Activation and therapeutic targeting of the NOTCH1 signaling in T-ALL. The NOTCH1 receptor is synthesized as a precursor protein that undergoes maturation in the trans-golgi network before being expressed in the plasma membrane. Maturation and processing of NOTCH1-mutant proteins that destabilize the NRR regulatory region are sensitive to inhibition of SERCA calcium channels with thapsigargin. Activation of NOTCH1 is initiated by cleavage of the receptor by ADAM10 protease. Antibodies (Ab) that recognize and protect the NRR preclude metalloprotease processing of NOTCH1, thus abrogating receptor activation. After ADAM10 processing, NOTCH1 is cleaved in the transmembrane region by the γ-secretase complex, which can be inhibited by small-molecule GSIs. After release from the membrane, the intracellular active portion of the receptor translocates to the nucleus where it interacts with the RBPJ DNA-binding protein and recruits the MAML1 transcriptional coactivator. Assembly of the ICN1-RBPJ-MAML1 complex and activation of NOTCH1 target genes can be inhibited by SAHM1, a stapled peptide. P, phosphorylation; pol II, polymerase II.