Identification of Plants That Inhibit Lipid Droplet Formation in Liver Cells: Rubus suavissimus Leaf Extract Protects Mice from High-Fat Diet-Induced Fatty Liver by Directly Affecting Liver Cells.

Fatty liver disease is a condition in which abnormally large numbers of lipid droplets accumulate in liver cells. Fatty liver disease induces inflammation under conditions of oxidative stress and may result in cancer. To identify plants that protect against fatty liver disease, we examined the inhibitory effects of plant extracts on lipid droplet formation in mouse hepatoma cells. A screen of 98 water extracts of plants revealed 4 extracts with inhibitory effects. One of these extracts, Rubus suavissimus S. Lee (Tien-cha or Chinese sweet tea) leaf extract, which showed strong inhibitory effects, was tested in a mouse fatty liver model. In these mouse experiments, intake of the plant extract significantly protected mice against fatty liver disease without affecting body weight gain. Our results suggest that RSE directly affects liver cells and protects them from fatty liver disease.

A small molecule inhibitor of Bcl-2, HA14-1, also inhibits ceramide glucosyltransferase.

HA14-1 is a Bcl-2 inhibitor that is widely used for studies of apoptosis. In the course of searching for a ceramide glucosyltransferase inhibitor that catalyzes the first glycosylation step of glycosphingolipid synthesis, we unexpectedly found that HA-14-1 also has the ability to inhibit ceramide glucosyltransferase. The IC50 value of HA14-1 against ceramide glucosyltransferase is 4.5µM, which is lower than that reported for Bcl-2 in vitro. Kinetic analyses revealed that HA14-1 is a competitive and mixed-type inhibitor with respect to C6-NBD-ceramide and UDP-glucose, respectively.

Biological effects of Mammalian translationally controlled tumor protein (TCTP) on cell death, proliferation, and tumorigenesis.

Translationally controlled tumor protein (TCTP) is a highly conserved protein found in eukaryotes, across animal and plant kingdoms and even in yeast. Mammalian TCTP is ubiquitously expressed in various tissues and cell types. TCTP is a multifunctional protein which plays important roles in a number of cell physiological events, such as immune responses, cell proliferation, tumorigenicity, and cell death, including apoptosis. Recent identification of TCTP as an antiapoptotic protein has attracted interest of many researchers in the field. The mechanism of antiapoptotic activity, however, has not been solved completely, and TCTP might inhibit other types of cell death. Cell death (including apoptosis) is closely linked to proliferation and tumorigenesis. In this context, we review recent findings regarding the role of TCTP in cell death, proliferation, and tumorigenesis and discuss the mechanisms.

Up-regulation of ceramide glucosyltransferase during the differentiation of U937 cells.

The phorbol ester tetradecanoylphorbol acetate (TPA) induces promyelocytic leukaemia cells to differentiate to macrophage-like cells in vitro. During the course of this differentiation, the cells adhere to the bottom of the culture dish, a process that requires an increase in cell surface glycosphingolipids (GSLs). We examined the cellular content of glucosylceramide (GlcCer), the simplest of the GSLs, in a TPA-treated leukaemia cell line, U937. Following TPA treatment, we observed a 3.5-fold increase in GlcCer levels that was caused by enhanced activity of ceramide glucosyltransferase (GlcT-1), which catalyses ceramide glycosylation. Furthermore, in TPA-treated cell GlcT-1 amounts were increased at both the mRNA and protein levels. We also found decreased activity of lactosylceramide synthase in TPA-treated cells, which could also contribute to the increase in cellular GlcCer content.

Functional cloning of genes that suppress oxidative stress-induced cell death: TCTP prevents hydrogen peroxide-induced cell death.

We used retroviral-mediated expression cloning to identify cDNAs that inhibit cell death induced by oxidative stress. To isolate the genes, we introduced a murine embryonic retroviral cDNA library into NIH/3T3 cells, and selected for cells resistant to hydrogen peroxide. The surviving cells were cloned, and the integrated cDNAs were rescued by polymerase chain reaction. Several of the isolated cDNAs are known to be involved in modulating the redox state of cells. Other cDNAs encode proteins known to suppress apoptosis caused by reasons other than oxidative stress. These included polyadenylate-binding protein, cytosolic 1 (Pabpc1) and translationally controlled tumor protein (TCTP).

Identification and characterization of a novel alternative splice variant of mouse GMx33alpha/GPP34.

We have cloned and characterized a novel splice variant of mouse GMx33alpha/Golgi-associated protein of 34 kDa (GPP34), hereby designated GMx33alphaV/GPP34V. This splice variant skips the second and third exons, and the resulting frame shift generates a stop codon in the fourth exon. GMx33alphaV/GPP34V is comprised of 81 amino acid residues derived from the N-terminal end of the full length protein and corresponds to approximately one-third of the full length GMx33alpha/GPP34 sequence with a calculated molecular mass of 8900. In contrast to GMx33alpha/GPP34 mRNA which is expressed at similar levels in various tissues, GMx33alphaV/GPP34V mRNA was differentially expressed when examined by RT-PCR. Compared to other tissues, skeletal muscle showed relatively strong expression of GMx33alphaV/GPP34V mRNA. This splice variant cDNA was also detected in a human cell line.