Inhibition of c-Kit signaling by diosmetin isolated from Chrysanthemum morifolium.

The interaction of stem cell factor (SCF) with its cognate receptor c-Kit is closely associated with the survival and maturation of melanocytes. To investigate novel depigmentation agents, we screened 2,000 plant extracts for c-Kit inhibitors to identify active small molecules by using time-resolved fluorescence enzyme assays. For the active extracts identified as inhibitors of c-Kit enzyme, we evaluated the effects of the active extracts and isolated flavonoids on c-Kit phosphorylation in MO7e/melanocytes. Anti-melanogenic activity was also examined in melanocytes and melanoderm model. The flavonoids such as diosmetin, apigenin, acacetin and luteolin isolated from Chrysanthemum morifolium were found to be active in inhibiting c-Kit both at enzyme and cellular levels. In addition, these flavonoids attenuated SCF-induced proliferation of human primary melanocytes without toxicity and suppressed ultraviolet (UV) B irradiation-mediated melanin synthesis significantly. Among the active flavonoids, diosmetin was found to inhibit SCF-induced melanogenesis in a human melanoderm model. These results strongly suggest that C. morifolium extract and diosmetin have potential to suppress SCF-/UVB-induced melanogenesis, and could be developed as anti-pigmentation agents.

Electroacupuncture at ST36 increases contraction of the gastric antrum and improves the SCF/c-kit pathway in diabetic rats.

Electroacupuncture (EA) at ST36 is effective for improving gastric motility. However, the underlying mechanism remains poorly understood. The aim of this study was to investigate the effects of EA on gastric contraction and to determine whether interstitial cells of Cajal (ICCs) are involved. Rats were randomized into control, diabetic (DM), diabetic with sham EA (DM + SEA), diabetic with low frequency EA (DM + LEA) and diabetic with high frequency EA (DM + HEA) groups. EA was performed everyday for four and eight weeks. Contractions in antrum strips were explored using the organ bath technique. Western blotting was employed to determine c-kit and transmembrane stem cell factor (M-SCF) expression in the gastric antrum, and levels of soluble stem cell factor (S-SCF) in serum were determined by enzyme-linked immunosorbent assay (ELISA). The distribution of ICCs was further assessed by immunohistochemistry. The results were as follows: (1) Contractions in the DM group were attenuated at four and eight weeks, but LEA and HEA restored the attenuated contraction. (2) ICCs were significantly decreased at eight weeks without alteration at four weeks in DM group, but were rescued in the LEA and HEA groups. (3) Whereas M-SCF and S-SCF in the DM group were slightly decreased at four weeks and were dramatically reduced at eight weeks, LEA and HEA markedly enhanced SCF at eight weeks. Collectively, the data suggest that in diabetic rats, LEA and HEA at ST36 could facilitate contraction of the gastric antrum, possibly by involving the SCF/c-kit pathway.

[Effect of acupoint-injection of stem cell factor antibody on electroacupuncture induced changes of count and degranulation of subcutaneous mast cells in the local region in rats].

OBJECTIVE: To observe the alternations of local mast cells (MCs) in the number and functional activities after electroacupuncture (EA) and injection of stem cell factor (SOF) antibody into "Weishu" (BL 21) and "Zusanli" (ST 36) in rats. METHODS: Thirty Wistar rats were randomly assigned to normal, EA, and EA + SCF antibody injection (EA-ABI) groups (n=10). EA was applied to the left "Weishu"(BL 21) and "Zusanli" (ST 36) for 25 min. For rats of EA+ ABI group, SOF-AB (1:200, 0.1 mL) was respectively injected into BL 21 and ST 36, following by EA. The tissues around the two acupoints areas were sampled to be stained with acetylcholine esterase (AchE) and toluidine blue (TB), respectively. The counts and degranulation ratio of MOs in the acupoint region were recorded and observed under microscope. RESULTS: In comparison with the normal group, MCs count was increased significantly in the EA of "Weishu" (BL 21) group (P < 0.05), mildly in the EA of "Zusanli" (ST 36) group (P > 0.05), and downregulated considerably in both EA-ABI-BL 21 and EA-ABI-ST 36 groups (P < 0.05) . Compared with the normal group, the degranulation ratio of MCs was increased significantly in EA-BL 21, EA-ST 36, EA-ABI-BL 21 and EA-ABI-ST 36 groups (P < 0.5). No significant differences were found between EA-BL 21 and EA-ABI-BL 21 groups, and between EA-ST 36 and EA-ABI-ST 36 groups in the degranulation ratios (P > 0.05). CONCLUSION: Local injection of SCF antibody in BL 21 and ST 36 can significantly suppress EA-induced increase of the number and degranulation ratio of local subcutaneous MCs in rats, suggesting that SCF is an important factor affecting the activity and recruitment of MCs around the acupoint during EA.

Geniposide enhances melanogenesis by stem cell factor/c-Kit signalling in norepinephrine-exposed normal human epidermal melanocyte.

Geniposide is an iridoid glycoside isolated from the fruit of Gardenia jasminoides Ellis used as a Chinese traditional medicine for treatment of generalized vitiligo. Stem cell factor from keratinocyte recognizes and activates its receptor c-kit carried by melanocyte to potent enhance melanocytic melanogenesis that can be suppressed by norepinephrine. This study addresses the action and mechanism of geniposide enhancing melanogenesis in norepinephrine-exposed normal human epidermal melanocyte. Flow cytometry results from this study exhibited the augmentation effect of geniposide on production of c-kit receptor by norepinephrine-exposed normal human epidermal melanocyte. However, geniposide did not affect the production of stem cell factor by norepinephrine-exposed normal human epidermal keratinocyte assessed by cellular enzyme-linked immunosorbent assay (ELISA). ELISA indicated that at the presence of stem cell factor, geniposide was capable of elevating the level of extracellular signal-regulated kinase 1/2 phosphorylation within norepinephrine-exposed normal human epidermal melanocyte, which is known to be involved in stem cell factor/c-kit downstream signalling. And inhibition of c-kit with inhibitory antibody K44.2 completely blocked the increase in geniposide-stimulated extracellular signal-regulated kinase 1/2 phosphorylation. In addition, spectrophotometry demonstrated the enhancement effect of geniposide on melanogenesis (tyrosinase activity and melanin production) in norepinephrine-exposed normal human epidermal melanocyte at the presence of stem cell factor, which was blocked by c-kit inhibitory antibody K44.2. Data from this study suggest that geniposide can enhance melanogenesis by stem cell factor/c-kit signalling in which the expression of c-kit receptor is augmented in norepinephrine-exposed normal human epidermal melanocyte.

Stem cell-derived neural stem/progenitor cell supporting factor is an autocrine/paracrine survival factor for adult neural stem/progenitor cells.

Recent evidence suggests that adult neural stem/progenitor cells (ANSCs) secrete autocrine/paracrine factors and that these intrinsic factors are involved in the maintenance of adult neurogenesis. We identified a novel secretory molecule, stem cell-derived neural stem/progenitor cell supporting factor (SDNSF), from adult hippocampal neural stem/progenitor cells by using the signal sequence trap method. The expression of SDNSF in adult central nervous system was localized to hippocampus including dentate gyrus, where the neurogenesis persists throughout life. In induced neurogenesis status seen in ischemically treated hippocampus, the expression of SDNSF was up-regulated. As functional aspects, SDNSF protein provided a dose-dependent survival effect for ANSC following basic fibroblast growth factor 2 (FGF-2) withdrawal. ANSCs treated by SDNSF also retain self-renewal potential and multipotency in the absence of FGF-2. However, SDNSF did not have mitogenic activity, nor was it a cofactor that promoted the mitogenic effects of FGF-2. These data suggested an important role of SDNSF as an autocrine/paracrine factor in maintaining stem cell potential and lifelong neurogenesis in adult central nervous system.

SU11248 inhibits KIT and platelet-derived growth factor receptor beta in preclinical models of human small cell lung cancer.

The purpose of this study was to evaluate the activity of the indolinone kinase inhibitor SU11248 against the receptor tyrosine kinase KIT in vitro and in vivo, examine the role of KIT in small cell lung cancer (SCLC), and anticipate clinical utility of SU11248 in SCLC. SU11248 is an oral, multitargeted tyrosine kinase inhibitor with direct antitumor and antiangiogenic activity through targeting platelet-derived growth factor receptor (PDGFR), vascular endothelial growth factor receptor, KIT, and FLT3 receptors. Treatment of the KIT-expressing SCLC-derived NCI-H526 cell line in vitro with SU11248 resulted in dose-dependent inhibition of stem cell factor-stimulated KIT phosphotyrosine levels and proliferation. The biological significance of KIT inhibition was evaluated in vivo by treating mice bearing s.c. NCI-H526 tumors with SU11248 or another structurally unrelated KIT inhibitor, STI571 (Gleevec), which is also known to inhibit Bcr-Abl and PDGFRbeta. SU11248 treatment resulted in significant tumor growth inhibition, whereas inhibition from STI571 treatment was less dramatic. Both compounds reduced phospho-KIT levels in NCI-H526 tumors, with a greater reduction by SU11248, correlating with efficacy. Likewise, phospho-PDGFRbeta levels contributed by tumor stroma and with known involvement in angiogenesis were strongly inhibited by SU11248 and less so by STI571. Because platinum-based chemotherapy is part of the standard of care for SCLC, SU11248 was combined with cisplatin, and significant tumor growth delay was measured compared with either agent alone. These results expand the profile of SU11248 as a KIT signaling inhibitor and suggest that SU11248 may have clinical potential in the treatment of SCLC via direct antitumor activity mediated via KIT as well as tumor angiogenesis via vascular endothelial growth factor receptor FLK1/KDR and PDGFRbeta.

Stem cell factor augments Fc epsilon RI-mediated TNF-alpha production and stimulates MAP kinases via a different pathway in MC/9 mast cells.

Mast cells express the receptor tyrosine kinase kit/stem cell factor receptor (SCFR) which is encoded by the proto-oncogene c-kit. Ligation of SCFR induces its dimerization and activation of its intrinsic tyrosine kinase activity leading to activation of Raf-1, phospholipases, phosphatidylinositol 3-kinase, and extracellular signal-regulated kinases. However, little is known about the downstream signals initiated by SCFR ligation except for activation of extracellular signal-regulated kinases. The murine mast cell line, MC/9, synthesizes and secretes TNF-alpha following the aggregation of high affinity Fc receptors for IgE (Fc epsilonRI). Ligation of SCFR or Fc epsilonRI on MC/9 cells resulted in the activation of all three MAP kinase family members, extracellular signal-regulated kinases, c-Jun amino-terminal kinase (JNK), and p38. Stem cell factor (SCF)-induced activation of JNK and p38 was insensitive to wortmannin, cyclosporin A, and FK506 whereas activation of these kinases through Fc epsilonRI was sensitive to these drugs. Coligation of SCFR augmented Fc epsilonRI-mediated activation of MAP kinases, especially JNK activation, and SCF augmented Fc epsilonRI-mediated TNF-alpha production in MC/9 cells, although SCF alone did not induce TNF-alpha production. This augmentation by SCF was regulated at the level of transcription, at least in part, since the promoter activity of TNF-alpha was enhanced following addition of SCF. These results demonstrate that SCF can augment Fc epsilonRI-mediated JNK activation and cytokine gene transcription but via pathways that are regulated differently than the ones activated through Fc epsilonRI.

Demonstration of mast-cell chemotactic activity in nasal lavage fluid: characterization of one chemotaxin as c-kit ligand, stem cell factor.

Mast cells are known to accumulate in tissue during allergic inflammation. However, the chemotaxins responsible are undefined. Using a modified Boyden chamber and the human mast-cell line HMC-1, we first identified mast-cell chemotactic activity in nasal lavage fluid collected before the pollen season after allergen provocation of allergic patients (n=29) (mean migratory response compared to medium control was 121%, range 85-198%). Mast-cell chemotactic activity was also detected in lavage fluid collected after allergen provocation at the end of a Swedish birch-pollen season from three different treatment groups: topical steroid treatment with budesonide; the topical antihistamine, levocabastine; and placebo. There was no significant difference in mast-cell chemotactic activity between nasal lavage fluid collected from the placebo group (mean=102%), the budesonide-treated group (mean=114%), or the levocabastine group (mean=125%). Stem cell factor (SCF), a known mast-cell chemotaxin, was present in the nasal lavage fluids from all three groups, and correlated with the mast-cell chemotactic activity (r=0.67, P<0.01). The mast-cell chemotactic activity was inhibited (range 5-100%) in some, but not all, nasal lavage fluids by a polyclonal antibody directed against SCF. This report describes the presence of mast-cell chemotactic activity in nasal lavage fluid during an allergic reaction. These findings show that SCF may play a pivotal role in the recruitment of mast cells in allergic rhinitis.