in 12-well tissue culture plates containing the polyacrylamide gel substrates

3-uptake into differentiating osteoclasts, whereas no C3-specific staining was detected in untreated control cells. The images of C2IN-C3lim-treated L67 osteoclasts show the distribution of internalized C2IN-C3lim in the cells. The punctual green staining likely indicated distinct localisation of C2IN-C3lim in endosomal vesicles while the more diffuse distribution of the green staining might represent C2IN-C3lim which had already been released from the endosomal vesicles into the cytosol. The distribution of the green staining over the whole cell bodies including the protrusions suggested an extensive uptake of C2IN-C3lim. However although C2IN-C3lim alone was taken up into differentiating osteoclasts in a INNO-406 sufficient amount to induce cellular effects, its uptake into the cytosol of osteoclasts was enhanced when the separate transport component C2IIa was added. Prompted by our earlier findings that clostridial C3bot1 and C3lim toxins are selectively taken up by cells of the monocyte/ macrophage line, we have performed a series of experiments to investigate the effects of C3-treatment on osteoclasts which were generated by RANKL-induced differentiation of murine osteoclastic RAW 264.7 cells. Like the clostridial C3 toxins, the recombinant C2IN-C3lim fusion toxin was selectively internalized into undifferentiated RAW 264.7 cells and already differentiated osteoclasts by the C3-specific uptake mechanism. Interestingly, C2IN-C3lim exhibited a stronger effect than C3lim alone or C3bot on undifferentiated RAW 264.7 cells. Although the reason for this unexpected effect is not known, one could speculate that the C2IN portion enhances the uptake of the C3 ADP-ribosyltransferase into the cytosol of the macrophages. In particular, C2IN could enhance endosomal membranes from the endosomal lumen into the cytosol since C2IN mediates this translocation step of the C2I ADP-ribosyltransferase through C2IIa-pores across endosomal membranes. Moreover, C2IN could serve as a scaffold protein which may facilitate refolding of C3lim in the cytosol if an unfolding of C3lim is required for membrane translocation, which is not clear so far. Therefore, C2IN-C3lim was used to investigate the effects mediated by C3-catalyzed Rho-inhibition in differentiating osteoclasts and in already differentiated osteoclasts. By using this fusion toxin, we