Genetic alterations of the tumor suppressor gene PTEN/MMAC1 in human brain metastases
ABSTRACT The high mutation rate in advanced brain tumors, recent functional studies, and the high frequency of mutations in prostate metastases all strongly suggest that PTEN/MMAC1 alterations are involved in the formation of metastases. We searched for genetic alterations in the PTEN/MMAC1 gene in 56 consecutive brain metastases from various primary tumors by loss of heterozygosity (LOH), direct sequence analysis, and differential PCR analysis. The highest LOH rates were detected in metastases deriving from lung (67%) and breast (64%) cancers. Three (25%) of the eight detected inactivating mutations (one nonsense mutation, one splice-site mutation, one 11-bp deletion, and five homozygous deletions) were found in metastases originating from 12 different lung carcinomas, suggesting that PTEN/MMAC1 alterations may play a role in the progression of this tumor. With the exception of lung carcinomas, our findings indicate that genetic abnormalities of the PTENM/MMAC1 gene are only involved in a relatively small subset of brain metastases. However, the discrepancy between the high overall LOH rate (50%) and the low frequency of PTEN/MMAC1 mutation detection rate (14%) suggests the presence of one or more additional tumor suppressor genes on chromosome 10q.
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ABSTRACT: The tumour suppressor gene PTEN, localized to 10q23.3, is the susceptibility gene for Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba (BRR) syndrome, two hamartoma syndromes with an increased risk of breast and thyroid tumours. Somatic mutations have been found in a variety of human tumours. Functional studies have revealed that PTEN plays a fundamental role in cellular growth, death, adhesion and migration. RNA in situ hybridization using the pten coding region in mouse embryos showed ubiquitous transcription, providing evidence that pten could play a versatile role throughout murine development. Nothing is known regarding the pattern of PTEN expression during human development. Here, we present the pattern of PTEN expression during human development using a specific monoclonal antibody and examine the relationship of the temporal and spatial expression pattern to the clinical manifestations of CS and BRR, the somatic genetic data in sporadic cancers, the murine knockout models and the RNA expression data in mouse embryos. We observed mainly high-level PTEN expression in tissues (e.g. skin, thyroid and central nervous system) known to be involved in CS and BRR. In addition, we identified tissues (e.g. peripheral nervous system, autonomomic nervous system and upper gastrointestinal tract) with high PTEN expression not commonly known to play a role in these syndromes nor in sporadic tumorigenesis in those organs. This knowledge may help in identifying roles for PTEN which, as of today, are unknown or even unsuspected.Human Molecular Genetics 08/2000; 9(11):1633-9. · 6.68 Impact Factor
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ABSTRACT: Indole-3-carbinol (I3C) is a promising phytochemical agent in chemoprevention of breast cancer. Our present study is the first description of I3C that significantly inhibits the cell adhesion, spreading and invasion associated with an up-regulation of PTEN (a tumor suppressor gene) and E-cadherin (a regulator of cell-cell adhesion) expression in T47-D human breast cancer cells. Therefore, I3C exhibits anti-cancer activities by suppressing breast tumor cell growth and metastatic spread. Metastatic breast cancer is a devastating problem, clinical application of I3C as a potent chemopreventive agent may be helpful in limiting breast cancer invasion and metastasis.Breast Cancer Research and Treatment 10/2000; 63(2):147-52. DOI:10.1023/A:1006495824158 · 4.20 Impact Factor
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ABSTRACT: The tumour suppressor gene PTEN/MMAC1/TEP1 has been implicated in a variety of human cancers and several inherited hamartoma tumour syndromes, including Cowden syndrome, which has a high risk of breast and thyroid cancer. We have previously reported that overexpression of PTEN in MCF-7 breast cancer cells induces cell cycle arrest and apoptosis. In this study, we analysed PTEN status at both the structural and expression levels and explored PTEN's growth-suppressive effects on thyroid. We found that 1 of 10 thyroid cancer lines [follicular thyroid carcinoma FTC-133] had hemizygous deletion and a splice variant IVS4--19G-->A in the remaining allele. Four lines, including FTC-133, express PTEN mRNA at low levels. In general, PTEN protein levels correlated with mRNA levels, except for NPA87, which has low levels of transcript and relatively high levels of PTEN protein. Transient expression of PTEN in seven thyroid cancer cell lines resulted in G(1) arrest in two well differentiated papillary thyroid cancer lines (PTCs) and both G(1) arrest and cell death in the remaining five lines, including three FTCs, one poorly differentiated PTC and one undifferentiated thyroid cancer. The level of phosphorylated Akt was inversely correlated with the endogenous level of PTEN protein and overexpression of PTEN-blocked Akt phosphorylation in all cells analysed. Our results suggest that downregulation of PTEN expression at the mRNA level plays a role in PTEN inactivation in thyroid cancer and PTEN exerts its tumour-suppressive effect on thyroid cancer through the inhibition of cell cycle progression alone or both cell cycle progression and cell death.Human Molecular Genetics 02/2001; 10(3):251-8. · 6.68 Impact Factor