LAMININ EXPRESSION IS CORRELATED TO DIFFE RENTIATION OF COLONIC-CANCER CELL-LINES

The level and molecular composition of laminin, a major basement membr ane glycoprotein formed of three chains (A, B1 and B2) have been analy zed in various human colonic cancer cells (Caco-2 and HT29). The synth esis of laminin over a 24 h period, corresponding to cellular and secr eted molecules purified by affinity chromatography, was the highest in the more differentiated cells. Immunocytochemical detection of the co nstituent chains of laminin in permeabilized cells as well as after se paration on polyacrylamide gels showed that A, B1 and B2 chains were e xpressed in Caco-2 cells, whereas A chain was not detected in HT29 cel ls. When cancer cells were cultured on a monolayer of confluent fibrob lastic cells, laminin was deposited at the basement membrane level onl y in the case of the most differentiated cells. In an attempt to defin e the role of laminin-A chain, transfection of Caco-2 cells with A cha in antisense cDNA was performed; among the clones obtained, 3 were def icient for the target polypeptide. The consequences of the absence of laminin-A chain on basement membrane formation, cellular differentiati on and tumor invasion will be currently determined.