Insertion sequence elements (IS elements) are proposed to play major roles in shaping the genetic and phenotypic landscapes of prokaryotic cells. Recent evidence has raised the possibility that environmental stress conditions increase IS hopping into new sites, and often such hopping has the phenotypic effect of relieving the stress. Although stress-induced targeted mutations have been reported for a number of E. coli genes, the glpFK (glycerol utilization) and the cryptic bglGFB (β-glucoside utilization) systems are among the best characterized where the effects of IS insertion-mediated gene activation are well-characterized at the molecular level. In the glpFK system, starvation of cells incapable of utilizing glycerol leads to an IS5 insertion event that activates the glpFK operon, and enables glycerol utilization. In the case of the cryptic bglGFB operon, insertion of IS5 (and other IS elements) into a specific region in the bglG upstream sequence has the effect of activating the operon in both growing cells, and in starving cells. However, a major unanswered question in the glpFK system, the bgl system, as well as other examples, has been why the insertion events are promoted at specific locations, and how the specific stress condition (glycerol starvation for example) can be mechanistically linked to enhanced insertion at a specific locus. In this paper, we show that a specific DNA structural feature (superhelical stress-induced duplex destabilization, SIDD) is associated with “stress-induced” IS5 insertion in the glpFK, bglGFB, flhDC, fucAO and nfsB systems. We propose a speculative mechanistic model that links specific environmental conditions to the unmasking of an insertional hotspot in the glpFK system. We demonstrate that experimentally altering the predicted stability of a SIDD element in the nfsB gene significantly impacts IS5 insertion at its hotspot.

A 54-year-old African American male with systemic lupus erythematosus and chronic alcoholic hepatitis presented with recurrent fever, pancytopenia, transaminitis, weight loss, and widespread violaceous tender plaques. Skin biopsy revealed hemophagocytic histiocytes leading to a diagnosis of cytophagic histiocytic panniculitis in the setting of lupus panniculitis. During workup, an axillary lymph node biopsy mimicked Kikuchi-Fujimoto's disease. Treatment with tapering high-dose glucocorticoids, mycophenolate mofetil, and hydroxychloroquine induced remission of the disease. We believe the comorbid conditions of Kikuchi-Fujimoto-like pathology and cytophagic histiocytic panniculitis have not been documented in the literature to date in a patient with systemic lupus erythematosus.

Herpesvirus entry mediator (HVEM; TNFRSF14) is frequently mutated in human cancer with a high degree of mutations in follicular and diffuse large B cell lymphoma. In lymphocytes, HVEM receptors are activated by its ligands LIGHT (TNFSF14) and Lymphotoxin-α, and engage in bi-directional signaling with the receptors B and T lymphocyte attenuator (BTLA) and CD160. We hypothesized that mutations in HVEM disrupted binding to either of its ligands resulting in altered cell-intrinsic HVEM signaling in lymphoma, or in altered activation of BTLA or CD160 in tumor infiltrating lymphocytes. Here, we show that point mutations identified in human lymphoma were localized to the extracellular domain and specifically target ligand binding, resulting in preferential loss of HVEM interactions with CD160 and BTLA compared to LIGHT (TNFSF14). Disrupted binding correlated with loss of receptor functionality resulting in abrogated cell-intrinsic HVEM activation of NF-κB, as well as reduced CD160 activation of ERK and AKT phosphorylation by HVEM ligation. We next identified HVEM-activated CD160 and BTLA signaling pathways through AP/MS and phospho-proteomic analysis in NK and T cells. Activation of CD160 versus BTLA resulted in contrasting phosphorylation status in a number of phospho-proteins, illustrating opposing functions of these receptors. In a mouse model of lymphoma we tested the impact of BTLA versus CD160 in regulating antigen-specific anti-tumor responses, demonstrating regulatory effects of these receptors in vivo. Together these data illustrate how selective pressures within the tumor microenvironment may drive cancer mutations that alter HVEM network signaling in vivo, and indicate potential targets for onco-immunotherapy.

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