CACO-2 CELLS EXPRESS A COMBINATION OF COLONOCYTE AND ENTEROCYTE PHENOTYPES

Caco-2 cells are derived from a human colonic adenocarcinoma, but diff erentiate into small intestinal-like cells after confluence. While thi s enterocytic differentiation has been well studied, the presumed para llel loss of colonocyte function has not been as thoroughly examined. To follow the phenotype for both tissues, Western blots were performed using antisera recognizing liver/bone/kidney alkaline phosphatase and surfactant-like particle proteins found in normal human colon, along with antisera against the small bower representatives of the same prot eins. Antisera against proteins enriched in either enterocytes (alpha( 1)-antitrypsin) or colonocytes (surfactant protein A) were also evalua ted. Alkaline phosphatase activity increased from 3 to 18 days post-co nfluence. Activity at 3 days post-confluence derived substantially fro m both isomers. Thereafter, the colonic (liver/bone/kidney) isomer dec lined to low levels as the content of the enterocytic isomer rose. A s imilar pattern was found with colonic (decreasing expression) and ente rocytic (increasing expression) surfactant-like particle proteins. In particular, the content of larger enterocytic particle proteins (97 an d 116 kDa) increased with time in culture. Expression of alpha(1)-anti trypsin increased early and remained high, whereas surfactant protein A generally declined after the third day post-confluency. In summary, undifferentiated Caco-2 cells express very low levels of proteins char acteristic of either colonocytes or enterocytes. Immediately after con fluence, they expressed proteins characteristic of both cell types. Th ereafter, the content of colonocyte-specific proteins decreased, where as those specific for the enterocyte increased. The timing and degree of this phenotypic switch have implications for the interpretation of experiments using Caco-2 cells as a model of small intestinal function . (C) 1998 Wiley-Liss, Inc.