RESUMO
Deleted in malignant brain tumors 1 (DMBT1) has been proposed as a candidate tumor suppressor for brain and epithelial cancer. Initial studies suggested loss of expression rather than mutation as the predominant mode of DMBT1 inactivation. However, in situ studies in lung cancer demonstrated highly sophisticated changes of DMBT1 expression and localization, pointing to a chronological order of events. Here we report on the investigation of DMBT1 in breast cancer in order to test whether these principles might also be attributable to other tumor types. Comprehensive mutational analyses did not uncover unambiguous inactivating DMBT1 mutations in breast cancer. Expression analyses in the human and mouse mammary glands pointed to the necessity of DMBT1 induction. While age-dependent and hormonal effects could be ruled out, 9 of 10 mice showed induction of Dmbt1 expression after administration of the carcinogen 7,12-dimethybenz(alpha)anthracene prior to the onset of tumorigenesis or other histopathological changes. DMBT1 displayed significant up-regulation in human tumor-flanking tissues compared to in normal breast tissues (P < 0.05). However, the breast tumor cells displayed a switch from lumenal secretion to secretion to the extracellular matrix and a significant down-regulation compared to that in matched normal flanking tissues (P < 0.01). We concluded that loss of expression also is the predominant mode of DMBT1 inactivation in breast cancer. The dynamic behavior of DMBT1 in lung carcinoma is fully reflected in breast cancer, which suggests that this behavior might be common to tumor types arising from monolayered epithelia.
Assuntos
Aglutininas , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Carcinógenos/metabolismo , Regulação para Baixo/genética , Receptores de Superfície Celular/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Animais , Neoplasias da Mama/metabolismo , Proteínas de Ligação ao Cálcio , Linhagem Celular Tumoral , Análise Mutacional de DNA/métodos , Proteínas de Ligação a DNA , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica/genética , Genes Supressores de Tumor , Humanos , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/patologia , Glândulas Mamárias Humanas/efeitos dos fármacos , Glândulas Mamárias Humanas/patologia , Glândulas Mamárias Humanas/fisiologia , Neoplasias Mamárias Experimentais/genética , Neoplasias Mamárias Experimentais/metabolismo , Neoplasias Mamárias Experimentais/patologia , Camundongos , Camundongos Endogâmicos BALB C , Pessoa de Meia-Idade , Mutação/efeitos dos fármacos , Mutação/genética , Receptores de Superfície Celular/biossíntese , Receptores de Superfície Celular/metabolismo , Proteínas Supressoras de TumorRESUMO
Deleted in malignant brain tumors 1 (DMBT1) at 10q25.3-q26.1 has been proposed as a candidate tumor-suppressor gene for brain and epithelial cancer. DMBT1 encodes a multifunctional mucin-like protein presumably involved in epithelial differentiation and protection. The gene consists of highly homologous and repeating exon and intron sequences. This specifically applies to the region coding for the repetitive scavenger receptor cysteine-rich (SRCR) domains and SRCR-interspersed domains (SIDs) that constitutes the major part of the gene. This particular structure may previously have interfered with the delineation of DMBT1 alterations in cancer. Uncovering these, however, is of mechanistic importance. By a combined approach, we conducted a detailed mutational analysis, starting from a panel of 51 tumors, including 46 tumor cell lines and five primary tumors. Alterations in the repetitive region were present in 22/31 (71%) tumors that were investigated in detail. Six tumors showed presumably de novo mutations, among these three with point mutations in combination with a loss of heterozygosity. However, none of the alterations unambiguously would be predicted to lead to an inactivation of DMBT1. We define seven distinct DMBT1 alleles based on variable numbers of tandem repeats (VNTRs). At least 11 tumors exclusively harbored these VNTRs. The data suggest that the SRCR/SID region defines a complex multi-allele system that has escaped previous analyses and that represents the major basis for the variability of DMBT1 in cancer. DMBT1 thus compares to mucins rather than to conventional tumor suppressors.
Assuntos
Alelos , Variação Genética/genética , Proteínas de Membrana , Neoplasias/genética , Receptores Imunológicos/genética , Receptores de Lipoproteínas , Neoplasias Encefálicas/genética , Neoplasias Encefálicas/patologia , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Análise Mutacional de DNA/métodos , DNA de Neoplasias/genética , Neoplasias do Endométrio/genética , Neoplasias do Endométrio/patologia , Éxons/genética , Feminino , Humanos , Perda de Heterozigosidade/genética , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/patologia , Masculino , Repetições Minissatélites/genética , Neoplasias/patologia , Neoplasias Pancreáticas/genética , Neoplasias Pancreáticas/patologia , Mutação Puntual/genética , Neoplasias da Próstata/genética , Neoplasias da Próstata/patologia , Receptores Depuradores , Receptores Depuradores Classe B , Células Tumorais CultivadasRESUMO
Deleted in Malignant Brain Tumors 1 (DMBT1) at chromosome region 10q25.3-q26.1 has been proposed as a candidate tumor-suppressor gene for brain, digestive tract, and lung cancer. Recent studies on its expression in lung cancer have led to divergent results and have raised a controversial discussion. Moreover, DMBT1 has been implicated with epithelial protection in the respiratory tract. We thus wondered how a loss of its expression could be related to carcinogenesis in the lung. To address these issues, we investigated the DMBT1 expression and location in the normal lung and lung cancer. By reverse-transcription PCR, a down-regulation of the DMBT1 expression in lung cancer cell lines is commonly detected. Immunohistochemical studies in situ demonstrate that there are also low steady-state levels of DMBT1 in the normal respiratory epithelium. However, an up-regulation takes place in the tumor-flanking epithelium and upon respiratory inflammation. Lung carcinomas show increased DMBT1 expression compared to that of undiseased lung tissue, but decreased DMBT1 levels compared to that of tumor-flanking and inflammatory tissue. A switch from a lumenal secretion to a secretion to the extracellular matrix takes place during lung carcinogenesis. Our data may resolve the controversial discussion on its expression in lung carcinomas. We hypothesize that the changes of the DMBT1 expression and location do reflect a time course that may point to possible mechanisms for its role in epithelial cancer.
