Rab3B is essential for GnRH-induced gonadotrophin release from anterior pituitary cells

Abstract

Gonadotrophin-releasing hormone (GnRH) induces the release of gonadotrophins via an increase in cytosolic Ca 2+ concentration ([Ca 2+ ]). Rab3B, a member of the small GTP-binding protein Rab family, is known to be involved in Ca 2+ -regulated exocytosis in pituitary cells. However, it is not known whether Rab3B functions in the physiological process regulated by GnRH in gonadotrophs. In this study using antisense oligonucleotide against Rab3B (AS-Rab3B) we determined that Rab3B is involved in GnRH-induced gonadotrophin release. Rab3B immunopositive cells were reduced in 24% of pituitary cells by AS-Rab3B. This treatment did not affect the population of gonadotrophs or the intracellular contents of gonadotrophins. However, AS-Rab3B significantly inhibited the total amount of basal and GnRH-induced gonadotrophin released from pituitary cells. These results show that Rab3B is involved in basal and GnRH-induced gonadotrophins release but not the storage of gonadotrophins. Next, the changes in [Ca 2+ ] and exocytosis in gonadotrophs treated with AS-Rab3B were compared among Rab3B-positive and -negative cells. The change in [Ca 2+ ] was not different in the two groups, but exocytosis was significantly inhibited in Rab3B-negative cells. These results suggest that Rab3B is essential for GnRH-regulated exocytosis downstream of cytosolic Ca 2+ in gonadotrophs.

Calcium-triggered acrosomal exocytosis in human spermatozoa requires the coordinated activation of Rab3A and N -ethylmaleimide-sensitive factor

“…The more conspicuous GTPases found in secretory granules with a function in exocytosis are Rab3 isoforms, but most studies report an inhibitory role for these proteins (12). However, a stimulatory role has been suggested in some secretory events (14)(15)(16). In this report we show that Rab3A is essential for the calcium-dependent acrosome reaction.…”

“…Rab3A is one of the best-characterized Rabs, whose three-dimensional crystal structure in association with a putative effector has been solved at 2.6-A resolution (13). Curiously, Rab3 isoforms seem to be negative regulators in several exocytotic events (12), although an activating role also has been proposed in other exocytotic models (14)(15)(16).…”

Dynamics of subcellular organelles, growth hormone, Rab3B, SNAP‐25, and syntaxin in rat pituitary cells caused by growth hormone releasing hormone and somatostatin

“…In a previous report by Tahara et al (1999), the expression of rab3 in human pituitary adenomas was found by immunohistochemical staining. Another report by Tasaka et al suggested that rab3B was indispensable for GnRH-induced gonadotropin release (Tasaka et al, 1998). However, the direct function of rab3B in conjunction with the secretion of pituitary hormones is not yet clear.…”

“…Since previous reports have either mainly studied rab family, or have focused exclusively on the SNARE system (Jacobsson and Meister, 1996;Lledo et al, 1993;Quintanar and Salinas, 2002;Salinas et al 1999;Tahara et al, 1999;Tasaka et al, 1998), to date these proteins have not yet been investigated together. Therefore, their mutual relationships have remained unclear.…”

Functional and Morphological Analyses of Rab Proteins and the Soluble N-ethylmaleimide-sensitive Factor Attachment Protein Receptor (SNARE) System in the Secretion of Pituitary Hormones

“…They concluded that rab3B is a key intracellular signaling molecule that can control exocytosis in anterior pituitary cells [16]. Tasaka et al suggested that rab3B is indispensable for gonadotropinreleasing hormone (GnRH)-induced gonadotropin release [39]. They reported that rab3B is involved in basal and GnRH-induced gonadotropin release but not gonadotropin storage, and that rab3B is essential for GnRH-regulated exocytosis downstream of cytosolic Ca 2+ in gonadotrophs.…”