All plakin family proteins are known to be autoantigens in paraneoplastic pemphigus (PNP). In this study, we first examined whether PNP sera also react with epiplakin, another plakin protein, by various immunological methods using 48 Japanese PNP sera. Immunofluorescence confirmed that cultured keratinocytes expressed epiplakin. Epiplakin was detected by 72.9% of PNP sera by immunoprecipitation-immunoblotting with KU-8 cell extract, but not by immunoblotting of either normal human epidermal extract or KU-8 cell extract. Epiplakin was essentially not detected by 95 disease and normal control sera. Statistical analyses of various clinical and immunological findings revealed significant correlation of the presence of anti-epiplakin antibodies with both bronchiolitis obliterans and mortality. No epiplakin-negative PNP case developed bronchiolitis obliterans. However, although 29.4% of European PNP patients had bronchiolitis obliterans, significant correlation with anti-epiplakin autoantibodies was not observed. In further studies for lung, immunofluorescence showed the presence of epiplakin in normal human lung, particularly respiratory bronchiole, immunoprecipitation-immunoblotting showed that PNP sera reacted with epiplakin in cultured lung cells, and mice injected with polyclonal antibody specific to epiplakin histopathologically showed abnormal changes in small airway epithelia. These results indicated that epiplakin is one of major PNP autoantigens and is related to PNP-related bronchiolitis obliterans.Journal of Investigative Dermatology accepted article preview online, 19 October 2015. doi:10.1038/jid.2015.408.

Epiplakin (EPPK) was originally identified as a human epidermal autoantigen. To identify the function of epiplakin, we generated epiplakin "knockout" mice. These mice developed normally, with apparently normal epidermis and hair. Electron microscopy after immunostaining revealed the presence of EPPK adjacent to keratin filaments in wild-type mice, suggesting that epiplakin might associate with keratin. The appearance and localization of keratin bundles in intact epidermal keratinocytes of EPPK ؊/؊ mice were similar to those in wild-type mice. Wounds on the backs of EPPK ؊/؊ mice closed more rapidly than those on the backs of wild-type and heterozygous mice. The outgrowth of keratinocytes from skin explants from knockout mice was enhanced compared to outgrowth from explants from wild-type mice, even in the presence of mitomycin C, suggesting that the difference in keratinocyte outgrowth might be due to a difference in the speed of migration of keratinocytes. At wound edges in wild-type mice, EPPK was expressed in proliferating keratinocytes in conjunction with keratin 6. In EPPK ؊/؊ mice, no similar proliferating keratinocytes were observed, but migrating keratinocytes weakly expressed keratin 6. EPPK was coexpressed with keratin 6 in some keratinocytes in explant cultures from wild mice. We propose that EPPK might be linked functionally with keratin 6. Epiplakin (EPPK) was originally identified as an autoantigen that reacted with serum from an individual with subepidermal blistering disease (5, 6). Human EPPK is a 552-kDa protein that is expressed not only in sheets of epidermis and the esophagus, but also in the outer root sheath of hair follicles and in mucous epithelial cells (7).Epiplakin is homologous to plectin and other members of the plakin family, but it belongs to a novel category of plakins because of the following unusual features (Fig. 1). Human epiplakin has 13 domains, and mouse epiplakin has 16 domains, that are homologous to the B domain, which is one of the plakin repeat domains (PRDs) found in the carboxy-terminal region of desmoplakin, and these domains are distributed along the amino acid sequence with relatively uniform spacing (7, 21). The amino acid sequences of the last five (human) or eight (mouse) of these B domains, starting from the carboxyl terminus, together with their associated linker regions, are particularly strongly conserved. Epiplakin lacks the coiled-coil rod domain and the amino-terminal domain that are found in all other known members of the plakin family. Furthermore, there is no dimerization motif in the entire amino acid sequence. Thus, it is likely that EPPK exists in vivo as a single-chain structure (7). The unique features of the repeated structures in EPPK undoubtedly contribute to the protein's function in vivo.It seems likely that the carboxy-terminal regions, includingPRDs and linker regions, of proteins in the plakin family, such as desmoplakin, BPAG1 (an autoantigen of bullous pemphigoid), and plectin (a protein responsible for epidermolysis bullosa with muscu...

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Epiplakin1 (Eppk1) is a plakin family gene with its function remains largely unknown, although the plakin genes are known to function in interconnecting cytoskeletal filaments and anchoring them at plasma membrane‐associated adhesive junction. Here we analyzed the expression patterns of Eppk1 in the developing and adult pancreas in the mice. In the embryonic pancreas, Eppk1+/Pdx1+ and Eppk1+/Sox9+ pancreatic progenitor cells were observed in early pancreatic epithelium. Since Pdx1 expression overlapped with that of Sox9 at this stage, these multipotent progenitor cells are Eppk1+/Pdx1+/Sox9+ cells. Then Eppk1 expression becomes confined to Ngn3+ or Sox9+ endocrine progenitor cells, and p48+ exocrine progenitor cells, and then restricted to the duct cells and a cells at birth. In the adult pancreas, Eppk1 is expressed in centroacinar cells (CACs) and in duct cells. Eppk1 is observed in pancreatic intraepithelial neoplasia (PanIN), previously identified as pancreatic ductal adenocarcinoma (PDAC) precursor lesions. In addition, the expansion of Eppk1‐positive cells occurs in a caerulein‐induced acute pancreatitis, an acinar cell regeneration model. Furthermore, in the partial pancreatectomy (Px) regeneration model using mice, Eppk1 is expressed in “ducts in foci”, a tubular structure transiently induced. These results suggest that Eppk1 serves as a useful marker for detecting pancreatic progenitor cells in developing and regenerating pancreas.

Mesenchymal stem cells (MSCs) isolated from adult human tissues are capable of proliferating in vitro and maintaining their multipotency, making them attractive cell sources for regenerative medicine. However, the availability and capability of self-renewal under current preparation regimes are limited. Induced pluripotent stem cells (iPSCs) now offer an alternative, similar cell source to MSCs. Herein, we established new methods for differentiating hiPSCs into MSCs via mesoderm-like and neuroepithelium-like cells. Both derived MSC populations exhibited self-renewal and multipotency, as well as therapeutic potential in mouse models of skin wounds, pressure ulcers, and osteoarthritis. Interestingly, the therapeutic effects differ between the two types of MSCs in the disease models, suggesting that the therapeutic effect depends on the cell origin. Our results provide valuable basic insights for the clinical application of such cells.