Annexin 5 messenger ribonucleic acid expression in pituitary gonadotropes is induced by gonadotropin-releasing hormone (GnRH) and modulates GnRH stimulation of gonadotropin release.
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 microg i.v.). Administration of a GnRH analog [GnRHa; Des-Gly 10 (Pro9) GnRH ethylamide, 0.2 ml of 2.5 microg/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 microg/ml) and GnRHa augmented the LH and FSH release induced by GnRHa. After a 1-hour incubation, cycloheximide (10 microg/ml) apparently inhibited the LH response to GnRHa, while annexin 5 (2 microg/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.
Kawaminami
Mitsumori
M
Department of Veterinary Physiology, School of Veterinary Medicine and Animal Sciences, Kitasato University, Towada, Japan. mitsumor@vmas.kitasato-u.ac.jp
Etoh
Seishi
S
Miyaoka
Hiroko
H
Sakai
Mina
M
Nishida
Mayumi
M
Kurusu
Shiro
S
Hashimoto
Inoru
I
D000818:Animals; D017304:Annexin A5 / Q000235:genetics* / Q000494:pharmacology; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology / Q000502:physiology*; D006062:Gonadotropins / Q000378:metabolism*; D066298:In Vitro Techniques; D007986:Luteinizing Hormone / Q000378:metabolism; D020319:Oligodeoxyribonucleotides, Antisense; D010052:Ovariectomy; D010902:Pituitary Gland / Q000166:cytology / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar
D017304:Annexin A5; D006062:Gonadotropins; D020319:Oligodeoxyribonucleotides, Antisense; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D003513:Cycloheximide