Novel homozygous deletions of chromosomal band 18q22 in pancreatic adenocarcinoma identified by STS marker scanning

Failure patterns in resected pancreas adenocarcinoma: lack of predicted benefit to SMAD4 expression

OBJECTIVE

To determine whether SMAD4 expression is associated with recurrence pattern after resection for pancreatic ductal adenocarcinoma (PDA).

BACKGROUND

SMAD4 expression status has been reported to be associated with patterns of failure in PDA, but studies have not examined recurrence patterns after resection.

METHODS

A tissue microarray was constructed including 127 patients with resected PDA and either short-term (<12 months) or long-term (>30 months) survival. SMAD4 expression was evaluated by immunohistochemistry and categorized as present or lost in tumor cells. Conventional pathologic features (lymph node metastases, positive resection margin, poor grade, and tumor size) were recorded, and disease-specific outcomes (eg, recurrence pattern and early cancer-specific mortality) were determined.

RESULTS

Loss of SMAD4 expression in pancreatic adenocarcinoma was identified in 40 of 127 patients (32%). SMAD4 loss occurred in 27% of patients who experienced isolated local recurrence, 33% of patients with a distant recurrence, 33% of patients who experienced local and distant site recurrences, and 25% of patients who were without evidence of recurrence (Fisher exact, P = 0.9). In a multivariate analysis, the presence of regional lymph node metastases was the only factor associated with the development of distant metastases (odds ratio = 4.7, P = 0.02). SMAD4 was neither associated with recurrence pattern (odds ratio = 0.9, P = 0.9) nor associated with early death (odds ratio = 0.5, P = 0.15).

CONCLUSIONS

Primary tumor SMAD4 expression status was not a predictor of recurrence pattern in a large cohort of patients with resected PDA.

Genomic organization and functional characterization of the promoter for the human suppressor of cytokine signaling 6 gene

In this study, we report the expression and genomic structure of the gene encoding human suppressor of cytokine signaling 6 (SOCS6), and the characterization of the functional promoter region. The human SOCS6 gene, spanning 40 kb on chromosome 18q22.2, is composed of two exons separated by an intron of 35 kb. Two transcripts are ubiquitously expressed, and both encode the full-length open reading frame of SOCS6. A primer extension assay revealed that the major transcription initiation site is located 469 bp upstream the ATG codon. Luciferase promoter analysis demonstrated that the 5'-flanking region is able to drive transcription, and the CpG-rich sequences near the transcription initiation site are important for the TATA-less SOCS6 promoter activity. Analogous to SOCS1 and SOCS3, which are down-regulated in several human cancers, SOCS6 is expressed at lower levels in carcinomas of stomach and colon. We demonstrated that hypermethylation of the SOCS6 promoter is one of the mechanisms for the epigenetic regulation of SOCS6 expression. Firstly, in vitro methylation of the reporter promoter plasmid significantly suppressed the promoter activity. Secondly, SOCS6 expression in vivo was enhanced by treating cells with a methyltransferase inhibitor. The SOCS6 gene from various species shares significant homology in amino acid sequences, transcription factor binding motifs in promoter regions and the two-exon genomic structure, suggesting that the SOCS6 gene is highly conserved.

Delineation and candidate gene mutation screening of the 18q22 minimal region of deletion in head and neck squamous cell carcinoma

The 18q chromosome arm is frequently lost in advanced head and neck squamous cell carcinoma. Twenty-four microsatellite markers located on chromosome 18q were genotyped in 145 primary tumors and 10 cell lines in order to identify putative tumor suppressor genes implicated in tumor progression. Two different minimal common regions of loss (MCRL) were identified at 18q22 and 18q23 respectively. To refine and delineate boundaries of an homozygous deletion found in one cell line, 44 extra markers located at 18q22 were analysed and the homozygous deletion was precisely defined within a critical region of 4.9 Mb. Four known genes (CDH7, CDH19, DNAM-1, FLJ23594) located in this critical region and two EST clusters (Hs.96900, Hs.98628) were selected for further investigations. For these six genes, genomic structures were established, somatic mutations were screened in 20 HNSCC and 10 cell lines and transcription levels were determined in eight cell lines. No somatic mutations were found in any of the candidate genes analysed (57 coding exons). However, differential transcription levels were observed for CDH19 and Hs.96900 in head and neck cancer cell lines supporting their putative involvement through down regulation mechanisms in head and neck cancer progression.

Exclusion of SMAD4 mutation as an early genetic change in human pancreatic ductal tumorigenesis

Pancreatic ductal carcinoma is one of the malignant diseases with the poorest prognosis. To develop effective methods for better treatment of pancreatic cancer patients, we tried to analyze the course of multistep carcinogenesis of the pancreatic ductal cells. IPMT (intraductal papillary-mucinous tumor) is thought to be one of the premalignant lesions of the pancreas, which would transform into carcinomas. Loss of 18q at the SMAD4 locus is known to be an early genetic change in pancreatic ductal carcinomas. It is not clear, however, whether or not the target gene for inactivation is SMAD4. Using 18 IPMTs, we analyzed LOH at the SMAD4 locus and observed frequent LOH (7/14, 50%). No mutations were observed in any of the tumors. Moreover, the expression level of the SMAD4 protein did not show a reduction in IPMTs. These results suggested that (i) inactivating mutation of the SMAD4 gene is a rather late genetic change in pancreatic carcinogenesis, and (ii) there may be an unknown tumor suppressor gene in 18q, other than SMAD4, that is involved in pancreatic ductal carcinogenesis.

Analysis of human meningiomas for aberrations of the MADH2, MADH4, APM-1 and DCC tumor suppressor genes on the long arm of chromosome 18

We have previously reported that losses of genomic material from the long arm of chromosome 18 are frequent in atypical and anaplastic meningiomas but rare in benign meningiomas. In the present study, we have investigated a series of 37 meningiomas for mutation and expression of 4 tumor suppressor genes (MADH2, MADH4, APM-1 and DCC) located at 18q21. Comparative genomic hybridization or loss of heterozygosity analysis showed losses on chromosome 18 that included sequences from 18q21 in 15 of 37 tumors. Mutation analysis of APM-1 revealed a missense mutation (c. 1819G>A: G607S) in 1 atypical meningioma. None of the tumors showed mutations of MADH2 and MADH4 or loss of detectable transcripts from MADH2, MADH4, APM-1 and DCC. In contrast to human brain tissue, normal leptomeninges and meningiomas showed preferential expression of a DCC splice variant lacking 60 base pairs from exon 17. Taken together, our data do not support a significant role for MADH2, MADH4, APM-1 and DCC alterations in the pathogenesis of meningiomas. The targeted gene that is inactivated in most meningiomas with 18q losses remains to be identified.

Physical and transcriptional map of a 311-kb segment of chromosome 18q21, a candidate lung tumor suppressor locus

Here, we report the complete genomic sequence and the characterization of the 311-kb region of 18q21, a candidate tumor suppressor locus containing a region of homozygous deletion in a lung cancer cell line, Ma29. This region contained two known genes, SMAD4 and ME2 (mitochondrial malate oxydoreductase), and two novel genes, D29 (deleted in Ma29 HGMW-approved symbol ELAC1), encoding an evolutionarily conserved protein, and B29 (beside the Ma29 deletion HGMW-approved symbol C18orf3), with no significant homology to any known genes. The deleted DNA segment in Ma29, which was estimated to be 195 kb in size, included all the coding exons of ME2 and D29, but not the coding exons of SMAD4 and B29. The deleted region also included exon 0, a 5'-noncoding exon, of SMAD4, and the expression of SMAD4 was greatly reduced in Ma29 cells. Mutations of SMAD4 and D29 were detected in 1 of 45 lung cancer cell lines examined, while those of ME2 and B29 were not detected, indicating that these four genes are not major targets for 18q21 deletions. The physical and transcriptional map constructed in this study will provide basic information for the identification of a tumor suppressor gene(s) at 18q21 involved in lung carcinogenesis.

Association of poor prognosis with loss of 12q, 17p, and 18q, and concordant loss of 6q/17p and 12q/18q in human pancreatic ductal adenocarcinoma

OBJECTIVE

Pancreatic cancer is one of the diseases with the poorest prognosis, but the associated genetic alterations are not yet well understood. The genetic alterations reported to date in pancreatic cancer include frequent mutations of the KRAS, TP53, p16, and SMAD4 genes. Mutation of the TP53 gene was reported to be associated with a poor prognosis. In this study, we analyzed the association of loss of heterozygosity (LOH) with clinicopathological features to attempt to devise effective methods in the future for clinically applying our results to diagnosis and treatment.

METHODS

A total of 55 tumors from patients with primary pancreatic ductal carcinomas (34 men and 21 women, mean average age 63.9 yr) in which all the relevant clinical and pathological data were available were analyzed. A total of 46 cases were surgically resected, and nine cases were not. Tumor cells as well as corresponding normal cells were collected by microdissection under a microscope, and DNAs were purified. Allelotype analysis was performed by the PCR-based method, and the results were statistically analyzed.

RESULTS

LOH of > or =30% were observed on chromosome arms 17p (47%, 17/36), 9p (45%, 14/31), 18q (43%, 15/35), 12q (34%, 10/29), and 6q (30%, 10/33). LOH of 12q, 17p, and 18q were significantly associated with a poor prognosis. Concordant losses of 6q with 17p and 18q were significantly associated with a poor prognosis. Concordant losses of 6q with 17p and of 12q with 18q were also found.

CONCLUSIONS

Because LOH of 12q, 17p, and 18q are significantly associated with a poor prognosis, mutation of the putative tumor suppressor genes on these chromosome arms may play significant roles in the disease progression. Concordant losses of 6q with 17p and of 12q with 18q suggest that protein products of putative tumor suppressor genes on 6q and 12q may function in association with TP53 and SMAD4, respectively.