Mechanism of CEA release from the malignant cells of colorectal carcinoma

Carcinoembryonic antigen (CEA) is one of the most frequently used tumor markers which is over-expressed in a variety of human cancers with epithelial origin such as colorectal, gastric, pancreatic, lung and breast cancers. The precise mechanism by which CEA is released from the cell surface into serum in cancer patients has not been clarified so far. CEA is attached to the plasma membrane by a glycophosphatidyl inositol (GPI) anchor. There have been some evidences indicating a possible role for involvement of an enzyme in CEA release from the cell surface. The GPI-anchor is a substrate for specific phospholipases. According to these information, we investigated the possible role of GPI-specific PI-PLD (GPI-PLD) in hydrolysis and CEA release. We have, therefore, used reverse transcription-polymerase chain reaction (RT-PCR) to verify GPI-PLD expression in some cell lines of colorectal adenocarcinoma. The amount of CEA released from a high CEA producing cell line in the presence or absence of specific activators/inhibitors of this enzyme was measured. Using RT-PCR, expression of GPI-PLD gene in these cell lines can be demonstrated. The amount of CEA released from high producing cell lines are increased or decreased in the presence or absence of specific activators/inhibitors. According to this study there are evidences implicating the role of GPI-PLD enzyme in releasing CEA from the surface of the cells of colorectal carcinoma.