ACTN4 (actinin alpha 4) is a non-muscle F-actin cross-linking protein that anchors actin to intracellular structures and functions as an actin bundling protein. Primary functions include cytoskeletal organization, with roles in vesicular trafficking via the CART complex for transferrin receptor recycling, and tight junction assembly in epithelial cells 1. ACTN4 also possesses transcriptional coactivator activity, stimulating nuclear hormone receptor-mediated transcription 2, and regulates immune synapse formation through IGSF8 interaction, required for T-cell activation 3. Mechanistically, ACTN4 regulates multiple signaling pathways. It interacts with HDAC5, which deacetylates ACTN4 at K417 to enable nuclear translocation and modulation of YBX1 transcriptional activity during wound healing 4. In cancer contexts, ACTN4 promotes tumor progression through epithelial-mesenchymal transition and metastasis 5. The CCT3/ACTN4/TFRC axis regulates ferroptosis in hepatocellular carcinoma by controlling iron endocytosis 6, while PDLIM1 competitively binds ACTN4 to regulate Hippo signaling and suppress HCC metastasis 7. CircACTN4 promotes intrahepatic cholangiocarcinoma through miR-424-5p sponging and YBX1-mediated FZD7 transcription 8. Clinically, ACTN4 variants associate with preeclampsia and hypertensive pregnancy disorders, linking to placental development, spiral artery remodeling, and kidney function 9. ACTN4 is also implicated in aortic aneurysm pathogenesis through vascular smooth muscle cell gene expression 10.