Sarcostemma viminale: a potential anticancer therapy

There is a need for cancer treatments to be selectively cytotoxic to cancer cells so as to reduce adverse side effects. In this study, a cancer cell line (HeLa cells) and a non-cancer cell line (HF-32) were exposed to an extract from the plant Sarcostemma viminale. Cytopathic effects and apoptosis were measured by morphological changes, annexin V/propidium iodide (PI) and 4′,6-diamidino-2-phenylindole (DAPI) staining assays. Also, a novel mixed culture flow cytometry assay was performed exploiting the overexpression of p16INK4a in HeLa cells to demonstrate the change in numbers of HeLa and HF-32 cells post-exposure to the extract. At 1 % (v/v) after 48 h of exposure, HeLa cells showed >75 % cytopathic effect, 77 % were in apoptosis or dead by the annexinV/PI assay, and 100 % had nuclear changes by DAPI staining; there was a reduction of 76 % in the number of cells by mixed culture assay. In contrast, for the HF-32 cells, only 5 % showed any cytopathic effect, there were no more cells in apoptosis or dead (34 %) than in the control by the annexinV/PI assay, <1 % of cells had nuclear changes by DAPI staining, and there was a slight increase in cell numbers by the mixed culture assay. Results from these assays clearly demonstrate that the extract from S. viminale destroyed the cancer HeLa cells quickly and at a low concentration, whilst the non-cancer HF-32 cells survive. This study indicates that extracts from S. viminale may be a specific anticancer agent

ArfGAP1 responds to membrane curvature through the folding of a lipid packing sensor motif

ArfGAP1 promotes GTP hydrolysis in Arf1, a small G protein that interacts with lipid membranes and drives the assembly of the COPI coat in a GTP-dependent manner. The activity of ArfGAP1 increases with membrane curvature, suggesting a negative feedback loop in which COPI-induced membrane deformation determines the timing and location of GTP hydrolysis within a coated bud. Here we show that a central sequence of about 40 amino acids in ArfGAP1 acts as a lipid-packing sensor. This ALPS motif (ArfGAP1 Lipid Packing Sensor) is also found in the yeast homologue Gcs1p and is necessary for coupling ArfGAP1 activity with membrane curvature. The ALPS motif binds avidly to small liposomes and shows the same hypersensitivity on liposome radius as full-length ArfGAP1. Site-directed mutagenesis, limited proteolysis and circular dichroism experiments suggest that the ALPS motif, which is unstructured in solution, inserts bulky hydrophobic residues between loosely packed lipids and forms an amphipathic helix on highly curved membranes. This helix differs from classical amphipathic helices by the abundance of serine and threonine residues on its polar face