Gonadotropin release and redistribution of calcium-activated, phospholipid-dependent protein kinase in phorbol-stimulated rat pituitary cells

Hirota, Kenji; Hirota, Takako; Aguilera, Greti; Catt, Kevin J.

doi:10.1016/0003-9861(86)90033-0

Cited by 65 publications

(75 citation statements)

References 35 publications

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“…On the other hand, these arguments do not detract from clear observations that GnRH does initiate PKC-dependent actions in gonadotropes. Thus GnRH causes translocation of several PKC isoforms to the membrane and, through a mechanism that is sensitive to BIS and mimicked by PMA, raises messenger-RNA levels for LH and follicle stimulating hormone ␣-and ␤-chains and for PKC-␤ within minutes (39)(40)(41).…”

Section: Discussionmentioning

confidence: 99%

Protein kinase C as a signal for exocytosis

Billiard

Koh

Babcock

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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We have studied signaling mechanisms that stimulate exocytosis and luteinizing hormone secretion in isolated male rat pituitary gonadotropes. As judged by reverse hemolytic plaque assays, phorbol-12-myristate-13-acetate (PMA) stimulates as many gonadotropes to secrete as does gonadotropin-releasing hormone (GnRH). However, PMA and GnRH use different signaling pathways. The secretagogue action of GnRH is not very sensitive to bisindolylmaleimide I, an inhibitor of protein kinase C, but is blocked by loading cells with a calcium chelator, 1,2-bis-(2-aminophenoxy)ethane-N,N,N,Ntetraacetic acid. The secretagogue action of PMA is blocked by bisindolylmaleimide I and is not very sensitive to the intracellular calcium chelator. GnRH induces intracellular calcium elevations, whereas PMA does not. As judged by amperometric measurements of quantal catecholamine secretion from dopamine-or serotonin-loaded gonadotropes, the secretagogue action of PMA develops more slowly (in several minutes) than that of GnRH. We conclude that exocytosis of secretory vesicles can be stimulated independently either by calcium elevations or by activation of protein kinase C.

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Section: Discussionmentioning

confidence: 99%

Protein kinase C as a signal for exocytosis

Billiard

Koh

Babcock

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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“…Certain agonistreceptor interactions, e.g. gonadotropin-releasing hormone and thyrotropin-releasing hormone [24,25], also promote redistribution of protein kinase C to the membranes, while other hormones (e.g. ACTH) or lectins like concanavalin A may promote either translocation of protein kinase C from membranes to cytosol [26], or a net increase in activity without translocation [27,28].…”

Section: Discussionmentioning

confidence: 99%

Insulin increases membrane protein kinase C activity in rat diaphragm

et al. 1987

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Calcium/phospholipid-dependent protein kinase activity (protein kinase C) was identified in rat diaphragm membrane and cytosol fractions by means of in vitro phosphorylation either of histones or of a specific 87 kDa protein substrate, combined with phosphopeptide-mapping techniques. Both insulin and tumor-promoting phorbol ester treatment of the diaphragm preparations led to increased protein kinase C activity in the membrane fractions. In contrast to the phorbol ester, however, insulin did not induce a concomitant decrease in cytosolic activity, indicating that translocation of the enzyme had not taken place. Thus, insulin appears to increase specifically membrane protein kinase C activity in rat skeletal muscle, possibly through a mechanism not identical to that induced by phorbol esters.Insulin; Protein kinase C; 87 kDa protein; (Rat diaphragm, Sarcolenna)

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“…The fact that positive cooperativity was not suppressed by the inhibitor precludes a PKCdependent step, in spite of the known capacity of GnRH to stimulate the enzyme under normal conditions (33)(34)(35).…”

Section: Discussionmentioning

confidence: 97%

Temperature and Protein Kinase C Modulation of Gonadotropin‐Releasing Hormone Receptors in Pituitary Cells from Intact or Castrated Male Rats

Leblanc

I’Heritier

Mounier

et al. 1990

J Neuroendocrinology

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Unite de recherches sur la dynamique des ensembles neuroendocriniens, U 159 INSERM, 2ter rue d'AIesia, 75014 Paris, France.t Pharmacologie Neuro-lmmuno-Endocrinienne (CNRS UA 11 13), lnstitut Pasteur, 28 rue du Dr Roux, 75015 Paris, France.Key words: gonadotropin-releasing hormone receptors, protein kinase C, pituitary cell culture, castration. AbstractBinding constants of ['251]Des-Gly,0-(D-Ala,)-gonadotropin-releasing hormone-ethylamide (GnRHa) to dispersed pituitary cells were evaluated in a 4-day culture. Cells were sampled either from intact or from castrated male rats and binding was measured at various temperatures before or after treatment with phorbol-12-myristate-13-acetate (PMA) or l-5-(isoquinolinyl-sulfc.xyl) 2-methylpiperazine (H7), which activate or inhibit, respectively, protein kinase C (PKC). In cells from intact rats incubated with increasing concentrations of ligand at 21 "C for 25 rnin, the Scatchard plot was not linear and calculation of the Hill coefficient (NH) was indicative of positive cooperativity (NH= 1.26_+0.02). Such non-linearity was not observed when cells were incubated at 0.5 "C for 3 h. In that condition the maximal number of binding sites measured at equilibrium (Bmax) increased (15.1 t0.05 versus 9.3k0.5 fmoles x mg-' proteins at 21 "C). Two control experiments permitted us to rule out the possibility that lower B , , , at 21 "C might reflect internalization: 1) Cells were first incubated with the ligand at 21 "C for 25 min and subsequently for 3 additional hours at 0.5 "C. Preincubation did not affect the B , , , obtained at 0.5 "C; 2) when the radioligand bound to the cell surface was washed out with an acidic buffer, only 13% of the specific radioactivity was retained irrespective of the ligand concentration applied, a much lower value than the 40% binding difference observed between 05°C and 21°C. When the cells were incubated with PMA, the Scatchard plot was linearized and the B, , , recorded at 21 "C increased by 50% over control cells (13k0.7 fmolesxrng-' proteins). Conversely, inhibition of PKC by H7, a preferential PKC inhibitor, was ineffective. In contrast, cells sampled from castrates exhibited linear and comparable Scatchard plots at either 0.5 or 21 "C, with B , , , values of 14.4k0.3 and 15k0.34 fmoles x mg-' proteins, respectively. PKC activation did not affect binding in that model, but H7 decreased the number of sites (B,,,= 10.7t0.9) and induced appearance of positive cooperativity (NH= 1.36k0.07). Taken together, these experiments reveal a pool of GnRH receptors in the pituitary of intact rats that recognizes the ligand in a phosphorylation-dependent manner. These binding sites also became evident when biological properties of the membrane were modified by temperature or cell homogenization. After castration, PKC activation was no longer a prerequisite for recruitment of the total population of receptors whereas protein kinase inhibition resulted in a reduction of maximal binding. Finally, our observations demonstrate that GnRH binding can exhibit positiv...

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Gonadotropin release and redistribution of calcium-activated, phospholipid-dependent protein kinase in phorbol-stimulated rat pituitary cells

Cited by 65 publications

References 35 publications

Protein kinase C as a signal for exocytosis

Protein kinase C as a signal for exocytosis

Insulin increases membrane protein kinase C activity in rat diaphragm

Temperature and Protein Kinase C Modulation of Gonadotropin‐Releasing Hormone Receptors in Pituitary Cells from Intact or Castrated Male Rats

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