RESUMO
MYCN is an oncogene frequently overexpressed in pediatric solid tumors whereas few evidences suggest his involvement in the pathogenesis of haematologic malignancies. Here we show that MYCN is overexpressed in a relevant proportion (40 to 50%) of adult and pediatric T-cell acute lymphoblastic leukemias (T-ALL). Focusing on pediatric T-ALL, MYCN-expressing samples were found almost exclusively in the TAL1-positive subgroup. Moreover, TAL1 knockdown in T-ALL cell lines resulted in a reduction of MYCN expression, and TAL1 directly binds to MYCN promoter region, suggesting that TAL1 pathway activation could sustain the up-regulation of MYCN. The role of MYCN in T-ALL was investigated by peptide nucleic acid (PNA-MYCN)-mediated transcriptional silencing of MYCN and by siRNAs. MYCN knockdown in T-ALL cell lines resulted in a reduction of cell viability, up to 50%, while no effect was elicited with a mismatch PNA. The inhibitory effect of PNA-MYCN on cell viability was due to a significant increase in apoptosis. PNA-MYCN treatment in pediatric T-ALL samples reduced cell viability of leukemic cells from patients with high MYCN expression, while no effect was obtained in MYCN-negative blast cells. These results showed that MYCN is frequently overexpressed in pediatric T-ALL and suggested his role as a candidate for molecularly-directed therapies.
Assuntos
Proteínas Nucleares/genética , Proteínas Oncogênicas/genética , Leucemia-Linfoma Linfoblástico de Células T Precursoras/genética , Fatores de Transcrição/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Estudos de Casos e Controles , Linhagem Celular Tumoral , Criança , Pré-Escolar , Feminino , Perfilação da Expressão Gênica , Regulação Leucêmica da Expressão Gênica , Técnicas de Silenciamento de Genes , Inativação Gênica , Humanos , Masculino , Terapia de Alvo Molecular , Proteína Proto-Oncogênica N-Myc , Proteínas Nucleares/biossíntese , Proteínas Nucleares/metabolismo , Proteínas Oncogênicas/biossíntese , Proteínas Oncogênicas/metabolismo , Leucemia-Linfoma Linfoblástico de Células T Precursoras/metabolismo , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/metabolismo , Proteína 1 de Leucemia Linfocítica Aguda de Células T , Transfecção , Resultado do TratamentoRESUMO
BACKGROUND: Histiocytoses represent a large, puzzling group of diseases which may involve the skin and other organs. At present, juvenile xanthogranuloma is the disorder most often confused with Langerhans cell histiocytosis. A complex overlap exists between juvenile xanthogranuloma and Langerhans cell histiocytosis, with lesions showing clinical and/or pathological features of both disorders. OBSERVATIONS: We report 2 patients affected by Langerhans cell histiocytosis who, during chemotherapy, presented cutaneous lesions with clinical and histological features of juvenile xanthogranuloma. During the therapy, in both cases, histological examination of new biopsies revealed the presence of Touton giant cells in the dermis with a few histiocytic cells; immunohistochemical staining was negative for CD1a, and no Birbeck granules were seen by ultrastructural examination. RESULTS AND CONCLUSION: A possible explanation for the link between Langerhans cell histiocytosis and juvenile xanthogranuloma regards the lineage development and the relationships of histiocytes. We suggest that chemotherapy can modify the production of cytokines by influencing the conversion or 'maturation' of pathological cells into macrophages or xanthomatous cells and fusing them to form multinucleated giant Touton cells. In our opinion, the modification of the cutaneous lesions during chemotherapy in Langerhans cell histiocytosis patients, as observed in our cases, could be a favorable prognostic factor.