Characterization of genomic alterations in hepatoblastomas. A role for gains on chromosomes 8q and 20 as predictors of poor outcome

Expression profiling and differential screening between hepatoblastomas and the corresponding normal livers: identification of high expression of the PLK1 oncogene as a poor-prognostic indicator of hepatoblastomas

Hepatoblastoma is one of the most common malignant liver tumors in young children. Recent evidences have suggested that the abnormalities in Wnt signaling pathway, as seen in frequent mutation of the beta-catenin gene, may play a role in the genesis of hepatoblastoma. However, the precise mechanism to cause the tumor has been elusive. To identify novel hepatoblastoma-related genes for unveiling the molecular mechanism of the tumorigenesis, a large-scale cloning of cDNAs and differential screening of their expression between hepatoblastomas and the corresponding normal livers were performed. We constructed four full-length-enriched cDNA libraries using an oligo-capping method from the primary tissues which included two hepatoblastomas with high levels of alpha-fetoprotein (AFP), a hepatoblastoma without production of AFP, and a normal liver tissue corresponded to the tumor. Among the 10,431 cDNAs randomly picked up and successfully sequenced, 847 (8.1%) were the genes with unknown function. Of interest, the expression profile among the two subsets of hepatoblastoma and a normal liver was extremely different. A semiquantitative RT-PCR analysis showed that 86 out of 1188 genes tested were differentially expressed between hepatoblastomas and the corresponding normal livers, but that only 11 of those were expressed at high levels in the tumors. Notably, PLK1 oncogene was expressed at very high levels in hepatoblastomas as compared to the normal infant's livers. Quantitative real-time RT-PCR analysis for the PLK1 mRNA levels in 74 primary hepatoblastomas and 29 corresponding nontumorous livers indicated that the patients with hepatoblastoma with high expression of PLK1 represented significantly poorer outcome than those with its low expression (5-year survival rate: 55.9 vs 87.0%, respectively, p=0.042), suggesting that the level of PLK1 expression is a novel marker to predict the prognosis of hepatoblastoma. Thus, the differentially expressed genes we have identified may become a useful tool to develop new diagnostic as well as therapeutic strategies of hepatoblastoma.

Allelic loss but absence of mutations in the polyspecific transporter geneBWR1Aon 11p15.5 in hepatoblastoma

Chromosomal region 11p15.5 shows frequent maternal allelic loss in embryonal tumors, including rhabdomyosarcoma (RMS), Wilms' tumor (WT) and hepatoblastoma (HB), consistent with the presence of at least one tumor suppressor gene in this region, which should be paternally imprinted, i.e., expressed from the maternal allele only. The BWR1A gene encodes a polyspecific transmembrane transporter and is located on 11p15.5. It is highly expressed in liver, paternally imprinted and was found to be mutated in an RMS cell line, making it a plausible tumor suppressor gene for HB. We therefore screened 62 HBs, 3 HB cell lines and 1 pediatric hepatocellular carcinoma for BWR1A mutations using single-strand conformation polymorphism analysis. Allelic loss on 11p15.5 was assessed by PCR-based microsatellite analysis in 56 of the cases for which constitutional DNA was available. BWR1A mRNA expression was determined in 14 HBs by differential RT-PCR of matched cDNA samples from tumor and normal liver. Western blot analysis was performed on 4 tumors and matching normal liver tissue. Except for sequence polymorphisms (in exons 2, 3 and 10 as well as in introns 6 and 7), no mutations were found. Thirteen HBs (23%) had allelic loss on 11p15.5; this included BWR1A in 12 but it was telomeric to BWR1A in 1. Expression of BWR1A mRNA was reduced in 11 out of 14 cases by 19-92%, independent from allelic loss of 11p15.5. By Western blot analysis, all 4 tumors and matching liver samples displayed a 48-51 kd band corresponding to BWR1A. These results make it unlikely that BWR1A is the target of the allelic deletions in HB. However, similar to the putative 11p15.5 tumor suppressor H19, BWR1A appears to be reduced in expression. Reduced expression in the absence of mutations may contribute to HB development; however, to understand the significance of this finding will require further studies on the function of BWR1A, specifically its role in liver development.

Amplification and overexpression of the IGF2 regulator PLAG1 in hepatoblastoma

There is evidence that 8q amplification is associated with poor prognosis in hepatoblastoma. A previous comparative genomic hybridization analysis identified a critical region in chromosomal bands 8q11.2-q13. Using restriction landmark genomic scanning in combination with a virtual genome scan, we showed that this region is delineated by sequences within contig NT_008183 of chromosomal subbands 8q11.22-q11.23. A real-time PCR-based genomic copy number assay of 20 hepatoblastomas revealed gain or amplification in this critical chromosomal region in eight tumors. The expression of four genes and expressed sequence tags (ESTs) within this newly defined region was assayed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) in four tumors with and six tumors without gain or amplification. The PLAG1 oncogene was found to be highly expressed in all but one tumor compared to normal liver tissue. Furthermore, quantitative RT-PCR revealed that the expression level of the developmentally regulated transcription factor PLAG1 was 3-12 times greater in hepatoblastoma tumors and cell lines compared to age-matched normal liver and comparable to the expression in fetal liver tissue. PLAG1 has been shown be a transcriptional activator of IGF2 in other tumor types. Using luciferase reporter assays, we demonstrated that PLAG1 transactivates transcription from the embryonic IGF2 promoter P3, also in hepatoblastoma cell lines. Thus, our results provide evidence that PLAG1 overexpression may be responsible for the frequently observed up-regulation of IGF2 in hepatoblastoma and therefore may be implicated in the molecular pathogenesis of this childhood neoplasia.

Genomic alterations in renal tumours: what have we learned in the era of comparative genomic hybridisation?

One of the major challenges in cancer research is to generate molecular profiles of tumours and establish correlations between genetic changes and clinical parameters by screening technologies. The identification of tumour-specific gene targets has potential diagnostic and therapeutic implications. Metaphase comparative genomic hybridisation has been used to detect relative DNA-sequence copy number gains (including high-level amplifications of chromosomal regions) and copy number losses in human neoplasms. In the past, metaphase comparative genomic hybridisation has been shown to be a powerful genome-wide screening method and this has considerably advanced our understanding of renal cancer biology. Novel molecular technologies, including array-based comparative genomic hybridisation, fluorescence in situ hybridisation (FISH), cDNA and tissue microarrays will serve to facilitate further characterisation of candidate genes residing in chromosomal regions defined by metaphase comparative genomic hybridisation. This review concentrates on the application of metaphase comparative genomic hybridisation in the area of renal cancer research and summarises data obtained from comparative genomic hybridisation studies.

Comparative genomic hybridization analysis of hepatoblastoma reveals high frequency of X-chromosome gains and similarities between epithelial and stromal components

Hepatoblastoma (HB) is the most common liver tumor in childhood and differs in its environmental risk factors and genetic background from hepatocellular carcinoma. HB is associated with inherited conditions such as familial adenomatous polyposis and Beckwith-Wiedemann syndrome, suggesting the importance of genetic abnormalities in the pathogenesis and progression of this disease. It has a very polymorphous morphology. A diverse range of cytogenetic alterations has been reported to date, the most frequent being trisomy 2 and trisomy 20. Thirty-five HB specimens from 31 patients (22 purely epithelial, 4 purely mesenchymal, 9 mixed) were examined by comparative genomic hybridization (CGH), a technique that enables us to screen the entire tumor genome for genetic losses and gains. Our aims were as follows: (1) to characterize chromosome abnormalities that appear in this tumor and (2) to identify possible differences between different histologic subtypes of HB. We found significant gains of genetic material, with very little difference in the number and type of alterations between the different histologic components of HB. The most frequent alterations were gains of Xp (15 cases, 43%) and Xq (21 cases, 60%). This finding was also confirmed by fluorescent in situ hybridization performed on nuclei extracted from 6 specimens. Other common alterations were 1p-, 2q+, 2q-, 4q-, and 4q+. We found no difference between different histologic subtypes, a finding that may be in agreement with the hypothesis of a common clonal origin for the different components. An hitherto-unreported high frequency of X chromosome gains may support the assumption that X-linked genes are involved in the development of this neoplasm.

Transcriptional profiling in hepatoblastomas using high-density oligonucleotide DNA array

Hepatoblastoma is a common hepatic tumor in children. Although evidence regarding cytogenetic and molecular genetic alterations in hepatoblastomas has been reported, the molecular events affecting the biologic characteristics of this tumor, including alterations of the gene expression profile, are largely unknown. To identify genes differentially expressed between nondiseased liver (NDL) and hepatoblastoma tumor (HBT), we analyzed the gene expression profile in 14 NDL and 16 HBT samples using a high-density oligonucleotide DNA array. Using Mann-Whitney U test followed by the k-nearest neighbor algorithm, we identified 26 genes (predictor genes) that were able to assign unknown samples derived from NDL and HBT to either the NDL group or HBT group with 100% accuracy. Using a cross-validation approach, we confirmed that the k-nearest neighbor algorithm assigned the particular samples derived from NDL and HBT to either the NDL or HBT group with 93.3% (28/30 samples) accuracy. In the 26 predictor genes, we found alteration of the expression of genes regulating cell division (NAP1L1, STMN1, CCNG2, and CDC7L1) and tumor cell growth (IGF2 and IGFBP4) in HBT. Four predictor genes (ETV3, TPR, CD34, and NR1I3) were also found to be mapped to the chromosomal region 1q21 approximately q32, which has been reported to be frequently involved in the development of hepatoblastoma. The findings obtained in this study suggest that alteration of the expression of some genes regulating cell division and tumor cell growth may be characteristics of the gene expression profile in HBT, and that alteration of the expression of the four predictor genes mapped to chromosomal region 1q21 approximately q32 may also contribute to the differences in gene expression profile between NDL and HBT.

Where do we stand with hepatoblastoma? A review

Hepatoblastoma (HB) is the most common pediatric liver malignancy, comprising approximately 1% of all pediatric cancers. The disparate clinical staging systems and histologic classifications that were developed during the last decades, nevertheless, reflect the remaining difficulties and uncertainties in characterizing HB. Furthermore, the combination of surgery and (neo)adjuvant chemotherapy has improved patient outcomes dramatically. A poor prognosis is associated with large tumor size, multifocality, extrahepatic disease, and metastatic spread. The exact etiology of HB remains unknown, but the cytogenetic alterations, phenotypic features, and biologic aspects that accompany this neoplasm yield more and more insight into its pathogenesis. New cell-biologic and molecular-biologic insights may lead to the development of new treatment modalities, especially for patients with a bad prognosis. This review summarizes the different aspects of this intriguing tumor and discusses the current status of research and treatment for patients with HB.

Two novel in vitro human hepatoblastoma models, HepU1 and HepU2, are highly characteristic of fetal-embryonal differentiation in hepatoblastoma

Using comparative genomic hybridization (CGH), we present a genome-wide screening of a mixed mesenchymal-epithelial hepatoblastoma, its recurrence and 2 novel hepatoblastoma cell lines raised from the ascites, 18 (HepU1) and 23 (HepU2) months after diagnosis of a hepatoblastoma in a 35-month-old boy. Both cell lines were also characterized by GTG-banding, multicolor-fluorescence in situ hybridization (M-FISH) and multicolor banding (M-Band). On the basis of CGH, we compared the cytogenetics of histologically different tumor areas of the parental tumor and its recurrence with the hepatoblastoma cell lines. We found different CGH profiles in the parental tumor rev ish enh(1q31-q32,8p,12,17,20,X), dim(4q34-q35,18q23)[cp] and its recurrence rev ish enh(8q24,17,Xq26-q28), dim(7q11.2-q21,13q34)[cp]. Although both epithelial cell lines were obtained at different times and the clonal ancestor of HepU2 had been exposed to a higher cumulative dose of chemotherapy, HepU1 and HepU2 have an identical karyotype: 48-56,XY,+Y,dup(2)(q32-q34),t(3;4)(q21;q34),+8,+12,+13, +17,+t(18;19)(q21;q?),+20[cp] and identical CGH profiles: rev ish enh(2q24-q33,8,12,13q,17,20), dim(4q34-q35,18q22-q23). In common with previously described hepatoblastoma cell lines, HepU1 and HepU2 demonstrate a gain of chromosome 20. The in situ aberrations most closely resembling that of HepU1 and HepU2 were found in areas of fetal-embryonal differentiation of the primary tumor. Interestingly, both cell lines mimic this histology in their three-dimensional growth pattern in vitro. HepU1 and HepU2 are thus cytogenetically and phenotypically highly characteristic of fetal-embryonal hepatoblastoma.

Overexpression of human Dickkopf-1, an antagonist of wingless/WNT signaling, in human hepatoblastomas and Wilms' tumors

Hepatoblastomas (HBs) represent the most frequent malignant liver tumors of childhood; yet little is known about the molecular pathogenesis and the alterations in expression patterns of these tumors. We used a suppression subtractive hybridization approach to identify new candidate genes that may play a role in HB tumorigenesis. cDNA species derived from corresponding liver and fetal liver were subtracted from HB cDNAs, and a series of interesting candidates were isolated that were differentially expressed. One of the transcripts overexpressed in HB was derived from the human Dickkopf-1 (hDkk-1) gene, which encodes a secreted protein acting as a potent inhibitor of the wingless/WNT signaling pathway. We examined the hDkk-1 expression levels in 32 HB biopsy specimens and in the corresponding liver samples, in 4 HB cell lines, and in a panel of other tumors and normal tissues using a differential PCR approach and Northern blotting. Eighty-one percent of the HBs but none of the normal pediatric or fetal liver tissues showed hDkk-1 expression. hDkk-1 transcripts were also present in 5 of 6 Wilms' tumors but only weakly detectable in 2 of 20 hepatocellular carcinoma samples and in 1 of 5 medulloblastoma cell lines; transcripts were absent in malignant gliomas and breast cancer. The central effector molecule in the WNT developmental control pathway is the beta-catenin protein. Interestingly, activating mutations of the beta-catenin gene have previously been identified in 48% of HBs, and more than 85% of HBs show accumulation of beta-catenin protein as the indicator for an activated pathway. The overexpression of the inhibitor Dkk-1 may therefore be related to uncontrolled wingless/WNT signaling and may represent a negative feedback mechanism. hDkk-1 expression represents a novel marker for HBs and Wilms' tumors.

Prognostic significance of c-myc and AIB1 amplification in hepatocellular carcinoma. A broad survey using high-throughput tissue microarray

BACKGROUND

Amplifications of 1q21, c-myc at 8q24.1, and AIB1 at 20q12 are genetic alterations that are detected frequently in hepatocellular carcinoma (HCC). The authors evaluated the association of these amplifications with the prognosis of patients with HCC.

METHODS

In the current study, amplification of 1q21, c-myc, and AIB1 was analyzed in 560 specimens from 400 patients with HCC and 20 patients with benign liver lesions using fluorescence in situ hybridization with high-throughput tissue microarray. Differences of amplification patterns were compared between small and large HCC, single nodular and multiple nodular HCC, primary and metastatic HCC, and primary and recurrent HCC.

RESULTS

Significant differences between single nodular and multiple nodular HCC were detected in c-myc amplification (12% vs. 38%; P < 0.01) and AIB1 amplification (16% vs. 30%; P < 0.05). More frequent c-myc amplification was detected in metastatic HCC (45%) compared with primary HCC (29%) and in recurrent HCC (60%) compared with primary HCC (38%). Similarly, more frequent AIB1 amplification was observed in metastatic HCC (41%) compared with primary HCC (23%) and in recurrent HCC (60%) compared with primary HCC (29%). However, no significant differences in 1q21 amplification were observed.

CONCLUSIONS

The current results strongly suggest that amplifications of the c-myc and AIB1 oncogenes are late genetic alterations in the progression of HCC and are correlated with a poor prognosis.

Fluorescent in situ hybridization (FISH) reveals frequent and recurrent numerical and structural abnormalities in hepatoblastoma with no informative karyotype

BACKGROUND

Hepatoblastoma (HB) is the most frequent malignant liver tumor in children. The few cytogenetic studies available indicate that HB is associated with recurring trisomies of chromosomes 2, 8, and 20; recurrent t(1;4) (q12;q34) has been reported in few cases. The abnormalities of chromosome 1q are relatively frequent and usually lead to overexpression of 1q material. A cluster of breakpoints is located at the level of bands 1q12 and 1q21. More work is needed to clarify their real incidence and prognostic significance. Cytogenetic analysis is limited by the requirement of suitable cells in metaphase. A different method that increases analysis sensitivity is fluorescent in situ hybridization (FISH).

PROCEDURE

We studied 10 cases of HB with no informative karyotype (normal karyotype or no metaphases). FISH was performed by the standard method, using cytospins and imprints obtained from frozen or cytogenetic samples of direct cultures. Alpha-satellite probes for centromeric DNA were used for chromosomes 2, 8, and 20 analysis; rearrangement of region 1q12-21 was detected with BAC (bacterial artificial chromosome) probe bA79E5.

RESULTS

We detected at least one trisomic clone in 5/10 of these cases. Trisomy 20 was the most frequently detected abnormality, followed by trisomy of the chromosomes 2 and 8. Analysis of 1q12 band revealed that the rearrangement of 1q usually is in pericentromeric heterochromatin, it was present in 5/10 of studied cases.

CONCLUSION

FISH analysis is recommended in all cases of HB with no informative karyotype to gain more information regarding the frequent trisomies encountered and their significance.

Genetic alterations in hepatoblastoma and hepatocellular carcinoma: common and distinctive aspects

Hepatoblastoma (HB) and hepatocellular carcinoma (HCC) are two different subtypes of primary tumors arising from liver parenchymal cells. These tumors differ by many histoclinical characteristics, and comparative analysis of genetic alterations in HB and HCC might provide some clues on the molecular oncogenic pathways leading to hepatocyte transformation. Recent outcomes have been provided by the assessment of global genetic changes in tumor cells, using conventional cytogenetic approaches, PCR-based microsatellite analysis and Comparative genomic Hybridization (CGH). Cytogenetic studies of HB, microsatellite analysis of HCC and recent CHG data have outlined common and distinctive characters between the two tumor types. HBs are characterized by a low number of chromosomal changes, consisting mainly of gains at chromosomes 1q, 2, 8q, 17q, and 20. By contrast, HCCs harbor multiple chromosomal abnormalities, predominantly losses, with increased chromosomal instability in tumors associated with hepatitis B virus infection. Common alterations in HB and HCC include gain of chromosomes 1q, 8q, and 17q, and loss of 4q. Another important common feature shared by the two tumor types is the frequent activation of Wnt/beta-catenin signaling by stabilizing mutations of beta-catenin. Immunohistochemical analysis of beta-catenin has demonstrated nuclear/cytoplasmic accumulation of the protein in most HBs and in more than one third of HCCs. Strikingly, beta-catenin mutations are associated with chromosomal stability in both tumor types. Together, these studies define different pathways in liver cell transformation, reflecting various developmental stages and multiple risk factors. A detailed understanding of the molecular hits underlying liver tumorigenesis, combined with clinicopathological parameters, will permit an accurate evaluation of major targets for prognostic and therapeutic intervention.

Fetal-type hepatoblastoma and del(3)(q11.2q13.2)

Hepatoblastoma is a rare embryonal malignancy of children. Trisomies or gains of chromosomes 1q, 2, 8, and 20 and a der(4)t(1;4)(q12;q34) have been described in hepatoblastoma. Herein, we describe a stage I fetal-type hepatoblastoma associated with a del(3)(q11.2q13.2).

Fluorescence in situ hybridization improves cytogenetic results in the analysis of hepatoblastoma

Hepatoblastoma (HB) is the most frequent malignant liver tumor in children. Cytogenetic data indicate the presence of recurring trisomies of the chromosomes 2, 8, and 20, but more work is needed to clarify their incidence and prognostic significance. Cytogenetic analysis is limited by the requirement of suitable cells in metaphase. A different method that increases analysis sensitivity is fluorescence in situ hybridization (FISH). We studied 20 cases of hepatoblastoma; FISH analysis obtained results in 10 cases of HB with no informative karyotype. In 5 of 10 of these cases at least one trisomic clone was detected, which always coexisted with a population of diploid cells. These results confirm that trisomy 20 and/or 2 and 8 coexisting with diploid cells is a frequent finding in hepatoblastoma and provide further support to the clonal evolution theory: indeed, trisomy 20 was the most frequently detected abnormality, followed by trisomy of chromosomes 2 and 8. In view of the high incidence of recurrent trisomies, FISH analysis should be recommended in all the cases of HB with no informative karyotype.

Positional cloning identifies a novel cyclophilin as a candidate amplified oncogene in 1q21

Gains of 1q21-q23 have been associated with metastasis and chemotherapy response, particularly in bladder cancer, hepatocellular carcinomas and sarcomas. By positional cloning of amplified genes by yeast artificial chromosome-mediated cDNA capture using magnetic beads, we have identified three candidate genes (COAS1, -2 and -3) in the amplified region in sarcomas. COAS1 and -2 showed higher amplification levels than COAS3. Most notably, amplification was very common in osteosarcomas, where in particular COAS2 was highly expressed. COAS1 has multiple repeats and shows no homology to previously described genes, whereas COAS2 is a novel member of the cyclosporin-binding peptidyl-prolyl isomerase family, very similar to cyclophilin A. COAS2 was overexpressed almost exclusively in aggressive metastatic or chemotherapy resistant tumours. Although COAS2 was generally more amplified than COAS1, it was not expressed in well-differentiated liposarcomas, where amplification of this region is very common. All three genes were found to be amplified and over-expressed also in breast carcinomas. The complex nature of the 1q21-23 amplicons and close proximity of the genes make unequivocal determination of the gene responsible difficult. Quite likely, the different genes may give selective advantages to different subsets of tumours.

Cytogenetic findings in two new cases of hepatoblastoma

We describe two cases of hepatoblastoma occurring in an 18-month-old boy and a 3-month-old girl. Cytogenetic analysis of the primary tumors revealed gain of 2q and 20 in both cases. In case 1, t(7;8;11) was seen as a secondary abnormality. Other chromosomal aberrations seen in case 2 were unbalanced t(1;1) and t(2;11), resulting in partial gains of 1q and 2q. These results support previous reports that gains of 2q and 20 and rearrangement of chromosome 1 are strongly associated with hepatoblastoma and may be essential for establishing this neoplasm. The 11q and 7q abnormalities may represent a pathway of genetic evolution associated with hepatoblastoma progression.

Prognostic impact of molecular genetic alterations in hepatoblastoma

BACKGROUND

During recent years, we identified characteristic genetic alterations in sporadic hepatoblastoma (HB). These include loss of heterozygosity (LOH) at the chromosomal region 11p15.5, LOH on chromosome arms 1p and 1q, activating mutations in exon 3 of the beta-catenin gene, as well as overexpression of the c-met oncogene, which encodes the hepatocyte growth factor receptor. We now wanted to evaluate the prognostic relevance of these abnormalities concerning the outcome in a large group of patients.

PROCEDURE

All but 7 of 56 patients with HB were treated either with primary resection for small tumors, or neo-adjuvant chemotherapy with ifosfamide, cisplatin and doxorubicin (IPA) before delayed surgery in case of extended disease and additional adjuvant IPA therapy in all cases. Seven tumors were primarily resected and adjuvantly treated with different cytotoxic drugs. LOH 11p15.5, LOH 1p, and LOH 1q were detected in tumor tissue in comparison to normal liver and/or peripheral blood leukocytes by PCR based microsatellite analysis. Beta-catenin mutations were analysed with SSCP, deletion screening and direct sequencing. RT-PCR was used for identification of c-met mRNA overexpression. The results were correlated with the tumors' stage, histological type and epithelial differentiation, as well as with the patients' outcome.

RESULTS

Overall disease-free survival after median follow-up of 5 years was 43/56 patients (77%). LOH 11p15.5 was found in 15/56, LOH1p in 11/53, LOH1q in 7/53 and beta-catenin mutations in 25/55 HB. 13/23 HB had a c-met overexpression. LOH 11p15.5 and LOH 1p were significantly more often found in embryonal HB, while there was no correlation of other genetic alterations with histological type or differentiation. Furthermore, statistical analysis revealed no correlation of any of these disorders with initial tumor stage, nor with the patients' outcome.

CONCLUSION

None of the investigated molecular genetic alterations are suited to serve as a prognostic indicator in HB. Further investigations, especially genetic screening of tumor tissue may reveal prognostic markers for this neoplasm.

An 8-cM interstitial deletion on 4q21-q22 in DNA from an infant with hepatoblastoma overlaps with a commonly deleted region in adult liver cancers

We performed molecular analysis of a germline interstitial deletion of chromosome 4 [del(4)(q21.22q23)], which had been observed in a male infant manifesting early-onset hepatoblastoma (HBL). The chromosomal anomaly in this child was associated with a unique congenital syndrome including HBL, atrial septal defect, ventricular septal defect, patent ductus arteriosus, mental retardation, and seizures. However, the patient did not exhibit a megalencephaly typical of 4q21-22 deletions. His HBL was associated with an increasing serum alpha-fetoprotein level and rapid growth. To define the chromosomal deletion at the molecular level in this child, we analyzed his lymphoblasts with fluorescence in situ hybridization, using as probes a panel of BAC/PAC genomic clones containing STS markers covering the 4q12-27 region. The analysis revealed that the affected chromosome had an 8-cM deletion within 4q21-q22, flanked by markers D4S2964 and D4S2966. This microdeletion overlaps with the commonly deleted region at 4q21-q22 that was recently defined in adult hepatocellular carcinomas.

Frequent increase of DNA copy number in the 2q24 chromosomal region and its association with a poor clinical outcome in hepatoblastoma: cytogenetic and comparative genomic hybridization analysis

In a cytogenetic and comparative genomic hybridization (CGH) study of 38 hepatoblastomas, we found gain of 1q in 17 tumors (44.7%), that of 2 / 2q in 14 (36.8%), that of 20 / 20q in 9 (23.7%) and that of 8 / 8q in 8 (21.0%), loss of 4q in 4 (10.5%) and no DNA copy changes with normal karyotype or no mitotic cells in 11 (28.9%). Eleven tumors with 2 / 2q gain detected by CGH had a total chromosome 2 gain, a partial 2q gain, or a total chromosome 2 gain with an augmented partial 2q region; the common region for DNA copy gain was 2q24. Two-color fluorescence in situ hybridization (FISH) analyses using probes covering the centromere of chromosome 2 or HOXD13 (2q31) confirmed the CGH findings, and showed that the common region for gain in 2q was centromeric to HOXD13. Event-free survival (EFS) +/- standard error (SE) at 5 years was lowest in patients with 2q gain [37 +/- 15%], highest in those with no DNA copy changes [82 +/- 12%], and intermediate in those with DNA copy changes other than 2q gain [74 +/- 13%] (P = 0.0549). Multivariate analysis showed that 2q gain was an independent factor predicting a poor outcome. These findings suggest the presence of a growth-promoting gene or an oncogene in the 2q24 chromosome band, and a tumor suppressor gene in terminal 4q, which have important roles in the development and progression of hepatoblastoma.

A comprehensive karyotypic study on human hepatocellular carcinoma by spectral karyotyping

The current paucity of cytogenetic information on hepatocellular carcinoma (HCC) reflects the difficulties in culturing hepatocytes in vitro. Here, we report on the successful culture of 15 HCC cases. Chromosome aneuploidy ranging from a near-diploid to hyperhexaploid karyotype was found, but their complete karyotypic interpretations were hampered by the presence of many unidentifiable rearrangements. Spectral karyotyping (SKY) was used to elucidate structural changes in these HCC samples and 3 liver cancer cell lines (PLC/PRF/5, Hep3B, and HepG2). Frequent structural abnormalities were found on chromosomes 1 (13 of 15 cases; 3 of 3 cell lines), 8 (10 of 15 cases; 2 of 3 cell lines), 17 (9 of 15 cases; 3 of 3 cell lines), and 19 (9 of 15 cases; 1 of 3 cell lines). In particular, the chromosome regions 1p13-q21, 8p12-q21, 17p11-q12, 17q22, and 19p10-q13.1 were involved in multiple rearrangements. SKY analysis also suggested several previously undescribed breakpoints in HCC. These breakpoints, predominantly pericentromeric, clustered around the chromosome bands 2q33-q34, 3p13-q12, 4p14-q12, 5p10-q11, 7p12-q11, 10q10-q11, 11q10, 11q13-q21, 12q10-q13, 12q22-q23, 13q10-q14, 15q10, 16q10-q13, 18p11-q11, 20p11-q13.1, 21q10, and 22q10. When tumor sizes were compared, a significantly higher number of structural abnormalities was found in tumors larger than 4 cm (P =.007). Rearrangements such as t(1;8), t(1;11), t(1;19), and t(17;21) that were identified in both primary tumors and cell lines might represent markers that reflect proliferative advantages. Although SKY analysis did not indicate consistent translocations, it suggested nonrandom breakpoints, predominantly in the pericentromeric region, on a number of chromosomes. These breakpoint clusters may thus prove to be more important in the liver carcinogenesis and targets for further molecular investigations.

p57(KIP2) is not mutated in hepatoblastoma but shows increased transcriptional activity in a comparative analysis of the three imprinted genes p57(KIP2), IGF2, and H19

Hepatoblastomas (HBs), representing malignant liver tumors of childhood, show frequent loss of heterozygosity (LOH) in the chromosomal region 11p15.5. This loss is of maternal origin suggesting the presence of a monoallelically expressed tumor suppressor gene in this region. p57(KIP2) (KIP2) located at 11p15.5 is predominantly expressed from the maternal allele and encodes a cyclin-dependent kinase inhibitor. We screened a series of 56 HB tumors and five HB cell lines for allelic loss (LOH) of the KIP2 locus by microsatellite analysis and KIP2 coding sequence mutations by single-strand conformation polymorphism analysis. Although LOH at the KIP2 locus occurred in 25% of the cases, no mutations were found. Analysis of KIP2 mRNA expression by competitive reverse transcriptase-polymerase chain reaction revealed up-regulation in nine of 12 HBs compared to matching liver samples. In contrast, mRNA levels of the putative suppressor gene H19 on 11p15.5 were decreased in 10 of 12 tumors, indicating that KIP2 and H19 are not co-regulated in HBs. IGF2 mRNA expression was increased in 11 of 12 HB samples. All HBs showed monoallelic KIP2 expression. However, the overexpression of KIP2 in HBs with maternal loss of 11p15.5 suggests a reactivation of the paternal allele in these cases. Overexpression of KIP2 in HBs argues against a role as a HB suppressor gene.