Damage/recovery by additive on lipid membrane as a mimicry of human stratum corneum.

The effects of sodium dodecyl sulfate (SDS) on the model lipid membrane of human stratum corneum, composed of three main lipids of ceramide III, palmitic acid, and cholesterol, have been examined as a function of exposure period. Cholesterol first got to elute, palmitic acid followed it late, and the remaining solid was mainly ceramide III. The removal of lipids influenced the configurational structure of remaining lipid and the intralayer structure of lamellae. Monitoring of structural reorganization in the damaged membrane was carried out on the recovering procedure of palmitic acid and cholesterol. Both lipids were penetrated in the damaged membrane and recovered mostly the configurational lipid structure and the lamellar structure. Especially, it can be noted that cholesterol is more effective than palmitic acid on recovery.

Cellular stresses induce the nuclear accumulation of importin alpha and cause a conventional nuclear import block.

We report here that importin alpha accumulates reversibly in the nucleus in response to cellular stresses including UV irradiation, oxidative stress, and heat shock. The nuclear accumulation of importin alpha appears to be triggered by a collapse in the Ran gradient, resulting in the suppression of the nuclear export of importin alpha. In addition, nuclear retention and the importin beta/Ran-independent import of importin alpha also facilitate its rapid nuclear accumulation. The findings herein show that the classical nuclear import pathway is down-regulated via the removal of importin alpha from the cytoplasm in response to stress. Moreover, whereas the nuclear accumulation of heat shock cognate 70 is more sensitive to heat shock than the other stresses, importin alpha is able to accumulate in the nucleus at all the stress conditions tested. These findings suggest that the stress-induced nuclear accumulation of importin alpha can be involved in a common physiological response to various stress conditions.

Visual observation of selective elution of components from skin-mimetic lipid membrane.

Selective elution of components was visually observed on a mixture of lipids (ceramide III, palmitic acid, and cholesterol) as a mimicry of stratum corneum (SC) which was melted and sandwiched between glass plates. The lipid membrane was exposed to an aqueous solution of sodium dodecyl sulphate (SDS) and observed by an optical microscope. The contact of the lipid membrane with a SDS solution caused the elution of the lipid component as "myelin-form", and the lipid membrane changed to a sponge structure. An infrared absorption spectroscopic study revealed that the SDS penetrated into the lipid mixture, and the fraction of ceramide in the sponge phase became higher than that in the lipid membrane before SDS treatment. The selective elution behaviour was confirmed by observing the behaviour of each component in lipid membrane by means of a fluorescence-staining method: The cholesterol was eluted with producing visual myelin-form on the contact with a SDS solution, and the following elution of palmitic acid occurred without myelin-form, while the ceramide III resisted the exposure to the SDS solution. These results are valid to elucidate the influence of surfactants on SC.

Mechanism of the stress-induced collapse of the Ran distribution.

The small GTPase Ran plays a central role in several key nuclear functions, including nucleocytoplasmic transport, cell cycle progression, and assembly of the nuclear envelope. In a previous study, we showed that cellular stress induces the nuclear accumulation of importin alpha, and that this appears to be triggered by a collapse in the Ran gradient, leading to the down-regulation of classical nuclear transport. We report here that a decrease in stress-induced ATP is associated with an increase in cytoplasmic Ran levels. A luciferin-luciferase assay showed that cellular stress decreased the intracellular levels of ATP. Treatment of the cells with ATP-depleting agents altered the distribution of Ran. Furthermore, when exogenous ATP was introduced in oxidative stress-treated cells, a normal distribution of Ran was restored. In addition, a pull-down experiment with an importin beta1 variant that binds to RanGTP showed that oxidative stress was accompanied by a decrease in intracellular RanGTP levels. These findings indicate that the decrease in ATP levels induced by cellular stress causes a decrease in RanGTP levels and a collapse of Ran distribution.

In vivo dynamics and kinetics of pKi-67: transition from a mobile to an immobile form at the onset of anaphase.

A cell proliferation marker protein, pKi-67, distributes to the chromosome periphery during mitosis and nucleolar heterochromatin in the interphase. We report here on the structural domains of pKi-67 that are required for its correct distribution. While both the LR domain and the conserved domain were involved in localization to the nucleolar heterochromatin, both the LR domain and the Ki-67 repeat domain were required for its distribution to the mitotic chromosome periphery. Using in vivo time-lapse microscopy, GFP-pKi-67 was dynamically tracked from the mitotic chromosome periphery to reforming nucleoli via prenucleolar bodies (PNBs). The signals in PNBs then moved towards and fused into the reforming nucleoli with a thin string-like fluorescence during early G1 phase. An analysis of the in vivo kinetics of pKi-67 using photobleaching indicated that the association of pKi-67 with chromatin was progressively altered from "loose" to "tight" after the onset of anaphase. These findings indicate that pKi-67 dynamically alters the nature of the interaction with chromatin structure during the cell cycle, which is closely related to the reformation process of the interphase nucleolar chromatin.

Importin alpha transports CaMKIV to the nucleus without utilizing importin beta.

Ca(2+)/calmodulin-dependent protein kinase type IV (CaMKIV) plays an essential role in the transcriptional activation of cAMP response element-binding protein-mediated signaling pathways. Although CaMKIV is localized predominantly in the nucleus, the molecular mechanism of the nuclear import of CaMKIV has not been elucidated. We report here that importin alpha is able to carry CaMKIV into the nucleus without the need for importin beta or any other soluble proteins in digitonin-permeabilized cells. An importin beta binding-deficient mutant (DeltaIBB) of importin alpha also carried CaMKIV into the nucleus, which strongly suggests that CaMKIV is transported in an importin beta-independent manner. While CaMKIV directly interacted with the C-terminal region of importin alpha, the CaMKIV/importin alpha complex did not form a ternary complex with importin beta, which explains the nonrequirement of importin beta for the nuclear transport of CaMKIV. The cytoplasmic microinjection of importin alpha-DeltaIBB enhanced the rate of nuclear translocation of CaMKIV in vivo. This is the first report to demonstrate definitely that mammalian importin alpha solely carries a cargo protein into the nucleus without utilizing the classical importin beta-dependent transport system.

A synthesized pyrimidine compound, MS-818, promotes walking function recovery from crush injury of the sciatic nerve through its indirect stimulation of Schwann cells.

Purpose: We evaluated the effects of the drug MS-818 (2-piperadino-6-methyl-5-oxo-5,6-dihydro-(7H) pyrrolo-[3,4-d] pyrimidine maleate), a synthesized pyrimidine compound, on regeneration in crush-injured sciatic nerves of rats. Methods: MS-818 at 1.0 or 10 mg/kg or the vehicle was intraperitoneally injected into rats daity. The pinch test (PT) was performed 5 days after the operation. Walking function recovery was assessed by the sciatic nerve functional index (SFI). Time-dependent changes in the levels of transcripts of nerve growth factor (NGF) and apolipoprotein E (ApoE) genes were monitored by RT-PCR. NGF peptide levels retained in the crushed nerves of rats 5 days after surgery and in the culture medium of IMS32 cells, a mouse Schwann cell line, incubated for 24 h with high or low doses of MS-818, were measured by enzyme immunoassay. Results: The PT showed that MS-818 injection promoted axonal elongation by 19.3 % compared to the vehicle injected control (n = 7, *p < 0.03). The SFIs 3 weeks after injection of MS-818 at 1.0 mg/kg and 1 0 mg/kg were significantly increased to the control level (n = 5-6, **p < 0.006 and *p < 0.03, respectively). Injection of MS-818 at 1.0 mg/kg induced NGF gene expression more than twofold compared to that of the control at 5 to 6 days after surgery (n = 4). NGF levels in crushed nerves after MS-818 injection at 1.0 and 10 mg/kg tended to be higher than those of the vehicle-injected controls by approximately 20 %, although it did not reach statistical significance. Treatment of IMS32 cells with MS-818 failed to give rise to NGF overproduction and its secretion into the culture medium. Conclusions: These present evidences suggest that MS-818 enhances functional recovery of damaged sciatic nerves by promoting axonal sprouting through indirect activation of Schwann cells and that local production of NGF rnay be activated by MS-818.

Complex formation between Tap and p15 affects binding to FG-repeat nucleoporins and nucleocytoplasmic shuttling.

Mammalian Tap-p15 and yeast Mex67p-Mtr2p are conserved and essential mRNA export factor complexes that transport mRNPs through the nuclear pore. Here, we report that the small subunit p15 affects the binding of the large subunit Tap to repeat nucleoporins. BIAcore measurements revealed that recombinant Tap binds with high affinity (K(d) in the nm range) to repeat nucleoporins and dissociates from them very slowly. In contrast, when recombinant Tap was bound to p15, the derived heterodimeric complex exhibited a significant lower affinity to FG-repeat nucleoporins (K(d) in the microm range). Furthermore, when recombinant Tap lacking the N-terminal nuclear localization sequences (TapDeltaNLS) was microinjected in mammalian cells, it did not shuttle; however, TapDeltaNLS with bound p15 efficiently shuttles between nucleus and cytoplasm. We conclude that heterodimerization of Tap and p15 is required for shuttling of the functional Tap-p15 mRNA exporter complex.

A newly established neuronal rho-0 cell line highly susceptible to oxidative stress accumulates iron and other metals. Relevance to the origin of metal ion deposits in brains with neurodegenerative disorders.

From human neuroblastoma-derived SILA cells we have established a rho-0 cell line that is deficient in both respiration and mitochondrial DNA. Lactate dehydrogenase activity, lactate production, and growth in the medium without glucose indicate that these cells shift from aerobic to anaerobic metabolism. Electron microscopic observations revealed abnormal mitochondria with unique cristae structures. Staining with MitoTracker dye showed that the mitochondrial transmembrane potential was reduced by 30-40% from the parent cell levels. These cells were markedly susceptible to H(2)O(2) and died apparently by a necrotic mechanism, a process blocked by deferoxamine in the parent cells but not rho-0 cells. Analysis by inductively coupled plasma-mass spectrometry revealed an approximately 3-fold accumulation of iron in the rho-0 cells at confluence (n = 4-6, three clones, *p < 0.05). Iron and four other metals were all elevated in the cells of one of the rho-0 clones and were similar to control levels in the control cybrid cells, which were replenished with normal mitochondrial DNA. Their sensitivity to H(2)O(2) was also similar to that of the parent cells. These results indicate that a newly established neuronal related rho-0 cell line is highly susceptible to active oxygen species and that these toxicity effects appear to be related to an accumulation of transition metals, which probably occurs through the respiratory impairment.

Importin alpha can migrate into the nucleus in an importin beta- and Ran-independent manner.

A classical nuclear localization signal (NLS)-containing protein is transported into the nucleus via the formation of a NLS-substrate/importin alpha/beta complex. In this study, we found that importin alpha migrated into the nucleus without the addition of importin beta, Ran or any other soluble factors in an in vitro transport assay. A mutant importin alpha lacking the importin beta-binding domain efficiently entered the nucleus. Competition experiments showed that this import pathway for importin alpha is distinct from that of importin beta. These results indicate that importin alpha alone can enter the nucleus via a novel pathway in an importin beta- and Ran-independent manner. Furthermore, this process is evolutionarily conserved as similar results were obtained in Saccharomyces cerevisiae. Moreover, the import rate of importin alpha differed among individual nuclei of permeabilized cells, as demonstrated by time-lapse experiments. This heterogeneous nuclear accumulation of importin alpha was affected by the addition of ATP, but not ATPgammaS. These results suggest that the nuclear import machinery for importin alpha at individual nuclear pore complexes may be regulated by reaction(s) that require ATP hydrolysis.