Structural mechanism of BRD4-NUT and p300 bipartite interaction in propagating aberrant gene transcription in chromatin in NUT carcinoma.

BRD4-NUT, a driver fusion mutant in rare and highly aggressive NUT carcinoma, acts in aberrant transcription of anti-differentiation genes by recruiting histone acetyltransferase (HAT) p300 and promoting p300-driven histone hyperacetylation and nuclear condensation in chromatin. However, the molecular basis of how BRD4-NUT recruits and activates p300 remains elusive. Here, we report that BRD4-NUT contains two transactivation domains (TADs) in NUT that bind to the TAZ2 domain in p300. Our NMR structures reveal that NUT TADs adopt amphipathic helices when bound to the four-helical bundle TAZ2 domain. The NUT protein forms liquid-like droplets in-vitro that are enhanced by TAZ2 binding in 1:2 stoichiometry. The TAD/TAZ2 bipartite binding in BRD4-NUT/p300 triggers allosteric activation of p300 and acetylation-driven liquid-like condensation on chromatin that comprise histone H3 lysine 27 and 18 acetylation and transcription proteins BRD4L/S, CDK9, MED1, and RNA polymerase II. The BRD4-NUT/p300 chromatin condensation is key for activating transcription of pro-proliferation genes such as ALX1, resulting ALX1/Snail signaling and epithelial-to-mesenchymal transition. Our study provides a previously underappreciated structural mechanism illuminating BRD4-NUT's bipartite p300 recruitment and activation in NUT carcinoma that nucleates a feed-forward loop for propagating histone hyperacetylation and chromatin condensation to sustain aberrant anti-differentiation gene transcription and perpetual tumor cell growth.

The Functions of BET Proteins in Gene Transcription of Biology and Diseases.

The BET (bromodomain and extra-terminal domain) family proteins, consisting of BRD2, BRD3, BRD4, and testis-specific BRDT, are widely acknowledged as major transcriptional regulators in biology. They are characterized by two tandem bromodomains (BDs) that bind to lysine-acetylated histones and transcription factors, recruit transcription factors and coactivators to target gene sites, and activate RNA polymerase II machinery for transcriptional elongation. Pharmacological inhibition of BET proteins with BD inhibitors has been shown as a promising therapeutic strategy for the treatment of many human diseases including cancer and inflammatory disorders. The recent advances in bromodomain protein biology have further uncovered the complex and versatile functions of BET proteins in the regulation of gene expression in chromatin. In this review article, we highlight our current understanding of BET proteins' functions in mediating protein-protein interactions required for chromatin-templated gene transcription and splicing, chromatin remodeling, DNA replication, and DNA damage repair. We further discuss context-dependent activator vs. repressor functions of individual BET proteins, isoforms, and bromodomains that may be harnessed for future development of BET bromodomain inhibitors as emerging epigenetic therapies for cancer and inflammatory disorders.

Repeated mild traumatic brain injury results in long-term white-matter disruption.

Mild traumatic brain injury (mTBI) is an increasing public health concern as repetitive injuries can exacerbate existing neuropathology and result in increased neurologic deficits. In contrast to other models of repeated mTBI (rmTBI), our study focused on long-term white-matter abnormalities after bilateral mTBIs induced 7 days apart. A controlled cortical impact (CCI) was used to induce an initial mTBI to the right cortex of Single and rmTBI Sprague Dawley rats, followed by a second injury to the left cortex of rmTBI animals. Shams received only a craniectomy. Ex vivo diffusion tensor imaging (DTI), transmission electron microscopy (TEM), and histology were performed on the anterior corpus callosum at 60 days after injury. The rmTBI animals showed a significant bilateral increase in radial diffusivity (myelin), while only modest changes in axial diffusivity (axonal) were seen between the groups. Further, the rmTBI group showed an increased g-ratio and axon caliber in addition to myelin sheath abnormalities using TEM. Our DTI results indicate ongoing myelin changes, while the TEM data show continuing axonal changes at 60 days after rmTBI. These data suggest that bilateral rmTBI induced 7 days apart leads to progressive alterations in white matter that are not observed after a single mTBI.

Outcomes comparison of HeRO and lower extremity arteriovenous grafts in patients with long-standing renal failure.

OBJECTIVE: The Hemodialysis Reliable Outflow (HeRO) graft is becoming a recognized alternative to lower extremity arteriovenous grafts (LEAVGs) as an option for patients who have exhausted traditional upper extremity access; however, which should be applied preferentially is unclear. METHODS: A retrospective review of LEAVG and HeRO implants from January 2004 to August 2010 was performed. Patient demographics, medical history, procedural data, and outcomes were evaluated. RESULTS: Within the time periods, 60 HeROs were placed in 59 patients and 22 LEAVGs were placed in 21 patients. Demographics were similar between the two groups for many factors; however, the patients who underwent HeRO placement had significantly higher body mass index compared with the LEAVG group. Mean follow-up was 13.9 months for the HeRO group and 11.9 months for the LEAVG group. The HeRO patients underwent a mean of 6.3 previous tunneled dialysis catheter insertions and 3.1 previous AVG/arteriovenous fistula placements. The LEAVG patients underwent placement of a mean of 4.1 previous tunneled dialysis catheters and 2.6 previous AVG/arteriovenous fistulas. The principal difference was the number of interventions to maintain patency, which was 2.21 per year in the HeRO group and 1.17 per year in the AVG group (P = .003) Secondary patency at 6 months was 77% for the HeRO patients and 83% for the LEAVG patients (P = .14). The HeRO and LEAVG groups had no difference in infection rate per 1000 days (0.61 vs 0.71; P = .77) or mortality rate (22% vs 19% respectively; P = .22) at 6 months. CONCLUSIONS: In access challenged patients, LEAVG and HeRO offer similar rates of secondary patency, infection, and all-cause mortality. The LEAVG required fewer interventions to maintain patency, and the HeRO maintains the benefit of utilizing the upper extremity site of venous drainage. In our practice, we prefer the HeRO to LEAVG, especially in patients with peripheral arterial disease and in the obese population, because it preserves lower extremity access options.

Achilles tendon lengthening: friend or foe in the diabetic foot?

BACKGROUND: Literature in the past decade has shown that Achilles tendon-lengthening surgery in addition to total contact casting decreases the rate of plantar ulcer recurrence in the forefoot and midfoot; however, the risk of heel ulceration or recurrent equinus deformity with new forefoot or midfoot wounds is not insignificant. The purpose of this study was to compare the rate of recurrent ulceration between the patient groups who have undergone soft-tissue repair of diabetic forefoot or midfoot wounds either with or without concomitant Achilles tendon-lengthening surgery. METHODS: All diabetic patients with plantar forefoot or midfoot ulceration who underwent soft-tissue reconstruction during two different time periods-from 1983 to 1991 or from 1996 to 2004-were reviewed. Multiple patient-related factors were compared. The "early group" consisted of 179 wounds in 149 patients who underwent wound closure surgery alone. The "later group" included 145 wounds in 138 patients who underwent similar wound closure procedures with the addition of Achilles tendon-lengthening surgery. RESULTS: Twenty-five percent in the early group and 2 percent of patients in the later group developed recurrent ulceration requiring reoperation, which resulted in 94 percent relative risk reduction (p < 0.001), whereas the risk factors and demographic data were similar in each group. In addition, 12 percent in the early group and 4 percent of the later group developed transfer lesions (p < 0.001). CONCLUSION: If one avoids excessive Achilles lengthening, the addition of an Achilles tendon-lengthening procedure can significantly reduce the risk of recurrent diabetic foot ulcerations. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.