POLYPEPTIDE PATTERN OF HUMAN BREAST EPITHELIAL-CELLS FOLLOWING HUMAN CHORIONIC-GONADOTROPIN (HCG) TREATMENT

Numerous attempts have made to describe the particular protein pattern of malignant cells by using high resolution two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). The placental hormone human chorionic gonadotropin (hCG) inhibits tumor initiation and progression in experimental animals and has an inhibitory effect on the proliferation of human breast epithelial cells (HBEC) in vitro. The inhibitory effect on the immortalized HBEC MCF-10F is accompanied by the immunocytochemical expression of inhibin alpha and beta subunits by treated cells. With the purpose of clarifying the molecular mechanisms involved in this effect, the pattern of protein synthesis and mRNA were studied by 2-D PAGE in the immortalized HBEC MCF-10F cells teated in vitro with 1001U for 24 h. The effect of hCG treatment on the synthesis of MCF-10F cells was monitored by labeling both control and treated cells with [S-35]methionine and separation by 2-D PAGE. At least 11 proteins were preferentially synthesized and five specific polypeptides were decreased in hCG treated cells in comparison with controls. The hCG induced at least four new mRNAs which encoded proteins in the molecular mass range of 24-72 kDa. It also increased the expression of at least six mRNAs and reduced the expression of least four mRNAs in comparision with control cells. The hCG-treated cells actively synthesized a 33-kDa polypeptide which was not present in control cells. The nature of this hCG-inducible 33 kDa protein elucidated by immunoprecipating [S-35]methione-labeled proteins with antisera directed against rat inhibin subunit alpha and beta b. The immunoprecipitation revealed a 14 kDa protein band and an 18 kDa band whose syntheses were stimulated by hCG treatment, which corresponds to the inhibin alpha and beta b subunits, respectively.