Significantly higher rates of gastrointestinal bleeding and thromboembolic events with left ventricular assist devices.

BACKGROUND & AIMS: The risk of gastrointestinal (GI) bleeding (GIB) and thromboembolic events may increase with continuous-flow left ventricular assist devices (CF-LVADs). We aimed to characterize GIB and thromboembolic events that occurred in patients with CF-LVADs and compare them with patients receiving anticoagulation therapy. METHODS: We performed a retrospective analysis of 159 patients who underwent CF-LVAD placement at 2 large academic medical centers (mean age, 55 ± 13 y). We identified and characterized episodes of GIB and thromboembolic events through chart review; data were collected from a time period of 292 ± 281 days. We compared the rates of GIB and thromboembolic events between patients who underwent CF-LVAD placement and a control group of 159 patients (mean age, 64 ± 15 y) who received a cardiac valve replacement and were discharged with anticoagulation therapy. RESULTS: Bleeding events occurred in 29 patients on CF-LVAD support (18%; 45 events total). Sixteen rebleeding events were identified among 10 patients (range, 1-3 rebleeding episodes/patient). There were 34 thrombotic events among 27 patients (17%). The most common source of bleeding was GI angiodysplastic lesions (n = 20; 44%). GIB and thromboembolic events were more common in patients on CF-LVAD support than controls; these included initial GIB (18% vs 4%, P < .001), rebleeding (6% vs none, P = .001), and thromboembolic events (17% vs 8%, P = .01). CONCLUSIONS: Patients with CF-LVADS receiving anticoagulants have a significantly higher risk of GIB and thromboembolic events than patients receiving anticoagulants after cardiac valve replacement surgery. GI angiodysplastic lesions are the most common source of bleeding.

p53 SUMOylation promotes its nuclear export by facilitating its release from the nuclear export receptor CRM1.

Chromosomal region maintenance 1 (CRM1) mediates p53 nuclear export. Although p53 SUMOylation promotes its nuclear export, the underlying mechanism is unclear. Here we show that tethering of a small, ubiquitin-like modifier (SUMO) moiety to p53 markedly increases its cytoplasmic localization. SUMO attachment to p53 does not affect its oligomerization, suggesting that subunit dissociation required for exposing p53's nuclear export signal (NES) is unnecessary for p53 nuclear export. Surprisingly, SUMO-mediated p53 nuclear export depends on the SUMO-interacting motif (SIM)-binding pocket of SUMO-1. The CRM1 C-terminal domain lacking the NES-binding groove interacts with tetrameric p53, and the proper folding of the p53 core domain, rather than the presence of the N- or C-terminal tails, appears to be important for p53-CRM1 interaction. The CRM1 Huntington, EF3, a subunit of PP2A, and TOR1 9 (HEAT9) loop, which regulates GTP-binding nuclear protein Ran binding and cargo release, contains a prototypical SIM. Remarkably, disruption of this SIM in conjunction with a mutated SIM-binding groove of SUMO-1 markedly enhances the binding of CRM1 to p53-SUMO-1 and their accumulation in the nuclear pore complexes (NPCs), as well as their persistent association in the cytoplasm. We propose that SUMOylation of a CRM1 cargo such as p53 at the NPCs unlocks the HEAT9 loop of CRM1 to facilitate the disassembly of the transporting complex and cargo release to the cytoplasm.

Identification of two independent SUMO-interacting motifs in Daxx: evolutionary conservation from Drosophila to humans and their biochemical functions.

Daxx is essential for embryonic development and implicated in apoptosis and transcriptional regulation. It is found only in the animal kingdom and appears to arise first in insects. In the Drosophila genus, the Daxx orthologs are much larger than those in other species. Here we show that in addition to a conserved core of approximately 200 residues, Daxx possesses several conserved domains and two essentially invariable short SUMO-interacting motifs (SIMs), each located at one or the other terminus of the protein. Both can independently interact with SUMO. The Daxx I7/733K double mutant with one mutation in each of the two SIMs no longer interacts with SUMO. Daxx interacts with Ubc9 and this interaction strictly requires at least one SIM. Interestingly, the Ubc9 H20D mutation that abolishes non-covalent Ubc9-SUMO interaction also interrupts Daxx-Ubc9 interaction. Thus, SUMO serves as the intermediate for Daxx-Ubc9 interaction. Surprisingly, Daxx I7/733K double mutant could still colocalize with PML. Furthermore, wt Daxx also strongly colocalizes with PMLDeltaS mutant, in which all three sumoylation sites are mutated, whereas PMLDeltaS only weakly colocalizes with Daxx I7/733K mutant, suggesting that SIM-SUMO interaction is not essential for but enhances PML-Daxx interaction. Remarkably, Daxx strongly stimulates c-Jun-mediated transcription and both SIMs are required for this stimulation. PML also activates c-Jun, which requires all three sumoylation sites. Coexpression of Daxx and PML revealed that they independently regulate c-Jun, with Daxx exerting a dominant role. These results suggest that the conserved SIMs are involved in mediating protein-protein interactions that underlie Daxx's diverse cellular functions.