Notch3 and pre-TCR interaction unveils distinct NF-κB pathways in T-cell development and leukemia

Notch signaling plays a critical role in T-cell differentiation and leukemogenesis. We previously demonstrated that, while pre-TCR is required for thymocytes proliferation and leukemogenesis, it is dispensable for thymocyte differentiation in Notch3-transgenic mice. Notch3-transgenic premalignant thymocytes and T lymphoma cells overexpress pT alpha/pre-TCR and display constitutive activation of NF-kappa B, providing survival signals for immature thymocytes. We provide genetic and biochemical evidence that Notch3 triggers multiple NF-kappa B activation pathways. A pre-TCR-dependent pathway preferentially activates NF-kappa B via IKK beta/IKK alpha/NIK complex, resulting in p50/p65 heterodimer nuclear entry and recruitment onto promoters of Cyclin D1, Bcl2-A1 and IL7-receptor-alpha genes. In contrast, upon pT alpha deletion, Notch3 binds IKK alpha and maintains NF-kappa B activation through an alternative pathway, depending on an NIK-independent IKKa homodimer activity. The consequent NF-kappa B2/p100 processing allows nuclear translocation of p52/RelB heterodimers, which only trigger transcription from Bcl2-A1 and IL7-receptor-alpha genes. Our data suggest that a finely tuned interplay between Notch3 and pre-TCR pathways converges on regulation of NF-kappa B activity, leading to differential NF-kappa B subunit dimerization that regulates distinct gene clusters involved in either cell differentiation or proliferation/leukemogenesis.