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.

Mutational and expression analysis of the NF1 gene argues against a role as tumor suppressor in sporadic pilocytic astrocytomas.

Children with neurofibromatosis type I (NF1) have a highly increased risk for developing optic nerve gliomas. Several lines of evidence support the notion that the NF1 gene functions as tumor suppressor in these pilocytic astrocytomas and therefore it is tempting to hypothesize that the NF1 gene plays a similar role in sporadic pilocytic astrocytomas. We searched for possible mechanisms of inactivation of the NF1 gene in pilocytic astrocytomas of different locations. Protein truncation testing (PTT) did not render indication for inactivating mutations in 10 analyzed tumors. Further, loss of heterozygosity analysis revealed maintenance of heterozygosity for 3 intragenic markers in 11 informative cases. Using a real-time PCR-based assay we showed that total NF1 transcript levels are high in pilocytic astrocytomas and that the NF1 type I and type II expression ratios in pilocytic astrocytomas are comparable to ratios in normal brain tissue and high-grade gliomas. Consequently, the data presented here argue against altered NF1 gene expression and the involvement of the NF1 gene in the tumorigenesis of sporadic pilocytic astrocytomas.

A patient severely affected by spinal neurofibromas carries a recurrent splice site mutation in the NF1 gene.

Spinal neurofibromas are found in up to 38% of NF1 patients. However, they cause clinical implications only in about 5% of the patients. In contrast, multiple symptomatic spinal neurofibromas are the main clinical finding in patients with familial spinal neurofibromatosis. Familial spinal neurofibromatosis has been considered to be a distinct clinical form of neurofibromatosis. Linkage analysis in two families and identification of a NF1 gene mutation in a third family strongly associate spinal neurofibromatosis with the NF1 gene. We describe a NF1 patient who satisfies the NIH diagnostic criteria and has severe spinal involvement with bilateral spinal root neurofibromas at every level. A recurrent splice site mutation (IVS19b-3C>G) was identified in the NF1 gene in the patient. We discuss the possibility that the clinical picture of this patient represents an additional example of spinal neurofibromatosis. By comparison of the clinical expression of NF1 in this patient and that in another patient with the identical mutation the hypothesis that spinal neurofibromatosis is associated with a particular mutation is highly unlikely. The involvement of other genes linked to the NF1 gene or modifying genes is currently the most likely explanation for the clinical phenotype of spinal neurofibromatosis.

Combined restriction landmark genomic scanning and virtual genome scans identify a novel human homeobox gene, ALX3, that is hypermethylated in neuroblastoma.

Restriction landmark genome scanning (RLGS) allows comparative analysis of several thousand DNA fragments in the genome and provides a means to identify CpG islands that are altered in tumor cells as a result of amplification, deletion, or methylation changes. We have developed a novel informatics tool, designated virtual genome scan (VGS), that makes it possible to predict automatically the sequence of fragments in RLGS patterns by matching to the human genome sequence. A combination of RLGS and VGS was utilized to identify changes of chromosome 1-derived fragments in neuroblastoma. A NotI-EcoRV fragment was found to be absent frequently in neuroblastoma cell line RLGS patterns. Sequence prediction by VGS as well as cloning of the fragment showed that it contained a CpG island that is part of the human orthologue of the hamster homeobox gene Alx3. Expression analysis in a panel of human and mouse tissues showed predominant expression of ALX3 in brain tissue. Methylation-sensitive sequence analysis of the promoter region in neuroblastoma cell lines indicated that methylation of specific sequences correlated with repression of the ALX3 gene. Expression was re-induced after treatment with the methylation inhibitor 5-aza-2'-deoxycytidine. Promoter methylation analysis of ALX3 in primary neuroblastoma tumors, using methylation-sensitive polymerase chain reaction, found preferential ALX3 methylation in advanced-stage tumors. The VGS approach we have implemented in combination with RLGS is useful for the identification of genomic CpG island-related methylation changes or deletions in cancer.