A Red Flag: A Case of Oropharyngeal Cancer Masquerading as an Ulcer of an Infective Origin

Oropharyngeal squamous cell carcinoma is a prevalent neoplastic condition. The incidence rate in Malaysia is rising, with human papillomavirus (HPV) infection being recognized as a significant contributing factor. Hence, it is paramount for physicians to effectively diagnose and identify significant indicators that may indicate a malignant etiology. In this study, we present a case of a middle-aged Malay male who presented with the primary symptom of persistent right throat discomfort for one month. The preliminary presentation, blood parameters, and initial histopathological examination (HPE) findings indicate the presence of an infection. However, despite undergoing several medical treatments, the patient's symptoms remain, albeit with only minor clinical improvement. Subsequently, the patient underwent a biopsy under general anesthesia, which subsequently yielded a report indicating the presence of oropharyngeal squamous cell carcinoma with a negative p16 status. Therefore, it is imperative for clinicians to possess knowledge of warning flags and exercise vigilance when encountering a patient who fails to respond despite thorough and precise evaluation. If there is a strong suspicion of malignancy, it is imperative to do a comprehensive clinical investigation and regular monitoring.

The role of chromatin-modifying enzymes and histone modifications in the modulation of p16 gene in fumonisin B1-induced toxicity in human kidney cells

Fumonisin B₁ (FB₁) poses a risk to animal and human health. Although the effects of FB₁ on sphingolipid metabolism are well documented, there are limited studies covering the epigenetic modifications and early molecular alterations associated with carcinogenesis pathways caused by FB₁ nephrotoxicity. The present study investigates the effects of FB₁ on global DNA methylation, chromatin-modifying enzymes, and histone modification levels of the p16 gene in human kidney cells (HK-2) after 24 h exposure. An increase (2.23-fold) in the levels of 5-methylcytosine (5-mC) at 100 µmol/L was observed, a change independent from the decrease in gene expression levels of DNA methyltransferase 1 (DNMT1) at 50 and 100 µmol/L; however, DNMT3a and DNMT3b were significantly upregulated at 100 µmol/L of FB₁. Dose-dependent downregulation of chromatin-modifying genes was observed after FB₁ exposure. In addition, chromatin immunoprecipitation results showed that 10 µmol/L of FB₁ induced a significant decrease in H3K9ac, H3K9me3 and H3K27me3 modifications of p16, while 100 µmol/L of FB₁ caused a significant increase in H3K27me3 levels of p16. Taken together, the results suggest that epigenetic mechanisms might play a role in FB₁ carcinogenesis through DNA methylation, and histone and chromatin modifications.

Prognostic significance of p16 protein in pancreatic ductal adenocarcinoma

The p16 gene, which is also known as CDKN2A, INK4A, or CDK4I, and its products that are known to be cell cycle inhibitors and tumor suppressors have been reported to be altered in various human tumor types. Altered p16 has been indicated to be correlated with negative p16 expression using immunohistochemistry (IHC). However, its association with the prognosis remains controversial because the findings of previous studies are inconsistent. The current study evaluated the relationship between the expression levels of p16 and the clinicopathological features associated with prognosis in patients with primary pancreatic ductal adenocarcinomas (PDACs). From January 2013 to December 2017, tissues of 103 PDAC patients who had undergone elective pancreatic resection were obtained and assessed for p16 expression by IHC. No correlation was observed between p16 status and clinicopathological factors (P>0.05). Notably, negative p16 expression on IHC was not significantly associated with poor prognosis using the Kaplan-Meier method.

Histone Deacetylation in the Promoter of p16 Is Involved in Fluoride-Induced Human Osteoblast Activation via the Inhibition of Sp1 Binding

Chronic fluorosis is a systemic condition which principally manifests as defects in the skeleton and teeth. Skeletal fluorosis is characterized by aberrant proliferation and activation of osteoblasts, however, the underlying mechanisms of osteoblast activation induced by fluoride are not fully understood. Therefore, we investigated the pathogenic mechanism of human primary osteoblast proliferation and activation in relation to histone acetylation of the promoter p16, a well-known cell cycle regulation-related gene. The results showed that sodium fluoride (NaF) induced deacetylation and decreased expression of the p16 gene via inhibition of specificity protein 1 (Sp1) binding to its response element, which accounts for NaF increasing cell viability and promoting proliferation in human primary osteoblasts. These results reveal the regulatory mechanism of histone acetylation of the p16 gene on osteoblast activation in skeletal fluorosis.

The hypermethylation of p16 gene exon 1 and exon 2: potential biomarkers for colorectal cancer and are associated with cancer pathological staging

Background

Tumor suppressor gene p16 promoter hypermethylation has been widely studied in colorectal cancer (CRC), yet its clinicopathological significance remains controversial. The methylation alterations of other regions within p16 gene are still rarely researched. The present study aimed to explore the methylation changes of p16 gene body in CRC and to find whether they were associated with clinicopathological staging of CRC.

Methods

Paired colorectal cancer tissues and corresponding adjacent normal tissues from 30 CRC patients were collected. The methylation levels of two CpG islands within p16 gene body, exon 1 and exon 2, were accurately assessed simultaneously by a LC-MS/MS method. The p16 protein expressions were assessed by immunohistochemistry assay. Statistical analyses were carried out using SPSS 17.0 software. Heat-map analysis was carried out by HemI 1.0 software.

Results

In the present study, CRC tissues showed more highly methylated than adjacent normal tissues at both CpG islands of p16 gene. And exon 2 hypermethylation was higher and more frequent than exon 1. The ROC curve analysis showed that the simultaneous use of both indicators had excellent sensitivity and specificity for distinguishing CRC tissues and adjacent normal tissues. Following, the methylation level of p16 exon 1/2 was negatively related to p16 protein expression. Further correlation analysis revealed that p16 exon 1 hypermethylation was associated with N/Dukes staging (p = 0.033), and p16 exon 2 hypermethylaiton was associated with T staging (p = 0.035).

Conclusions

The p16 gene body was remarkably hyper-methylated in CRC tissues and associated with p16 protein expression and cancer clinicopathological staging. The combination of p16 exon 1 and exon 2 could better reflect the overall methylation status of p16 gene body and provide potential biomarkers of CRC.

Double signal enhancement strategy based on rolling circle amplification and photoinduced electron transfer for ultrasensitive fluorometric detection of methylated DNA

The authors describe a novel assay for the detection of methylated DNA site. Rolling circle amplification and CdSe/ZnS quantum dots with high fluorescence efficiency are applied in this method. The CdSe/ZnS quantum dots act as electron donors, and hemin and oxygen (derived from hydrogen peroxide act as acceptors in photoinduced electron transfer. The assay, best performed at excitation/emission peaks of 450/620 nm, is sensitive and specific. Fluorometric response is linear in the 1 pM to 100 nM DNA concentration range, and the lowest detectable concentration of methylated DNA is 142 fM (S/N = 3). The method is capable of recognizing 0.01% methylated DNA in a mixture of methylated/unmethylated DNA. Graphical abstract A novel method for methylated sites detection in DNA is established. Rolling circle amplification and photoinduced electron transfer. CdSe/ZnS quantum dots with high fluorescence efficiency act as the electron donor, while G-quadruplex/hemin and hydrogen peroxide derived oxygen act as electron acceptor. It presents a linear response towards 1 pM to 100 nM methylated DNA with a correlation coefficient of 0.9968, and the lowest detectable concentration of methylated DNA was 142 fM, with selectivity significantly superior to other methods.

The synergic effect of HPV infection and epigenetic anomaly of the p16 gene in the development of cervical cancer

BACKGROUND

Cervical cancer is the most common cancer in Indian women. Infection with a high-risk human papillomavirus (HR-HPV) is the greatest risk factor for developing cervical cancer. The genetic and epigenetic changes in the tumor suppressor p16 gene is play an important role in the development of cervical cancer.

OBJECTIVE

To evaluate the expression and promoter methylation of p16 gene in HR-HPV infected squamous cell carcinoma of the uterine cervix.

METHODS

To find out p16INK4a expression and methylation status 105 squamous cell carcinoma of the uterine cervix were investigated by using immunohistochemistry and Methylation Specific PCR techniques.

RESULTS

HPV16/18 was amplified in 83.8% cases of the cervix. 80% of them were positive for HPV type 16, while only 3.8% were positive for HPV type 18. Promoter CpG island hypermethylation of p16 gene was detected in 20.9% tissue samples of cervical carcinoma. Of these hypermethylated samples 90.9% cases showed nil/very low p16INK4a expression (P= 0.001). Overexpression of p16INK4a was observed in 73.3% cases of HR-HPV infected squamous cell carcinoma of the cervix.

CONCLUSION

An association between p16 methylation, expression, and HR-HPV infection suggested the compliance of HPV infection and aberration of p16 gene have a synergic effect on initiation and progression of cervical carcinoma.

The innovative regularity and role of p16 methylation in blood during HCC development

Purpose: This study was performed to examine the regularity and role of p16 methylation in hepatocellular carcinoma (HCC) blood.

Methods: Big data of the case-control studies due to blood p16 methylation detection were collected in English and Chinese Journals. The risk of HCC's histologic process was investigated using both Meta-analysis and the quantitative correlation analysis.

Results: p16 methylation frequencies in blood were gradually increased from 0 % in normal to 10 % in benign disease, and to 60 % in HCC development. Based on p16 methylation of normal control blood, p16 methylation between normal and benign disease had no risk, and the methylation risk in HCC was significantly increased from normal to HCC through benign disease OR, 95% CI =16.23 ( 11.66, 22.58 ). Compared with the benign disease matched by HCC patient, the methylation risk of p16 in HCC was found, with the pooled OR value of 10.06 (95% IC = 7.64, 13.21) in blood. In addition, the regulatory mechanism affecting p16 methylation risk in normal blood had no role, and the strength of p16 methylation risk was rapidly increased between benign diseases and HCC blood. p16 methylation risk started from the patients with benign disease in blood. These results in blood and tissue detection were basically consistent.

Conclusions: HCC pathogenesis affecting p16 methylation don't work during normal blood, when from benign diseases to HCC bloods, can produce powerful role. The transcriptional inactivation associated with p16 methylation might start from benign liver disease, and might be increased from benign liver disease to HCC process. p16 methylation in blood can be used as a promising non-invasive biomarker to HCC's prediction and diagnosis.

Low-dose decitabine enhances chidamide-induced apoptosis in adult acute lymphoblast leukemia, especially for p16-deleted patients through DNA damage

AIM

To investigate the combined action of decitabine (DAC) with chidamide (CS055) on acute lymphoblastic leukemia (ALL) cells.

MATERIALS & METHODS

ALL cell lines as well as primary cells from 17 ALL patients were subjected to different treatments and thereafter cell counting Kit-8 (CCK-8) assay, flow cytometry and western blot were employed to determine IC₅₀, apoptosis and checkpoint kinase 1 and γH2A.X expression.

RESULTS

Low-dose DAC combined with CS055 could effectively kill ALL cells by the reduction of cell viability and induction of apoptosis. This was also observed in primary cells from 17 ALL patients, especially for those with p16 gene deletion. Suppression of checkpoint kinase 1 phosphorylation and upregulation of γH2A.X expression was demonstrated to participate in DAC plus CS055-induced apoptosis.

CONCLUSION

Low-dose DAC could enhance chidamide-induced apoptosis in adult ALL, especially for patients with p16 gene deletion through DNA damage.

p16 gene silencing along with p53 single-nucleotide polymorphism and risk of esophageal cancer in Northeast India

The high incidence of esophageal cancer in Northeast India and the unique ethnic background and dietary habits provide a great opportunity to study the molecular genetics behind esophageal squamous cell carcinoma in this part of the region. We hypothesized that in addition to currently known environmental risk factors for esophageal cancer, genetic and epigenetic factors are also involved in esophageal carcinogenesis in Northeast India. Therefore, in this study, we explored the possible association between the two important G1 cell cycle regulatory genes p16 and p53 and environmental risk factors and risk of esophageal carcinogenesis. A total of 100 newly diagnosed esophageal cancer cases along with equal number of age-, sex-, and ethnicity-matched controls were included in this study. Methylation-specific polymerase chain reaction was used to determine the p16 promoter methylation status. Single-nucleotide polymorphism at codon 72 of p53 gene was assessed by the polymerase chain reaction-restriction fragment length polymorphism method. Aberrant methylation of p16 gene was seen in 81% of esophageal cancer cases. Hypermethylation of p16 gene was not found in healthy controls. p53 Pro/Pro genotype was found to be a risk genotype in Northeast India compared with Arg/Pro and Arg/Arg. p53 variant/polymorphism was significantly associated with esophageal cancer risk in the study population under all three genetic models, namely, dominant model (Arg/Pro + Pro/Pro vs Arg/Arg odds ratio = 2.25, confidence interval = 1.19-4.26; p = 0.012), recessive model (Arg/Arg + Arg/Pro vs Pro/Pro odds ratio = 2.35, confidence interval = 1.24-4.44; p = 0.008), and homozygous model (Pro/Pro vs Arg/Arg odds ratio = 3.33, confidence interval = 1.54-7.20; p = 0.002). However, p53 variant/polymorphism was not statistically associated with esophageal cancer risk under the heterozygous model (Pro/Pro vs Arg/Pro). In the case-only analysis based on p16 methylation, the p53 variant/polymorphism (Pro/Pro or Arg/Pro) showed significant association for esophageal cancer risk (odds ratio = 3.33, confidence interval = 1.54-7.20; p = 0.002). Gene-gene and gene-environment interaction using the case-only approach revealed a strong association between p16 methylation, p53 single-nucleotide polymorphism, and environmental factors and esophageal cancer risk. Cases with p16 methylation and p53 variant/polymorphism (Pro/Pro or Arg/Pro) along with both betel quid and tobacco chewing habit (odds ratio = 8.29, confidence interval = 1.14-60.23; p = 0.037) conferred eightfold increased risk toward esophageal cancer development. This study reveals a synergistic interaction between epigenetic, genetic, and environmental factors and risk of esophageal cancer in this high-incidence region of Northeast India. The inactivation of either p16 or p53 in a majority of esophageal cancer cases in this study suggests the possible crosstalk between the important cell cycle genes.

Use of p16 FISH for differential diagnosis of mesothelioma in smear preparations

Because most of malignant pleural mesothelioma (MPM) patients first present with pleural effusion, detection of mesothelioma cells on effusion smears is critical for early diagnosis. Recently, accumulating evidence indicating that the cytological diagnosis of MPM supported by ancillary techniques is as reliable as that based on histopathology has led to new guidelines for the cytopathologic diagnosis of MPM. Based on the guidelines, a combination of cytomorphological criteria and verification by ancillary techniques is required for the cytologic diagnosis of MPM. Detection of p16 homozygous deletion by fluorescence in situ hybridization (FISH) is the most reliable ancillary technique for differentiating MPM from reactive mesothelial cells (RMC) because of its relatively high sensitivity and extremely high specificity. We showed that the p16 deletion status of MPM cells in pleural effusions reflected that of the underlying invasive MPM tissues, indicating the usefulness of p16 FISH in effusion smear cytology for MPM diagnosis. Thus, for differentiating MPM from RMC, we propose to perform p16 FISH as often as possible. A positive p16 homozygous deletion supports the diagnosis of MPM. However, a negative result does not rule out the possibility of MPM. In such cases, a morphological assessment is critical. Therefore, we analyzed the morphological characteristics of p16 deletion-positive mesothelioma cells using a combination of virtual microscopy and p16 FISH, and identified three morphological characteristics useful for the differentiation, including cell-in-cell engulfment with or without hump formation, multinucleate cells, and larger berry-like cell aggregates. Diagn. Cytopathol. 2016;44:774-780. © 2016 Wiley Periodicals, Inc.

Hepatitis B virus X protein induces the histone H3 lysine 9 trimethylation on the promoter of p16 gene in hepatocarcinogenesis

Our previous study showed hepatitis B virus X protein (HBx) suppresses the p16 expression in hepatocarcinogenesis. In this study we explored the relationship between HBx and trimethylation of H3K9 (H3K9me3), and elucidated the underlying mechanisms in HBx inducing the tumor suppressor p16 gene silence. SMMC-7721 and HepG2 hepatoma cell lines were transfected with HBx-expressing plasmid. Immunohistochemistry, Western blotting and real-time polymerase chain reaction, were performed to detect the expressions of HBx, H3K9me3, and jumonji domain-containing protein 2B (JMJd2B). H3K9me3 enrichment on the p16 promoter was measured by immunoprecipitation-PCR (ChIP-PCR) analyses, and 39 cases of hepatitis B virus (HBV) associated-hepatocellular carcinoma (HCC) and corresponding noncancerous liver tissues were also examined. We demonstrated that HBx was able to upregulate H3K9me3 and suppress JMJd2B mRNA and protein levels in SMMC-7721 and HepG2 hepatoma cell lines. JMJd2B, as a specific target of H3K9me3 for demethylation, was inversely correlated with the levels of H3K9me3 in SMMC-7721 (r=-0.666, P<0.05) and HepG2 cells (r=-0.625, P<0.05). The ChIP-PCR data indicated that HBx remarkably increased H3K9me3 on the p16 promoter region. Immunohistochemistry analysis showed that H3K9me3 expression in HBx positive HCC samples were significantly higher than that in HBx negative HCC tissues and were associated with decreased levels of JMJd2B expression. JMJd2B immunoreactivity was also remarkably inversed to that of HBx in HCC tissues (r=-0.630, P<0.05). Our results provide evidence that HBx is able to induce H3K9me3 on the p16 promoter via the decrease of demethylase JMJd2B expression and thus promote the repression of p16 gene expression to enhance hepatocarcinogenesis.

Analysis of p16 gene mutations and their expression using exhaled breath condensate in non-small-cell lung cancer

The aim of the present study was to investigate the mutational status of exons 1 and 2 of the p16 gene in the exhaled breath condensate (EBC) of patients with non-small-cell lung cancer (NSCLC) and determine the feasibility and clinical significance of applying EBC in the diagnosis of NSCLC. Polymerase chain reaction and DNA sequencing were applied to detect exon 1 and 2 alterations of the p16 gene in EBC by comparing 58 samples from NSCLC patients and 30 from healthy controls. Of the 58 EBC samples from NSCLC patients, 54 were successfully tested and 8 cases of mutations were identified, of which 3 were in exon 1 and 5 in exon 2. The mutation rate was 14.81% (8/54). There were no p16 gene mutations in the 30 samples obtained from healthy controls. EBC p16 gene mutations exhibited no statistically significant differences according to gender, smoking history, pathological type, degree of differentiation and presence or absence of lymph node metastasis. The p16 gene mutation rate was proportional to the tumor stage (P<0.05). Therefore, the detection of the p16 gene mutation in EBC may be used as a novel molecular marker to assist in the diagnosis of NSCLC.

High metastatic node number, not extracapsular spread or N-classification is a node-related prognosticator in transorally-resected, neck-dissected p16-positive oropharynx cancer

BACKGROUND

Due to unique biology and prognosis, precise identification of predictive parameters is critical for p16+ oropharyngeal squamous cell carcinoma (OPSCC). Prior studies showing absence of prognostication from extracapsular spread (ECS) and/or high N-classification in surgically-treated p16+ OPSCC necessitate new, evidence-based prognosticators.

METHODS

A prospectively assembled cohort of 220, transoral surgery+neck dissection±adjuvant therapy-treated, p16+ OPSCC patients was analyzed. Disease recurrence and disease-specific survival (DSS) were primary endpoints.

RESULTS

Median follow-up was 59 (12-189) months. Distribution of metastatic node numbers was: 0 in 9.5% (n=21), 1 in 33.6% (n=74), 2 in 17% (n=38), 3 in 14.5% (n=32), 4 in 8.2% (n=18), and ⩾5 in 17% (n=37). ECS was recorded in 80% (n=159), and N2c-N3 in 17% (n=38). Adjuvant radiotherapy and chemoradiotherapy was administered in 44% and 34%. Recurrence developed in 22 patients (10%); 4 local, 5 regional, 2 regional and distant, and 11 distant. The 3- and 5-year DSS estimates were 94.6% and 93%. Multivariable logistic regression identified ⩾5 nodes and T3-T4 classification as predictors for recurrence. In multivariable Cox analyses, ⩾5 nodes, T3-T4 classification and margins were prognostic for DSS. ECS, N2c-N3 classification and smoking were not prognostic.

CONCLUSIONS

Metastatic node number, not ECS or high N-classification is an independent nodal predictor of outcomes in surgically-treated p16+ OPSCC patients. Despite high DSS (~80%), closer surveillance for recurrence is recommended for patients with ⩾5 metastatic nodes.

Arsenic exposure is associated with DNA hypermethylation of the tumor suppressor gene p16

Background

Occupational and environmental exposure to inorganic arsenic leads to development of cancer and represents a significant health hazard in more than 70 countries. The underlying mechanism for arsenic-induced carcinogenesis remains unclear. Laboratory studies suggest that arsenic is a poor mutagen but may cause epigenetic silencing of key tumor suppressor genes such as p16 through DNA hypermethylation. However, the evidence for an association between human arsenic exposure and abnormal DNA methylation of tumor suppressor genes is lacking.

Findings

Paired case–control studies were conducted involving 40 individuals with high arsenic exposure and arsenicosis, 40 individuals with similarly high exposure to arsenic but without arsenicosis, and 40 individuals with normal exposure to arsenic. DNA methylation status of p16 was determined using methylation-specific PCR. Conditional logistic regression analysis showed that DNA hypermethylation of p16 gene was significantly associated with high arsenic exposure (Odds Ratio = 10.0, P = 0.0019) independently of the development of arsenicosis (Odds Ratio = 2.0, P = 0.1343).

Conclusions

High exposure of arsenic in human is positively linked to DNA hypermethylation of p16 gene, suggesting that epigenetic silencing of key tumor suppressor may be an important mechanism by which arsenic promotes cancer initiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12995-014-0042-5) contains supplementary material, which is available to authorized users.

Enhanced serum methylated p16 DNAs is associated with the progression of gastric cancer

OBJECTIVE

The present study is to evaluate the effect of methylated p16 on the progression in patients with gastric cancer (GC), and develop a useful biomarker for predicting patient's prognosis.

DESIGN AND METHODS

Methylation status of p16 in GC, their corresponding para-cancerous histological normal tissues (PCHNTs), preoperative peritoneal washes (PPWs) and serum were assessed using real-time methylation specific-PCR (MSP).

RESULTS

The frequency of p16 methylation was significantly higher in GC tissues (85.9%; 79/92) than that in paired PCHNTs (12.0%; 11/92) (P<0.0001). p16 methylation correlated closely with lymph node metastasis, peritoneal metastasis, TNM stage, et al (all P<0.05). Both frequency of p16 methylation in PPWs and serum were 79.7% (63/92). The Aζ value of the receiver-operator characteristic curve for methylated p16 was 0.899 for serum and PPWs, compared to that in GC tissues. The patients with elevated methylated p16 levels in tumor tissues had poorer disease-free survival (DFS) rates than those without (P=0.042). There is a narrow significant difference in median survival time of more than 30 months between patients with and without preoperatively detectable methylated p16 in serum (P=0.057). Methylated p16 in PPWs revealed no significant association with survival (P=0.129). Cox regression analysis showed that serum methylated p16 DNAs was an independent risk factor for GC patients, with a remarkable decrease in DFS 30 months after surgical resection of the gastric tumor.

CONCLUSIONS

Serum methylated p16 DNAs might serve as a potential biomarker for the progression and a prognostic factor in gastric cancer patients.

Cytological examination of pleural cavity lavage accompanied by the study of gene promoter hypermethylation of p16 and O6-methylguanine-DNA-methyltransferase genes in diagnostics of non-small cell lung cancer metastatic changes into pleura

AIM OF THE STUDY

Metastases of non-small cell lung cancer (NSCLC) into pleura disqualify a patient from surgery and present a bad prognostic index. The aim of the study was to find out whether washing out the pleural cavity in such cases and examining obtained washings for presence of cancer cells will help to detect early NSCLC metastases into pleura, and also whether negative results of the cytology determine whether hypermethylation of these genes will increase the sensitivity of this examination.

MATERIAL AND METHODS

The study consisted of the examination of 76 patients, including 59 operated on for NSCLC and 17 operated on for other reasons. Pleural washing fluid collected during the surgery was subjected to cytological examination as well as examined to determine the presence of promoter region hypermethylation of p16 and MGMT genes.

RESULTS

Positive cytological results of pleural lavage were confirmed in 4 persons (7%) with NSCLC. The presence of promoter region hypermethylation of one or both examined genes was found in 3 patients (18%) in the control group and in 47 (80%) in the study group. Sex, occupational exposure, smoking cigarettes, and NSCLC histological type did not have an influence on the presence of cancer cells or hypermethylation in the pleural lavage fluid. Positive cytology results were more frequent at the T4 stage of NSCLC. Hypermethylation was more frequent in the research group (p < 0.01). Cancer cells and hypermethylation did not occur more frequently in pleural lavage fluid of patients with metastases into pleura.

CONCLUSIONS

The cytological examination and promoter region hypermethylation assessment of the p16 gene and MGMT gene in pleural lavage cells do not allow one to detect early metastasis of NSCLC into pleura.

5-aza-2'-deoxycytidine induces demethylation of p16 gene in human gastric cancer cells and up-regulates its expression

AIM: To investigate the effects of 5-aza-2'-deoxycytidine (5-Aza-CdR) on methylation and expression of p16 gene in the human gastric cancer cell line SGC7901, and to discuss the mechanism of p16 gene silencing in human gastric cancer cells, as well as the regulating effect of the demethylating agent on p16 gene expression.

METHODS: SGC7901 cells were cultured in RPMI 1640 medium and were treated with different concentrations (1 × 10^-7 mol/L, 5 × 10^-7 mol/L, 1 × 10^-6 mol/L, 5 × 10^-6 mol/L) of DNA methyltransferase inhibitor 5-Aza-CdR. Methylation-specific polymerase chain reaction (MSP) was used to detect the promoter methylation state of the p16 gene. RT-PCR and Western blotting were used to detect expression of p16 mRNA and protein before and after treatment with 5-Aza-CdR, respectively.

RESULTS: Promoter hypermethylation of the p16 gene was detected in SGC7901 cells, and p16 was expressed at a low level before treatment. After treatment with 5-Aza-CdR, the promoter region of the p16 gene exhibited a demethylation state, and its expression was increased at the mRNA and protein levels.

CONCLUSION: Promoter hypermethylation is a major mechanism of p16 gene silencing in human gastric cancer cells, and can be reversed by the demethylating agent 5-Aza-CdR. Demethylating agents can regulate the expression of the p16 gene. The corresponding ratio of the group mRNA and protein expression prior to treatment when the concentration of 5-Aza-CdR is 1 × 10^-7, 5 × 10^-7, 1 × 10^-6, 5 × 10^-6 mol/L are 2.21 ± 0.36, 2.01 ± 0.31; 2.82 ± 0.39, 2.22 ± 0.33; 2.98 ± 0.42, 3.15 ± 0.43, 3.35 ± 0.55, and 3.75 ± 0.61 respectively.

Retroviral introduction of the p16 gene into murine cell lines to elicit marked antiproliferative effects

The p16 gene is a candidate tumor suppressor, because mutation of the gene has been reported in many transformed cell lines and some primary tumor tissues. We have examined this possibility in murine cell lines (NIH3T3 and RSV-M) which lack p16 gene expression. Full-length human p16 cDNA was obtained from a HeLa cell line using polymerase chain reaction amplification. We constructed two separate retrovirus vectors carrying this p16 cDNA. First, we transduced the p16 cDNA into the murine cell lines using a retrovirus vector harboring the neomycin-resistance gene. The p16 gene-transduced cells formed no colonies after selection with G418, in contrast to the vector-transduced cells. Next, we used another retrovirus vector that expresses both the p16 cDNA and the Lac Z gene, which enabled us to distinguish affected cells from unaffected ones. Proliferation of the p16 gene-transduced cells was markedly inhibited and morphological change in the cells was also observed. Thus, we concluded that the p16 gene has an antiproliferative effect on the cell cycle and that the loss of its function may play a major role in dysregulated proliferation of the cells.

Loss of heterozygosity on the short arm of chromosome 9 without p16 gene mutation in gastric carcinomas

A putative tumor suppressor gene, p16 (MST1; multiple tumor suppressor 1/CDK4I; cyclin-dependent kinase 4 inhibitor), was isolated and mapped on the short arm of chromosome 9 (9p). The significance of p16 mutations in gastric tumorigenesis was examined by assessing p16 mutations as well as loss of heterozygosity (LOH) on 9p in 13 gastric adenomas and 45 adenocarcinomas. LOH on 9p (IFNA; alpha-interferon locus) was detected in 22% (5/23 informative cases) of differentiated adenocarcinomas, 10% (1/10) of undifferentiated carcinomas and none (0/6) of the adenomas. Although we found a sequence polymorphism at the second position of codon 99 (CGC/CAC) of the p16 in one gastric adenoma patient, no somatic mutations were detected in any of the gastric adenomas or adenocarcinomas. These results suggest that p16 mutations probably do not contribute to gastric tumorigenesis. However, these data suggest that another tumor suppressor gene on 9p (near the IFNA locus) may contribute to the progression of differentiated adenocarcinoma of the stomach.