Malignant ascites-derived exosomes of ovarian carcinoma patients contain CD24 and EpCAM.
OBJECTIVE
CD24 is an established marker for poor prognosis in ovarian and other carcinomas. Acquisition of cytoplasmic CD24, as opposed to membranous expression, has been correlated with a higher invasiveness of tumor cells. Exosomes are small vesicles of endosomal origin that are often secreted by tumor cells. Given the emerging role of exosomes in tumor progression, we investigated whether cytoplasmic CD24 expression is correlated with the secretion of CD24 in exosomes.


METHODS
We used CD24 transfected carcinoma cell lines, ovarian carcinoma cell lines and malignant ascites fluid of ovarian carcinoma patients. Exosomes were isolated via ultracentrifugation and sucrose density fractionation and subsequently examined by Western blot analysis and gelatine zymography. In tissue sections CD24 was detected by immunohistochemical staining.


RESULTS
We show that CD24 is released by transfected as well as endogenously expressing cells in vesicles that represent exosomes. CD24 was also identified in exosomes isolated from ascites fluid of ovarian carcinoma patients. In 16 ovarian carcinomas analyzed no correlation between CD24 in tumor tissue sections and the appearance of CD24 in exosomes was detected. Furthermore, we provide evidence that the epithelial cell adhesion molecule (EpCAM), known to be overexpressed in ovarian carcinomas, is secreted in exosomes. The ascites exosomes contain gelatinolytic enzymes.


CONCLUSIONS
Our study identifies CD24 and EpCAM as cargo proteins of exosomes of cultured cell lines and malignant ascites. The exosome-associated proteolytic activity in the tumor vicinity might augment tumor invasion into the stroma.
Runz
Steffen
S
Tumor Immunology Programme (D010), German Cancer Research Center, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany.
Keller
Sascha
S
Rupp
Christian
C
Stoeck
Alexander
A
Issa
Yasmin
Y
Koensgen
Dominique
D
Mustea
Alexander
A
Sehouli
Jalid
J
Kristiansen
Glen
G
Altevogt
Peter
P
D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000951:Antigens, Neoplasm / Q000378:metabolism*; D001201:Ascites / Q000378:metabolism; D051927:CD24 Antigen / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D045744:Cell Line, Tumor; D000071858:Epithelial Cell Adhesion Molecule; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D022142:Secretory Vesicles / Q000378:metabolism*; D014162:Transfection
D000951:Antigens, Neoplasm; D051927:CD24 Antigen; C497889:CD24 protein, human; D015815:Cell Adhesion Molecules; C499379:EPCAM protein, human; D000071858:Epithelial Cell Adhesion Molecule; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9