Our previous studies on annexin 5, a member of the annexin family of proteins, have shown its expression in the anterior pituitary gland, its preferential distribution in gonadotropes, and its increase after ovariectomy. In the present study, we examined (1) whether annexin 5 is synthesized in gonadotropes, (2) whether its expression is under the control of gonadotropin-releasing hormone (GnRH), and (3) the effect of annexin 5 on gonadotropin release. Large cells, also called castration cells, appeared in anterior pituitary tissue 3 weeks after ovariectomy. These cells have been confirmed to be hyperfunctioning gonadotropes and are easily discriminated from other pituitary cells without immunostaining. Using in situ hybridization with a digoxigenin-labeled ribonucleic acid probe, enhanced expression of annexin 5 messenger ribonucleic acid (mRNA) in these gonadotropes was clearly demonstrated. Northern blot analysis showed an increase in the level of annexin 5 mRNA expression 3 weeks after ovariectomy. It was lessened 3 h after the injection of Cetrorelix (GnRH antagonist, 10 µg i.v.). Administration of a GnRH analog [GnRHa; Des-Gly 10 (Pro9) GnRH ethylamide, 0.2 ml of 2.5 µg/ml saline ten times intraperitoneally at 30-min intervals] significantly increased pituitary annexin 5 mRNA. In primary cultures of anterior pituitary cells, recombinant rat annexin 5 stimulated luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release in a dose-dependent manner. Concomitant administration of annexin 5 (1 µg/ml) and GnRHa augmented the LH and FSH release induced by GnRHa. After a 1-hour incubation, cycloheximide (10 µg/ml) apparently inhibited the LH response to GnRHa, while annexin 5 (2 µg/ml) moderated this inhibition. Further, the antisense oligodeoxynucleotide to annexin 5 mRNA blunted the LH response to GnRHa. It is thus concluded that annexin 5 is synthesized in the gonadotropes under the effect of GnRH, and it is suggested that annexin 5 synthesis mediates at least partly GnRH receptor signaling to stimulate gonadotropin secretion.
Antiphospholipid syndrome is associated with an increased risk of thrombosis and pregnancy loss. Annexin A5 (Anxa5) is a candidate autoantigen. It is not known, however, whether endogenous Anxa5 prevents foetal loss during normal pregnancy. We found significant reductions in litter size and foetal weight in Anxa5-null mice (Anxa5-KO). These changes occurred even when only the mother was Anxa5-KO. A small amount of placental fibrin deposition was observed in the decidual tissues, but did not noticeably differ between wild-type and Anxa5-KO mice. However, immunoreactivity for integrin beta 3/CD61, a platelet marker, was demonstrated within thrombi in the arterial canals only in Anxa5-KO mothers. Subcutaneous administration of the anticoagulant heparin to pregnant Anxa5-KO mice significantly reduced pregnancy loss, suggesting that maternal Anxa5 is crucial for maintaining intact placental circulation. Hence, the presence of maternal Anxa5 minimises the risk of thrombosis in the placental circulation and reduces the risk of foetal loss.
Variations in mRNA levels and sources of metastin/kisspeptin, neurokinin B (NKB), dynorphin, and kisspeptin receptor GPR54 were examined in the ovaries of cycling rats. Kisspeptin and dynorphin mRNAs dramatically increased at 2000 h of the proestrous day. NKB mRNA also increased, but the peak was delayed by 6 h. GPR54 mRNA declined inversely with kisspeptin. Whole-ovary expressions of kisspeptin and dynorphin mRNAs, but not of NKB mRNA, were augmented by the administration of human chorionic gonadotropin (hCG). By means of laser-capture microdissection, kisspeptin mRNA was shown mostly in follicles at 2000 h of proestrus, whereas NKB and dynorphin were expressed mainly in interstitial tissues. GPR54 mRNA was detected equally in follicles, corpora lutea, and interstitial tissues. The hCG stimulated the follicular expression of kisspeptin and interstitial tissue expression of dynorphin mRNA. In primary cultures of granulosa cells prepared from equine chorionic gonadotropin-pretreated immature rats, hCG stimulated the expression of kisspeptin, dynorphin, and NKB mRNAs. Distortion of the corpus luteum and surrounding tissue borders was sometimes seen after intra-ovarian bursa administration of kisspeptin antagonist p234 for 3 days from proestrus. Progesterone production stimulated by hCG in granulosa cell culture was suppressed by p234. These data demonstrate that significant amounts of kisspeptin are synthesized in granulosa cells and dynorphin in interstitial tissues, in response to the proestrous luteinizing hormone surge, whereas granulosa cells also contain dynorphin and NKB, suggesting at least a role for kisspeptin in the luteinization of granulosa cells.
Controversy exists concerning the role of the long prolactin receptor (PRLR) in the progression of breast cancer. By targeting pre-mRNA splicing, we succeeded in knocking down only the long PRLR in vivo, leaving the short forms unaffected. Using two orthotopic and highly-metastatic models of breast cancer, one of which was syngeneic (mouse 4T1) to allow assessment of tumor-immune interactions and one of which was endocrinologically humanized (human BT-474) to activate human PRLRs, we examined the effect of long PRLR knockdown on disease progression. In both models, knockdown dramatically inhibited metastatic spread to the lungs and liver and resulted in increased central death in the primary tumor. In the syngeneic model, immune infiltrates in metastatic sites were changed from innate inflammatory cells to lymphocytes, with an increase in the incidence of tumor-specific cytotoxic T cells. Long PRLR knockdown in three-dimensional culture induced apoptosis of tumor-initiating/cancer stem cells (death of 95% of cells displaying stem cell markers in 15 days). We conclude that the long PRLR plays an important role in breast cancer metastasis.
We investigated a specific relationship between the expression of annexin 5 and prolactin in the corpus luteum of pseudopregnant rats, with particular interest in GnRH and apoptosis of luteal cells. The expression of ovarian annexin 5 mRNA was significantly decreased at mid-pseudopregnancy and recovered at the end, whereas it remained low on the corresponding day of pregnancy. The dopamine agonist CB-154, administered at mid-pseudopregnancy (d 5), increased ovarian annexin 5 mRNA, whereas prolactin, given daily for 3 d to cycling rats, decreased it. An immunocytochemical study also showed that annexin 5 increased in the corpus luteum on d 6 and 7 of pseudopregnancy after treatment with CB-154 on d 5. The distribution of annexin 5-positive cells was not uniform in the corpus luteum and matched that of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL)-positive cells. Because GnRH stimulates annexin 5 mRNA expression in the gonadotropes, involvement of the GnRH receptor was examined. Local administration of a GnRH antagonist, Cetrorelix, to hemilateral ovarian bursa of pseudopregnant rats simultaneously receiving CB-154 abrogated both the expression of annexin 5 and the TUNEL reaction. The present results clearly demonstrate that prolactin decreases annexin 5 mRNA in the luteal cells during pseudopregnancy. Prolactin is suggested to suppress the local action of GnRH, which stimulates annexin 5 synthesis and apoptosis of functional luteal cells during pseudopregnancy.
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