Hypermethylation of the p16 gene and lack of p16 expression in hepatoblastoma

Summary of biological research on hepatoblastoma: a scoping review

Background

Hepatoblastoma is the most prevalent primary hepatic malignancy in children, comprising 80% of pediatric hepatic malignancies and 1% of all pediatric malignancies. However, traditional treatments have proven inadequate in effectively curing hepatoblastoma, leading to a poor prognosis.

Methods

A literature search was conducted on multiple electronic databases (PubMed and Google Scholar). A total of 86 articles were eligible for inclusion in this review.

Result

This review aims to consolidate recent developments in hepatoblastoma research, focusing on the latest advances in cancer-associated genomics, epigenetic studies, transcriptional programs and molecular subtypes. We also discuss the current treatment approaches and forthcoming strategies to address cancer-associated biological challenges.

Conclusion

To provide a comprehensive summary of the molecular mechanisms associated with hepatoblastoma occurrence, this review highlights three key aspects: genomics, epigenetics, and transcriptomics. Our review aims to facilitate the exploration of novel molecular mechanisms and the development of innovative clinical treatment strategies for hepatoblastoma.

A "Null" Pattern of p16 Immunostaining in Endometrial Serous Carcinoma: An Under-recognized and Important Aberrant Staining Pattern

The ability to distinguish endometrial serous carcinoma (SC) from high-grade endometrioid adenocarcinoma is of great importance given their differences in prognosis and management. In practice, this distinction typically relies upon the use of a focused immunohistochemical panel including p53, p16, and mismatch repair proteins. The expression of p16 is characteristically strong and diffuse in SCs, and weak and/or patchy in many high-grade endometrioid adenocarcinomas. Here, we report a subset of SCs that are entirely negative for p16 immunostaining, a pattern we refer to as "p16 null." This pattern was identified in 2 of 63 cases of SC diagnosed at our institution-1 with histologically classic features and 1 with ambiguous high-grade histologic features. These tumors otherwise showed a SC signature by immunohistochemical and demonstrated an SC pattern of genetic mutations. No mutation in the gene for p16, cyclin-dependent kinase inhibitor 2A (CDKN2A), was identified in either case. However, molecular correlates for the absent p16 expression were present, including homozygous deletion of CDKN2A in one case and hemizygous deletion of CDKN2A with promotor hypermethylation of the remaining allele in the other case. To our knowledge, this constitutes the first report conclusively demonstrating the existence of a small subset of SCs that are completely negative by p16 immunohistochemistry, and the molecular lesions responsible for this pattern. In the context of an otherwise clinically and histologically classic example of SC, we endorse this "null" p16 staining pattern as an alternative aberrant staining pattern that should not deter one from committing to this diagnosis.

DNA methylation in Hepatoblastoma-a literature review

Hepatoblastoma (HB) is the most common malignant liver tumor in children. Abnormal activation of the Wnt/β-catenin signaling pathway plays an important role in the formation and development of HB. Genes in HB show a global hypomethylation change, accompanied by hypermethylation of specific tumor suppressor genes (TSGs). This article reviews the hypermethylation changes in several TSGs, such as RASSF1A, SOCS1, APC, HHIP, and P16, and analyzes the pathways and mechanisms of TSGs regulating gene expression. The role of the methylation-regulating enzymes DNA methyltransferases (DNMTs) and ten-eleven translocation (TET) family members enzymes in the methylation changes of HB was analyzed, and it was speculated that the occurrence of HB is partly due to the obstruction of liver differentiation in the early stage of differentiation. The origin cells may be incompletely differentiated hepatocytes remaining in the liver of children after birth. Therefore, further studying the role of methylation regulating enzymes in methylation changes in HB is a promising future research direction.

EZH2 inhibition sensitizes tamoxifen‑resistant breast cancer cells through cell cycle regulation

Enhancer of zeste homologue 2 (EZH2), a catalytic subunit of polycomb repressive complex 2, is overexpressed in a number of different tumors including breast cancer, and serves important roles in cell cycle regulation, proliferation, apoptosis, tumorigenesis and drug resistance. However, it remains unclear whether EZH2 contributes to tamoxifen resistance in breast cancer. In the present study, the role of EZH2 in tamoxifen resistance in MCF‑7 cells was investigated. EZH2 was overexpressed in MCF‑7 tamoxifen‑resistant (MCF‑7 TamR) cells. EZH2 overexpression decreased the sensitivity of MCF‑7 cells to tamoxifen, and EZH2 knockdown improved the sensitivity of MCF‑7 TamR cells to tamoxifen. Furthermore, EZH2 knockdown induced cell cycle arrest in MCF‑7 TamR cells, accompanied by a decrease in cyclin D1 expression and an increase in p16 expression. EZH2 knockdown reduced p16 gene methylation in MCF‑7 TamR cells. These findings suggested that EZH2 overexpression may contribute to tamoxifen resistance in breast cancer, and EZH2 inhibition may reverse tamoxifen resistance in breast cancer by regulating the cell cycle via the demethylation of the p16 gene. Thus, EZH2 inhibitors may be effective for treating tamoxifen resistance in breast cancer.

DNA methylation landscape of hepatoblastomas reveals arrest at early stages of liver differentiation and cancer-related alterations

Hepatoblastomas are uncommon embryonal liver tumors accounting for approximately 80% of childhood hepatic cancer. We hypothesized that epigenetic changes, including DNA methylation, could be relevant to hepatoblastoma onset. The methylomes of eight matched hepatoblastomas and non-tumoral liver tissues were characterized, and data were validated in an independent group (11 hepatoblastomas). In comparison to differentiated livers, hepatoblastomas exhibited a widespread and non-stochastic pattern of global low-level hypomethylation. The analysis revealed 1,359 differentially methylated CpG sites (DMSs) between hepatoblastomas and control livers, which are associated with 765 genes. Hypomethylation was detected in hepatoblastomas for ~58% of the DMSs with enrichment at intergenic sites, and most of the hypermethylated CpGs were located in CpG islands. Functional analyses revealed enrichment in signaling pathways involved in metabolism, negative regulation of cell differentiation, liver development, cancer, and Wnt signaling pathway. Strikingly, an important overlap was observed between the 1,359 DMSs and the CpG sites reported to exhibit methylation changes through liver development (p<0.0001), with similar patterns of methylation in both hepatoblastomas and fetal livers compared to adult livers. Overall, our results suggest an arrest at early stages of liver cell differentiation, in line with the hypothesis that hepatoblastoma ontogeny involves the disruption of liver development. This genome-wide methylation dysfunction, taken together with a relatively small number of driver genetic mutations reported for both adult and pediatric liver cancers, shed light on the relevance of epigenetic mechanisms for hepatic tumorigenesis.

Global increase of p16INK4a in APC-deficient mouse liver drives clonal growth of p16INK4a-negative tumors

Reduction of β-catenin (CTNNB1) destroying complex components, for example, adenomatous polyposis coli (APC), induces β-catenin signaling and subsequently triggers activation of genes involved in proliferation and tumorigenesis. Though diminished expression of APC has organ-specific and threshold-dependent influence on the development of liver tumors in mice, the molecular basis is poorly understood. Therefore, a detailed investigation was conducted to determine the underlying mechanism in the development of liver tumors under reduced APC levels. Mouse liver at different developmental stages was analyzed in terms of β-catenin target genes including Cyp2e1, Glul, and Ihh using real-time RT-PCR, reporter gene assays, and immunohistologic methods with consideration of liver zonation. Data from human livers with mutations in APC derived from patients with familial adenomatous polyposis (FAP) were also included. Hepatocyte senescence was investigated by determining p16(INK4a) expression level, presence of senescence-associated β-galactosidase activity, and assessing ploidy. A β-catenin activation of hepatocytes does not always result in β-catenin positive but unexpectedly also in mixed and β-catenin-negative tumors. In summary, a senescence-inducing program was found in hepatocytes with increased β-catenin levels and a positive selection of hepatocytes lacking p16(INK4a), by epigenetic silencing, drives the development of liver tumors in mice with reduced APC expression (Apc(580S) mice). The lack of p16(INK4a) was also detected in liver tumors of mice with triggers other than APC reduction.

IMPLICATIONS

Epigenetic silencing of p16(Ink4a) in selected liver cells bypassing senescence is a general principle for development of liver tumors with β-catenin involvement in mice independent of the initial stimulus.

p16INK4a hypermethylation and p53, p16 and MDM2 protein expression in esophageal squamous cell carcinoma

BACKGROUND

Tumor suppressor genes p53 and p16INK4a and the proto-oncogene MDM2 are considered to be essential G1 cell cycle regulatory genes whose loss of function is associated with ESCC carcinogenesis. We assessed the aberrant methylation of the p16 gene and its impact on p16INK4a protein expression and correlations with p53 and MDM2 protein expressions in patients with ESCC in the Golestan province of northeastern Iran in which ESCC has the highest incidence of cancer, well above the world average.

METHODS

Cancerous tissues and the adjacent normal tissue obtained from 50 ESCC patients were assessed with Methylation-Specific-PCR to examine the methylation status of p16. The expression of p16, p53 and MDM2 proteins was detected by immunohistochemical staining.

RESULTS

Abnormal expression of p16 and p53, but not MDM2, was significantly higher in the tumoral tissue. p53 was concomitantly accumulated in ESCC tumor along with MDM2 overexpression and p16 negative expression. Aberrant methylation of the p16INK4a gene was detected in 31/50 (62%) of esophageal tumor samples, while two of the adjacent normal mucosa were methylated (P < 0.001). p16INK4a aberrant methylation was significantly associated with decreased p16 protein expression (P = 0.033), as well as the overexpression of p53 (P = 0.020).

CONCLUSIONS

p16 hypermethylation is the principal mechanism of p16 protein underexpression and plays an important role in ESCC development. It is associated with p53 protein overexpression and may influence the accumulation of abnormally expressed proteins in p53-MDM2 and p16-Rb pathways, suggesting a possible cross-talk of the involved pathways in ESCC development.

MT1G hypermethylation: a potential prognostic marker for hepatoblastoma

Hepatoblastoma comprises only 1% of all cancers in childhood. Because of its low frequency, a small number of prognostic factors are described in hepatoblastoma and most of them are related to resectability. Microarray studies showed a large number of underexpressed genes in hepatoblastoma. Because aberrant DNA methylation has been recognized as an alternative mechanism for tumor suppressor gene inactivation, this could be involved with gene downregulation in these tumors. Despite the rarity of hepatoblastoma, this study evaluated the methylation pattern of 25 genes in 20 paraffin-embedded tumor specimens and five non-neoplastic liver samples (normal control) by quantitative methylation-specific PCR (QMSP). The examination of the methylation profile of hepatoblastoma samples and normal liver specimens revealed a high tumor-specific DNA hypermethylation in the promoter regions of five genes (APC, CDH1, MT1G, RASSF1A, and SOCS1). Furthermore, MT1G hypermethylation showed a significant correlation with poor prognosis of patients with hepatoblastoma. This study represents the first quantitative evaluation of promoter hypermethylation in hepatoblastoma and demonstrated that aberrant methylation is a frequent event in this malignancy. Furthermore, our data provide evidence that MT1G hypermethylation may be useful as prognostic indicator for this disease and suggest that patients with hepatoblastoma may benefit from demethylating drug treatments.

Liver tumors in children

Malignant liver tumors account for slightly >1% of all pediatric malignancies, with roughly 150 new cases of liver tumors diagnosed in the U.S. annually. The embryonal tumor, hepatoblastoma, accounts for two thirds of malignant liver tumors in children. Other liver malignancies in children include hepatocellular carcinoma, sarcomas, germ cell tumors, and rhabdoid tumors. Benign tumors of the liver in children include vascular tumors, hamartomas, and adenomas. There is an apparent increase in the incidence of hepatoblastoma with perinatal exposures and decreased premature infant mortality as postulated causes for this increased risk. The known causes and associations of liver tumors in children as well as the approaches to diagnosis and treatment of children are discussed in this review article.

Oval cell proliferation in p16INK4a expressing mouse liver is triggered by chronic growth stimuli

Terminal differentiation requires molecules also involved in aging such as the cell cycle inhibitor p16^INK4a.Like other organs, the adult liver represents a quiescent organ with terminal differentiated cells, hepatocytes and cholangiocytes. These cells retain the ability to proliferate in response to liver injury or reduction of liver mass. However, under conditions which prevent mitotic activation of hepatocytes, regeneration can occur instead from facultative hepatic stem cells.For therapeutic application a non-toxic activation of this stem cell compartment is required. We have established transgenic mice with conditional overexpression of the cell cycle inhibitor p16^INK4a in hepatocytes and have provoked and examined oval cell activation in adult liver in response to a range of proliferative stimuli.We could show that the liver specific expression of p16^INK4a leads to a faster differentiation of hepatocytes and an activation of oval cells already in postnatal mice without negative consequences on liver function.

Promoter hypermethylation of p16INK4A, p14ARF, CyclinD2 and Slit2 in serum and tumor DNA from breast cancer patients

Epigenetic mechanisms such as DNA methylation play important role in cancer. Epigenetic alterations involved in the onset and progression of breast cancer may serve as biomarkers for early detection and prediction of disease prognosis. Furthermore, using body fluids such as serum offers a non-invasive method to procure multiple samples for biomarker analyses. The aim of this study is to determine the correlation between methylation status of multiple cancer genes, p16(INK4A), p14(ARF), Cyclin D2 and Slit2 in invasive ductal carcinoma of the breast and paired serum DNA and clinicopathological parameters. Of the 36 breast cancer patients investigated, 31 (86%) tumors and 30 (83%) paired sera showed methylation of at least one of these 4 genes. Methylation frequencies varied from 27% for CyclinD2, 44% for p16(INK4A), 47% for p14(ARF) to 58% for Slit2. There was concordance between DNA methylation in tumor and paired serum DNA of each gene. This study underscores the potential utility of DNA methylation based screening of serum as a surrogate marker for tumor DNA methylation status of these genes in breast cancer. Further, expression profile of p16(INK4A) could be linked to epigenetic events, thus suggesting this pathway as a potential target for therapeutic strategies based on reversal of epigenetic silencing.

Tumor Suppressor p16INK4A Regulates Polycomb-mediated DNA Hypermethylation in Human Mammary Epithelial Cells

Alterations in DNA methylation are important in cancer, but the acquisition of these alterations is poorly understood. Using an unbiased global screen for CpG island methylation events, we have identified a non-random pattern of DNA hypermethylation acquired in p16-repressed cells. Interestingly, this pattern included loci located upstream of a number of homeobox genes. Upon removal of p16(INK4A) activity in primary human mammary epithelial cells, polycomb repressors, EZH2 and SUZ12, are up-regulated and recruited to HOXA9, a locus expressed during normal breast development and epigenetically silenced in breast cancer. We demonstrate that at this targeted locus, the up-regulation of polycomb repressors is accompanied by the recruitment of DNA methyltransferases and the hypermethylation of DNA, an endpoint, which we show to be dependent on SUZ12 expression. These results demonstrate a causal role of p16(INK4A) disruption in modulating DNA hypermethylation, and identify a dynamic and active process whereby epigenetic modulation of gene expression is activated as an early event in breast tumor progression.

Promoter hypermethylation of the p16 gene and loss of its protein expression is correlated with tumor progression in extrahepatic bile duct carcinomas

CONTEXT

The p16 gene is one of the tumor suppressor genes, and its inactivation results in abnormal regulation of the cell cycle in human neoplasms. Promoter hypermethylation, a mechanism of p16 gene inactivation, has been reported to play an important role in tumorigenesis and to be related to patient prognosis in several carcinomas.

OBJECTIVE

To determine the role of the p16 gene in extrahepatic bile duct (EBD) carcinomas.

DESIGN

We examined promoter hypermethylation of the p16 gene using a methylation-specific polymerase chain reaction and the expression of the p16 protein using an immunohistochemical staining method in 90 cases of EBD carcinomas. We then compared the data with various clinicopathologic parameters, including survival rate.

RESULTS

Promoter hypermethylation was observed in 69 (77%) of the 90 cases. Of 69 hypermethylated cases, 32 (46%) demonstrated loss of p16 expression. Promoter hypermethylation of the p16 gene was more commonly observed in tumors with vascular invasion (22 [92%] of 24 cases) than without vascular invasion (71%, P = .03). Furthermore, p16 promoter hypermethylation with loss of p16 expression was more frequently observed in cases with lymph node metastasis (P = .006) and higher tumor stage group (P = .04). However, there was no significant difference in survival rate according to the status of p16 promoter methylation and/or p16 expression.

CONCLUSION

Promoter hypermethylation is an important mechanism in the inactivation of the p16 gene in EBD carcinogenesis. Furthermore, the loss of p16 expression, with or without p16 gene promoter hypermethylation, is closely related to the tumor progression in EBD carcinomas.

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Overview of the molecular biology of hepatocellular neoplasms and hepatoblastomas of the mouse liver

The molecular pathogenesis of chemically induced hepatocellular neoplasms and hepatoblastomas in the B6C3FI mouse is unclear but may involve alterations in the fi-catenin/Wnt signaling pathway as was recently described for human liver neoplasms. The objectives of this research were to characterize the mutation frequency and spectrum of P-catenin mutations and the intracellular localization of I-catenin protein accumulation in chemically induced hepatoblastomas and hepatocellular neoplasms. In the majority of the hepatoblastomas examined by immunohistochemical methods, both nuclear and cytoplasmic localization of P-catenin protein were detected, whereas in hepatocellular adenomas and carcinomas and normal liver only membrane staining was observed. Genomic DNA was isolated from paraffin sections of each liver tumor. P-catenin exon 2 (corresponds to exon 3 in humans) genetic alterations were identified in the majority of hepatoblastomas from exposed mice. Deletion mutations were identified more frequently than point mutations in hepatoblastomas. Hepatocellular adenomas and carcinomas from treated mice had mutations in exon 2 of the B-catenin gene which ranged from 32-43%, while 10% P-catenin mutations were detected in spontaneous neoplasms. By immunohistochemical methods cyclin Dl was observed in most nuclei of hepatoblastomas and strong expression of cyclin Dl was confirmed by Western analysis regardless of treatment. The cumulative data suggests that P-catenin mutations with upregulation of the B-catenin protein and Wnt signaling most likely increased cyclin Dl expression. Cyclin D1 may provide an advantage during tumor progression of hepatocellular neoplasms and hepatoblastomas. The review will also focus on other genes which are important in mouse and human liver tumors.

In situ analysis of p16/INK4 promoter hypermethylation in esophageal carcinoma and gastric carcinoma

OBJECTIVE

Inactivation of the tumor suppressor gene by CpG hypermethylation is a common event in a variety of tumors. The present study was designed to be a comprehensive analysis of p16/INK4 methylation in carcinomas of the upper digestive tract.

METHODS

Series of esophageal carcinomas (34 cases) and gastric carcinomas (25 cases) were examined for CpG methylation in p16/INK4 using methylation-specific PCR (MSP). The tissue sections underwent MSP in situ and were then examined microscopically. Immunohistochemical detection of the expression of p16 in the tumor specimens was also performed.

RESULTS

Immunohistochemistry detected positive p16 expression in 8 cases of esophageal squamous cell carcinoma and 15 cases of gastric carcinoma. In esophageal carcinoma, hypermethylation of the p16/INK4 promoter region was detected in 5 cases without statistical correlation with its loss of expression, whereas in the gastric carcinomas, p16 expression was positively correlated with the T-classification (r = 0.488, P = 0.01); p16/INK4 methylation was identified in 8 cases. In addition, p16 expression was lower in the methylated samples than in the non-methylated samples (25% vs 76.47%, P = 0.03). Analysis of the MSP-in-situ sections showed that the distribution of methylated cells in esophageal carcinoma differed from that in gastric carcinoma.

CONCLUSION

The role of DNA methylation in the silence of p16/INK4 may different between these two types of upper digestive tract tumor.

Aberrant methylation of HIN-1 (high in normal-1) is a frequent event in many human malignancies

HIN-1 (high in normal-1) is a putative cytokine with growth inhibitory activities and is downregulated by aberrant methylation in breast cancers. We studied HIN-1 methylation status in many types of adult and pediatric malignancies and cell lines. We examined the expression of HIN-1 mRNA in 52 cell lines and the promoter methylation status in the cell lines and in over 800 primary tumors representing 17 tumor types using methylation specific PCR. Promoter methylation was observed in 73% of breast cancer, 67% of nonsmall cell lung cancer (NSCLC), 30% of small cell lung cancer (SCLC) and 57% of malignant mesothelioma (MM) cell lines, and methylation was completely correlated with loss of expression. Expression negative cell lines restored HIN-1 expression after treatment with 5-aza-2'-deoxycytidine. Promoter methylation of HIN-1 was found in 90% of retinoblastomas, 73% of Wilms' tumors, 61% of rhabdomyosarcomas, 57% of breast cancers, 52% of prostate cancers, 40% of MMs, 28% of NSCLCs and 27% of lymphomas. Methylation frequencies in colorectal cancers, cervical cancers, bronchial carcinoids, SCLCs, neuroblastomas, osteosarcomas, leukemia, medulloblastomas and bladder cancers were lower (4-21%), while hepatoblastomas lacked methylation. HIN-1 methylation was rarely detected in nonmalignant tissues (8 of 165, 5%). Aberrant methylation of HIN-1 with loss of expression is a common event and may contribute to the pathogenesis of many types of human malignancies.

Potential efficacy ofp16 gene therapy for EBV-positive nasopharyngeal carcinoma

The p16 cell cycle inhibitory gene is a potentially critical molecular abnormality in nasopharyngeal carcinoma (NPC). Its expression is silenced through either deletion or promoter methylation in the vast majority of NPC. This in turn is associated with absent or reduced protein expression, which has been previously demonstrated by our group to correlate with inferior clinical outcome. Therefore, we were interested in evaluating the potential of adenoviral mediated p16 gene therapy (adv.p16) in an EBV-positive NPC model (C666-1). We confirm that under basal conditions, p16 protein is undetectable in C666-1 cells, which, in turn, is associated with retention of retinoblastoma protein (pRb) expression. P16 expression was observed as early as 4 hr after infection of C666-1 cells with adv.p16 (10 pfu/cell) with no discernible perturbation in pRb for up to 24 hr. At 48 hr post-infection, p16 expression continued to increase, but at this point, pRb expression started to decline significantly. Cell viability decreased in a dose-dependent manner, down to 20% using 50 pfu/cell of adv.p16. The addition of radiation therapy (RT) administered 24 hr post-infection achieved only a slightly additive cytotoxicity. Adv.p16 therapy resulted in multiple mechanisms of cytotoxicity, including cell cycle arrest at the G0/G1 phase, induction of senescence, along with apoptosis. Ex vivo infection of C666-1 cells with adv.p16 (25 pfu/cell) with subsequent implantation into scid mice completely prevented tumor formation, followed for up to 51 days. Our study demonstrates the potential efficacy of adv.p16 gene therapy for NPC, mediated through multimodal mechanisms of cytotoxicity. Future evaluations will examine strategies to increase in vivo tumor transduction with a view towards future clinical applications.