Capsaicin Modifies Responses of Rat Chorda Tympani Nerve Fibers to NaCl

Single-fiber preparations of the rat chorda tympani (CT) nervewere used to study the mechanism of action of capsaicin on salt-tastetransduction. Capsaicin selectively suppressed the responsesto NaCl of the CT nerve fibers (N-fibers) that are sodium-specific(insensitive or poorly sensitive to potassium). Among the morebroadly responsive, cation-sensitive fibers (E-fibers) thereare two subtypes, both of which responded to capsaicin but indifferent ways (‘enhanced’ type and ‘suppressed’type). In both N- and E-fibers, 5% ethanol (the vehicle forcapsaicin) slightly reduced the response to 100 mM NaCl. Thesuppressive effect of capsaicin on the response of the N-typefibers to 100 mM NaCl was significantly stronger than the effectof 5% ethanol. The suppression lasted for at least 20 s afterthe simultaneous application of 100 p.p.m. capsaicin-100 mMNaCl. These results indicate that 100 p.p.m. capsaicin can modifythe response of CT fibers to NaCl. The observed effect of capsaicinon gustatory fibers could be the net result of opposite suppressiveand enhancing processes in the taste buds cells and excitedintra- or extragemmal trigeminal nerve endings. Chem. Senses22: 249–255, 1997. ^*These authors contributed equally to this study     

Protein tyrosine phosphatase LMW-PTP exhibits distinct roles between vascular endothelial and smooth muscle cells

The present study examined the cellular functions of low-molecular-weight protein tyrosine phosphatase (LMW-PTP), which consists of two active isoforms IF-1 and IF-2, in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), focusing on cell growth and migration. We transduced recombinant IF-1 and IF-2, and ribozyme targeting both isoforms using an adenovirus vector in these cells. We detected the expression of IF-1 and IF-2 in both types of cells. IF-1 as well as IF-2 inhibited PDGF-induced DNA synthesis and migration in VSMCs. In contrast, both isoforms enhanced lysophosphatidic acid-stimulated cell migration without change in DNA synthesis in ECs. Whereas there is a report indicating that reactive oxygen species-dependent inactivation of LMW-PTP regulates actin cytoskeleton reorganization during cell spreading and migration, the isoforms conversely suppressed the PDGF-induced H2O2 generation with subsequent decrease in the p38 activity in VSMCs. Catalytically inactive LMW-PTP exerted the opposite and similar effects to the wild type in ECs and in VSMCs, respectively, suggesting that substrates for the phosphatase differ between these cells. Moreover, high concentrations of glucose suppressed the expression of LMW-PTP in both cells. These data suggest that LMW-PTP negatively regulates the pathogenesis of atherosclerosis and that glucose-dependent suppression of LMW-PTP expression may promote the development of atherosclerosis in diabetics.     

Link between the ubiquitin conjugation system and the ISG15 conjugation system: ISG15 conjugation to the UbcH6 ubiquitin E2 enzyme

ISG15 is a ubiquitin-like protein that is upregulated on treatment with interferon. ISG15 is considered to be covalently conjugated to cellular proteins through a sequential reaction similar to that of the ubiquitin conjugation system consisting of E1/E2/E3 enzymes: UBE1L and UbcH8 have been reported to function as E1 and E2 enzymes, respectively, for ISG15 conjugation. Several cellular proteins have been identified as targets for ISG15 conjugation, but the roles of ISG15 conjugation remain unclear. In this study, we found that UbcH6 and UbcH8, E2 enzymes for ubiquitin conjugation, are covalently modified by ISG15. We also found that UbcH6 is capable of forming a thioester intermediate with ISG15 through Cys131. We determined that the Lys136 residue near the catalytic site Cys131 is the ISG15 conjugation site in UbcH6. We isolated ISG15-modified and unmodified UbcH6 proteins, and analyzed their abilities to form thioester intermediates with ubiquitin. A ubiquitin thioester intermediate was detected in the case of unmodified UbcH6, but not in that of ISG15-modified UbcH6, strongly suggesting that ISG15 conjugation to UbcH6 suppresses its ubiquitin E2 enzyme activity. Thus, we provide evidence for a link between the ubiquitin conjugation system and the ISG15 conjugation system.     

Cytokeratin 18 is a specific marker of bovine intestinal M cell

Microfold (M) cells in the follicle-associated epithelium (FAE) of Peyer's patches have an important role in mucosal immune responses. A primary difficulty for investigations of bovine M cells is the lack of a specific molecular marker. To identify such a marker, we investigated the expression of several kinds of intermediate filament proteins using calf Peyer's patches. The expression patterns of cytokeratin (CK) 18 in jejunal and ileal FAE were very similar to the localization pattern of M cells recognized by scanning electron microscopy. Mirror sections revealed that jejunal CK18-positive cells had irregular and sparse microvilli, as well as pocket-like structures containing lymphocytes, typical morphological characteristic of M cells. However, CK18-negative cells had regular and dense microvilli on their surface, typical of the morphology of enterocytes. In contrast, CK20 immunoreactivity was detected in almost all villous epithelial cells and CK18-negative cells in the FAE. CK18-positive proliferating transit-amplifying cells in the crypt exchanged CK18 for CK20 above the mouth of the crypt and after moving to the villi; however, CK18-positive M cells in the crypt continued their expression of CK18 during movement to the FAE region. Terminal deoxynucleotidyl-transferase-mediated deoxyuridine-triphosphate-biotin nick-end labeling-positive apoptotic cells were specifically detected at the apical region of villi and FAE in the jejunum and ileum, and all were also stained for CK20. These data indicate that CK18 may be a molecular marker for bovine M cells in FAE and that M cells may transdifferentiate to CK20-positive enterocytes and die by apoptosis in the apex of the FAE.     

Involvement of Oct3/4 in the enhancement of neuronal differentiation of ES cells in neurogenesis-inducing cultures

Oct3/4 plays a critical role in maintaining embryonic stem cell pluripotency. Regulatable transgene-mediated sustained Oct3/4 expression in ES cells cultured in serum-free LIF-deficient medium caused accelerated differentiation to neuroectoderm-like cells that expressed Sox2, Otx1 and Emx2 and subsequently differentiated into neurons. Neurogenesis of ES cells is promoted by SDIA (stromal cell-derived inducing activity), which accumulates on the PA6 stromal cell surface. Oct3/4 expression in ES cells was maintained by SDIA whereas without it expression was promptly downregulated. Suppression of Oct3/4 abolished neuronal differentiation even after stimulation by SDIA. In contrast, sustained upregulated Oct3/4 expression enhanced SDIA-mediated neurogenesis of ES cells. Therefore, Oct3/4 appears to promote neuroectoderm formation and subsequent neuronal differentiation from ES cells.     

Properties of rice cooked with commercial water-soluble soybean polysaccharides extracted under weakly acidic conditions from soybean cotyledons

It has been found that commercial water-soluble soybean polysaccharides (SSPS) can make cooked rice and noodles non-sticky and prevent rice grains and noodles from adhering to each other. We studied in detail the phenomenon of rice cooked with SSPS. We assumed that the phenomenon resulted from the interaction between SSPS and starch during cooking, and studied the effects of SSPS on the gelatinizing behavior of rice starch by using a Rapid-Visco-Analyzer. The addition of SSPS reduced the viscosity of the gelatinized starch. This lower final viscosity of the rice starch was more distinct from than that of potato starch. These results imply that the properties of SSPS in forming a non-sticky condition might result from a decrease in the viscosity of the gelatinized starch.     

Rho and Rab Small G Proteins Coordinately Reorganize Stress Fibers and Focal Adhesions in MDCK Cells

The Rho subfamily of the Rho small G protein family (Rho) regulates formation of stress fibers and focal adhesions in many types of cultured cells. In moving cells, dynamic and coordinate disassembly and reassembly of stress fibers and focal adhesions are observed, but the precise mechanisms in the regulation of these processes are poorly understood. We previously showed that 12-O-tetradecanoylphorbol-13-acetate (TPA) first induced disassembly of stress fibers and focal adhesions followed by their reassembly in MDCK cells. The reassembled stress fibers showed radial-like morphology that was apparently different from the original. We analyzed here the mechanisms of these TPA-induced processes. Rho inactivation and activation were necessary for the TPA-induced disassembly and reassembly, respectively, of stress fibers and focal adhesions. Both inactivation and activation of the Rac subfamily of the Rho family (Rac) inhibited the TPA-induced reassembly of stress fibers and focal adhesions but not their TPA-induced disassembly. Moreover, microinjection or transient expression of Rab GDI, a regulator of all the Rab small G protein family members, inhibited the TPA-induced reassembly of stress fibers and focal adhesions but not their TPA-induced disassembly, indicating that, furthermore, activation of some Rab family members is necessary for their TPA-induced reassembly. Of the Rab family members, at least Rab5 activation was necessary for the TPA-induced reassembly of stress fibers and focal adhesions. The TPA-induced, small G protein-mediated reorganization of stress fibers and focal adhesions was closely related to the TPA-induced cell motility. These results indicate that the Rho and Rab family members coordinately regulate the TPA-induced reorganization of stress fibers and focal adhesions that may cause cell motility.     

The Future Vocation of Neural Stem Cells: Lineage Commitment in Brain Development and Evolution

Understanding the fate commitment of neural stem cells is critical to identify the regulatory mechanisms in developing brains. Genetic lineage-tracing has provided a powerful strategy to unveil the heterogeneous nature of stem cells and their descendants. However, recent studies have reported controversial data regarding the heterogeneity of neural stem cells in the developing mouse neocortex, which prevents a decisive conclusion on this issue. Here, we review the progress that has been made using lineage-tracing analyses of the developing neocortex and discuss stem cell heterogeneity from the viewpoint of comparative and evolutionary biology.