Specific association between alcohol intake, high grade of differentiation and 4q34-q35 deletions in hepatocellular carcinomas identified by high resolution allelotyping

Antler-derived microRNA PC-5p-1090 inhibits HCC cell proliferation, migration, and invasion by targeting MARCKS, SMARCAD1, and SOX9

The capability of microRNAs (miRNAs) to regulate gene expression across species has opened new avenues for miRNA-based therapeutics. Here, we investigated the potential of PC-5p-1090 (miR-PC-1090), a miRNA found in deer antlers, to control the malignant phenotypes of hepatocellular carcinoma (HCC) cells. Using Cell Counting Kit-8 and transwell assays, we found that heterologous expression of miR-PC-1090 inhibited HCC cell proliferation, migration, and invasion. Bioinformatics analysis indicated that predicted miR-PC-1090 targets, including MARCKS, SMARCAD1, and SOX9, were significantly elevated in HCC tissues, and their high expressions were associated with poor overall survival of HCC patients. Moreover, mechanistic investigations revealed that miR-PC-1090 promoted the degradation of MARCKS and SMARCAD1 mRNAs and hindered the translation of SOX9 mRNA by recognizing their 3' untranslated regions. Subsequent loss-of-function and rescue experiments confirmed the involvement of MARCKS, SMARCAD1, and SOX9 in miR-PC-1090-suppressed HCC cell proliferation, migration, and invasion. Notably, MARCKS knockdown induced the downregulation of phosphorylated MARCKS and a corresponding upregulation of phosphorylated AKT in HCC. Conversely, miR-PC-1090 repressed MARCKS phosphorylation and effectively circumvented the activation of the PI3K/AKT pathway. Furthermore, miR-PC-1090 regulates the Wnt/β-catenin pathway through SMARCAD1- and SOX9-mediated reduction of β-catenin expression. Overall, our results illustrate the tumor-suppressive activity and molecular mechanism of antler-derived miR-PC-1090 in HCC cells, indicating its potential as a multiple-target agent for HCC treatment.

Development and validation of 3-CpG methylation prognostic signature based on different survival indicators for colorectal cancer

Abnormal DNA methylation is considered a vital hallmark to regulate gene expression and influence the development and progression of colorectal cancer (CRC). Although CRC-related methylation prognostic models have been developed, their clinical application is limited due to the lack of external validation and extension to other survival evaluation indicators. Therefore, this study aimed to develop and validate novel methylation prognostic models correlated with different survival indicators for individualized prognosis prediction for CRC patients. The prognostic-related CpG sites of methylation-driven genes screened by the MethylMix algorithm were identified and validated in The Cancer Genome Atlas (TCGA) CRC methylation data and our methylation data. The prognostic models correlated with different survival evaluation indicators (overall survival [OS] and disease-free survival [DFS]) were developed and validated in the TCGA CRC dataset (N = 376) and our independent CRC dataset (N = 227). We utilized the combination of selected 3-CpG methylation sites in three genes (DAPP1, FAM3D, and PIGR) to construct a prognostic risk-score model. In the training dataset, Kaplan-Meier survival analysis demonstrated that high-risk patients had significantly poorer survival than low-risk patients (p_OS  = .0014; p_DFS  < .001). Then, the 3-CpG methylation signature was successfully validated as an independent predictor in the testing data set (p_OS  = .016; p_DFS  = .016). A prognostic nomogram was constructed and validated. Additionally, mediation analysis revealed the direct effect of the methylation signature on CRC prognosis (p_OS  = 9.149e-06; p_DFS  = .001). In summary, our study revealed that the 3-CpG methylation signature might be a potential prognostic indicator to facilitate individualized survival prediction for CRC patients.

Hepatocyte Nuclear Factor 1α-Mutated Hepatocellular Adenomas: An Atypical Presentation

Hepatocellular adenomas (HCAs) are rare benign monoclonal hepatic tumors that commonly occur in females (3-4 per 100,000 women) due to the use of oral contraceptives, its primary risk factor. Recently, HCAs have been classified into 4 distinct subtypes according to genotypic and phenotypic characteristics and clinical features: inflammatory HCA (40-50%), which are hypervascular with marked peliosis and a tendency to bleed; hepatocyte nuclear factor 1α (HNF1A)-mutated HCA (H-HCA, 30-40%) that are diffusely steatotic and rarely undergo malignant transformation; β-catenin activated HCA (10-15%), which frequently undergo malignant transformation and may seem hepatocellular carcinoma on imaging; and unclassified HCA (10-25%). In this study, we report the case of a 23-year-old female oral contraceptive user with H-HCA. Usually, H-HCA is considered to be nonsevere in most cases and often requires outpatient follow-up. However, in this case, the injury had substantially increased in volume and evolved with a major bleeding frame, which was an unusual finding for this subtype of adenoma. The therapeutic used for this patient was a laparoscopic left hepatic segmentectomy. Thus, the choice of treatment to be performed in a patient with H-HCA can depend on the tumor size (>5 cm), the outcome of previous bleeding, and the risk of bleeding recurrence.

Treatment efficacy differences of sorafenib for advanced hepatocellular carcinoma: a meta-analysis of randomized clinical trials

OBJECTIVES

Hepatocellular carcinoma (HCC) is a heterogeneous disease. We explored whether any specific subgroups of patients may gain more survival benefits from sorafenib as the first-line therapy for advanced HCC.

METHODS

PubMed and the Cochrane library were searched for phase III clinical trials that compared sorafenib with other treatments as first-line therapy for advanced HCC. We retrieved data from the published articles and then calculated synthesized hazard ratios (HRs) of overall mortality for patients of different subgroups, using patients who received other treatments as the reference.

RESULTS

Four phase III clinical trials comparing sorafenib with other treatments were included in this study. The HRs were not significantly different between patients from various geographic regions (p = 0.183), patients with different Eastern Cooperative Oncology Group performance statuses (p = 0.699), or patients with different tumor involvement (p = 0.221). By contrast, the synthesized HR for hepatitis C virus (HCV)+ patients was 0.65 [95% confidence interval (CI) 0.53-0.80], which was significantly lower than that for HCV- patients (0.87, 95% CI 0.79-0.96, p = 0.013).

CONCLUSIONS

As the first-line therapy for advanced HCC, sorafenib might provide more survival benefits to HCV+ patients than to HCV- patients.

The Complex Relationship between Liver Cancer and the Cell Cycle: A Story of Multiple Regulations

The liver acts as a hub for metabolic reactions to keep a homeostatic balance during development and growth. The process of liver cancer development, although poorly understood, is related to different etiologic factors like toxins, alcohol, or viral infection. At the molecular level, liver cancer is characterized by a disruption of cell cycle regulation through many molecular mechanisms. In this review, we focus on the mechanisms underlying the lack of regulation of the cell cycle during liver cancer, focusing mainly on hepatocellular carcinoma (HCC). We also provide a brief summary of novel therapies connected to cell cycle regulation.

Tumor suppressor genes FHIT and WWOX are deleted in primary effusion lymphoma (PEL) cell lines

Primary effusion lymphoma (PEL) is a diffuse-large B-cell lymphoma with poor prognosis. One hundred percent of PELs carry the genome of Kaposi sarcoma-associated herpesvirus and a majority are coinfected with Epstein-Barr virus (EBV). We profiled genomic aberrations in PEL cells using the Affymetrix 6.0 SNP array. This identified for the first time individual genes that are altered in PEL cells. Eleven of 13 samples (85%) were deleted for the fragile site tumor suppressors WWOX and FHIT. Alterations were also observed in the DERL1, ETV1, RASA4, TPK1, TRIM56, and VPS41 genes, which are yet to be characterized for their roles in cancer. Coinfection with EBV was associated with significantly fewer gross genomic aberrations, and PEL could be segregated into EBV-positive and EBV-negative clusters on the basis of host chromosome alterations. This suggests a model in which both host genetic aberrations and the 2 viruses contribute to the PEL phenotype.

The association of frequent allelic loss on 17p13.1 with early metastatic recurrence of hepatocellular carcinoma after liver transplantation

BACKGROUND AND OBJECTIVES

Identification and characterization of loss of heterozygosity (LOH) can determine putative tumor suppressor genes (TSGs) and provide a variety of molecular markers for hepatocellular carcinoma (HCC). This study aimed to investigate LOH status on chromosomes 4q, 6q, 8p, 9p, and 17p, and to explore their clinical significances in HCC post-liver transplantation.

METHODS

A total of 37 patients with HCC who underwent liver transplantation were enrolled. LOH was examined using 34 microsatellite markers located on 4q13-3q5, 6q27, 8p22-p23, 9p21-p22, and 17p12-p13.

RESULTS

The frequency of LOH at each microsatellite locus ranged from 23% to 75%, with a mean value of 53.1%. Frequencies of LOH on 4q, 6q, 8p, 9p, and 17p were 62% (23 of 37), 30% (11 of 37), 49% (18 of 37), 46% (16 of 35), and 68% (25 of 37), respectively. LOHs on certain chromosomal regions were significantly associated with age, AFP level, tumor size, tumor multiplicity, histological grade, and metastatic recurrence.

CONCLUSIONS

LOH on 17p13.1 correlated to metastatic HCC recurrence, while LOH on 4q and 8p was found to be associated with progression of HCC. Thus, potential novel biomarkers or TSGs for prognosis and treatment of HCC may harbor on these regions.

Epigenetic inactivation of the tumor suppressor gene RIZ1 in hepatocellular carcinoma involves both DNA methylation and histone modifications

BACKGROUND & AIMS

The retinoblastoma-interacting zinc finger gene RIZ1 is inactivated in many cancers, but the underlying mechanisms remain unknown. This study aimed to investigate the epigenetic mechanisms of RIZ1 inactivation by analyzing the relationship between DNA methylation and histone modifications during regulation of RIZ1 expression.

METHODS

Methylation-specific PCR, RT-PCR, and immunohistochemistry were performed to examine RIZ1 methylation and expression. Dynamic changes in histone H3 lysine 9 (H3K9) modifications and histone deacetylases (HDACs) associated with the promoter were analyzed by chromatin immunoprecipitation (ChIP).

RESULTS

RIZ1 methylation was detected in 66.7% (32/48) HCC tissues, 6.3% (3/48) corresponding non-cancerous tissues, and 66.7% (4/6) HCC cell lines. All 32 HCC tissues with promoter methylation showed complete loss of RIZ1 protein, whereas RIZ1 protein was present in all the corresponding non-cancerous tissues. Neither 5-aza-2-deoxycitidine (5-Aza-dC) nor Trichostatin A (TSA) reversed promoter methylation, but did restore RIZ1 mRNA and resulted in the downregulation of HDAC1 but not HDAC3. However, 5-Aza-dC+TSA induced a partial reversal of promoter methylation and a markedly synergistic reactivation of RIZ1. Moreover, both HDAC1 and HDAC3 were downregulated. The ChIP assays showed 5-Aza-dC and/or TSA also contributed to the dynamic conversion of trimethylated to acetylated H3K9 at the promoter. Furthermore, a decrease in H3K9 trimethylation preceded an increase in H3K9 acetylation.

CONCLUSIONS

Our results suggest that promoter methylation and H3K9 modifications work together to silence the RIZ1 gene in HCC. 5-Aza-dC can restore the expression of RIZ1, as reflected by its effects on histone modification levels. This finding indicates that cooperative effects between these epigenetic modifications exist.

Molecular classification of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most frequent tumour derived from the malignant transformation of hepatocytes. It is well established that cancer is a disease of the genome and, as in other types of solid tumours, a large number of genetic and epigenetic alterations are accumulated during the hepatocarcinogenesis process. Recent developments using comprehensive genomic tools have enabled the identification of the molecular diversity in human HCC. Consequently, several molecular classifications have been described using different approaches and important progress has been made particularly with the transcriptomic, genetic, chromosomal, miRNA and methylation profiling. On the whole, all these molecular classifications are related and one of the major determinants of the identified subgroups of tumours are gene mutations found in oncogenes and tumour suppressors. However, the full understanding of the HCC molecular classification requires additional comprehensive studies using both genomic and pathway analyses. Finally, a refinement of the molecular classification of HCC, taking into account the geographical and genetic diversity of the patients, will be essential for an efficient design of the forthcoming personalized clinical treatments.

Contribution of alcohol and tobacco use in gastrointestinal cancer development

Tobacco smoke and alcohol are major risk factors for a variety of cancer sites, including those of the gastrointestinal tract. Tobacco smoke contains a great number of mutagenic and carcinogenic compounds, including polycyclic carbohydrates, nitrosamines, and nicotine, while ethanol per se has only weak carcinogenic potential, but its first metabolite, acetaldehyde, is a mutagen and carcinogen, since it forms stable adducts with DNA. The possibility of proto-oncogene mutation in gastrointestinal mucosa cells may be associated with tobacco smoking-induced cancers through the formation of unfavorable DNA adducts. Individuals with defective DNA repair mechanisms and unfavorable genetic make-up for carcinogen metabolism may be at increased risk for gastrointestinal cancers. Individuals with a high production rate of acetaldehyde from ethanol also have an increased cancer risk when they drink chronically. These include individuals with a genetically determined increased acetaldehyde production due to alcohol dehydrogenase polymorphism and those with a decreased detoxification of acetaldehyde due to acetaldehyde dehydrogenase mutation. In addition, oral bacterial overgrowth due to poor oral hygiene also increases salivary acetaldehyde. Dietary deficiencies such as a lack of folate, riboflavine, and zinc may also contribute to the increase cancer risk in the alcoholic patient. It is of considerable importance that smoking and drinking act synergistically. Smoking increases the acetaldehyde burden following alcohol consumption and drinking enhances the activation of various procarcinogens present in tobacco smoke due to increased metabolic activation by an induced cytochrome P450-2E1-dependent microsomal biotransformation system in the mucosa of the upper digestive tract and the liver.

Tumor suppress genes screening analysis on 4q in sporadic colorectal carcinoma

AIM: To search candidate tumor suppressor genes (TSGs) on chromosome 4q through detecting high loss of heterozygosity (LOH) regions in sporadic colorectal carcinoma in Chinese patients.

METHODS: Thirteen fluorescent labeled polymorphic microsatellite markers were analyzed in 83 cases of colorectal carcinoma and matched normal tissue DNA by polymerase chain reaction (PCR). PCR products were electrophoresed on an ABI 377 DNA sequencer. Genescan 3.7 and Genotype 3.7 software were used for LOH scanning and analysis. Comparison between LOH frequency and clinicopathological factors were performed by χ² test.

RESULTS: Data were collected on all informative loci. The average LOH frequency on 4q was 28.56%. The D4S2915 locus showed highest LOH frequency (36.17%). Two obvious deletion regions were detected: one between D4S3000 and D4S2915 locus (4q12-21.1), another flanked by D4S407 and D4S2939 locus (4q25-31.1). None case showed complete deletion of 4q, most cases displayed interstitial deletion pattern solely. Furthermore, compared with clinicopathological features, a significant relationship was observed between LOH frequencies on D4S3018 locus. In tumors larger than 5 cm in diameter, LOH frequency was significantly higher than tumors that were less than 5 cm (56% vs 13.79%, P = 0.01). On D4S1534 locus, LOH was significantly associated with liver metastasis (80% vs 17.25%, P = 0.012). No relationship was detected on other locus compared with clinicopathological features.

CONCLUSION: By high resolution deletion mapping, two high frequency regions of LOH (4q12-21.1 and 4q25-31.1) were detected, which may contribute to locate TSGs on chromosome 4q involved in carcinogenesis and progression of sporadic colorectal carcinoma.

Genetic diversity of hepatocellular carcinomas and its potential impact on targeted therapies

Hepatocellular carcinoma (HCC) is one of the most frequent solid tumors worldwide and represents the third cause of mortality among deaths from cancer. It has been extensively studied in terms of genetic alteration in the last 10 years and our knowledge has dramatically increased in this field, leading to the definition of different altered pathways in hepatocarcinogenesis. Recently, a comprehensive study of genetic and transcriptomic alterations in a large series of HCC tumors enabled the identification of a six-group molecular-based classification of HCC, defined by a simple 16-gene signature. This classification is closely related to specific alteration of WNT and AKT oncogenic pathways. Together with the analysis of defined oncogenic proteins, such global classifications could be useful in the prediction of future-targeted therapy efficiency.

Decreased expression of ING2 gene and its clinicopathological significance in hepatocellular carcinoma

The inhibitor of growth (ING) family member 2 (ING2) is a newly discovered member of ING family that can regulate a wide range of cellular processes including cell growth arrest, apoptosis, and DNA repair. Researches have shown that ING2 can activate p53 and p53-mediated apoptotic pathway involved in the hepatocarcinogenesis. To investigate the role of ING2 in hepatocellular carcinoma (HCC) pathogenesis, we analyzed the correlations between the ING2 expression level and clinicopathologic factors and studied its prognostic role in primary HCC. Using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, ING2 transcription and post-transcription level was found to be downregulated in the majority of tumors compared with matched non-tumors liver tissues (p=0.004 and p=0.014, respectively). The immunohistochemistry data indicated significant reduction of ING2 expression level in 44 of 84 (52.4%) HCC cases. In addition, the expression level of ING2 correlated with tumor size, histopathologic classification, serum AFP (p<0.05). Kaplan-Meier curves demonstrated that patients with reduced ING2 expression were at significantly increased risk for shortened survival time (p=0.009). Using multivariate analysis, ING2 expression was found to be an independent prognostic factor. Our data suggest that ING2 is involved in the progression of HCC, therefore it is considered to be a candidate tumor suppressor gene and its significantly decreased expression in HCC may lead to an unfavorable prognosis.

A Girl with del(4)(q33) And Occipital Encephalocele: Clinical Description And Molecular Genetic Characterization of A Rare Patient

We present clinical and developmental data on a girl with a de novo terminal deletion of the long arm of chromosome 4, del(4)(q33). The patient was evaluated at birth and followed up until 5 years of age. She showed facial and digital dysmorphism, a complex congenital heart defect, a large occipital encephalocele, and postnatal growth deficiency. Her neuropsychomotor milestones were delayed, and she developed learning difficulties. Apart from standard Giemsa banding, a molecular genetic analysis was performed using a comparative genomic hybridization (CGH) array. This revealed a terminal deletion at the band 4q32.3, which is directly adjacent to 4q33. The clinical findings in our patient differ from those described previously in patients with del(4)(q33) and del(4)(q32), respectively. In particular, the prominent occipital encephalocele has not been observed before in a terminal 4q deletion.

Marked genomic differences characterize primary and secondary glioblastoma subtypes and identify two distinct molecular and clinical secondary glioblastoma entities

Glioblastoma is classified into two subtypes on the basis of clinical history: "primary glioblastoma" arising de novo without detectable antecedent disease and "secondary glioblastoma" evolving from a low-grade astrocytoma. Despite their distinctive clinical courses, they arrive at an indistinguishable clinical and pathologic end point highlighted by widespread invasion and resistance to therapy and, as such, are managed clinically as if they are one disease entity. Because the life history of a cancer cell is often reflected in the pattern of genomic alterations, we sought to determine whether primary and secondary glioblastomas evolve through similar or different molecular pathogenetic routes. Clinically annotated primary and secondary glioblastoma samples were subjected to high-resolution copy number analysis using oligonucleotide-based array comparative genomic hybridization. Unsupervised classification using genomic nonnegative matrix factorization methods identified three distinct genomic subclasses. Whereas one corresponded to clinically defined primary glioblastomas, the remaining two stratified secondary glioblastoma into two genetically distinct cohorts. Thus, this global genomic analysis showed wide-scale differences between primary and secondary glioblastomas that were previously unappreciated, and has shown for the first time that secondary glioblastoma is heterogeneous in its molecular pathogenesis. Consistent with these findings, analysis of regional recurrent copy number alterations revealed many more events unique to these subclasses than shared. The pathobiological significance of these shared and subtype-specific copy number alterations is reinforced by their frequent occurrence, resident genes with clear links to cancer, recurrence in diverse cancer types, and apparent association with clinical outcome. We conclude that glioblastoma is composed of at least three distinct molecular subtypes, including novel subgroups of secondary glioblastoma, which may benefit from different therapeutic strategies.

Mapping a Sex Hormone–Sensitive Gene Determining Female Resistance to Liver Carcinogenesis in a Congenic F344.BN-Hcs4Rat

Hepatocellular carcinoma (HCC) is prevalent in human and rodent males. Hepatocarcinogenesis is controlled by various genes in susceptible F344 and resistant Brown Norway (BN) rats. B alleles at Hcs4 locus, on RNO16, control neoplastic nodule volume. We constructed the F344.BN-Hcs4 recombinant congenic strain (RCS) by introgressing a 4.41-cM portion of Hcs4 from BN strain in an isogenic F344 background. Preneoplastic and neoplastic lesions were induced by the "resistant hepatocyte" protocol. Eight weeks after initiation, lesion volume and positivity for proliferating cell nuclear antigen (PCNA) were much higher in lesions of F344 than BN rats of both sexes. These variables were lower in females than in males. Lesion volume and PCNA values of male RCS were similar to those of F344 rats, but in females corresponded to those of BN females. Carcinomatous nodules and HCC developed at 32 and 60 weeks, respectively, in male F344 and congenics and, rarely, in F344 females. BN and congenic females developed only eosinophilic/clear cells nodules. Gonadectomy of congenic males, followed by beta-estradiol administration, caused a decrease in Ar expression, an increase in Er-alpha expression, and development of preneoplastic lesions comparable to those from BN females. Administration of testosterone to gonadectomized females led to Ar increase and development of preneoplastic lesions as in F344 males. This indicates a role of homozygous B alleles at Hcs4 in the determination of phenotypic patterns of female RCS and presence at Hcs4 locus of a high penetrance gene(s), activated by estrogens and inhibited/unaffected by testosterone, conferring resistance to females in which the B alleles provide higher resistance.

4q loss is potentially an important genetic event in MM tumorigenesis: identification of a tumor suppressor gene regulated by promoter methylation at 4q13.3, platelet factor 4

In this study, we have elucidated the chromosomal imbalances in the multistep pathogenesis and delineated several critical tumor suppressor gene (TSG) loci in multiple myeloma (MM). By using comparative genomic hybridization, allelotyping, and multicolor interphase fluorescence in situ hybridization, 5 MM cell lines and bone marrow CD138+ plasma cells from 88 Chinese patients with monoclonal gammopathy of undetermined significance (MGUS) and early and advanced stages of MM were investigated. In all MGUS and MM samples, chromosome copy number abnormalities were detected. A higher number of chromosomal imbalances and specific genetic alterations are involved in MGUS to MM transition (−6q, +3p, and +1p) and MM progression (+2p and +9q). In addition to −13q, we first found high frequencies (42% to 46%) of −4q involving high percentages (70% to 74%) of clonal plasma cells in both MGUS and MM, suggesting that inactivation of TSG in this region is also a potentially critical genetic event in MM tumorigenesis. By high-resolution allelotyping, we defined a common deletion region on 4q13.3 and found that a candidate TSG, platelet factor 4, was frequently silenced by promoter hypermethylation in MM (15 of 28) and MM cell lines (5 of 5). These data have opened up a new approach in the molecular targeting therapy and provide novel insights into MM tumorigenesis.

Large common fragile site genes and cancer

The common fragile sites are large regions of genomic instability that are found in all individuals and are hot spots for chromosomal rearrangements and deletions. A number of the common fragile sites have been found to span genes that are encoded by very large genomic regions. Two of these genes, FHIT and WWOX, have already been demonstrated to function as tumor suppressors. In this review we will discuss the large common fragile site genes that have been identified to date, and the role that these genes appear to play both in cellular responses to stress and in the development of cancer.

Mutational and LOH analyses of the chromosome 4q region in esophageal adenocarcinoma

OBJECTIVE

Mortality due to esophageal adenocarcinoma has risen markedly, but the molecular mechanisms underlying this carcinogenesis are still incompletely understood. Findings from loss of heterozygosity (LOH) studies have suggested that the long arm of chromosome 4 might harbor tumor suppressor genes relevant to esophageal adenocarcinoma.

METHODS

We performed LOH analysis of 4q in esophageal adenocarcinomas. Regions of LOH were further evaluated by studying two candidate tumor suppressor genes, hCDC4 and CARF, located within them.

RESULTS

54% of the adenocarcinomas examined showed allelic deletion. LOH was observed in 53, 40, 32, 38, and 27% of tumors at positions D4S1554 (the locus of CARF), D4S1572, D4S1548, D4S2934, and D4S3021, respectively. An area of allelic deletion (spanning 3 million bases) was identified at 4q31.1-3 in 37% of tumors. This region harbors a candidate tumor suppressor gene: hCDC4. However, sequencing of the coding regions of CARF and hCDC4 at 4q35 and 4q31, respectively, did not identify mutations.

CONCLUSIONS

Our findings demonstrate frequent LOH in esophageal adenocarcinoma at several loci including a novel area of allelic deletion at 4q31.1-3. The results imply that mutational or other alterations at these loci may be involved in the pathogenesis of esophageal adenocarcinoma. Candidate tumor suppressor genes located within these regions merit further study.

Risk factors and mechanisms of hepatocarcinogenesis with special emphasis on alcohol and oxidative stress

Hepatocellular cancer is the fifth most frequent cancer in men and the eighth in women worldwide. Established risk factors are chronic hepatitis B and C infection, chronic heavy alcohol consumption, obesity and type 2 diabetes, tobacco use, use of oral contraceptives, and aflatoxin-contaminated food. Almost 90% of all hepatocellular carcinomas develop in cirrhotic livers. In Western countries, attributable risks are highest for cirrhosis due to chronic alcohol abuse and viral hepatitis B and C infection. Among those with alcoholic cirrhosis, the annual incidence of hepatocellular cancer is 1-2%. An important mechanism implicated in alcohol-related hepatocarcinogenesis is oxidative stress from alcohol metabolism, inflammation, and increased iron storage. Ethanol-induced cytochrome P-450 2E1 produces various reactive oxygen species, leading to the formation of lipid peroxides such as 4-hydroxy-nonenal. Furthermore, alcohol impairs the antioxidant defense system, resulting in mitochondrial damage and apoptosis. Chronic alcohol exposure elicits hepatocyte hyperregeneration due to the activation of survival factors and interference with retinoid metabolism. Direct DNA damage results from acetaldehyde, which can bind to DNA, inhibit DNA repair systems, and lead to the formation of carcinogenic exocyclic DNA etheno adducts. Finally, chronic alcohol abuse interferes with methyl group transfer and may thereby alter gene expression.

Localization of a susceptibility locus for hepatocellular carcinoma to chromosome 4q in a hepatitis B hyperendemic area

Chromosome 4q is one of the most common regions with a high frequency of allelic loss in hepatocellular carcinoma (HCC). To identify the HCC-susceptibility locus on chromosome 4q, we have performed linkage and family-based association analyses on Chinese families with HCC from Taiwan, where hepatitis B is hyperendemic. Using 77 microsatellite markers spanning chromosome 4q on 52 multiplex families, we found suggestive evidence of linkage to 4q22.3-28.1 with a maximum two-point heterogeneity LOD (HLOD) score of 2.55 at marker D4S3240 on chromosome 4q25. Multipoint analyses with microsatellite markers in the region 4q22.3-28.1 resulted in a maximum HLOD score of 3.12 and a maximum nonparametric linkage (NPL) Z score of 1.98 (pointwise P=0.0080; region-wide empirical P=0.021) for D4S3240. The evidence for linkage to D4S3240 was seen mostly in a subset of 28 families lacking affected parents, which showed multipoint HLOD and NPL scores of 3.25 and 2.79 (pointwise P=0.0028; region-wide empirical P=0.008), respectively. Family-based association analyses of the 77 microsatellite markers in 191 families (53 multiplex plus 138 singleton families) using the pedigree disequilibrium test provide further support for observed linkage. Additional genotyping in the 52 multiplex families informative for linkage analyses was performed for 29 single-nucleotide polymorphisms around D4S3240. A common haplotype (at markers rs7442180 and rs221330) positioned approximately 873 kb away from D4S3240 was associated with HCC, with P=0.0074.

Mutation analysis of the 8p22 candidate tumor suppressor gene ATIP/MTUS1 in hepatocellular carcinoma

A high frequency of allelic loss affecting chromosome 8p and a minimal region of deletion at p21-22 have been previously reported in hepatocellular carcinoma (HCC), suggesting that at least one tumor suppressor gene is present in this region. In this study, we assessed whether the angiotensin II AT2 receptor interacting protein (ATIP)/mitochondrial tumor suppressor gene (MTUS1), a gene newly identified at position 8p22, may be a candidate tumor suppressor gene mutated in HCC. We searched for alterations in the 17 coding exons of ATIP/MTUS1 by means of denaturating high-performance liquid chromatography and sequencing, in 51 HCC tumors and 58 cell lines for which loss of heterozygosity status was known. Five major nucleotide substitutions were identified, all located in exons used by the ATIP3 transcript which is the only ATIP transcript variant expressed in liver. These nucleotide variations result in amino-acid substitution or deletion of conserved structural motifs (nuclear localisation signal, polyproline motif, leucine zipper) and also affect exonic splicing enhancer motifs and physiological splice sites, suggesting potential deleterious effects on ATIP3 function and/or expression.

Genetics of hepatocellular tumors

Numerous genetic alterations are accumulated during the process of hepatocarcinogenesis. These genetic alterations can be divided into two groups. The first set of genetic alterations is specific of hepatocellular tumor risk factors. It includes integration of hepatitis B virus (HBV) DNA, R249S TP53 (tumor protein p53) mutation in aflatoxin B1-exposed patients, KRAS mutations related to vinyl chloride exposure, hepatocyte nuclear factor 1alpha (HNF1alpha) mutations associated to hepatocellular adenomas and adenomatosis polyposis coli (APC) germline mutations predisposing to hepatoblastomas. The second set of genetic alterations are etiological nonspecific, it includes recurrent gains and losses of chromosomes, alteration of TP53 gene, activation of WNT/beta-catenin pathway through CTNNB1/beta-catenin and AXIN (axis inhibition protein) mutations, inactivation of retinoblastoma and IGF2R (insulin-like growth factor 2 receptor) pathways through inactivation of RB1 (retinoblastoma 1), P16 and IGF2R. Comprehensive analyses of these genetic alterations have defined two pathways of hepatocarcinogenesis according to the presence or the absence of chromosomal instability. Hepatitis B virus and poorly differentiated tumors are related to chromosome instable tumors associated with frequent TP53 mutations, whereas non-HBV and well-differentiated tumors are related to chromosomal stable samples that are frequently beta-catenin activated. These classifications have clinical relevance as genetic alterations may also be related to prognosis.

Hath1 up-regulates gastric mucin gene expression in gastric cells

The Notch signaling pathway is known to mediate the differentiation and fate specification of cells in embryonic stage and adult tissues. Several tumors exhibit aberrant expression of Notch signaling component genes, such as Notch1/2/3 and Hath1. In this study, we investigated the mRNA expression of seven Notch-related genes, Notch1/2/3, Hes1/2/3, and Hath1, and then compared it with the expression of gastric mucin genes, MUC5AC and MUC6, in eight gastric cancer (GC) cell lines. Notch1/2/3 and Hes1 were expressed in most GC cell lines as well as normal gastric mucosae, while Hes2/3 were expressed in neither these cell lines nor the normal stomach. As for Hath1, five GC cell lines exhibited undetectable levels, while normal gastric mucosa expressed Hath1. The expression patterns of Hath1 and MUC6 were closely related in most GC cell lines. Many MUC5AC-positive cases also tended to show Hath1 expression. Over-expression of Math1, a mouse Hath1 homolog, in the GC cells strongly enhanced both the MUC6 and MUC5AC mRNA levels. Moreover, knockdown of Hath1 by means of RNA interference significantly decreased the expression of both mucin genes. These data indicate that Hath1 is one of the transcriptional regulators for MUC6 and MUC5AC in GC cells. It is also possible that loss of Hath1 expression may play a role in gastric carcinogenesis.

Common chromosomal fragile sites and cancer: focus on FRA16D

A growing body of experimental evidence supports the view that certain human chromosomal fragile sites have roles to play in cancer. The principle lines of evidence are at the level of mutation mechanism and gene function. Most research in this area has previously focussed on the FRA3B common fragile site and the FHIT gene that spans this site. Here we review recent progress in characterising the second most readily observed common fragile site, FRA16D, and the WWOX gene that spans it. Comparative analyses of FRA3B/FHIT and FRA16D/WWOX reveal some striking similarities suggesting that these sites and their associated genes may play a part in a normal protective response of cells to environmental stress.

Common fragile sites, extremely large genes, neural development and cancer

Common fragile sites (CFSs) are large regions of profound genomic instability found in all individuals. They are biologically significant due to their role in a number of genomic alterations that are frequently found in many different types of cancer. The first CFS to be cloned and characterized was FRA3B, the most active CFS in the human genome. Instability within this region extends for over 4.0 Mbs and contained within the center of this CFS is the FHIT gene spanning 1.5 Mbs of genomic sequence. There are frequent deletions and other alterations within this gene in multiple tumor types and the protein encoded by this gene has been demonstrated to function as a tumor suppressor in vitro and in vivo. In spite of this, FHIT is not a traditional mutational target in cancer and many tumors have large intronic deletions without any exonic alterations. There are several other very large genes found within CFS regions including Parkin (1.37 Mbs in FRA6E), GRID2 (1.47 Mbs within 4q22.3), and WWOX (1.11 Mbs within FRA16D). These genes also appear to function as tumor suppressors but are not traditional mutational targets in cancer. Each of these genes is highly conserved and the regions spanning them are CFSs in mice. We have now examined lists of the largest human genes and found forty that span over one megabase. Many of these are derived from chromosomal bands containing CFSs. BACs within these genes are being utilized as FISH probes to determine if these are also CFS genes. Thus far we have identified the following as CFS genes: CNTNAP2 (2.3 Mbs in FRA7I), DMD (2.09 Mbs in FRAXC), LRP1B (1.9 Mbs in FRA2F), CTNNA3 (1.78 Mbs in FRA10D), DAB1 (1.55 Mbs in FRA1B), and IL1RAPL1 (1.36 Mbs in FRAXC). Although, these genes are also not traditional mutational targets in cancer they do exhibit loss of expression in multiple tumor types suggesting that they may also function as tumor suppressors. Many of the large CFS genes are involved in neurological development. Parkin is mutated in autosomal recessive juvenile Parkinsonism and deletions in mice are associated with the mouse mutant Quaking (viable). Spontaneous mouse mutants in GRID2 and DAB1 are associated with Lurcher and Reelin, respectively. In humans, alterations in IL1RAPL1 cause X-linked mental retardation and loss of WWOX is associated with Tau phosphorylation. We propose that the instability-induced alterations in these genes contribute to cancer development in a two-step process. Initial alterations will primarily occur within intronic regions, as these genes are greater than 99% intronic. These are not benign. Instead, they alter the repertoire of transcripts produced from these genes. As cancer progresses deletions will begin to encompass exons resulting in gene inactivation. These two types of alterations occurring in multiple large CFS genes may contribute significantly to the heterogeneity observed in cancer. There are also important potential linkages between normal neurological development and the development of cancer mediated by alterations in these genes.

Plk4 haploinsufficiency causes mitotic infidelity and carcinogenesis

The polo-like kinase Plk4 (also called Sak) is required for late mitotic progression, cell survival and postgastrulation embryonic development. Here we identified a phenotype resulting from Plk4 haploinsufficiency in Plk4 heterozygous cells and mice. Plk4+/- embryonic fibroblasts had increased centrosomal amplification, multipolar spindle formation and aneuploidy compared with wild-type cells. The incidence of spontaneous liver and lung cancers was approximately 15 times high in elderly Plk4+/- mice than in Plk4+/+ littermates. Using the in vivo model of partial hepatectomy to induce synchronous cell cycle entry, we determined that the precise regulation of cyclins D1, E and B1 and of Cdk1 was impaired in Plk4+/- regenerating liver, and p53 activation and p21 and BubR1 expression were suppressed. These defects were associated with progressive cell cycle delays, increased spindle irregularities and accelerated hepatocellular carcinogenesis in Plk4+/- mice. Loss of heterozygosity occurs frequently (approximately 60%) at polymorphic markers adjacent to the PLK4 locus in human hepatoma. Reduced Plk4 gene dosage increases the probability of mitotic errors and cancer development.

FRA16D common chromosomal fragile site oxido-reductase (FOR/WWOX) protects against the effects of ionizing radiation in Drosophila

Fragile sites are chromosomal structures that have been proposed to have a determining role in cancer-associated DNA instability. The human WWOX gene spans the FRA16D chromosomal fragile site, the common minimal region of homozygous deletion found in adenocarcinomas and three out of five translocation breakpoints in multiple myeloma. Transcripts from the alternatively spliced WWOX gene encode proteins with common N-terminal WW domains and variable homology to the oxidoreductase family of proteins. In this study, the Drosophila orthologue of the WWOX gene was identified and subjected to mutagenesis via homologous recombination. The resultant DmWWOX1 mutants were viable but exhibited an increased sensitivity to ionizing radiation. This radiation sensitivity was rescued by reintroduction and expression of either the wild-type Drosophila or human WWOX genes. Thus, the protective function of DmWWOX in response to irradiation in Drosophila is conserved with human WWOX (hWWOX). This is consistent with a protective role for hWWOX where aberrant expression, as a result of breakage at the associated fragile site, could contribute directly to cancer progression.

Distinct chromosomal bias of gene expression signatures in the progression of hepatocellular carcinoma

To identify the chromosomal aberrations associated with the progression of liver cancer, we applied expression imbalance map analysis to gene expression data from 31 hepatocellular carcinomas and 19 noncancerous tissues. Expression imbalance map analysis, which detects mRNA expression imbalance correlated with chromosomal regions, showed that expression gains of 1q21-23 (74%), 8q13-21 (48%), 12q23-24 (41%), 17q12-21(48%), 17q25 (25%), and 20q11 (22%) and losses of 4q13 (48%), 8p12-21 (32%), 13q14 (32%), and 17p13 (29%) were significantly associated with hepatocellular carcinoma. Most regions with altered expression identified by expression imbalance map were also identified in previous reports using comparative genomic hybridization. We demonstrated chromosomal copy number gain in 1q21-23 and loss in 17p13 by genomic quantitative PCR, suggesting that gene expression profiles reflect chromosomal alterations. Furthermore, expression imbalance map analysis revealed that more poorly differentiated hepatocellular carcinoma contain more chromosomal alterations, which are accumulated in a stepwise manner in the course of hepatocellular carcinoma progression: expression imbalance of 1q, 8p, 8q, and 17p occur as early events in hepatocarcinogenesis, and 12q, 17q25 and 20q occur as later events. In particular, expression gain of 17q12-21 and loss of 4q were seen to accumulate constantly through the dedifferentiation process. Our data suggest that gene expression profiles are subject to chromosomal bias and that expression imbalance map can correlate gene expression to gene loci with high resolution and sensitivity.

Alcohol and hepatocellular carcinoma

More than 18 million adults in the United States abuse alcohol, a prevalence 5 times higher than that of hepatitis C. Chronic alcohol use of greater than 80 g/day for more than 10 years increases the risk for hepatocellular carcinoma (HCC) approximately 5-fold; alcohol use of less than 80 g/day is associated with a nonsignificant increased risk for HCC. The risk for HCC in decompensated alcohol induced cirrhosis approaches 1% per year. The risk does not decrease with abstinence, and HCC can occur in a noncirrhotic liver. Alcohol use in chronic hepatitis C doubles the risk for HCC as compared with the risk in hepatitis C alone. Furthermore, there may be synergism between alcohol and hepatitis C in the development of HCC, and in these patients HCC may occur at an earlier age and the HCC may be histologically more advanced. Studies in the United States and Italy suggest that alcohol is the most common cause of HCC (accounting for 32%-45% of HCC). The mechanisms by which alcohol causes HCC are incompletely understood, but may include chromosomal loss, oxidative stress, a decreased retinoic acid level in the liver, altered DNA methylation, and genetic susceptibility. Alcohol use is increasing in many countries, suggesting that alcohol will continue to be a common cause of HCC throughout the world.

Allelic loss of chromosome 4q21 approximately 23 associates with hepatitis B virus-related hepatocarcinogenesis and elevated alpha-fetoprotein

Allelic loss of chromosome 4q is one of the most frequent genetic aberrations found in human hepatocellular carcinoma (HCC) and suggests the presence of putative tumor suppressor genes within this region. To precisely define the region containing these tumor suppressor genes for further positional cloning, we tried a detailed deletion mapping strategy in 149 HCCs by using 49 microsatellite markers covering 4q12 approximately 25. A common region with allelic loss has been identified based on the interstitial deletions occurring within it; this region is found between D4S1534 and D4S1572 (a 17.5-cM genetic interval). When we included all cases with limited aberration regions for comparison, 2 smaller regions were derived: 1 between D4S1534 and D4S2460 (3.52 cM) and 1 between D4S2433 and D4S1572 (8.44 cM). A few candidate genes were found to be down-regulated in HCCs, but without sequence mutations. In these HCCs, 4q alleleic loss was associated with hepatitis B virus infection status and the elevation of serum alpha-fetoprotein (>/=400 ng/mL). In conclusion, the current study not only mapped a common allelic loss region on chromosome 4q, but it also revealed that its loss may be involved in hepatitis B virus-related hepatocarcinogenesis and the elevation of serum alpha-fetoprotein.

Characterization of a conserved aphidicolin-sensitive common fragile site at human 4q22 and mouse 6C1: possible association with an inherited disease and cancer

Fragile sites are classified as common or rare depending on their occurrence in the populations. While rare sites are mainly associated with inherited diseases, common sites have been involved in somatic rearrangements found in the chromosomes of cancer cells. Here we study a mouse locus containing the ionotropic glutamate receptor delta 2 (grid2) gene in which spontaneous chromosome rearrangements occur frequently, giving rise to mutant animals in inbred populations. We identify and clone common fragile sites overlapping the mouse grid2 gene and its human ortholog GRID2, lying respectively at bands 6C1 and 4q22 in a 7-Mb-long region of synteny. These results show a third example of orthologous common sites conserved at the molecular level, and reveal an unexpected link between an inherited disease and an aphidicolin-sensitive region. Recurrent deletions of subregions of band 4q22 have been previously described in human hepatocellular carcinomas. This 15-Mb-long region appears precisely centered on the site described here, which strongly suggests that it also plays a specific role in hepatic carcinogenesis.

Habitual betel quid chewing and risk for hepatocellular carcinoma complicating cirrhosis

This case-control study aimed to assess the independent and interactive role of habitual betel quid chewing and known risk factors for hepatocellular carcinoma (HCC). Subjects enrolled included 210 pairs of sex- and age-matched cirrhotic patients with HCC, patients with cirrhosis alone, and healthy controls. Information on risk factors was obtained through serologic examination of hepatitis B surface antigen (HBsAg) and antibodies to hepatitis C virus (anti-HCV), and a standardized personal interview with a structured questionnaire. Multivariate analysis indicated that betel quid chewing (odds ratio [OR], 5.81; 95% confidence interval [CI], 2.26-14.94); HBsAg (OR, 37.98; 95% CI, 19.65-73.42); and anti-HCV (OR, 47.23; 95% CI, 18.86-118.25) were independent risk factors for HCC when HCC patients were compared with healthy controls. Using patients with cirrhosis alone as a reference group, multivariate analysis indicated that only betel quid chewing (OR, 1.69; 95% CI, 1.04-2.76) and HBsAg (OR, 1.54; 95% CI, l.01-2.37) were independent risk factors for HCC. There was an additive interaction between betel quid chewing and the presence of either HBsAg (synergy index, 5.22) or anti-HCV (synergy index, 1.35). Moreover, a higher risk of HCC was associated with a longer duration of betel quid chewing and a larger amount of betel quid consumed (each p(for trend) < 0.0001). In conclusion, betel quid chewing is an independent risk factor for cirrhotic HCC. There is an additive interaction between betel quid chewing and chronic hepatitis B and/or hepatitis C virus infection.

Multiple chromosomal abnormalities in human liver (pre)neoplasia

BACKGROUND/AIMS

In human hepatocarcinogenesis the tumor precursor lesions and the sequence of genetic aberrations are not known. We therefore compared genetic alterations of different types of benign liver lesions to those of hepatocellular carcinoma.

METHODS

By comparative genomic hybridisation (CGH) 40 cases, including cirrhotic liver (CL), focal nodular hyperplasia (FNHs), hepatocellular adenoma (HCAs), dysplastic nodules (DNs), primary hepatocellular carcinoma (HCCs), and hepatocellular metastases to the lung were studied.

RESULTS

FNHs and HCAs exhibited few chromosomal abnormalities. Frequency and pattern of genetic alterations in DNs highly resembled those in HCCs: gains of DNA clustered in chromosome arms 1p/q, 7q, 15q, 16p, 17q, and 20q and losses were often found at 3p, 4q, 9p, and 11q. Aberrations on 1p, 6q, 8p/q, and 13q occurred almost exclusively in HCCs; the gain at 8q encompassed amplification of c-myc, as verified by fluorescence in situ hybridisation.

CONCLUSIONS

The pattern of genetic alterations in HCCs resembled more the alterations found in DNs than in FNHs and HCAs, suggesting that DNs may be the actual tumor precursors. Furthermore, alterations at 4q, 9p, 11q, 16p, and 17q appear as early genetic events being crucial for hepatocarcinogenesis.

Genomic shotgun array: a procedure linking large-scale DNA sequencing with regional transcript mapping

To facilitate transcript mapping and to investigate alterations in genomic structure and gene expression in a defined genomic target, we developed a novel microarray-based method to detect transcriptional activity of the human chromosome 4q22-24 region. Loss of heterozygosity of human 4q22-24 is frequently observed in hepatocellular carcinoma (HCC). One hundred and eighteen well-characterized genes have been identified from this region. We took previously sequenced shotgun subclones as templates to amplify overlapping sequences for the genomic segment and constructed a chromosome-region-specific microarray. Using genomic DNA fragments as probes, we detected transcriptional activity from within this region among five different tissues. The hybridization results indicate that there are new transcripts that have not yet been identified by other methods. The existence of new transcripts encoded by genes in this region was confirmed by PCR cloning or cDNA library screening. The procedure reported here allows coupling of shotgun sequencing with transcript mapping and, potentially, detailed analysis of gene expression and chromosomal copy of the genomic sequence for the putative HCC tumor suppressor gene(s) in the 4q candidate region.

Allelotypic Characteristics of Thorotrast-Induced Intrahepatic Cholangiocarcinoma: Comparison to Liver Cancers not Associated with Thorotrast

To elucidate the genetic alterations that are specific to Thorotrast-induced liver cancers and their possible roles in tumorigenesis, we analyzed loss of heterozygosity (LOH) at 37 loci. Our previous study of liver cancers that were not associated with Thorotrast found LOH at 9 of these loci to be characteristic of intrahepatic cholangiocarcinoma (ICC), at 19 to be characteristic of hepatocellular carcinoma (HCC), and at 9 to be common to both ICC and HCC. LOH analysis was also performed in tissues of cholangiolocellular carcinoma, which is thought to originate from a common stem cell progenitor of hepatocytes and bile duct epithelial cells. We found frequent LOH at D4S1538, D16S2624 and D17S1303 to be common to all the subtypes of liver cancers, independent of the specific carcinogenic agent. In contrast, LOH at D4S1652 generally was not observed in Thorotrast-induced ICC. LOH analysis revealed that Thorotrast-induced ICC shares some LOH features with both ICC and HCC that were not induced by Thorotrast; however, it is more similar to ICC than to HCC in terms of genetic changes. This study could narrow down the crucial chromosomal loci whose deletions are relevant to hepatobiliary carcinogenesis irrespective of the carcinogenic agent. The study of LOH at loci other the those crucial ones may help us understand how the phenotype of liver cancers is determined.

Genome-wide detection of LOH in prostate cancer using human SNP microarray technology

Loss of heterozygosity (LOH) of chromosomal regions is crucial in tumor progression. In this study we assessed the potential of the Affymetrix GeneChip HuSNP mapping assay for detecting genome-wide LOH in prostate tumors. We analyzed two human prostate cell lines, P69SV40Tag (P69) and its tumorigenic subline, M12, and 11 prostate cancer cases. The M12 cells showed LOH in chromosomes 3p12.1-p22.1, 11q22.1-q24.2, 19p13.12, and 19q13.42. All of the prostate cases with informative single-nucleotide polymorphism (SNP) markers showed LOH in 1p31.2, 10q11.21, 12p13.1, 16q23.1-q23.2, 17p13.3, 17q21.31, and 21q21.2. Additionally, a high percentage of cases showed LOH at 6p25.1-p25.3 (75%), 8p22-p23.2, and 10q22.1 (70%). Several tumor suppressor genes (TSGs) have been mapped in these loci. These results demonstrate that the HuSNP mapping assay can serve as an alternative to comparative genomic hybridization for assessing genome-wide LOH and can identify chromosomal regions harboring candidate TSGs implicated in prostate cancer.

A mortality gene(s) for the human adenocarcinoma line HeLa maps to a 130-kb region of human chromosome 4q22-q23

Human chromosome 4 was previously shown to elicit features of senescence when introduced into cell lines that map to complementation group B for senescence, including HeLa cells. Subsequently, a DNA segment encoding the pseudogene Mortality Factor 4 (MORF4) was shown to reproduce some of the effects of the intact chromosome 4 and was suggested to be a candidate mortality gene. We have identified multiple MORF4 alleles in several cell lines and tissues by sequencing and have failed to detect any cancer-specific mutations in three of the complementation group B lines (HeLa, T98G, and J82). Furthermore, MORF4 was heterozygous in these lines. These results question whether MORF4 is the chromosome 4 mortality gene. To map other candidate mortality gene(s) on this chromosome, we employed microcell-mediated monochromosome transfer to introduce either a complete copy, or defined fragments of the chromosome into HeLa cells. The introduced chromosome 4 fragments mapped the mortality gene to a region between the centromere and the marker D4S2975 (4q27), thus excluding MORF4, which maps to 4q33-q34.1. Analysis of microsatellite markers on the introduced chromosome in 59 immortal segregants identified a frequently deleted region, spanning the markers BIR0110 and D4S1557. This defines a new candidate interval of 130 kb at 4q22-q23.

Functional evidence for a squamous cell carcinoma mortality gene(s) on human chromosome 4

Squamous cell carcinoma (SCC) immortality is associated with p53 and INK4A dysfunction, high levels of telomerase and loss of heterozygosity (LOH) of other chromosomes, including chromosome 4. To test for a functional cancer mortality gene on human chromosome 4 we introduced a complete or fragmented copy of the chromosome into SCC lines by microcell-mediated chromosome transfer (MMCT). Human chromosome 4 caused a delayed crisis, specifically in SCC lines with LOH on chromosome 4, but chromosomes 3, 6, 11 and 15 were without effect. The introduction of the telomerase reverse transcriptase into the target lines extended the average telomere terminal fragment length but did not affect the frequency of mortal hybrids following MMCT of chromosome 4. Furthermore, telomerase activity was still present in hybrids displaying the mortal phenotype. The MMCT of chromosomal fragments into BICR6 mapped the mortality gene to between the centromere and 4q23. Deletion analysis of the introduced chromosome in immortal segregants narrowed the candidate interval to 2.7 Mb spanning D4S423 and D4S1557. The results suggest the existence of a gene on human chromosome 4 whose dysfunction contributes to the continuous proliferation of SCC and that this gene operates independently from telomeres, p53 and INK4A.