Year-end Sale % OFF 
Abstract
The effect of gonadotropin-releasing hormone (GnRH) upon protein kinase C (PKC) delta and PKCepsilon gene expression was investigated in the gonadotroph-derived alphaT3-1 cell line. Stimulation of the cells with a stable analog [D-Trp6]GnRH (GnRH-A) resulted in a rapid elevation of PKCepsilon mRNA levels (1 h), while PKCdelta mRNA levels were elevated only after 24 h of incubation. The rapid elevation of PKCepsilon mRNA by GnRH-A was blocked by pretreatment with a GnRH antagonist or actinomycin D. The PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA), but not the Ca2+ ionophore ionomycin, mimicked the rapid effect of GnRH-A upon PKCepsilon mRNA elevation. Additionally, the rapid stimulatory effect of GnRH-A was blocked by the selective PKC inhibitor GF109203X, by TPA-mediated down-regulation of endogenous PKC, or by Ca2+ removal. Interestingly, serum-starvation (24 h) advanced the stimulation of PKCdelta mRNA levels by GnRH-A and the effect could be detected at 1 h of incubation. The rapid effect of GnRH-A upon PKCdelta mRNA levels in serum-starved cells was mimicked by TPA, but not by ionomycin, and was abolished by down-regulation of PKC or by Ca2+ removal. Preactivation of alphaT3-1 cells with GnRH-A for 1 h followed by removal of ligand and serum resulted in elevation of PKCdelta mRNA levels after 24 h of incubation. Western blot analysis revealed that GnRH-A and TPA stimulated (within 5 min) the activation and some degradation of PKCdelta and PKCepsilon. We conclude that Ca2+ and PKC are involved in GnRH-A elevation of PKCdelta and PKCepsilon mRNA levels, with Ca2+ being necessary but not sufficient, while PKC is both necessary and sufficient to mediate the GnRH-A response. A serum factor masks PKCdelta but not PKCepsilon mRNA elevation by GnRH-A, and its removal exposes preactivation of PKCdelta mRNA by GnRH-A which can be memorized for 24 h. PKCdelta and PKCepsilon gene expression evoked by GnRH-A is autoregulated by PKC, and both isotypes might participate in the neurohormone action.
Highlights
The effect of gonadotropin-releasing hormone (GnRH) upon protein kinase C (PKC) ␦ and PKC⑀ gene expression was investigated in the gonadotroph-derived ␣T3-1 cell line
We demonstrate that GnRH analog [D-Trp6]GnRH (GnRH-A) directs differential autoregulation of PKC␦ and PKC⑀ gene expression, which is dependent upon growth conditions and Ca2ϩ, and reveals a memory mechanism, which might participate in PKC␦ autoregulation
We first studied the cellular redistribution of PKC␦ and PKC⑀ following GnRH-A and TPA stimulation, since it is a criterion for PKC activation by extracellular signals [5,6,7,8]
Summary
The effect of gonadotropin-releasing hormone (GnRH) upon protein kinase C (PKC) ␦ and PKC⑀ gene expression was investigated in the gonadotroph-derived ␣T3-1 cell line. The PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA), but not the Ca2؉ ionophore ionomycin, mimicked the rapid effect of GnRH-A upon PKC⑀ mRNA elevation. The rapid effect of GnRH-A upon PKC␦ mRNA levels in serum-starved cells was mimicked by TPA, but not by ionomycin, and was abolished by down-regulation of PKC or by Ca2؉ removal. Preactivation of ␣T3-1 cells with GnRH-A for 1 h followed by removal of ligand and serum resulted in elevation of PKC␦ mRNA levels after 24 h of incubation. Since PKC␦ and PKC⑀ of the novel PKC group are major subspecies in the pituitary [26], we decided to investigate the effect of GnRH-A on the mRNA levels of both isotypes in the ␣T3-1 cell line. We demonstrate that GnRH-A directs differential autoregulation of PKC␦ and PKC⑀ gene expression, which is dependent upon growth conditions and Ca2ϩ, and reveals a memory mechanism, which might participate in PKC␦ autoregulation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
