A dual role for PSIP1/LEDGF in T-cell acute lymphoblastic leukemia [CUT&RUN]

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy. Although intensified therapeutic protocols have improved the outcome of T-ALL patients, they coincide with severe short- and long-term side effects. In addition, no salvage therapeutic strategies are available for primary therapy-resistant or relapsed T-ALL, resulting in a dismal outcome for these patients. It highlights the need to identify new targets in T-ALL biology that allow the development of less toxic targeted therapies. PSIP1, a histone mark reader, is a dependency factor in KMT2A-rearranged myeloid leukemia, but is dispensable for normal hematopoiesis, making it an attractive therapeutic target. Nonetheless, rare recurrent inactivating mutations and deletions of PSIP1, suggest that PSIP1 could act as a tumor suppressor in T-ALL. Here, we demonstrate that the loss of Psip1 accelerates T-ALL initiation in mice and we identified a correlation with reduced H3K27me3 binding. Contrastingly, loss of PSIP1 impaired cell proliferation in several human and murine T-ALL cell lines. In these cell lines, PSIP1 loss leads to a significant downregulation of COX20, an assembly factor of the cytochrome c oxidase in the mitochondria, and is associated with a reduction in mitochondrial respiration. Similarly to what was observed for PSIP1, loss of COX20 expression also leads to an impairment of proliferation in these T-ALL cell lines. These data corroborate that PSIP1 can exert a dual role in the context of T-ALL, either as a tumor suppressor gene during tumor initiation or as a dependency factor in tumor maintenance.