Growth Inhibition and Apoptosis Due to Restoration of E2A Activity in T Cell Acute Lymphoblastic Leukemia Cells

Two models have been proposed for the molecular mechanism by which the Tal1 oncogene causes T cell acute lymphoblastic leukemia (T-ALL). The activation model suggests that Tal1 as heterodimers with the E2A transcription factor activates the expression of oncogenes. The inhibition model postulates that Tal1 interferes with the tumor-suppressing function of E2A. In the Jurkat T cell line, originally derived from a patient with T-ALL, Tal1 is complexed with E2A proteins and the transcriptional activity of E2A is very low. When E2A activity was restored by expressing an E2A–Tal1 fusion protein, E-T/2, the Jurkat cells underwent growth arrest and subsequently apoptosis, thus supporting the inhibition model and suggesting that E2A loss may contribute to leukemic progression.