| Securin, encoded by the pituitary tumor‑transforming gene 1 (PTTG1), is a multifunctional regulatory protein that governs mitotic checkpoint fidelity, chromosome segregation, and non‑mitotic processes such as migration and gene expression. Securin functions as a dimeric inhibitor that binds and suppresses the protease separase, preventing precocious cleavage of the cohesin complex and thereby holding sister chromatids together until anaphase onset, while distinct domains also support separase‑independent activities that modulate microtubule nucleation, DNA‑repair responses, and p53‑linked transcription. Securin ensures accurate anaphase timing by coordinating the activation of separase with completion of spindle‑attachment and checkpoint satisfaction, and its ubiquitin‑mediated degradation by the anaphase‑promoting complex/cyclosome (APC/C) releases separase to drive cohesin removal and chromosome segregation, defects in which promote aneuploidy and genomic instability. In interphase and migrating cells, cytoplasmic securin localizes to the centrosome and Golgi where it associates with microtubule‑organizing‑center proteins such as GM130, AKAP450, and γ‑tubulin, stimulating microtubule nucleation and remodeling necessary for cell polarization, directed migration, and invasion, and securin overexpression enhances these motile behaviors in cancer models. Securin expression correlates with proliferation status and clinical outcomes, and mouse‑genetic studies show that Pttg1/securin loss predisposes to spontaneous mammary‑gland tumors and disrupts ductal morphogenesis. |
Lane 1: HT-29, Lane 2: HT-29 (Thymidine, 2 mM, 16 h)
