Phosphorylation and degradation of tomosyn-2 de-represses insulin secretion.

The abundance and functional activity of proteins involved in the formation of the SNARE complex are tightly regulated for efficient exocytosis. Tomosyn proteins are negative regulators of exocytosis. Tomosyn causes an attenuation of insulin secretion by limiting the formation of the SNARE complex. We hypothesized that glucose-dependent stimulation of insulin secretion from ß-cells must involve reversing the inhibitory action of tomosyn. Here, we show that glucose increases tomosyn protein turnover. Within 1 h of exposure to 15 mM glucose, ~50% of tomosyn was degraded. The degradation of tomosyn in response to high glucose was blocked by inhibitors of the proteasomal pathway. Using (32)P labeling and mass spectrometry, we showed that tomosyn-2 is phosphorylated in response to high glucose, phorbol esters, and analogs of cAMP, all key insulin secretagogues. We identified 11 phosphorylation sites in tomosyn-2. Site-directed mutagenesis was used to generate phosphomimetic (Ser → Asp) and loss-of-function (Ser → Ala) mutants. The Ser → Asp mutant had enhanced protein turnover compared with the Ser → Ala mutant and wild type tomosyn-2. Additionally, the Ser → Asp tomosyn-2 mutant was ineffective at inhibiting insulin secretion. Using a proteomic screen for tomosyn-2-binding proteins, we identified Hrd-1, an E3-ubiquitin ligase. We showed that tomosyn-2 ubiquitination is increased by Hrd-1, and knockdown of Hrd-1 by short hairpin RNA resulted in increased abundance in tomosyn-2 protein levels. Taken together, our results reveal a mechanism by which enhanced phosphorylation of a negative regulator of secretion, tomosyn-2, in response to insulin secretagogues targets it to degradation by the Hrd-1 E3-ubiquitin ligase.

SORCS1 is necessary for normal insulin secretory granule biogenesis in metabolically stressed ß cells.

We previously positionally cloned Sorcs1 as a diabetes quantitative trait locus. Sorcs1 belongs to the Vacuolar protein sorting-10 (Vps10) gene family. In yeast, Vps10 transports enzymes from the trans-Golgi network (TGN) to the vacuole. Whole-body Sorcs1 KO mice, when made obese with the leptin(ob) mutation (ob/ob), developed diabetes. ß Cells from these mice had a severe deficiency of secretory granules (SGs) and insulin. Interestingly, a single secretagogue challenge failed to consistently elicit an insulin secretory dysfunction. However, multiple challenges of the Sorcs1 KO ob/ob islets consistently revealed an insulin secretion defect. The luminal domain of SORCS1 (Lum-Sorcs1), when expressed in a ß cell line, acted as a dominant-negative, leading to SG and insulin deficiency. Using syncollin-dsRed5TIMER adenovirus, we found that the loss of Sorcs1 function greatly impairs the rapid replenishment of SGs following secretagogue challenge. Chronic exposure of islets from lean Sorcs1 KO mice to high glucose and palmitate depleted insulin content and evoked an insulin secretion defect. Thus, in metabolically stressed mice, Sorcs1 is important for SG replenishment, and under chronic challenge by insulin secretagogues, loss of Sorcs1 leads to diabetes. Overexpression of full-length SORCS1 led to a 2-fold increase in SG content, suggesting that SORCS1 is sufficient to promote SG biogenesis.

Postoperative management after hepatic resection.

Hepatic resection has become the mainstay of treatment for both primary and certain secondary malignancies. Outcomes after hepatic resection have significantly improved with advances in surgical and anesthetic techniques and perioperative care. Metabolic and functional changes after hepatic resection are unique and cause significant challenges in management. In-depth understanding of hepatic physiology is essential to properly address the postoperative issues. Strategies implemented in the postoperative period to improve outcomes include adequate nutritional support, proper glycemic control, and interventions to reduce postoperative infectious complications among several others. This review article focuses on the major postoperative issues after hepatic resection and presents the current management.

Stapled intestinal anastomoses in infants.

BACKGROUND: We reviewed our experience with stapled intestinal anastomoses in infants younger than 1 year and compared operative data and outcome to that of infants who underwent hand-sewn anastomoses. METHODS: Infants younger than 1 year who underwent an intestinal anastomosis over an 8-year period were identified. Stapled anastomoses were constructed in a side-to-side fashion using standard or endoscopic linear cutters. Outcome variables including operative time, anastomotic failure, and death were recorded. RESULTS: Two hundred ninety-five subjects were identified. Hand-sewn anastomoses were performed in 189 cases and stapled anastomoses in 106. Patients who had a stapled anastomosis were older (105 vs 44 days) and larger (5.2 vs 3.1 kg), although 25 stapled anastomoses were performed in infants between 600 and 1000 g. When a stapled anastomosis was used operative time was significantly reduced overall (102 vs 128 minutes) and for individual procedures including resection for necrotizing enterocolitis (85 vs 132 minutes) and colostomy closure (104 vs 141 minutes). There was no difference between hand-sewn and stapled anastomoses in the incidence of adhesive obstruction, stricture, or leak. CONCLUSIONS: When permitted by intestinal size in infants younger than 1 year, stapled anastomoses were safe and effective and significantly reduced operative time.