Abstract

Syndecan4 (SDC4), a well-characterized plasma membrane glycoprotein that functions as an extracellular matrix receptor and growth factor co-receptor, is frequently overexpressed in tumors. Its accumulation is associated with increased generation of small extracellular vesicles (sEVs), promoting tumor development and metastasis. However, the underlying mechanism of SDC4 degradation remains poorly understood. This study reveals that SDC4 undergoes constitutive shedding, generating a transmembrane C-terminal fragment (CTF). This fragment is subsequently cleaved by γ-secretase, leading to rapid, likely proteasome-dependent degradation under basal conditions, thereby maintaining SDC4 homeostasis. During endocytic or stress conditions, SDC4-CTF is alternatively degraded via the endocytosis-lysosome pathway. Overexpression of Syntenin protects SDC4-CTF from endo-lysosomal degradation. To identify small molecules that directly modulate SDC4 stability, we employed a microscale thermophoresis (MST) screening approach and identified Andrographolide (AGO), a natural compound that directly binds to SDC4 and selectively blocks its interaction with Syntenin. Further studies have shown that AGO promotes SDC4-CTF lysosomal degradation and reduces the production of sEVs. In summary, our findings demonstrate that AGO blocks SDC4-Syntenin interaction and inhibits sEVs biogenesis, providing a new pharmacological ligand for targeting SDC4.