CONTRIBUTION OF TRYPSIN SENSITIVE PROTEINS TO BINDING OF CATIONIC LIPOSOMES TO THE MOUSE MACROPHAGE-LIKE CELL-LINE RAW264.7

We studied the binding of cationic liposomes, including didodecyl N(al pha-(trimethylammonio)acetyl)-D-glutamate chloride (TMAG), to a mouse macrophage-like cell line RAW264.7 to clarify which molecules contribu te to the binding of TMAG liposomes to the cell surface. Several types of TMAG liposomes encapsulating [H-3]inulin, intra-aqueous markers of liposomes, were prepared and their binding characteristics were compa red with those of neutral and negatively charged liposomes. The bindin g of TMAG liposomes to cells was superior to those of neutral and nega tively charged liposomes and increased with increasing TMAG content. S catchard plots for the binding of TMAG liposomes to the cells were app roximately linear, indicating a single class of binding sites. Pretrea tment of the cell surface with heparinase, heparitinase, chondroitinas e ABC, or neuraminidase did not reduce the binding of TMAG liposomes. These results suggested that neuraminic acid and glycosaminoglycan on the cell surface have little contribution to TMAG liposome binding. Pr etreatment of the cells with trypsin reduced the binding of TMAG lipos omes in a concentration-dependent manner but did not detach the cells from the culture plates. In addition, alpha-chymotrypsin pretreatment had no effect even up to 5 mu g/mL. Post-treatment with trypsin enhanc ed the release of TMAG liposomes from the cell surface in a concentrat ion-dependent manner. These results demonstrated that TMAG liposomes b ind to trypsin-sensitive proteins on the cell surface.