Detection by in situ hybridization of messenger RNAs of collagen types I and IV in murine mammary cancer.

Ten breast carcinomas developing in C3H/Bi female mice were studied by an in situ hybridization technique using cDNA probes encoding alpha-I chains of collagens of types I and IV. The results obtained are compared to histochemical data on antibodies to collagens of types I and IV and ultrastructural observations on these tumors. Immunohistochemistry has revealed the presence of type-IV collagen in basement membranes lining intraductal and well-differentiated cancer nests. Type-I collagen was detected in the stroma surrounding these cells. There was no cellular labelling when these antisera were used. In situ hybridization has shown that type-IV collagen mRNA is detected in non-invasive intraductal and well-differentiated tumor cells and in endothelial cells in the stroma. Good correlation between detection of type-IV collagen lining these cells and evidence of mRNA by in situ hybridization was thus observed. Invasive cancer cells did not express hybridization grains with the type-IV collagen probe. Type-I collagen mRNA was visualized in stromal cells, probably fibroblasts and myofibroblasts as shown by electron microscopy. The most active cells were localized close to non-invasive areas. Our data indicate persistent in-vivo biosynthesis of type-IV collagen by some cancer cells that produce their own limitative environment; they suggest that type-IV collagen is not produced by invasive tumor cells and that stromal cells lining the non-invasive regions have a peculiar behavior.