RESUMEN
Malignant cell accumulation in B-cell chronic lymphocytic leukemia (B-CLL) is primarily caused by defective apoptosis rather than increased proliferation. To further understand the role of Bcl-2 family members, known regulators of apoptosis, in the abnormal B-CLL survival, we have measured their mRNA levels in fresh B-CLL cells and in cultures undergoing spontaneous apoptosis. Using RNA protection assays we found constitutive expression of most bcl-2 members with high levels of bcl2, bcl-w, bad, bak, bax, and the bcl-2/bax ratio, compared to normal PBL. Spontaneous apoptosis of B-CLL cells by in vitro culture resulted in decreased bcl-2, bcl-w, bfl-1, mcl-1, bak, bax, and bcl-2/bax expression. The pro-apoptotic member bik was only expressed in 5/19 cases and was not modulated during apoptosis, suggesting that bik is not involved in this process. Thus, several Bcl-2 family genes are regulated during B-CLL spontaneous apoptosis and their relative levels may contribute to in vivo progression of the disease.
Asunto(s)
Apoptosis/genética , Genes bcl-2 , Leucemia Linfocítica Crónica de Células B/genética , Proteínas Reguladoras de la Apoptosis , Linfocitos B/metabolismo , Línea Celular Tumoral , Femenino , Perfilación de la Expresión Génica/métodos , Regulación Leucémica de la Expresión Génica , Humanos , Leucemia Linfocítica Crónica de Células B/metabolismo , Leucemia Linfocítica Crónica de Células B/patología , Masculino , Proteínas de la Membrana/biosíntesis , Proteínas Mitocondriales , Estadificación de Neoplasias , Proteínas Proto-Oncogénicas c-bcl-2/biosíntesis , ARN Mensajero/análisis , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Ribonucleasas/genéticaRESUMEN
B-cell chronic lymphocytic leukemia is characterized by the accumulation of malignant B lymphocytes as a result of abnormal survival signals operating in vivo. Previously, we showed that adhesion of B-CLL cells to the fibronectin fragment H89, a ligand for alpha4beta1 integrin, prevents their spontaneous apoptosis in vitro. We have now studied whether alpha4beta1/H89 interaction affected the response of B-CLL cells to the therapeutic drug fludarabine. B-CLL cells cultured on H89 during treatment with fludarabine showed significantly higher mean viability (P<0.05) than cells cultured on the control polylysine for all doses of drug tested. Similar results were obtained with the EHEB cell line. Analysis of the expression of Bcl-2-family proteins after 48 h of fludarabine treatment revealed that Bcl-xL levels were significantly higher (P<0.05) for cells cultured on H89 than on polylysine and correlated (r=0.56, P<0.05) with the increased cell viability observed on H89 cultures. These results indicate that Bcl-xL is involved in the survival signals induced by alpha4beta1 ligation and may contribute to the progressive drug resistance observed in B-CLL.