α-Actinin-1 in Megakaryocytes: Its Structure, Interacting Proteins and Implications for Thrombopoiesis.

Mutations in the ACTN1 gene, which encodes the cytoskeletal protein α-actinin-1, have been implicated in the etiology of autosomal dominant congenital macrothrombocytopenia. α-Actinin-1 is a member of the spectrin superfamily and is essential for key physiological processes in megakaryocytes and platelets. The pathophysiological mechanisms by which α-actinin-1 mutations lead to macrothrombocytopenia have been attributed to alterations in actin organization, increased binding affinity of α-actinin-1 to actin filaments, and modulation of integrin αIIbβ3 signaling. In previous studies, we utilized megakaryocyte-specific α-actinin-1 knockout (PF4-ACTN1-/-) mice to explore the influence of α-actinin-1 on megakaryocyte and platelet function. Despite these efforts, the precise mechanisms remain inadequately understood. To advance our understanding and clarify the role of α-actinin-1 in thrombopoiesis, we first delineated the functions of α-actinin-1 in megakaryocytes and platelets, followed by a comprehensive overview of the proteins known to interact with α-actinin-1. As a pivotal scaffold protein, α-actinin-1 interacts with a complex network of partners, including integrin αIIbβ3, and actin filaments, to modulate cytoskeletal dynamics, megakaryocyte maturation, and proplatelet formation. In addition to its well-documented proteins that interact with α-actinin-1 within megakaryocytes and platelets, α-actinin-1 also associates with proteins outside the megakaryocytic lineage, such as cytohesin-2 and MOB1, which have been predominantly examined in other cellular contexts. These varied interactions imply that α-actinin-1 may influence megakaryocyte and platelet functions through multiple mechanisms. This review provides a comprehensive synthesis of current knowledge regarding the structure, binding partners of α-actinin-1, and essential roles of α-actinin-1 in thrombopoiesis.