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PubMed1992

Activators of protein kinase C increase the phosphorylation of the synapsins at sites phosphorylated by cAMP-dependent and Ca2+/calmodulin-dependent protein kinase in the rat hippocampal slice.

Previous studies have shown that activators of protein kinase C (C kinase) produce synaptic potentiation in the hippocampus. For example, the C kinase activator phorbol dibutyrate has been shown to increase transmitter release in the hippocampus. In addition, a role for C kinase in long-term potentiation has been proposed. A common assumption in such studies has been that substrates for C kinase were responsible for producing these forms of synaptic potentiation. However, we have recently shown that phorbol dibutyrate increased the phosphorylated of synapsin II (formerly protein III, Browning et al., 1987) in chromaffin cells (Haycock et al., 1988). Synapsin II is a synaptic vesicle-associated phosphoprotein that is a very poor substrate for C kinase but an excellent substrate for cAMP-dependent and Ca2+/calmodulin-dependent protein kinase. We felt, therefore, that activation of C kinase might lead to activation of a kinase cascade. Thus effects of C kinase activation might be produced via the phosphorylation of proteins that are not substrates for C kinase. In this report we test the hypothesis that activators of C kinase increase the phosphorylation of synapsin II and an homologous protein synapsin I. Our data indicate that PdBu produced dose-dependent increases in the phosphorylation of synapsin I and synapsin II. We also performed phospho-site analysis of synapsin I using limited proteolysis. These studies indicated that PdBu increased the phosphorylation of multiple sites on synapsin I. These sites have previously been shown to be phosphorylated by both cAMP-dependent protein kinase and the multifunctional Ca2+/calmodulin-dependent protein kinase II.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1998

The hCSE1/CAS protein is phosphorylated by HeLa extracts and MEK-1: MEK-1 phosphorylation may modulate the intracellular localization of CAS.

hCSE1/CAS (CAS), the human homologue of the yeast chromosome segregation gene CSE1, is a nuclear transport factor that plays a role in proliferation and apoptosis. A MEK-1 phosphorylation sequence in CAS raises the possibility that MEK-phosphorylation regulates the function of CAS. CAS protein from cell extracts shows covalent charge modifications; one of these charge variants contains phosphotyrosine. CAS protein can be captured from cell extracts by immobilized anti-phosphotyrosine antibodies. We have produced recombinant protein fragments containing the N-terminal or central portion of CAS and found that the N-terminal fragment, which contains a putative MEK phosphorylation site, is phosphorylated by the HeLa extracts and MEK-1. Treatment of cells with an inhibitor of MEK-1 phosphorylation in vivo changes the intracellular localization of CAS from predominantly cytoplasmic to nuclear. This suggests that a function of CAS in nuclear transport may be regulated by phosphorylation.

Apoptosis↗
PubMed1996

Regulation of protein tyrosine phosphorylation in human sperm by a calcium/calmodulin-dependent mechanism: identification of A kinase anchor proteins as major substrates for tyrosine phosphorylation.

Signal transduction pathways regulate various aspects of mammalian sperm function. When human sperm were incubated in a medium supporting capacitation, proteins became tyrosine-phosphorylated in a time-dependent manner. This phosphorylation was inhibited by genistein, a protein tyrosine kinase inhibitor. Phosphorylation was also reduced when sperm were incubated either in the presence of increasing concentrations of extracellular Ca2+ or in a medium containing the Ca2+ ionophore A23187. This Ca2+-induced dephosphorylation was calmodulin-dependent, suggesting that calcineurin was involved. In this regard, the calcineurin inhibitor deltamethrin inhibited the Ca2+ ionophore-induced dephosphorylation. A limited number of Mr 80,000-105,000 polypeptides were the most prominent phosphotyrosine-containing proteins present in human sperm. Unlike mouse sperm, which contains a tyrosine-phosphorylated isoform of hexokinase, a phosphotyrosine-containing hexokinase in human sperm was not detected. Most of the tyrosine-phosphorylated proteins were Triton X-100-insoluble and were localized to the principal piece of the flagellum, the region where the cytoskeletal fibrous sheath is found. Prominent phosphotyrosine-containing proteins of Mr 82,000 and 97,000 were identified as the human homologues of mouse sperm AKAP82, the major fibrous sheath protein, and pro-AKAP82, its precursor polypeptide, respectively. These proteins are A Kinase Anchor Proteins, polypeptides that sequester protein kinase A to subcellular locations. Taken together, these results suggest that protein tyrosine phosphorylation may be part of a signal transduction cascade(s) regulating events pertaining to capacitation and/or motility in mammalian sperm and that an interrelationship between tyrosine kinase and cAMP signaling pathways exists in these cells.

Alkaloids↗
PubMed2005

Identification of tyrosine-phosphorylated proteins of the mitochondrial oxidative phosphorylation machinery.

The role of some serine/threonine kinases in the regulation of mitochondrial physiology is now well established, but little is known about mitochondrial tyrosine kinases. We showed that tyrosine phosphorylation of rat brain mitochondrial proteins was increased by in vitro addition of ATP and H2O2, and also during in situ ATP production at state 3, and maximal reactive oxygen species production. The Src kinase inhibitor PP2 decreased tyrosine phosphorylation and respiratory rates at state 3. We found that the 39-kDa subunit of complex I was tyrosine phosphorylated, and we identified putative tyrosine-phosphorylated subunits for the other complexes. We also have strong evidence that the FoF1-ATP synthase alpha chain is probably tyrosine-phosphorylated, but demonstrated that the beta chain is not. The tyrosine phosphatase PTP 1B was found in brain but not in muscle, heart or liver mitochondria. Our results suggest that tyrosine kinases and phosphatases are involved in the regulation of oxidative phosphorylation.

Animals↗
PubMed2005

Non-enzymatic phosphorylation of bovine serum albumin by Cr(V) complexes: role in Cr(VI)-induced phosphorylation and toxicity.

Evidence for the non-enzymatic phosphorylation of bovine serum albumin (BSA) by sodium bis(2-ethyl-2-hydroxybutyrato)oxochromate(V), Na[CrVO(ehba)2], 1, sodium bis(2-hydroxy-2-methylbutyrato)oxochromate(V), Na[CrVO(hmba)2], 2 and potassium dichromate, K2Cr2O7, 3 in the presence of labeled adenosine-5'-triphosphate (ATP) under conditions of physiological pH is presented. Aggregation and extent of phosphorylation of BSA mediated by 1, 2 or 3 seems to increase with the concentration and time of incubation of the reaction mixture containing all the reactants. The [gamma-32P] label in ATP is incorporated into aggregates of BSA in the in vitro reaction of the protein with ATP in the presence of 1, 2 or 3. Phosphorylation of BSA by ATP in the absence of 1, 2 or 3 is negligible. Addition of EDTA reverses aggregation of protein and liberates partially the incorporated phosphate label. The stoichiometry of phosphorylation is found to be the highest and is equal to 12.25 mol PO4(3-)/mol BSA in the presence of 500 microM of 1, which decreases to 10.56 mol PO4(3-)/mol BSA after EDTA treatment. Resistance to the removal of phosphate label by EDTA increases with increase in time of incubation. Dialysis of phosphorylated BSA reverses the incorporated [gamma-(32)P] label only partially, indicating the formation of covalent links of phosphate groups to BSA. Evidence for the site of phosphorylation in the reaction mediated by 1, 2 or 3 being hydroxyl side groups of tyrosine and serine/threonine residues has been gained. Based on the results, a possibility that 1, 2 and 3 mimic the function of tyrosine and serine/threonine kinases has been invoked.

Adenosine Triphosphate↗
PubMed1991

Zn(2+)-dependent tyrosine phosphorylation of a 68-kDa protein and its differentiation from Mg(2+)-dependent tyrosine phosphorylation in sheep platelets.

A 68-kDa protein that was tyrosine phosphorylated in the presence of Zn2+ and two proteins of 52 and 46 kDa that were tyrosine phosphorylated in the presence of Mg2+ were separated by column chromatography of a sheep platelet high speed supernatant on poly(Glu, Tyr)4:1 copolymer-Sepharose or tyrosine-Sepharose. Phosphorylation of the 68-kDa protein occurred maximally in the presence of Zn2+ while Mg2+ was ineffective. The kinases responsible for the Zn(2+)- and Mg(2+)-dependent tyrosine phosphorylation could also tyrosine phosphorylate poly(Glu, Tyr)4:1, histone, and angiotensin II with the same metal ion specificity. The two tyrosine kinase activities could be also distinguished by their differential response to polyamines and quercetin. Zn2+ stimulation did not appear to be due to the inhibition of a protein tyrosine phosphatase. Sephadex G-100 gel filtration of the fraction showing Zn(2+)-dependent tyrosine phosphorylation of the 68-kDa protein showed that the tyrosine kinase activity corresponded to a molecular mass of 68,000 and it showed a protein band of 68 kDa as detected by silver staining on sodium dodecyl sulfate-polyacrylamide gel.

Animals↗
PubMed1991

Three regions of erythrocyte band 3 protein are phosphorylated on tyrosines: characterization of the phosphorylation sites by solid phase sequencing combined with capillary electrophoresis.

The major part of band 3 phosphorylation was recently shown to concern the first tryptic peptide of the protein (Yannoukakos et al. (1991) Biochim. Biophys. Acta 1061, 253-266). Tyrosine 8 is the prevalent site of phosphorylation, but other phosphorylated regions were found which could not be analyzed with certainty. Direct characterization of the phosphorylated residues in all these phosphorylated fragments was made possible due to recent advances in protein chemistry techniques, such as solid phase sequence analysis and capillary electrophoresis. The present report establishes that band 3 phosphorylation occurs predominantly on tyrosines: besides tyrosine 8 already known in the N-terminal region, two other tyrosines are demonstrated to be targets for the tyrosine kinase, tyrosine 359 and tyrosine 904. These residues lie in regions of band 3 exposed to the cytoplasm, the junction of the cytoplasmic and the membrane-spanning domains, and the C-terminal end of the protein which is also cytosolic, respectively.

Amino Acid Sequence↗
PubMed1996

Tyrosine hydroxylase phosphorylation in bovine adrenal chromaffin cells. Clonidine stimulates basal but inhibits nicotinic receptor evoked phosphorylation.

Clonidine inhibited the uptake of calcium and the overall phosphorylation of tyrosine hydroxylase induced by nicotinic receptor activation in bovine adrenal medullary chromaffin cells in culture. However, clonidine did not inhibit the increase in these parameters that accompanied K+ depolarisation of the cells. There was also no effect of clonidine on the overall phosphorylation of tyrosine hydroxylase when cells were stimulated by muscarine. Nicotinic receptor activation increased the phosphorylation of Ser-19, Ser-31, and Ser-40 on tyrosine hydroxylase, and this was inhibited by clonidine in a concentration-dependent manner. On the other hand, clonidine had no effect on calcium uptake, yet increased the phosphorylation of Ser-19 under basal conditions. Using calcium and calmodulin-stimulated protein kinase II obtained from rat brain clonidine increased the autophosphorylation of the alpha-subunit of the kinase by 37%, and also its activity against an exogenous peptide substrate by 29%. These data are consistent with the hypothesis that clonidine inhibits nicotinic receptor-induced tyrosine hydroxylase phosphorylation by decreasing calcium influx into chromaffin cells, perhaps by an action at the nicotinic receptor. Clonidine also increases the basal phosphorylation of tyrosine hydroxylase at Ser-19, perhaps by directly activating calcium and calmodulin-stimulated protein kinase II.

Adrenal Medulla↗
PubMed1989

Mechanism of elongation factor 2 (EF-2) inactivation upon phosphorylation. Phosphorylated EF-2 is unable to catalyze translocation.

Previously we have found that elongation factor 2 (EF-2) from mammalian cells can be phosphorylated by a special Ca2+/calmodulin-dependent protein kinase (EF-2 kinase). Phosphorylation results in complete inactivation of EF-2 in the poly(U)-directed cell-free translation system. However, the partial function of EF-2 affected by phosphorylation remained unknown. Here we show that phosphorylated EF-2, unlike non-phosphorylated EF-2, is unable to switch ribosomes carrying poly(U) and Phe-tRNA in the A site to a puromycin-reactive state. Thus, phosphorylation of EF-2 seems to block its ability to promote a shift of the aminoacyl(peptidyl)-tRNA from the A site to the P site, i.e. translocation itself.

Animals↗
PubMed1990

Protein phosphorylation in isolated human adipocytes-adrenergic control of the phosphorylation of hormone-sensitive lipase.

The effect of adrenergic agents on protein phosphorylation in human adipocytes was examined. Freshly isolated human fat cells were incubated with 32PO4 in order to label intracellular ATP, then treated with a variety of adrenergic and other pharmacologic agents. Treatment with the beta-adrenergic agonist isoproterenol led to a significant increase in phosphate content of at least five protein bands (Mr 52, 53, 63, 67, 84 kDa). The increase in phosphorylation was partially inhibited by the alpha-2 agonist clonidine. Epinephrine, a combined alpha and beta agonist, was less effective at increasing phosphate content of the proteins than was isoproterenol. Neither insulin nor the alpha-1 agonist phenylephrine had any discernible effect on the pattern of protein phosphorylation. The 84 kDa phosphorylated peptide band appears to contain hormone-sensitive lipase, a key enzyme in the lipolytic pathway which is activated by phosphorylation. These results are somewhat different than previously reported results for rat adipocytes, and represent the first report of overall pattern and adrenergic modulation of protein phosphorylation in human adipocytes.

Adipose Tissue↗
PubMed1986

Non-phosphorylated and phosphorylated neurofilaments in the cerebellum of the rat: an immunocytochemical study using monoclonal antibodies. Development in normal and thyroid-deficient animals.

The immunocytochemical staining patterns of two monoclonal antibodies specifically directed against non-phosphorylated and phosphorylated neurofilaments were studied during development of cerebellum in normal and thyroid-deficient rats. In normal animals, non-phosphorylated neurofilaments first appeared in Purkinje cell cytoplasm, then in dendritic tree and axon. They were also observed in basket cell axons running in the lower parts of the molecular layer and thereafter around the initial segment of Purkinje cell axons. Thyroid deficiency markedly retarded the appearance of these non-phosphorylated neurofilaments in Purkinje cells. More strikingly, the labelling in basket cell axons never appeared. In normal animals, phosphorylated neurofilaments were localized only in axons. They were first restricted to Purkinje cell axons and then appeared in basket cell axons. In thyroid-deficient rats, a transient weak labelling was observed in the cytoplasm of the Purkinje cells. Moreover, the characteristic arrangement of basket cell axons around the Purkinje cell body and proximal axon was never observed. Hypothyroidism thus retards the appearance of neurofilaments in Purkinje and basket cells and transiently disturbs their phosphorylation state. It also disorganized the basket cell morphogenesis and consequently the major inhibitory pathway of the cerebellar cortex. This last effect is only poorly corrected when the animals are allowed to return to an euthyroid state after one month of postnatal antithyroid treatment.

Animals↗
PubMedDate not supplied

Studies of the phosphorylation of Escherichia coli isocitrate dehydrogenase. Recognition of the enzyme by isocitrate dehydrogenase kinase/phosphatase and effects of phosphorylation on its structure and properties.

Escherichia coli isocitrate dehydrogenase is completely inactivated by phosphorylation of a single serine residue per subunit. We have examined the conformations of the active and phosphorylated forms of the enzyme using circular dichroism spectroscopy. The results support the view that phosphorylation prevents the binding of NADP, probably by direct blocking of the coenzyme-binding site. Labelling studies suggest that an arginine residue at the coenzyme-binding site may be close to the phosphorylatable serine residue. The phosphorylation of isocitrate dehydrogenase is thus unusual in that it occurs at the active site of the enzyme. We therefore investigated the recognition of isocitrate dehydrogenase by isocitrate dehydrogenase kinase/phosphatase. The kinase activity of this enzyme can phosphorylate intact isocitrate dehydrogenase but not proteolytic fragments derived from it, nor a synthetic peptide corresponding to the sequence round the phosphorylation site.

Arginine↗
PubMed2004

Anti-apoptotic action of (2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378) by suppression of the phosphatase and tensin homolog deleted from chromosome 10 phosphorylation and increased phosphorylation of casein kinase2/Akt/ cyclic AMP response element binding protein via maxi-K channel opening in neuronal cells.

This study shows the signaling pathway by which (2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methyl-2-dimethoxymethyl-2H-benzopyran-4-yl)-N'-benzylguanidine (KR-31378) prevents tumor necrosis factor (TNF)-alpha-induced neuronal cell death. KR-31378 restored TNF-alpha-induced decreased cell viability of SK-N-SH. U87-MG cells (PTEN-null glioblastoma cell line) transfected with expression vectors for sense PTEN (phosphatase and tensin homolog deleted from chromosome 10) showed significantly decreased cell viability, which was restored by KR-31378. TNF-alpha-induced increased PTEN phosphorylation and decreased phosphorylation of Akt/cyclic AMP response element-binding protein (CREB) in SK-N-SH cells were concentration-dependently reversed by KR-31378, those of which were antagonized by iberiotoxin, a maxi-K channel blocker. TNF-alpha and apigenin, a casein kinase2 (CK2) inhibitor, showed decreased CK2 phosphorylation and increased PTEN phosphorylation, which were reversed by KR-31378. KR-31378 increased K(+) currents by activating the maxi-K channels in SK-N-SH cells, with suppression of TNF-alpha-induced increase in cytosolic Ca(2+) and elevation of suppressed mitochondrial membrane potential, all of which were antagonized by iberiotoxin. It is suggested that increase in cell viability by KR-31378 is ascribed to the maxi-K channel opening-coupled upregulation of CK2/Akt/CREB phosphorylation and downregulation of PTEN phosphorylation in association with increased Bcl-2 and decreased Bax levels.

Apoptosis↗
PubMed2006

Expression and purification of phosphorylated and non-phosphorylated human MEK1.

Kinases exist in either a high or low activity form depending on the phosphorylation state of the activating lip. These two different forms of the same kinase may adopt different conformations that affect not only activity but also inhibitor binding and the ability to crystallize the protein. Therefore, isolation of homogenous preparations of the phosphorylated and non-phosphorylated versions of a kinase is critical for accurate biophysical measurements of activity, stability and ligand binding as well as for protein crystallization. The aim of the present study is the expression, purification and characterization of recombinant human MEK1 protein in both the activated and low-activity states. A baculovirus co-expression system was developed for obtaining high levels of activated, phosphorylated human MEK1 kinase. High-Five cells were co-infected with human MEK1 virus and Raf-BXB, an untagged constitutively active version of Raf which is the activating kinase for MEK1. Unphosphorylated MEK1 was generated by treating MEK1 isolated from High-Five baculovirus expression with lambda-phosphatase. The proteins were characterized by SDS-PAGE, LC-MS, Western blotting, enzymatic activity, and circular dichroism. Previous reports of MEK1 expression and purification yielded lower levels of protein and purity. The yield using High-Five cells was 5mg/L for phosphorylated MEK1 and 10mg/L for unphosphorylated MEK1. For phosphorylated MEK1, the specific activity was 3530U/mg, the IC(50) values for the non-specific kinase inhibitors K252a and K252b were 8 and 47nM, respectively, and the IC(50) for the MEK1 non-ATP competitive inhibitor, PD0325901, was 43nM.

Animals↗
PubMed2005

Species differences in the effects of prostanoids on MAP kinase phosphorylation, myosin light chain phosphorylation and contraction in bovine and cat iris sphincter smooth muscle.

There is evidence from our own laboratory and that of others that EP-receptor ligands are strong contractile agonists in bovine iris sphincter and that FP-receptor agonists are strong contractile agonists in cat iris sphincter. Here, we have investigated the effects of prostaglandin (PG) receptor agonists of the FP-, EP-, TP- and DP-class on myosin light chain (MLC) phosphorylation, p42/p44 MAP kinase phosphorylation and contraction in the iris sphincter of bovine and cat. Using three signal transduction mechanism assays, namely MLC phosphorylation, MAP kinase phosphorylation and contraction, we demonstrated that in bovine iris sphincter the rank order of potency of the PG agonists in the contractile and MLC phosphorylation assays is as follows: E2>U46619>F2alpha>D2, and in cat F2alpha>D2>E2>U46619. In the MAP kinase assay, in bovine iris sphincter the rank order of potency is E2>F2alpha and in cat F2alpha>E2. These conclusions are supported by the following findings: (1) In the contractile assay, in the bovine sphincter the EC50s for PGF2alpha, PGE2, U46619 and PGD2 were found to be 1.4x10(-7), 5.0x10(-9), 9.0x10(-9) and 1.3x10(-6)M, respectively, and the corresponding values in the cat were 1.9x10(-8), 2.3x10(-7), 1.5x10(-6) and 6.9x10(-8)M, respectively. (2) In the MLC phophorylation assay, in the bovine sphincter PGF2alpha, PGE2, U46619 and PGD2 increased MLC phophorylation by 118%, 165%, 153% and 72%, respectively, and the corresponding values in cat were 175%, 99%, 90% and 95%, respectively. (3) In the MAP kinase assay, in the bovine iris sphincter PGF2alpha and PGE2, increased MAP kinase phosphorylation by 276% and 328%, respectively, and the corresponding values in cat were 308% and 245%, respectively. The data presented demonstrate pronounced species differences in the effects of the prostanoids on the MLC kinase signaling pathway in bovine and cat irides and furthermore confirm the existence of FP-receptors in that of the bovine.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2000

Phosphorylation of telokin by cyclic nucleotide kinases and the identification of in vivo phosphorylation sites in smooth muscle.

The Ca(2+)-independent acceleration of dephosphorylation of the regulatory light chain of smooth muscle myosin and relaxation of smooth muscle by telokin are enhanced by cyclic nucleotide-activated protein kinase(s) [Wu et al. (1998) J. Biol. Chem. 273, 11362-113691. The purpose of this study was to determine the in vivo site(s) and in vitro rates of telokin phosphorylation and to evaluate the possible effects of sequential phosphorylation by different kinases. The in vivo site(s) of phosphorylation of telokin were determined in rabbit smooth muscles of longitudinal ileum and portal vein. Following stimulation of ileum with forskolin (20 microM) the serine at position 13 was the only amino acid to exhibit increased phosphorylation. Rabbit portal vein telokin was phosphorylated on both Ser-13 and -19 as a result of forskolin and GTPgammaS stimulation in vivo. Point mutation of Ser-13 (to Ala or Asp) abolished in vitro phosphorylation by cyclic nucleotide-dependent protein kinases.

Animals↗
PubMed1999

Serum-stimulated cell cycle entry of fibroblasts requires undisturbed phosphorylation and non-phosphorylation interactions of the catalytic subunits of protein kinase CK2.

Protein kinase CK2 is a pleiotropic Ser/Thr kinase occurring as alpha2beta2, alpha'2beta2, or alphaalpha'beta2 tetramers. A requirement in serum-stimulated cell cycle entry in both the cytoplasm and the nucleus of human fibroblasts for phosphorylation(s) by CK2 has been concluded from stimulation inhibition by microinjected antibodies against the regulatory subunit (beta). We have now examined this idea more directly by microinjection-mediated perturbation of phosphorylation and non-phosphorylation interactions of the catalytic subunits (alpha and alpha'), and by verifying the supposed matching of the cellular partition of CK2 subunits in the fibroblasts employed. While immunostaining and cell fractionation indicate that the partitions of subunits indeed match each other (with their predominant location in the nucleus in both quiescent and serum-stimulated cells), microinjection of substrate or pseudosubstrate peptides competing for the CK2-mediated phosphorylation in vitro resulted in significant inhibition of serum stimulation when placed into the nucleus but not when placed into the cytoplasm. Also inhibitory were nuclear but not cytoplasmic injections of antibodies against alpha and alpha' that affect neither their kinase activity in vitro nor their complexing to beta. The data indicate that the role played by CK2 in serum-stimulated cell cycle entry is predominantly nuclear and more complex than previously assumed, involving not only phosphorylation but also experimentally separable non-phosphorylation interactions by the catalytic subunits.

Casein Kinase II↗
PubMed2000

beta2-adaptin is constitutively de-phosphorylated by serine/threonine protein phosphatase PP2A and phosphorylated by a staurosporine-sensitive kinase.

Clathrin-mediated endocytosis includes cycles of assembly and disassembly of the clathrin-coated vesicle constituents. How these cycles are regulated is still not fully known but previous studies have indicated that phosphorylation of coat subunits may play a role. Here we describe that beta2-adaptin undergoes cycles of phosphorylation/de-phosphorylation in intact cells. Thus, beta2-adaptin was constitutively de-phosphorylated by serine/threonine protein phosphatase 2A and phosphorylated by a staurosporine-sensitive kinase in vivo. Confocal laser scanning microscopy demonstrated that phosphorylated AP2 complexes were found more evenly distributed at the plasma membrane compared to non-phosphorylated AP2 complexes which were found in aggregates. Finally, we found that phosphorylation of beta2-adaptin correlated with inhibition of clathrin-mediated endocytosis. Our results support the hypothesis that phosphorylation/de-phosphorylation of coat proteins plays a regulatory role in the assembly/disassembly cycle of clathrin-coated vesicles.

Adaptor Protein Complex beta Subunits↗