Activated Notch counteracts Ikaros tumor suppression in mouse and human T-cell acute lymphoblastic leukemia

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Activating NOTCH1 mutations are prevalent in T-cell acute lymphoblastic leukemia (T-ALL).
• IKZF1 (IKAROS) mutations are less common but also implicated in T-ALL pathogenesis.
• The regulatory relationship between NOTCH1 and IKAROS in T-ALL is not fully understood.

Purpose of the Study:

• To investigate the interplay between NOTCH1 and IKAROS in T-ALL.
• To determine if IKAROS can reverse established T-ALL driven by NOTCH1.
• To elucidate the mechanism by which NOTCH1 signaling affects IKAROS function.

Main Methods:

• Utilized a novel transgenic RNA interference mouse model for reversible Ikaros knockdown.
• Generated primary T-ALLs in mice to study disease dynamics.
• Analyzed IKAROS mRNA expression in human T-ALL cell lines and patient samples.
• Assessed the impact of Ikaros restoration and NOTCH1 inhibition on leukemia progression and regression.

Main Results:

• Reversible Ikaros knockdown initiated T-ALL in mice.
• Restoring Ikaros expression in established T-ALL repressed Notch1 and its targets, leading to disease regression.
• Leukemias with activated Notch1 (ICN1) relapsed rapidly after Ikaros restoration, indicating functional antagonism.
• IKAROS mRNA was reduced in human T-ALL with NOTCH1/FBXW7 mutations and upregulated upon NOTCH inhibition.

Conclusions:

• Aberrant NOTCH activity compromises IKAROS function in both mouse and human T-ALL.
• NOTCH1 signaling antagonizes IKAROS in established T-ALL, potentially explaining the lower frequency of IKAROS mutations in human T-ALL.
• Targeting NOTCH1 signaling may restore IKAROS function and offer therapeutic strategies for T-ALL.