SIPA1L1 (signal induced proliferation associated 1 like 1) is a RapGAP protein that regulates small GTPase signaling and cytoskeletal organization with diverse physiological roles. The protein functions as a GTPase-activating protein that modulates Rap signaling pathways, with CKIε phosphorylating SIPA1L1 to reduce its stability and increase Rap1 activation during Wnt-mediated gastrulation 1. In neuronal contexts, SIPA1L1 is essential for synaptic function and dendritic spine development, as disruption affects neurodevelopmental pathways 2. The protein plays a critical role in renal physiology by binding to aquaporin-2's PDZ-ligand motif and accelerating its endocytosis, with vasopressin-induced phosphorylation disrupting this interaction to regulate water transport 3. SIPA1L1 also contributes to pathological processes, including primary open-angle glaucoma where TGF-β2 increases SIPA1L1 expression, promoting extracellular matrix accumulation in trabecular meshwork cells while inhibiting phagocytosis through actin cytoskeleton reorganization 4. Additionally, circular RNA derived from SIPA1L1 (circSIPA1L1) acts as an oncogenic factor in osteosarcoma, functioning as a microRNA sponge to promote tumor progression 56. These findings establish SIPA1L1 as a multifunctional regulator of cellular signaling, cytoskeletal dynamics, and tissue homeostasis.