Fibrinogen assembly, secretion, and deposition into extracellular matrix by MCF-7 human breast carcinoma cells

A hallmark of breast carcinoma is the deposition of fibrinogen (FBG) without subsequent conversion to fibrin in the tumor stroma. In this study, the ability of the MCF-7 human breast cancer epithelial cell line to synthesize, secrete, and deposit FBG into the extracellular matrix (ECM) was examined. Whereas MCF-7 cells produced low levels of intact FBG, abundant levels of FBG intermediate complexes or degraded Aalpha, Bbeta, and gamma chain polypeptides were observed. Most of the Bbeta chain was degraded and missing an NH2-terminal peptide fragment. Reverse transcription-PCR analysis indicated that only gamma chain mRNA was present in detectable steady-state levels, although Southern hybridization revealed that the FBG Aalpha, Bbeta, and gamma chain genes were intact in MCF-7 cells. Immunostaining showed that extracellular FBG was bound to the surface of MCF-7 cells in a punctate pattern, reminiscent of receptor binding, rather than a fibrillar pattern characteristic of mature ECM. A similar punctate pattern of staining was observed when MCF-7 FBG was added to fibroblasts that normally assemble exogenous FBG into an extensive, fibrillar ECM, suggesting that MCF-7 cells are defective in assembly of a fibrillar ECM. The loss of FBG Bbeta chain NH2-terminal peptides may contribute to the lack of intact FBG assembly in MCF-7 cells, which may further affect its ability to assemble FBG into a fibrillar ECM. Taken together, the data suggest that endogenous synthesis and secretion of FBG is, at least in part, the source of FBG deposition in the ECM of breast cell carcinomas.