Soluble E-Cadherin Facilitates Pre-Metastatic Niche Hyperpermeability Via Rac2

Lung metastasis is the main cause of mortality in salivary adenoid cystic carcinoma (SACC). Preventing vascular barrier leakiness in the pre-metastatic niche is a key strategy for inhibiting metastasis. Stable bounded of ZO-1 and filament actin (F-actin) forms tight junction and regulates permeability. This study aims to clarify the SACC derived effector for promoting vascular permeability and mechanism. Conditional media (CM) from SACC cell lines were intraperitoneally injected into C57BL/6J mice for 24 hours. FITC-dextran or GFP-labeled SACC cells were then injected into the tail vein to assess endothelial barrier leakiness. Transwell invasion assay, immunocytochemistry staining, co-immunoprecipitation and G-actin/F-actin separation were used to investigate the effects of SACC on tight junctions and actin filament arrangement in lung microvascular endothelial cells (LMECs). Western blot, qRT-PCR, and mass spectrometry were employed to study the Rac2/Cofilin/LIMK pathway activation and SACC-secreted proteins regulating membrane dynamics. ACC-CM facilitated phosphorylation of cofilin and LIMK1/2 by driving Rac2 translocation from the nuclear membrane to the plasma membrane (PM). Over-polymerization of F-actin in the PM resulted in decreased ZO-1 binding and tight junction damage. Mass spectrometry and clinical data indicated significant overexpression of soluble E-cadherin in SACC patients with lung metastasis. Soluble E-cadherin from SACC contributes to tumor extravasation by inducing vascular permeability in PMNs, mediated through activation of the Rac2/Cofilin/LIMK pathway. These findings may provide a therapeutic target for preventing SACC lung metastasis.