From Adhesion to Bone Resorption: The Role of Dynamin in Osteoclasts

Funder(s): NIH/National Institute of Arthritis and Musculoskeletal and Skin Diseases

Bone resorption is performed by the mature osteoclast. To resorb bone, osteoclasts require both the presence of dynamic actin adhesion structures in the sealing zone (podosomes) and very efficient endocytosis in the ruffled-border domain. Data generated in our laboratory within the last five years has clearly established that two signaling enzyme activities are directly involved in the regulation of both bone resorption and actin dynamics in the osteoclast. On the one hand, we have shown that both Src tyrosine kinase activity and the binding of Src to Pyk2 are required, for bone resorption and for the dynamic assembly and disassembly of podosomes. On the other hand, we have also shown that dynamin 2 and its GTPase activity are involved in the dynamic assembly and disassembly of podosomes and are required for bone resorption by osteoclasts. Further, we have shown that dynamin, itself a substrate of Src, interacts with Pyk2 and with Cbl.

This current study therefore explores the role of dynamin in the integrin-dependent signaling cascade that regulates podosome assembly and disassembly and the initiation of endocytosis at the ruffled border, and how dynamin 2 GTPase activity and the Pyk2 and Src tyrosine kinase activities regulate bone resorption in a coordinated manner. The first aim focuses on the early integrin signaling events involving dynamin/Pyk2 interaction and taking place upstream of Cbl, their regulation, and their link to actin dynamics and/or endocytosis in osteoclasts. The second aim explores the signaling events involving the dynamin/Cbl interaction that take place downstream of Cbl, their regulation, and their link to both actin dynamics and endocytosis. The third aim focuses on determining the role of dynamin in genetic experiments in vitro and in vivo: analyzing the skeletal and osteoclastic effects of dynamin knockouts/knockdowns and transgenic expression of mutants, selected from the results obtained in aims 1 and 2. This project explores a novel concept, based on strong (and partially published) preliminary data, which we believe will help further understand the mechanisms that regulate bone resorption.