RESUMO
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.
Assuntos
Cromossomos Humanos Par 12 , Peptídeos e Proteínas de Sinalização Intracelular/deficiência , Peptídeos e Proteínas de Sinalização Intracelular/genética , Leucemia Prolinfocítica de Células T/genética , Deleção de Sequência , Animais , Proteínas Mutadas de Ataxia Telangiectasia , Proteínas de Ciclo Celular/genética , Mapeamento Cromossômico , Inibidor de Quinase Dependente de Ciclina p27 , Primers do DNA , Proteínas de Ligação a DNA/genética , Deleção de Genes , Humanos , Leucemia Prolinfocítica de Células T/patologia , Camundongos , Camundongos Transgênicos , Fases de Leitura Aberta , Reação em Cadeia da Polimerase , Polimorfismo de Nucleotídeo Único , Proteínas Serina-Treonina Quinases/genética , Células Tumorais Cultivadas , Proteínas Supressoras de Tumor/genéticaRESUMO
Mutations in the CSA or CSB complementation genes cause the Cockayne syndrome, a severe genetic disorder that results in patients' death in early adulthood. CSA and CSB act in a transcription-coupled repair (TCR) pathway, but their functional relationship is not understood. We have previously shown that CSA is a subunit of an E3 ubiquitin ligase complex. Here we demonstrate that CSB is a substrate of this ligase: Following UV irradiation, CSB is degraded at a late stage of the repair process in a proteasome- and CSA-dependent manner. Moreover, we demonstrate the importance of CSB degradation for post-TCR recovery of transcription and for the Cockayne syndrome. Our results unravel for the first time the functional relationship between CSA and CSB.