Alternative spliced variants of the alpha-methylacyl-CoA racemase gene and their expression in prostate cancer.

Alpha-methyacyl-CoA racemase (AMACR), a mitochondrial and peroxisomal enzyme essential in lipid metabolism, is overexpressed in prostate cancer. Two different AMACR transcripts (designated IA and IIA), each derived from five exons, have been reported. AMACR IA, the most abundant form, encodes a 382-amino acid protein (Mw 42 kDa, pI 6.07). AMACR IIA contains an alternative fifth exon that has extensive homology to the human fumarate hydratase (FH) and encodes a 288-amino acid protein (Mw 32 kDa, pI 9.6). Here we report additional variants of IA and IIA whereby the transcripts lack exon 3 and are designated as IB (Mw 22 kDa, pI 10.31) and IIB (Mw 31 kDa, pI 9.44). Due to a frameshift, the alternative fifth exon in the IIA transcript encodes a polypeptide that differs from FH. In contrast, the IIB transcript, generated as a result of the dual alternative splicing events, encodes a polypeptide homologous with a highly conserved region of FH. We also identified a shorter variant form of IIA (IIAs, Mw 28 kDa, pI 9.65), which lacks the 5' half of the alternative fifth exon. The carboxy termini of all five gene products differ as a result of the alternative splicing events. In prostate tumor tissues that overexpressed AMACR, both the A and B forms were overexpressed, suggesting coregulation. Only the predominant AMACR IA has an acidic pI and contains the previously identified peroxisomal targeting signal (PTS1) peptide, while the other four variants are basic proteins that lack the peroxisomal targeting signal peptide. These observations have implications for the cellular localization and function of these AMACR variants.

Highly expressed genes in pancreatic ductal adenocarcinomas: a comprehensive characterization and comparison of the transcription profiles obtained from three major technologies.

When using gene expression profiling to understand human tumors, one is often confronted with long lists of genes that need to be further categorized into meaningful data. We performed a comprehensive evaluation and comparison of gene expression profiles obtained from pancreatic cancers to determine those genes most differentially expressed and thus with the most promise for translation into clinically useful targets. cDNA was prepared from 50 samples of normal pancreas or duodenal mucosal tissues, 7 samples of chronic pancreatitis, and 39 samples of pancreas cancer tissues or cancer cell lines and hybridized to the complete Affymetrix Human Genome U133 GeneChip set (arrays U133A and U133B) for simultaneous analysis of 45,000 fragments corresponding to 33,000 known genes and 6,000 expressed sequence tags. Genes expressed at levels at least 3-fold greater in the pancreatic cancers as compared with nonneoplastic tissues were identified. Three hundred seventy-seven Affymetrix fragments were identified as having > or = 3-fold expression levels in pancreas cancer specimens as compared with nonneoplastic tissues, corresponding to 234 known genes. Serial analysis of gene expression libraries (http://www.ncbi.nlm.nih.gov/SAGE/) of two normal pancreatic ductal cell cultures (HX and H126) were used to exclude 17 genes with high expression levels in the normal duct epithelium (more than five tags/library). Of the remaining 217 known genes, 75 have been previously reported as highly expressed in pancreatic cancers, while the remaining 142 genes are novel. We used principal components analysis (PCA) to identify the genes among these 217 identified as the most differentially expressed and specific to pancreatic cancer tissues or cell lines. Among the most differentially expressed genes identified by PCA were Mesothelin, Muc4, Muc5A/C, Kallikrein 10, Transglutaminase 2, Fascin, TMPRSS3 and stratifin. The differential expression identified by PCA for these genes indicates they are among the more attractive targets for novel therapeutic targets, tumor markers, or as a means of screening pancreatic cancer samples for information regarding tumor classification or potential therapeutic responses. Our findings were also compared in detail to the previously reported findings of highly expressed genes in other studies of global gene expression in pancreatic cancers. We found that robust changes in gene expression were most often identified by more than one gene expression platform. Forty genes were identified by more than one method (U133 oligonucleotide arrays, cDNA arrays or serial analysis of gene expression), and 6 of these genes were identified by all three methods. Our findings identify a novel set of genes as highly expressed in pancreatic cancer, validate the differential expression of previously reported genes, and provide additional support for those genes most differentially expressed to be translated into clinically useful targets.

Expression profiling identifies a novel alpha-methylacyl-CoA racemase exon with fumarate hydratase homology.

Human alpha-methylacyl-CoA racemase (AMACR) was overexpressed in prostate cancer compared with nonmalignant tissues. The Gene Logic Inc. BioExpress database containing Affymetrix U133 GeneChip expression profiles of 4400 human normal, benign, diseased, and tumor samples from >60 tissue types was examined to determine the specificity of AMACR mRNA expression. One particular AMACR probeset was derived from an alternatively spliced exon with 88% identity to a 521-bp sequence that spans four exons of the fumarate hydratase. The predicted protein sequence revealed a novel GLGELIL peptide shared by both proteins. Whether the mitochondrial and peroxisomal AMACR described previously are distinct products from alternatively spliced transcripts remains to be determined. The determination of the cellular location and function of the altered AMACR will be critical in the elucidation of the role of AMACR in prostate cancer diagnosis and pathogenesis.

Discovery of novel tumor markers of pancreatic cancer using global gene expression technology.

Despite several advances in our basic understanding and in the clinical management of pancreatic cancer, virtually all patients who will be diagnosed with pancreatic cancer will die from this disease. The high mortality of pancreatic cancer is predominantly because of diagnosis at an advanced stage of disease and a lack of effective treatments. We used the Gene Logic Inc. BioExpress platform and Affymetrix GeneChip arrays to identify genes differentially expressed in pancreatic cancer. cDNA was prepared from samples of normal pancreas (n = 11), normal gastrointestinal mucosa (n = 22), resected pancreas cancer tissues (n = 14), and pancreas cancer cell lines (n = 8), and was hybridized to the complete Affymetrix Human Genome U95 GeneChip set (arrays U95 A, B, C, D, and E) for simultaneous analysis of 60,000 cDNA fragments, with 12,000 fragments covering full-length genes and 48,000 fragments covering expressed sequence tags (ESTs). Genes expressed at levels at least fivefold greater in the pancreatic cancers ascompared to normal tissues were identified. Serial analysis of gene expression (SAGE) libraries (http://www.ncbi.nlm.nih.gov/SAGE/) of two normal pancreatic ductal cell cultures (HX and H126) were used to exclude genes expressed in the normal ducts (more than five tags per library). Differential expression of selected candidate genes was validated by immunohistochemical analysis (n = 3), by in situ hybridization (n = 1), and by reverse transcriptase-polymerase chain reaction (n = 8). One hundred eighty fragments were identified as having fivefold or greater expression levels in pancreas cancer specimens as compared to normal tissue, of which 124 corresponded to known genes and 56 to ESTs. Of these 124 fragments, 10 genes were represented by two or more fragments, resulting in 107 known genes identified as differentially expressed in pancreatic cancer. An additional 10 genes were expressed in the SAGE libraries of normal pancreatic duct epithelium, and were excluded from further analysis. A literature search indicated that 28 of the remaining 97 genes have been reported in association with pancreatic cancer, validating this approach. The remaining 69 genes have not been implicated in pancreatic cancer before, and have immediate potential as novel therapeutic targets and tumor markers of pancreatic cancer.