Plasma membrane-derived vesicles: composition and function

Plasma membrane-derived vesicles (PMVs) are small, intact, membrane vesicles, which are released by most cells upon activation with various extracellular stimuli. This study identified that procedures used in the isolation of PMVs could be further improved by first sonicating (sonicating water-bath) samples prior to isolation of PMVs. Following water-sonication, centrifugation of cell-debris-free supernatants at 25,000 g for 2 h, yielded mostly PMVs with minimal contamination with exosomes.Agents (Histamine, PMA, ATRA) currently used in differentiation therapy for the treatment of acute myelocytic leukaemia (AML), are reported here to induce the release of PMVs from various cells and to halt the overproliferation of THP-1 promonocytes in vitro. Further investigations with the TGF-p receptor antagonist, SB-431542, showed that this inhibition was due to TGF-ß1 present on PMVs, which initiates TGF-ß signalling. This thesis also identified a novel host cell entry strategy involving PMVs, employed by T. cruzi during infection. T. cruzi metacyclic trypomastigotes trigger the release of PMVs through integrins, lipid raft microdomains and Cat' channels such as stretchactivated channels (SAC) from several cell types. Released PMVs bound to the surface of T. cruzi and abolished its complement-mediated lysis by inhibiting activation of the C3 convertase. These PMVs also carried TGF-ß, which enhanced mammalian cell invasion by T. cruzi metacyclics. Furthermore, T. cruzi-elicited release of PMVs, results in damage to the host plasma membrane. Parasites take advantage of the resulting membrane breach to enter cells before lysosomal membrane repair. Together, these results postulate important functions for PMVs in both mammalian cells and pathogens

Human plasma membrane-derived vesicles halt proliferation and induce differentiation of THP-1 acute monocytic leukemia cells.

Plasma membrane-derived vesicles (PMVs) are small intact vesicles released from the cell surface that play a role in intercellular communication. We have examined the role of PMVs in the terminal differentiation of monocytes. The myeloid-differentiating agents all-trans retinoic acid/PMA and histamine, the inflammatory mediator that inhibits promonocyte proliferation, induced an intracellular Ca(2+)-mediated PMV (as opposed to exosome) release from THP-1 promonocytes. These PMVs cause THP-1 cells to enter G(0)-G(1) cell cycle arrest and induce terminal monocyte-to-macrophage differentiation. Use of the TGF-β receptor antagonist SB-431542 and anti-TGF-β1 Ab showed that this was due to TGF-β1 carried on PMVs. Although TGF-β1 levels have been shown to increase in cell culture supernatants during macrophage differentiation and dendritic cell maturation, the presence of TGF-β1 in PMVs is yet to be reported. In this study, to our knowledge we show for the first time that TGF-β1 is carried on the surface of PMVs, and we confirm the presence within PMVs of certain leaderless proteins, with reported roles in myeloid cell differentiation. Our in vitro findings support a model in which TGF-β1-bearing PMVs, released from promonocytic leukemia cells (THP-1) or primary peripheral blood monocytes on exposure to sublytic complement or after treatment with a differentiation therapy agent, such as all-trans retinoic acid, significantly reduce proliferation of THP-1 cells. Such PMVs also induce the terminal differentiation of primary peripheral blood monocytes as well as THP-1 monocytes