TOX Regulates Growth, DNA Repair, and Genomic Instability in T-cell Acute Lymphoblastic Leukemia

Abstract

T-cell Acute Lymphoblastic Leukemia (T-ALL) is an aggressive malignancy of thymocytes. Using a transgenic screen in zebrafish, thymocyte selection-associated high mobility box protein (TOX) was uncovered as a collaborating oncogenic driver that accelerated T-ALL onset by expanding the initiating pool of transformed clones and elevating genomic instability. TOX is highly expressed in a majority of human T-ALL and is required for proliferation and continued xenograft growth in mice. Using a wide array of functional analyses, we uncovered that TOX binds directly to KU70/80 and suppresses recruitment of this complex to DNA breaks to inhibit Non-Homologous End Joining repair (NHEJ). Impaired NHEJ is well known to cause genomic instability, including development of T cell malignancies in Ku70 and Ku80 deficient mice. Collectively, our work has uncovered important roles for TOX in regulating NHEJ by elevating genomic instability during leukemia initiation and sustaining leukemic cell proliferation following transformation.

BCL6 Evolved to Enable Stress Tolerance in Vertebrates and Is Broadly Required by Cancer Cells to Adapt to Stress

“…HMG-box proteins bind to chromatin and modify the architecture of DNA. However, recent studies in a T-ALL model suggest that TOX does not bind chromatin and instead inhibits NHEJ by directly binding and suppressing recruitment of Ku70/80 to sites of DNA breaks (41). In contrast, HSF1 has been shown to facilitate DNA repair (both homologous recombination repair and NHEJ) by forming a ternary complex with PARP proteins (47).…”

“…Because TOX was shown to inhibit error-prone nonhomologous end joining (NHEJ) DNA repair in T-cell acute lymphoblastic leukemia (T-ALL; ref. 41), we hypothesized that BCL6 repression of TOX promotes chemotolerance by enhancing DNA repair. To test this notion, we exposed parental and TOX-silenced MDA-MB-468 and NCI-H460 cells to doxorubicin alone or in combination with the BCL6 BTB inhibitor FX1 and assessed DNA damage by single-cell gel electrophoresis.…”

Simultaneous B and T cell acute lymphoblastic leukemias in zebrafish driven by transgenic MYC: implications for oncogenesis and lymphopoiesis

“…Zebrafish ( Danio rerio ) provide one potential solution, since they can model human leukemias accurately (4), have practical advantages (genetic tractability, high-throughput screens, cost), and share hematopoietic, oncogenic, and tumor suppressive pathways with humans (5). These features permitted the creation of several zebrafish T cell ALL (T-ALL) models that mimic the human disease (6-10), which subsequently led to key findings in T-ALL genetics, disease progression mechanisms, and signaling (11-16), as well as facilitating screens for new treatment agents (17, 18). However, despite the even greater clinical impact of pre-B ALL, effective zebrafish models lag behind.…”

Zebrafish B cell acute lymphoblastic leukemia: new findings in an old model

“…myeloid leukemia (AML) and T-ALL [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. For T-ALL in particular, zebrafish models have been highly informative, advancing our understanding of T-ALL genetics, pro-and anti-oncogenic interactions between different genes and pathways, tumor heterogeneity, leukemia stem cells, and in screens for new therapeutics [28,[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53]. However, despite the fact that zebrafish T-ALL models had proven to be fertile grounds for study, B-ALL modeling in D. rerio had not been fruitful, with only one low penetrance and long latency line reported [54].…”