p16INK4a and p14ARF tumor suppressor genes are commonly inactivated in cutaneous squamous cell carcinoma

The p16(INK4a) and p14(ARF) tumor suppressor genes (TSGs) are encoded within the CDKN2A locus on chromosome 9p21 and function as cell cycle regulatory proteins in the p53 and RB pathways. Inactivation of these genes by genetic and epigenetic changes has been described in some human cancers, but their importance in cutaneous squamous cell carcinoma (SCC) has not been established. Our detailed examination of 40 cutaneous SCC revealed loss of heterozygosity of 9p21 markers in 32.5% of cases. Mutational analysis confirmed five point mutations in four of 40 SCCs. These mutations changed the amino acid sequence of p16(INK4a) in four tumors and p14(ARF) in three tumors. Promoter methylation of p16(INK4a) and p14(ARF) was detected in 13 of 36 (36%) and 16 of 38 (42%) cases, respectively. Absent protein expression was confirmed by immunohistochemistry in 13 of 16 (82%) of the tumors with biallelic inactivating events. Overall, the frequency of 9p21 alterations was 76% and for both p16(INK4a) and p14(ARF), promoter methylation is the commonest mechanism of gene inactivation. Alterations at this locus were significantly more common in tumors from immunocompetent compared with immunosuppressed individuals. These data confirm the importance of inactivation of p16(INK4a) and p14(ARF) TSGs in the pathogenesis of cutaneous SCCs.     

Epigenetic alterations in sporadic basal cell carcinomas

Basal cell carcinoma (BCC) is the most common malignant human neoplasm characterized by slow growth and virtual absence of metastases. Recently, it has become evident that along with genetic mutations epigenetic alterations play a key role in the pathogenesis of human cancer. We searched for promoter methylation of hMLH1, RASSF1A, DAPK, APC, DCR1 and DCR2 genes and BRAF mutations in BCCs in association with the clinicopathological parameters and the histological subtypes of the tumours. Fifty-two BCCs, 17 FFPE along with 35 fresh tissue samples with matching normal tissues for 26 cases were analyzed by methylation-specific PCR to assess the methylation status of hMLH1, RASSF1A, DAPK, APC, DCR1 and DCR2 genes after sodium bisulfite treatment of the tumour and normal DNA. hMLH1 and DCR1 gene expression was investigated by immunohistochemistry. BRAF mutations were studied by high resolution melting analysis. Methylation was detected at a variable frequency of 44, 33, 32.5, 32 and 14 % of DCR2, APC, DCR1, RASSF1 and DAPK promoters, respectively, whereas methylation of hMLH1 promoter was absent. No BRAF mutations were found. There was no correlation between the frequency of the promoter methylation of the above-mentioned genes and the clinicopathological features or the histological subtypes of the tumours. The relatively high frequency of RASSF1A, DCR1, DCR2 and APC promoter methylation may imply that methylation constitutes an important pathway in the tumourigenesis of BCC that could provide new opportunities in developing epigenetic therapies for BCC patients. Nevertheless, further studies are needed to establish the above-mentioned hypothesis.     

寻常性银屑病患者表皮p16INK4a基因启动子高甲基化与临床资料的相关性研究

目的：探讨斑块状银屑病患者表皮p16^INK4a基因启动子甲基化状态,并分析与其临床资料的相关性。方法：按银屑病皮损面积和严重度指数（PASI）评分评估患者病情严重程度。采用甲基化特异PCR（MAP）方法检测p16^INK4a甲基化状态。结果：①银屑病患者皮损和非皮损表皮p16^INK4a基因的甲基化率分别为32．14％（9／28）和7．14％（2／28）,皮损处明显高于非皮损处（P〈0．05）,正常对照组中无表皮p16^INK4a基因甲基化（0/38）;②进行期皮损表皮p16^INK4a基因的甲基化率明显高于稳定期皮损（P〈0．05）;③皮损表皮p16^INK4a基因甲基化阳性患者的PASI评分明显高于甲基化阴性患者（P〈0．05）。结论：斑块状银屑病患者皮损表皮p16^INK4a基因启动子甲基化率明显增高,并与皮损严重程度和活动性有关,提示p16^INK4a基因启动子高甲基化在银屑病的发病中可能起作用。     

系统性红斑狼疮患者血浆DNA p16基因启动子的甲基化状态

目的 探讨系统性红斑狼疮(SLF)患者中p16基因的甲基化状态及其在发病机制中的作用。方法 检测45例SLE患者及20例健康对照者血浆DNA甲基化状态。应用甲基化特异PcR(MSP)方法检测p16基因启动子区甲基化状态,并分析与临床表现及常规实验室检查结果之间的关联。结果 在SLE患者血浆DNA中p16基因呈现高甲基化状态,占64.44%(29/45),而健康对照组中只有1例检测到p16基因高甲基化(1/20,5%),两组间差异有统计学意义(x²=19.69,P<0.01)。活动期SLE组p16基因呈高甲基化状态者所占比率83.33%(20/24),比非活动期SLE组42.85%,(9/21)高,差异也有统计学意义(x²=8.01;P<0.01)。但初发SLE组p16基因呈高甲基化状态者所占比例(71.43%,15/21)与复发SLE组(58.33%,14/24)相比差异无统计学意义(P=0.37)。具有下列临床表现的SLE患者其血浆p16基因高甲基化状态者所占比率相对较高:关节炎(57.5%,15/26),白细胞减少(42.3%,11/26),血沉增快(56%,14/25)。结论 活动期SLE患者血浆DNAp16基因启动子区呈现明显高甲基化状态,并与关节炎、白细胞减少及血沉增快等临床表现相关;提示p16基因启动子区高甲基化可能在SLE的发病机制中起作用。     

Inactivation of tumor suppressor genes p15(INK4b) and p16(INK4a) in primary cutaneous B cell lymphoma

Primary cutaneous B cell lymphomas represent a distinct group of lymphoproliferative disorders that can be distinguished from systemic lymphoma by their good response to local treatment and favorable prognosis. In systemic B cell lymphoma, inactivation of p15(INK4b) and p16(INK4a) is frequently observed and may be associated with a poor prognosis. There have been no comprehensive studies in primary cutaneous B cell lymphomas, however. Mechanisms of p15/p16 inactivation include loss of heterozygosity, homozygous deletion, promotor region hypermethylation, and point mutation. We analyzed DNA from 36 cases of primary cutaneous B cell lymphomas, four systemic B cell lymphomas, and six benign B cell lymphoproliferative infiltrates for abnormalities of p15 and p16 using microsatellite markers for 9p21, methylation specific polymerase chain reaction, and polymerase chain reaction/single stranded conformational polymorphism analysis with exon specific primers. Expression of both p15 and p16 protein was assessed by immunohistochemistry. Loss of heterozygosity at 9p21 was identified in 2 out of 36 primary cutaneous B cell lymphomas. Hypermethylation of p15 and p16 promotor regions was identified in 8 of 35 (23%) and 15 of 35 (43%) cases, respectively. In two cases p16 hypermethylation was identified in recurrent disease but not in the initial tumor. No point mutations were identified. In seven patients, however, a polymorphism was observed in exon 3 of the p16 gene. In primary cutaneous B cell lymphomas with allelic loss or promotor hypermethylation of either p15 or p16, loss of expression in tumor cells was identified in 5 of 8 and 9 of 10 cases, respectively. Our findings suggest that p15(INK4b) and p16(INK4a) biallelic gene abnormalities are common in primary cutaneous B cell lymphomas, most frequently as a result of promotor hypermethylation. The presence of abnormalities in recurrent disease in some cases suggests that inactivation of p15 and p16 may be involved in disease progression.     

斑块状银屑病外周血单一核细胞p16基因甲基化状态的研究

目的探讨银屑病患者外周血单一核细胞p16基因甲基化状态。方法采用甲基化特异的聚合酶链反应对34例斑块状银屑病患者和35例正常人外周血单一核细胞p16基因甲基化状态进行分析,银屑病的严重程度按PASI评分评估。结果斑块状银屑病外周血单一核细胞p16基因甲基化率高于正常人,差异有统计学意义(P<0.05),但单一核细胞p16基因甲基化状态对疾病的严重程度和病程无明显影响(P>0.05)。结论斑块状银屑病外周血单一核细胞p16基因甲基化率明显增高,在银屑病的发病机制中可能起某些作用。     

Inactivation of the CDKN2A and the p53 tumour suppressor genes in external genital carcinomas and their precursors

BACKGROUND: p53 has been extensively studied in external genital carcinoma (EGC), and is frequently inactivated, but little is known about the role of the CDKN2A tumour suppressor gene in the oncogenesis of EGC. OBJECTIVES: To investigate the role of CDKN2A and p53 in the pathogenesis of EGCs and their precursor lesions vulval intraepithelial neoplasia (VIN3), penile intraepithelial neoplasia and lichen sclerosus (LS). METHODS: By means of CDKN2A and p53 mutation screening (single-strand conformational polymorphism analysis and sequencing), methylation analysis of alternative CDKN2A promoters (methylation-specific polymerase chain reaction) and p53 immununochemistry, we analysed eight invasive EGCs (five from vulva and three from penis) and 25 precancerous lesions (two undifferentiated VIN3 and 23 vulval/penile lesions of LS) from 33 patients. RESULTS: p53 mutations (mainly transversions) and CDKN2A mutations (including one hot spot) were present in 75% and 50% of invasive tumours, respectively, but were absent in all precancerous lesions. Remarkably, all CDKN2A-mutated tumours also harboured a p53 mutation. CDKN2A or p53 mutations were observed more frequently in LS-derived EGCs than in human papillomavirus-derived EGCs (P = 0.053). A positive anti-p53 staining, but without p53 mutations, was also detected in 30% of LS lesions, suggesting a p53 stabilization in response to inflammation and carcinogenic insult. Methylation of p16(INK4a) and p14(ARF) promoters was not a frequent mechanism of CDKN2A inactivation. CONCLUSIONS: Our study shows a high prevalence of co-inactivating mutations of p53 and/or CDKN2A genes in EGC, that seem to occur preferentially in LS-derived tumours and late in oncogenesis.     

p14ARF hypermethylation is common but INK4a-ARF locus or p53 mutations are rare in Merkel cell carcinoma

Although the exact molecular mechanisms of Merkel cell carcinoma (MCC) tumorigenesis are unknown, they likely involve complex genetic alterations and mutations similar to those seen in many other cancers. In this study, we obtained MCCs from 21 elderly patients (19 women, 2 men) and analyzed their DNA for mutation of exons of interest in several tumor-suppressor genes or oncogenes known to be frequently mutated in skin cancer: p53 (exons 4-8), Ras (exons 1 and 2), c-Kit (exon 11), and the INK4a-ARF locus (encoding p14 and p16) (exons 1 and 2). Direct sequence analysis revealed p53 mutations (that is, at codons 224, 234, and 294) in three tumors (14%) and p16INK4a mutations (that is, at codon 6) in one (5%). No mutations were detected in Ha-Ras, Ki-Ras, N-Ras, c-Kit, or p14ARF. On the other hand, methylation-specific PCR revealed methylation of p14ARF promoter DNA in eight of 19 analyzable tumor samples (42%) and p16INK4a promoter DNA in one of 19 analyzable tumor samples (5%). Together, these findings suggest that p14ARF silencing may be an important mechanism in MCC tumorigenesis, and thus a potential target for therapeutic intervention in this highly aggressive tumor type.     

系统性红斑狼疮患者外周血单一核细胞及中性粒细胞p16基因甲基化状态研究

目的：研究系统性红斑狼疮（SLE）患者外周血单一核细胞（PBMC）及中性粒细胞（PMNL）的P16基因甲基化状态,探讨其在SLE发病中的作用。方法：采用甲基化特异的PCR方法对25例活动期SLE患者PBMC及PMNL的P16基因甲基化状态进行分析,并与21名健康者进行对照？结果：SLE患者PBMCP16基因甲基化阳性率为76．0％（19／25）,对照组为47．6％（10／21）。两者比较差异有统计学意义（P〈0．05）;两组PMNL．P16基因甲基化率分别为54．3％（12／25）和45．7％（11／21）,差异无统计学意义（P〉0．05）。在PBMCP16基因高甲基化的SLE患者中,IgG升高者占78．9％（15／19）,与该细胞系P16基因甲基化阴性的SLE患者IgG平均水平比较,差异有统计学意义（P〈0．05）。结论：SLE患者PBMCP16基因甲基化明显异常,IgG升高与之相关,p16基因高甲基化可能在SLE的发病中起一定的作用。     

FOXE1 is a target for aberrant methylation in cutaneous squamous cell carcinoma

Background Several cancer‐related genes are silenced by promoter hypermethylation in skin cancers. However, to date the somatic epigenetic events that occur in cutaneous squamous cell carcinoma (SCC) tumorigenesis have not been well defined. Objectives To examine epigenetic abnormalities of FOXE1, a gene located on chromosome 9q22, a region frequently lost in SCC. Methods We investigated the methylation status of FOXE1 in 60 cases of cutaneous SCC by methylation‐specific polymerase chain reaction, and comparatively examined mRNA and protein expression by real‐time polymerase chain reaction and Western blot, respectively. Results We found a higher frequency of FOXE1 promoter hypermethylation in SCCs (55%), as compared with the adjacent uninvolved skin (12%) and blood control samples (9·5%). FOXE1 methylation was frequently seen in association with a complete absence of or downregulated gene expression. Treatment with the demethylating agent 5‐Aza‐2′‐deoxycytidine resulted in profound reactivation of FOXE1 expression. Conclusions These results indicate that FOXE1 is a crucial player in development of cutaneous SCC.     

Frequent abnormalities of the p15 and p16 genes in mycosis fungoides and sezary syndrome

There are few data on the molecular pathogenesis of cutaneous T cell lymphomas. A recent allelotyping study by our group identified frequent allelic loss on 9p, 10q, and 17p including losses on 9p21 in 16% of patients with mycosis fungoides and 46% with Sezary syndrome. The P15 and P16 genes are intricately linked on 9p21 and can be inactivated in melanoma and non-Hodgkin's lymphoma. We have therefore studied 76 patients with either mycosis fungoides or Sezary syndrome for abnormalities of these genes. DNA samples were analyzed for loss of heterozygosity, homozygous deletion, intragenic mutations, and promoter methylation. In addition P15 and P16 protein expression was assessed. Microsatellite analysis was informative in 73 of 76 cases: allelic loss on 9p21 was identified in 18 patients (25%), including 12 of 57 with mycosis fungoides (21%) and six of 16 with Sezary syndrome (37%). Single strand conformation polymorphism analysis of the entire coding regions of both genes did not identify any mutations, although two polymorphisms were identified including C613A, which has not previously been described. P15 and P16 gene promoter methylation was found in 45% and 29% of patients, respectively. Furthermore aberrant P15 protein expression was detected in 85% of patients analyzed with P15 gene abnormalities and abnormal P16 expression in 59% with P16 gene abnormalities. These abnormalities were not dependent on cutaneous stage of disease. This study suggests that abnormalities of the P15 and P16 genes are common in both early and advanced stages of mycosis fungoides and Sezary syndrome and that these genes may be inactivated by allelic loss and aberrant promoter methylation.     

Loss of CDKN2A and p14ARF expression occurs frequently in human nonmelanoma skin cancers.

BACKGROUND: The CDKN2A locus on human chromosome 9p21 encodes two proteins named p16INK4a and p14ARF, known to function as tumour suppressors via the retinoblastoma (Rb) or the p53 pathway. The p53 tumour suppressor gene is the most commonly mutated gene in human and mouse cancers. Disruption of the p53 and Rb pathways is a fundamental trend of most human cancer cells. Recent studies have shown that the CDKN2A gene plays an active role in the p53 and Rb tumour suppressor pathways. Genetic abnormalities in CDKN2A have been well documented in human melanoma, but their involvement in nonmelanoma skin cancer (NMSC) is less clear. OBJECTIVES: To determine whether genetic abnormalities in CDKN2A and p53 genes play a role in the development of NMSC. METHODS: We analysed 40 primary NMSCs in 40 patients (21 squamous cell carcinomas, 17 basal cell carcinomas and two actinic keratoses) for p16INK4a and p14ARF protein expression and for genetic alterations in exons 1alpha, 1beta and 2 of CDKN2A. RESULTS: Immunohistochemical analysis revealed loss of expression of p16INK4a and p14ARF proteins in 38 and 39 of 40 NMSCs, respectively. Amplification of genomic DNA by polymerase chain reaction revealed homozygous deletion of exon 1beta in 20% of tumours and of exon 2 in 82.5% of tumours. Of 22 NMSCs with p53 mutations, 13 (59%) had ultraviolet (UV) signature mutations in the p53 gene; all of them were strongly positive for p53 immunostaining. CONCLUSIONS: In addition to mutations in the p53 gene, loss of expression of CDKN2A via deletion also plays an important role in the pathogenesis of human NMSC. While p53 mutations are induced by UVB, deletions in CDKN2A could arise spontaneously, perhaps during tumour progression.     

Long-term growth arrest of PUVA-treated fibroblasts in G2/M in the absence of p16(INK4a) p21(CIP1) or p53

Premature aging of the skin is a prominent side-effect of psoralen photoactivation, a therapy used for different skin disorders. Recently, we demonstrated that treatment of fibroblasts with 8-methoxypsoralen and ultraviolet A irradiation resulted in growth arrest with morphological and functional changes reminiscent of replicative senescence. To further elucidate the underlying molecular mechanisms, we analysed the cell-cycle phases of the growth-arrested fibroblasts. After PUVA treatment, fibroblasts arrested in G2/M, in contrast to spontaneously senesced fibroblasts arresting in a cell-cycle phase with many features similar to G1. To address the role of the cell-cycle controlling genes p16(INK4a), p21(CIP1) and p53, we analysed the expression of these genes. p16(INK4a), p21(CIP1) and p53 protein levels increased substantially with different time kinetics in growth-arrested fibroblasts. Because p16(INK4a), p21(CIP1) and p53 are involved in replicative senescence, we applied the PUVA regimen to fibroblasts deficient in either of these genes. p16(INK4a), p21(CIP1) and p53 null mutant fibroblast strains underwent growth arrest with a senescent phenotype similar to wild-type human fibroblasts. Based on these results, we propose that redundant or alternate pathways are involved in the response of dermal fibroblasts to PUVA treatment resulting in a phenocopy of replicative senescence in vitro.     

SLE患者外周血CD4~+ T淋巴细胞DNA中p16基因启动子区甲基化研究

目的 检测SIJE患者外周血CD4~+T淋巴细胞DNA中p16基因的甲基化状态及其在SLE发病机制中的作用.方法 以Taqman探针为基础的实时定量PCR(Methylight)方法检测28例SLE患者和20例正常人CD4~+T淋巴细胞中p16基因启动子区甲基化状态.结果 SLE患者CD4~+T淋巴细胞的p16基因启动子区甲基化率(35.7%,10/28)高于对照组(10.0%,2/20).两者比较筹异有统计学意义(x~2=4.11,P<0.05).SLE患者疾病严重程度评分与对应的标准甲基化指数无统计学相父性(r_s=-0.29,P>0.05).结论 SLE患者CD4~+T淋巴细胞p16基凶甲基化异常,提示p16基因的高甲基化在SLE的发病中起一定作用.     

Deregulation of the tumour suppressor genes p14ARF, p15INK4b, p16INK4a and p53 in basal cell carcinoma

Background  Basal cell carcinoma (BCC) is a locally aggressive slowly growing tumour that rarely metastasizes and is mostly seen in older members of the population.
Objectives  To determine the involvement of the tumour suppressor genes p14^ARF, p15^INK4b, p16^INK4a and p53 in BCC.
Methods  We investigated the integrity of the CDKN2A locus in 15 BCC samples by analysing the presence of allelic imbalance/loss of heterozygosity (LOH). Moreover, we studied the mRNA expression levels of the tumour suppressor genes p14^ARF, p15^INK4b, p16^INK4a and p53 in the BCC samples and compared them with mRNA levels in the corresponding normal tissue. The presence of mutations was examined by sequencing for exons 1a and 2 of p16^INK4a.
Results  We found LOH in one BCC sample for the marker D9S1748. A polymorphism (G442A) of exon 2 was detected in three cases. p14^ARF, p15^INK4b and p53 presented high expression levels, whereas p16^INK4a exhibited low mRNA levels compared with the corresponding normal tissue. Significant correlations were detected among the genes studied.
Conclusions  Our results demonstrate a different expression profile between p16^INK4a and p14^ARF, p15^INK4b and p53 in BCC. Moreover, we found a low percentage of LOH and of a polymorphic sequence variant (Ala148Thr) for the CDKN2A locus.     

DNA hypermethylation is associated with invasive phenotype of malignant melanoma

Tumor cell invasion is one of the key processes during cancer progression, leading to life-threatening metastatic lesions in melanoma. As methylation of cancer-related genes plays a fundamental role during tumorigenesis and may lead to cellular plasticity which promotes invasion, our aim was to identify novel epigenetic markers on selected invasive melanoma cells. Using Illumina BeadChip assays and Affymetrix Human Gene 1.0 microarrays, we explored the DNA methylation landscape of selected invasive melanoma cells and examined the impact of DNA methylation on gene expression patterns. Our data revealed predominantly hypermethylated genes in the invasive cells affecting the neural crest differentiation pathway and regulation of the actin cytoskeleton. Integrative analysis of the methylation and gene expression profiles resulted in a cohort of hypermethylated genes (IL12RB2, LYPD6B, CHL1, SLC9A3, BAALC, FAM213A, SORCS1, GPR158, FBN1 and ADORA2B) with decreased expression. On the other hand, hypermethylation in the gene body of the EGFR and RBP4 genes was positively correlated with overexpression of the genes. We identified several methylation changes that can have role during melanoma progression, including hypermethylation of the promoter regions of the ARHGAP22 and NAV2 genes that are commonly altered in locally invasive primary melanomas as well as during metastasis. Interestingly, the down-regulation of the methylcytosine dioxygenase TET2 gene, which regulates DNA methylation, was associated with hypermethylated promoter region of the gene. This can probably lead to the observed global hypermethylation pattern of invasive cells and might be one of the key changes during the development of malignant melanoma cells.     

Malignant melanoma arising from nevi, p53, p16, and Bcl-2: expression in benign versus malignant components

BACKGROUND: The etiology of malignant melanoma has been the subject of much study. Tumour suppressor genes p53 and p16 and the antiapoptotic, Bcl-2, are implicated in the development and progression of malignant melanoma. OBJECTIVE: To compare the expression of p53, p16, and the Bcl-2 genes in both benign and malignant components of malignant melanoma arising from pre-existing nevocellular nevi. METHODS: Twenty cases of malignant melanoma arising from pre-existing nevi were selected and studied by immunohistochemistry for the expression of p53 (D07) CDK4I/MTS-1/INK <4, which detects both wild and mutant type, p16 CDK4I/MTS-1/INK <4, and Bcl-2 using an avidin-biotin technique on formalin-fixed, paraffin-embedded sections. RESULTS: Fifteen cases demonstrated p53 immunoreactivity in the malignant components ranging from 5 to 20% with no expression being seen in the benign components. The p16 gene showed strong nuclear reactivity in the benign components of 14 cases and weak reaction in 6 cases; the malignant components expressed weak nuclear staining in 18 cases and cytoplasmic staining in all cases. The Bcl-2 gene was expressed strongly to moderately in benign components and weakly in malignant components of nine cases, and was negative in 11 cases. CONCLUSION: Immunostaining for p53 is expressed only in the malignant component, whereas p16 and Bcl-2 showed decreased staining and a different pattern in malignant compared with benign components. These findings suggest that expression and alterations in the subcellular localization of the cell cycle regulators may contribute to the mechanism of tumourigenesis.