Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.1 (alkaline phosphatase)
 47,916 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID: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. 216 Aug 8

The influence of mammalian DNA topoisomerase I phosphorylation on enzyme activity has been investigated. Dephosphorylation by calf intestine alkaline phosphatase abolished the DNA relaxing activity of DNA topoisomerase I and the sensitivity of the enzyme to its specific inhibitor, camptothecin. DNA topoisomerase I could be reactivated by incubation with purified protein kinase C. DNA topoisomerase I was then able to relax supercoiled DNA processively, like the native enzyme, and to cleave 32P-end-labeled SV40 DNA fragments at the same sequences as the native enzyme in the presence of camptothecin. These results show that active DNA topoisomerase I is a phosphoprotein and suggest a possible regulatory role of protein kinase on topoisomerase I activity and on its sensitivity to camptothecin.
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PMID:Phosphorylation of mammalian DNA topoisomerase I and activation by protein kinase C. 216 Sep 79

A number of studies have shown membrane phospholipid metabolism to have an important role in biological mineralization. We considered the effects of exogenously applied phosphatidic acid (PA), a minor component of membrane phospholipids, on an osteoblast-like cell line, MOB 3-4. Exogenous PA (10-40 micrograms/ml) raised the level of cytoplasmic free Ca2+ [( Ca2+]i), independent of the level of extracellular Ca2+, in a dose-dependent fashion, and this Ca2+ response to PA gradually fell on serial application of PA. In a dose-dependent manner, exogenous PA also increased inositol 1,4,5-trisphosphate (IP3) accumulation and cytoplasmic pH, but decreased basal cAMP level. This cytoplasmic alkalinization was inhibited by pretreatment with nonspecific protein kinase C (PKC) inhibitors, such as sphingosine or H-7. A long-term incubation with PA increased alkaline phosphatase (ALP) activity and cell proliferation. Exogenous PA thus appeared to increase IP3 accumulation by activating phospholipase C, raise [Ca2+] by releasing Ca2+ from intracellular stores, induce cytoplasmic alkalinization via a PKC-dependent mechanism, and simultaneously decrease basal cAMP level. We suggest that these initial responses may be responsible for the increase in ALP activity and the proliferation of PA-treated MOB 3-4 cells.
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PMID:Initial responses of a clonal osteoblast-like cell line, MOB 3-4, to phosphatidic acid in vitro. 216 76

The far-ultraviolet circular dichroism spectra of fibrinogens phosphorylated by protein kinase C or casein kinase II indicated a conformational change corresponding to an increase in ordered secondary structure. The spectra of protein kinase A- or casein kinase I-phosphorylated fibrinogens did not differ substantially from the control. Fluorescence studies indicated changes in the tertiary structure around tryptophan residues for protein kinase A- or C-phosphorylated fibrinogens, but failed to show any such change for fibrinogen phosphorylated by either of the casein kinases. This latter result was also confirmed by circular dichroism measurements in the near-ultraviolet region. The apparent increase in ordered structure was proposed as an explanation for the slower rate of plasmin degradation seen in fibrinogens after phosphorylation by protein kinase C [6], and casein kinase II, especially as both spectral changes and plasmin degradation rate were unaffected by alkaline phosphatase.
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PMID:Conformational changes in human fibrinogen after in vitro phosphorylation and their relation to fibrinogen behaviour. 222 21

In rat parotid acinar cells prelabelled with [3H]-inositol, sphingosine stimulated the accumulation of [3H]-inositol polyphosphates. When the cells were exposed to sphingosine, [3H]-inositol trisphosphate (InsP3) was accumulated in a time- and dose-dependent manner. When the extracellular Ca2+ was chelated by 1 mM EGTA, the effect of sphingosine on InsP3 accumulation was completely inhibited. Ionophores, A23187 and ionomycin, had no significant effect on InsP3 accumulation. An inhibitor of protein kinase C, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), failed to stimulate InsP3 accumulation. In the homogenate of parotid acinar cells, InsP3 3-kinase and 5-phosphomonoesterase activities were not affected by sphingosine. These results suggest that sphingosine activates phosphoinositide turnover by a mechanism dependent upon extracellular Ca2+, but different from that of an ionophore, and independent of protein kinase C.
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PMID:Sphingosine increases inositol trisphosphate in rat parotid acinar cells by a mechanism that is independent of protein kinase C but dependent on extracellular calcium. 227 81

Studies were conducted to define primary pharmacological and toxicological properties of two arotinoids, SMR-2 and SMR-6, in male B6D2F1 mice. Mice were gavaged daily for up to 22 days with retinoids in corn oil (0.1, 0.2, or 0.4 mg/kg day SMR-2 or SMR-6 or 2.5, 10, or 30 mg/kg all-trans-retinoic acid as a reference control). Toxicological and biochemical endpoints were assayed after 8, 15, and 22 days. At toxic doses, i.e., those inducing weight loss, morphological changes were observed in skin, lymph nodes, spleen, bone marrow, liver, thymus, forestomach, adrenal, bone, and testes. Biochemical alterations included elevated serum alkaline phosphatase, corticosterone, and interleukins-1, -2, and -3. Additional immune alterations included increased responsiveness of spleen cells to both thymus-dependent and thymus-independent mitogens and increases in the total number of B cells in the spleen. At doses not inducing weight loss, target organ effects included the appearance of plasma cells and infiltration of polymorphonuclear cells in lymph nodes; myeloid cell hypercellularity in bone marrow; hematopoiesis in spleen; subacute inflammation in forestomach; and periportal cytoplasmic vacuolization in liver. At the low doses, SMR-2 resulted in decreased responsiveness of spleen cells to mitogens and SMR-6 caused increased responsiveness. SMR-6 also increased interleukin-1 and-2 production at low doses. Biochemical effects included reduced activities of liver aryl hydrocarbon hydroxylase (AHH) and soluble brain protein kinase C. Overall, the results suggest that leukopoiesis and reduced liver AHH and reduced soluble protein kinase C activities are the primary and initial pharmacological and toxicological effects of retinoids.
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PMID:Pharmacological and toxicological properties of arotinoids SMR-2 and SMR-6 in mice. 230 14

Phosphorylation of the insulin receptor beta-subunit on serine/threonine residues by protein kinase C reduces both receptor kinase activity and insulin action in cultured cells. Whether this mechanism regulates insulin action in intact animals was investigated in rats rendered insulin-resistant by 3 days of starvation. Insulin-stimulated autophosphorylation of the partially purified hepatic insulin receptor beta-subunit was decreased by 45% in starved animals compared to fed controls. This autophosphorylation defect was entirely reversed by removal of pre-existing phosphate from the receptor with alkaline phosphatase, suggesting that increased basal phosphorylation on serine/threonine residues may cause the decreased receptor tyrosine kinase activity. Tryptic removal of a C-terminal region of the receptor beta-subunit containing the Ser/Thr phosphorylation sites similarly normalized receptor autophosphorylation. To investigate which kinase(s) may be responsible for such increased Ser/Thr phosphorylation in vivo, protein kinase C and cAMP-dependent protein kinase A in liver were studied. A 2-fold increase in protein kinase C activity was found in both cytosol and membrane extracts from starved rats as compared to controls, while protein kinase A activity was diminished in the cytosol of starved rats. A parallel increase in protein kinase C was demonstrated by immunoblotting with a polyclonal antibody which recognizes several protein kinase C isoforms. These findings suggest that in starved, insulin-resistant animals, an increase in hepatic protein kinase C activity is associated with increased Ser/Thr phosphorylation which in turn decreases autophosphorylation and function of the insulin receptor kinase.
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PMID:Increased protein kinase C activity is linked to reduced insulin receptor autophosphorylation in liver of starved rats. 235 98

The molecular nature of the structural changes on the T cell-CD6 glycoprotein upon cell activation has been investigated. Cell surface 125I labeling and immunoprecipitation studies from PBMC revealed that after stimulation by different activators of protein kinase C, or after exposure to either human or FCS, the anti-CD6 mAb precipitated an additional protein of 130 kDa, together with the 105-kDa protein present in resting cells. Cell surface expression of this 130-kDa CD6 protein form could be detected as early as 15 min after PKC activation, without requiring de novo protein synthesis. Pulse and chase activation experiments of radioiodinated cells suggested that the 130-kDa molecule is the result of a posttranslational modification of the 105-kDa protein and that this conversion is a reversible process. Studies of 32P-cell labeling and immunoprecipitation by anti-CD6 mAb revealed that only the 130-kDa form was phosphorylated, whereas the 105-kDa protein was unphosphorylated both in resting and activated cells. Moreover, the removal of phosphate groups from the 130-kDa CD6-form by enzymatic treatment with alkaline phosphatase resulted in its conversion to the 105-kDa form. Taken together, these results demonstrate the existence of two CD6 molecular forms that are in a dynamic equilibrium and differ only at their degree of phosphorylation: a 105-kDa unphosphorylated form present in resting T cells that changes very rapidly to a 130-kDa phosphorylated form by exposure of cells either to serum or to activators of PKC.
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PMID:Phosphorylation-dephosphorylation of the CD6 glycoprotein renders two isoforms of 130 and 105 kilodaltons. Effect of serum and protein kinase C activators. 238 66

By using a retrovirus-derived vector system, we generated derivatives of the human colon cancer cell line HT29 that stably overexpress a full-length cDNA encoding the beta 1 isoform of rat protein kinase C (PKC). Two of these cell lines, PKC6 and PKC7, displayed an 11- to 15-fold increase in PKC activity when compared with the C1 control cell line that carries the vector lacking the PKC cDNA insert. Both of the overexpresser cell lines exhibited striking alterations in morphology when exposed to the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Following exposure to TPA, PKC6 and PKC7 cells displayed increased doubling time, decreased saturation density, and loss of anchorage-independent growth in soft agar; but these effects were not seen with the C1 cells. Also, in contrast to the control cells, the PKC-overproducing cells failed to display evidence of differentiation, as measured by alkaline phosphatase activity, when exposed to sodium butyrate. In addition, the PKC-overexpresser cells displayed decreased tumorigenicity in nude mice, even in the absence of treatment with TPA. These results provide the first direct evidence that PKC can inhibit tumor cell growth. Thus, in some tumors, PKC might act as a growth-suppressor gene.
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PMID:Overexpression of protein kinase C in HT29 colon cancer cells causes growth inhibition and tumor suppression. 238 20

Thrombin-stimulated (10 s) human platelets produce Ins(1,4,5)P3 and an additional inositol trisphosphate (InsP3), in approximately a 1:20 ratio. The major InsP3 co-migrates with Ins(1,3,4)P3 on strong-anion-exchange h.p.l.c. To identify this species unequivocally, we treated putative Ins(1,3,4)P3 obtained from thrombin-stimulated myo-[3H]inositol-labelled platelets with NaIO4/NaBH4 or 4-phosphomonoesterase. The products indicate that the major InsP3 is at least 90% D-Ins(1,3,4)P3. D-[3H]Ins(1,3,4)P3 added to saponin-permeabilized platelets is hydrolysed to an InsP2 (7.8%) and phosphorylated by a kinase to yield an inositol polyphosphate (0.9%) in 5 min. The phosphorylation product co-migrates with Ins(1,3,4,6)P4 on Partisphere WAX h.p.l.c. Under similar conditions, L-[3H]Ins(1,3,4)P3 is dephosphorylated but not phosphorylated. Relative phosphatase:kinase ratios are 8.7:1 (Vmax. values) and 0.86:1 (Km values) with respect to D-Ins(1,3,4)P3. The kinase activity is predominantly cytosolic (96.8% of total activity) in freeze-thaw-disrupted platelets, and the accumulation of its product is Ca2(+)-dependent. The activity is identified as a 6-kinase on the basis of its product's insensitivity to 5-phosphomonoesterase, resistance to periodate oxidation and co-migration with standard Ins(1,3,4,6)P4 on h.p.l.c. Incubation of platelets with beta-phorbol dibutyrate (beta-PDBu, 76 nM), causing activation of protein kinase C, results in a 57.5% inhibition (reversible by the protein kinase C inhibitor staurosporine) of Ins(1,3,4,6)P4 accumulation. alpha-PDBu, which does not stimulate protein kinase C, has no effect. Stimulation of intact platelets with thrombin results in the production of Ins(1,3,4,6)P4 (1.4-fold rise in 30 s) and Ins(1,3,4,5)P4, with the latter being the major InsP4 species. Accumulation of Ins(1,3,4,6)P4 is slightly delayed in comparison with Ins(1,3,4)P3 and is relatively small. We propose that the major route of Ins(1,3,4)P3 metabolism in stimulated human platelets is via phosphatase action.
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PMID:Ca2(+)-stimulatable and protein kinase C-inhibitable accumulation of inositol 1,3,4,6-tetrakisphosphate in human platelets. 239 72


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