RNA-lipid complexes released from the plasma membrane of human colon carcinoma cells

Cultured cells from human colon adenocarcinoma spontaneously release structures which display an intense 31P NMR signal from RNA and mobile phospholipids. Furthermore, the DPH probe in the cell supernatant shows an intense fluorescence, thus indicating its insertion in lipid vesicles. The total membranes, prepared from the same cells, also release similar structures. The fatty acid chain signals from the mobile lipids, observable in the H NMR spectrum, and the fluorescence polarization of the DPH probe are strongly affected by RNAase digestion, thus indicating an association between RNA molecules and lipids. The enzymatic marker cytochrome c reductase was assayed to rule out possible contamination from endoplasmatic reticulum. A high alkaline phosphatase activity was instead found in the supernatant samples, thus indicating that the shed material is released by the plasma membrane.