20.500.12556/DKUM-66291 Rab3a is critical for trapping alpha-MSH granules in the high Ca2+-affinity pool by preventing constitutive exocytosis Rab3a is a small GTPase of the Rab3 subfamily that acts during late stages of Ca2+-regulated exocytosis. Previous functional analysis in pituitary melanotrophs described Rab3a as a positive regulator of Ca2+-dependent exocytosis. However, the precise role of the Rab3a isoform on the kinetics and intracellular [Ca2+] sensitivity of regulated exocytosis, which may affect the availability of two major peptide hormones, -melanocyte stimulating hormone (-MSH) and -endorphin in plasma, remain elusive. We employed Rab3a knock-out mice (Rab3a KO) to explore the secretory phenotype in melanotrophs from fresh pituitary tissue slices. High resolution capacitance measurements showed that Rab3a KO melanotrophs possessed impaired Ca2+-triggered secretory activity as compared to wild-type cells. The hampered secretion was associated with the absence of cAMP-guanine exchange factor II/ Epac2-dependent secretory component. This component has been attributed to high Ca2+-sensitive release-ready vesicles as determined by slow photo-release of caged Ca2+. Radioimmunoassay revealed that -MSH, but not -endorphin, was elevated in the plasma of Rab3a KO mice, indicating increased constitutive exocytosis of -MSH. Increased constitutive secretion of -MSH from incubated tissue slices was associated with reduced -MSH cellular content in Rab3a-deficient pituitary cells. Viral re-expression of the Rab3a protein in vitro rescued the secretory phenotype of melanotrophs from Rab3a KO mice. In conclusion, we suggest that Rab3a deficiency promotes constitutive secretion and underlies selective impairment of Ca2+-dependent release of -MSH. melanotrophs exocytosis melanotrofi eksocitoza true false true Angleški jezik Slovenski jezik Znanstveno delo 2017-06-19 12:07:53 2017-06-19 12:08:46 2022-07-11 03:06:05 2019-07-11 15:42:33 2013 0 0 str. 1-12 št. 10 Letn. 8 2013 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 1932-6203 612 2005896 512349240 10.1371/journal.pone.0078883 1932-6203 URN:SI:UM:DK:VIPE630F PLoS_ONE_2013_Sedej_et_al._Rab3a_Is_Critical_for_Trapping_Alpha-MSH_Granules_in_the_High_Ca2-Affinity_Pool_by_Preventing_Constitutive_Ex.PDF PLoS_ONE_2013_Sedej_et_al._Rab3a_Is_Critical_for_Trapping_Alpha-MSH_Granules_in_the_High_Ca2-Affinity_Pool_by_Preventing_Constitutive_Ex.PDF 1 D3DA454C74312949060D30CB29B545B9 df2241346275f48c943ae7c006ab583183afad0ae1f49d82c211c48eadb9638b 43940a96-7c0e-11eb-bb7a-00155d0001ca https://dk.um.si/Dokument.php?lang=slv&id=112770 http://dx.plos.org/10.1371/journal.pone.0078883 1 https://dk.um.si/Dokument.php?lang=slv&id=112769 Medicinska fakulteta 0 0 0