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. 2013 Mar;12(3):587-98.
doi: 10.1074/mcp.M112.021303. Epub 2012 Dec 10.

Two distinct populations of exosomes are released from LIM1863 colon carcinoma cell-derived organoids

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Two distinct populations of exosomes are released from LIM1863 colon carcinoma cell-derived organoids

Bow J Tauro et al. Mol Cell Proteomics. 2013 Mar.

Abstract

Exosomes are naturally occurring biological nanomembranous vesicles (∼40 to 100 nm) of endocytic origin that are released from diverse cell types into the extracellular space. They have pleiotropic functions such as antigen presentation and intercellular transfer of protein cargo, mRNA, microRNA, lipids, and oncogenic potential. Here we describe the isolation, via sequential immunocapture using anti-A33- and anti-EpCAM-coupled magnetic beads, of two distinct populations of exosomes released from organoids derived from human colon carcinoma cell line LIM1863. The exosome populations (A33-Exos and EpCAM-Exos) could not be distinguished via electron microscopy and contained stereotypical exosome markers such as TSG101, Alix, and HSP70. The salient finding of this study, revealed via gel-based LC-MS/MS, was the exclusive identification in EpCAM-Exos of the classical apical trafficking molecules CD63 (LAMP3), mucin 13 and the apical intestinal enzyme sucrase isomaltase and increased expression of dipeptidyl peptidase IV and the apically restricted pentaspan membrane glycoprotein prominin 1. In contrast, the A33-Exos preparation was enriched with basolateral trafficking molecules such as early endosome antigen 1, the Golgi membrane protein ADP-ribosylation factor, and clathrin. Our observations are consistent with EpCAM- and A33-Exos being released from the apical and basolateral surfaces, respectively, and the EpCAM-Exos proteome profile with widely published stereotypical exosomes. A proteome analysis of LIM1863-derived shed microvesicles (sMVs) was also performed in order to clearly distinguish A33- and EpCAM-Exos from sMVs. Intriguingly, several members of the MHC class I family of antigen presentation molecules were exclusively observed in A33-Exos, whereas neither MHC class I nor MHC class II molecules were observed via MS in EpCAM-Exos. Additionally, we report for the first time in any extracellular vesicle study the colocalization of EpCAM, claudin-7, and CD44 in EpCAM-Exos. Given that these molecules are known to complex together to promote tumor progression, further characterization of exosome subpopulations will enable a deeper understanding of their possible role in regulation of the tumor microenvironment.

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Figures

Fig. 1.
Fig. 1.
Isolation of exosomes and shed microvesicles from the colon carcinoma cell line LIM1863. LIM1863 cells were grown in serum-free medium supplemented with insulin-transferrin-selenium for 24 h, and then the CM was collected. Shed microvesicles (sMVs) were first isolated from the CM by means of differential centrifugation. The supernatant was then filtered (0.1 μm) and concentrated via centrifugal ultrafiltration through a 5K nominal molecular weight limit membrane. A33-positive exosomes (A33-Exos) were isolated from the CCM via anti-A33 antibody immunocapture. EpCAM-Exos were isolated from A33-Exos-depleted CCM by means of immunocapture using EpCAM-loaded magnetic beads.
Fig. 2.
Fig. 2.
Morphological characterization and proteome analysis of LIM1863 cell-derived A33- and EpCAM-Exos. A, electron micrographs of A33- and EpCAM-Exos negatively stained with uranyl acetate and examined at 200 kV; scale bar = 100 nm. B, Western blot analysis of A33-Exos, unbound material (flow-through of anti-A33 antibody capture beads), and EpCAM-Exos (10 μg per lane) for Alix (PDCD6IP), TSG101, A33, and EpCAM. C, two-way Venn diagram depicting the overlap of exosomal proteins derived from A33- and EpCAM-Exos. 684 proteins were common to both exosomal datasets, and 340 and 214 proteins were unique to A33- and EpCAM-Exos, respectively.
Fig. 3.
Fig. 3.
A confocal optical section through a preparation of LIM1863 organoids. LIM1863 cells were incubated with mouse anti-A33 antigen IgG and rabbit anti-EpCAM antigen IgG (1 μg/ml) followed by Alexa Fluor® 546-conjugated goat anti-rabbit IgG and Alexa Fluor® 488-conjugated goat anti-mouse IgG secondary antibodies (1:200). The A33 antigen (green) distributes to the basolateral cell periphery, and the EpCAM antigen to the apical ring (red). Scale bar, 30 μm.
Fig. 4.
Fig. 4.
A model depicting the molecular structure of two discrete populations of LIM1863-derived exosomes. Selected proteins expressed in both apical exosomes (EpCAM-Exos) and basolateral exosomes (A33-Exos) include exosomal marker proteins (Alix, TSG101, HSP70, and CD9), integrins (ITGA2, ITGAV, ITGA6, and ITGB6), ephrin receptors (EPHB1, -B2, -B3, -B4, -A2, -A5, -A6, and -A7), tetraspanin proteins (TSPAN8, TSAN14, TSPAN15, and CD81), and the tetraspanin-like claudin proteins (CLDN3, CLDN4, and CLDN15). For a detailed list of ubiquitously expressed proteins found in both A33- and EpCAM-Exos, see supplemental Table S1. Apical exosomes also contained (i) tetraspanin proteins (CD63, TSPAN3, and TSPAN6) and tetraspanin-like claudin 7 (CLDN7), (ii) apically localized sucrase isomaltase (SI) and mucin 13 (MUC13), (iii) complement-mediated lysis inhibitors (CD46, CD59), and (iv) innate immunity response high-mobility group box proteins (HMGB2, HMGB3). Apical exosomes contained EpCAM, CLDN7, and CD44, which are reported to complex together to mediate tumor progression. Basolateral exosomes contained early endosome antigen 1 (EEA1), RAB13, and basolateral sorting proteins (clathrins CLTA and CLTB; clathrin adaptor proteins AP1G1, AP1M1, AP1M2, and AP3B1; coatomer subunit COPB2; and ADP-ribosylation factor 1). Basolateral exosomes also contained the cell-membrane-spanning proteins colon-specific antigen GPA33, calsyntenin 1 (CLSTN1), receptor accessory protein 6 (REEP6), and MHC class I molecules (HLA-A, -B, -C, -E, and -A29.1).

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