Endocytosis inhibits the vesicular secretion of exosome marker proteins, particularly CD63, and triggers their destruction. Exosomes are small extracellular vesicles (30–150 nm) that play critical roles in human health and disease. The study examines the biogenesis of exosome marker proteins, including CD81, CD9, and CD63, which are highly enriched in exosomes. The research reveals that endocytosis inhibits the vesicular secretion of these proteins, with CD9 and CD81 being destroyed. Syntenin, a known exosome biogenesis factor, blocks CD63 endocytosis, promoting its vesicular secretion. Other endocytosis inhibitors also induce CD63's plasma membrane accumulation and vesicular secretion. CD63 is an expression-dependent inhibitor of endocytosis, triggering the vesicular secretion of lysosomal proteins and the clathrin adaptor AP-2 mu2. These findings suggest that exosome marker proteins are primarily secreted via an endocytosis-independent pathway. The study also shows that high-level CD63 expression increases the plasma membrane accumulation of YxxΦ proteins like Lamp1 and Lamp2, and induces their vesicular secretion. CD63 expression also triggers the vesicular secretion of AP-2 mu2. Bafilomycin, a vacuolar adenosine triphosphatase inhibitor, increases plasma membrane CD63 staining. Endocytosis inhibits CD9 secretion and triggers its destruction. These results highlight the complex interplay between endocytosis and exosome biogenesis, suggesting that exosome marker proteins are primarily secreted from the plasma membrane via an endocytosis-independent pathway.Endocytosis inhibits the vesicular secretion of exosome marker proteins, particularly CD63, and triggers their destruction. Exosomes are small extracellular vesicles (30–150 nm) that play critical roles in human health and disease. The study examines the biogenesis of exosome marker proteins, including CD81, CD9, and CD63, which are highly enriched in exosomes. The research reveals that endocytosis inhibits the vesicular secretion of these proteins, with CD9 and CD81 being destroyed. Syntenin, a known exosome biogenesis factor, blocks CD63 endocytosis, promoting its vesicular secretion. Other endocytosis inhibitors also induce CD63's plasma membrane accumulation and vesicular secretion. CD63 is an expression-dependent inhibitor of endocytosis, triggering the vesicular secretion of lysosomal proteins and the clathrin adaptor AP-2 mu2. These findings suggest that exosome marker proteins are primarily secreted via an endocytosis-independent pathway. The study also shows that high-level CD63 expression increases the plasma membrane accumulation of YxxΦ proteins like Lamp1 and Lamp2, and induces their vesicular secretion. CD63 expression also triggers the vesicular secretion of AP-2 mu2. Bafilomycin, a vacuolar adenosine triphosphatase inhibitor, increases plasma membrane CD63 staining. Endocytosis inhibits CD9 secretion and triggers its destruction. These results highlight the complex interplay between endocytosis and exosome biogenesis, suggesting that exosome marker proteins are primarily secreted from the plasma membrane via an endocytosis-independent pathway.