RASIP1 (Ras interacting protein 1) is a vascular-specific GTPase regulator essential for endothelial cell morphogenesis and vascular development. Primary function: RASIP1 acts as a dimeric Ras/Rap1 effector protein that controls endothelial cell architecture and adhesion 1. The protein negatively regulates RhoA signaling by recruiting ARHGAP29, thereby suppressing ROCK and myosin activity critical for maintaining endothelial junctional integrity 2. RASIP1 localizes to cell-cell junctions through direct binding to HEG1, where it stabilizes vascular barriers 3. Mechanism: RASIP1 functions downstream of Sox17 in hematopoietic stem cell cluster formation during embryonic development 4, and participates in multi-protein effector complexes regulating circumferential actin cable tension 2. Disease relevance: Beyond its vascular role, RASIP1 is aberrantly upregulated in diffuse large B-cell lymphoma (DLBCL), where it promotes cell proliferation, invasion, and cell cycle progression; FOXO3 suppresses RASIP1 transcription to inhibit DLBCL malignancy 5. RASIP1 emerges as a novel genetic risk locus for venous thromboembolism 6, and as a shared dysregulated gene in type 2 diabetes and osteoarthritis comorbidity 7. High RASIP1 activity in endothelial cells associates with pulmonary arterial hypertension pathogenesis 8. Clinical significance: RASIP1 represents both a vascular development regulator and an emerging therapeutic target across malignancy and thrombotic disease.