RESUMO
Microarray-based expression profiling studies of lung adenocarcinomas have defined neuroendocrine subclasses with poor prognosis. As neuroendocrine development is regulated by members of the achaete-scute and atonal classes of basic helix-loop-helix (bHLH) transcription factors, we analyzed lung tumors for expression of these factors. Out of 13 bHLH genes tested, 4 genes, i.e., achaete-scute complex-like 1 (ASCL1, HASH1, Mash1), atonal homolog 1 (ATOH1, HATH1, MATH1), NEUROD4 (ATH-3, Atoh3, MATH-3) and neurogenic differentiation factor 1 (NEUROD1, NEUROD, BETA2), showed differential expression among lung tumors and absent or low expression in normal lung. As expected, tumors that have high levels of ASCL1 also express neuroendocrine markers, and we found that this is accompanied by increased levels of NEUROD1. In addition, we found ATOH1 expression in 9 (16%) out of 56 analyzed adenocarcinomas and these tumors showed neuroendocrine features as shown by dopa decarboxylase mRNA expression and immunostaining for neuroendocrine markers. ATOH1 expression as well as NEUROD4 was observed in small cell lung carcinoma (SCLC), a known neuroendocrine tumor. Since ATOH1 is not known to be involved in normal lung development, our results suggest that aberrant activation of ATOH1 leads to a neuroendocrine phenotype similar to what is observed for ASCL1 activation during normal neuroendocrine development and in lung malignancies. Our preliminary data indicate that patients with ATOH1-expressing adenocarcinomas might have a worse prognosis.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Carcinoma Neuroendócrino/genética , Perfilação da Expressão Gênica , Neoplasias Pulmonares/genética , Carcinoma Neuroendócrino/mortalidade , Primers do DNA , Regulação Neoplásica da Expressão Gênica , Humanos , Pulmão/patologia , Proteínas do Tecido Nervoso/genética , Prognóstico , RNA Neoplásico/genética , RNA Neoplásico/isolamento & purificação , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Análise de SobrevidaRESUMO
The molecular basis of lung carcinogenesis must be understood more fully and exploited to enhance survival rates of patients suffering from lung cancer. In this review we will discuss the major molecular alterations that occur in lung cancer. Emphasis is placed on alterations that occur early during carcinogenesis since they might be relevant for future screening programs. Finally we will shortly review new approaches that are used to study the molecular pathology of lung cancer and how they can be applied in a clinical setting.
Assuntos
Carcinoma Pulmonar de Células não Pequenas/genética , Neoplasias Pulmonares/genética , Apoptose/genética , Carcinoma Pulmonar de Células não Pequenas/enzimologia , Cromossomos Humanos Par 3/genética , Genes Supressores de Tumor , Predisposição Genética para Doença/genética , Instabilidade Genômica/genética , Humanos , Perda de Heterozigosidade/genética , Neoplasias Pulmonares/enzimologia , Repetições de Microssatélites/genética , Oncogenes/genética , Proteômica/tendências , Proteína Supressora de Tumor p53/genética , Proteínas Supressoras de Tumor/genéticaRESUMO
It is generally assumed that squamous cell carcinoma develops in a stepwise manner from normal bronchial epithelium towards cancer by the accumulation of (epi)genetic alterations. Several mechanisms including mutations and homozygous deletions or hypermethylation of the p16(INK4a) promoter region can cause loss of p16 expression. Recent studies suggest overexpression of the polycomb-group gene BMI-1 might also down-regulate p16 expression. In this study, we analyzed the p16 expression in relation to the methylation status of the p16 promoter region of the p16(INK4a) gene and the expression of BMI-1 in bronchial squamous cell carcinomas (SCC) and its premalignant lesions. Nine (69%) SCC showed loss of p16 expression and 10 (77%) showed expression of BMI-1. Of four p16 positive samples two (50%) were BMI-1 positive, whereas among nine p16 negative samples, eight (89%) revealed BMI-1 staining. Four (44%) p16 negative samples were hypermethylated at the p16(INK4a) promoter region; the other p16 negative tumors that showed no hypermethylation revealed BMI-1 staining. Only two premalignant lesions showed absence of p16 expression, of which one (carcinoma in situ) was hypermethylated at the p16(INK4a) promoter region and the other (severe dysplasia) showed BMI-1 expression. In total, 11 precursor lesions (48%) revealed BMI-1 expression. In conclusion, the results of this study suggest that loss of p16 expression by promoter hypermethylation is inconsistently and occurs late in the carcinogenic process at the level of severe dysplasia. To what extent overexpression of the polycomb-group protein BMI-1 attributes to down regulating of p16 expression remains unclear.
