Identification of “Big”Human Placental Lactogen in Placenta and Serum¹

Abstract

Because of increasing evidence for the heterogeneity of polypeptide hormones, studies of the molecular species of human placental lactogen (hPL) were initiated. When extracts of freshly delivered human placentas were passed over Sephadex G-100 in 0.05M ammonium carbonate, three immunoreactive peaks were detected. In addition to a peak corresponding to native hPL (Kav = 0.39) and one in the void volume, a consistent peak which eluted before hPL (Kav = 0.20) was present. The latter represented 2-25% of total hormonal activity and could be rerun without significant conversion to hPL. In 8M urea, the peak continued to behave as a large molecular weight form on both Sephadex chromatography and on polyacrylamide disc gel electrophoresis. Extraction procedures at both neutral and alkaline pH produced similar quantities of the larger material. [125I]iodo-hPL was not converted to the larger form by the conditions of extraction or analysis. These properties are consistent with a larger molecular weight, non-aggregated form of hPL. In comparison with the native hormone, the idsplacement curves for the larger form were parallel in radioimmunoassay studies. Sera obtained from pregnant women during various stages of gestation also showed consistent evidence for a large molecular weight form of the hormone. These observations provide direct evidence, both in placental tissue and in serum for "big" hPL.

Lysyl Oxidase Interacts with Hormone Placental Lactogen and Synergistically Promotes Breast Epithelial Cell Proliferation and Migration

“…1C shows the secretion of PL by the invasive/ metastatic cell lines Hs578T and MDA-MB-231, the noninvasive/poorly metastatic MCF-7 cell line, and a small amount by T47D cells. PL from cell culture media was detected as a 42 kDa band, which is consistent with the molecular weight of a homodimer as previously reported (14). As a positive control for the immunoblots, cell medium protein was used from the PL-expressing-choriocarcinoma cell line, JAR.…”

“…PL is produced by the placental syncytiotrophoblasts as a single chain polypeptide hormone of 191 amino acids that has been shown to form biologically active homodimers in vivo (13)(14)(15). In humans, PL is only expressed in the placenta during pregnancy, and it replaces the down-regulated pituitary PRL as the placental growth hormone (GH-V) replaces the down-regulated pituitary GH (16).…”

Immunologically undetectable human placental lactogen in a normal pregnancy.

“…Placental tissues from our patient and from a normal patient, used as a control, were washed in phosphate buffered saline (pH 7.4), immediately frozen in liquid nitrogen and stored at -8OOC. They were extracted as described by Schneider et al (1975) with some modifications. In brief, samples were kept on ice and minced with scissors: fragments of terminal villi were placed in 0.1 M ammonium bicarbonate (pH 7.85) and homogenized on ice with an Ultra Turrax homogenizer, twice for I min, at a setting of half the maximum.…”

Preparation of a disulfide-linked dimer of human placental lactogen fragment 1--134 with immunologic and biologic activity.

“…Gels were stained with Coomassie blue. The radioimmunoassay of hPL was performed by a double antibody method (5,6). Antibodies to purified hPL were produced in guinea pigs.…”