Expression of p53 N-terminal isoforms in B-cell precursor acute lymphoblastic leukemia and its correlation with clinicopathological profiles

Abstract

Background: TP53 mutations occur in only about 3% of primary and 10-20% of relapse B-cell precursor acute lymphoblastic leukaemia (BCP-ALL). However, alternative mechanisms may contribute to functionally impairing the p53 pathway in the absence of a mutation. Candidate mechanisms include overexpression of p53 mRNA variants encoding either dominant-negative p53 protein isoforms such as Delta40p53 and Delta133p53, or modulatory isoforms such as p53beta, which counteract the effects of Delta133p53 on replicative senescence in T-lymphocytes. Methods: We used semi-quantitative reverse-transcriptase PCR (RT-PCR) and Western blot to investigate the expression of full length p53 (TAp53), Delta40p53, Delta133p53 or p53beta in diagnostic marrow from a clinical cohort of 50 BCP-ALL patients without TP53 mutation (29 males and 21 females, age range 2-14 years) and in the bone marrow cells of 4 healthy donors (used as controls). Results: Irrespective of isoforms, levels of p53 mRNA were low in controls but were increased by 2 to 20-fold in primary or relapse BCP-ALL. TAp53 was increased in primary BCP-ALL, Delta40p53 was elevated in relapse BCP-ALL, whereas Delta133p53 and p53beta were increased in both. Next, mRNA levels were used as a basis to infer the ratio between protein isoform levels. This inference suggested that, in primary BCP-ALL, p53 was predominantly in active oligomeric conformations dominated by TAp53. In contrast, p53 mostly existed in inactive quaternary conformations containing ≥2 Delta40 or Delta133p53 in relapse BCP-ALL. Western blot analysis of blasts from BCP-ALL showed a complex pattern of N-terminally truncated p53 isoforms, whereas TAp53beta was detected as a major isoform. The hypothesis that p53 is in an active form in primary BALL was consistent with elevated level of p53 target genes CDKN1A and MDM2 in primary cases, whereas in relapse BCP-ALL, only CDKN1A was increased as compared to controls. Conclusion: Expression of p53 isoforms is deregulated in BCP-ALL in the absence of TP53 mutation, with increased expression of alternative isoforms in relapse BCP-ALL. Variations in isoform expression may contribute to functional deregulation of the p53 pathway in BCP-ALL, specifically contributing to its down-regulation in relapse forms.

The Δ133p53 Isoforms, Tuners of the p53 Pathway

“…Critically, Δ133p53α may have a similar impact on other DNA-damage inducing cancer therapies. Similar upregulation of total Δ133p53 mRNAs has been observed in B-cell precursor acute lymphoblastic leukemia [ 55 ] and in lung carcinomas as compared to adjacent non-cancerous tissue [ 44 ] and is reported to increase cancer cell survival in pathogen-driven cancers such as gastric tumors associated with H. pylori [ 56 ]. In the case of gastric cancer, total Δ133p53 mRNAs expression correlates with the NF-κB p65 subunit expression and may promote gastric cell growth [ 57 ].…”

Good Cop, Bad Cop: Defining the Roles of Δ40p53 in Cancer and Aging

“…In conclusion, although research on this p53 isoform is continuing, there is still a need to understand the cellular contexts in which ∆40p53 acts in a positive or negative manner. While elevated levels of ∆40p53 have been associated with worse prognosis in some cancers, such as breast cancer [57,69] and ALL [77], ∆40p53 harbours tumour suppressor functions in melanoma [66] and is associated with increased recurrence-free survival in mucinous ovarian cancer [76]. Consequently, molecular profiling of individual cancers, including sequencing of TP53 to determine mutation status and detection of endogenous levels of both FLp53 and ∆40p53, is necessary prior to altering ∆40p53 levels, if it was to be used as a targeted therapy in cancer or aging related diseases.…”

“…Δ40p53 is expressed in normal tissues and cell lines at varying concentrations [ 14 , 75 ]. The expression of Δ40p53 is upregulated in several cancerous tissues and cells including serous ovarian cancer [ 76 ], acute lymphoblastic leukaemia (ALL) [ 77 ], glioblastoma (GBM) [ 78 ], melanoma [ 5 ], EC [ 68 ], and breast cancer, when compared to normal cells and tissues. Due to its upregulated expression in cancer, it has been suggested that it could potentially be used as a diagnostic or predictive marker [ 14 ].…”

“…Therefore, it seems that p53 variants could impair the canonical p53 pathway. Recently, Oh et al [ 77 ] investigated p53 isoform expression in marrow from a clinical cohort of 50 patients (40 primary and 10 relapse patients) without mutations in TP53 by using RT-PCR and western blot. The authors showed that Δ40p53 expression was significantly increased in relapsed patients when compared to control bone marrow cells.…”

“…There was a higher probability of Δ40p53-FLp53 hetero-oligomers in relapse samples than in primary samples, suggesting that Δ40p53 may impair p53 transcriptional activity and that it is associated with the progression of the disease. Even though the small number of healthy controls ( n = 4) and the heterogeneity of the groups are limitations of this study, their findings present some important insights into the expression of the p53 isoforms in leukaemia [ 77 ].…”