HOX proteins define a family of key transcription factors regulating animal embryogenesis. HOX genes have also been linked to oncogenesis and HOXA1 has been described to be active in several cancers, including breast cancer. Through a proteome-wide interaction screening, we previously identified the TNFR-associated proteins RBCK1/HOIL-1 and TRAF2 as HOXA1 interactors suggesting that HOXA1 is functionally linked to the TNF/NF-κB signaling pathway. Here, we reveal a strong positive correlation between expression of HOXA1 and of members of the TNF/NF-κB pathway in breast tumor datasets. Functionally, we demonstrate that HOXA1 can activate NF-κB and operates upstream of the NF-κB inhibitor IκB. Consistently, we next demonstrate that the HOXA1-mediated activation of NF-κB is non-transcriptional and that RBCK1 and TRAF2 influences on NF-κB are epistatic to HOXA1. We also identify an 11 Histidine repeat and the homeodomain of HOXA1 to be required both for RBCK1 and TRAF2 interaction and NF-κB stimulation. Finally, we highlight that activation of NF-κB is crucial for HOXA1 oncogenic activity.

The Tn3 family is a widespread group of replicative transposons that are notorious for their contribution to the dissemination of antibiotic resistance and the emergence of multiresistant pathogens worldwide. The TnpA transposase of these elements catalyzes DNA breakage and rejoining reactions required for transposition. It also is responsible for target immunity, a phenomenon that prevents multiple insertions of the transposon into the same genomic region. However, the molecular mechanisms whereby TnpA acts in both processes remain unknown. Here, we have developed sensitive biochemical assays for the TnpA transposase of the Tn3-family transposon Tn4430 and used these assays to characterize previously isolated TnpA mutants that are selectively affected in immunity. Compared with wild-type TnpA, these mutants exhibit deregulated activities. They spontaneously assemble a unique asymmetric synaptic complex in which one TnpA molecule simultaneously binds two transposon ends. In this complex, TnpA is in an activated state competent for DNA cleavage and strand transfer. Wild-type TnpA can form this complex only on precleaved ends mimicking the initial step of transposition. The data suggest that transposition is controlled at an early stage of transpososome assembly, before DNA cleavage, and that mutations affecting immunity have unlocked TnpA by stabilizing the protein in a monomeric activated synaptic configuration. We propose an asymmetric pathway for coupling active transpososome assembly with proper target recruitment and discuss this model with respect to possible immunity mechanisms.

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Post-translational modifications (PTMs) are important determinants which contribute to modulating the turn-over, intracellular localisation, molecular interactions and activity of most eukaryotic proteins. Such modifications and their consequences have been extensively examined for some proteins or classes of proteins. This is not the case for the HOX transcription factors which are crucial regulators of animal development. In this review, we provide a survey of the literature and data repositories pertaining to HOX-associated PTMs. This highlights that HOX proteins are also likely widely post-translationally modified, and defines HOX PTMs as an under-valued facet of their biology.

HOXA1 belongs to the HOX family of transcription factors which are key regulators of animal development. Little is known about the molecular pathways controlling HOXA1. Recent data from our group revealed distinct partner proteins interacting with HOXA1. Among them, OGT is an O-linked N-acetylglucosamine (O-GlcNAc) transferase modifying a variety of proteins involved in different cellular processes including transcription. Here, we confirm OGT as a HOXA1 interactor, we characterise which domains of HOXA1 and OGT are required for the interaction, and we provide evidence that OGT post-translationally modifies HOXA1. Mass spectrometry experiments indeed reveal that HOXA1 can be phosphorylated on the AGGTVGSPQYIHHSY peptide and that upon OGT expression, the phosphate adduct is replaced by an O-GlcNAc group.