title: PTEN mutation, loss of heterozygosity, promoter methylation and expression in colorectal carcinoma: two hits on the gene?
abstract: The phosphatase and tensin homologue (PTEN) gene is considered to be a tumour-suppressor gene in various types of cancer, colorectal carcinoma among them. According to the 'two-hit' tumour-suppressor gene concept, inactivation occurs by any combination of the following three pathogenetic processes: mutation, loss of one allele [i.e. loss of heterozygosity (LOH)] or promoter methylation. To determine the frequencies of PTEN tumour-suppressor gene features in colorectal carcinoma, we used DNA from colorectal carcinoma xenografts/primary tumour cell lines (N=22) or neoplastic glands isolated by laser-capture microdissection (N=20). Sequencing exons 1-9 of the gene revealed a total of 8 somatic mutations in 5 tumours (3 with high-degree microsatellite instability). In 1 tumour, a truncating mutation of one allele was combined with two missense mutations of the other allele. Polymorphic microsatellite marker analyses (D10S5412, D10S579 and D10S1765) showed complete loss of one allele (i.e. LOH sensu stricto) in 3 tumours, but combined LOH and mutation was found only once. Promoter methylation, tested by MethyLight technology, was found in only 1 of the tumours, not combined with mutation or LOH. In contrast, by immunohistochemistry (mAb 6H2.1), reduction or even loss of PTEN expression was found in 18 tumours. Taken together, PTEN downregulation is a fairly frequent event in colorectal carcinoma, but this apparently is not usually caused by two hits on the gene.
authors.affiliation: Institute of Pathology, Rostock University, D-18055 Rostock, Germany.
authors.forename: Maja
authors.initials: M
authors.lastname: Hühns
authors.affiliation: Institute of Pathology, Rostock University, D-18055 Rostock, Germany.
authors.forename: Tareq
authors.initials: T
authors.lastname: Salem
authors.affiliation: Institute of Pathology, Rostock University, D-18055 Rostock, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Schneider
authors.affiliation: Department of Surgery, Rostock University, D-18055 Rostock, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Krohn
authors.affiliation: Department of Surgery, Rostock University, D-18055 Rostock, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Linnebacher
authors.affiliation: Institute of Pathology, Rostock University, D-18055 Rostock, Germany.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Prall
mesh_terms: D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics*; D019175:DNA Methylation / Q000235:genetics*; D006801:Humans; D019656:Loss of Heterozygosity / Q000235:genetics*; D051379:Mice; D008819:Mice, Nude; D018895:Microsatellite Repeats / Q000235:genetics; D009154:Mutation; D009368:Neoplasm Transplantation; D051059:PTEN Phosphohydrolase / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D017422:Sequence Analysis, DNA; D014183:Transplantation, Heterologous
chemical_list: D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human