ASPP1, a common activator of TP53, is inactivated by aberrant methylation of its promoter in acute lymphoblastic leukemia

Abstract

We have analyzed the regulation and expression of ASPP members, genes implicated in the regulation of the apoptotic function of the TP53 tumor-suppressor gene, in acute lymphoblastic leukemia (ALL). Expression of ASPP1 was significantly reduced in ALL and was dependent on hypermethylation of the ASPP1 gene promoter. Abnormal ASPP1 expression was associated with normal function of the tumor-suppressor gene TP53 in ALL. The analyses of 180 patients with ALL at diagnosis showed that the ASPP1 promoter was hypermethylated in 25% of cases with decreased mRNA expression. Methylation was significantly higher in adult ALL vs childhood ALL (32 vs 17%, P ¼ 0.03) and T-ALL vs B-ALL (50 vs 9%, P ¼ 0.001). Relapse rate (62 vs 44%, P ¼ 0.05) and mortality (59 vs 43%, P ¼ 0.05) were significantly higher in patients with methylated ASPP1. DFS and OS were 32.8 and 33.7% for patients with unmethylated ASPP1 and 6.1 and 9.9% for methylated patients (Po0.001 y Po0.02, respectively). On the multivariate analysis, methylation of the ASPP1 gene promoter was an independent poor prognosis factor in ALL patients. Our results demonstrate that decreased expression of ASPP1 in patients with ALL is due to an abnormal methylation of its promoter and is associated with a poor prognosis.Oncogene ( Mutations of TP53 may result in an inhibition of protein function, which is associated with tumor progression and genetic instability (Caron de Fromentel and Soussi, 1992;Hollstein et al., 1994;Soussi et al., 1994). Although 40-50% of human tumors have mutations on TP53, the percentage of mutations in patients with leukemia is significantly lower (less that 10%), suggesting that other mechanisms may be involved in the inability of p53 to induce apoptosis since p53 does not suppress tumor growth or induce apoptosis in tumors with wild-type TP53.The recently described ASPP family of proteins comprised of ASPP1, ASPP2 and iASPP has been implicated in the apoptotic function of TP53 and p53 family members TP73L (p63) and TP73 (Bergamaschi et al., 2004). Different studies have shown that ASPP1 and ASPP2 increase the apoptotic effect of p53 by inducing the transcription of proapoptotic genes such as BAX and PIG3 mediated by TP53, while they have no influence on the transcription of MDM2 and CDKN1A (p21, Cip1), which mediate p53-dependent cell cycle arrest (Samuels-Lev et al., 2001;Slee and Lu, 2003;Bergamaschi et al., 2004). Transactivation of TP53-mediated transcription of proapoptotic genes mediated by ASPP1 and ASPP2 is completely abolished by increased expression of the evolutionary conserved TP53 inhibitor and third member of the ASPP family, iASPP (Bergamaschi et al., 2003).It has been hypothesized that in wild-type TP53 tumors, alterations of ASPP1 and/or ASPP2, can produce a selective advantage due to the lack of stimulation of apoptosis (Samuels-Lev et al., 2001;Slee and Lu, 2003;Bergamaschi et al., 2004). Samuels-Lev et al. (2001) These two authors contributed equally to this work.

Downregulation of ASPP1 in gestational trophoblastic disease: correlation with hypermethylation, apoptotic activity and clinical outcome

“…Methylation-(M) and unmethylation (U)-sensitive primers, as listed in Table 1, were designed to amplify the promoter region (À681 to À476) of ASPP1 (GeneBank NM 015316) according to a previous study 16 for MS-PCR analysis. Universal methylated DNA (Chemicon, Atlanta, GA, USA) and water blanks without template were used as positive and negative controls for each PCR set, respectively.…”

“…Recently, it has been demonstrated that ASPP1 is downregulated in human cancer cell lines expressing wild-type p53, 14,15 including breast cancer and acute lymphoblastic leukemia. 11,16 Hypermethylation of gene promoter or the 5 0 untranslated region was shown to be a possible epigenetic mechanism that inactivates ASPP1. 14,16 In this study, we evaluated the expression and methylation profiles of ASPP1 in normal placentas and gestational trophoblastic disease in correlation with clinical parameters, followed by an in vitro functional analysis, in an attempt to unveil the possible role of ASPP1 in the pathogenesis of gestational trophoblastic disease.…”

Restoring the tumour suppressive function of p53 as a parallel strategy in melanoma therapy

“…In many cancers, ASPP1 and ASPP2 have been found to be down-regulated by promoter methylation [48,49]. For example, reduced ASPP1 expression by promoter methylation is associated with high relapse rate and mortality in acute lymphoblastic leukaemia [48]. Down-regulation of ASPP2 in diffuse large B-cell and follicular centre lymphoma is also associated with poor prognosis [47].…”

“…ASPP1 and ASPP2 are transcriptional targets of E2F1, a key transcription factor that promotes cell cycle G1 to S phase transition. In many cancers, ASPP1 and ASPP2 have been found to be down-regulated by promoter methylation [48,49]. For example, reduced ASPP1 expression by promoter methylation is associated with high relapse rate and mortality in acute lymphoblastic leukaemia [48].…”

LMO2 expression reflects the different stages of blast maturation and genetic features in B-cell acute lymphoblastic leukemia and predicts clinical outcome

“…12,13 Full clinical and laboratory data were available for 39 T-ALL and 145 B-ALL patients (one of them lacking survival data) with a median age of 11.5 years (range 0.5-87 years), including 100 children under 15 years of age (median 5.5 years, range 0. [5][6][7][8][9][10][11][12][13][14] and 84 patients over 15 years of age (mean age 34.5, range 15-87). Sample collection was approved by the individual institutional review boards of the participating institutions and informed consent was obtained from all adult patients and children's parents or legal guardians.…”