A specific antibody to a new peptide growth factor from human placenta: immunocytochemical studies on its location and biosynthesis

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Abstract
Recently, we isolated a new peptide growth factor of Mr 34,000 from synctial membranes of human placenta. In its polypeptide molecular weight and receptor binding specificity it is unlike several known growth factors. In this paper we describe immunocytochemical studies on its cellular location and biosynthesis. A rabbit antiserum was raised against a homogeneous preparations of the placental peptide. The specificity of the antibody was established by immunoprecipitation and immonoblot analyses. The antibody recognized both the native and denatured 34-kilodalton (kDa) peptide but showed no binding to a variety of other growth factors and hormones tested. The antibody was used to investigate the genesis and location of the 34-kDa membranous mitogen. Immunoperoxidase staining of placental tissue slices revealed a restricted localization of the antigen in the cytoplasmic organnelles of cytotrophoblasts and in ithe brush border membranes of syncytiotrophoblasts. No other placental structures contained the antigen. A developmentally regulated appearance of the mitogen was suggested by the fact that first trimester placenta consistently stained far more strongly than term placenta. These studies show that the 34-kDa mitogenic protein originates in the placenta from embryo-derived cellular structures and suggest that in its strategic location it may influence trophoblastic growth in an autocrine manner. In other studies we investigated the presence and biosynthesis of the 34-kDa peptide in the A431 vulval carcinoma cell line, which was shown earlier to contain a membrane-associated 34-kDa growth factor. The studies demonstrate that this cell line, as well as some other human carcinomas of breast and bladder origin, actively expresses this peptide. The tight, but peripheral, association of the growth factor with membranes of producer cells (cytotrophoblasts and carcinomas) suggests binging to a receptor and an autocrine mechanism of stimulation.

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