CONSTITUTIVE INSULIN-LIKE GROWTH FACTOR-II EXPRESSION INTERFERES WITHTHE ENTEROCYTE-LIKE DIFFERENTIATION OF CACO-2 CELLS

In this study we have examined the role of insulin-like growth factor- II (IGF-II) in the differentiation of the CaCo-2 human colon carcinoma cell line. We have shown previously that IGF-II is an autocrine growt h factor for CaCo-2 cells, IGF-II expression is high in proliferating, undifferentiated CaCo-2 cells and markedly decreases when cells becom e confluent and start to differentiate, To evaluate whether differenti ation of CaCo-2 cells depends on an IGF-II related pathway, we treated cells with a blocking antibody to the IGF-I receptor that mediates mo st IGF-II biological effects, Treatment of preconfluent CaCo-2 cells w ith this antibody decreased by 40% autonomous cell proliferation and i nduced differentiation as shown by an increase in sucrase isomaltase a ctivity and apolipoprotein A-I (apoA-I) mRNA levels. To examine the si gnificance of autocrine IGF-II production in CaCo-2 cell differentiati on, we generated stable CaCo-2 cell lines that constitutively express rat IGF-II under the control of a Rous sarcoma virus promoter. Sustain ed expression of IGF-II resulted in: (a) increased proliferative rate; (b) high IGF I receptor number, even after reaching confluence; (c) i ncreased capability of anchorage-independent growth; (d) inhibition of the expression of apoA-I and SI mRNAs, Analysis of several independen t IGF-II-transfected clones showed an inverse correlation between IGF- II mRNA levels and expression of the differentiation markers, the cell s expressing the higher levels of the transfected IGF-II being the les s differentiated ones. Our data suggest that perturbation of IGF-II-me diated cell proliferation interferes with the enterocyte-like differen tiation pathway of CaCo-2 cells.