Internalization and Decrease of Duodenal DMT1 Involved in Transient Suppression of Iron Uptake in Short-Acting Mucosal Block.

Mucosal block (MB) is induced by the oral administration of excess iron (10 mg) and suppresses intestinal iron absorption for 3-72 h. The inhibition of iron absorption is accompanied by the downregulation of molecules associated with intestinal iron absorption. Recently, we found that a smaller amount of iron (1 mg) also induced a transient suppression of iron uptake without affecting gene expression levels (short-acting mucosal block, SAMB), which is specific to iron-deficient rats. In this study, we investigated how the nonheme iron transporters divalent metal transporter 1 (DMT1) and ferroportin (FPN) are involved in the transient suppression of iron uptake in SAMB. To induce SAMB, a test solution containing 1 mg iron was infused into the duodenum loop in iron-sufficient and iron-deficient rats. Total duodenal DMT1 and DMT1-IRE expression were increased during iron deficiency. After 15 min of 1 mg iron loading, the fluorescence intensity of duodenal DMT1 in iron-deficient rats was decreased and was comparable to that in iron-sufficient rats. Internalized DMT1-IRE as puncta was observed at 15 and 60 min after 1 mg iron loading, and the number of punctas was significantly increased after 60 min compared with control. There was no effect of 1 mg iron loading on the intracellular distribution of duodenal FPN. Our results suggest that the decrease and internalization of DMT1-IRE protein may be related, at least in part, to iron uptake suppression in SAMB.

Marginally excessive iron loading transiently blocks mucosal iron uptake in iron-deficient rats.

Regular "mucosal block" is characterized by decreased uptake of a normal iron load 3-72 h after the administration of excess iron (generally 10 mg) to iron-deficient animals. We found that short-acting mucosal block could be induced by much lower iron concentration and much shorter induction time than previously reported, without affecting levels of gene expression. A rapid endocytic mechanism was reported to decrease intestinal iron absorption after a high iron load, but the activating iron load and the time to decreased absorption were undetermined. We assessed the effects of 30-2,000 µg iron load on iron uptake in the duodenal loop of iron-deficient and iron-sufficient rats under anesthesia. One hour later, mucosal cellular iron uptake in iron-deficient rats administered 30 µg iron was 76.1%, decreasing 25% to 50.7% in rats administered 2,000 µg iron. In contrast, iron uptake by iron-sufficient rats was 63% (range 60.3-65.5%) regardless of iron load. Duodenal mucosal iron concentration was significantly lower in iron-deficient than in iron-sufficient rats. Iron levels in portal blood were consistently higher in iron-deficient rats regardless of iron load, in contrast to the decreased iron uptake on the luminal side. Iron loading blocked mucosal uptake of marginally excess iron (1,000 µg), with a greater effect at 15 min than at 30 min. The rapid induction of short-acting mucosal block only in iron-deficient rats suggests DMT1 internalization.

The IL6 gene polymorphism -634C>G and IL17F gene polymorphism 7488T>C influence bone mineral density in young and elderly Japanese women.

Osteoporosis is an important public health problem because of the significant morbidity and mortality associated with its complications, particularly fractures. An important clinical risk factor in the pathogenesis of osteoporosis is the presence of genetic polymorphisms in susceptibility genes. However, few studies have investigated the relevance of these polymorphisms in premenopausal women. Recent studies have demonstrated interactions between bone and immune cells, and that cytokines produced by immune cells regulate bone turnover. In this study, we examined the associations between bone mineral density (BMD) and polymorphisms in genes encoding interleukin (IL)-6 (-634C>G; rs1800796), tumor necrosis factor (TNF)-α (-308G>A; rs1800629), IL-17F (7488T>C; rs763780), transforming growth factor (TGF)-ß (869T>C; rs1800470), osteoprotegerin (OPG; 163A>G; rs3102735) and methylenetetrahydrofolate reductase (MTHFR; 677C>T; rs1801133) in young and elderly Japanese women. Whole-body, lumbar spine (L(1) or L(2)-L(4)), and femoral neck BMD were measured in 100 young subjects (18-23 years), and 100 elderly subjects (60-83 years). Whole-body, lumbar spine, and femoral neck BMD were 1.13±0.06, 1.14±0.12, and 1.00±0.11 g/cm(2), respectively, in young subjects, and 0.92±0.09, 0.86±0.15, and 0.63±0.10 g/cm(2), respectively, in elderly subjects. The frequencies of the IL-6 CC, CG, and GG genotypes were 48%, 49%, and 3%, respectively. The frequencies of the IL17F TT, TC, and CC genotypes were 79%, 15%, and 6%, respectively, in young subjects. Polymorphisms of the IL-6 and IL17F genes were significantly associated with BMD. To our knowledge, this is the first report to examine these associations in a cohort of 200 Japanese women.

Pause-and-stop: the effects of osmotic stress on cell proliferation during early leaf development in Arabidopsis and a role for ethylene signaling in cell cycle arrest.

Despite its relevance for agricultural production, environmental stress-induced growth inhibition, which is responsible for significant yield reductions, is only poorly understood. Here, we investigated the molecular mechanisms underlying cell cycle inhibition in young proliferating leaves of the model plant Arabidopsis thaliana when subjected to mild osmotic stress. A detailed cellular analysis demonstrated that as soon as osmotic stress is sensed, cell cycle progression rapidly arrests, but cells are kept in a latent ambivalent state allowing a quick recovery (pause). Remarkably, cell cycle arrest coincides with an increase in 1-aminocyclopropane-1-carboxylate levels and the activation of ethylene signaling. Our work showed that ethylene acts on cell cycle progression via inhibition of cyclin-dependent kinase A activity independently of EIN3 transcriptional control. When the stress persists, cells exit the mitotic cell cycle and initiate the differentiation process (stop). This stop is reflected by early endoreduplication onset, in a process independent of ethylene. Nonetheless, the potential to partially recover the decreased cell numbers remains due to the activity of meristemoids. Together, these data present a conceptual framework to understand how environmental stress reduces plant growth.

12-oxo-phytodienoic acid-glutathione conjugate is transported into the vacuole in Arabidopsis.

While exogenous toxic compounds such as herbicides are thought to be sequestered into vacuoles in the form of glutathione (GSH) conjugates, little is understood about natural plant products conjugated with GSH. To identify natural products conjugated with GSH in plants, metabolites in the Arabidopsis γ-glutamyl transpeptidase (ggt) 4 knockout mutants that are blocked in the degradation of GSH conjugates in the vacuole were compared with those in wild-type plants. Among the metabolites identified, one was confirmed to be the 12-oxo-phytodienoic acid (OPDA)-GSH conjugate, indicating that OPDA, a precursor of jasmonic acid (JA), is transported into the vacuole as a GSH conjugate.

Rapid regulation of intestinal divalent metal (cation) transporter 1 (DMT1/DCT1) and ferritin mRNA expression in response to excess iron loading in iron-deficient rats.

We determined the effects of excess iron on the expression of duodenal divalent metal transporter 1 (DMT1) and ferritin (Ft) in iron-deficient rats which had increased iron absorption. DMT1 mRNA was down-regulated and Ft mRNA was up-regulated 2 h after administering the iron. However, more than 2 h was needed for Ft protein synthesis to occur in the duodenal mucosa.

Ethylene promotes submergence-induced expression of OsABA8ox1, a gene that encodes ABA 8'-hydroxylase in rice.

A rapid decrease of the plant hormone ABA under submergence is thought to be a prerequisite for the enhanced elongation of submerged shoots of rice (Oryza sativa L.). Here, we report that the level of phaseic acid (PA), an oxidized form of ABA, increased with decreasing ABA level during submergence. The oxidation of ABA to PA is catalyzed by ABA 8'-hydroxylase, which is possibly encoded by three genes (OsABA8ox1, -2 and -3) in rice. The ABA 8'-hydroxylase activity was confirmed in microsomes from yeast expressing OsABA8ox1. OsABA8ox1-green fluorescent protein (GFP) fusion protein in onion cells was localized to the endoplasmic reticulum. The mRNA level of OsABA8ox1, but not the mRNA levels of other OsABA8ox genes, increased dramatically within 1 h after submergence. On the other hand, the mRNA levels of genes involved in ABA biosynthesis (OsZEP and OsNCEDs) decreased after 1-2 h of submergence. Treatment of aerobic seedlings with ethylene and its precursor, 1-aminocyclopropane-1-carboxylate (ACC), rapidly induced the expression of OsABA8ox1, but the ethylene treatment did not strongly affect the expression of ABA biosynthetic genes. Moreover, pre-treatment with 1-methylcyclopropene (1-MCP), a potent inhibitor of ethylene action, partially suppressed induction of OsABA8ox1 expression under submergence. The ABA level was found to be negatively correlated with OsABA8ox1 expression under ACC or 1-MCP treatment. Together, these results indicate that the rapid decrease in ABA levels in submerged rice shoots is controlled partly by ethylene-induced expression of OsABA8ox1 and partly by ethylene-independent suppression of genes involved in the biosynthesis of ABA.

A plant growth retardant, uniconazole, is a potent inhibitor of ABA catabolism in Arabidopsis.

Plant growth retardants (PGRs) reduce the shoot growth of plants by inhibiting gibberellin biosynthesis. In this study, we performed detailed analyses of the inhibitory effects of PGRs on Arabidopsis abscisic acid (ABA) 8'-hydroxylase, a major ABA catabolic enzyme, recently identified as CYP707As. In an in vitro assay with CYP707A3 microsomes expressed in insect cells, uniconazole-P inhibited CYP707A3 activity more effectively than paclobutrazol or tetcyclacis, whereas the other PGRs tested did not inhibit it significantly. Uniconazole-P was found to be a strong competitive inhibitor (K(i)=8.0 nM) of ABA 8'-hydroxylase. Uniconazole-P-treated Arabidopsis plants showed enhanced drought tolerance. In uniconazole-P-treated plants, endogenous ABA levels increased 2-fold as compared with the control, and co-application of GA(4) did not suppress the effects, indicating that the effects were not due to gibberellin deficiency. Thus uniconazole-P effectively inhibits ABA catabolism in Arabidopsis plants. We also discuss the structure-activity relationship of the azole-type compounds on ABA 8'-hydroxylase inhibitory activity.

Field studies on the regulation of abscisic acid content and germinability during grain development of barley: molecular and chemical analysis of pre-harvest sprouting.

To investigate whether the regulation of abscisic acid (ABA) content was related to germinability during grain development, two cDNAs for 9-cis-epoxycarotenoid dioxygenase (HvNCED1 and HvNCED2) and one cDNA for ABA 8'-hydroxylase (HvCYP707A1), which are enzymes thought to catalyse key regulatory steps in ABA biosynthesis and catabolism, respectively, were cloned from barley (Hordeum vulgare L.). Expression and ABA-quantification analysis in embryo revealed that HvNCED2 is responsible for a significant increase in ABA levels during the early to middle stages of grain development, and HvCYP707A1 is responsible for a rapid decrease in ABA level thereafter. The change in the embryonic ABA content of imbibing grains following dormancy release is likely to reflect changes in the expression patterns of HvNCEDs and HvCYP707A1. A major change between dormant and after-ripened grains occurred in HvCYP707A1; the increased expression of HvCYP707A1 in response to imbibition, followed by a rapid ABA decrease and a high germination percentage, was observed in the after-ripened grains, but not in the dormant grains. Under field conditions, HvNCED2 showed the same expression level and pattern during grain development in 2002, 2003, and 2004, indicating that HvNCED2 expression is regulated in a growth-dependent manner in the grains. By contrast, HvNCED1 and HvCYP707A1 showed a different expression pattern in each year, indicating that the expression of these genes is affected by environmental conditions during grain development. The varied expression levels of these genes during grain development and imbibition, which would have effects on the activity of ABA biosynthesis and catabolism, might be reflected, in part, in the germinability in field-grown barley.

Preventive effect of oral administration of 6-(methylsulfinyl)hexyl isothiocyanate derived from wasabi (Wasabia japonica Matsum) against pulmonary metastasis of B16-BL6 mouse melanoma cells.

AIM: Effect of oral administration of 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC) or a 6-MITC-containing T-wasabi fraction from wasabi root (Wasabia japonica Matsum) to inhibit the macroscopic pulmonary metastasis was studied with a murine B16-BL6 melanoma model. METHOD: Two administration routes, subcutaneous or intravenous, and two administration times, prior to or concomitant with tumor inoculation, of 6-MITC or T-wasabi against the metastatic foci formation in C57BL/6J mouse lungs were compared. RESULTS: The number of metastasized foci per lung in either subcutaneous or intravenous injection was significantly reduced by intake of 6-MITC or a T-wasabi fraction. The maximum reduction by a T-wasabi fraction reached to 82%. Fifty-six percent of foci formation was inhibited by a 2 week-prior administration of 6-MITC (200 microM), whereas only 27% inhibition was obtained by a concomitant administration with tumor inoculation. Neither 6-MITC nor T-wasabi at tested concentrations showed any toxic effects. DISCUSSION: Together with our previous results, a component of the Japanese pungent spice, wasabi appears to inhibit not only tumor cell growth but also tumor metastasis. Therefore, 6-MITC from wasabi is apparently a useful dietary candidate for controlling tumor progression.

Selective sensitivity to wasabi-derived 6-(methylsulfinyl)hexyl isothiocyanate of human breast cancer and melanoma cell lines studied in vitro.

Recently, attention has focused on the anticancer properties of an aromatic component 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC) in a typical Japanese spice, wasabi. In this paper, anticancer activity of 6-MITC in vitro was studied by using a human cancer cell (HCC) panel. 6-MITC directly affected the cells in the HCC panel and inhibited their growth in culture. The mean concentration required to inhibit 50% of control cell growth was 3.9 microM, which is a sufficiently low dosage for practical use. The suppression influenced not only the cell growth, but also the survival of these cells. The mean concentration to suppress cells to a 50% survival was 43.7 microM. The reduction activity of 6-MITC was differential, and it suppressed specific cells. These severely suppressed cell lines included breast cancer and melanoma cell lines. For example, one melanoma line was seriously damaged at a concentration of 0.3 microM of 6-MITC. Compared with other MITCs (2-MITC, 4-MITC and 8-MITC), 6-MITC showed the most effective suppression and with the most specific manner of the cells mentioned above. A "COMPARE" analysis using a computerized algorithm, which was based on the HCC database, suggested that the suppression mechanism of 6-MITC is unique and may be different from that of other known chemicals. The actual mechanism may not a simple one but may involve multiple pathways. On account of its sufficiently small size, 6-MITC is a new possible candidate for controlling cancer cells.