PubMed Health⌕ Search

Biomedical subjects

E Villa-Moruzzi

Publications and source records attributed to E Villa-Moruzzi.

At least 37 records · Page 2Linked to original sources
PubMed1994

Differential activities of protein phosphatase types 1 and 2A in cytosolic and particulate fractions from rat forebrain.

The activities and concentrations of protein phosphatase type 1 (PP1) and type 2A (PP2A) were compared in cytosol and particulate fractions of rat forebrain. Although the activity of PP2A was highest in the cytosol, immunoblot analysis with a PP2A-specific antibody showed that there were significant levels of the enzyme in the particulate fraction. There was no significant difference between the concentration of PP2A in the cytosol and particulate fractions such that the low activity of PP2A in the particulate fraction represents an inactivation of this form of the enzyme. Similar analysis in skeletal muscle, heart, and liver showed this finding was unique to the brain. Similarly, the majority of PP1 activity was recovered in the cytosol, but most PP1 enzyme was associated with the particulate fraction. Comparison with other tissues showed that the activities of PP1 in the particulate fractions were similar but that the forebrain contained significantly more enzyme than the other tissues. Thus, like PP2A it appears that the specific activity of PP1 in the particulate fraction of rat forebrain is much lower than that of the cytosol and of the particulate fractions of other tissues. Elution of PP1 and PP2A from membranes with 0.5 M NaCl plus 0.3% Triton X-100 resulted in severalfold activation of both enzymes. That the majority of PP1 and PP2A in rat forebrain are associated with membrane structures but in a low activity state suggests that novel regulatory mechanisms exist that have considerable and unique potential for activation of protein dephosphorylation.

Animals↗
PubMed1993

Activation of the cdc25C phosphatase in mitotic HeLa cells.

The cdc2-activator cdc25C was immunoprecipitated from HeLa cell extracts and assayed as tyrosine phosphatase (PTP) using tyrosine-phosphorylated myelin basic protein. The PTP activity was 12-fold higher in immunocomplexes from mitotic (nocodazole-arrested) than from asynchronous cells. This difference is due to enzyme activation, since the same amount of cdc25C was immunodetected in both conditions. However, mitotic cdc25C had M(r) 59,000, while a 56,000-59,000 doublet was detected in immunocomplexes from asynchronous cells. The PTP activity of mitotic cdc25C was decreased by treatment with Phosphatase-2A catalytic subunit (but not with Phosphatase-1), with re-appearance of the 56,000 polypeptide. cdc25C was also found associated with cdc2-p13-Sepharose complex and its PTP activity was 7-fold higher in samples from mitotic than from asynchronous cells. cdc25C and cdc2 co-migrated during gel filtration and the higher activity of mitotic cdc25C was retained through gel filtration.

Chromatography, Gel↗
PubMed1993

A protein tyrosine phosphatase activity associated with the hepatocyte growth factor/scatter factor receptor.

The receptor for the growth and motility factor, hepatocyte growth factor/scatter factor (HGF/SF), is a transmembrane tyrosine kinase encoded by the MET oncogene. Previous work has shown that receptor phosphorylation on tyrosine is critical for both kinase activation and association with intracellular signal transducers. In this paper, we report that a protein tyrosine phosphatase activity (PTP) coprecipitates with the HGF/SF receptor. The associated PTP activity correlates with the kinase activation of the receptor, increasing up to 5-fold over the basal level after HGF/SF stimulation. The increase is reversible and time- and dose-dependent. A comparable level of activity is associated with constitutively tyrosine-phosphorylated receptors immunoprecipitated from cells where the MET oncogene is amplified and overexpressed. In these cells, a parallel decrease in PTP activity is observed after inhibition of receptor tyrosine phosphorylation following protein kinase C activation. The associated PTP activity is effective in dephosphorylating the HGF/SF receptor. These data show that a protein tyrosine phosphatase is functionally coupled to the HGF/SF receptor.

Cell Line↗
PubMed1992

Activation of type-1 protein phosphatase by cdc2 kinase.

Purified cdc2 or cdc2 obtained from HeLa cells in association with p13suc1 activate inactive type-1 protein phosphatase (PP1) (catalytic subunit.inhibitor-2 complex, purified from skeletal muscle). Likewise in the case of PP1 activation by FA/GSK3, activation by cdc2 is accompanied by phosphorylation of inhibitor-2 (I2) and free I2 can be phosphorylated as well. Correlation between PP1 activation and I2 phosphorylation is suggested by the fact that both activation and phosphorylation (a) increase in parallel during incubation with cdc2, (b) decrease in parallel upon subsequent cdc2 inhibition by EDTA, and (c) are inhibited by the cdc2 inhibitor 5,6-dichlorobenzimidazole riboside. cdc2 also phosphorylates the catalytic subunit of PP1, whether in the complex with I2 or as free molecule. The activation of PP1 by cdc2 and by FA/GSK3 is compared.

CDC2 Protein Kinase↗
PubMed1991

Phosphorylation of the catalytic subunit of type-1 protein phosphatase by the v-abl tyrosine kinase.

The catalytic subunit of type-1 protein phosphatase (PP1) was phosphorylated by the tyrosine kinase v-abl as follows: (i) cytosolic PP1 was phosphorylated more (0.73 mol/mol) than PP1 obtained from the glycogen particles (0.076 mol/mol), while free catalytic subunit isolated in the active or inactive form from cytosolic PP1 was phosphorylated even less and catalytic subunit complexed with inhibitor-2 was not phosphorylated; (ii) phosphorylation stoichiometry was dependent on the concentration of PP1 and 3 h incubation at 30 degrees C was required for maximal phosphorylation; (iii) phosphorylation was on a tyrosine residue located in the C-terminal region of PP1 which is lost during proteolysis; (iv) phosphorylation did not affect enzyme activity but allowed conversion from the active to the inactive form upon incubation with inhibitor-2 of a PP1 form that in its dephospho-form did not convert.

Animals↗
PubMed1991

Stimulation of FA and casein kinase II by insulin in 3T3-L1 cells.

Insulin stimulates protein phosphatase-1 and FA, assayed as phosphatase-1 activator, in 3T3-L1 cells. Since other kinases, such as casein kinase-II may also contribute to such FA activity, we assayed casein kinase-II and FA as peptide kinase on extracts from 3T3-L1 cells that had been exposed to insulin for various times. Under such conditions FA, assayed as phosphatase-1 activator, was stimulated 2-3-fold within 1-2 min. Casein kinase-II was stimulated about 2-fold but at a slightly later time (2-3 min) than FA, making it unlikely that casein kinase-II contributes to FA stimulation. Insulin slightly stimulated also the kinase activity of FA towards a synthetic peptide at 2 min, thus confirming the FA activation seen when FA was assayed as activator of phosphatase-1.

Amino Acid Sequence↗
PubMed1991

Protein phosphatase-1 and -2A, kinase FA, and casein kinase II in skeletal muscle of streptozotocin diabetic rats.

Protein phosphatase-1 (PP-1) and -2A (PP-2A), two regulatory subunits of PP-1, the glycogen-binding subunit G and inhibitor-2 (I-2), kinase FA, and casein kinase II (CK-II) were investigated in skeletal muscle of diabetic rats 2 days after streptozotocin injection. FA and CK-II activate PP-1 in vitro and might be involved in the activation of PP-1 by insulin. Following muscle fractionation we found that (1) diabetes decreased both basal and trypsin-stimulated PP-1 activities; the decrease was more significant in the glycogen-bound and microsomal fractions than in the cytosol (cytosolic PP-1 decreased as specific activity but not as activity/g of muscle); also PP-2A was lower in diabetic cytosols; (2) less G was immunoprecipitated from diabetic glycogen-bound fractions compared to controls, while I-2 was not significantly changed; (3) diabetes decreased also FA (assayed as PP-1 activator) and CK-II (assayed using a synthetic peptide as substrate); (4) diabetes did not have any effect on phosphorylase (a + b) activity in the glycogen-bound fraction. Altogether the data show that acute diabetes decreased PP-1, one of its regulatory subunits and two potentially physiological regulators of PP-1, in addition to PP-2A. This may indicate that insulin is responsible for the long-term regulation of the same enzymes that are also under acute insulin control.

Animals↗
PubMed1990

Effect of NaF on type-1 phosphatase aggregation.

In muscle cytosolic and glycogen fractions prepared in the presence of 50 mM NaF phosphorylase phosphatase was a approximately 70 kDa complex instead of the 250 kDa or higher seen in the absence of NaF. A approximately 70 kDa complex was also formed when purified 37 kDa phosphatase-1 catalytic subunit (but not its 33 kDa tryptic fragment) was exposed to NaF. Treating this latter complex with a cross-linker led to disappearance of the 37 kDa protein and formation of a approximately 66 kDa band (detected by SDS electrophoresis), thus indicating the dimeric nature of the approximately 70 kDa complex.

Animals↗
PubMed1989

Stimulation of FA and phosphatase-1 activities by insulin in 3T3-L1 cells.

The phosphatase-1 activator FA and phosphatase-1 were assayed in 3T3-L1 cells exposed to insulin. The cytosolic FA activity was transiently stimulated (7-8-fold) 1 and 2 min after exposure to 10(-8) M insulin and returned to control values within 5-10 min. Cytosolic phosphatase-1 (assayed after trypsin treatment) was activated (120-140% of controls) between 2 and 5 min and returned to control values within 10 min. Insulin effects were dose-dependent, with maximum stimulation of both activities at 10(-8) M insulin. The possibility that FA and other kinases mediate phosphatase activation by insulin is discussed.

Animals↗
PubMed1989

Glycogen-bound type-1 phosphatase: isolation and dissociation of a complex containing undegraded G-subunit.

A high molecular mass type-1 phosphatase complex can be isolated from muscle glycogen particles by a fast procedure that preserves the glycogen-binding subunit of phosphatase called G from proteolysis. G can be dissociated from such complex by ion exchange chromatography on FPLC SI column, with recovery of unproteolyzed G completely separated from phosphatase catalytic subunit.

Animals↗
PubMed1987

Phosphorylase phosphatase from skeletal muscle membranes.

Microsomes containing 12-15 U/mg phosphorylase phosphatase were obtained from skeletal muscle glycogen particles following glycogen digestion and differential centrifugation. The phosphatase associated with the membranes is in an inhibited state; dilution induces dissociation and deinhibition of the enzyme. Phosphatase-depleted membranes can rebind purified phosphatase catalytic subunit but not the complex between catalytic subunit and inhibitor 2. Binding involves a receptor, deduced from saturation phenomena, which is responsible for inhibition of the bound enzyme and which is a protein, since trypsin treatment releases all bound enzyme and prevents rebinding. The phosphatase extracted from the membranes is of type 1 and is a mixture of complexes, the major ones displaying a Mr of 300,000 and 70,000. From these complexes the 35-kDa catalytic subunit can be obtained either by trypsin treatment or by acetone precipitation. Purification to homogeneity involves chromatography on polylysine and FPLC chromatography on Mono Q and Polyanion SI columns. The purified enzyme exhibits a specific activity of 26,800 U/mg (27,900 U/mg after trypsin treatment) and consists of a major protein of 38 kDa (SDS gel electrophoresis). A minor component of 33 kDa, which may represent either a proteolytic product or an isozyme, can be separated. Both 38-kDa and 33-kDa catalytic subunits form a 70-kDa inactive complex with inhibitor 2 and upon incubation of the complexes the catalytic subunit is slowly converted to the inactive conformation which can then be reactivated by either the kinase FA or trypsin and Mn2+. Alternatively the inactive catalytic subunit is reactivated by Mn2+ alone once it has been isolated by FPLC chromatography on SI. The observation that the same catalytic subunit is present at various cell locations (namely cytosol, glycogen particles and microsomes), though in different conformations, is in favour of the hypothesis that displacement of the catalytic subunit from one cell site to the other may represent a new mechanism for phosphatase regulation in skeletal muscle.

Animals↗
PubMed1986

Identification of a 68 kDa protein which copurifies with type-1 protein phosphatase as albumin.

Proteins of 60-70 kDa copurify with some preparations of type-1 or type-2 phosphatases. In our system chromatography on polylysine-Affi-Gel 10 separates a 68 kDa protein from rabbit muscle glycogen particle phosphorylase phosphatase. The separation affects neither the activity nor the size of the phosphatase. The 68 kDa protein, although pure by SDS gel electrophoresis criteria, still displays phosphatase activity of approx. 6-8 U/mg. However, rechromatography either on Bio-Gel A-0.5 m or on Blue Sepharose CL-6B followed by gel filtration shows that the activity is due to a contamination with phosphatases of type 1 and type 2, displaying a molecular mass of 35 kDa, which can be totally removed from the 68 kDa protein. The amino acid composition of the 68 kDa protein is identical to that of rabbit serum albumin, within the limits of variation for the method. Furthermore, the sequence of the 38 N-terminal amino acids is the same in the isolated 68 kDa protein and in rabbit serum albumin.

Albumins↗
PubMed1986

Purification and inactivation-reactivation of phosphorylase phosphatase from the protein-glycogen complex.

Phosphorylase phosphatase purified from the protein-glycogen complex of rabbit muscle has a Mr of 34,000 by gel filtration and migrates as a single band of Mr 38,000 on sodium dodecyl sulfate gel electrophoresis, i.e., of the same size as the catalytic subunit of the sarcoplasmic complex of type 1 phosphatase (L. M. Ballou, D. L. Brautigan, and E. H. Fischer (1983) Biochemistry 22, 3393-3399). The enzyme, called PG-Ea, has a specific activity of 12,000 units/mg of protein and is essentially fully active, displaying at most a 20% further increase in activity on treatment with trypsin. As in the case of the catalytic subunit of the sarcoplasmic enzyme, tryptic attack decreases the size of PG-Ea to 33,000. PG-Ea is completely inhibited by the modulator protein (inhibitor 2) after formation of a complex of Mr 70,000. On incubation of this complex at 30 degrees C, the catalytic subunit is converted (t 1/2 = 30 min) to an inactive form (Ei) that can be reactivated by the protein kinase FA (J. R. Vandenheede, S.-D. Yang, J. Goris, and W. Merlevede (1980) J. Biol. Chem. 255, 11,768-11,774) or to a lower extent by trypsin-Mn2+. Also the trypsinized PG-Ea is inhibited by inhibitor 2, it forms with this a Mr 70,000 complex and undergoes an even faster (t 1/2 = 10 min) conversion to an Ei form that can be reactivated by the kinase FA or to a lower extent by trypsin-Mn2+. Enzymological comparison of PG-Ea and trypsinized PG-Ea with the FA-activated, isolated catalytic subunit of the sarcoplasmic phosphatase (called EaFA, E. Villa-Moruzzi, L. M. Ballou, and E. H. Fischer (1984) J. Biol. Chem. 259, 5857-5863) and with its trypsinized form shows several similarities. The most relevant of these is the very specific interaction with inhibitor 2, that takes to inactivation and allows the following reactivation by FA or by trypsin-Mn2+. However, the inactivation-reactivation patterns show also some differences, namely (i) the t 1/2 of the conversion to Ei is longer for PG-Ea than for EaFA, and (ii) the reactivation of PG-Ea and trypsinized PG-Ea with trypsin-Mn2+ is only partial. Altogether the similarity but not identity of PG-Ea and EaFA would suggest that they are either two different conformations of the same molecule or two isozymes.

Animals↗
PubMed1986

Effects of streptozotocin-diabetes, fasting and adrenaline on phosphorylase phosphatase activities of rat skeletal muscle.

The distribution of the spontaneous and trypsin-stimulated phosphorylase phosphatase activities between glycogen particles and cytosol was examined in muscle extracts obtained from rats that had been fasted, made diabetic with streptozotocin or injected with adrenaline. In all conditions the particle-bound phosphatase activities decreased, glycogen was degraded and phosphorylase was released from the particles into the cytosol. However, in fasting and diabetes (but not after adrenaline) the combined glycogen particle + cytosolic phosphatase activities decreased, indicating that the activity lost from the particles was not simply shifted to the cytosol. Fasting and diabetes (but not adrenaline) also decreased the phosphatase-activating ability of the muscle extracts, which was, at least in part, attributable to the protein kinase FA. These data indicate the presence of at least two different mechanisms affecting the phosphatase system, one modified by fasting and diabetes, the other by adrenaline.

Animals↗
PubMed1985

Phosphorylase phosphatase and phosphatase activating-kinase FA in growing rat muscles.

The activities of phosphorylase phosphatase and of FA, the kinase that activates phosphatase, were measured in rat skeletal muscle from birth to 200 g body weight. Throughout this period part of phosphatase was always spontaneously active. The activity could be further increased by trypsin, but did not additionally increase when Mn2+ was present. During the first 15-20 days of life most of the phosphatase was cytosolic. Then it decreased in this fraction and more phosphatase was found in glycogen particles, to reach the adult level at about 50 g body weight. Also the activity of the kinase FA was lower for the first 10 days, then it increased attaining the adult level again at about 50 g. These results are compared to those on phosphorylase activity and glycogen level in muscle and on serum insulin during growth.

Aging↗
PubMed1984

Phosphorylase phosphatase. Interconversion of active and inactive forms.

Phosphorylase phosphatase is isolated as an inactive Mr = 70,000 complex made up of a catalytic and a regulatory subunit (inhibitor 2). Separation of the two components yields the free catalytic subunit in a completely inactive state. It can be activated by Mn2+ or Co2+, not Mg2+ or Ca2+. No metal ion is incorporated during this process, as shown by the use of 54Mn2+. The inactive complex, but not the isolated catalytic subunit, can be activated by the protein kinase FA (Vandenheede, J.R., Yang, S.-D., Goris, J., and Merlevede, W. (1980) J. Biol. Chem. 255, 11768-11774), which causes the simultaneous phosphorylation of inhibitor 2 and conversion of the catalytic subunit to an active conformation. The activated enzyme undergoes autodephosphorylation to produce a complex that is inactive even though the catalytic subunit is still in the active form; in a slower step, it returns to its original inactive state. No such conversion occurs in the absence of inhibitor 2, indicating that the regulatory subunit is required for both the activation and inactivation reactions. Complexes were prepared by adding inhibitor 2 to various isolated catalytic subunits. Only the one reconstituted with the FA-activated species behaved like the native enzyme in that the catalytic subunit underwent transformation to the inactive form, then could be reactivated by FA. These data suggest that the two subunits must interact in a highly specific manner to allow the structural changes accompanying the activation-inactivation process. Models are proposed for the changes in conformation induced by Mn2+ or FA.

Animals↗