A 450-kDa human epidermal autoantigen was originally identified as a protein that reacted with the serum from an individual with a subepidermal blistering disease. Molecular cloning of this protein has now shown that it contains 5065 amino acids and has a molecular mass of 552 kDa. As reported previously this protein, which we call epiplakin, belongs to the plakin family, but it has some very unusual features. Epiplakin has 13 domains that are homologous to the B domain in the COOH-terminal region of desmoplakin. The last five of these B domains, together with their associated linker regions, are particularly strongly conserved. However, epiplakin lacks a coiled-coil rod domain and an aminoterminal domain, both of which are found in all other known members of the plakin family. Furthermore, no dimerization motif was found in the sequence. Thus, it is likely that epiplakin exists in vivo as a single-chain structure. Epitope mapping experiments showed that the original patient's serum recognized a sequence unique to epiplakin, which was not found in plectin. Immunofluorescence staining revealed the presence of epiplakin in whole sheets of epidermis and esophagus, in glandular cells of eccrine sweat and parotid glands and in mucous epithelial cells in the stomach and colon.Clarification of the basic structure of desmoplakin has been followed by the identification of many related proteins, such as BPAG1, 1 plectin, envoplakin, and periplakin (1-7). These proteins form a family known as the "plakin family" (8). Almost all members of this family have a common structure, with predicted globular amino-terminal and COOH-terminal domains that are separated by a central rod domain. Some homologous domain structures have been identified in both globular domains of many plakins, while the central domain is rich in heptad repeats and is believed to form a parallel ␣-helical coiled-coil structure with a dimerization partner (9). As suggested by this model, it has been demonstrated that desmoplakin I can form homodimers in vitro (10). Early investigations revealed that the COOH-terminal domains of plakins are involved in binding to intermediate filaments (11)(12)(13). The amino-terminal domains of desmoplakin and of BPAG1 are believed to bind to desmosomes or hemidesmosomes. Furthermore, some splicing variants of plectin and BPAG1 have actinor microtubule-binding domains at their amino termini, and it has been proposed that these domains form cross-links between microfilaments and/or microtubules and intermediate filaments (14 -16). Studies of a few inheritable diseases that appear to involve plectin or desmoplakin and of a BPAG1 null mouse have shown that each plakin plays a critical role in the tissue integrity in specific tissues (5,(17)(18)(19). Moreover, it seems likely that, in many autoimmune blistering diseases, plakins, located in the epidermis, might be target antigens, and these plakins are used for markers of specific diseases (2, 20 -22). However, their pathological roles remain to be clarified. Several years ago ...

Background: NASH is a disease characterized by fat accumulation and chronic inflammation in the liver. Results: Pin1 expression was increased in NASH model mouse livers. Pin1 KO mice were resistant to NASH development. Conclusion: Pin1 plays critical roles in NASH development. Significance: A Pin1 inhibitor might be a novel agent for treating NASH.

Glucose transporter 1 (GLUT1) is widely distributed throughout various tissues and contributes to insulin-independent basal glucose uptake. Using a split-ubiquitin membrane yeast two-hybrid system, we newly identified 4F2 heavy chain (4F2hc) as a membrane protein interacting with GLUT1. Though 4F2hc reportedly forms heterodimeric complexes between amino acid transporters, such as LAT1 and LAT2, and regulates amino acid uptake, we investigated the effects of 4F2hc on GLUT1 expression and the associated glucose uptake. First, FLAG-tagged 4F2hc and hemagglutinin-tagged GLUT1 were overexpressed in human embryonic kidney 293 cells and their association was confirmed by coimmunoprecipitation. The green fluorescent protein-tagged 4F2hc and DsRed-tagged GLUT1 showed significant, but incomplete, colocalization at the plasma membrane. In addition, an endogenous association between GLUT1 and 4F2hc was demonstrated using mouse brain tissue and HeLa cells. Interestingly, overexpression of 4F2hc increased the amount of GLUT1 protein in HeLa and HepG2 cells with increased glucose uptake. In contrast, small interfering RNA (siRNA)-mediated 4F2hc gene suppression markedly reduced GLUT1 protein in both cell types, with reduced glucose uptake. While GLUT1 mRNA levels were not affected by overexpression or gene silencing of 4F2hc, GLUT1 degradation after the addition of cycloheximide was significantly suppressed by 4F2hc overexpression and increased by 4F2hc siRNA treatment. Taken together, these observations indicate that 4F2hc is likely to be involved in GLUT1 stabilization and to contribute to the regulation of not only amino acid but also glucose metabolism.

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Background: Par14 is a parvulin-type peptidyl-prolyl cis/trans isomerase homologous with Pin1, but its functions remain largely unknown. Results: Par14 markedly enhanced insulin signaling by associating with IRS-1, and hepatic overexpression of Par14 normalized hyperglycemia in diabetic mice. Conclusion: Par14 exhibits an insulin-sensitizing effect. Significance: This is the first report showing the roles of Par14 in metabolism and signal transduction.