Conditioned medium from MCF-7 cell line induces myofibroblast differentiation, decreased cell proliferation, and increased apoptosis in cultured normal fibroblasts but not in fibroblasts from malignant breast tissue

We studied the effect of conditioned medium (CM) obtained from cultures of oestrogen-receptor positive breast cancer MCF7 cell line on the differentiation, proliferation and apoptosis patterns of cultured breast fibroblasts from normal interstitial and malignant stromal tissue. Fibroblasts were grown in the presence or absence of CM and examined for the differentiation pattern by immunofluorescence and Western blotting procedures, for proliferation profile by Ki67 expression, and for apoptosis by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling technique. Monoclonal antibodies specific for non-muscle (NM), smooth muscle (SM) lineage and differentiation markers were applied to these cultures. CM is able to induce a SM-like differentiation in interstitial fibroblasts, i.e., essentially myofibroblast formation. Fibroblasts from tumour stroma showed the presence of a small number of smooth muscle cells (SMC) along with a large number of myofibroblasts. Treatment of these cultures with CM was unable to change this pattern. Only normal fibroblasts were responsive to the proliferation/apoptotic-inhibitory effect of the CM. These data suggest that structural and functional differences exist between stromal fibroblasts from normal breast and breast cancer with respect to the responsiveness to soluble factors present in the CM. We hypothesize that the lack of in vitro sensitivity to CM shown by 'tumour' fibroblasts is the result of an in vivo inherent and stable phenotypic change on the fibroblasts surrounding breast tumour cells occurring via a paracrine mechanism.