Exosome Like Vesicles
Exosomes are 50-150 nm diameter vesicles secreted by different cell types including epithelial (4), haematopoietic (reticulocytes, dendritic cells, B cells, T cells, mast cells) and some tumour cells (5). In addition, exosomes has been isolated and characterized from different biological fluids such as urine (6), BAL fluid (7) and serum (8).The molecular organisation of this structure is depends mainly on the source from which they are derived. Functional diversity of the exosomal proteins is limited. Typical proteomics analysis of exosomes suggests the absence of nuclear, mitochondrial and endoplasmic reticulum and golgi originated proteins. However most of the exosomal proteins are to be found in the cytosol, cytoskeletal and plasma membrane of the original cell. Our initial studies on the isolation of HTBE mucins and induced sputum indicated that isolated mucin rich fractions contain lipid/carbohydrate/protein rich vesicular/exosomal material. Further fractionation and preliminary proteomics analysis on these fractions revealed proteins characteristic of exosomes (9). Some 35, readily detectable proteins were available in the isolated exosomes including the membrane bound mucin MUC1 as well as cytoskeleton proteins such as actin and tubulin and their associated proteins ezrin, moesin and EBP50. Some of the proteins we identified were previously associated with exosomes such as annexines, tetraspanins 14-3-3 proteins. In contrast to most of the other exosome identified, our proteomics and immunoblotting analysis showed that HTBE exosomes contain no MHC class I and II proteins. In other words they are not antigen presenting exosomes unlike the ones derived from B and T cells, dendritic cells, enterocytes and tumor cells.
Support: American Lung Association RG-167538-N Kesimer (PI)