Adiponectin is associated with obesity and insulin resistance. To date, there has been no genome-wide association study (GWAS) of adiponectin levels in Asians. Here we present a GWAS of a cohort of Korean volunteers. A total of 4,001 subjects were genotyped by using a genome-wide marker panel in a two-stage design (979 subjects initially and 3,022 in a second stage). Another 2,304 subjects were used for follow-up replication studies with selected markers. In the discovery phase, the top SNP associated with mean log adiponectin was rs3865188 in CDH13 on chromosome 16 (p = 1.69 × 10(-15) in the initial sample, p = 6.58 × 10(-39) in the second genome-wide sample, and p = 2.12 × 10(-32) in the replication sample). The meta-analysis p value for rs3865188 in all 6,305 individuals was 2.82 × 10(-83). The association of rs3865188 with high-molecular-weight adiponectin (p = 7.36 × 10(-58)) was even stronger in the third sample. A reporter assay that evaluated the effects of a CDH13 promoter SNP in complete linkage disequilibrium with rs3865188 revealed that the major allele increased expression 2.2-fold. This study clearly shows that genetic variants in CDH13 influence adiponectin levels in Korean adults.

In a process seeking out a good model cell line for Epstein-Barr virus (EBV)-associated gastric cancer, we found that one previously established gastric adenocarcinoma cell line is infected with type 1 EBV. This SNU-719 cell line from a Korean patient expressed cytokeratin without CD19 or CD21 expression. In SNU-719, EBNA1 and LMP2A were expressed, while LMP1 and EBNA2 were not. None of the tested lytic EBV proteins were detected in this cell line unless stimulated with phorbol ester. EBV infection was also shown in the original carcinoma tissue of SNU-719 cell line. Our results support the possibility of a CD21-independent EBV infection of gastric epithelial cells in vivo. As the latent EBV gene expression pattern of SNU-719 closely resembles that of the EBV-associated gastric cancer, this naturally derived cell line may serve as a valuable model system to clarify the precise role of EBV in gastric carcinogenesis.

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The ubiquitin fusion degradation (UFD) pathway is a proteolytic system conserved in yeast and mammals in which an uncleavable ubiquitin moiety linked to the N terminus of a protein functions as a degradation signal of the fusion protein. Although key components of the UFD pathway in yeast have been identified, the E3 enzyme of the human UFD pathway has not been studied. In this work, we show that TRIP12 is the E3 enzyme of the human UFD pathway. Thus, TRIP12 catalyzes in vitro ubiquitination of UFD substrates in conjunction with E1, E2, and E4 enzymes. Knockdown of TRIP12 stabilizes not only artificial UFD substrates but a physiological substrate UBB ؉1. Moreover, TRIP12 knockdown reduces UBB ؉1-induced cell death in human neuroblastoma cells. Surprisingly, complementation of TRIP12 knockdown cells with the TRIP12 HECT domain mostly restores efficient degradation of UFD substrates, indicating that the TRIP12 HECT domain can act as the E3 enzyme for the UFD pathway in human cells. The TRIP12 HECT domain directs ubiquitination of UFD substrates in vitro and can be specifically cross-linked to the ubiquitin moiety of the substrates in vivo, suggesting that the TRIP12 HECT domain possesses a noncovalent ubiquitin-binding site. In addition, we demonstrate that Ub⌬GG, a mutant ubiquitin that cannot be conjugated to other proteins, is a substrate of the TRIP12 HECT domain both in vivo and in vitro, indicating that the C-terminal extension fused to the uncleavable ubiquitin is not required for substrate recognition in the UFD pathway. These results provide new insights into the mechanism of the mammalian UFD pathway and the functional nonequivalence of different HECT domains.Ubiquitin-dependent proteolysis plays an important role in various cellular events, such as cell cycle regulation and signal transduction (1). The covalent conjugation of ubiquitin to a target protein involves an enzyme cascade. The ubiquitin-activating enzyme (E1) 2 activates ubiquitin in an ATP-dependent reaction by forming a thioester bond with the C-terminal glycine of ubiquitin. The ubiquitin is then transferred to a specific sulfhydryl group on a ubiquitin-conjugating enzyme (E2). A ubiquitin-protein ligase (E3) transfers the activated ubiquitin from E2 to a lysine residue of a bound substrate, forming an isopeptide bond. Substrate specificity is determined primarily by E3, which binds both the protein substrate and the cognate E2. Once the multiubiquitin chain is assembled on a protein substrate, the target protein is recognized and degraded by the 26S proteasome (1-3). E3 enzymes are classified into two main families: HECT (homologous to E6AP C terminus) domain E3s and RING (really interesting new gene) domain E3s (2). Members of the HECT family contain a diverse N-terminal region and a conserved C-terminal HECT domain, which has a reactive Cys residue. HECT E3s form a thioester intermediate with ubiquitin at the conserved Cys residue before transfer of ubiquitin to substrates (4), whereas RING E3s do not form a covalent bond with ubiquitin....

Marie Unna hereditary hypotrichosis (MUHH) is a rare autosomal dominant hair disorder. Through the study of a mouse model, we identified a mutation in the 5'-untranslated region of the hairless (HR) gene in patients with MUHH in a Caucasian family. The corresponding mutation, named 'hairpoor', was found in mutant mice that were generated through N-ethyl-N-nitrosourea mutagenesis. Hairpoor mouse mutants display partial hair loss at an early age and progress to near alopecia, which resembles the MUHH phenotype. This mutation conferred overexpression of HR through translational derepression and, in turn, decreased the expression of Sfrp2, an inhibitor of the Wnt signaling pathway. This study indicates that the gain in function of HR also results in alopecia, as seen with the loss of function of HR, via abnormal upregulation of the Wnt signaling pathway.

Osmotic stress causes profound perturbations of cell functions. Although the adaptive responses required for cell survival upon osmotic stress are being unraveled, little is known about the effects of osmotic stress on ubiquitin-dependent proteolysis. We now report that hyperosmotic stress inhibits proteasome activity by activating p38 MAPK. Osmotic stress increased the level of polyubiquitinated proteins in the cell. The selective p38 inhibitor SB202190 decreased osmotic stress-associated accumulation of polyubiquitinated proteins, indicating that p38 MAPK plays an inhibitory role in the ubiquitin proteasome system. Activated p38 MAPK stabilized various substrates of the proteasome and increased polyubiquitinated proteins. Proteasome preparations purified from cells expressing activated p38 MAPK had substantially lower peptidase activities than control proteasome samples. Proteasome phosphorylation sites dependent on p38 were identified by measuring changes in the extent of proteasome phosphorylation in response to p38 MAPK activation. The residue Thr-273 of Rpn2 is the major phosphorylation site affected by p38 MAPK. The mutation T273A in Rpn2 blocked the proteasome inhibition that is mediated by p38 MAPK. These results suggest that p38 MAPK negatively regulates the proteasome activity by phosphorylating Thr-273 of Rpn2.

Several types of genetic and epigenetic regulation have been implicated in the development of drug resistance, one significant challenge for cancer therapy. Although changes in the expression of non-coding RNA are also responsible for drug resistance, the specific identities and roles of them remain to be elucidated. Long non-coding RNAs (lncRNAs) are a type of ncRNA (> 200 nt) that influence the regulation of gene expression in various ways. In this study, we aimed to identify differentially expressed lncRNAs in 5-fluorouracil-resistant colon cancer cells. Using two pairs of 5-FU-resistant cells derived from the human colon cancer cell lines SNU-C4 and SNU-C5, we analyzed the expression of 90 lncRNAs by qPCR-based profiling and found that 19 and 23 lncRNAs were differentially expressed in SNU-C4R and SNU-C5R cells, respectively. We confirmed that snaR and BACE1AS were downregulated in resistant cells. To further investigate the effects of snaR on cell growth, cell viability and cell cycle were analyzed after transfection of siRNAs targeting snaR. Down-regulation of snaR decreased cell death after 5-FU treatment, which indicates that snaR loss decreases in vitro sensitivity to 5-FU. Our results provide an important insight into the involvement of lncRNAs in 5-FU resistance in colon cancer cells.

The 26S proteasome, composed of the 20S core and the 19S regulatory complex, plays a central role in ubiquitin-dependent proteolysis by catalyzing degradation of polyubiquitinated proteins. In a search for proteins involved in regulation of the proteasome, we affinity purified the 19S regulatory complex from HeLa cells and identified a novel protein of 43 kDa in size as an associated protein. Immunoprecipitation analyses suggested that this protein specifically interacted with the proteasomal ATPases. Hence the protein was named proteasomal ATPase-associated factor 1 (PAAF1). Immunoaffinity purification of PAAF1 confirmed its interaction with the 19S regulatory complex and further showed that the 19S regulatory complex bound with PAAF1 was not stably associated with the 20S core. Overexpression of PAAF1 in HeLa cells decreased the level of the 20S core associated with the 19S complex in a dose-dependent fashion, suggesting that PAAF1 binding to proteasomal ATPases inhibited the assembly of the 26S proteasome. Proteasomal degradation assays using reporters based on green fluorescent protein revealed that overexpression of PAAF1 inhibited the proteasome activity in vivo. Furthermore, the suppression of PAAF1 expression that is mediated by small inhibitory RNA enhanced the proteasome activity. These results suggest that PAAF1 functions as a negative regulator of the proteasome by controlling the assembly/disassembly of the proteasome.