NOTCH3: A MORE PROMINENT PLAYER THAN NOTCH1 IN THE PATHOGENESIS OF T-ALL?
E Radwan,1 E Ferretti,2 S Checquolo,2 P Grazioli,2 C Talora,2 H Moussa,3 A Campese,2 M El-Ansary,1 S Hussein,1 D Yassin,3 A Kamel,3 I Screpanti2
Background. T-acute lymphoblastic leukemia (T-ALL) includes several subtypes that correlate with genetic aberrations at different stages of thymocyte differentiation. NOTCH family controls various steps of T-cell development; hence dysregulated NOTCH signaling could be involved in the development of T-ALL. NOTCH3 gene was previously shown to be expressed in all T-ALL patients, whereas its expression was reduced in remission; it is associated with the expression of HES1 and the invariant chain of pre-TCR (p-Talpha). Thus, a T-ALL signature characterizes the active or relapsing disease. NOTCH1 was discovered as a partner gene in the rare t(7;9), representing <1% of T-ALLs, yet about 50% of human T-ALLs were noted to harbor activating point mutations in NOTCH1 that lead to aberrant activation of NOTCH signaling, placing it at the center of T-ALL pathogenesis. Other studies reported that NOTCH1 expression was not pathognomonic for T-ALL, as it was detected not only in normal peripheral blood T lymphocytes but also in non-T cell leukemias. More recently NOTCH1 activating mutations were reported as secondary events in T-ALL. Aims. The aim was to study the expression of the main genes involved in the NOTCH pathway, to verify the possible specific role of NOTCH1 versus NOTCH3 in the pathogenesis of T-ALL and to correlate the level of the expression of such genes to other prognostic parameters. Methods. Under informed consent the study was performed on 46 T-ALL patients (38 children/8 adults, 33 males/13 females); 12 cases of precursor B-ALL and 13 healthy subjects served as control groups. Gene expression was evaluated using Real Time PCR. Results. NOTCH1, NOTCH3, pTalpha and HES1 expression was increased in T-ALL compared to precursor B-ALL (P=0.015-0.044) and healthy subjects (P=0.0001-0.022). Genes expression was higher in children compared to adults; the difference was significant for NOTCH3 (P=0.02) and pTalpha (P=0.005). The genes level in early, intermediate and late T-ALL was examined. Due to the comparable level of gene expression in both intermediate and late T-ALL they were considered as one group in comparison with early T-ALL. Gene expression was higher in intermediate and late T-ALL group compared to early T-ALL for all the studied genes (P=0.006-0.016) except for HES1 (P=0.11). A correlation was found between NOTCH1 and NOTCH3 (r=0.508/P=0.0001) and between each of them and pTalpha (r=0.481, P=0.0001 and r=0.871,P=0.0001 respectively). HES1 moderately correlated with NOTCH1 (r=0.48, P=0.021). No association was encountered between genes expression and any of the prognostic parameters: age, TLC, mediastinal involvement, CNS involvement, hepatosplenomegaly, or lymphadenopathy except for a high expression of NOTCH1 in association with hemoglobin level <10 g/dL (P=0.049) and a negative correlation between them (r=-0.476/P=0.003). NOTCH3/NOTCH1 ratio was calculated for the different groups. Both T-ALL and precursor B-ALL showed comparable ratios to each other (P=0.312) while both showed a higher ratio in comparison to healthy subjects (P=0.0001 and 0.013 respectively) Conclusions. Our study confirms a pivotal role of NOTCH pathway in the pathogenesis of T-ALL together with pTalpha and HES1. The higher NOTCH3/NOTCH1 ratio suggests that NOTCH3 dysregulation may play a more central role than NOTCH1 in ALL pathogenesis.