Proteins involved in pRb and p53 pathways are differentially expressed in thin and thick superficial spreading melanomas

"Paradoxical" p16 overexpression in cutaneous melanoma: Molecular and immunohistochemical analysis of a rare phenomenon with a focus on cell cycle regulatory molecules

BACKGROUND

One of the most relevant genetic alterations in cutaneous melanoma (CM) is the biallelic inactivation/loss-of-heterozygosis (LOH) of cyclin-dependent kinase inhibitor 2 A (CDKN2A), which results in the immunohistochemical loss of p16 frequently found in CM. However, we recently described a rare case of dermal/deep-seated melanoma arising in giant congenital nevus (DDM-GCN) with p16 overexpression combined with p53 loss and tumor protein 53 (TP53) mutation. Herein, we reported a case series of CM with p16 overexpression and analyzed their clinicopathologic features, immunohistochemical expression of the cell cycle regulatory molecules (CCRM: p53, p21, Cyclin D1, Rb), and mutational landscape.

METHODS

We retrospectively tested for p16 all cases of CM diagnosed at our institution between January 1st 2019-April 1st 2022. In CM with p16 overexpression, we reported clinicopathologic features, immunohistochemical results for melanocytic markers and CCRM, and mutational landscape investigated with a next-generation sequencing (NGS) panel. In cases with zonal p16 overexpression, the immunohistochemical assessment for melanocytic markers and CCRM, as well as the NGS analysis have been performed in both components {with and without p16 overexpression [p16(+)c and p16(-)]}.

RESULTS

Overexpression of p16 was found in 10/2879 (0.35%) CM [5/10 (50%) diffuse and 5/10 (50%) zonal]. We combined the immunohistochemical results for CCRM and molecular data to classify the cases as follows: a) Group 1 with altered expression of at least one CCRM but no TP53 mutations [3/10 (30%), all with Rb altered/lost]; b) Group 2 with altered expression of at least one CCRM and TP53 mutations [4/10 (40%), all with p53 altered]; c) Group 3 with normal expression of CCRM and no TP53 mutations [3/10 (30%), all with mutations in MAPK pathway genes (NRAS and BRAF)]. In CM with zonal p16 overexpression, the histologic appearance of p16(+)c was heterogeneous, whereas combining CCRM profiles and molecular data the cases could be categorized as follows: a) cases with the same CCRM and molecular profiles in both p16(+)c and p16(-)c; b) cases with p16(+)c showing additional genetic mutations and/or modifications of CCRM expression.

CONCLUSIONS

p16 overexpression is a rare event, occurring in advanced-stage, clinically- and histologically-heterogeneous CM. These lesions may be classified into three different groups based on CCRM expression and mutational profiles (including TP53 mutation). The analysis of CM with zonal p16 overexpression suggests that, at least in a subset of cases, this phenomenon could represent a sign of "molecular progression" due to the acquisition of additional genetic mutations and/or modifications of the CCRM profile.

Targeting the USP7/RRM2 axis drives senescence and sensitizes melanoma cells to HDAC/LSD1 inhibitors

Deubiquitinating enzymes are key regulators of the ubiquitin-proteasome system and cell cycle, and their dysfunction leads to tumorigenesis. Our in vivo drop-out screens in patient-derived xenograft models identify USP7 as a regulator of melanoma. We show that USP7 downregulation induces cellular senescence, arresting melanoma growth in vivo and proliferation in vitro in BRAF- and NRAS-mutant melanoma. We provide a comprehensive understanding of targets and networks affected by USP7 depletion by performing a global transcriptomic and proteomics analysis. We show that RRM2 is a USP7 target and is regulated by USP7 during S phase of the cell cycle. Ectopic expression of RRM2 in USP7-depleted cells rescues the senescent phenotype. Pharmacological inhibition of USP7 by P5091 phenocopies the shUSP7-induced senescent phenotype. We show that the bifunctional histone deacetylase (HDAC)/LSD1 inhibitor domatinostat has an additive antitumor effect, eliminating P5091-induced senescent cells, paving the way to a therapeutic combination for individuals with melanoma.

High prevalence of p16 staining in malignant tumors

p16 (CDKN2A) is a member of the INK4 class of cell cycle inhibitors, which is often dysregulated in cancer. However, the prevalence of p16 expression in different cancer types is controversial. 15,783 samples from 124 different tumor types and 76 different normal tissue types were analyzed by immunohistochemistry in a tissue microarray format. p16 was detectable in 5,292 (45.0%) of 11,759 interpretable tumors. Except from adenohypophysis in islets of Langerhans, p16 staining was largely absent in normal tissues. In cancer, highest positivity rates were observed in uterine cervix squamous cell carcinomas (94.4%), non-invasive papillary urothelial carcinoma, pTaG2 (100%), Merkel cell carcinoma (97.7%), and small cell carcinomas of various sites of origin (54.5%-100%). All 124 tumor categories showed at least occasional p16 immunostaining. Comparison with clinico-pathological data in 128 vulvar, 149 endometrial, 295 serous ovarian, 396 pancreatic, 1365 colorectal, 284 gastric, and 1245 urinary bladder cancers, 910 breast carcinomas, 620 clear cell renal cell carcinomas, and 414 testicular germ cell tumors revealed only few statistically significant associations. Comparison of human papilloma virus (HPV) status and p16 in 497 squamous cell carcinomas of different organs revealed HPV in 80.4% of p16 positive and in 20.6% of p16 negative cancers (p<0.0001). It is concluded, that a positive and especially strong p16 immunostaining is a feature for malignancy which may be diagnostically useful in lipomatous, urothelial and possibly other tumors. The imperfect association between p16 immunostaining and HPV infection with high variability between different sites of origin challenges the use of p16 immunohistochemistry as a surrogate for HPV positivity, except in tumors of cervix uteri and the penis.

Epigenetics in the Diagnosis and Therapy of Malignant Melanoma

Epigenetic mechanisms are fundamentally important for cancer initiation and development. However, a survey of the literature reveals that, to date, they appear less comprehensively investigated in melanoma than in many other cancers, e.g., prostate, breast, and colon carcinoma. The aim of this review is to provide a short summary of epigenetic aspects of functional relevance for melanoma pathogenesis. In addition, some new perspectives from epigenetic research in other cancers with potential for melanoma diagnosis and therapy are introduced. For example, the PrimeEpiHit hypothesis in urothelial carcinoma, which, similarly to malignant melanoma, can also be triggered by a single exogenous noxa, states that one of the first steps for cancer initiation could be epigenetic changes in key genes of one-carbon metabolism. The application of such insights may contribute to further progress in the diagnosis and therapy of melanoma, a deadly type of cancer.

Immunohistochemical Expression of p16 in Melanocytic Lesions: An Updated Review and Meta-analysis

CONTEXT

- Making an accurate diagnosis for melanocytic lesions has always been challenging for pathologists, especially when dealing with difficult-to-diagnose cases. Misdiagnosis of melanoma and melanocytic lesions in general has tremendous medical-legal implications, often leading to unnecessary and excessive use of adjunctive tests. Although molecular testing is of much interest and there is great support for its development, currently, for most melanocytic lesions, immunohistochemical studies remain the most practical method for assistance in the routine diagnosis of melanocytic lesions for the average pathologist.

OBJECTIVES

- To review the practical use of p16 immunohistochemistry for evaluating melanocytic lesions, particularly for differentiating benign from malignant tumors, and to perform a meta-analysis of primary studies evaluating p16 immunohistochemistry in melanocytic lesions.

DATA SOURCES

- A PubMed database search for literature reporting melanocytic lesions and p16 immunohistochemistry was performed. Essential information from each study (number of samples, antibody used, collection dates, overall p16 immunohistochemistry results, and general method of interpretation) was tabulated and analyzed. Examples of representative cases showing p16 immunostaining pattern are also illustrated.

CONCLUSIONS

- Incorporation of p16 immunohistochemistry for the diagnosis of melanocytic lesions is of limited use, especially for the purpose of differentiating benign from malignant lesions. Evaluation of multiple studies reveals a wide range of results. However, there appears to be some value for the use of p16 in distinguishing nodal nevi from metastatic melanoma within nodes. The method of interpretation (nuclear versus cytoplasmic staining) also appears to give differing results, as studies considering only nuclear staining appeared to show more consistent results from study to study.

Cell cycle analysis can differentiate thin melanomas from dysplastic nevi and reveals accelerated replication in thick melanomas

Cell replication integrates aberrations of cell cycle regulation and diverse upstream pathways which all can contribute to melanoma development and progression. In this study, cell cycle regulatory proteins were detected in situ in benign and malignant melanocytic tumors to allow correlation of major cell cycle fractions (G1, S-G2, and G2-M) with melanoma evolution. Dysplastic nevi expressed early cell cycle markers (cyclin D1 and cyclin-dependent kinase 2; Cdk2) significantly more (p < 0.05) than common nevi. Post-G1 phase markers such as cyclin A, geminin, topoisomerase IIα (peaking at S-G2) and aurora kinase B (peaking at G2-M) were expressed in thin (≤1 mm) melanomas but not in dysplastic nevi, suggesting that dysplastic melanocytes engaged in the cell cycle do not complete replication and remain arrested in G1 phase. In malignant melanomas, the expression of general and post-G1 phase markers correlated well with each other implying negligible cell cycle arrest. Post-G1 phase markers and Ki67 but none of the early markers cyclin D1, Cdk2 or minichromosome maintenance protein 6 (Mcm6) were expressed significantly more often in thick (>1 mm) than in thin melanomas. Marker expression did not differ between metastatic melanomas and thick melanomas, with the exception of aurora kinase A of which the expression was higher in metastatic melanomas. Combined detection of cyclin A (post-G1 phase) with Mcm6 (replication licensing) and Ki67 correctly classified thin melanomas and dysplastic nevi in 95.9 % of the original samples and in 93.2 % of cross-validated grouped cases at 89.5 % sensitivity and 92.6 % specificity. Therefore, cell cycle phase marker detection can indicate malignancy in early melanocytic lesions and accelerated cell cycle progression during vertical melanoma growth.

p16 Expression Is Lost in Severely Atypical Cellular Blue Nevi and Melanoma Compared to Conventional, Mildly, and Moderately Atypical Cellular Blue Nevi

Background. Significant decreases in p16 expression have been shown to occur in melanoma compared to Spitz tumors, and loss of p16 staining has been found to correlate with melanoma tumor progression. However, comparison of p16 between atypical cellular blue nevi (CBN) and melanoma has not been reported previously. Methods. p16 immunohistochemical staining was evaluated in 14 atypical CBN, 8 conventional and atypical melanocytic nevi, and 16 melanomas, including 4 malignant CBN. p16 staining intensity was graded on a scale of 0–3 and the percentage of melanocytes stained with p16 was determined. Results. p16 staining was significantly higher in all CBN as a group when compared to melanomas (P = 0.001) and malignant CBN (P = 0.00008). Higher p16 expression was also seen in mildly (P = 0.0002) and moderately atypical (P = 0.02), but not severely atypical, CBN compared to melanomas. Conclusions. p16 immunohistochemical expression is higher in mildly and moderately atypical CBN compared to severely atypical CBN and melanomas. In conjunction with additional markers and histology, p16 staining may be useful in confirming the benign nature of these tumors, but is not useful in distinguishing severely atypical CBN from malignant cases, consistent with the overlapping histologic features between these tumors.

The specificity and patterns of staining in human cells and tissues of p16INK4a antibodies demonstrate variant antigen binding

The validity of the identification and classification of human cancer using antibodies to detect biomarker proteins depends upon antibody specificity. Antibodies that bind to the tumour-suppressor protein p16INK4a are widely used for cancer diagnosis and research. In this study we examined the specificity of four commercially available anti-p16INK4a antibodies in four immunological applications. The antibodies H-156 and JC8 detected the same 16 kDa protein in western blot and immunoprecipitation tests, whereas the antibody F-12 did not detect any protein in western blot analysis or capture a protein that could be recognised by the H-156 antibody. In immunocytochemistry tests, the antibodies JC8 and H-156 detected a predominately cytoplasmic localised antigen, whose signal was depleted in p16INK4a siRNA experiments. F-12, in contrast, detected a predominately nuclear located antigen and there was no noticeable reduction in this signal after siRNA knockdown. Furthermore in immunohistochemistry tests, F-12 generated a different pattern of staining compared to the JC8 and E6H4 antibodies. These results demonstrate that three out of four commercially available p16INK4a antibodies are specific to, and indicate a mainly cytoplasmic localisation for, the p16INK4a protein. The F-12 antibody, which has been widely used in previous studies, gave different results to the other antibodies and did not demonstrate specificity to human p16INK4a. This work emphasizes the importance of the validation of commercial antibodies, aside to the previously reported use, for the full verification of immunoreaction specificity.

Correlation of cell cycle regulatory proteins (p53 and p16(ink)⁴(a)) and bcl-2 oncoprotein with mitotic index and thickness of primary cutaneous malignant melanoma

The purpose of the study was to determine the frequency of expression p53 and p16INK4a proteins and bcl-2 oncoprotein in malignant skin melanoma and to determine their correlation with the proliferative index and tumor thickness. The study involved 53 patients: 27 (51%) male and 26 (49%) female. Mitotic index showed a correlation with p53 protein expression, a negative correlation with p16INK4a protein expression. Statistically significant correlations were determined between the Breslow tumor thickness, Clark invasion level and p53 protein expression, as well as Breslow tumor thickness and bcl-2 oncoprotein expression (p<0.05), whereas there was no correlation between the p16INK4a protein expression and melanoma thicknes and Clark invasion level. Overexpression p53 protein and bcl-2 oncoprotein, with the loss p16INK4a protein of expression in the nodular melanoma, confirms a frequent loss of function of these tumor suppressor gene and oncogene, and indicates a vertical tumor growth phase. The loss of tumor suppression function the p53 protein and bcl-2 oncoprotein overexpression in cutaneous melanoma correlates with larger tumor thickness, whereas the overexpression of mutated p53 protein and loss p16INK4a protein of expression indicate a higher proliferative tumour potential. Therefore, these evaluated proteins may be the aggressive biological tumour activity markers.

Fractal dimension of chromatin is an independent prognostic factor for survival in melanoma

Background

Prognostic factors in malignant melanoma are currently based on clinical data and morphologic examination. Other prognostic features, however, which are not yet used in daily practice, might add important information and thus improve prognosis, treatment, and survival. Therefore a search for new markers is desirable. Previous studies have demonstrated that fractal characteristics of nuclear chromatin are of prognostic importance in neoplasias. We have therefore investigated whether the fractal dimension of nuclear chromatin measured in routine histological preparations of malignant melanomas could be a prognostic factor for survival.

Methods

We examined 71 primary superficial spreading cutaneous melanoma specimens (thickness ≥ 1 mm) from patients with a minimum follow up of 5 years. Nuclear area, form factor and fractal dimension of chromatin texture were obtained from digitalized images of hematoxylin-eosin stained tissue micro array sections. Clark's level, tumor thickness and mitotic rate were also determined.

Results

The median follow-up was 104 months. Tumor thickness, Clark's level, mitotic rate, nuclear area and fractal dimension were significant risk factors in univariate Cox regressions. In the multivariate Cox regression, stratified for the presence or absence of metastases at diagnosis, only the Clark level and fractal dimension of the nuclear chromatin were included as independent prognostic factors in the final regression model.

Conclusion

In general, a more aggressive behaviour is usually found in genetically unstable neoplasias with a higher number of genetic or epigenetic changes, which on the other hand, provoke a more complex chromatin rearrangement. The increased nuclear fractal dimension found in the more aggressive melanomas is the mathematical equivalent of a higher complexity of the chromatin architecture. So, there is strong evidence that the fractal dimension of the nuclear chromatin texture is a new and promising variable in prognostic models of malignant melanomas.

Cyclin D1 and D3 expression in melanocytic skin lesions

Cyclins, cyclin-dependent kinases, as well as proteins cooperating with them are responsible for cell cycle regulation which is crucial for normal development, injury repair, and tumorigenesis. D-type cyclins regulate G1 cell cycle progression by enhancing the activities of cyclin-dependent kinases, and their expression is frequently altered in tumors. Disturbances in cyclin expression were also reported in melanocytic skin lesions. The objective of the study was to evaluate the expression of cyclins D1 and D3 in common, dysplastic, and malignant melanocytic skin lesions. Forty-eight melanocytic skin lesions including common nevi (10), dysplastic nevi (24), and melanomas (14) were diagnosed by dermoscopy and excised. Expression of cyclin D1 and D3 was detected by immunohistochemistry and quantified as percentage of immunostained cell nuclei in each sample. In normal skin, expression of cyclins D1 and D3 was not detected. The mean percentage of cyclin D1-positive nuclei was 7.75% for melanoma samples, 5% for dysplastic nevi samples, and 0.34% for common nevi samples. For cyclin D3, the respective values were 17.8, 6.4, and 1.8%. Statistically significant differences in cyclin D1 expression were observed between melanomas and common nevi as well as between dysplastic and common nevi (p = 0.0001), but not between melanomas and dysplastic nevi. Cyclin D3 expression revealed significant differences between all investigated lesion types (p = 0.0000). The mean cyclin D1 and D3 scores of melanomas with Breslow thickness <1 mm and >1 mm were not significantly different. G1/S abnormalities are crucial for the progression of malignant melanoma, and enhanced cyclin D1 and D3 expression leading to increased melanocyte proliferation is observed in both melanoma and dysplastic nevi. In histopathologically ambiguous cases, lower cyclin D3 expression in dysplastic nevi can be a diagnostic marker for that lesion type.

Cell cycle inhibitor p21/ WAF1/ CIP1 as a cofactor of MITF expression in melanoma cells

p21/ WAF1/ Cip1 (p21), a cyclin-dependent kinase inhibitor, may act as an antioncogene, but may also behave as a tumor promoting factor by inhibiting apoptosis. p21 is also a transcriptional regulator, exerting this activity independently of cyclin-dependent kinases. Increased p21 protein levels were found in a subset of melanomas. However, the mechanism(s) contributing to the tolerance of high p21 levels in melanoma cells remains unexplained. Here, we show that the p21 protein positively regulates the promoter of microphthalmia-associated transcription factor (MITF), a transcription factor which plays a central role in the expression of melanocyte-specific genes, lineage determination, and survival of melanoma cells. p21 activated the MITF promoter-reporter, occupied the promoter in vivo and cooperated with cAMP response element binding protein (CREB) in promoter activation. In addition, p21 knockdown by shRNA resulted in a decrease of MITF protein and promoter activity, and p21 protein levels correlated with MITF mRNA in most cell lines tested. As the p21 gene is a known transcriptional target of MITF, the reciprocal stimulation of transcription may constitute a positive-feedback loop reinforcing MITF expression in melanoma cells. Our results might help explain the tolerance of increased p21 levels found in some melanomas.

Zebrafish have a competent p53-dependent nucleotide excision repair pathway to resolve ultraviolet B-induced DNA damage in the skin

Ultraviolet (UV) light is a primary environmental risk factor for melanoma, a deadly form of skin cancer derived from the pigmented cells called melanocytes. UVB irradiation causes DNA damage, mainly in the form of pyrimidine dimers (cis-syn cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts), and organisms have developed complex multiprotein repair processes to cope with the DNA damage. Zebrafish is becoming an important model system to study the effects of UV light in animals, in part because the embryos are easily treated with UV irradiation, and the DNA damage repair pathways appear to be conserved in zebrafish and mammals. We are interested in exploring the effects of UV irradiation in young adult zebrafish, so that we can apply them to the study of gene-environment interactions in models of skin cancer. Using the Xiphophorus UV melanoma model as a starting point, we have developed a UV irradiation treatment chamber, and established UV treatment conditions at different ages of development. By translating the Xiphophorus UV treatment methodology to the zebrafish system, we show that the adult zebrafish skin is competent for nucleotide excision DNA damage repair, and that like in mammalian cells, UV treatment promotes phosphorylation of H2AX and a p53-dependent response. These studies provide the groundwork for exploring the role of UV light in melanoma development in zebrafish.