Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Kidney proximal tubule Na/H exchange is inhibited by PTH. To analyze further the cellular mechanisms involved in this regulation we have used MCT cells (a culture of SV-40 immortalized mouse cortical tubule cells) grown on permeant filter supports. Na/H exchange was measured using single cell fluorescence microscopy (BCECF) and phosphate transport (measured for comparisons) by tracer techniques. MCT cells express apical and basolateral Na/H exchangers which respond differently to inhibition by ethylisopropylamiloride and by dimethylamiloride, the basolateral membrane transporter being more sensitive. Apical membrane Na/H exchange was inhibited by PTH (10(-8) M; by an average of 25%); similar degrees of inhibition were observed when cells were exposed either to forskolin, 8-bromo-cAMP or phorbol ester. Basolateral membrane Na/H exchange was stimulated either by incubation with PTH (to 129% above control levels) or by addition of phorbol ester (to 120% above control levels); it was inhibited after exposure to either forskolin or 8-bromo-cAMP. The above effects of PTH and phorbol ester (apical and basolateral) were prevented by preincubation of cells with protein kinase C antagonists, staurosporine and calphostin C; both compounds did not affect forskolin or 8-bromo-cAMP induced effects. PTH also inhibited apical Na-dependent phosphate influx (29% inhibition at 10(-8) M); it had no effect on basolateral phosphate fluxes (Na-dependent and Na-independent). Incubation with PTH (10(-8) M) resulted in a rapid and transient increase in [Ca2+]i (measured with the fluorescent indicator, fura-2), due to stimulation of a Ca2+ release from intracellular stores. Exposure of MCT cells to PTH did not elevate cellular levels of cAMP. Taken together, these results suggest that PTH utilizes in MCT cells the phospholipase C/protein kinase C pathway to differently control Na/H exchangers (apical vs. basolateral) and to inhibit apical Na/Pi cotransport.
...
PMID:Apical and basolateral Na/H exchange in cultured murine proximal tubule cells (MCT): effect of parathyroid hormone (PTH). 128 13

Parathyroid hormone action on renal proximal tubule function involves phospholipase C/protein kinase C as well as adenylate cyclase/protein kinase A mediated regulatory pathways. Tissue culture experiments suggest that low concentrations of PTH affect preferentially the phospholipase C/protein kinase C pathway. In vivo, both regulatory cascades are probably involved in the regulation of proximal tubule function. It is not clear at present whether the two intracellular pathways are linked to one or two PTH receptors. A polarized distribution of PTH receptor(s) involving different second messengers appears possible in proximal tubule epithelial cells. High-affinity (Kd 10(-11)-10(-12) M) PTH receptors in the range of circulating PTH concentrations in vivo remain to be identified. Structural and functional characterization of PTH receptors as well as of the PTH-sensitive intracellular mediators and transport systems form the basis for a better understanding of PTH-dependent regulation of proximal tubule function.
...
PMID:Parathyroid hormone receptors in control of proximal tubule function. 131 47

PTH is a major regulator of renal proximal tubule 1,25(OH)2D3 biosynthesis. However, the intracellular pathways involved in PTH activation of the mitochondrial 25-hydroxyvitamin D3-1 alpha-hydroxylase (1-OHase) remain unknown. PTH can activate both the adenylate cyclase/protein kinase A (PKA) and the plasma membrane phospholipase C/protein kinase C (PKC) pathways. The present study was undertaken to determine whether PKC may mediate PTH activation of renal 25-hydroxyvitamin D3-1 alpha-hydroxylase activity. Rat PTH 1-34 fragment in vitro translocated PKC activity from cytosolic to soluble membrane fraction from freshly prepared rat proximal tubules. Physiologic concentrations (10(-11)-10(-10) M) of rat PTH 1-34 fragment increased PKC translocation three- to fourfold while PKA activity ratio increased at PTH 10(-7) M. PTH stimulation of PKC and PKA was reduced in the presence of staurosporine (10 nM) by 41 and 29%, respectively. Sangivamycin (10 and 50 microM) also reduced PTH-stimulated PKC translocation, but did not alter PKA activity ratio. In vitro perifusion of renal proximal tubules with PTH (10(-11) M) increased 1,25(OH)2D3 steady-state secretion two- to fourfold. Sangivamycin at the same concentration that inhibited PKC translocation by 52% completely inhibited PTH-stimulated 1,25(OH)2D3 secretion. The present studies indicate that the phospholipase C/PKC pathway may mediate PTH stimulation of mammalian renal proximal tubule 1,25(OH)2D3 secretion.
...
PMID:Role of protein kinase C in parathyroid hormone stimulation of renal 1,25-dihydroxyvitamin D3 secretion. 133 73

Insulin modifies the effects of PTH on osteoblast-like cells. However, the basis for this effect is unknown. In bone and kidney cells, the effects of PTH on cellular function are mediated by second messengers generated through both the phospholipase C and adenylate cyclase systems. Therefore, we examined the effects of insulin on PTH second messenger generation in UMR-106-01 rat osteoblastic osteosarcoma cells. PTH produced a rapid, transient increase in intracellular free calcium concentration ([Ca2+]i) which was maximal at 30 sec and was only minimally reduced in the absence of extracellular calcium. Inositol-triphosphate (IP3) production was increased in parallel. PTH stimulation of [Ca2+]i was concentration-dependent from 0.5-1,000 nM, with half-maximal stimulation at approximately 50 nM PTH. A 30-sec exposure to 50 nM PTH produced 32% and 23% increases in IP1 and IP3 production, respectively (both P less than 0.05). Although insulin alone did not significantly alter basal [Ca2+]i, a 1-min exposure to 1-100 nM insulin produced a concentration-dependent suppression of the PTH-stimulated transient increase in [Ca2+]i and IP3 generation. 100 nM insulin decreased 50 nM PTH stimulation of [Ca2+]i and IP3 levels by 84% (P less than 0.02) and 80% (P less than 0.001), respectively. Preexposure to insulin also decreased PTH stimulation of intracellular cAMP levels, but to a lesser degree. A 1-min exposure to 100 nM insulin produced a 32% (P less than 0.01) decrease in PTH-stimulated cAMP generation, but lower insulin concentrations were without significant effects. These results demonstrate that in UMR-106-01 cells, insulin suppresses PTH stimulation of second messengers generated through both the phospholipase C and adenylate cyclase systems, but has a more marked effect on the former.
...
PMID:Insulin acutely suppresses parathyroid hormone second messenger generation in UMR-106-01 osteoblast-like cells: differential effects on phospholipase C and adenylate cyclase activation. 185 51

We examined changes in cAMP and inositol phosphate metabolism to assess the contribution of the guanine nucleotide regulatory (G) protein(s) regulating adenylate cyclase and phospholipase C in mediating the stimulatory effects of GppNHp on PTH release from permeabilized bovine parathyroid cells. To examine the role of Gs, the G protein stimulating adenylate cyclase, and cAMP on PTH release, permeabilized cells were incubated with either GppNHp or isoproterenol, and the effects of these agents on PTH release and cellular cAMP content were determined by RIA. To study the effects of GppNHp on inositol phosphate accumulation, permeabilized cells prelabeled with [3H]inositol were exposed to GppNHp, and inositol phosphates were measured using ion-exchange chromatography. These studies revealed that isoproterenol produced a dose-dependent increment in cAMP content in permeabilized cells with no significant effect on PTH release. Conversely, GppNHp rapidly and markedly elevated PTH release with a smaller and delayed rise in cAMP content. GppNHp- also promoted a dose-dependent increase in inositol monophosphate (IP), inositol bisphosphate (IP2), and inositol trisphosphate (IP3) accumulation, suggesting activation of phosphoinositide hydrolysis. Addition of dioctanoylglycerol, however, a synthetic diacylglycerol (DG) that activates protein kinase C, produced a much smaller increment in PTH release than GppNHp. Moreover, reducing the free calcium concentration to less than 10(-9) M by adding 10 mM EGTA to the permeabilization medium dissociated the effects of GppNHp and DG on secretion, increasing GppNHp-stimulated PTH release while reducing PTH secretion evoked by DG.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Mechanisms underlying the stimulation of PTH release by GppNHp in permeabilized bovine parathyroid cells. 216 60

In parathyroid cells, high extracellular Ca2+ promotes a rapid increase in inositol trisphosphate (IP3), suggesting activation of phospholipase C. Available data, however, indicate a high Ca2+-induced decrease in sn-1,2-diacylglycerol (DG), rather than the increase expected with hydrolysis of phosphoinositides. To explore this apparent discrepancy between IP3 and DG, we used three methods to quantify DG levels in parathyroid cells in response to high Ca2+ over the time course when IP3 levels increase. A simple enzymatic method was developed for the quantitation of the mass of DG present in crude lipid extracts. The assay employed rat brain DG kinase and defined mixed micellar conditions to solubilize the DG present and allow its quantitative conversion to [32P]phosphatidic acid. [32P]Phosphatidic acid formed in the assay was directly proportional to the amount of DG added over the range of 25 pmol to 25 nmol or to the number of parathyroid cells (5 X 10(5) to 2 X 10(6) cells). Parathyroid cells were also labeled with [3H]glycerol (24 h) or [3H]arachidonic acid (2 or 18 h) and exposed to various extracellular Ca2+ concentrations for different times. The total lipids were then extracted and separated by TLC. Using each of the three methods to measure DG, parathyroid cells showed a rapid increase in DG when extracellular Ca2+ was increased from 0.5 to 2.0 or 3.0 mM. The maximal increase occurred at 5-20 s. The levels of DG at high Ca2+ then decreased to levels 20-50% higher than those at 0.5 mM Ca2+ from 60 sec to 10 min. DG levels remained higher at 2-3 mM Ca2+ than at 0.5 mM Ca2+ even at 30 min. Similar results were obtained in 10 independent experiments with the kinase method, 7 independent experiments with the [3H]glycerol method, and 12 independent experiments with the [3H]arachidonic acid method. These results show the high Ca2+ rapidly increases intracellular levels of DG as well as IP3 in bovine parathyroid cells, consistent with activation of phospholipase C. Thus, the initial rapid decrease in PTH release at high Ca2+ is not caused by a concomitant decrease in DG, but is presumably related to additional inhibitory mechanisms that override the high Ca2+-induced increases in DG and cytosolic Ca2+.
...
PMID:Relationship between diacylglycerol levels and extracellular Ca2+ in dispersed bovine parathyroid cells. 284 84

The properties of phospholipase C (PL-C) in the plasma membranes (PM) and the cytosol of osteoblast-like osteosarcoma cells, UMR-106, were analyzed to see if separate enzymes or similar enzymes were involved in signalling, transduction, and arachidonate release. The cytosolic PL-C displayed substrate affinities in the order of phosphatidylinositol (PI) greater than phosphatidylinositol-4-phosphate (PIP) or phosphatidylinoisitol-4, 5-bisphosphate (PIP2). Hydrolysis of PI, PIP, and PIP2 by cytosolic PL-C was not affected by GTP or GTP gamma S and other nucleotides. PI hydrolysis by PM and cytosolic PL-C was undetectable in the presence of 500 microM EGTA and displayed two activity plateaus at various concentrations of Ca2+. The Km for Ca2+ in the PL-C activity of the first plateau was 0.08 microM. Significant hydrolysis of PIP2 by cytosolic PL-C was observed in the absence of Ca2+. In contrast to the enzyme(s) predominant in the cytosol, the order of substrate affinities for PM PL-C was PIP2 greater than PIP greater than PI. Only PIP2 hydrolysis by PM PL-C was stimulated by both GTP and GTP gamma S in a dose-dependent manner. PIP2 hydrolysis by PL-C of the PM was not observed in the absence of Ca2+, serving to further discriminate this enzyme activity from that of the cytosol. PIP2 hydrolysis by PL-C of the PM also was biphasic in the dependence on Ca2+. At resting cytosolic Ca2+ levels, the Vmax of the high affinity activity already had been achieved. Guanine nucleotide stimulation of PIP2 hydrolysis by PM PL-C was characterized by increased maximum activity with an unchanged Km for Ca2+ or for PIP2. The pH optimum of PIP2 hydrolysis was similar between cytosolic and PM forms of PL-C. PIP2 hydrolysis with production of IP3 (PL-C activity) in UMR-106 cells treated with [2-3H]-myoinositol was stimulated by PTH, and this stimulation was not inhibited by pertussis toxin. These data suggest that UMR-106 cells possess at least two distinct PL-C activities, one predominant in the cytosol and activated by increasing cytosolic Ca2+ with PI as the substrate. The second enzyme, a GTP-activated PIP2-specific PL-C in the plasma membranes may play an important role in hormone-induced PIP2 hydrolysis mediated through guanine nucleotide regulatory proteins and may participate in the hormonal regulation of osteoblast cytosolic Ca2+ and bone remodeling functions.
...
PMID:Characterization of phospholipase C activity of the plasma membrane and cytosol of an osteoblast-like cell line. 292 33

While protein kinase C (PKC) appears to play a role in the action of PTH in renal cells, direct evidence of activation by PTH is lacking. Rat PTH (1-34) caused a rapid, transient translocation of PKC in opossum kidney (OK) cells from a basal value of 0.09 to maximum of 0.24 at 10-15 sec. Both the time course and dose-response relationship of translocation matched a corresponding increase in cytosolic Ca2+. In contrast, PTH activation of cAMP-dependent protein kinase (PKA), while also rapid, was greater in magnitude (0.10 to 0.50), persistent, and occurred at a threshold level of 3 x 10(-10)M PTH, compared to 10(-8)M for PKC. Neither bPTH(3-34) nor bPTH(7-34) activated either protein kinase, while both antagonized rPTH(1-34)-induced PKC translocation more effectively than PKA activation. These differential effects of PTH agonist and antagonists further support the suggestion that PTH acts through two signal transduction mechanisms in which one or more receptors is linked in distinct ways to adenylate cyclase and phospholipase C.
...
PMID:Parathyroid hormone 1-34, but not 3-34 or 7-34, transiently translocates protein kinase C in cultured renal (OK) cells. 293 May 65

The unique features of renal phosphoinositide metabolism include an increase in tissue phosphoinositide levels induced by PTH. The significance of this finding remains unclear. Another unusual finding is the localization of phospholipase C activity in a BBMV preparation. As suggested in the review, the transducing mechanism involving cleavage of phosphoinositides by a phospholipase C would be expected to include a close association between phospholipase C and the plasma membrane. However, few attempts to localize phospholipase C activity in the plasma membrane have succeeded. The kidney also plays an unusual role in inositol metabolism in that it is the only organ that significantly catabolizes inositol. The kidneys also synthesize inositol. There is an enormous concentration of inositol in the outer medulla. This coexistence of significant inositol synthesis, breakdown, and the presence of extremely high amounts of free inositol is an intriguing but unexplained phenomenon. The substantial rate of endogenous renal inositol synthesis does not, however, preclude inositol deficiency states. There is a deficiency of inositol in diabetic peripheral nerve and in glomeruli isolated from diabetic rats. Such deficiencies may arise from a disturbance in the balance of synthesis, breakdown, and excretion of inositol, and particularly from the competition of glucose with the inositol transporter in the proximal tubule. Future studies of renal phosphoinositide metabolism need to address both basic cell biological questions and broader physiological or functional questions. The more basic issues include the question of which phosphoinositide is being attacked by agonist-stimulated phospholipase C. That is, are all the events explained by hydrolysis of PtdIns(4,5)P2, or are the other phosphoinositides hydrolyzed as well? Also, it would appear that stimulated phosphoinositide metabolism occurs quite early following receptor occupation, but there is still no way of selectively blocking stimulated phosphoinositide metabolism to see if it is a necessary first step in a cascade of events leading to cell response. Thus, the relationship of stimulated phosphoinositide metabolism to cell functions remains incompletely understood. At least two cellular functional or biochemical changes associated with stimulated phosphoinositide metabolism in the kidney have been identified, prostaglandin production and mesangial cell contraction. The regulation of prostaglandin production and its relationship to stimulated phosphoinositide metabolism are subjects of continuing study. The topic was recently reviewed by Hassid.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Inositol phospholipid metabolism in the kidney. 301 Aug 24

We examined the effects of the divalent cations Ca2+ and Mg2+ on inositol phosphate accumulation in bovine parathyroid cells prelabelled with [3H]inositol to determine whether the high extracellular Ca2+ and Mg2+-evoked transients in cytosolic Ca2+ in these cells might result from increases in cellular IP3 levels. In the presence of Li+, both Ca2+ and Mg2+ produced rapid, 2-6-fold increases in IP3 and IP2 and a linear increase in IP of 6-8-fold at 30 min. Smaller (1.5-2-fold) increases in IP2 and IP3 were evident within 7.5-15 s upon exposure to high (3 mM) Ca2+ in the absence of Li+. The relative potencies of Ca2+ and Mg2+ (Ca2+ 3-fold more potent than Mg2+) in elevating inositol phosphates were similar to those for their effects in inhibiting PTH release. Fluoride (5 and 10 mM) also produced similar increases in inositol phosphate accumulation, presumably through activation of phospholipase C by a guanine nucleotide (G) protein-dependent process. Thus, high extracellular Ca2+ and Mg2+-induced spikes in cytosolic Ca2+ in bovine parathyroid cells may be mediated by increases in IP3, perhaps through a receptor-mediated process linked to phospholipase C by a G-protein.
...
PMID:High extracellular Ca2+ and Mg2+ stimulate accumulation of inositol phosphates in bovine parathyroid cells. 310 45


1 2 3 4 5 Next >>

---