scholarly journals Metabolism of the biologically active inositol phosphates Ins(1,4,5)P3 and Ins(1,3,4,5)P4 by ovarian follicles of Xenopus laevis

1990 ◽  
Vol 268 (1) ◽  
pp. 141-145 ◽  
Author(s):  
R P McIntosh ◽  
J E A McIntosh
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Xenopus Laevis ◽  
Inositol Phosphates ◽  
Follicle Cell ◽  
Ovarian Follicles ◽  
Biologically Active ◽  
Follicle Cells ◽  
Kinase C ◽  
Cell Layers

The metabolism of biologically active inositol phosphates in developed ovarian follicles from Xenopus laevis was investigated. Techniques used were microinjection of tracer into the intact oocyte coupled by gap junctions to follicle cells, as well as addition of tracer to homogenates of ovarian follicles and to homogenates of oocytes stripped of outer follicle-cell layers. Metabolism was similar to that previously described for other types of cell and tissue, with several unusual features. Homogenates of ovarian follicles were shown to contain an apparent 3′-phosphomonoesterase capable of converting [3H]Ins(1,3,4,5)P4 predominantly into a substance with h.p.l.c. elution characteristics of Ins(1,4,5)P3. In intact ovarian follicles, little Ins(1,4,5)P3 was formed but the esterase was activated by the phorbol ester activator of protein kinase C, PMA (phorbol 12-myristate 13-acetate; 60 nM), as well as by acetylcholine (200 microM). In follicle homogenates, this enzyme also appeared to be active in converting [3H]Ins(1,3,4)P3 into a substance eluting as Ins(1,4)P2. The apparent 3′-phosphomonoesterase activity was not inhibited by intracellular (or higher) levels of Mg2+. Although PMA activated this enzyme in intact oocytes relative to 5′-phosphomonoesterase activation, it did not enhance overall metabolism, in contrast with reports on other tissues. Compared with the processing of inositol phosphates injected into the intact follicle, homogenization in simulated intracellular medium appeared to alter the activity and/or accessibility of several enzymes. The metabolism of inositol phosphates appears to occur predominantly in the follicle cells surrounding the oocyte, as collagenase treatment followed by defolliculation greatly diminished the rates of metabolism of several inositol phosphates. The presence in Xenopus ovarian follicles of a 3′-phosphomonoesterase activated by protein kinase C in addition to the well-known 3′-kinase suggests that, by forming a reversible interconversion between Ins(1,4,5)P3 and Ins(1,3,4,5)P4, this tissue may have the potential to prolong stimulatory signals on binding of appropriate agonists to receptors.

scholarly journals Activators of protein kinase C trigger cortical granule exocytosis, cortical contraction, and cleavage furrow formation in Xenopus laevis oocytes and eggs.

1989 ◽  
Vol 108 (3) ◽  
pp. 885-892 ◽  
Author(s):  
W M Bement ◽  
D G Capco
Keyword(s):  
Protein Kinase C ◽  
Retinoic Acid ◽  
Protein Kinase ◽  
Xenopus Laevis ◽  
Follicle Cells ◽  
Cortical Granule ◽  
Cleavage Furrow ◽  
Granule Exocytosis ◽  
Kinase C ◽  
Cortical Granule Exocytosis

Prophase I oocytes, free of follicle cells, and metaphase II eggs of the amphibian Xenopus laevis were subjected to transient treatments with the protein kinase C activators, phorbol 12-myristate 13-acetate (PMA), phorbol 12,13-didecanoate, and 1-olyeoyl-2-acetyl-sn-glycerol. In both oocytes and eggs, these treatments triggered early events of amphibian development: cortical granule exocytosis, cortical contraction, and cleavage furrow formation. Surprisingly, activation of oocytes occurred in the absence of meiotic resumption, resulting in cells with an oocytelike nucleus and interior cytoplasm, but with a zygotelike cortex. PMA-induced activation of oocytes and eggs did not require external calcium, a prerequisite for normal activation of eggs. PMA-induced activation of eggs was inhibited by retinoic acid, a known inhibitor of protein kinase C. In addition, pretreatment of eggs with retinoic acid prevented activation by mechanical stimulation and inhibited activation by calcium ionophore A23187. The results suggest that protein kinase C activation is an integral component of the Xenopus fertilization pathway.

scholarly journals Protein kinase C acts downstream of calcium at entry into the first mitotic interphase of Xenopus laevis.

1990 ◽  
Vol 1 (3) ◽  
pp. 315-326 ◽  
Author(s):  
W M Bement ◽  
D G Capco
Keyword(s):  
Cell Cycle ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Xenopus Laevis ◽  
Mitotic Cell ◽  
Cortical Granule ◽  
Mitotic Cell Cycle ◽  
Cleavage Furrow ◽  
Kinase C ◽  
Cortical Granule Exocytosis

Transit into interphase of the first mitotic cell cycle in amphibian eggs is a process referred to as activation and is accompanied by an increase in intracellular free calcium [( Ca2+]i), which may be transduced into cytoplasmic events characteristic of interphase by protein kinase C (PKC). To investigate the respective roles of [Ca2+]i and PKC in Xenopus laevis egg activation, the calcium signal was blocked by microinjection of the calcium chelator BAPTA, or the activity of PKC was blocked by PKC inhibitors sphingosine or H7. Eggs were then challenged for activation by treatment with either calcium ionophore A23187 or the PKC activator PMA. BAPTA prevented cortical contraction, cortical granule exocytosis, and cleavage furrow formation in eggs challenged with A23187 but not with PMA. In contrast, sphingosine and H7 inhibited cortical granule exocytosis, cortical contraction, and cleavage furrow formation in eggs challenged with either A23187 or PMA. Measurement of egg [Ca2+]i with calcium-sensitive electrodes demonstrated that PMA treatment does not increase egg [Ca2+]i in BAPTA-injected eggs. Further, PMA does not increase [Ca2+]i in eggs that have not been injected with BAPTA. These results show that PKC acts downstream of the [Ca2+]i increase to induce cytoplasmic events of the first Xenopus mitotic cell cycle.

scholarly journals Bombesin and platelet-derived growth factor stimulate formation of inositol phosphates and Ca2+ mobilization in Swiss 3T3 cells by different mechanisms

1989 ◽  
Vol 258 (1) ◽  
pp. 177-185 ◽  
Author(s):  
D M Blakeley ◽  
A N Corps ◽  
K D Brown
Keyword(s):  
Protein Kinase C ◽  
Growth Factor ◽  
Protein Kinase ◽  
Phorbol Esters ◽  
Inositol Phosphates ◽  
Platelet Derived Growth Factor ◽  
3T3 Cells ◽  
Kinase C ◽  
Swiss 3T3 ◽  
Stimulation Of

Highly purified platelet-derived growth factor (PDGF) or recombinant PDGF stimulate DNA synthesis in quiescent Swiss 3T3 cells. The dose-response curves for the natural and recombinant factors were similar, with half-maximal responses at 2-3 ng/ml and maximal responses at approx. 10 ng/ml. Over this dose range, both natural and recombinant PDGF stimulated a pronounced accumulation of [3H]inositol phosphates in cells labelled for 72 h with [3H]inositol. In addition, mitogenic concentrations of PDGF stimulated the release of 45Ca2+ from cells prelabelled with the radioisotope. However, in comparison with the response to the peptide mitogens bombesin and vasopressin, a pronounced lag was evident in both the generation of inositol phosphates and the stimulation of 45Ca2+ efflux in response to PDGF. Furthermore, although the bombesin-stimulated efflux of 45Ca2+ was independent of extracellular Ca2+, the PDGF-stimulated efflux was markedly inhibited by chelation of external Ca2+ by using EGTA. Neither the stimulation of formation of inositol phosphates nor the stimulation of 45Ca2+ efflux in response to PDGF were affected by tumour-promoting phorbol esters such as 12-O-tetradecanoylphorbol 13-acetate (TPA). In contrast, TPA inhibited phosphoinositide hydrolysis and 45Ca2+ efflux stimulated by either bombesin or vasopressin. Furthermore, whereas formation of inositol phosphates in response to both vasopressin and bombesin was increased in cells in which protein kinase C had been down-modulated by prolonged exposure to phorbol esters, the response to PDGF was decreased in these cells. These results suggest that, in Swiss 3T3 cells, PDGF receptors are coupled to phosphoinositidase activation by a mechanism that does not exhibit protein kinase C-mediated negative-feedback control and which appears to be fundamentally different from the coupling mechanism utilized by the receptors for bombesin and vasopressin.

scholarly journals Protein kinase C activation antagonizes melatonin-induced pigment aggregation in Xenopus laevis melanophores.

1992 ◽  
Vol 119 (6) ◽  
pp. 1515-1521 ◽  
Author(s):  
D Sugden ◽  
S J Rowe
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Xenopus Laevis ◽  
Pigment Granule ◽  
Melatonin Receptors ◽  
Kinase C ◽  
Pigment Granules ◽  
Slow Aggregation ◽  
Pigment Aggregation ◽  
Induced Aggregation

The pineal hormone, melatonin (5-methoxy N-acetyltryptamine) induces a rapid aggregation of melanin-containing pigment granules in isolated melanophores of Xenopus laevis. Treatment of melanophores with activators of protein kinase C (PKC), including phorbol esters, mezerein and a synthetic diacylglycerol, did not affect pigment granule distribution but did prevent and reverse melatonin-induced pigment aggregation. This effect was blocked by an inhibitor of PKC, Ro 31-8220. The inhibitory effect was not a direct effect on melatonin receptors, per se, as the slow aggregation induced by a high concentration of an inhibitor of cyclic AMP-dependent protein kinase (PKA), adenosine 3',5'-cyclic monophosphothioate, Rp-diastereomer (Rp-cAMPS), was also reversed by PKC activation. Presumably activation of PKC, like PKA activation, stimulates the intracellular machinery involved in the centrifugal translocation of pigment granules along microtubules. alpha-Melanocyte stimulating hormone (alpha-MSH), like PKC activators, overcame melatonin-induced aggregation but this response was not blocked by the PKC inhibitor, Ro 31-8220. This data indicates that centrifugal translocation (dispersion) of pigment granules in Xenopus melanophores can be triggered by activation of either PKA, as occurs after alpha-MSH treatment, or PKC. The very slow aggregation in response to inhibition of PKA with high concentrations of Rp-cAMPS, suggests that the rapid aggregation in response to melatonin may involve multiple intracellular signals in addition to the documented Gi-mediated inhibition of adenylate cyclase.

Mechanism of action of luteinizing hormone-releasing hormone in rat ovarian cells

1989 ◽  
Vol 67 (8) ◽  
pp. 962-967 ◽  
Author(s):  
Peter C. K. Leung ◽  
Jian Wang ◽  
Kenneth G. Baimbridge
Keyword(s):  
Signal Transduction ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Luteinizing Hormone ◽  
Inositol Phosphates ◽  
Ionophore A23187 ◽  
Luteinizing Hormone Releasing Hormone ◽  
Releasing Hormone ◽  
Ovarian Cells ◽  
Kinase C

The initial step in the signal transduction of luteinizing hormone-releasing hormone (LHRH) in rat ovarian cells is the hydrolysis of membrane polyphosphoinositides into inositol phosphates and 1,2-diacylglycerol. The former compounds, especially inositol 1,4,5-triphosphate, are known to cause the release of calcium from intracellular stores, while diacylglycerol is a potent activator of protein kinase C. LHRH causes a rapid and transient increase in intracellular concentrations of free calcium ions, by approximately 4.5-fold, in the majority of granulosa cells as assessed by fura-2 microspectrofluorimetry. Like LHRH, a calcium ionophore (A23187) and activators of protein kinase C attenuate the steroidogenic response of the cells to follicle-stimulating hormone, but enhance the formation of gonadotropin-induced prostaglandin formation. These results support the concept that stimulation of polyphosphoinositide hydrolysis is intimitely involved in the direct action of LHRH at the level of the ovary.Key words: signal transduction, calcium, protein kinase C, ovary, steroid hormones.

Sign in / Sign up

Export Citation Format

Share Document