Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P10636 (tau protein)
 5,110 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have analyzed the in vitro phosphorylation of tau protein by Ca2+/calmodulin-dependent protein kinase, casein kinase II, and proline-directed serine/threonine protein kinase. These kinases phosphorylate tau protein in sites localized in different regions of the molecule, as determined by peptide mapping analyses. Focusing on the phosphorylation of tau by protein kinase C, it was calculated as an incorporation of 4 mol of phosphate/mol of tau. Limited proteolysis assays suggest that the phosphorylation sites could be located within the tubulin-binding domain. Direct phosphorylation of synthetic peptides corresponding to the cysteine-containing tubulin-binding region present in both fetal and adult tau isoforms demonstrates that serine 313 is modified by protein kinase C. Phosphorylation of the synthetic peptide by protein kinase C diminishes its binding to tubulin, as compared with the unphosphorylated peptide.
 ...
PMID:Microtubule-associated protein tau is phosphorylated by protein kinase C on its tubulin binding domain. 163 8

We introduce a new procedure to study kinase substrates in postmortem human brain. By adding purified exogenous protein kinase C (PKC) and the phospholipid phosphatidylserine to brain homogenates in vitro we are able to analyze PKC substrates. A human 53-kDa phosphoprotein is described that appears to be homologous to rat and monkey protein F1 (GAP-43). This identity is based on molecular weight, isoelectric point, phosphorylation by exogenous protein kinase C, enhancement of its phosphorylation by three activators (phospholipids, calcium and phorbol esters), phosphopeptide maps, and cross-reactivity with an antibody raised against rat protein F1. Protein F1 is a PKC substrate associated with synaptic plasticity and nerve growth. Its phosphorylation in rat brain has been correlated with long-term potentiation, an electrophysiological model of memory. In the present study of normal brain, human protein F1 shows an occipitotemporal in vitro phosphorylation gradient. This is consistent with previous observations in nonhuman primates. This gradient is less pronounced in Alzheimer's disease (AD). Changes in the in vitro phosphorylation pattern of three other non-PKC substrates in Alzheimer's disease, including one with characteristics similar to microtubule-associated protein tau, are also reported. These results suggest that protein phosphorylation can be studied in postmortem human brain and that PKC-mediated phosphorylation of protein F1, already linked to synaptic plasticity and memory, may be altered in AD.
 ...
PMID:Contrasting patterns of protein phosphorylation in human normal and Alzheimer brain: focus on protein kinase C and protein F1/GAP-43. 182 25

Roles of protein kinases in mediating adaptive neuronal responses to activation of signal transduction pathways are well known. Recent findings suggest that kinases may also be involved in pathological processes in the nervous system. The present study employed cultured human cerebral cortical neurons to test the hypothesis that overactivation of protein kinase C (PKC) can result in neurodegeneration. Phorbol 12-myristate 13-acetate (PMA), an activator of PKC, caused the degeneration of neurons over a period of 3-24 h. The PKC inhibitor H-7 prevented the neurodegeneration normally caused by PMA, and an inactive phorbol (4 alpha-phorbol 12,13-didecanoate; PDD) did not cause neurodegeneration. The neurodegeneration caused by PMA was independent of calcium influx. Immunoreactivity toward antibodies that recognize the microtubule-associated protein tau in Alzheimer neurofibrillary tangles (Alz-50 and 5E2) was greatly increased in neurons exposed to PMA. The antigenic changes were prevented by H-7. These findings indicate that high levels of activation of PKC can cause neurodegeneration and are consistent with the possibility that altered cellular signaling contributes to pathological neuronal degeneration in the intact nervous system.
 ...
PMID:Evidence for the involvement of protein kinase C in neurodegenerative changes in cultured human cortical neurons. 201 10

The microtubule array in neuronal cells undergoes extensive growth, dynamics and rearrangements during neurite outgrowth. While little is known about how these changes are regulated, microtubule-associated proteins (MAPs) including tau protein are likely to perform an important role. Tau is one of the MAPs in mammalian brain. When isolated it is usually a mixture of several isoforms containing between 341 and 441 residues that arise from alternative splicing. Tau can be phosphorylated by several protein kinases. Phosphorylation at certain sites results in major structural and functional changes, as seen by changes in electrophoretic mobility, interaction with microtubules, molecular length and elasticity. Here we show that the sites of phosphorylation by four kinases (PKA, PKC, CK and CaMK) all lie in the C-terminal microtubule-binding half of tau, but only the phosphorylation by CaM kinase shows the pronounced shift in electrophoretic mobility characteristic for tau from Alzheimer neurofibrillary tangles. By using a combination of limited proteolysis, protein sequencing and protein engineering we show that a single phosphorylation site is responsible for this shift, located at Ser 405 in the C-terminal tail of the protein outside the region of internal repeats. Phosphorylation at this site not only reduces the electrophoretic mobility of tau, it also makes the protein long and stiff, as shown earlier. The site is likely to be phosphorylated in tau from Alzheimer neurofibrillary tangles.
 ...
PMID:Phosphorylation of microtubule-associated protein tau: identification of the site for Ca2(+)-calmodulin dependent kinase and relationship with tau phosphorylation in Alzheimer tangles. 212 43

Abnormal protein phosphorylation has been identified in Alzheimer's disease (AD) for several proteins including a Mr 60,000 protein, a Mr 86,000 protein and a microtubule-associated protein tau. The Mr 86,000 protein is phosphorylated by protein kinase C, whereas protein kinases responsible for other aberrant phosphorylation reactions are not known. In addition to protein kinase C, another kinase, casein kinase II (CK-II), has now been shown to be aberrant in AD. The spermine-dependent CK-II activity is reduced by 84% in AD and the amount of CK-II as determined by its immunoreactivity on a Western blot is reduced by 63%. Furthermore, the distribution of CK-II in AD is altered. Although the neuronal cell body reacts well with CK-II antisera in the normal cortex, the non-tangle-bearing neurons in the AD cortex showed a 15-30% decrease in anti-CK-II immunoreactivity. The neurofibrillary tangles, on the other hand, stain very strongly with rabbit anti-CK-II and indicates that CK-II may be involved in the pathology of AD. The study of CK-II immunoreactivity for dementing diseases other than AD revealed a similar reduction, suggesting the CK-II involvement in the common process of neurodegeneration.
 ...
PMID:Aberrant casein kinase II in Alzheimer's disease. 233 67

Bovine brain tau protein (tau) consists of four closely related phosphoproteins named tau 1, tau 2, tau 3 and tau 4, that range in size from 55 to 68 kDa (as determined by gel electrophoresis). Here we report an improved large-scale purification method for tau protein and the separation of the four individual tau protein species. The separation of the individual tau protein was accomplished by two chromatographic techniques: hydroxyapatite chromatography allowed the separation of two pairs of tau protein (tau 1 and tau 3) and (tau 2 and tau 4); fast protein liquid chromatography on a Mono Q column at basic pH achieved the resolution of the individual tau protein species in each pair derived from hydroxyapatite columns. Chromatography on the Mono Q column revealed that tau protein possesses previously unrecognized, highly reactive sulfhydryl groups that may oxidize to form intermolecular disulfide bridges. The isolation of individual species of tau in substantial quantities permitted an improved amino acid analysis that demonstrated the occurrence of cysteine and tryptophan in the protein. The availability of individual tau protein species greatly simplified the analysis for mode II phosphorylation of tau, which was found to be catalyzed by the calcium/phospholipid-dependent protein kinase C. The mode II phosphorylation of tau by protein kinase C was not associated with a mobility shift for tau protein in SDS-polyacrylamide gel electrophoresis, in contrast to mode I phosphorylation of tau by the Ca2+/calmodulin-dependent kinase, which produces a substantial shift in mobility.
 ...
PMID:Separation of the different microtubule-associated tau protein species from bovine brain and their mode II phosphorylation by Ca2+/phospholipid-dependent protein kinase C. 312 2

The phosphorylation state of the CD18-chain of beta 2-integrins have been shown not to mediate changes in the avidity of these receptors (i.e., inside-out signaling); however, no alternative functional significance has been proposed. Our study focused on how changes in the phosphorylation state of beta 2-integrin-receptors on HL60-granulocytic cells are related to its intracellular signal transduction properties (i.e., outside-in signaling). Engagement of beta 2-integrins on differentiated HL60 cells induced a transient increase in the cytosolic free Ca2+ concentration and an increased tyrosine phosphorylation of three major protein bands (70, 115, and 140 kDa). These signaling events occurred without any detectable phosphorylation of the CD18-chain. However, a strong phosphorylation of the CD18-chain by preexposure to phorbol myristate acetate (PMA) coincided with an abolishment of both the beta 2-integrin-induced Ca2+ signal and the protein tyrosine phosphorylations. By comparison, none of these effects were exhibited by 4-alpha-PMA, an analogue that does not activate protein kinase C. Thus, phosphorylation of the CD18-chain of beta 2-integrins is not required for outside-in signal transduction by these receptors, but it could constitute an effective mechanism by which the signaling properties of beta 2-integrins can be modulated by exogenous factors and possibly also by intracellular signals induced by other receptors. The fact that both the cytosolic free Ca2+ signal and protein tyrosine phosphorylations were abrogated by PMA suggests an intimate relationship between these two intracellular signals. To explore this possible relationship, we chelated the beta 2-integrin-induced Ca2+ signal with BAPTA. The beta 2-integrin-induced protein tyrosine phosphorylations were blocked by BAPTA but not by abolishment of the Ca2+ signal due to chelation with MAPT or by pretreatment with thapsigargin. These findings and the observation that pretreatment of cells with methyl-2,5-dihydroxycinnamate (a tyrosine kinase inhibitor) blocked the beta 2-integrin- but not the fMet-Leu-Phe-induced Ca2+ signal suggest that beta 2-integrin-induced tyrosine kinase activation occurs prior to and is a prerequisite for the subsequent Ca2+ signal.
 ...
PMID:The Ca2+ signaling capacity of the beta 2-integrin on HL60-granulocytic cells is abrogated following phosphorylation of its CD18-chain: relation to impaired protein tyrosine phosphorylation. 753 90

We identified two major substrates for the proline-directed protein kinases--cdc2 kinase and tau protein kinase II (TPKII)--in the cytosol fraction from rat brains. The molecular masses of the proteins were 80 and 46 kDa. Because the 80-kDa protein was phosphorylated by protein kinase C and was heat stable, we examined the possibility that the protein might be myristoylated alanine-rich C kinase substrate (MARCKS). On the basis of a comparison between the properties of the 80-kDa protein and purified MARCKS, we concluded that the 80-kDa protein is indeed MARCKS. The amounts of phosphate incorporated into MARCKS by protein kinase C, cdc2 kinase, and TPKII were 1.7, 1.4, and 0.6 mol/mol of the protein, respectively. Two-dimensional tryptic peptide mapping indicated that phosphorylation sites by protein kinase C and proline-directed protein kinases completely differed. Only the seryl residue was phosphorylated by protein kinase C, whereas both seryl and threonyl residues were phosphorylated by cdc2 kinase and TPKII. Phosphorylation of MARCKS by protein kinase C inhibited the binding to calmodulin, whereas phosphorylation by cdc2 kinase and TPKII significantly increased the binding to calmodulin. The holoenzyme of protein phosphatase 2A dephosphorylated MARCKS that had been phosphorylated by protein kinase C, cdc2 kinase, or TPKII, whereas calcineurin was unable to dephosphorylate it. These results suggest that cdc2 kinase and TPKII regulate the functions of MARCKS in different ways from protein kinase C.
 ...
PMID:Phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) by proline-directed protein kinases and its dephosphorylation. 761 38

Microtubule-associated protein tau from Alzheimer brain has been shown to be phosphorylated at several ser/thr-pro and ser/thr-X sites (Hasegawa, M. et al., J. Biol. Chem. 267, 17047-17054, 1992). Several proline-dependent protein kinases (PDPKs) (MAP kinase, cdc2 kinase, glycogen synthase kinase-3, tubulin-activated protein kinase, and 40 kDa neurofilament kinase) are implicated in the phosphorylation of the ser-thr-pro sites. The identity of the kinase(s) that phosphorylate the ser/thr-X sites are unknown. To identify the latter kinase(s) we have compared the phosphorylation of bovine tau by several brain protein kinases. Stoichiometric phosphorylation of tau was achieved by casein kinase-1, calmodulin-dependent protein kinase II, Gr kinase, protein kinase C and cyclic AMP-dependent protein kinase, but not with casein kinase-2 or phosphorylase kinase. Casein kinase-1 and calmodulin-dependent protein kinase II were the best tau kinases, with greater than 4 mol and 3 mol 32P incorporated, respectively, into each mol of tau. With the sequential addition of these two kinases, 32P incorporation approached 6 mol. Peptide mapping revealed that the different kinases largely phosphorylate different sites on tau. After phosphorylation by casein kinase-1, calmodulin-dependent protein kinase II, Gr kinase, cyclic AMP-dependent protein kinase and casein kinase-2, the mobility of tau isoforms as detected by SDS-PAGE was decreased. Protein kinase C phosphorylation did not produce such a mobility shift. Our results suggest that one or more of the kinases studied here may participate in the hyperphosphorylation of tau in Alzheimer disease.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Comparison of the phosphorylation of microtubule-associated protein tau by non-proline dependent protein kinases. 803 84

Phosphorylation is an indispensable process for energy and signal transduction in biological systems. AlCl3 at 10 nM to 10 microM range activated in-vitro [gamma-32P]ATP phosphorylation of the brain (tau) tau protein in both normal human or E. coli expressed tau forms; in the presence of the kinases P34, PKP, and PKC. However, higher concentrations of ALCl3 inhibited the tau phosphorylation with P34, PKP, and PKC to a maximum at 1 mM level. AlCl3 at 100 microM to 500 microM range induced non-enzymatic phosphorylation of tau with gamma-ATP, gamma-GTP, and alpha-GTP. AlCl3 activated histone phosphorylation by P34 in a similar pattern. The hyperphosphorylation of tau by Al3+ was accompanied by molecular shift and mobility retardation in SDS-PAGE. This may demonstrate the mechanism of the longterm neurological effect of Al3+ in human brain leading to the formation of the neurofibrillary tangles related to Alzheimer's disease.
 ...
PMID:Aluminum interaction with human brain tau protein phosphorylation by various kinases. 827 Jul 65


1 2 3 4 Next >>