Ligularia fischeri ethanol extract: An inhibitor of alpha-melanocyte-stimulating hormone-stimulated melanogenesis in B16F10 melanoma cells.

BACKGROUND: Ligularia fischeri is a perennial herb isolated from plants of the Asteraceae family. Ligularia fischeri is distributed throughout Korea, Japan, eastern Siberia, and China. AIMS: The aim of this study is to examine the intracellular inhibitory effect of Ligularia fischeri ethanol extract on melanin synthesis and expression of tyrosinase and tyrosinase-related protein 1 and 2. In addition, we analyzed the mitogen-activated protein kinase signaling pathway and microphthalmia-associated transcription factor in alpha-melanocyte-stimulating hormone-stimulated B16F10 melanoma cells. METHODS: To assess the inhibition of melanogenesis in alpha-melanocyte-stimulating hormone-stimulated B16F10 melanoma cells, the expression of melanogenesis-related genes was investigated by quantitative real-time polymerase chain reaction, while western blotting was performed to determine protein expression levels. RESULTS: We confirmed that the ethanol extract of Ligularia fischeri inhibited melanin synthesis in vitro by decreasing tyrosinase and tyrosinase-related protein 1 and 2 expression. Furthermore, we revealed that tyrosinase expression was regulated by the suppression of microphthalmia-associated transcription factor expression and activation of extracellular signal-regulated kinase phosphorylation. The ethanol extract of Ligularia fischeri inhibited melanogenesis by activating extracellular signal-regulated kinase phosphorylation and suppressing microphthalmia-associated transcription factor and tyrosinase expression. CONCLUSIONS: Ligularia fischeri ethanol extract may be used as an effective skin whitening agent in functional cosmetics.

A self-regulatory circuit of CIRCADIAN CLOCK-ASSOCIATED1 underlies the circadian clock regulation of temperature responses in Arabidopsis.

The circadian clock synchronizes biological processes to daily cycles of light and temperature. Clock components, including CIRCADIAN CLOCK-ASSOCIATED1 (CCA1), are also associated with cold acclimation. However, it is unknown how CCA1 activity is modulated in coordinating circadian rhythms and cold acclimation. Here, we report that self-regulation of Arabidopsis thaliana CCA1 activity by a splice variant, CCA1ß, links the clock to cold acclimation. CCA1ß interferes with the formation of CCA1α-CCA1α and LATE ELONGATED HYPOCOTYL (LHY)-LHY homodimers, as well as CCA1α-LHY heterodimers, by forming nonfunctional heterodimers with reduced DNA binding affinity. Accordingly, the periods of circadian rhythms were shortened in CCA1ß-overexpressing transgenic plants (35S:CCA1ß), as observed in the cca1 lhy double mutant. In addition, the elongated hypocotyl and leaf petiole phenotypes of CCA1α-overexpressing transgenic plants (35S:CCA1α) were repressed by CCA1ß coexpression. Notably, low temperatures suppressed CCA1 alternative splicing and thus reduced CCA1ß production. Consequently, whereas the 35S:CCA1α transgenic plants exhibited enhanced freezing tolerance, the 35S:CCA1ß transgenic plants were sensitive to freezing, indicating that cold regulation of CCA1 alternative splicing contributes to freezing tolerance. On the basis of these findings, we propose that dynamic self-regulation of CCA1 underlies the clock regulation of temperature responses in Arabidopsis.

Homocysteine and pulsatility index of cerebral arteries.

BACKGROUND AND PURPOSE: A pulsatility index (PI) represents vascular resistance distal to an examined artery. The purpose of the present study was to evaluate an association between plasma total homocysteine (tHcy) and PIs of the cerebral arteries in patients with ischemic stroke. METHODS: Consecutive patients with ischemic stroke referred to a neurovascular ultrasound laboratory were evaluated from March 2007 to February 2008. PI was defined as (peak systolic velocity-end-diastolic velocity)/mean flow velocity as recommended. Transcranial Doppler was examined in both middle cerebral arteries and vertebral arteries, and basilar arteries. All patients with ischemic stroke were subdivided according to the presence of proximal internal carotid arterial steno-occlusion (ICS). RESULTS: The numbers of patients enrolled for the present analysis as ischemic stroke without and with ICS were 272 and 92, respectively. PIs measured in the cerebral arteries did not show a significant difference in the two groups, in spite of the fact that mean flow velocities of both basilar arteries and vertebral arteries were significantly elevated in the patients with ICS. Plasma tHcy was found to be independently associated with graded increases of PIs in all cerebral arteries in the patients without ICS, even adjusted for the potential confounders. However, there was no association between tHcy and PI in the patients with ICS. CONCLUSION: Plasma tHcy was directly associated with increased cerebral arterial resistance. But in clinical situations when the cerebral arterial hemodynamics were altered as in the patients with ICS, the effect of tHcy on arterial remodeling could be obscured.

A membrane-bound NAC transcription factor regulates cell division in Arabidopsis.

Controlled release of membrane-tethered, dormant precursors is an intriguing activation mechanism that regulates diverse cellular functions in eukaryotes. An exquisite example is the proteolytic activation of membrane-bound transcription factors. The proteolytic cleavage liberates active transcription factors from the membranes that can enter the nucleus and evokes rapid transcriptional responses to incoming stimuli. Here, we show that a membrane-bound NAC (for NAM, ATAF1/2, CUC2) transcription factor, designated NTM1 (for NAC with transmembrane motif1), is activated by proteolytic cleavage through regulated intramembrane proteolysis and mediates cytokinin signaling during cell division in Arabidopsis thaliana. Cell proliferation was greatly reduced in an Arabidopsis mutant with retarded growth and serrated leaves in which a transcriptionally active NTM1 form was constitutively expressed. Accordingly, a subset of cyclin-dependent kinase (CDK) inhibitor genes (the KIP-related proteins) was induced in this mutant with a significant reduction in histone H4 gene expression and in CDK activity. Consistent with a role for NTM1 in cell cycling, a Ds element insertional mutant was morphologically normal but displayed enhanced hypocotyl growth with accelerated cell division. Interestingly, cytokinins were found to regulate NTM1 activity by controlling its stability. These results indicate that the membrane-mediated activation of NTM1 defines a molecular mechanism by which cytokinin signaling is tightly regulated during cell cycling.

A new Arabidopsis gene, FLK, encodes an RNA binding protein with K homology motifs and regulates flowering time via FLOWERING LOCUS C.

Posttranscriptional RNA metabolism plays versatile roles in the regulation of gene expression during eukaryotic growth and development. It is mediated by a group of RNA binding proteins with distinct conserved motifs. In this study, an Arabidopsis (Arabidopsis thaliana) gene, designated FLK, was identified and shown to encode a putative RNA binding protein with K homology motifs. A mutant in which FLK was inactivated by T-DNA insertion exhibited a severe late flowering phenotype both in long and short days. The late flowering phenotype was reversed by gibberellin and vernalization treatments. The FLOWERING LOCUS C (FLC) transcription was greatly upregulated, whereas those of FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 decreased in the mutant. These observations demonstrate that FLK regulates the autonomous flowering pathway via FLC. It is now evident that a battery of different RNA binding proteins are involved in the posttranscriptional regulation of flowering time in Arabidopsis.