The Effects Of Ginseng Pectins On Cell Migration And Their Mechanisms

Panax ginseng C. A. Meyer has a long history of use as an herbal medicine in Asian countries. There are numerous different compounds in ginseng, including ginseng polysaccharides, ginsenosides, ginseng peptides and other small molecules. It has been reported that ginseng polysaccharides have many bioactivities. It is so hard to separate and purify the ginseng polysaccharides that the structural features related to the effects and the underlying mechanisms are less known. Therefore, we tested the effect of different fractions from ginseng polysaccharides on cell migration in this paper, and demonstrated on structure-activities and mechanisms in detail.Ginseng polysaccharides are mainly composed of neutral polysaccharides (starch-like glucans) and acidic substances (ginseng pectin, GP). In our study, ginseng pectin was examined for its effect on cell migration. Ginseng pectin impaired the migration of L-929 cells and reduced their migration speed by up to 60% of control. Cell migration was reduced to the same extent in the presence or absence of serum, which suggested that ginseng pectin acted as a common inhibitor to both serum-dependent and serum-independent migration pathways.To demonstrate the structure-activities, ginseng pectin was fractionated according to the previous methods in our lab, and nine fractions were characterized, including four homogalacturonan (HG)-domain rich fractions (WGPA-1-HG, WGPA-2-HG, WGPA-3-HG, WGPA-4-HG); two containing both HG- and Rhamnogalacturonan I (RG-I)-domains fractions (WGPA-3-RG, WGPA-4-RG); one glucan rich fraction (WGPA-N); two arabinogalactan rich fractions (WGPA-1-RG, WGPA-2-RG). We tested the effect of each fraction on cell migration. The HG-domain rich pectins caused significant inhibition on cell migration. The order of the inhibitory effects is WGPA-1-HG < -2-HG < -3-HG < -4-HG. At 0.015 mg/mL, WGPA-3-HG significantly inhibited L-929 cell migration. WGPA-3-RG and -4-RG showed a slightly stronger inhibition than the HG-domain rich fractions. WGPA-N, WGPA-1-RG and -2-RG, containing no, trace or minor HG and RG-I domains, showed less effects on cell migration. The inhibitory effect of ginseng pectic polysaccharides was related to HG domain content and RG-I domain content.To confirm the inhibitory effect of RG-I domain on cell migration, we prepared two kinds of RG-I-rich pectins: g-RGI-low (low RG-I domain content) and g-RGI-high (high RG-I domain content). The datas on cell migration showed RG-I-rich pectins inhibited cell migration in dose-dependent manner. Their inhibitory effects became significant even at less than 0.015 mg/mL. Further studies revealed that combination of HG- and RG-I-rich pectins exerted stronger effects than either HG- or RG-I-rich pectin alone.On the basis of results above, we studied the mechanisms of RG-I and HG pectins on cell migration. Experiment datas showed that the effects of RG-I- and HG-rich pectins were dependent on pretreatment and the pretreatment caused alterations in cell morphologies such as cell size and shape, focal adhesion, the organization of actin filaments, and the tyrosine phosphorylation of signaling molecules, suggesting that HG and RG-I pectins did not act simply as blocking agents during cell migration. Further studies showed that RG-I- and HG-rich pectin treatment decreased cell adhesion and cell spreading on the substratum, indicating that RG-I- and HG-rich pectins might exert their effects on cell migration via decreasing cell adhesion and cell spreading. Besides, we explored the target molecules on cell membrane of RG-I- and HG-rich pectins. Due to the ability of galectin-3 to bind some pectins, and has been postulated to mediate the actions of pectins in various cellular processes, we investigated if galectin-3 participated in RG-I- and HG-rich pectin mediated migration inhibition. The results suggested that RG-I- and HG-rich pectins did not target galectin-3 for their effects on cell migration.Cell migration plays an important role in cancerometastasis and tumorigenesis, impairment of cell migration has been the new tool for inhibiting tumor. Therefore, these findings represent a significant contribution towards understanding the anti-tumor activities of ginseng polysaccharides and applying them to health food and medicine.