Background: IFITM3 is a protein of the innate immune system that inhibits viral infections. Results: S-palmitoylation enhances IFITM3 membrane affinity and antiviral activity, whereas ubiquitination decreases endolysosome localization and antiviral activity. Conclusion: IFITM3 is dually and opposingly regulated by posttranslational modifications, and study of these modifications has led to an unpredicted intramembrane topology model. Significance: Understanding modes of IFITM3 regulation is critical for dissecting molecular mechanisms controlling viral inhibition.

SUMMARY Increased mobility of chromatin surrounding Double Strand Breaks (DSBs) has been noted in yeast and mammalian cells but how it is driven and whether it contributes to DSB repair remain unclear. Here, we use a telomere-based system to track DNA damage foci with high resolution in living cells. We find that the greater mobility of damaged chromatin requires 53BP1, SUN1/2 in the Linker of the Nucleoskeleton and Cytoskeleton (LINC) complex and dynamic microtubules. The data further demonstrate that the excursions promote non-homologous end joining of dysfunctional telomeres and implicated Nesprin-4 and kinesins in telomere fusion. 53BP1/LINC/microtubule-dependent mobility is also evident at irradiation-induced DSBs and contributes to the mis-rejoining of drug-induced DSBs in BRCA1-deficient cells showing that DSB mobility can be detrimental in cells with numerous DSBs. In contrast, under physiological conditions where cells have only one or a few lesions, DSB mobility is proposed to prevent errors in DNA repair.

Using a new mouse model, the specific deletion of monocytes and macrophages reveals that, although not required to initiate immunity to Citrobacter rodentium, they contribute to the adaptive response via IL-12 secretion to induced IFN-γ+ Th1 polarization.

IntroductionFc receptors are receptors for immunoglobulins that play a central role in immunity. On human leukocytes, a myriad of Fc␥ receptors are expressed; among these receptors, Fc␥RI is the only known high-affinity receptor for immunoglobulin G (IgG). 1 Fc␥RI is constitutively expressed on monocytes, macrophages, and myeloid dendritic cells. Interferon␥ (IFN␥) can enhance surface expression of Fc␥RI on these cells, and Fc␥RI expression can be induced on granulocytes by IFN␥ or granulocyte colony-stimulating factor (G-CSF) stimulation. In contrast, cytokines such as interleukin-4 (IL-4), IL-10, and transforming growth factor-␤ (TGF-␤) downregulate activating Fc receptors, including Fc␥RI, and enhance expression of the inhibitory receptor Fc␥RIIb. 2,3 In vitro, IFN␥ treatment leads to increased Fc␥ receptor-induced cytokine production. 4 In vivo, the role of Fc␥RI in immunity remains unclear, as due to its high affinity Fc␥RI is believed to be saturated with monomeric IgG. This has led to the concept that prebound monomeric IgG prevents participation of Fc␥RI in clearing immune complexes by extravasated effector cells. 5 Nevertheless, several in vivo studies documented a role for Fc␥RI, varying from a contribution during inflammation and autoimmune reactions, 6-8 or, during monoclonal antibody (mAb)-based immunotherapy in melanoma and B-cell lymphoma models, 9,10 to a malaria model in which transgenic expression of human Fc␥RI was central for effective mAb treatment. 11 Furthermore, Fc␥RI can induce potent proinflammatory signaling compared with Fc␥RIIa, 12 and can efficiently mediate both major histocompatibility complex class II (MHC-II) antigen presentation and cross-presentation. [13][14][15][16] It remains unclear how Fc␥RI contributes to immune complex clearance in the presence of high IgG levels. For Fc␣RI 17,18 and Fc␥RIIa 19,20 it has been shown that cytokine stimulation can increase ligand binding of these receptors. This appears analogous to inside-out regulation described for integrins. Many integrins are expressed in a low-affinity binding state, which can be transformed to a high-affinity form upon cellular activation. 21 We hypothesized that inside-out regulation could contribute to immune complex binding to Fc␥R occupied by IgG. Indeed, several studies support intracellular proteins interacting with Fc␥RI and possibly affecting ligand binding. 22,23 In this study, we investigated the effect of cytokine stimulation on Fc␥RI ligand binding. Stimulation of Fc␥RI-expressing Ba/F3 cells and primary monocytes resulted in increased binding of immune complexes, whereas binding of monomeric IgG was only moderately enhanced. Upon cellular activation, Fc␥RI could readily bind immune complexes despite pre-engaged monomeric IgG. Taken together, these data might explain how Fc␥RI supports leukocyte interaction with immune complexes. Methods Antibodies and reagentsAnti-Fc␥RI-A647 was from BioLegend (clone 10.1). Unlabeled 10.1 mAb and mouse IgG1/IgG2a isotype were from eBioscience and BD Pharmingen, respect...