RESUMEN
T-cell prolymphocytic leukemia (T-PLL) is consistently associated with inactivation of the ATM gene and chromosomal re-arrangements leading to an overexpression of MTCP1/TCL1 oncoproteins. These alterations are present at the earliest stage of malignant transformation, suggesting that additional events are required for overt malignancy. In this study, we pursued the investigation of the 12p13 deletion, previously shown to occur in approximately half of T-PLLs. We refined the minimal region of deletion by single nucleotide and microsatellite polymorphism allelotyping. We defined a 216-kb region containing the CDKN1B gene that encodes the cyclin-dependent kinase inhibitory protein p27(KIP1). Sequencing this gene in 47 T-PLL patient samples revealed a nonsense mutation in one case without 12p13 deletion. The absence of biallelic inactivation of CDKN1B for most patients suggested a haploinsufficiency mechanism for tumor suppression, which was investigated in an animal model of the disease. In a Cdkn1b(+/-) background, MTCP1 transgenics had consistent and multiple emergences of preleukemic clones not observed in control cohorts. The second Cdkn1b allele was maintained and expressed in these preleukemic clones. Altogether, these data strongly implicate CDKN1B haploinsufficiency in the pathogenesis of T-PLL.
Asunto(s)
Cromosomas Humanos Par 12 , Péptidos y Proteínas de Señalización Intracelular/deficiencia , Péptidos y Proteínas de Señalización Intracelular/genética , Leucemia Prolinfocítica de Células T/genética , Eliminación de Secuencia , Animales , Proteínas de la Ataxia Telangiectasia Mutada , Proteínas de Ciclo Celular/genética , Mapeo Cromosómico , Inhibidor p27 de las Quinasas Dependientes de la Ciclina , Cartilla de ADN , Proteínas de Unión al ADN/genética , Eliminación de Gen , Humanos , Leucemia Prolinfocítica de Células T/patología , Ratones , Ratones Transgénicos , Sistemas de Lectura Abierta , Reacción en Cadena de la Polimerasa , Polimorfismo de Nucleótido Simple , Proteínas Serina-Treonina Quinasas/genética , Células Tumorales Cultivadas , Proteínas Supresoras de Tumor/genéticaRESUMEN
The TCL1/MTCP1 oncogenes were identified on the basis of their involvement in T-cell prolymphocytic leukemia (T-PLL). TCL1 and MTCP1 proteins directly interact with AKT and modulate the AKT signal-transduction pathway, but the relevance of this mechanism in leukemogenesis remains unclear. We investigate the biologic functions of TCL1 in the T-cell lineage using various cell lines, and primary malignant and normal lymphocytes. In the Jurkat cell line, expression of TCL1 had no effect in unstimulated cells, whereas it abrogated activation-induced cell death (AICD). These cellular effects were concomitant with a major inhibition by TCL1 of PKCtheta and ERK pathways. Secondly, the TCL1-driven T-cell leukemia cell line SUP-T11 was shown to have impaired PKCtheta and ERK phosphorylation upon stimulation, which were restored by TCL1 inhibition using RNA interference. Finally, defects in these pathways were also observed in primary malignant (T-PLL) and transduced normal T lymphocytes expressing TCL1. Altogether, our data demonstrated that TCL1 inhibits AICD in T cells by blocking PKCtheta and ERK activation, upon cellular activation.
