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Repairing double-strand breaks (DSBs) is particularly challenging in heterochromatin, where the abundance of repeated sequences exacerbates the risk of ectopic recombination and chromosome rearrangements. In Drosophila cells, faithful homologous recombination (HR) repair of heterochromatic DSBs relies on a specialized pathway that relocalizes repair sites to the nuclear periphery before Rad51 recruitment. Here we show that HR progression is initially blocked inside the heterochromatin domain by SUMOylation and the coordinated activity of two distinct Nse2 SUMO E3 ligases: Quijote (Qjt) and Cervantes (Cerv). In addition, the SUMO-targeted ubiquitin ligase (STUbL) Dgrn, but not its partner dRad60, is recruited to heterochromatic DSBs at early stages of repair and mediates relocalization. However, Dgrn is not required to prevent Rad51 recruitment inside the heterochromatin domain, suggesting that the block to HR progression inside the domain and relocalization to the nuclear periphery are genetically separable pathways. Further, SUMOylation defects affect relocalization without blocking heterochromatin expansion, revealing that expansion is not required for relocalization. Finally, nuclear pores and inner nuclear membrane proteins (INMPs) anchor STUbL/RENi components and repair sites to the nuclear periphery, where repair continues. Together, these studies reveal a critical role of SUMOylation and nuclear architecture in the spatial and temporal regulation of heterochromatin repair and the protection of genome integrity.

Understanding the mechanism by which single-stranded oligonucleotides (ODNs) elicit targeted nucleotide exchange (TNE) is imperative to achieving optimal correction efficiencies and medical applicability. It has been previously shown that introduction of an ODN into cells results in the activation of DNA damage response pathways, but there has been no evaluation of the damage created at the level of the DNA. The activation of H2AX, a hallmark protein of DNA breakage, suggests that a double-strand break (DSB) could be occurring during the targeted gene alteration (TGA) reaction. Using the human HCT116 cell line with a single integrated mutant eGFP gene as our model system, we demonstrate that the DNA strand breakage occurs when a specific ODN, designed to direct TGA, is transfected into the cells. Both single- and double-stranded DNA cleavage is observed dependent on the level of ODN added to the reaction. Possible mechanisms of ODN-dependent DSB formation, as a function of TGA, are discussed herein.

Entamoeba histolytica is the causative agent of amoebic dysentery. Uptake of iron is critical for E. histolytica growth and iron-bound human transferrin (holo-transferrin) has been shown to serve as an iron source in vitro. Although a transferrin-binding protein has been identified in E. histolytica, the mechanism by which this iron source is taken up by this pathogen is not well understood. To gain insight into this process, the uptake of fluorescent-dextran, -holo-transferrin, and human red blood cells (hRBCs) was compared. Both dextran and transferrin were taken up in an apparent receptor-independent fashion as compared to hRBCs, which were taken up in a receptor-mediated fashion. Interestingly, the uptake of FITC-dextran and FITC-holo-transferrin differentially relied on an intact actin cytoskeleton suggesting that their internalization routes may be regulated independently.

Platelets function physiologically in mediating hemostasis, but are also associated with many pathological conditions, such as thrombosis, which can lead to myocardial infarction and/or stroke. Therefore, the study of platelet regulation and signaling has been of great interest and is necessary for generating effective anti-platelet therapeutics. One platelet signaling molecule of particular interest is the integrin alphaIIb beta3, which binds Fg and mediates platelet cross-linking. The integrin itself as well as cytoplasmic proteins that interact with alphaIIb beta3 have become potential targets for anti-platelet therapies. One such protein that has been shown to directly regulate alphaIIb beta3 function is calcium- and integrin-binding protein 1 (CIB1). CIB1 has been implicated in alphaIIb beta3 activation and outside-in signaling through the integrin. By increasing our understanding of CIB1 and other proteins that like it, associate with integrin alphaIIb beta3, and the signaling events that result from those interactions, we may bring ourselves closer to more effective therapies. In the present work, we explore known cytoplasmic binding partners of the integrin alphaIIb beta3 and their effect on alphaIIb beta3, focusing on CIB1.

Platelets function physiologically in mediating hemostasis, but are also associated with many pathological conditions, such as thrombosis, which can lead to myocardial infarction and/or stroke. Therefore, the study of platelet regulation and signaling has been of great interest and is necessary for generating effective anti-platelet therapeutics. One platelet signaling molecule of particular interest is the integrin alphaIIb beta3, which binds Fg and mediates platelet cross-linking. The integrin itself as well as cytoplasmic proteins that interact with alphaIIb beta3 have become potential targets for anti-platelet therapies. One such protein that has been shown to directly regulate alphaIIb beta3 function is calcium- and integrin-binding protein 1 (CIB1). CIB1 has been implicated in alphaIIb beta3 activation and outside-in signaling through the integrin. By increasing our understanding of CIB1 and other proteins that like it, associate with integrin alphaIIb beta3, and the signaling events that result from those interactions, we may bring ourselves closer to more effective therapies. In the present work, we explore known cytoplasmic binding partners of the integrin alphaIIb beta3 and their effect on alphaIIb beta3, focusing on CIB1.