Methylation of PTCH1a gene in a subset of gastric cancers

The Role of Smoothened-Dependent and -Independent Hedgehog Signaling Pathway in Tumorigenesis

The Hedgehog (Hh)-glioma-associated oncogene homolog (GLI) signaling pathway is highly conserved among mammals, with crucial roles in regulating embryonic development as well as in cancer initiation and progression. The GLI transcription factors (GLI1, GLI2, and GLI3) are effectors of the Hh pathway and are regulated via Smoothened (SMO)-dependent and SMO-independent mechanisms. The SMO-dependent route involves the common Hh-PTCH-SMO axis, and mutations or transcriptional and epigenetic dysregulation at these levels lead to the constitutive activation of GLI transcription factors. Conversely, the SMO-independent route involves the SMO bypass regulation of GLI transcription factors by external signaling pathways and their interacting proteins or by epigenetic and transcriptional regulation of GLI transcription factors expression. Both routes of GLI activation, when dysregulated, have been heavily implicated in tumorigenesis of many known cancers, making them important targets for cancer treatment. Hence, this review describes the various SMO-dependent and SMO-independent routes of GLI regulation in the tumorigenesis of multiple cancers in order to provide a holistic view of the paradigms of hedgehog signaling networks involving GLI regulation. An in-depth understanding of the complex interplay between GLI and various signaling elements could help inspire new therapeutic breakthroughs for the treatment of Hh-GLI-dependent cancers in the future. Lastly, we have presented an up-to-date summary of the latest findings concerning the use of Hh inhibitors in clinical developmental studies and discussed the challenges, perspectives, and possible directions regarding the use of SMO/GLI inhibitors in clinical settings.

Genetic and Epigenetic Regulation of the Smoothened Gene (SMO) in Cancer Cells

(1) Background: The hedgehog (HH) signaling pathway is a key regulator of embryonic patterning, tissue regeneration, stem cell renewal, and cancer growth. The smoothened (SMO) protein regulates the HH signaling pathway and has demonstrated oncogenic activity. (2) Methods: To clarify the role of the HH signaling pathway in tumorigenesis, the expression profile of key HH signaling molecules, including SMO, PTCH1, GLI1, GLI2, and GLI3, were determined in 33 cancer cell lines and normal prostate cells and tissues. We performed a computational analysis of the upstream region of the SMO gene to identify the regulatory elements. (3) Results: Three potential CpG islands and several putative SMO promoter elements were identified. Luciferase reporter assays mapped key SMO promoter elements, and functional binding sites for SP1, AP1, CREB, and AP-2α transcription factors in the core SMO promoter region were confirmed. A hypermethylated SMO promoter was identified in several cancer cell lines suggesting an important role for epigenetic silencing of SMO expression in certain cancer cells. (4) Discussion: These results have important implications for our understanding of regulatory mechanisms controlling HH pathway activity and the molecular basis of SMO gene function. Moreover, this study may prove valuable for future research aimed at producing therapeutic downregulation of SMO expression in cancer cells.

DNA methyltransferases and gastric cancer: insight into targeted therapy

Gastric cancer is a major health problem worldwide occupying most frequent causes of cancer-related mortality. In addition to genetic modifications, epigenetic alterations catalyzed by DNA methyltransferases (DNMTs) are a well-characterized epigenetic hallmark in gastric cancer. The reversible nature of epigenetic alterations and central role of DNA methylation in diverse biological processes provides an opportunity for using DNMT inhibitors to enhance the efficacy of chemotherapeutics. In this review, we discussed key factors or mechanisms such as SNPs, infections and genetic modifications that trigger DNMTs level modification in gastric cancer, and their potential roles in cancer progression. Finally, we focused on how inhibitors of the DNMTs can most effectively be used for the treatment of gastric cancer with multidrug resistance.

Overexpression of mutant Ptch in rhabdomyosarcomas is associated with promoter hypomethylation and increased Gli1 and H3K4me3 occupancy

Mice with heterozygous loss of the tumor suppressor Patched1 (Ptch) develop rhabdomyosarcoma (RMS)-like tumors. However, Ptch transcripts are consistently overexpressed in these tumors. We have recently shown that the upregulated transcripts are derived from the mutated Ptch allele thus leading to the hypothesis that the wild-type allele is repressed during RMS development. Here we describe epigenetic changes taking place at the Ptch locus during RMS development. We showed a lower degree of DNA-methylation in methylation-sensitive CpG regions of the Ptch promoter in RMS compared to normal muscle from heterozygous Ptch animals. In agreement with these results, treatment of heterozygous Ptch mice with the DNA demethylating agent 5-aza-2-deoxycytidine (5-aza-dC) between embryonic days E9.5–E11.5 significantly accelerated RMS formation. Since Ptch promoter methylation occurs after/around E13.5, the window for RMS initiation during embryogenesis, these results provide additional evidence that Ptch promoter hypomethylation may contribute to RMS formation. We have also demonstrated increased trimethylation of histone H3 lysine 4 (H3K4me3) and preferential binding of Gli1, a known Ptch activator, to the mutant locus in RMS. Together, these findings support an alternative model for RMS formation in heterozygous Ptch mice including loss of methylation and concomitant occupancy by activating histone marks of mutant Ptch.

Tea polyphenols epigallocatechin gallete and theaflavin restrict mouse liver carcinogenesis through modulation of self-renewal Wnt and hedgehog pathways

The aim of this study is to evaluate chemopreventive and therapeutic efficacy of tea polyphenols epigallocatechin gallete (EGCG) and theaflavin (TF) on self-renewal Wnt and Hedgehog (Hh) pathways during CCl4/N-nitosodiethylamine-induced mouse liver carcinogenesis. For this purpose, the effect of EGCG/TF was investigated in liver lesions of different groups at pre-, continuous and post initiation stages of carcinogenesis. Comparatively increased body weights were evident due to EGCG/TF treatment than carcinogen control mice. Both EGCG and TF could restrict the development of hepatocellular carcinoma at 30th week of carcinogen application showing potential chemoprevention in continuous treated group (mild dysplasia) followed by pretreated (moderate dysplasia) and therapeutic efficacy in posttreated group (mild dysplasia). This restriction was associated with significantly reduced proliferation, increased apoptosis, decreased prevalence of hepatocyte progenitor cell (AFP) and stem cell population (CD44) irrespective of EGCG/TF treatments. The EGCG/TF could modulate the Wnt pathway by reducing β-catenin and phospho-β-catenin-Y-654 expressions along with up-regulation of sFRP1 (secreted frizzled-related protein 1) and adenomatosis polyposis coli during the restriction. In case of the Hh pathway, EGCG/TF could also reduce expressions of glioma-associated oncogene homolog 1 (Gli1) and SMO (smoothened homolog) along with up-regulation of PTCH1 (patched homolog 1). As a result, in Wnt/Hh regulatory pathways decreased expressions of β-catenin/Gli1 target genes like CyclinD1, cMyc and EGFR/phospho-EGFR-Y-1173 and up-regulation of E-cadherin were seen during the restriction. Thus, the restriction of liver carcinogenesis by EGCG/TF was due to reduction in hepatocyte progenitor cell/stem cell population along with modulation of Wnt/Hh and other regulatory pathways.

New advances of DNA methylation in liver fibrosis, with special emphasis on the crosstalk between microRNAs and DNA methylation machinery

Epigenetics refers to the study of heritable changes in the pattern of gene expression that is controlled by a mechanism specifically not due to changes the primary DNA sequence. Well-known epigenetic mechanisms include DNA methylation, post-translational histone modifications and RNA-based mechanisms including those controlled by small non-coding RNAs (miRNAs). Recent studies have shown that epigenetic modifications orchestrate the hepatic stellate cell (HSC) activation and liver fibrosis. In this review we focus on the aberrant methylation of CpG island promoters of select genes is the prominent epigenetic mechanism to effectively silence gene transcription facilitating HSC activation and liver fibrosis. Furthermore, we also discuss epigenetic dysregulation of tumor-suppressor miRNA genes by promoter DNA methylation and the interaction of DNA methylation with miRNAs involved in the regulation of HSC activation and liver fibrosis. Recent advances in epigenetics alterations in the pathogenesis of liver fibrosis and their possible use as new therapeutic targets and biomarkers.

Aberrant methylation of the PTCH1 gene promoter region in aberrant crypt foci

Patched homolog 1 (PTCH1) is a known tumor suppressor that regulates the Hedgehog (Hh) pathway and has been implicated in tumorigenesis. The role of PTCH1 in colon carcinogenesis, however, is controversial. The aim of the present study was to investigate epigenetic modifications of PTCH1 in aberrant crypt foci (ACF), the earliest precursor lesion of colorectal cancer (CRC). Using laser-capture microdissection (LCM), a pure population of ACF epithelial cells was isolated and studied. The inherent protein expression levels of SHH, PTCH1, SMO and GLI1 were assessed by immunohistochemistry for 405 ACF, including 54 dysplastic ACF (d-ACF) and 351 non-dysplastic ACF (n-ACF). The mRNA levels and methylation status of PTCH1 were also determined in 54 d-ACF and 96 n-ACF. Our data showed that the expression of SHH, SMO and GLI1 was significantly up-regulated in d-ACF, compared to n-ACF. Also, the mRNA and protein levels of PTCH1 were lower in d-ACF than n-ACF. Using MSP or MS-HRM, PTCH1 methylation was present in 64.8% (35/54) or 63.3% (34/54), respectively, of d-ACF and 19.8% (19/96) or 22.9% (11/48), respectively, of n-ACF. PTCH1 methylation was more frequent in d-ACF than n-ACF (p < 0.001) and was associated with PTCH1 mRNA levels (r = 0.358, p < 0.01). There was a statistically significant correlation between PTCH1 methylation status and the prevalence of colorectal neoplasms. In conclusion, this study suggests that aberrant methylation of the PTCH1 promoter may be an early, initiating event of colon carcinogenesis.

Expression of SOCS3 throughout liver regeneration is not regulated by DNA methylation

BACKGROUND

While suppressor of cytokine signaling 3 (SOCS3) plays a crucial role in suppressing dysplasia and tumorigenesis, it also offers a typical instance of DNA methylation in the regulation of gene transcription, since the promoter region of the SOCS3 gene is rich in CpG islands (CGIs). During liver regeneration initiated by partial hepatectomy, SOCS3 acts as a suppressor to balance the acute-phase response and terminate the regeneration. This study aimed to determine whether the variation of SOCS3 expression throughout liver regeneration is also regulated by its DNA methylation.

METHODS

We established a 70% partial hepatectomy mouse model and the animals were sacrificed at indicated times to assess the SOCS3 expression. We performed bisulfite sequencing PCR and DNA sequencing to investigate the detailed cytosine methylation in the SOCS3 gene.

RESULTS

Within the promoter sequence, 58 CGIs were identified and 30 were found variously methylated before or after operation; however, methylation remained at a very low level. No evidence indicated that the total methylation level or the methylation of any CpG site regularly changed throughout liver regeneration.

CONCLUSION

DNA methylation or demethylation seems to be a relatively stable modification of cytosine, but not a dynamic and reversible process to regulate gene transcription in daily and acute pathophysiological events.

Alteration in methylation pattern of oncogene Akt1 promoter region in bladder cancer

The oncogene Akt1 plays a pivotal role in regulating growth factor-associated cell survival. The activity of Akt must be carefully regulated as it has been reported that an increase in Akt signaling is frequently associated with cancer. Phosphorylated Akt, as the constitutively activated form of Akt, has been observed in many kinds of cancer, but the clinical relevance of the (DNA) methylation profile of Akt1 in cancer is not well understood. This study aims to investigate the methylation level of Akt1 in bladder cancer tissues and their clinical significance. Methylation of the oncogene Akt1 transcriptional regulation region (TRR) was detected using bisulfite-specific (BSP) PCR-based sequencing analysis in cases of bladder cancer and the normal tissues, including 15 bladder cancer tissues, and five normal bladder tissues. BSP cloning-based sequencing analysis was also performed in selected cases. Clinicopathological data from the cancer patients were collected and analyzed. Analysis of Akt1 gene TRR methylation showed decreased methylation level in bladder cancer than normal. Methylation level of Akt1 has clinical relevance (P = 0.0043 by unpaired student's t test) with bladder cancer. Abnormal methylation of the Akt1 gene may be an early event during urocystic tumorigenesis and should be further evaluated as a tumorigenesis marker for early detection of bladder cancer.

Recent progress in the study of methylated tumor suppressor genes in gastric cancer

Gastric cancer is one of the most common malignancies and a leading cause of cancer mortality worldwide. The pathogenesis mechanisms of gastric cancer are still not fully clear. Inactivation of tumor suppressor genes and activation of oncogenes caused by genetic and epigenetic alterations are known to play significant roles in Carcinogenesis. Accumulating evidence has shown that epigenetic silencing of the tumor suppressor genes, particularly caused by hypermethylation of CpG islands in promoters, is critical to Carcinogenesis and metastasis. Here, we review the recent progress in the study of methylations of tumor suppressor genes involved in the pathogenesis of gastric cancer. We also briefly describe the mechanisms that induce tumor suppressor gene methylation and the status of translating these molecular mechanisms into clinical applications.

Aberrant gene methylation is a biomarker for the detection of cancer cells in peritoneal wash samples from advanced gastric cancer patients

PURPOSE

To assess whether gene methylation in peritoneal fluid (PF) is clinically feasible for determining micrometastasis to the peritoneum in gastric cancer.

METHODS

The gene methylation of BNIP3, CHFR, CYP1B1, MINT25, SFRP2, and RASSF2 were analyzed in 107 specimens of PF by quantitative methylation-specific polymerase chain reaction. All patients were placed into one of 3 groups: group A (n = 42), patients with depth of cancer invasion at muscularis propria (MP) or less than MP; group B (n = 45), depth of cancer invasion beyond the MP; and group C (n = 20), histologically diagnosed peritoneal metastasis or cancer cells cytologically defined in the peritoneal cavity. Patients in both groups A and B were diagnosed as having no cancer cells by peritoneal cytology and histology.

RESULTS

The methylation status of the 6 genes was found to be significantly different among the 3 groups (group A, 0-5%; group B, 0-15%; group C, 15-45%; P < 0.01). Furthermore, the rate of positive methylation in any of the 6 genes was significantly different in each group (group A, 7%; group B, 20%; group C, 75%; P < 0.001). Three of 9 patients in group B with positive methylation in any of 6 genes experienced peritoneal recurrence. On the other hand, only 1 of 36 patients without gene methylation experienced peritoneal recurrence (P < 0.05).

CONCLUSIONS

DNA methylation in PFs is a possible marker detecting occult neoplastic cells on the peritoneum. Methylation analysis along with a cytological examination might therefore improve the positive detection of cancer cells in PF of gastric cancer.

APP-dependent up-regulation of Ptch1 underlies proliferation impairment of neural precursors in Down syndrome

Mental retardation in Down syndrome (DS) appears to be related to severe neurogenesis impairment during critical phases of brain development. Recent lines of evidence in the cerebellum of a mouse model for DS (the Ts65Dn mouse) have shown a defective responsiveness to Sonic Hedgehog (Shh), a potent mitogen that controls cell division during brain development, suggesting involvement of the Shh pathway in the neurogenesis defects of DS. Based on these premises, we sought to identify the molecular mechanisms underlying derangement of the Shh pathway in neural precursor cells (NPCs) from Ts65Dn mice. By using an in vitro model of NPCs obtained from the subventricular zone and hippocampus, we found that trisomic NPCs had an increased expression of the Shh receptor Patched1 (Ptch1), a membrane protein that suppresses the action of a second receptor, Smoothened (Smo), thereby maintaining the pathway in a repressed state. Partial silencing of Ptch1 expression in trisomic NPCs restored cell proliferation, indicating that proliferation impairment was due to Ptch1 overexpression. The overexpression of Ptch1 in trisomic NPCs resulted from increased levels of AICD [a transcription-promoting fragment of amyloid precursor protein (APP)] and increased AICD binding to the Ptch1 promoter. Our data provide novel evidence that Ptch1 overexpression underlies derangement of the Shh pathway in trisomic NPCs with consequent proliferation impairment. The demonstration that Ptch1 overexpression in trisomic NPCs is due to an APP fragment provides a link between this trisomic gene and the defective neuronal production that characterizes the DS brain.

Downregulation of the hedgehog receptor PTCH1 in colorectal serrated adenocarcinomas is not caused by PTCH1 mutations

Colorectal serrated adenocarcinoma forms about 15-20% of colorectal carcinomas. We have previously shown that downregulation of PTCH1 is distinctive for this type of colorectal cancer. In several other tumor types, somatic inactivating PTCH1 mutations have been shown to lead to aberrant Hedgehog signaling, but in colorectal cancer the role of PTCH1 mutations has not been thoroughly studied. Here, we have analyzed the mutation status of PTCH1 in a series of 33 colorectal serrated adenocarcinomas by sequencing all 23 coding exons. We detected 11 previously known SNPs and eight new alterations. The latter included five synonymous changes and two previously unknown missense variations, somatic M319V, and germline V1231A. V1231A was also present in population controls and likely represents polymorphism. The somatic M319V variant does not appear to be an attractive candidate for a disease-associated mutation because in silico analyses did not support the pathogenic nature of the change. A somatic, intronic 1-bp deletion was detected in a short poly(T) stretch in two microsatellite unstable tumors. None of the three changes had predicted effect on splicing when analyzed in silico. Our results did not reveal any clearly deleterious inactivating PTCH1 mutations in our collection of colorectal serrated adenocarcinomas. This suggests that other mechanisms are involved in the observed downregulation of the PTCH1 gene. These might include, e.g., constantly active MAPK signaling by KRAS or BRAF mutations or silencing of PTCH1 by hypermethylation, and further studies are needed to reveal these mechanisms.

Genetic and epigenetic alteration in gastric carcinogenesis

Gastric cancer (GC) is an important cause of morbidity and mortality worldwide. In addition to environmental factors, genetic factors also play an important role in GC etiology, as demonstrated by the fact that only a small proportion of individuals exposed to the known environmental risk factors develop GC. Molecular studies have provided evidence that GC arises not only from the combined effects of environmental factors and susceptible genetic variants but also from the accumulation of genetic and epigenetic alterations that play crucial roles in the process of cellular immortalization and tumorigenesis. This review is intended to focus on the recently described basic aspects that play key roles in the process of gastric carcinogenesis. Genetic variation in the genes DNMT3A, PSCA, VEGF, and XRCC1 has been reported to modify the risk of developing gastric carcinoma. Several genes have been newly associated with gastric carcinogenesis, both through oncogenic activation (MYC, SEMA5A, BCL2L12, RBP2 and BUBR1) and tumor suppressor gene inactivation mechanisms (KLF6, RELN, PTCH1A, CLDN11, and SFRP5). At the level of gastric carcinoma treatment, the HER-2 tyrosine kinase receptor has been demonstrated to be a molecular target of therapy.