Studies have shown that the NS2B cofactor is required by the protease form a proteolytic

toxin C2IN-C3lim consists of enzymatically active C3lim and the enzymatically inactive N-terminal domain of C2I. When applied together with C2IIa, C2INC3lim is efficiently delivered into the cytosol of all mammalian cell types tested so far because its C2IN domain interacts with C2IIa and this triggers specific internalization via the C2 toxin uptake pathway. However, in the absence of C2IIa, C2IN-C3lim is taken up into monocytes/macrophages but not into other cell types. Like the clostridial C3 toxins, C2INC3lim is selectively taken up into macrophage-like cells by the C3-specific uptake mechanism via acidified endosomal vesicles. Regarding its Rho-selective ADPribosyltransferase activity and the cellular effects, C2IN-C3lim behaves like C3lim. Since C3 toxins are the only known Rho-inhibitors and selectively target cells from the monocyte/macrophage-line, C3 toxins and C3-KW-2449 structure derived fusion toxins such as C2IN-C3lim are ideal tools for investigation and targeted pharmacological manipulation of Rho-dependent signal transduction in cells which are related to this cell line such as osteoclasts. In vivo, monocytes/macrophages and osteoclasts are derived from pluripotent hematopoietic stem cells and in vitro, osteoclasts differentiate from macrophage-like RAW 264.7 cells. Osteoclasts form a tight sealing zone on mineralized surfaces which is essential for resorption of matrix, during reorganization of bone tissue. It was reported earlier that the C3-catalyzed ADP-ribosylation of Rho in osteoclasts resulted in disruption of their sealing zone and their resorption activity, indicating that Rho plays a crucial role for osteoclast activity. Here, we demonstrate that C2IN-C3lim is efficiently taken up into the cytosol of RAW 264.7 cells and derived osteoclasts. Treatment with C2IN-C3lim inhibited the resorption activity of already differentiated osteoclasts but also the formation of osteoclasts from RAW 264.7 cells due to the C3-catalyzed ADP-ribosylation of Rho. In contrast, C2IN-C3lim had no effects on other cultured bone cell types such as murine pre-osteoblastic MC3T3 cells, confirming its monocyte/macrophage-selective mode of action. When the buy MS023 effect of increasing concentrations of C3bot1, C3lim and C2IN-C3lim on the morphology of RAW 264.7 was compared after a 24