Mervi Julkunen

Pregnancy proteins in seminal plasma, seminal vesicles, preovulatory follicular fluid, and ovary.

A number of proteins previously thought to be specific for the placenta or pregnancy have been identified in the fluids bathing both the oocyte and the sperm. In many cases their concentrations in follicular fluid and seminal plasma greatly exceeded those in the serum of nonpregnant women or men, and sometimes they even exceeded the levels in pregnancy sera. We report here the occurrence of PP5, PP12, PP14 and PAPP-A in follicular fluid and seminal plasma. In follicular fluid, the levels of PP5, PP12, and PAPP-A correlate with the estrogen concentration of the same fluid, and the PP12 and PAPP-A levels also bear a positive correlation to the progesterone concentration. The levels of PP12 and PAPP-A increase as the follicle grows, as do the levels of many steroid hormones. Therefore, the apparent correlations observed may be merely coincidental. However, circumstantial evidence from other reproductive organs indicates that the synthesis of PP12 and PAPP-A is stimulated by progesterone. Results of immunohistochemical staining show that PP12 and PAPP-A are localized in the luteinized granulosa cells and the corpus luteum. Previous studies indicate that PP5 and PAPP-A inhibit the action of proteolytic enzymes plasmin and elastase, which are believed to be involved in the mechanisms of ovulation. The study of the significance of these various placental proteins for human reproduction is only at its beginning. Clearly, elucidation of their function is the key to a more fundamental understanding of their role in the events governing ovulation and implantation.

Progesterone-associated proteins PP12 and PP14 in the human endometrium

Two proteins, designated as PP12 and PP14 were originally isolated from soluble extracts of the human placenta and its adjacent membranes. We have shown that they are synthesized by decidualized/secretory endometrium and not by placenta. Both proteins occur at high concentrations in human amniotic fluid, which is therefore an excellent source for purification. PP12 is a 34-kDa glycoprotein, which has an N-terminal amino acid sequence of Ala-Pro-Trp-Gln-Cys-Ala-Pro-Cys-Ser-Ala. This is identical with that of somatomedin-binding protein purified from the amniotic fluid. PP12 too binds somatomedin-C, or IGF-I (insulin-like growth factor-I). Human secretory endometrium synthesizes and secretes PP12, and progesterone stimulates its secretion. PP14 is a 28-kDa glycoprotein. Its N-terminal sequence shows homology to that of beta-lactoglobulins from various species. We have found PP14 in the human endometrium, serum and milk. Immunologically, PP14 is related to progestagen-associated endometrial protein (PEP), alpha-2 pregnancy-associated endometrial protein (alpha-2, PEG), endometrial protein 15 (EP15), alpha-uterine protein (AUP) and chorionic alpha-2 microglobulin (CAG-2). In ovulatory menstrual cycles, the concentration of PP14 increases in endometrial tissue as the secretory changes advance. In serum, the PP14 concentration begins to rise later than the progesterone levels, and high serum PP14 levels are maintained for the first days of the next cycle. By contrast, no elevation of serum PP14 level is seen in anovulatory cycles. Our results show that progesterone-associated proteins are synthesized by the human endometrium and appear in the peripheral circulation, where they can be quantitatively measured using immunochemical techniques.

The gene encoding human low-molecular weight insulin-like growth-factor binding protein (IGF-BP25): regional localization to 7p12-p13 and description of a DNA polymorphism

SummaryThe low-molecular weight insulin-like growth-factor binding protein (IGF-BP25) is synthesized by human liver, secretory endometrium and decidua, and is also present in human serum. It binds insulin-like growth factors IGF-I and IGF-II with high affinity, and is proposed to act as a paracrine regulator of cell growth. In situ hybridization studies with a cDNA encompassing the entire protein coding region of IGF-BP25 localized the gene to bands p12–p13 on chromosome 7. Southern blot analysis with the enzyme BglII revealed a common restriction fragment length polymorphism: the presence of the polymorphic BglII site results in the formation of two fragments 4.6 kb and 1.6 kb in size whereas its absence produces a single 6.2 kb fragment. The frequencies of the two alleles were 0.73 and 0.27, respectively. IGF-BP25 constitutes a useful genetic marker for the proximal short arm of chromosome 7.

Serum levels of placental protein 14 reflect ovulation in nonconceptional menstrual cycles**Supported by grants from the Academy of Finland, the Research and Science Foundation of Farmos, Turku, the Cancer Society of Finland, and the Sigrid Juselius Foundation.

Placental protein 14 (PP14), originally isolated from the human placenta and its adjacent membranes, was detected in the serum of nonpregnant women. The levels were measured by radioimmunoassay in 218 serum samples from 19 women throughout the menstrual cycle. In 13 women with a normal ovulatory cycle, the levels showed consistent variation. They were highest (up to 172 ng/ml) in the late secretory phase and remained high for the first days of the next cycle. Low concentrations were found from the midproliferative to the early luteal phase of the cycle. No similar variation was seen in anovulatory cycles of six other women. Compared with ovulatory cycles, anovulatory cycles exhibited lower PP14 levels in the latter part of the cycle (P less than 0.001) and in the beginning of the next cycle (P less than 0.01). In ovulatory cycles, the sustained elevation of serum PP14 concentration over the following period may be explained by the fairly long half-life (42 hours) of PP14 in serum: once the level has increased, it declines slowly. These results suggest that PP14 measurement may become a novel means to distinguish between ovulatory and anovulatory cycles even after the onset of the next period.