Disruption of the dynein-dynactin complex unveils motor-specific functions in osteoclast formation and bone resorption

Abstract

Osteoclastic bone resorption requires strict interplay between acidified carrier vesicles, motor proteins, and the underlying cytoskeleton in order to sustain the specialized structural and functional polarization of the ruffled border. Cytoplasmic dynein, a large processive mechanochemical motor comprising heavy, intermediate, and light chains coupled to the dynactin cofactor complex, powers unilateral motility of diverse cargos to microtubule minus-ends. We have recently shown that regulators of the dynein motor complex constitute critical components of the osteoclastic bone resorptive machinery. Here, by selectively modulating endogenous dynein activity, we show that the integrity of the dynein-dynactin motor complex is an essential requirement for both osteoclast formation and function. Systematic dissection of the osteoclast dynein-dynactin complex revealed that it is differentially localized throughout RANKL-induced osteoclast formation and activation, undergoing microtubule-coupled reorganization upon the establishment of cellular polarization. In osteoclasts actively resorbing bone, dynein-dynactin intimately co-localizes with the CAP-Gly domain-containing microtubule plus-end protein CLIP-170 at the resorptive front, thus orientating the ruffled border as a microtubule plus-end domain. Unexpectedly, disruption of the dynein-dynactin complex by exogenous p50/dynamitin expression retards osteoclast formation in vitro, owing largely to prolonged mitotic stasis of osteoclast progenitor cells. More importantly, loss of osteoclastic dynein activity results in a drastic redistribution of key intracellular organelles, including the Golgi and lysosomes, an effect that coincides with impaired cathepsin K secretion and diminished bone resorptive function. Collectively, these data unveil a previously unrecognized role for the dynein-dynactin motor complex in osteoclast formation and function, serving not only to regulate their timely maturation but also the delivery of osteolytic cargo that is essential to the bone resorptive process. ß

PLEKHM1/DEF8/RAB7 complex regulates lysosome positioning and bone homeostasis

“…Consistent with this possibility, we have previously found that LIS1 regulates the survival of osteoclast precursors by modulating JNK activation (38). Similarly, disturbance of dynein function impairs osteoclast differentiation and function (80). Loss of Plekhm1 caused dramatic morphological changes in osteoclasts but did not affect the number of mature osteoclasts cultured on plastic (Figure 4 and Supplemental Figure 3).…”

Microtubule Dynamic Instability Controls Podosome Patterning in Osteoclasts through EB1, Cortactin, and Src

“…MTs play a central role in processes essential for OC activity and bone resorption: polarization of the cells (66), vesicular traffic (67)(68)(69)(70)(71)(72), motility (68), and podosome belt formation (21,23,24,70,(73)(74)(75). Formation of the podosome belt has been the focus of this study because if other cell types use podosomes/invadosomes to migrate, adhere, and degrade the extracellular matrix (7), OCs are the only cells where podosomes follow a precise patterning such that clusters form rings that fuse and expand to form a characteristic peripheral belt (6,7,12), establishing the sealing zone when OCs are plated on bone or dentin (11).…”

Dynein Light Chain LC8 Inhibits Osteoclast Differentiation and Prevents Bone Loss in Mice

“…Microtubule organization, intracellular vesicular trafficking, and the activity of dynein motor are critical for the activation and function of osteoclasts (46)(47)(48). LIS1 was recently identified as a microtubule regulator that interacts with both Plekhm1, a component of late endosomal trafficking, and the dynein-dynactin motor complex in osteoclasts (47).…”

“…Depletion of LIS1 dramatically inhibited the formation and bone resorption function of osteoclasts by interfering with dynein function and microtubule organization (47). Exogenous expression of dynamitin, a component of the dynactin complex, disrupted the dynein-dynactin complex, leading to retardation of osteoclast formation (48). Therefore, the role of LC8 in osteoclast differentiation as an essential component of the dynein motor complex may be worthy to be studied.…”