CHANGE OF CALRETININ EXPRESSION IN THE HUMAN COLON ADENOCARCINOMA CELL-LINE HT29 AFTER DIFFERENTIATION

Calretinin is a Ca2+-binding protein of the EF-hand family which is ex pressed in colon adenocarcinomas and colon-derived tumor cell lines (e .g. WiDr), but is absent from normal human enterocytes. Its function h as not as yet been elucidated, but some lines of evidence lead us to p ostulate its involvement in cell proliferation in these cells. In orde r to test whether calretinin is correlated with an undifferentiated, p roliferating, or with a differentiated, state of cells, its expression was studied in the human colon adenocarcinoma clonal cell line HT29-1 8, which can be caused to differentiate into enterocyte-like cells by replacing glucose with galactose in the culture medium (glucose starva tion differentiation). Treatment of HT29-18 cells with galactose led t o a drop in the calretinin mRNA level and in protein expression as evi denced by immunocytochemical staining and Western blot analysis of cyt osolic cell extracts. These results suggest that calretinin is present in HT29-18 cancer cells, mostly in those which are in the undifferent iated state. The possibility that calretinin is involved in maintainin g the cells in an undifferentiated (cancerous) state is discussed.