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Bone disease: scaffolding protein essential for bone resorption The interaction between RACK1, a so-called scaffolding protein that can assemble components of a signaling pathway into complexes, and c-Src, an enzyme involved in the re-organization of the actin cytoskeleton, is crucial for bone resorption. Previous studies have implicated RACK1 in differentiation of osteoclasts, bone cells that resorb bone, but a study led by Soo Young Lee at Ewha Womans University, Seoul, South Korea, shows that it is also required for mature osteoclast function. Mutations in RACK1 or c-Src that prevented them from binding to each other impaired the bone resorption activity of osteoclasts seeded on bone slices. Osteoclasts bearing the mutated proteins were unable to form transient actin rings, cytoskeleton structures that are typically observed during bone resorption. These findings could lead to new targeted therapies against diseases characterized by bone loss such as osteoporosis.