Effect of Basic Fibroblast Growth Factor on Synthesis/Secretion of pS2 Protein by Human Breast Cancer Cells (MCF‐7)

Abstract

pS2 is an estrogen-induced mRNA species that was originally identified in the breast cancer cell line MCF-7. Exposure of the cells to basic fibroblast growth factor (bFGF) at the concentration of 10-100 ng/ml for 48-72 h resulted in a marked increase in the concentration of pS2 protein in the medium. The polymerase chain reaction with reverse transcriptase revealed that bFGF increased the amount of intracellular pS2 mRNA ; immunocytochemical studies showed that exposure to the factor increased the amount of intracellular pS2 protein. Simultaneous addition of cycloheximide with bFGF completely abolished induction of pS2 protein, although it did not affect the induction of pS2 mRNA. Actinomycin D did not affect the stimulatory effect of bFGF on synthesis/secretion of pS2 protein. bFGF effectively abolished decay of the pS2 mRNA level caused by actinomycin D. These results suggest that the induction of the synthesis/secretion of pS2 protein by bFGF occurs at the post-transcriptional level, most probably due to the stabilization of pS2 mRNA. Another finding, that bFGF and estradiol have a synergistic effect on induction of pS2 protein, suggests the possibility that these two inducers act by a different but partly overlapping mechanism.The human pS2 gene encodes a cysteine-rich, 84-aminoacid peptide of molecular mass 9140 Da, containing at its amino terminus a signal peptide characteristic of secreted proteins [l]. The secreted mature protein (pS2 protein) is 60 amino acids long [2], and has a domain, the P domain [3], containing strikingly conserved cysteine residues that are presumed to participate in a trefoil disulfide loop structure.Very little is known about the biological function of pS2 protein. At the time of its discovery, estrogen-inducible pS2 protein was considered to be a key regulatory component in the proliferation of MCF-7 cells [4-71 but we have recently shown that this is not possible [8, 91. pS2 protein may possess multi-functional properties in some tissues. First, the possibility that pS2 protein might be involved in the maintenance of mucosal integrity was presented, because pS2 protein is normally expressed and secreted in individuals of both sexes by gastric mucosa cells [lo], and pS2 protein has remarkable similarity in sequence and expression to other trefoil factors such as porcine pancreatic spasmolytic polypeptide, whose function is the repression of gastrointestinal motility and the inhibition of pentagastrin-induced gastric acid secretion [3,11, 121. Second, the sequence similarity between pS2 protein and sucrase-isomaltase (oligo-I ,6-glucosidase, a carbohydrate-degrading enzyme) raised the possibility that pS2 protein secreted by breast tumor cells might contribute to degradation of the extracellular glycoprotein matrix [3] of breast tissue.Correspondence to K. Hayashi,