6533b824fe1ef96bd12808f3

RESEARCH PRODUCT

Shed membrane vesicles and clustering of membrane-bound proteolytic enzymes

subject

description

Publisher Summary Eukaryotic cells appear to release into the extracellular medium several populations of exovesicles, which are suggested to have different origins and functions and are identified by different names. This chapter deals with vesicles believed to originate from the cell membrane and named membrane vesicles. These are structures in which membrane-bound proteolytic enzymes are clustered and they play important roles in matrix remodeling. Relatively large membrane vesicles (diameters ranging from 100 nm to 1 μm) are shed from plasma membranes through unidentified budding mechanisms. These membrane structures are enriched in selected plasma-membrane components including integrins, HLA molecules, and cell surface-associated proteolytic enzymes. MMP-9, MMP-2, MMP-13, MT1-MMP, MMP-1, uPA, and seprase have been detected in vesicles shed by one or more cell lines. Highly motile cells and cells actively involved in bone formation release more vesicles, and these vesicles are richer in membrane-bound proteolytic enzymes. Vesicle membranes are capable of promoting the activation of proteolytic cascades in the pericellular space, facilitating cell motility and tumor invasion. In hypertrophic chondrocytes, shed vesicles promote the first steps of bone mineralization and the following steps of matrix remodeling needed for bone formation. Vesicles shed by platelets and by some tumor cells exert a procoagulant activity. Shed vesicles appear also to be involved in the release of several signaling molecules and in tumor escape from immune rejection. Many studies indicate that cells can produce not only these relatively large membrane vesicles, but also other populations of exovesicles having specific characteristics and functions (exosomes and argosomes).