RESUMEN
The purpose of this study was to compare the expression and function of NOTCH1 in chronic lymphocytic leukemia (CLL) patients harboring a wild-type (WT) or mutated NOTCH1 gene. NOTCH1 mRNA and surface protein expression levels were independent of the NOTCH1 gene mutational status, consistent with the requirement for NOTCH1 signaling in this leukemia. However, compared with NOTCH1-WT CLL, mutated cases displayed biochemical and transcriptional evidence of an intense activation of the NOTCH1 pathway. In vivo, expression and activation of NOTCH1 was highest in CLL cells from the lymph nodes as confirmed by immunohistochemistry. In vitro, the NOTCH1 pathway was rapidly downregulated, suggesting that signaling relies upon micro-environmental interactions even in NOTCH1-mutated cases. Accordingly, co-culture of Jagged1(+) (the NOTCH1 ligand) nurse-like cells with autologous CLL cells sustained NOTCH1 activity over time and mediated CLL survival and resistance against pro-apoptotic stimuli, both abrogated when NOTCH1 signaling was pharmacologically switched off. Together, these results show that NOTCH1 mutations have stabilizing effects on the NOTCH1 pathway in CLL. Furthermore, micro-environmental interactions appear critical in activating the NOTCH1 pathway both in WT and mutated patients. Finally, NOTCH1 signals may create conditions that favor drug resistance, thus making NOTCH1 a potential molecular target in CLL.
Asunto(s)
Leucemia Linfocítica Crónica de Células B/genética , Mutación , Receptor Notch1/genética , Regulación hacia Abajo , Citometría de Flujo , Humanos , ARN Mensajero/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Transducción de SeñalRESUMEN
Next-generation whole-exome sequencing has revealed two novel genes, namely NOTCH1 and SF3B1, whose mutations predict poor outcome and preferentially associate with chemorefractory chronic lymphocytic leukemia (CLL). Analysis of 539 CLL cases documents that NOTCH1 mutations i) represent one of the most frequent cancer gene mutations involved at presentation; ii) cluster with cases harboring trisomy 12 and tend to be mutually exclusive with TP53 disruption among genetic subgroups; iii) identify high-risk patients showing poor survival similar to that associated with TP53 abnormalities; and iv) exert a prognostic role independent of widely accepted clinical and genetic risk factors. Mutations of SF3B1, a splicing factor that is a critical component of the spliceosome, recurrently associate with fludarabine-refractory CLL, occur at a low rate at CLL presentation and have a minor role in Richter transformation, corroborating the notion that CLL histological shift is molecularly distinct from chemorefractory progression without the Richter transformation.