MONENSIN STIMULATES EXOSOME RELEASE BY A CALCIUM-DEPENDENT MECHANISM

SAVINA, A., FADER, C., FURLAN, M., VIDAL, M. AND COLOMBO M.I

Villa Carlos Paz, Córdoba. Argentina

Congreso; XXX VIII Annual Meeting SAIB 2002; 2002

SAIB (Sociedad Argentina de Investigación Bioquímica y Biología Molecular)

Multibesicular bodies (MVB) are endocytic structures that contain small vesicles formed by budding of endosomal membrane onto the lumen of the compartment. Fusion of MVB with the plasma membrane result in secretion of internal vesicles termed exosomes. K562 cells are a hematopoietic cell line that release exosomes. Application of monensin (MON) generates large MVB that were labelled with fluorescent lipid N-Rh-PE. Interestingly, the release of exosomes was markedly enhances by MON treatment. It has been shown that MON, a Na+/H+ exchanger, induces changes in intracellular calcium (Ca+2). To explore the possibility that the effect of MON on exosomes release was caused via an increase in Ca+2 we have used A23187, a calcium ionophore, and BAPTA-AM, a calcium chelator. Our result indicates that increasing Ca+2 via A23187 also stimulates exosome secretion. Furthermore the MON-stimulated exosome release was completely abrogated by BAPTA-AM, indicating the requirement for Ca+ for this process. Surprisingly, we have observed that the large MVBs generated by labelling with Fluo3-AM, suggesting that intralumenal Ca+2 might play a critical role in the secretory process.