Observing the nonvectorial yet cotranslational folding of a multidomain protein, LDL receptor, in the ER of mammalian cells.

Proteins have evolved by incorporating several structural units within a single polypeptide. As a result, multidomain proteins constitute a large fraction of all proteomes. Their domains often fold to their native structures individually and vectorially as each domain emerges from the ribosome or the protein translocation channel, leading to the decreased risk of interdomain misfolding. However, some multidomain proteins fold in the endoplasmic reticulum (ER) nonvectorially via intermediates with nonnative disulfide bonds, which were believed to be shuffled to native ones slowly after synthesis. Yet, the mechanism by which they fold nonvectorially remains unclear. Using two-dimensional (2D) gel electrophoresis and a conformation-specific antibody that recognizes a correctly folded domain, we show here that shuffling of nonnative disulfide bonds to native ones in the most N-terminal region of LDL receptor (LDLR) started at a specific timing during synthesis. Deletion analysis identified a region on LDLR that assisted with disulfide shuffling in the upstream domain, thereby promoting its cotranslational folding. Thus, a plasma membrane-bound multidomain protein has evolved a sequence that promotes the nonvectorial folding of its upstream domains. These findings demonstrate that nonvectorial folding of a multidomain protein in the ER of mammalian cells is more coordinated and elaborated than previously thought. Thus, our findings alter our current view of how a multidomain protein folds nonvectorially in the ER of living cells.

Factors predicting survival and pathological subtype in patients with ampullary adenocarcinoma.

BACKGROUND: Carcinoma of the ampulla of Vater is uncommon. This study aimed to clarify predictors of survival for ampullary adenocarcinoma and to identify characteristics of its two major pathological subtypes. METHODS: Medical records were reviewed for 86 patients who underwent curative resection for ampullary adenocarcinoma between 2000 and 2012 at 12 principal hospitals in Kagawa, Japan. RESULTS: Resection was most common among 75-79-year-old patients. Actuarial 1-, 3-, and 5-year postoperative survival rates for ampullary adenocarcinoma were 90%, 72.3%, and 69.1%, respectively. Preoperative biliary drainage; serum CA19-9 and total bilirubin levels; pathological grade; perineural, vascular, pancreatic, and duodenal invasion; nodal metastasis; UICC-T stage; and pancreatobiliary subtype were predictors of poor survival. An elevated serum CA19-9 level; an elevated total bilirubin level; lymphatic, vascular, perineural, and pancreatic invasion; and advanced overall tumor stage were more common in patients with pancreatobiliary-type tumors than in patients with intestinal-type tumors. Additionally, pathologic subtype analysis showed that each subtype had distinct prognostic factors. CONCLUSIONS: Preoperative elevated serum CA19-9 and total bilirubin levels are prognostic factors for ampullary adenocarcinoma, and are both associated with pancreatobiliary-type tumors. Surgeons should be aware of these factors because pancreatobiliary-type adenocarcinoma is aggressively invasive and is associated with poor survival.