Absence of deletions but frequent loss of expression of p16INK4 in human ovarian tumours

Meta-analysis demonstrates no association between p16 ink4a promoter methylation and epithelial ovarian cancer

BACKGROUND

p16 ^INK4A (p16) functions as a tumor suppressor gene in various malignancies. Aberrant p16 methylation has been proposed to be essential in ovarian carcinogenesis. However, it is unclear whether p16 can be used as a diagnostic marker owing to the small sample sizes in previous studies.

METHODS

To determine whether p16 promoter methylation is associated with epithelial ovarian cancer and can thus be used as a diagnostic marker, we performed a meta-analysis of published studies. The following databases were searched using a systematic search method: PubMed, Web of Science, EMBASE, and Chinese National Knowledge Infrastructure. We used a random-effects model to analyze the relative risk (RR); we also evaluated between-study heterogeneity, subgroup heterogeneity, and publication bias.

RESULTS

Our meta-analysis included eight eligible studies, with 428 ovarian cancers and 278 normal tissue samples and benign neoplasms. p16 promoter methylation was identified in 5.4 to 43.2% (median 27.86%) of ovarian cancers and 0 to 37.5% (median 15.8%) of normal tissue and benign neoplasms indicating that no significant association exists between p16 promoter methylation and epithelial ovarian cancer. However, the pooled results also showed that the RR was 1.52 (95% CI 0.80-2.87) in the ovarian cancer cases versus the corresponding normal and benign cases under the random-effects model. Between-study heterogeneity was determined through a sensitivity analysis; the I ² value did not change when one study was excluded.

CONCLUSIONS

Our study showed that p16 promoter methylation cannot be used to differentiate benign from malignant epithelial ovarian tumors. Therefore, p16 promoter methylation cannot be used as a marker for diagnosing the early stage of ovarian cancer.

Epigenetic alteration of p16 and retinoic acid receptor beta genes in the development of epithelial ovarian carcinoma

Silencing of tumor suppressor and tumor-related genes by promoter hypermethylation is one of the major events in ovarian carcinogenesis. In this study, we analyzed aberrant promoter methylation of p16 and RAR-β genes in 134 epithelial ovarian carcinomas (EOCs), 23 low malignant potential (LMP) tumors, 26 benign cystadenomas, and 15 normal ovarian tissues. Methylation was investigated by methylation-specific PCR (MSP), and the results were confirmed by bisulfite DNA sequencing. Relative gene expression of p16 and RAR-β was done using quantitative reverse transcriptase PCR (qRT-PCR) on 51 EOC cases, 9 LMP tumors, and 7 benign cystadenomas with 5 normal ovarian tissues. Aberrant methylation for p16 and RAR-β was present in 43 % (58/134) and 31 % (41/134) in carcinoma cases, 22 % (05/23) and 52 % (12/23) in LMP tumors, and 42 % (11/26) and 69 % (18/26) in benign cystadenomas. No methylation was observed in any of the normal ovarian tissues. The mRNA expression level of p16 and RAR-β was significantly downregulated in EOC and LMP tumors than the corresponding normal tissues whereas the expression level was normal in benign cystadenomas for p16 and slightly reduced for RAR-β. A significant correlation of p16 promoter methylation was observed with reduced gene expression in EOC. For RAR-β, no significant correlation was observed between promoter methylation and gene expression. Our results suggest that epigenetic alterations of p16 and RAR-β have an important role in ovarian carcinogenesis and that mechanism along with methylation plays a significant role in downregulation of RAR-β gene in ovarian cancer.

DNA methylation markers in colorectal cancer

Colorectal cancer (CRC) arises as a consequence of the accumulation of genetic and epigenetic alterations in colonic epithelial cells during neoplastic transformation. Epigenetic modifications, particularly DNA methylation in selected gene promoters, are recognized as common molecular alterations in human tumors. Substantial efforts have been made to determine the cause and role of aberrant DNA methylation ("epigenomic instability") in colon carcinogenesis. In the colon, aberrant DNA methylation arises in tumor-adjacent, normal-appearing mucosa. Aberrant methylation also contributes to later stages of colon carcinogenesis through simultaneous methylation in key specific genes that alter specific oncogenic pathways. Hypermethylation of several gene clusters has been termed CpG island methylator phenotype and appears to define a subgroup of colon cancer distinctly characterized by pathological, clinical, and molecular features. DNA methylation of multiple promoters may serve as a biomarker for early detection in stool and blood DNA and as a tool for monitoring patients with CRC. DNA methylation patterns may also be predictors of metastatic or aggressive CRC. Therefore, the aim of this review is to understand DNA methylation as a driving force in colorectal neoplasia and its emerging value as a molecular marker in the clinic.

Alteration of cell-cycle regulation in epithelial ovarian cancer

In spite of the clinical importance of epithelial ovarian cancer (EOC), little is known about the pathobiology of its precursor lesions and progression. Regulatory mechanisms of the cell cycle are mainly composed of cyclins, cyclin-dependent kinases (CDK), and CDK inhibitors. Alteration of these mechanisms results in uncontrolled cell proliferation, which is a distinctive feature of human cancers. This review describes the current state of knowledge about the alterations of cell-cycle regulations in the context of p16-cyclin D1-CDK4/6-pRb pathway, p21-p27-cyclin E-CDK2 pathway, p14-MDM2-p53 pathway, and ATM-Chk2-CDC25 pathway, respectively. Recent evidence suggests that ovarian cancer is a heterogenous group of neoplasms with several different histologic types, each with its own underlying molecular genetic mechanism. Therefore, expression of cell cycle regulatory proteins should be tested separately according to each histologic type. In serous ovarian carcinoma, high expression of p16, p53, and p27 and low expression of p21 and cyclin E were shown. In addition, this review focuses on the prognostic significance of cell cycle-regulating proteins in EOC. However, it is difficult to compare the results from different groups due to diverse methodologies and interpretations. Accordingly, researchers should establish standardized criteria for the interpretation of immunohistochemical results.

The clinical importance of Ki-67, p16, p14, and p57 expression in patients with advanced ovarian carcinoma

The present study addressed the impact of p14, p16, p57, and Ki-67 in a large cohort of uniformly treated patients with stage III ovarian cancer in relation to other clinicopathologic variables and prognosis. We immunohistochemically studied 171 primary tumors from previously untreated patients with advanced ovarian carcinomas for expression of Ki-67, p16, p14, and p57. High protein levels of Ki-67 (>10% positive nuclei) were found in 144 cases (84%), p16 (>50% positive nuclei) in 53 cases (31%), p57 (>10% positive nuclei) in 41 cases (24%), and p14 (any positive nuclei) in 19 cases (11%). A correlation between high Ki-67 expression and presence of residual disease after primary surgery (P = 0.019), ascites (P = 0.006), higher International Federation of Gynecology and Obstetrics substage (P < 0.001), poor differentiation (P < 0.001), and higher Silverberg histopathologic grade (P < 0.0001) was seen. High expression of p16 correlated to poor differentiation (P = 0.033) and higher Silverberg histopathologic grade (P = 0.018). In univariate analysis, high expression of Ki-67 (P = 0.0001) and p16 (P = 0.005) was associated with poor survival. However, in multivariate analysis, only high expression of Ki-67 was significantly associated with shorter survival (P = 0.025). No correlations were seen between expression of p14 and p57 and clinicopathologic parameters. None of the factors studied was able to predict response to chemotherapy. Our results showed that Ki-67 represents an independent prognostic predictor in stage III ovarian cancer. We did not find p16, p14, and p57 to be useful as prognostic markers.

Analysis of p16 gene mutation, deletion and methylation in patients with arseniasis produced by indoor unventilated-stove coal usage in Guizhou, China

The aim of this study was to determine p16 gene mutation, deletion, and promoter 5' CpG island hypermethylation in peripheral blood mononuclear leukocyte of patients with arseniasis as attributed to exposure to indoor unventilated coal stove. The role of the aberrant change of p16 gene in the induction and development of carcinogenesis in endemic arsenisiasis region in China was also examined. Polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP), multiplex PCR (mPCR), methylation-specific PCR (MSP), and sequencing techniques were performed to detect (1) mutation of the p16 gene exon 2, (2) homozygous deletion of the p16 gene exon 1 and exon 2, and (3) hypermethylation of the promoter CpG island in peripheral blood mononuclear leukocyte of patients with arseniasis. Results showed no mutation was found in exon 2 of p16 gene. The homozygous deletion frequency of p16 gene was 5 and 15% in control and arseniasis patients, respectively. The homozygous deletion occurred mainly in exon 2, with significant deletion frequencies of 9, 13, and 20% in mild, intermediate, and severe arseniasis groups. The significant homozygous deletion frequency was 9 and 39% in noncarcinoma and carcinoma individuals. The positive rate of p16 gene promoter CpG island hyermethylation was 42 and 2% in the exposed group and the control group, respectively. The positive rate was 26, 42, and 50% in mild, intermediate, and severe arseniasis. The marked different positive rate was 22 and 56% in noncarcinoma and carcinoma individuals, respectively. In conclusion, homozygous deletion and hypermethylation of p16 gene may play an important role in the initiation and development of manifestations seen in endemic arseniasis including carcinogenesis.

p16(CDKN2) gene polymorphism: association with histologic subtypes of epithelial ovarian cancer in China

p16 is an important tumor suppressor gene, which is inactivated in many kinds of tumors. The common variants of p16 may be associated with the risk of certain tumors development. We analyzed the frequency of two adjacent polymorphisms in p16 exon 3 (540C-->G and 580C-->T) and their haplotype in blood samples from epithelial ovarian cancer (EOC) patients and healthy controls using polymerase chain reaction-restriction fragment length polymorphism. The results showed that the genotype frequency of p16 580C-->T polymorphism was significantly different among histologic subtypes of EOC (P= 0.02). T allele carriers significantly reduced the risk of serous EOC; the adjusted odds ratio was 0.40 (95% CI = 0.19-0.84). There are neither association between p16 540C-->G polymorphism and EOC development, progression, nor association between the haplotypes of two single nucleotide polymorphisms and the tumor development. Our results suggested that the p16 580C-->T polymorphism might affect the individual susceptibility to specific subtypes of EOC. Different types of ovarian cancer might adopt distinct carcinogenetic pathways. However, this result may be further validated in a larger sample of patients.

Abnormalities of the RB1 pathway in ovarian serous papillary carcinoma as determined by overexpression of the p16(INK4A) protein

Dysfunction of proteins involved in the G1 to S transition of the cell cycle, such as p16(INK4A) and RB1, is common in many cancer types. A screen of p16 protein expression was performed in benign, borderline, and invasive ovarian tumors, together with endometrial cancers, aligned on a tissue microarray. We observed frequent p16 overexpression in serous papillary carcinomas of ovarian and endometrial origin. An extended cohort of ovarian serous papillary carcinomas was examined to further evaluate the frequency of p16 overexpression. Strong, uniform staining in the majority of cancer cells occurred commonly in invasive serous papillary ovarian cancers, particularly in grade 3 carcinomas. RB1 protein expression abnormalities were rare. Our data indicate that abnormalities in the retinoblastoma pathway, as determined by p16 overexpression, are common in serous papillary carcinomas and are probably an early event.

Methylation and messenger RNA expression of p15INK4b but not p16INK4a are independent risk factors for ovarian cancer

PURPOSE

The purpose of this research was to compare methylation status and mRNA expression of p15INK4b and p16INK4a in serous epithelial ovarian cancer tissues and normal ovarian tissues.

EXPERIMENTAL DESIGN

We analyzed the DNA methylation status and mRNA expression of p15INK4b and p16INK4a in 52 ovarian cancer specimens and 40 normal ovarian specimens by using methylation-specific PCR and real-time reverse transcription-PCR, respectively.

RESULTS

Although the p15INK4b and p16INK4a mRNA expression levels were highly correlated with each other (P < 0.001), the methylation status did not seem to be linked with levels of mRNA expression, as no association between the two events was found for either gene. Promoter hypermethylation of p15(INK4b) was more common in ovarian cancer (30.8% for the 52 cases) than in normal ovaries (5% for the 40 controls without ovarian cancer; P = 0.005) but not methylation of p16INK4a (25% for cancer versus 37.5% for normal; P = 0.288). The relative mRNA expression levels of p15INK4b were significantly lower in ovarian cancer (12.9%) than in normal ovaries (41.7%; P = 0.008) but not those of p16INK4a (27% for cases versus 32.8% for controls; P = 0.754). Only high methylation rate and low mRNA expression of p15INK4b were independent risk factors for ovarian cancer (adjusted odds ratio, 5.67; 95% confidence interval, 0.85-37.9 for high methylation rate and odds ratio, 8.98; 95% confidence interval, 1.58-50.9 for low mRNA expression, respectively).

CONCLUSIONS

Our results suggest that epigenetic alterations in p15INK4b but not p16INK4a have an important role in ovarian carcinogenesis and that mechanisms other than methylation may exist to reduce gene expression of p15INK4b in ovarian cancer.

Cyclin D1, p53, and p21Waf1/Cip1 expression is predictive of poor clinical outcome in serous epithelial ovarian cancer

PURPOSE

Dysregulation of cell cycle control, in particular G(1)-S-phase transition, is implicated in the pathogenesis of most human cancers, including epithelial ovarian cancer (EOC). However, the prognostic significance of aberrant cell cycle gene expression in EOC remains unclear.

EXPERIMENTAL DESIGN

The expression of selected genes from the pRb pathway that regulates G(1)-S-phase progression, including cyclin D1, p16(Ink4a), cyclin E, p27(Kip1), p21(Waf1/Cip1), and p53, was examined in a consecutive series of 134 serous EOC using immunohistochemistry and the results correlated to disease outcome.

RESULTS

Molecular markers predictive of reduced overall survival in univariate analysis were overexpression of cyclin D1 (P = 0.03) and p53 (P = 0.03) and reduced expression of p27(Kip1) (P = 0.05) and p21(Waf1/Cip1) (P = 0.02), with the latter three also being prognostic for a shorter progression-free interval. In addition, patients displaying overexpression of p53 with concurrent loss of p21(Waf1/Cip1) had a significantly shorter overall (P = 0.0008) and progression-free survival (P = 0.0001). On multivariate analysis, overexpression of cyclin D1 and combined loss of p21(Waf1/Cip1) in the presence of p53 overexpression were independent predictors of overall survival. Similarly, the combination of p21(Waf1/Cip1) loss and p53 overexpression was independently predictive of a shorter progression-free interval. Overexpression of p53 and cyclin E and reduced expression of p27(Kip1) and p21(Waf1/Cip1) were significantly associated with increasing tumor grade.

CONCLUSIONS

This study confirms that dysregulation of cell cycle genes is common in EOC, and that aberrant expression of critical cell cycle regulatory proteins can predict patient outcome in serous EOC.

Methylation of tumor suppressor gene p16 and prognosis of epithelial ovarian cancer

OBJECTIVE

Methylation of p16 promoter was evaluated in ovarian cancer to determine the role of p16 methylation in ovarian cancer prognosis.

METHODS

Two hundred and forty-nine patients with primary epithelial ovarian cancer were selected for the study; these patients were followed for a median of 31 months. Genomic DNA extracted from fresh frozen tumor tissues were treated with sodium bisulfite and were analyzed for p16 methylation using methylation-specific PCR (MSP). Cox regression survival analysis was performed to examine the associations of p16 methylation with progression-free and overall survivals.

RESULTS

Of the 249 patients, 100 (40%) were tested positive for p16 promoter methylation. The status of p16 methylation did not change significantly with patient age, disease stage, histological grade, residual tumor size, and debulking results, although p16 methylation seemed to occur more often in patients with advanced diseases or aggressive tumors. Compared to those without p16 methylation, patients with p16 methylation had significantly higher risk for disease progression (P = 0.01). The relative risk for progression was 1.69 (95% CI: 1.12-2.54), and the association remained statistically significant (RR = 1.54, 95% CI: 1.01-2.34) after adjusting for clinical and pathological variables. The risk for death was also higher in methylation positive patients than in methylation negative patients (RR = 1.33, 95% CI: 0.88-2.00), but the difference was not statistically significant.

CONCLUSION

The study suggests that promoter methylation in the p16 gene is associated with ovarian cancer progression, and evaluation of p16 methylation may have values in predicting ovarian cancer prognosis.

Role of cell-cycle regulatory proteins in gynecological cancer

Human malignant tumors are characterized by abnormal proliferation resulting from alterations in cell-cycle regulatory mechanisms. This review summarizes the current knowledge about these aberrations in malignant tumors of the ovary, endometrium, cervix uteri, and vulva. The data indicate that analysis of single cell cycle stimulating or inhibiting proteins partly produces unexpected, apparently paradoxical results, and cell-cycle regulatory pathways should be regarded as a whole in order to identify the molecular mechanisms leading to abnormal tumor cell proliferation. For the papillomavirus (HPV)- associated cervical and vulvar carcinomas, the manifold effects of the viral oncogenes E6 and E7 on cell-cycle control are described.

Gene therapy for ovarian cancer: progress and potential

Gene therapy remains a promising therapeutic modality for ovarian cancer. Yet much work remains to be done to see gene therapy realize its full potential in elucidating the complex genetic interactions of delivered genes within target cancer cells and in the development of improved vector systems. Because most neoplasms involve multiple mutations, the targeting of a single mutation is unlikely to achieve total tumor control: gene therapy strategies that target multiple cellular processes or invoke various antitumor approaches need to be investigated. Additionally, current vector systems do not transduce ovarian cancer cells efficiently and are hampered by immune responses that further limit their efficacy. Additionally, limitations in vector specificity lead to transduction of normal cells and subsequent toxicity. Investigators are developing refinements to current gene therapy approaches that would address these limitations and that are soon to be incorporated into clinical trials. It is hoped that these advances will lead to improvements in the therapeutic index for ovarian cancer gene therapy and provide another effective therapeutic tool for this deadly disease.

P16INK4a protein expression is associated with poor survival of the breast cancer patients after CMF chemotherapy

Immunohistochemical assay for p16 protein expession was performed in 192 breast carcinoma patients treated with adjuvant chemotherapy. p16 expression was observed in 78 cases (40.6%). The frequency of p16 expression significantly decreased in moderately differentiated (histologic grade II) cancers, 20 (19.6%) of 102. In poorly differentiated cancers (histologic grade III), p16 expression was not observed in all 16 cases. p16 expression was significantly associated with histologic grade of the breast carcinomas (p < 0.001). The proliferative index (PI: S + G2/M) of individual tumors was measured by DNA flow cytometry. In 114 tumors with PI less than 20%, p16 expression was observed in 59 tumors (49.1%). In the tumors with PI equal or more than 20%, p16 expression was observed in 22 (28.2%) of 78 cases. p16 expression was significantly decreased in the tumor with higher PI (p =0.003). For the other clinicopathologic variables, no significant association was found with p16 expression status. Immunohistochemical assay for p53 protein expression was performed on the same breast carcinomas. There was no significant association between p16 and p53 expression in breast carcinomas. During median follow-up period of 52 months (range: 40-72 months), 46 patients (25.8%) had recurrent disease and 32 patients (18.91%) died of recurrent disease. p16 expression was observed in 20 (43.5%) of 46 patients with recurrent disease, while its expression was observed in 58 patients (39.7%) of 146 patients who were free of recurrence during the study period. p16 expression had no significant impact on predicting recurrence of breast carcinoma. Fourteen patients (12.2%) of 114 patients whose tumors did not show p16 expression died of recurrent breast carcinoma, whereas 18 patients (23.1%) of 78 patients with p16 expressing tumor died during the follow-up period. There was a significant difference of patient survival according to p16 expression status (p = 0.039). These results indicate that p16 expression is useful in predicting response to chemotherapy in breast cancer patients. p16 protein seems to have a role in tumor growth and differentiation of the breast carcinoma.

Loss of expression of the p16 tumor suppressor gene is more frequent in advanced ovarian cancers lacking p53 mutations

OBJECTIVE

The aim of this study was to test the hypothesis that p53 mutations are less frequent in ovarian cancers with alterations in other genes that regulate G1 progression.

METHODS

Expression of G1 stimulatory (cyclins D1 and E, cdk4, Ki67) and inhibitory (p16, Rb, p27, p14) genes was analyzed using Western blots in 84 primary ovarian cancers and seven cell lines of known p53 mutation status. Expression of p16 and Rb also was determined using immunohistochemistry and the p16 gene was examined for homozygous deletions and mutations.

RESULTS

Loss of p16 protein was more frequent in ovarian cancers with wild-type p53. All four cell lines with wild-type p53 had lost p16 compared to only one of three with mutant p53 genes. p16 expression was absent in 34% (28/82) of primary ovarian cancers, and this was significantly more common in cases with wild-type p53 (14/28, 50%) compared to those with p53 mutations (14/54, 26%, P = 0.03). Homozygous deletion of the p16 gene was found in cell lines lacking p16, but not in any primary cancers. p16 loss was more common in serous (21/52, 40%) than nonserous cancers (4/23, 17%, P = 0.07). Cases that expressed p16 were more likely to express high levels of Rb (47/55, 85%) than p16-negative cases (12/28, 43%, P < 0.001). Loss of Rb occurred in 5/30 (17%) ovarian cancers lacking p53 mutations compared to 5/54 (9%) cases with p53 mutations (P = 0.48). Expression of G1 stimulatory proteins (cyclins D1 and E, cdk4, Ki67) did not correlate with p53 mutation status.

CONCLUSIONS

Loss of expression of the p16 tumor suppressor occurs more often in ovarian cancers lacking p53 mutations. These data are consistent with the paradigm that inactivation of p53 is less of a requisite event in ovarian carcinogenesis when another G1 regulatory gene such as p16 already has been inactivated.

Müllerian inhibiting substance: an instructive developmental hormone with diagnostic and possible therapeutic applications

Dr. Alfred Jost pioneered the field of reproductive endocrinology with his seminal observation that two hormones produced by the testes are required for the male embryo to develop a normal internal reproductive tract. T induces the Wolffian ducts to differentiate into epididymides, vasa deferens, and seminal vesicles. Müllerian inhibiting substance (MIS) causes regression of the Müllerian ducts, which in its absence would normally develop into the Fallopian tubes, uterus, and upper vagina as is observed in female embryos. This review will summarize our current understanding of molecular mechanisms underlying the function of MIS both as a fetal gonadal hormone that causes Müllerian duct regression and as an adult hormone, the roles for which are currently being investigated, i.e., inhibition of steroidogenesis, germ cell development, and cancer. We will also address the regulation of MIS expression as one of the first genes expressed after the commitment of the bipotential gonads to differentiate into testes under the influence of SRY, the gene on the sex-determining region of the Y chromosome. We will discuss what is known regarding MIS signal transduction, which as with other members of the TGFbeta family of growth and differentiation factors, occurs through a heteromeric complex of single transmembrane serine/threonine kinase receptors to effect downstream signaling events, including Smad, nuclear factor-kappaB, beta-catenin, and p16 activation. Finally, we will assess the clinical relevance of studying MIS in patients with persistent Müllerian duct syndrome and our efforts to determine the therapeutic value of MIS for patients with ovarian and other MIS receptor-expressing cancers.

Possible associations among expression of p14(ARF), p16(INK4a), p21(WAF1/CIP1), p27(KIP1), and p53 accumulation and the balance of apoptosis and cell proliferation in ovarian carcinomas

BACKGROUND

Although there are several reports of changes in expression of cyclin-dependent kinase inhibitors in ovarian carcinomas, little is known about their associations with tissue kinetics in the various histologic subtypes.

METHODS

In total, 131 carcinomas were immunohistochemically investigated for expression of p14(ARF) (p14), p16(INK4a) (p16), p21(WAF1/Cip1) (p21), and p27(Kip1) (p27). The results also were compared with data for apoptosis, cell proliferation, p53 status, and survival. Western blot and mRNA analyses were conducted on 35 malignant ovarian tumor samples.

RESULTS

Significant differences in tissue kinetics determined by ratios of apoptotic relative to mitotic indices were observed among histologic subtypes of ovarian carcinomas, showing a shift toward predominance of cell proliferation in serous and cell deletion in clear cell types. The expression of p16, p21, p27, and p53 was associated closely with changes in cell proliferation rather than apoptosis and survival, dependent on the subtype. Positivity for p16 and p21 in the Western blot assay was significantly related to the results for immunohistochemical but not mRNA analyses, indicating possible posttranscriptional regulation of these genes.

CONCLUSIONS

The findings indicate that the several cyclin-dependent kinase inhibitors investigated are expressed differently among histologic subtypes of ovarian carcinomas, associated with differences in tissue kinetics and the balance of apoptosis and cell proliferation.

Mullerian inhibiting substance inhibits ovarian cell growth through an Rb-independent mechanism

Müllerian inhibiting substance (MIS), a transforming growth factor-beta family member, causes regression of the Müllerian duct in male embryos. MIS overexpression in transgenic mice ablates the ovary, and MIS inhibits the growth of ovarian cancer cell lines in vitro, suggesting a key role for this hormone in postnatal development of the ovary. This report describes a mechanism for MIS-mediated growth inhibition in both a human epithelial ovarian cancer cell line and a cell line derived from normal ovarian surface epithelium, which is the origin of human epithelial ovarian cancers. MIS-treated cells accumulated in the G(1) phase of the cell cycle and subsequently underwent apoptosis. MIS up-regulated the cyclin-dependent kinase inhibitor p16 through an MIS type II receptor-mediated mechanism and inhibited growth in the absence of detectable or inactive Rb protein. Prolonged treatment with MIS down-regulated the Rb-related protein p130 and increased the Rb family-regulated transcription factor E2F1, overexpression of which inhibited growth. These findings demonstrate that p16 is required for MIS-mediated growth inhibition in ovarian epithelial cells and tumor cells and suggest that up-regulation of E2F1 also plays a role in this process.

Inverse expression of Cdk4 and p16 in epithelial ovarian tumors

OBJECTIVES

The aim of this study was to elucidate the expression and the correlation of two cell cycle regulators, cdk4 and its inhibitor p16, in a series of benign, borderline, and malignant ovarian tumors and to evaluate whether their alterations correlate with clinicopathologial parameters and patients' prognosis in epithelial ovarian carcinomas.

METHODS

Immunohistochemical analysis using anti-cdk4 and anti-p16 antibodies was carried out for 103 paraffin sections of ovarian tumors, and Western blot analysis and cdk4 activity assay were performed in 26 fresh ovarian tumor samples.

RESULTS

The results of immunohistochemistry showed that 60.61 and 69.70% of benign, 69.57 and 56.52% of borderline, and 74.47 and 40. 43% of malignant tumors expressed cdk4 and p16, respectively, demonstrating increased cdk4 and decreased p16 expression in ovarian carcinomas. A significant inverse relationship between cdk4 and p16 expression was found. The loss of p16 expression was more correlated with G(2) and G(3) tumors in contrast with G(1) tumors. No significant correlation was observed between cdk4 expression and clinicopathological parameters. Neither cdk4 nor p16 expression has significant effects on overall survival by the Kaplan-Meier method. When the combined phenotypes of the two proteins were analyzed, patients with cdk4-positive/p16-negative expression had a reduced overall survival than other phenotypes of cdk4/p16.

CONCLUSIONS

These data suggest that inverse expression of cdk4 and p16 may be involved in the development and progression of epithelial ovarian carcinomas. The combined phenotypes of cdk4 and p16 proteins could provide a useful prognostic indicator for patients with epithelial ovarian carcinoma.

Positive display of methylated sites: a novel method for the detection of promoter methylation

Promoter methylation represents an important mechanism for silencing gene expression in higher eukaryotes. To study methylation of the promoter of the tumor suppressor p16INK4a, a fast and simple method was developed that, in contrast to previous studies, relies on the positive display of methylated sites (PDM). The method is based on bisulfite treatment of DNA, polymerase chain reaction (PCR)-amplification of the modified DNA and restriction digest of de novo created restriction sites to positively display DNA methylation in a background of unmethylated DNA. Since methylated as well as unmethylated DNA is amplified, information on the proportion of both is provided. Using this approach, 33 ductal invasive carcinomas, 4 normal mammary tissues, and 4 cell lines were analyzed for methylation. Methylation in the p16INK4a promoter was detected in 1 of 33 carcinomas (3%) and in 0 of 4 normal tissues. The conclusion is that PDM provides a useful tool in determining the degree and pattern of promoter methylation and is suitable to screen large series of tissue samples.

Lack of mutation at p16INK4A gene but expression of aberrant p16INK4A RNA transcripts in human ovarian carcinoma

Alterations of the p16INK4A gene are frequent in various human cancers. We investigated p16INK4A gene status in 20 ovarian carcinomas by PCR (polymerase chain reaction), PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism) and sequencing techniques. None of the primary tumors showed any mutational or deletional events. However, 19 out of 20 tumors displayed both a methylated and an unmethylated p16INK4A promoter. In some of these samples, we detected aberrant p16INK4A transcripts, with partial deletions of both exons 1 and 2, which could not encode a functional p16INK4A protein. The sequences of the aberrant mRNA revealed common 4-7 nucleotide sequences before and after the deleted region, which might cause abnormal splicing of mRNA transcripts. These results suggest that both promoter methylation and aberrant mRNA processing may interfere with p16INK4A expression in ovarian tumors.

The role of p16-cyclin d/CDK-pRb pathway in the tumorigenesis of endometrioid-type endometrial carcinoma

We analysed p16 gene alteration and p16, cyclin-dependent kinase 4 (CDK4), CDK6, cyclin D1, cyclin D2, cyclin D3 and retinoblastoma protein (pRb) expression in ten normal endometriums (PE), 18 endometrial hyperplasias (EH) and 35 endometrial cancers (EC). Two of ten PE (20%), nine of 18 EH (50.0%) and 29 of 35 EC (82.9%) exhibited p16 nuclear staining. p16 expression was significantly higher in EC than EH (P = 0.0119). In the six p16 (-) EC, one was considered to have reduced gene dosage consistent with possible homozygous deletion of the CDKN2 gene and three had methylation in 5'CpG island in the promoter region of the p16 gene, whereas none showed such reduced gene dosage and four had methylation in the nine p16 (-) EH. Strong CDK4 staining was observed in 12 of 35 EC (34.3%) and one of 18 EH (5.6%). The strong expression of CDK4 was higher in EC than in EH (P = 0.0399). The expression of CDK4 was higher in EH than PE (P = 0.0054). The abnormalities of p16-cyclin D/CDK-pRb pathway were detected in 18 of 35 EC (51.4%). In conclusion, the expression of p16 and CDK4 may be an early event in the neoplastic transformation of endometrial cancer.

Ovarian cancer cells that coexpress endogenous Rb and p16 are insensitive to overexpression of functional p16 protein

Defects of the 'Rb/cyclin D1/p16 pathway' have been shown to play a critical role in the development of virtually all human malignancies assessed. To determine the contribution of G1 phase cell cycle defects to ovarian tumorigenesis, we have examined a panel of normal and tumor ovarian tissues and ovarian cancer cell lines for the expression of Rb, p16 and cyclin D1 proteins. Unlike most types of human cancer whose development involves the loss of either Rb or p16 expression, we observed the coexpression of Rb, p16 and cyclin D1 in 82% of ovarian cancer tissues and cell lines. Furthermore, the growth and cell cycle distribution profiles of three ovarian cancer cell lines (ES-2, PA-1 and NIH OVCAR-3) that coexpressed Rb and p16, were found to be unaffected by adenoviral-mediated overexpression of functional p16 protein, indicating the existence of a defect(s) downstream from p16 in these cells. By contrast overexpression of ectopic p16 in the one ovarian cancer cell line (SK-OV-3) that expressed Rb but lacked p16 protein, resulted in a G1 growth arrest. These data suggest that defects of the 'Rb/cyclin D1/p16 pathway', other than the loss of Rb or p16, may play a major role in the development of ovarian cancer.

Alteration of pRb/p16/cdk4 regulation in human osteosarcoma

Cell-cycle regulation depends on a fine balance between cyclin-cyclin-dependent kinase complexes and a family of kinase inhibitors that bind cyclin-cdk complexes and block their activity. To investigate the role of mechanisms regulating cell-cycle progression in human osteosarcomas (OS), pRb/p16/cdk4 expression was analyzed in 39 high-grade OS; 19 of these developed metastasis during follow-up. Positive reaction for functional pRB was shown by 18/39 (46%) OS, while 21/39 (54%) were negative. A higher probability of metastasis was seen in patients with negative pRb expression (p < 0.05). Furthermore, while functional pRb and D1 expression are inversely associated to metastasis occurrence, the presence of D1/cdk4 complex in our study was related to poor prognosis. We found that 10/18 pRb-positive and 14/21 pRb-negative tumors were p16-positive. No significant correlation was found between pRb and p16 expression. On the other hand, high cdk4 levels in p16-positive tumors as compared with p16-negative tumors resulted in a positive association between p16 and cdk4 expression (Chi squared = 5.98; p = 0.01). No extensive p16INK4A genomic alterations were found in tumors lacking p16-protein expression. To determine which mechanisms are involved in the down-regulation of p16 protein, the methylation status of the p16INK4 gene was evaluated on the 15 p16-negative tumors: 8 samples showed 5' CpG-island methylation; 4/8 had a complete methylation status, while in the remaining 4 the gene was only partially methylated. These data confirm the role of the pRb/p16/cdk4 pathway in OS development.

p16INK4a inactivation is not frequent in uncultured sporadic primary cutaneous melanoma

In an attempt to examine whether the inactivation of p16INK4a is an important early event in the development of sporadic melanoma in vivo, we have systematically analysed 46 uncultured primary cutaneous melanomas. Loss of heterozygosity (LOH) of chromosome region 9p21-22 (where the p16INK4a resides) was detected in 11 tumours (24%) by PCR-based LOH analyses. Direct sequencing of all three exons of the p16INK4a gene in these 11 tumours revealed no somatic mutation although germline mutations which have not been reported previously as common polymorphisms were detected in two patients. Further sequencing analyses of the p16INK4a gene exon 2 in 19 additional tumours with no evidence of LOH on 9p21-22 identified only one heterozygous C- >T mutation at codon 81 altering a proline to a leucine. A sensitive methylation-specific PCR assay did not reveal de novo methylation of the 5'CpG island in exon 1 of the p16INK4a gene in any of the tumours showing 9p21-22 allelic loss or a heterozygous p16INK4a mutation. Complete loss of p16INK4a protein, most likely due to homozygous deletion of the p16INK4a gene, was observed in 6 (15%) out of 39 evaluable cases by immunohistochemical analyses on frozen sections using two different anti-p16INK4a antibodies. The results show that inactivation of p16INK4a is not as frequent in primary melanoma as has been reported in cell lines, and warrant further search for another tumour suppressor on 9p21-22. This study also emphasizes the importance of examining uncultured primary tumours rather than cell lines to define early events in tumorigenesis.

Growth suppression of human ovarian cancer cell lines by the introduction of a p16 gene via a recombinant adenovirus

OBJECTIVE

The cell cycle regulatory protein p16 (CDKN2/cyclin dependent kinase 4 inhibitor/multiple tumor suppressor-1) causes cell cycle arrest at the G1 checkpoint by inhibiting activity of cyclin D-CDK4 complexes. The purpose of this study is to assess the effect of introduction of the p16 gene into two ovarian cancer cell lines via a recombinant adenoviral vector (Ad5CMV-p16).

METHODS

Cells lines used were SKOV3, which has a p16 deletion, and OVCA420, which has normal p16. Transduction efficiency was established by infecting cells with an adenovirus containing the Escherichia coli beta-galactosidase gene (Ad5CMV-beta-gal) at multiplicity of infection from 0 to 1000 and staining for X-gal. Cells were infected with Ad5CMV-p16 and cell growth was assessed by counting cells every other day for up to 7 days. Western blotting was done to assess for p16 expression after infection. Fluorescence-activated cell sorting after staining with propidium iodide was done to assess the effect of p16 on the cell cycle.

RESULTS

The SKOV3 cell line was transduced with the adenovirus at a slightly lower MOI than the OVCA420 cell line. Growth of the Ad5CMV-p16-infected cells was suppressed 75-80% by cell count in both cell lines and caused morphologic changes of the cells consistent with apoptosis. The p16 protein expression was seen to increase within 24 h after introduction of the p16 gene. G1 arrest of cells occurred beginning 24 h after introduction of the p16 gene.

CONCLUSIONS

These results suggest that Ad5CMV-p16 may be further studied as a potential therapeutic agent for ovarian cancer as introduction of the p16 gene into ovarian cancer cell lines causes a G1 arrest and attenuation of growth, regardless of the endogenous p16 status of the cells.

Methylation of p16INK4A in primary gynecologic malignancy

The p16INK4A gene mapped on band p21 of chromosome 9 can be inactivated via multiple mechanisms including homozygous deletion, point mutation and promoter hypermethylation in various human tumors. A polymerase chain reaction (PCR) based analysis was performed to examine methylation of the p16INK4A gene promoter in 196 primary gynecologic malignancies including 98 cervical, 49 endometrial and 49 ovarian carcinomas. Methylation of p16INK4A was detected in 31% of cervical, 20% of endometrial, and 4% of ovarian carcinomas, respectively. The incidence of p16INK4A methylation in patients with cervical and endometrial carcinomas at advanced stages (stages III-IV) was statistically higher than those at early stages (stages I-II). There were also significant differences in the incidence of p16INK4A methylation in both cancers between the patients who had died of their disease or were alive with evidence of disease, and those without evidence of disease. The results indicate that methylation of the p16INK4A gene is present in a proportion of primary gynecologic malignancies and this alteration may be associated with poor outcome in cervical and endometrial carcinomas.

Correlation between methylation status of the p16/CDKN2 gene and the expression of p16 and Rb proteins in primary non-small cell lung cancers

In order to clarify the frequency of p16 gene inactivation and its relationship with Rb expression, immunohistochemical analysis of p16 and Rb proteins was carried out on 82 paraffin-embedded sections of primary non-small cell lung cancers (NSCLCs). From immunohistochemical results, abnormal p16 expression was observed in 66% of NSCLCs, 80% in squamous cell carcinomas and 46% in adenocarcinomas. An inverse correlation between p16 and Rb expressions was noted. Moreover, the methylation status of the p16 gene was investigated by the methylation-specific polymerase chain reaction (MS-PCR) using 29 frozen samples of NSCLCs. MS-PCR revealed the methylation of the p16 gene in 10(34%)of 29 NSCLCs. All NSCLCs exhibiting methylation exhibited abnormal p16 expression and were positive for Rb. In NSCLCs, no difference in methylation status was observed with respect to clinico-pathological characteristics including histological subtype and tumor stage. Our results demonstrate that abnormality of p16 expression is frequent in primary NSCLCs and methylation of the promoter of the p16 gene occurs in 34% of primary NSCLCs, which might play a significant role in the inactivation of the p16 gene.