Human fibroblasts from normal and malignant breast tissue grown in vitro show a distinct senescence profle and telomerase activity

The telomerase activity and the senescence profile of cultured breast fibroblasts from normal human interstitial and malignant stromal tissue were studied in comparison with their proliferation and differentiation pattern. Fibroblasts were grown either in the presence or absence of a conditioned medium (CM) obtained from cultures of the oestrogen receptor-positive breast cancer MCF-7 cell line. At different passages (from the 2nd up to the 48th), fibroblasts were examined for the telomerase activity by the Telomerase Repeats Amplification Protocol (TRAP) assay, for proliferation profile by Ki-67 antigen expression, and the myofibroblast or smooth muscle cell-like differentiation pattern by immunofluorescence with monoclonal antibodies specific for smooth muscle markers. Serial passages of fibroblasts from normal or tumour breast reveal that the relationship between the levels of telomerase activity and phenotypic/proliferation profile changes with cell subcultivation in a different manner in the two cell populations. The fibroblasts from normal tissue completed 12 passages in a CM-independent way prior to senescence whereas fibroblasts from tumour stroma senescence were attained after 48 passages. These cells showed a marked decrease of telomerase activity, growth rate and smooth muscle alpha-actin expressing myofibroblasts after the 32nd passage. CM treatment of this fibroblast population induces a decline in the myofibroblast content, which precedes the changes in telomerase activity. Passaged fibroblasts from normal breast tissue can be converted to myofibroblasts upon CM treatment whereas those from tumour stroma were CM-insensitive. Taken together our data suggest that a heterogeneous fibroblast population with different life span is activated/recruited in the breast interstitium and poses the problem of a unique activation/recruitment of fibroblasts in neoplastic conditions.