Differential expression of p73 isoforms in relation to drug resistance in childhood T-lineage acute lymphoblastic leukaemia

The T-lineage phenotype of childhood acute lymphoblastic leukaemia ( ALL) is associated with an increased relapse-risk and in vitro resistance to drugs as compared to a precursor B phenotype. Antiapoptotic isoforms of p73 that lack part of the transactivation (TA) domain (Delta TA-p73, i.e. p73 Delta ex2, p73 Delta ex3, p73 Delta ex2/3 and Delta N-p73) may cause resistance to anticancer agents through inhibition of p53 and/or proapoptotic p73 family members (TA-p73). We demonstrate in our study that the expression of total p73 mRNA was higher in childhood T-ALL compared to controls (P = 0.004). In T-ALL, the relative contribution of antiapoptotic Delta TA-p73 (88%) was larger than of proapoptotic TA- p73 (12%). Leukaemic cells of T-ALL patients expressing higher levels of antiapoptotic p73 were more resistant to the DNA-damaging drug daunorubicin compared to cells of patients with low or negative expression or these isoforms (P-trend = 0.045). Interestingly, p73Dex2 was the most abundantly expressed antiapoptotic isoform in daunorubicin-resistant patient cells (44% of total p73). No association was found between high expression of proapoptotic Delta TA- p73 or antiapoptotic DTA-p73 and relapse-risk. Our results suggest that childhood T-ALL is associated with a high expression of Delta TA-p73. These isoforms may play a role in cellular resistance to DNA-damaging drugs in children at initial diagnosis of T-ALL.