some clinicopathologic parameters of prognostic significance in OSCC.

METHODS

Formalin-fixed paraffin-embedded sections from 106 patients were used for study together with the following data: primary site, histologic differentiation, recurrences, metastasis, disease-free survival and overall survival (OS).

RESULTS

In OSCCs, the positive rate for p63 protein immunoexpression (87.8%) was higher than p53 (52.8%). p53 expression correlated with metastasis. Tumors negative for p53 and with strong intensity for p63 expression had a significantly higher OS.

CONCLUSIONS

p53 overexpression is associated with a larger number of metastases and is correlated with a poor outcome as well as decreased intensity in p63 immunoexpression.

Limbal stem cells, a review of their identification and culture for clinical use

The surface of the eye is covered by two distinct epithelial populations, the conjunctival and corneal epithelia. The stem cell population for the corneal epithelia has been found to be located at the area known as the limbus. This is a narrow ring of tissue at the transitional zone between the cornea and conjunctiva. This stem cell population is responsible for generating transient amplifying cells which are responsible for renewing the cornea epithelia. There are currently no definitive markers for the stem cell population in the limbus. Instead using morphological features, such as small cells with a high nucleus-to-cytoplasm ratio, in conjunction with the presence of certain markers e.g. DeltaNP63alpha and the absence of others, e.g. the cytokeratin pair 3 & 12, are taken as being indicative of the stem cell population. Damage can occur to the corneal epithelium due to a number of causes including, Steven-Johnson syndrome, and chemical or thermal burns. This results in invasion of the cornea by the conjunctival epithelium resulting in impaired vision. In 1997 Pellegrini et al. (Lancet 349, 990) successfully used cells sheets from cultured limbal cells to successfully treat patients with corneal damage. Since then several other groups, have successfully treated patients, using similar methods.

p63 and p73 in human cancer: defining the network

The p53-related genes p63 and p73 exhibit significant structural homology to p53; however, they do not function as classical tumor suppressors and are rarely mutated in human cancers. Both p63 and p73 exhibit tissue-specific roles in normal development and a complex contribution to tumorigenesis that is due to their expression as multiple protein isoforms. The predominant p63/p73 isoforms expressed both in normal development and in many tumors lack the conserved transactivation (TA) domain; these isoforms instead exhibit a truncated N-terminus (DeltaN) and function at least in part as transcriptional repressors. p63 and p73 isoforms are regulated through both transcriptional and post-translational mechanisms, and they in turn regulate diverse cellular functions including proliferation, survival and differentiation. The net effect of p63/p73 expression in a given context depends on the ratio of TA/DeltaN isoforms expressed, on physical interaction between p63 and p73 isoforms, and on functional interactions with p53 at the promoters of specific downstream target genes. These multifaceted interactions occur in diverse ways in tumor-specific contexts, demonstrating a functional 'p53 family network' in human tumorigenesis. Understanding the regulation and mechanistic contributions of p63 and p73 in human cancers may ultimately provide new therapeutic opportunities for a variety of these diseases.

Expression of p63 in the mouse ovary

Transcription factor p63, a member of the tumor suppressor p53 family, plays an important role in epithelial development, and its expression is found in many epithelial tissues. Our previous reports have shown that p63 is expressed in primordial and testicular germ cells. In this study, we investigated the expression and distribution of p63 isoforms (TAp63alpha, TAp63beta, TAp63gamma, DeltaNp63alpha, DeltaNp63beta and DeltaNp63gamma) in the mouse ovary. Reverse transcription-polymerase chain reaction experiments with primers specific for different p63 isoforms demonstrated that transcripts encoding the transactivation domain and alpha isoforms were preferentially expressed in the ovary. Immunolocalization of p63 proteins, presumably that of full-length p63alpha isoform, was observed in the oocytes of primordial, primary and two-layered secondary follicles. However, positive staining was not detected in the oocytes of multi-layered secondary follicles and antral follicles as they continued to develop. This data suggests that p63 may be implicated in the meiosis and cell cycle control of germ cells in the mouse ovary.

Poorly differentiated tumours of the anal canal: a diagnostic strategy for the surgical pathologist

Poorly differentiated malignancies affecting the anal canal are uncommon but pose diagnostic difficulties because of the wide range of normal cell types that may occur within a limited anatomical region. The range of lesions that may present as poorly differentiated tumours includes squamous cell carcinoma, adenocarcinoma, small and large cell neuroendocrine carcinoma, neuroendocrine carcinoma expressing epithelial cytokeratins and other patterns of mixed differentiation, undifferentiated carcinoma, malignant melanoma, lymphoma and secondary tumours. This review discusses the differential diagnosis of these neoplasms with the aid of short illustrative case studies.

p63 induces key target genes required for epidermal morphogenesis

Mice lacking p63, a single gene that encodes a group of transcription factors that either contain (TA) or lack (DeltaN) a transactivation domain, fail to develop stratified epithelia as well as epithelial appendages and limbs. DeltaNp63 isoforms are predominantly expressed during late embryonic and postnatal epidermal development, however, the function of these proteins remains elusive. Using an epidermal-specific inducible knockdown mouse model, we demonstrate that DeltaNp63 proteins are essential for maintaining basement membrane integrity and terminal differentiation of keratinocytes. Furthermore, we have identified two DeltaNp63alpha target genes that mediate these processes. We propose that DeltaNp63alpha initially induces expression of the extracellular matrix component Fras1, which is required for maintaining the integrity of the epidermal-dermal interface at the basement membrane. Subsequently, induction of IkappaB kinase-alpha by DeltaNp63alpha initiates epidermal terminal differentiation resulting in the formation of the spinous layer. Our data provide insights into the role of DeltaNp63alpha in epidermal morphogenesis and homeostasis, and may contribute to our understanding of the pathogenic mechanisms underlying disorders caused by p63 mutations.

Effect of limbal explant orientation on the histology, phenotype, ultrastructure and barrier function of cultured limbal epithelial cells

PURPOSE

To compare the histology, phenotype, ultrastructure and barrier function of cultured limbal epithelial cells using two explant culture protocols.

METHODS

Epithelial cells were cultured for 16 days from limbal explants, positioned with either the stromal side (stromal group) or the epithelial side (epithelial group) on intact amniotic membranes. The cultured epithelium (n = 56) was examined using light microscopy, immunohistochemistry for K3, Cx43, ABCG2 and p63 expression, Western blot analysis of DeltaNp63alpha, transmission electron microscopy, a horseradish peroxidase (HRP) permeability assay and scanning electron microscopy.

RESULTS

The epithelial group demonstrated a significantly higher expression of p63-positive cells (85.7 +/- 4.2%) than the stromal group (75.3 +/- 8.9%), and Western blots showed a stronger band of DeltaNp63alpha. K3 and ABCG2 were not detected in either group, whereas Cx43 displayed moderate immunostaining in the suprabasal layer. The number of cell layers, the desmosome number and the undulation length in the epithelial group were not significantly different from those in the stromal group. In both groups, HRP accumulated on the apical surface of the superficial cells, and scanning electron microscopy demonstrated tightly apposed superficial cells.

CONCLUSIONS

Our findings indicate that limbal explants positioned epithelial side down may give rise to cultured epithelia with higher expression of p63 and DeltaNp63alpha.

The contribution of epidermal stem cells to skin cancer

Tumors arising from the skin are of multiple phenotypes, with differing degrees of malignant potential. In mouse models of skin carcinogenesis, tumors of squamous phenotype are the most common; however, human disease indicates that multiple phenotypes may arise from a common pool of stem cells that are then influenced by epigenetic factors. The use of transgenic and knockout gene technologies with mice is unraveling some of the specific genes regulating fate determination in stem cells other than squamous lineage, including basal cell carcinoma and sebaceous adenomas. The following review examines the evidence for the stem cell origin of epidermal tumors and the contribution of some specific gene families toward stem cell fate decisions during epidermal tumor progression.

p53 homologue, p51/p63, maintains the immaturity of keratinocyte stem cells by inhibiting Notch1 activity

p53 homologue, p51/p63, predominantly expressed in keratinocyte stem cells, is indispensable for the formation of epidermis. Notch1, another such gene indispensable for the process, induces growth arrest and differentiation in keratinocytes. We found that exogenous expression of DeltaNp51B (DeltaNp63alpha), one of the isoforms of p51 specifically expressed in basal keratinocytes, blocked Notch 1-dependent growth arrest and differentiation in mouse keratinocytes by inhibiting p21 expression and maintaining integrins expression. Furthermore, DeltaNp51B by itself was found to have ability to induce expression of integrin alpha6beta4, which promotes attachment of basal cells to basal membrane thereby keeping the cells in immature state. Therefore, we conclude that DeltaNp51B expression warrants integrin expression even under the influence of Notch1 and that DeltaNp51B is a long-sought factor required to maintain basal cell keratinocytes immaturity by inhibiting Notch1 activity. We will postulate a plausible model explaining the maintenance of the squamous epithelium architectures as well as offering mechanistic explanations for pathological features of skin diseases, including cancers, psoriasis along with physiological wound healings.

Periacinar Clefting and p63 Immunostaining in Prostatic Intraepithelial Neoplasia and Prostatic Carcinoma

The aim of the present study was to correlate the presence and extent of retraction clefting and the expression of p63 in neoplastic glands and glands with prostatic intraepithelial neoplasia (PIN) in needle core biopsies. We analyzed needle core biopsies from 28 patients with PIN and 41 patients with adenocarcinoma. Neoplastic glands and those with PIN were analyzed on high power field (400x) and classified in three groups according to the extent of clefting. Immunohistochemical staining was performed following Microwave Streptavidin ImmunoPeroxidase (MSIP) protocol on DAKO TechMate Horizon automated immunostainer. Periacinar retraction clefting was significantly more prominent in prostatic carcinoma compared to PIN (p<0.0001) and nonneoplastic glands (p<0.0001). There was no difference between normal glands and PIN regarding clefting (p=0.8064). p63 was positive around the whole circumference in 12 out of 28 cases with PIN, and discontinuously positive in remaining 16 PIN cases suggesting initial disruption of the basal cell layer. p63 immunostaining was also positive in all nonneoplastic glands, and negative in all carcinomas. We conclude that retraction clefting was associated with cancer and lack of basal cells, but not with PIN. The relationship between clefting and p63 immunostaining in prostatic cancer should be further analyzed.