Structural basis of DUX4/IGH-driven transactivation

Abstract

Oncogenic fusions are major drivers in leukemogenesis and may serve as potent targets for treatment. DUX4/IGHs have been shown to trigger the abnormal expression of ERGalt through binding to DUX4-Responsive-Element (DRE), which leads to B-cell differentiation arrest and a full-fledged B-ALL. Here, we determined the crystal structures of Apo- and DNADRE-bound DUX4HD2 and revealed a clamp-like transactivation mechanism via the double homeobox domain. Biophysical characterization showed that mutations in the interacting interfaces significantly impaired the DNA binding affinity of DUX4 homeobox. These mutations, when introduced into DUX4/IGH, abrogated its transactivation activity in Reh cells. More importantly, the structure-based mutants significantly impaired the inhibitory effects of DUX4/IGH upon B-cell differentiation in mouse progenitor cells. All these results help to define a key DUX4/IGH-DRE recognition/step in B-ALL.

DUX4 regulates oocyte to embryo transition in human

“…6 f-i), the intermediate linker loop imparts flexibility, which could be vital to accommodate DNA once DUX4 enters the nucleus and locates its binding motif. Indeed, the double homeodomain without DNA opened dramatically, by over 38 Å, and the stabile open conformation would be suited to initial interactions with DNA and be consistent with the proposed two-step clamp-like binding mechanism 26 .…”

Crystal Structure of the Double Homeodomain of DUX4 in Complex with DNA

“…Thus, DUX4 recognizes its target sequence as an inverted repeat, where HD1 and HD2 recognize different sequences, 5′-TAAT-3′and 5′-TGAT-3′, respectiveely. As observed in other structurally characterized homeodomain-DNA complexes (Hirsch and Aggarwal, 1995; Kissinger et al, 1990; Li et al, 1995; Passner et al, 1999; Piper et al, 1999; Wilson et al, 1995) and for DUX4 HD2 (Aihara et al, 2018; Dong et al, 2018), the sequence readout by each homeodomain of DUX4 involves interactions in both the major and minor grooves of DNA. The third α-helix (α3) of both HD1 and HD2 is inserted into the DNA major groove for direct base contacts (Figures 1B, 1D, 2A, and 2B).…”

“…Assuming the highly related homeodomains recognize the same core, one could envision the DUX4 homeo-domains recognizing TAAT in tandem on the same strand (5′- TAAT C TAAT CA-3′) forcing them into a head-to-tail dimer configuration. This would be similar to the modes of DNA binding by Even-skipped homeodomain (Hirsch and Aggarwal, 1995) and the Hox-Pbx hetero-dimeric homeodomains (LaRonde-LeBlanc and Wolberger, 2003; Passner et al, 1999; Piper et al, 1999) (Figure S1A) and was suggested in a recent structural study of the isolated second homeodomain of DUX4 (Dong et al, 2018). However, this latter structure does not actually show a home-odomain positioned over the TAAT core, and therefore its significance remains unclear (Aihara et al, 2018).…”

Lymphocytes contribute to DUX4 target genes in FSHD muscle biopsies

“…These target genes lead to pro-apoptotic and anti-myogenic effects 18,38 but importantly, certain immune system processes have also been found dysregulated by DUX4 20 . In addition, a DUX4-IGH fusion gene is present in a significant proportion of adult B-ALL, where it binds DUX4 response elements, and inhibits lymphocytic differentiation 34,35 . These findings point to a role for DUX4 in modification of immune cell function.…”

“…Of further relevance, an in frame DUX4-IGH fusion gene in which the homeodomains of DUX4 are fused to a clamp-like transactivation domain of IGH, presents in a significant subset of B-cell Acute Lymphoblastic Leukaemia (B-ALL). DUX4-IGH can inhibit terminal differentiation and induce transformation 34,35 .…”