Requirement for TP73 and genetic alterations originating from its intragenic super-enhancer in adult T-cell leukemia.

Adult T-cell leukemia/lymphoma (ATL) is a genetically complex hematological malignancy derived from mature T cells. Using an integrative approach, we previously identified genes recurrently associated with super-enhancers in ATL. One of those genes was TP73, a TP53 family gene; however, the roles and function of TP73 and its super-enhancer in ATL pathogenesis are poorly understood. Our study demonstrates that TP73 is highly activated under the control of a super-enhancer in ATL cells but not in normal T cells or other hematological malignancies examined. Full-length TP73 is required for ATL cell maintenance in vitro and in vivo via the regulation of cell proliferation and DNA damage response pathways. Notably, recurrent deletions of TP73 exons 2-3 were observed in a fraction of primary ATL cases that harbored the super-enhancer, while induction of this deletion in cell lines further increased proliferation and mutational burden. Our study suggests that formation of the TP73 intragenic super-enhancer and genetic deletion are likely sequentially acquired in relation to intracellular state of ATL cells, which leads to functional alteration of TP73 that confers additional clonal advantage.