Mutant p53 expression in solar keratosis: an immunohistochemical study

Utilization of patterned bioprinting for heterogeneous and physiologically representative reconstructed epidermal skin models

Organotypic skin tissue models have decades of use for basic research applications, the treatment of burns, and for efficacy/safety evaluation studies. The complex and heterogeneous nature of native human skin however creates difficulties for the construction of physiologically comparable organotypic models. Within the present study, we utilized bioprinting technology for the controlled deposition of separate keratinocyte subpopulations to create a reconstructed epidermis with two distinct halves in a single insert, each comprised of a different keratinocyte sub-population, in order to better model heterogonous skin and reduce inter-sample variability. As an initial proof-of-concept, we created a patterned epidermal skin model using GPF positive and negative keratinocyte subpopulations, both printed into 2 halves of a reconstructed skin insert, demonstrating the feasibility of this approach. We then demonstrated the physiological relevance of this bioprinting technique by generating a heterogeneous model comprised of dual keratinocyte population with either normal or low filaggrin expression. The resultant model exhibited a well-organized epidermal structure with each half possessing the phenotypic characteristics of its constituent cells, indicative of a successful and stable tissue reconstruction. This patterned skin model aims to mimic the edge of lesions as seen in atopic dermatitis or ichthyosis vulgaris, while the use of two populations within a single insert allows for paired statistics in evaluation studies, likely increasing study statistical power and reducing the number of models required per study. This is the first report of human patterned epidermal model using a predefined bioprinted designs, and demonstrates the relevance of bioprinting to faithfully reproduce human skin microanatomy.

Reduced P53 Staining in Actinic Keratosis is Associated with Squamous Cell Carcinoma: A Preliminary Study

Background:

Actinic keratosis (AK) is a cutaneous neoplasm caused by prolonged sun exposure, and may progress into squamous cell carcinoma (SCC). The p53 gene plays a central role in the development of SCC, and mutations in this gene are found in 90% of SCC and up to 100% of AK cases.

Objective:

To identify AK cases that are highly susceptible to developing SCC.

Materials and Methods:

Fifty-six AK cases were classified into two groups: AK adjacent to “normal” skin and AK adjacent to SCC. The groups were compared based on epithelial atypia, inflammation, solar elastosis, histopathological AK classification and p53 protein expression.

Results:

Of the 56 AK cases analyzed, 23% were associated with SCC. The types of AK observed were classified as follows: common, hypertrophic, atrophic, acantholytic, pigmented and bowenoid. SCC was associated with common and hypertrophic AK, and p53 staining was observed in 78% of AK cases. The mean difference in p53 immunopositivity between common AK cases associated with SCC (17%) and not associated with SCC (45.4%) was significant (p=0.011).

Conclusions:

Hypertrophic and common AK are associated with SCC, and the low percentage of p53 immunopositivity in the common type indicates a greater probability of developing into SCC.

Expression of p53 in the evolution of squamous cell carcinoma: Correlation with the histology of the lesion

BACKGROUND

The evolution of squamous cell carcinoma (SCC) on sun-exposed areas is a multistep process triggered by ultraviolet radiation (UVR), in which precursor lesions exist. However, the exact classification of the various lesions in this process, mainly solar keratosis (SK), is still disputed, and its pathogenesis requires further clarification.

OBJECTIVE

To further elucidate the evolution of SCC on sun-damaged skin by correlating the levels of p53 protein expression, a parameter that reflects UVR damage to cells, and the morphology of the lesions that develop on sun-exposed areas.

METHODS

Biopsy specimens from normal skin (n = 4), normal skin with various degrees of solar elastosis (SE) (n = 16), various degrees of SK (n = 17) and SCCs from sun-exposed (n = 12) and sun-protected (n = 7) areas were stained with anti-p53 antibodies. A semiquantitative evaluation of the degree of staining was performed and correlated with the histological features.

RESULTS

Nuclear staining in keratinocytes was observed already in normal skin with mild SE and was increased gradually to its highest level of expression in advanced SK. It was also expressed in SCCs, but to a lesser degree. Statistical analysis revealed association between the morphology of the lesion and the level of p53 expression (P < .01); it also showed that in general the level of p53 is correlated with the histology of the lesion (P < .001). Furthermore, with regard to p53 expression, two groups of lesions exist: one showing a low level of expression of p53 that includes normal skin, skin with various degrees of SE and SCC from sun-protected areas, and a second group showing a high level of expression that includes SK and SCC occurring on sun-damaged skin.

LIMITATION

This is an immunohistochemical study of relatively few cases and in which the antibody detects all types of p53 protein.

CONCLUSIONS

This study furnishes further evidence that the development of SCC on sun-damaged skin is a gradual process not only morphologically but also on the molecular level. The process starts already in normal-appearing epidermis with SE. In that respect, SK should be regarded as a part of the continuum in the development of SCC, analogous to the situation in other epithelia. The molecular events involved in the development of SCC on sun-exposed areas may be different from those involving the development of SCC on sun-protected areas.

Reproducibility and Expression of Skin Biomarkers in Sun-Damaged Skin and Actinic Keratoses

OBJECTIVES

To explore p53 and proliferating cell nuclear antigen (PCNA) expression and polyamine content as biomarkers in skin cancer chemoprevention trials, we evaluated their expression in early stages of UV-induced squamous cell tumorigenesis.

METHODS

Biopsies were collected from three groups: 78 subjects with sun damage on forearms, 33 with actinic keratosis (AK) on forearms, and 32 with previous squamous cell carcinoma. Participants with sun damage were randomized to sunscreen or no sunscreen.

RESULTS

We found significant differences in p53 and polyamines in forearms from the sun-damaged group (11.5 +/- 1.2% for p53, 65.5 +/- 1.9 nmol/g for putrescine, and 187.7 +/- 3.3 nmol/g for spermidine) compared with the group with sun damage plus AK (20.9 +/- 2.3% for p53, P = 0.0001; 81.7 +/- 3.9 nmol/g for putrescine, P = 0.0001; 209.4 +/- 8.2 nmol/g for spermidine, P < 0.06). PCNA was not different. When lesion histology was considered, there was a stepwise significant increase in p53 in biopsies without characteristics of AK compared with early AK (P = 0.02) and AK (P = 0.0006) and a similar pattern for PCNA with the only significant difference between early AK and AK. There was a stepwise increase in putrescine and spermidine in normal, sun-damaged forearm, forearm from subjects with AK, and the AK lesion itself (P < 0.0001). No significant differences in p53 or polyamines were seen in 3-month biopsies or, as a result of sunscreen use, although PCNA in the sun-damaged group not using sunscreen decreased significantly.

CONCLUSIONS

p53 expression and polyamines in skin were elevated in early stages of skin tumorigenesis and were not affected by sunscreen, adding validity to their use as biomarkers in skin cancer chemoprevention trials.

Actinic cheilitis: histopathology and p53

BACKGROUND

Chronic actinic cheilitis (AC) is a precursor of squamous cell carcinoma (SCC) of the lip.

OBJECTIVES

To evaluate the histopathological characteristics that may help to identify AC more susceptible to carcinomatous transformation, to assess the p53 protein expression in AC, and to determine the value of the p53 expression as a marker of transformation into SCC of the lip.

METHODS

Seventy cases of chronic AC were reviewed, 31 of which were associated with SCCs. The samples were obtained from pathology reports of AC and SCC of the lip. Histopathology and immunohistochemical expression of the p53 protein were evaluated in isolated AC and in AC adjacent to SCC.

RESULTS

The intensity of the inflammatory infiltrate in the corium was the only histopathological finding significantly associated both with the presence of an invasive tumor and with the degree of epithelial atypia. Most AC (85%) were immunoreactive to the p53 protein. The p53 protein expression in cheilitis was not statistically associated with any other histopathological criteria.

CONCLUSIONS

An intense inflammatory infiltrate in AC was predictive of an adjacent invasive SCC. In this study, the p53 protein immunoreactivity was not a marker of malignant transformation.

Immunohistochemical study of cyclooxygenase-2 and p53 expression in skin tumors

Overexpression of cyclooxygenase-2 (COX-2) has been demonstrated in various cancers, including experimentally promoted tumors, gastrointestinal cancers, breast tumors and skin tumors. The mechanism that controls COX-2 expression is not yet clear. Currently, it is reported that COX-2 expression is frequently associated with mutated p53 genes. The goal of this study was to evaluate the expression patterns of COX-2 and p53 in several skin tumors and their correlation. An immunohistochemical method was used to investigate the expression of COX-2 and p53 proteins on formalin-fixed, paraffin-embedded tissue specimens of squamous cell carcinomas (SCC), basal cell carcinomas (BCC), Bowen's disease (BD), actinic keratosis (AK) and porokeratosis. The expression of COX-2 increased in 50% (5/10) of SCC, 80% (8/10) of BCC, 40% (4/10) of BD, 50% (5/10) of AK, and 20% (2/10) of porokeratosis cases. The expression of p53 increased in 90% (9/10) of SCC, 70% (7/10) of BCC, 70% (7/10) of BD, 50% (5/10) of AK, and 40% (4/10) of porokeratosis cases. COX-2 positivity rates of the p53-positive skin tumors were 56%, 100%, 57%, 80% and 25% in SCC, BCC, BD, AK and porokeratosis, respectively. However, the correlation between p53 and COX-2 expression in skin tumors was not statistically significant (P > 0.05). Our results indicate that skin COX-2 and p53 may play roles in skin tumors, but that there is no apparent correlation between the two markers.

Correlation between Bcl-2 and Bax in atrophic and hypertrophic type of actinic keratosis

BACKGROUND

Recent investigations consider actinic keratosis (AK) as an earliest visible pattern of squamous cell carcinoma (SCC). We have analysed the expression of apoptosis-related proteins TP53, Bcl-2 and Bax in 30 atrophic and 30 hypertrophic AK cases.

MATERIAL AND METHODS

Immunohistochemical analysis was performed following microwave streptavidin immunoperoxidase protocol on DAKO TechMate Horizon automated immunostainer (DAKO, Copenhagen, Denmark). Monoclonal antibody for TP53 and Bcl-2 and polyclonal antibody for Bax (DAKO, Copenhagen, Denmark) were used.

RESULTS

Expression of TP53 showed no significant differences between two analysed groups (chi2-test, P = 0.35636) whereas expression of Bcl-2 and Bax protein was significantly higher in atrophic compared to hypertrophic AK (chi2-test, P = 0.01458 and P = 0.00358, respectively). Comparison of Bcl-2 : Bax ratio in two analysed AK showed significantly higher value in hypertrophic compared to atrophic AK (Mann-Whitney U test, P = 0.02272). Statistical analysis did not show any correlation between patient's sex and age, localization and size of the lesion with expression of investigated oncoproteins (anova, P > 0.05).

CONCLUSIONS

Our results may indicate higher resistance of keratinocytes on apoptotic stimuli in hypertrophic compared to atrophic AK. Thus, we suppose that keratinocytes in hypertrophic AK live longer and probably have higher propensity for additional mutations and conversion to overt SCC.

Immunophenotypic analysis of the p53 gene in non-melanoma skin cancer and correlation with apoptosis and cell proliferation

BACKGROUND

Sunlight precipitates a series of genetic events that lead to the development of skin cancers such as basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). The p53 tumour suppressor gene, which plays a pivotal role in cell division and apoptosis, is frequently found mutated in sunlight-induced skin tumours.

OBJECTIVE

To investigate the immunoreactivity of the p53 gene in non-melanoma skin cancers and to correlate its expression with apoptotic and cell proliferation markers.

METHODS

We analysed 35 non-melanoma tumours including 19 BCCs and 16 SCCs from sun-exposed skin areas. p53 protein expression was studied immunohistochemically using the DO7 monoclonal antibody against wild-type and mutant p53 forms. The percentage of p53-immunopositive nuclei was measured by image analysis. Cell proliferation and apoptosis were also assessed by image analysis following Ki-67 immunostaining and application of the TUNEL method on paraffin sections, respectively.

RESULTS

The percentage of p53-expressing cells varied from 3.5 to 90 in BCCs (median value 54.4%) and from 3.7 to 94 in SCCs (median value 40.3%). The mean value of Ki-67-positive cells was comparable in both groups of tumours with a mean value of 40.6% in BCCs and 34.6% in SCCs. Conversely, the TUNEL assay showed sporadic staining of apoptotic cells within the tumours with a mean value of 1.12% in BCCs and 1.8% in SCCs. p53 protein expression was correlated positively with cell proliferation (r = 0.75, P = 0.000001) and negatively with apoptosis (r = -0.23, P = 0.05).

CONCLUSION

p53 immunoreactivity was high in the majority of the skin carcinomas examined and correlated positively with cell proliferation and negatively with apoptosis. The p53 protein overexpression appears to be related to an inactivated protein resulting from mutations of the p53 gene or other unclear molecular mechanisms.

Gene expression in actinic keratoses: pharmacological modulation by imiquimod

BACKGROUND

Actinic keratoses (AKs) are premalignant lesions that can progress into squamous cell carcinoma. Imiquimod, which belongs to the new class of immune-response modifiers, was recently shown to be effective in the treatment of AKs. The underlying mechanisms are not fully understood.

OBJECTIVES

To study the expression of individual genes in uninvolved skin and AKs before therapy and to elucidate the way in which the expression of these genes is influenced by imiquimod therapy.

METHODS

We treated 13 patients with AK with imiquimod and compared gene expression before, during (five patients) and after (eight patients) therapy with that in uninvolved skin. We analysed genes coding for inflammatory cytokines or their receptors, adhesion molecules, anti-apoptotic proteins, p53 and toll-like receptors (TLRs) by reverse-transcriptase polymerase chain reaction.

RESULTS

Comparing uninvolved skin and untreated AK, we found significant differences in the expression of interleukin (IL)-6, hurpin, TLR7 and TLR8. During imiquimod therapy, we detected a further upregulation of interferon-alpha, IL-6, IL-10 receptor 1 and TLR7. In contrast, two anti-apoptotic genes, hurpin and HAX-1, were downregulated. We did not detect significant differences in gene expression for p53, tumour necrosis factor-alpha and alpha- and beta-catenins. Clinically, the upregulated expression of the proinflammatory cytokines correlated with the local inflammation induced by imiquimod.

CONCLUSIONS

Our results indicate that specific differences in gene expression are detectable between AK and uninvolved skin. Imiquimod influenced the expression of most genes analysed in this study. This work extends previous findings on the effects of imiquimod on gene regulation in AKs.

Skin cancer chemoprevention: strategies to save our skin

There are over 1 million cases of skin cancer diagnosed yearly in the United States. The majority of these are nonmelanoma (NMSCs) and are associated with chronic exposure to ultraviolet light (UV). Actinic keratosis (AK) has been identified as a precursor for SCC, but not for BCC. AKs are far more common than SCC, making them excellent targets for chemoprevention. Cancer chemoprevention can prevent or delay the occurrence of cancer in high-risk populations using dietary or chemical interventions. We have developed strategies that have rational mechanisms of action and demonstrate activity in preclinical models of skin cancer. Promising agents proceed to phase I-III trials in subjects at high risk of skin cancer. UV light induces molecular signaling pathways and results in specific genetic alterations (i.e., mutation of p53) that are likely critical to skin cancer development. UVB-induced changes serve as a basis for the development of novel agents. Targets include inhibition of polyamine or prostaglandin synthesis, specific retinoid receptors, and components of the Ras and MAP kinase signaling pathways. Agents under study include: epigallocatechin gallate (EGCG), a green tea catechin with antioxidant and sunscreen activity, as well as UVB signal transduction blocking activity; perillyl alcohol, a monoterpene derived from citrus peel that inhibits Ras farnesylation; difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase and polyamines; retinoids that target retinoid X receptors and AP-1 activity; and nonsteroidal anti-inflammatory agents that inhibit cylooxygenase and prostaglandin synthesis. We performed a series of Phase I-II trials in subjects with multiple AK. For example, a phase II randomized trial of topical DFMO reduced AK number, suppressed polyamines, and reduced p53 protein. Our goal is to develop agents for use in combination and/or incorporation into sunscreens to improve chemoprevention efficacy and reduce skin cancer incidence.

An assessment of the malignant potential of actinic keratoses and Bowen's disease: p53 and PCNA expression pattern correlate with the number of desmosomes

Actinic keratoses (AK) and Bowen's disease (BD), both intraepidermal skin tumors, have a potential progression to squamous cell carcinoma (SCC). To evaluate the malignant potential of AK and BD, the expression pattern of p53 protein and proliferating cell nuclear antigen (PCNA) were examined in five types of AK and BD by immunohistochemistry. The ultrastructural difference of epidermal cells between AK and BD lesions was investigated. In the study of p53 and PCNA expression, the atrophic and acantholytic types of AK showed lower positive rates compared to others. These two types did not demonstrate all layers expression pattern. The number of desmosomes of the epidermal cells was significantly reduced in BD, and in the bowenoid and hypertrophic types of AK compared with other types of AK The number of hemi-desmosomes showed greatest reduction in BD and the bowenoid type of AK On the basis of our findings, it is hypothesized that atrophic and acantholytic types of AK may have the lowest, and the bowenoid type of AK and BD may have the highest, malignant potential.

Chemoprevention of human skin cancer

The incidence of skin cancer has been rising in recent years with significant effects on public health. Primary prevention has proven inadequate in impacting the incidence of skin cancer, thus stimulating the development of chemopreventive strategies. The majority of skin cancer chemoprevention studies focus on occurrence of new nonmelanoma skin cancers (NMSC) in individuals with a previous NMSC, or on reduction in the number of premalignant skin lesions such as actinic keratoses (AK). Dysplastic nevi, a likely precursor of melanoma, are also potential targets for chemoprevention strategies. Premalignant lesions are especially attractive as endpoints since they are more common than frank cancer, resulting in reduced sample size, length, and cost of clinical trials. Development of new agents that affect the pathogenesis of skin cancer will be discussed, from elucidation of molecular targets to implementation of trials designed to determine the effects of chemopreventive interventions on human skin cancer.

p53 gene mutations in squamous cell carcinoma occurring in scars: comparison with p53 protein immunoreactivity

We determined the relationship between p53 expression and p53 gene mutations in squamous cell carcinoma occurring in scars and unrelated to UV light irradiation. We analyzed biopsy specimens obtained from three patients with squamous cell carcinoma. A monoclonal antibody against p53 (DO-7) was used for the immunohistochemical analysis. p53 gene mutations were detected by the polymerase chain reaction and single-strand conformation polymorphism analysis and direct DNA sequencing. p53 overexpression was observed in atypical squamous cells of one case. Those of two other cases, however, showed negative immunoreactivity to p53. Exon 6 of the p53 gene in all three cases and exon 7 in one case showed electrophoretic mobility shifts in polymerase chain reaction and single-strand conformation polymorphism analysis. DNA sequencing analysis showed a missense mutation and a silent mutation in exon 6 of the case with p53 overexpression, a three-base deletion in exon 6 of one case with no p53 overexpression, and a three-base deletion in exon 6 and a missense mutation in exon 7 of another such case. Although immunohistochemical overexpression of p53 has been thought to result from p53 gene mutations, our results suggest that negative immunoreactivity to p53 also can result from p53 gene mutations, for example, short gene deletions.

p53-regulated apoptosis is differentiation dependent in ultraviolet B-irradiated mouse keratinocytes

Previous studies from our laboratory, using p53 transgenic mice, have suggested that ultraviolet (UV) light-induced keratinocyte apoptosis in the skin is not affected by overexpression of mutant p53 protein. To further elucidate a possible role for p53 in UV-induced keratinocyte cell death, we now examine apoptosis in skin and isolated keratinocytes from p53 null (-/-) mice and assess the influence of cell differentiation on this process. In vivo, using this knockout model, epidermal keratinocytes in p53-/- mice exhibited only a 5.2-fold increase in apoptosis after 2000 J/m2 UVB irradiation compared with a 26.3-fold increase in normal control animals. If this p53-dependent apoptosis is important in elimination of precancerous, UV-damaged keratinocytes, then it should be active in the undifferentiated cells of the epidermal basal layer. To test this hypothesis, we examined the effect of differentiation on UV-induced apoptosis in primary cultures of murine and human keratinocytes. Apoptosis was p53-independent in undifferentiated murine keratinocytes, which exhibited relative resistance to UVB-induced killing with only a 1.5-fold increase in apoptosis in p53+/+ cells and a 1.4-fold increase in p53-/- cells. Differentiated keratinocytes, in contrast, showed a 9.4-fold UVB induction of apoptosis in p53+/+ cells, almost three times the induction observed in p53-/- cells. This UV-induced difference in apoptosis was observed when keratinocytes were cultured on type IV collagen substrate, but not on plastic alone. Western blotting of UV-irradiated, differentiated keratinocytes did not support a role for either Bax or Bcl-2 in this process. In support of these findings in mice, cell death in human cultured keratinocytes also occurred in a differentiation-associated fashion. We conclude that p53-induced apoptosis eliminates damaged keratinocytes in the differentiated cell compartment, but this mechanism is not active in the basal, undifferentiated cells and is therefore of questionable significance in protection against skin cancer induction.

p53 expression in skin carcinogenesis and its relationship to cell proliferation and tumour growth

The immunoreactivity of p53 protein was studied in relation to tumour development, histopathological characteristics, cell proliferation, and basement membrane organisation following the induction of skin carcinogenesis in tumour-sensitive and -resistant mouse strains by ultraviolet (UV) irradiation or 7,12-dimethylbenz(a)anthracene (DMBA). In non-neoplastic skin exposed to UV irradiation or DMBA, p53 immunoreactivity was observed in nearly 50% of the basal layer cells. These cells were morphologically and histochemically indistinguishable from the p53-negative cells, occurring similarly in the tumour-producing and the tumour-negative mouse strains and regardless of subsequent tumour formation. In induced epidermal hyperplasia and in benign tumours, p53-positive and proliferating cells constituted 40-50% of all cells in the basal layer, while superficial cells were p53 negative. In dysplastic epidermis, p53-positive cells and proliferating cells were seen in all cell layers. In the case of squamous cell carcinomas, p53-positive proliferating cells in differentiated neoplasms were localised close to the basement membrane and, more frequently, in border areas showing invasion and basement membrane destruction. In horn cysts, centrally located cells were non-proliferating and p53 negative. In moderately differentiated neoplasms, proliferating cells were located closer to the basement membrane, while p53-positive cells were distributed diffusely in the neoplasm. In poorly differentiated neoplasms, p53-positive cells were more common than proliferating cells and were arranged in a diffuse pattern. The results showed that the number and location of p53-positive cells depended upon histology, with a close relationship to tumour type and degree of malignancy, but not on the mode of induction, nor on the animal strain or the relationship to subsequent tumour formation.

Apoptosis and cellular proliferation in human epidermal squamous cell neoplasia

We examined cell loss (apoptosis) and proliferation in a histopathological spectrum of epidermal squamous cell neoplasia, including 11 cases of solar keratosis (SK), 18 Bowen's diseases (BD) and 19 invasive squamous cell carcinomas (SCC). Apoptotic and proliferative cells were determined by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end labeling (TUNEL) and by the detection of nuclear antigen Ki-67, respectively. Few apoptotic cells were observed in normal epidermis, while TUNEL index (TI; percentage of TUNEL-positive cells) was highest for SCCs, followed by BDs and SKs, in the order given. Although the mean Ki-67 index did not differ between SCCs and BDs, both disease types showed a significantly higher index than the SKs. Of SCCs, both TI and Ki-67 index values were significantly higher in poorly than in well differentiated carcinomas. TI was significantly higher in SCCs without P53 immunohistochemical expression than in SCCs with P53 expression, while TI and Ki-67 indices did not correlate with P53 expression in the SKs and BDs. These results suggest that apoptosis reflects not only cell loss, but also proliferative activity in the epidermal neoplastic lesions.

Induction of squamous cell carcinoma in p53-deficient mice after ultraviolet irradiation

Mutations of the p53 gene have been implicated as an important factor in the pathogenesis of ultraviolet light induced skin cancers. To examine the role of p53 in skin carcinogenesis, we observed the development of skin cancers in homozygous p53-deficient (-/-) mice and wild-type p53 (+/+) mice, after chronic ultraviolet B (290-320 nm) exposure. At a dose of 2 J per m2 per s of ultraviolet B for 30 min three times per week, all p53-/- mice developed skin tumors by week 12. All the p53-/- mice developed multiple tumors by week 16. The majority of the tumors occurred on the ears. None of the p53+/+ mice developed skin tumors after 17 wk of UV exposure. Ten p53-/- tumors were examined histologically: five invasive squamous cell carcinomas, four squamous cell carcinomas in situ, and one actinic keratosis. p53-/- mice have a short life-span due to internal tumors or a deficiency in the immune system; however, ultraviolet B exposure did not significantly reduce the life-span of p53-/- mice. These results demonstrate that loss of wild-type p53 function shortens the latent period and predisposes the animals to the development of squamous cell carcinomas after ultraviolet irradiation.

Actinic keratoses. Differential diagnosis and treatment

Actinic keratoses are extremely common premalignant keratinocytic neoplastic lesions that develop primarily in fair-complexioned individuals during midlife or beyond. Genetic, occupational and other environmental factors predispose to the development of these lesions. Without treatment, a significant number may progress to fully developed neoplasms, especially squamous cell carcinoma, over a period of 20 to 50 years. The multistep theory of carcinogenesis is helpful in understanding the pathogenesis and progression of this important and highly prevalent lesion.

Cell proliferation and p53 protein expressions in cutaneous epithelial neoplasms

We investigated correlations between cell proliferation, p53 overexpression, and degree of malignancy in cutaneous epithelial neoplasms. One hundred and fourteen cases of epithelial neoplasms, including seborrheic keratosis (SEB), basal cell carcinomas (BCCs), solar keratosis (SK), Bowen's disease (BD), and squamous cell carcinomas (SCCs) were examined using argyrophilic nucleolar organizer region (AgNOR) staining. In addition, immunohistochemical analysis using the Ki-67 (MIB-1) and anti-p53 (DO-7) monoclonal antibodies was performed. The ratio of tumorous to normal cells according to AgNOR staining was defined as the AgNOR rate, and the ratio of tumorous to normal cells according to Ki-67 recognition was defined as the Ki-67 rate. SCC lesions showed the highest AgNOR rate among the investigated epithelial neoplasms, followed in order by BD, BCC, SK, and SEB lesions. The Ki-67 rate was highest in BD lesions, followed in order by SK, SCC, BCC, and SEB lesions. Expression of p53 protein was highest in SK lesions. SCC is generally considered to be the most malignant neoplasm, followed in order by BCC, BD, and SK. Thus, our results suggest that the Ki-67 rate and overexpression of p53 protein do not always reflect the degree of malignancy in neoplasms.

Immunohistochemistry: a prognostic as well as diagnostic tool?

The assessment of proliferating cell populations has been used to aid in the differentiation of benign from malignant neoplasms, and it has been hoped that assessment of proliferation markers and oncogenic determinants holds information regarding prognosis. Various markers, including Ki-67, p53 protein, bcl-2, and proliferating cell nuclear or paraffin-embedded tissue. These determinants may prove useful in understanding the biology of certain neoplasms and may carry prognostic information that influences clinical management. Results in this developing field must always be interpreted in the clinical and histological context. This article reviews the applicability of some commonly available markers to selected skin disorders.

p53 mutations in solar keratoses

To understand how sunlight acts as a carcinogen, the authors analyzed p53 gene mutations including point mutation, loss of heterozygosity (LOH), and overexpression in solar keratoses. Exons 4 to 9 of the p53 gene were amplified by polymerase chain reaction (PCR) and directly sequenced. To determine allelic loss of p53, the region containing polymorphic codon 72 was amplified and digested with BstUI restriction nuclease. Overexpression of p53 protein was detected in paraffin section using mouse monoclonal antibody (PAb 1801). Point mutations of the p53 gene were detected in 7 (28%) of 25 solar keratoses and predominant in pyrimidines (86%). Loss of allele was found in 29% of informative samples. Seven (28%) cases showed immunopositivity; four cases had point mutation, but three cases did not. Two cases with point mutation were immunonegative. Characteristically point mutations, LOH and immunopositivity of p53 were seen predominantly as bowenoid and hypertrophic type lesion. These results suggest that sunlight can cause mutations of p53 gene and that p53 gene mutations may play an important role in skin carcinogenesis.

An immunohistochemical study of p53 protein expression in classical Kaposi's sarcoma

The present study was performed to determine the frequency of p53 protein immunoreactivity in classical Kaposi's sarcoma (KS) as a whole and in relation to the histological subtypes which are considered to correspond to the developmental stages of the tumor. The accumulation of p53 protein was studied immunohistochemically using monoclonal antibody BP53-12 on formalin-fixed paraffin-embedded sections of 36 KS lesions, of which 14 were classified histologically as early type and 22 as spindle-cell or mixed type. No positive immunoreactivity was detected in any of the 14 early-type lesions. Among the 22 spindle-cell and mixed variants, positive staining was detected in 5-10% of the tumor cells in one lesion, 1-5% of the cells in six lesions, and in < 1% of the cells in two lesions. These very small percentages of positively stained cells in less than half of the cases of the spindle-cell and mixed variants do not support a significant role for p53 in tumor progression and evolution in KS.

p53 protein expression in malignant, pre-malignant and non-malignant lesions of the lip

AIM

To elucidate the role of the p53 tumour suppressor gene in the pathogenesis of lip cancer.

METHODS

Expression of p53 was evaluated immunocytochemically in a retrospective study of formalin fixed, paraffin wax embedded tissue. Five cases each of four types of lip lesions were studied; these comprised squamous cell carcinoma (SCC), solar keratosis (SK), chronic hyperplastic candidosis (CHC), and lichen planus (LP). Five cases each of normal lip mucosa, SCC, and SK from sun exposed facial skin as well as LP, CHC, and SCC from buccal mucosa were also analysed. Immunolocalisation of p53 was scored semiquantitatively. The degree of apoptosis was also assessed in selected lesions by determining cell nuclear fragmentation.

RESULTS

All SCCs from lip lesions were immunopositive for p53. All cases of SK and two of five CHC lip lesions were also p53 positive. Normal lip mucosa samples were p53 negative. Sun exposed skin lesions of SCC and SK were all positive for p53, but only three of five cases of SCC from the buccal mucosa had detectable levels of p53. p53 expression was not detected in CHC and LP lesions of the buccal mucosa.

CONCLUSIONS

The aberrant expression of p53 is likely to occur early in the pathogenesis of lip cancer and may be related to exposure to the sun. The immunopositive p53 cells identified in the benign LP lesions do not necessarily correlate with commitment of cells within the lesion to programmed cell death. In light of the prior reports which indicate that p53 positive cells may progress to form malignant tumours, it is suggested that patients with p53 positive but otherwise benign lesions should be followed more closely.

p53 immunoreactivity in non-melanoma skin cancer from immunosuppressed and immunocompetent individuals: a comparative study of 246 tumours

p53 immunoreactivity was examined in 132 cutaneous non-melanoma tumours from renal transplant recipients and in 114 histologically matched specimens from immunocompetent individuals. Skin lesions examined included 52 viral warts, 50 dysplastic keratoses, 51 intraepidermal carcinomas (IEC), 50 invasive squamous cell carcinomas (SCC) and 43 basal cell carcinomas (BCC). Overall, 51% (51/101) pre-malignant skin lesions and 45% (42/93) non-melanoma skin cancers (NMSC) showed p53 immunoreactivity, with extensive (> 50% cells positive) p53 staining in 27% (27/101) of pre-malignant and 20% (19/93) of malignant lesions. 17% (9/52) viral warts showed p53 immunoreactivity, but this was limited to focal or basal p53 staining. p53 immunoreactivity in all tumours was less in transplant than in non-transplant patients and this reached statistical significance for SCCs (p = 0.03).

Antigen retrieval: p53 staining in benign, pre-malignant and malignant tissues of the larynx

Antigen retrieval techniques have been reported to increase p53 detection. Using an antigen retrieval technique applied to immunohistochemistry, a study was performed on 67 laryngeal lesions (21 benign, 16 carcinoma in situ, 30 squamous cell carcinoma). p53 staining was observed in 30% of carcinoma in situ specimens and 53% of squamous cell carcinomas but was not detected prior to antigen retrieval in any benign lesion. However, over-expression of p53 was identified in 92.5% of benign lesions after antigen retrieval using the microwave oven heating. There was also increased p53 staining in both the carcinoma in situ (43.7%) and squamous cell carcinomas (30.0%) after antigen retrieval. We conclude that antigen retrieval using microwave oven heating increases immunohistochemical detection of p53 such that positive staining is observed in benign conditions. We postulate that this apparent over-expression is a manifestation of the wild-type protein, which may be found in more evidence in basal cells than suprabasal cells. Our results thus offer a cautionary note to such studies involving squamous cell cancers that attempt to correlate p53 over-expression with clinical parameters.

Site-specific comparison of p53 immunostaining in squamous cell carcinomas

The p53 tumor suppressor gene is believed to be the most commonly mutated gene in human cancer. p53 is thought to function as a negative regulator of the cell cycle, arresting cells in the G1 phase. This study examined the effects of different mutagenic environments on the incidence of p53 overexpression in squamous cell carcinomas (SCCs) from sun exposed and non-sun exposed squamous epithelium. An immunohistochemical analysis was undertaken in an attempt to assay SSC for p53 overexpression, an indirect measure of missense mutant p53. Positive nuclear staining for p53 was observed in 14 of 21 sun exposed SCCs, two of 19 vulvar/perianal SCCs, and 15 of 20 oral cavity SCCs. The number of positive anogenital tumors was low compared with that of both sun exposed (chi-squared, 1 df, P = .0004) and oral (chi-squared, 1 df, P < .0001) sites. It was concluded that p53 protein accumulation is common in sun-exposed cutaneous SCC and oral SCC compared with anogenital SCC, and thus it is hypothesized that the nature of the mutagenic environment in which SCC develops directly affects the incidence of immunohistochemically detectable p53-positive cells.

Aberrations of the tumor suppressor p53 gene and p53 protein in solar keratosis in human skin

Aberrations of the p53 gene in 27 solar keratoses were examined by the polymerase chain reaction and single-strand conformation polymorphism and DNA sequencing analyses. In a series of Japanese patients, eight of 27 cases (30%) of solar keratosis showed structural abnormalities of the p53 gene. Six of eight aberrations of p53 gene were determined to be single nucleotide substitutions, and five of these were located at a dipyrimidine site. In solar keratosis, noticeable mutations were C to T in three cases, and one each of C to A and T to C nucleotide changes. p53 protein was detected immunohistochemically in the nuclei of six of 27 cases (22%) of solar keratosis. Nuclear staining for p53 protein was only significantly correlated with the presence of missense mutation of p53 gene (p < 0.01). Aberrations of the p53 gene in solar keratosis may be a marker to predict early cancerous lesions.

Analysis of the p53 gene in human precancerous actinic keratosis lesions and squamous cell cancers

A biomarker of skin cancer would be beneficial in evaluating the efficacy of potential cancer chemoprevention agents. To this end, we investigated the tumor suppressor gene p53 in precancerous actinic keratosis lesions (AK) and malignant squamous cell carcinomas (SCCs) using polymerase chain reaction and single-strand conformation polymorphism analysis (PCR-SSCP) techniques. In addition, p53 protein expression was evaluated using immunohistochemistical analysis with the PAB 1801 monoclonal antibody. Nine out of 13 (69%) SCCs and 8 of 15 (53%) AKs were positive for p53 mutations. In contrast, normal skin samples were negative for p53 mutations. Sequence analysis of AKs and SCCs showed primarily C to T transition mutations. Nuclear immunochemical staining for p53 was observed in 12/15 (80%) AK and 12/13 (92%) SSCs. These results suggest that p53 mutations may be involved in the malignant conversion of AKs to SCCs and that p53 may be useful as a biomarker to study the potential modulatory effects of cancer chemopreventive agents against skin cancer.

Altered p53 expression and epidermal cell proliferation is seen in vulval lichen sclerosus

Aberrant p53 immunoreactivity has been found in skin pre-malignancies and dysplasias such as Bowen's disease and actinic keratoses. Vulval lichen sclerosus (LS) has been reported to be pre-malignant, with an association of vulval carcinoma in 3% to 6% of patients. In contrast, non-genital LS appears to have no malignant potential. In this immunocytochemical study, we investigated p53 expression in 10 cases of histologically proven vulval LS and 9 cases of non-genital LS using the murine monoclonal antibody Do-1 raised against recombinant human p53 which reacts with both wild-type and mutant p53. None of the vulval specimens had epithelial dysplasia or malignancy. Normal vulval (7 cases) and non-genital skin (5 cases) were used as tissue controls, respectively. The cell proliferation index was also studied using the MIB 1 monoclonal antibody which detects the cell-cycle associated Ki-67 antigen. The technique of microwave irradiation for antigen unmasking was employed on formalin-fixed and paraffin-embedded tissues. There was a significant increase in p53 immunoreactivity in vulval LS (32.13 +/- 15.11 epidermal cells per 100 basal cells) compared to normal vulval skin (7.52 +/- 5.04 epidermal cells per 100 basal cells) (p < 0.001), whereas the MIB 1 labelling index was lower in vulval LS (39.45 +/- 15.88 epidermal cells per 100 basal cells) than in normal controls (86.26 +/- 32.31 epidermal cells per 100 basal cells) (0.001 < p < 0.01). In contrast, there was no significant difference in p53 immunoreactivity or MIB 1 labelling index between non-genital LS and normal controls.(ABSTRACT TRUNCATED AT 250 WORDS)

HPV-associated epithelial atypia in oral warts in HIV+ patients

Reported are oral mucosal warts (HPV common antigen-positive) from 7 adult HIV+ patients in which there was cytologic atypia and disordered growth. Lesions were papillary, white to red in color, and were located on the lip, gingiva, palate, tongue, and buccal mucosa. Histologically, the keratinocytes in the lesions exhibited atypical features in the form of hyperchromatism and karyomegaly. Koilocytes were frequently seen in the upper level keratinocytes where HPV common antigen was identified. The dysplastic areas, which ranged from mild to severe, typically showed abrupt limiting margins. All lesions exhibited intense PCNA reactivity from basement membrane to surface. Nuclei of mid-level and basal keratinocytes of 3 specimens stained positively for p53 protein. We believe that the atypia found in these lesions represents cytologic change that has malignant potential. The subtype of the HPV in these lesions has not yet been determined.

p53 expression in pseudoepitheliomatous hyperplasia, keratoacanthoma, and squamous cell carcinoma of skin

BACKGROUND

Expression of p53 protein has been described in a variety of human malignant tumors. Recent reports have also demonstrated its presence in benign and reactive lesions. The significance of p53 expression is unclear.

METHODS

This study examines the p53 expression in proliferative lesions of skin, including 6 pseudoepitheliomatous hyperplasia, 33 keratoacanthoma, and 45 squamous cell carcinoma, and to evaluate its significance.

RESULTS

p53 expression was observed in all of the six cases of pseudoepitheliomatous hyperplasia, 78.8% of keratoacanthoma, and 75.5% of squamous cell carcinoma. The staining pattern of pseudoepitheliomatous hyperplasia and keratoacanthoma was generally less intense and extensive compared with that of squamous cell carcinoma. A keratoacanthoma with nuclear atypia that showed strong and extensive p53 staining was also encountered. The perilesional skin in sun-exposed sites often showed the presence of p53-positive keratinocytes. Control skin taken from the buttock was negative for p53 protein. Conversely, p53 was often expressed in carcinomas arising from sun-exposed as well as sun-protected sites. p53 positivity involved mainly the undifferentiated cells at the base of the epidermis or periphery of tumor cords. Differentiated keratinized cells were not stained. p53-positive fibroblasts were also noted in the inflammatory and granulation tissues of pseudoepitheliomatous hyperplasia.

CONCLUSIONS

p53 expression in skin is common and appears to be an early event in a series of genetic alterations reflecting underlying actinic damage, which may lead to but does not necessarily indicate neoplastic or malignant transformation. Because p53 staining is seen in proliferative and undifferentiated cells and ceases to be expressed when the cells differentiate, it appears that the expression of p53 protein, mutant or wild-type, is an indicator of immaturity and proliferative capacity of the cell rather than one of neoplasia or malignancy.

p53 gene mutations in human skin cancers and precancerous lesions: comparison with immunohistochemical analysis

Mutations of exons 3 through 9 of the p53 gene in skin lesions were screened in 23 cases of squamous cell carcinoma (SCC), 25 cases of basal cell carcinoma (BCC), two cases of Bowen's disease, 10 cases of solar keratosis, and five cases of keratoacanthoma by polymerase chain reaction--single strand conformation polymorphism analysis. Mutations of the p53 gene were detected in seven of 23 SCCs (30%), three of 25 BCCs (12%), and none in all cases of Bowen's disease, solar keratosis, or keratoacanthoma. Of 23 cases of SCC, mutations were detected in four of 15 SCCs (27%) that originated in the sunlight-exposed skin region, in two of three SCCs (67%) that originated in the scar tissue, and in one of three SCCs (33%) that originated in radiation dermatitis. Mutations of C-->T transition predominated in SCC and BCC that originated in the sunlight-exposed skin region. Mutations of C-->A or CC-->AT observed in tumors that originated in the predisposed conditions, presumably unrelated to UV light, are different from those found in UV light-related SCC or BCC. Twelve cases of SCC were comparatively analyzed with the immunohistochemical staining with anti-p53 antibody. Two of four cases with positive staining had missense mutations, and three of eight cases with negative staining had nonsense mutations. Based on these findings, immunohistochemical results do not necessarily mean the presence or absence of p53 gene mutations in skin tumors, and sequence analysis is essential for determining whether the gene is mutated.

p53 immunoreactivity in cutaneous PUVA tumors is similar to that in other non-melanoma skin neoplasms

Expression of the p53 tumor suppressor gene product was determined in keratoses and skin cancers associated with psoralen photochemotherapy (PUVA). An immunocytochemical study was employed using CM-1 (polyclonal) and Do-1 (monoclonal) antibodies to human wild-type p53. Thirty-two cutaneous lesions and 20 perilesional PUVA-irradiated skin biopsies were examined from 7 patients, all of whom had received more than 200 PUVA treatments and/or a cumulative UVA dose of greater than 1000J/cm2 as treatment for widespread plaque psoriasis. p53 immunoreactivity was seen in 7 of 15 squamous cell carcinomas (46.7%), 5 of 8 dysplastic keratoses (62.5%) and in no basal cell carcinomas or benign keratoses. The overall prevalence of p53 immunoreactivity in 46.2% of malignant or dysplastic PUVA-associated skin tumors is similar to that previously found by our group in comparable skin tumors from the general population. Most patients with lesions showing positive p53 immunoreactivity had, however, been exposed to additional risk factors before receiving PUVA therapy. p53 gene sequencing of PUVA-associated non-melanoma skin cancer (NMSC) may clarify whether p53 mutation contributes to the development of these tumors and whether this relates to PUVA therapy or prior carcinogen exposure.

The relation between p53 mutation and p53 immunostaining in non-melanoma skin cancer

Extensive study of the p53 gene has established its role as a tumour-suppressor gene, and the involvement of mutant p53 in a wide spectrum of human malignancy. Many mutations of p53 result in a protein product that is abnormally stable, so that it becomes readily detectable by immunocytochemistry. In contrast, under normal conditions, it has been considered that levels of wild-type p53 were too low to be detectable. Although positive immunocytochemistry has been used as a marker of mutation, recent evidence suggests that this assumption may not always be valid. We have carried out both PCR-sequencing of exons 5-8 of the p53 gene in 20 basal cell carcinomas (BCC), and immunocytochemistry of these tumours with the anti-p53 antibody DO7. Twenty cases of Bowen's disease, in which we had previously documented mutations, were also immunostained. We report a low rate of p53 mutation in the BCCs we examined (2/20), and a discrepancy between tumours with positive immunostaining and those with mutation in both Bowen's disease and BCC. Of eight tumours in which we detected mutation, only four were immunopositive: of 19 immunopositive samples, only four showed detectable mutation. We discuss the implications of our results for the use of positive immunostaining in clinical diagnosis, and the involvement of p53 in skin carcinogenesis.