A sensitive method for detection of calmodulin-dependent protein kinase II activity in sodium dodecyl sulfate-polyacrylamide gel

A new approach for the detection of multiple protein kinases using monoclonal antibodies directed to the highly conserved region of protein kinases

To explore the protein kinase family enzymes expressed in cells, we attempted to generate antibodies that could detect a wide variety of protein kinases. For the production of such antibodies, synthetic peptides corresponding to amino acid sequences of a highly conserved subdomain (subdomain VIB) of the protein kinase family were used for immunization. Among the various peptide antigens, a peptide with 16 amino acids, CVVHRDLKPENLLLAS, effectively produced polyclonal antibodies with broad cross-reactivities to protein kinases. Two monoclonal antibodies, designated M8C and M1C, detected a variety of protein kinases such as calmodulin-dependent protein kinase II, calmodulin-dependent protein kinase IV, cAMP-dependent protein kinase, and mitogen-activated protein kinases, on Western blotting. The antibodies also immunoprecipitated various protein kinases in cell extracts. Furthermore, these antibodies could be used for detection of positive clones in the expression cloning of various protein kinases. Among 39 positive clones obtained from mouse brain cDNA library, 36 clones were identified as cDNA clones for various known and novel protein serine/threonine kinases, suggesting that the antibodies reacted highly specifically with various protein kinases. These results indicate that the present monoclonal antibodies directed to multiple protein kinases will be a powerful tool for the detection of a variety of known and novel protein kinases in cells.

Caspase-activated PAK-2 is regulated by subcellular targeting and proteasomal degradation

p21-activated protein kinases (PAKs) are a family of serine/threonine protein kinases that are activated by binding of the p21 G proteins Cdc42 or Rac. The ubiquitous PAK-2 (gamma-PAK) is unique among the PAK isoforms because it is also activated through proteolytic cleavage by caspases or caspase-like proteases. In response to stress stimulants such as tumor necrosis factor alpha or growth factor withdrawal, PAK-2 is activated as a full-length enzyme and as a proteolytic PAK-2p34 fragment. Activation of full-length PAK-2 stimulates cell survival, whereas proteolytic activation of PAK-2p34 is involved in programmed cell death. Here we provide evidence that the proapoptotic effect of PAK-2p34 is regulated by subcellular targeting and degradation by the proteasome. Full-length PAK-2 is localized in the cytoplasm, whereas the proteolytic PAK-2p34 fragment translocates to the nucleus. Subcellular localization of PAK-2 is regulated by nuclear localization and nuclear export signal motifs. A nuclear export signal motif within the regulatory domain prevents nuclear localization of full-length PAK-2. Proteolytic activation removes most of the regulatory domain and disrupts the nuclear export signal. The activated PAK-2p34 fragment contains a nuclear localization signal and translocates to the nucleus. However, levels of activated PAK-2p34 are tightly regulated through ubiquitination and degradation by the proteasome. Inhibition of degradation by blocking polyubiquitination results in significantly increased levels of PAK-2p34 and as a consequence, in stimulation of programmed cell death. Therefore, nuclear targeting and inhibition of degradation appear to be critical for stimulation of the cell death response by PAK-2p34.

A mitotic cascade of NIMA family kinases. Nercc1/Nek9 activates the Nek6 and Nek7 kinases

The Nek family of protein kinases in humans is composed of 11 members that share an amino-terminal catalytic domain related to NIMA, an Aspergillus kinase involved in the control of several aspects of mitosis, and divergent carboxyl-terminal tails of varying length. Nek6 (314AA) and Nek7 (303AA), 76% identical, have little noncatalytic sequence but bind to the carboxyl-terminal noncatalytic tail of Nercc1/Nek9, a NIMA family protein kinase that is activated in mitosis. Microinjection of anti-Nercc1 antibodies leads to spindle abnormalities and prometaphase arrest or chromosome missegregation. Herein we show that Nek6 is increased in abundance and activity during mitosis; activation requires the phosphorylation of Ser206 on the Nek6 activation loop. This phosphorylation and the activity of recombinant Nek6 is stimulated by coexpression with an activated mutant of Nercc1. Moreover, Nercc1 catalyzes the direct phosphorylation of prokaryotic recombinant Nek6 at Ser206 in vitro concomitant with 20-25-fold activation of Nek6 activity; Nercc1 activates Nek7 in vitro in a similar manner. Nercc1/Nek9 is likely to be responsible for the activation of Nek6 during mitosis and probably participates in the regulation of Nek7 as well. These findings support the conclusion that Nercc1/Nek9 and Nek6 represent a novel cascade of mitotic NIMA family protein kinases whose combined function is important for mitotic progression.

The protein kinase 60S is a free catalytic CK2alpha' subunit and forms an inactive complex with superoxide dismutase SOD1

The 60S ribosomes from Saccharomyces cerevisiae contain a set of acidic P-proteins playing an important role in the ribosome function. Reversible phosphorylation of those proteins is a mechanism regulating translational activity of ribosomes. The key role in regulation of this process is played by specific, second messenger-independent protein kinases. The PK60S kinase was one of the enzymes phosphorylating P-proteins. The enzyme has been purified from yeast and characterised. Pure enzyme has properties similar to those reported for casein kinase type 2. Peptide mass fingerprinting (PMF) has identified the PK60S as a catalytic alpha(') subunit of casein kinase type 2 (CK2alpha(')). Protein kinase activity is inhibited by SOD1 and by highly specific CK2 inhibitor-4,5,6,7-tetrabromo-benzotriazole (TBBt). The possible mechanism of regulation of CK2alpha(') activity in stress conditions, by superoxide dismutase in regulation of 80S-ribosome activity, is discussed.

Mammalian transcription factor LSF is a target of ERK signaling

LSF is a mammalian transcription factor that is rapidly and quantitatively phosphorylated upon growth induction of resting, peripheral human T cells, as assayed by a reduction in its electrophoretic mobility. The DNA-binding activity of LSF in primary T cells is greatly increased after this phosphorylation event (Volker et al. [1997]: Genes Dev 11:1435-1446). We demonstrate here that LSF is also rapidly and quantitatively phosphorylated upon growth induction in NIH 3T3 cells, although its DNA-binding activity is not significantly altered. Three lines of experimentation established that ERK is responsible for phosphorylating LSF upon growth induction in both cell types. First, phosphorylation of LSF by ERK is sufficient to cause the reduced electrophoretic mobility of LSF. Second, the amount of ERK activity correlates with the extent of LSF phosphorylation in both primary human T cells and NIH 3T3 cells. Finally, specific inhibitors of the Ras/Raf/MEK/ERK pathway inhibit LSF modification in vivo. This phosphorylation by ERK is not sufficient for activation of LSF DNA-binding activity, as evidenced both in vitro and in mouse fibroblasts. Nonetheless, activation of ERK is a prerequisite for the substantial increase in LSF DNA-binding activity upon activation of resting T cells, indicating that ERK phosphorylation is necessary but not sufficient for activation of LSF in this cell type.

Changes in phosphorylation of 50 and 53 kDa soluble proteins in graviresponding oat (Avena sativa) shoots

The present work indicates that phosphorylation of a 50 kDa soluble protein is involved in the gravitropic response in graviresponsive pulvini of oat (Avena sativa) stems. This 50 kDa protein shows a differential pattern of phosphorylation between lower and upper halves of pulvini both in vivo and in vitro. The differential phosphorylation of this protein is detected only when stem segments are gravistimulated for short and long time periods. The differential phosphorylation of the 50 kDa protein occurs as early as 5 min after the initiation of gravistimulation. This corresponds closely to the presentation time of 5.2 min. This differential phosphorylation pattern was changed by treatments with cycloheximide, implying that a newly-synthesized protein is involved in the differential phosphorylation during the gravitropic response. An autophosphorylation experiment shows that the 50 kDa protein has kinase activity. The phosphorylation patterns of a 53 kDa protein were similar to those of the 50 kDa protein, but were only expressed in vitro. These findings indicate that the differential phosphorylation of the 50 (and 53 kDa) soluble proteins in graviresponding oat shoots may be an important component of the gravity signal transduction pathway.

Evidence for cAMP-dependent protein kinase in the dinoflagellate, Amphidinium operculatum

A cAMP dependent protein kinase (PKA) was identified in the dinoflagellate Amphidinium operculum. In vitro kinase activity towards kemptide, a PKA-specific substrate, was not detectable in crude lysates. However, fractionation of dinoflagellate extracts by gel filtration chromatography showed PKA-like activity toward kemptide at approximately 66 kDa. These findings suggest that possible low molecular mass inhibitors in crude lysates were removed by the gel filtration chromatography. Pre-incubation of extracts with cAMP prior to chromatography resulted in an apparent molecular mass shift in the in vitro kinase assay to 40 kDa. An in-gel kinase assay reflected activity of the free catalytic subunit at approximately 40 kDa. Furthermore, western blotting with an antibody to the human PKA catalytic subunit confirmed a catalytic subunit with a mass of approximately 40 kDa. Results from this study indicate that the PKA in A. operculatum has a catalytic subunit of similar size to that in higher eukaryotes, but with a holoenzyme of a size suggesting a dimeric, rather than tetrameric structure.

Characterization of the phosphorylation status of the hepatitis B virus X-associated protein 2

The cytosolic Ah receptor (AhR) heterocomplex consists of one molecule of the AhR, a 90-kDa heat shock protein (Hsp90) dimer, and one molecule of the hepatitis B virus X-associated protein 2 (XAP2). Serine residues 43,53,131-2, and 329 on XAP2-FLAG were identified as putative phosphorylation sites using site-directed mutagenesis followed by two-dimensional phosphopeptide mapping analysis. Protein kinase CK2 (CK2) was identified as the 45-kDa kinase from COS 1 cell or liver extracts that was responsible for phosphorylation of serine 43 in the XAP2 peptide 39-57. Loss of phosphorylation at any or all of the serine residues did not significantly affect the ability of XAP2-FLAG to bind to the murine AhR in rabbit reticulocyte lysate or Hsp90 in COS-1 cells. Furthermore, all of these serine mutants were able to sequester murine AhR-YFP into the cytoplasm as well as wild-type XAP2. YFP-XAP2 S53A was unable to enter the nucleus, indicating a potential role of phosphorylation in nuclear translocation of XAP2.

In-gel kinase assay as a method to identify kinase substrates

Phosphorylation of proteins by kinases is central to many cellular processes, including signal transduction. Thus, assays to identify or characterize kinases are a key tool for research in this area. Kinase substrates can be incorporated into polyacrylamide gels and used to characterize kinase activity in mixed samples. This methodology can be adapted for the identification of novel kinase-substrates or kinase-kinases that participate in the regulation of cell signaling. Here, I review the rationale and principles of an in-gel kinase assay. This strategy relies on co-polymerization of a substrate within the gel matrix, followed by detection of enzymatic activity in situ. The following Protocol provides a detailed method for performing the in-gel kinase assay and discusses the uses of the assay to evaluate kinase activity in the context of proliferation, differentiation, and survival pathways.

Primary structure of equine myelin basic protein by mass spectrometry

Equine myelin basic protein (MBP) has been isolated from spinal cord and shown to consist of a number of components (charge isomers) by alkaline-urea gel electrophoresis. Mass analyses of several of these components showed that each was posttranslationally modified and some have been identified. Component 1, the most cationic charge isomer, was sequenced by a combination of liquid chromatography and mass spectrometry of peptides obtained by proteolytic digestion. At 172 residues it is slightly larger than the bovine (169) and the human (170). A major difference between bovine and equine sequences was the replacement of AQGH (bovine residues 76-79) by SRDG (equine). A number of other replacements involving single amino acids were also found. Methylated arginine (residue 108 equine) was found as both the mono- and the dimethylated derivative and represents the first MS/MS evidence for this modification in any MBP.

Caspase 3 activity is required for skeletal muscle differentiation

The cellular alterations associated with skeletal muscle differentiation share a high degree of similarity with key phenotypic changes usually ascribed to apoptosis. For example, actin fiber disassembly/reorganization is a conserved feature of both apoptosis and differentiating myoblasts and the conserved muscle contractile protein, myosin light chain kinase, is required for the apoptotic feature of membrane blebbing. As such, these observations suggest that the induction of differentiation and apoptosis in the myogenic lineage may use overlapping cellular mechanisms. Here, we report that skeletal muscle differentiation depends on the activity of the key apoptotic protease, caspase 3. Peptide inhibition of caspase 3 activity or homologous deletion of caspase 3 leads to dramatic reduction in both myotube/myofiber formation and expression of muscle-specific proteins. Subsequently, we have identified Mammalian Sterile Twenty-like kinase as a crucial caspase 3 effector in this cellular process. Mammalian Sterile Twenty-like kinase is cleavage-activated by caspase 3, and restoration of this truncated kinase in caspase 3 null myoblasts restores the differentiation phenotype. Taken together, these results confirm a unique and unanticipated role for a caspase 3-mediated signal cascade in the promotion of myogenesis.

A protein kinase activated by darkness phosphorylates nitrate reductase in Komatsuna (Brassica campestris) leaves

Although it has been shown that leaf nitrate reductase (NR: EC 1.6.6.1) is phosphorylated by subjecting plants to darkness, there is no evidence for the existence of dark-activated or dark-induced NR kinase. This study was undertaken to investigate the occurrence of a protein kinase phosphorylating NR in response to dark treatments. Immediately after transferring Komatsuna (Brassica campestris L.) plants to darkness, we observed rapid increases in the phosphorylating activity of the synthetic peptide, which is designed for the amino acid sequence surrounding the regulatory serine residue of the hinge 1 region of Komatsuna NR, in crude extracts from leaves. The activity reached a maximum after 10 min of darkness. Inactivation states of NR estimated from relative activities with or without Mg2+ were correlated to activities of the putative dark-activated protein kinase. Using the synthetic peptide as a substrate, we purified a protein kinase from dark-treated leaves by means of successive chromatographies on Q-Sepharose, Blue Sepharose, FPLC Q-Sepharose, and ATP-gamma-Sepharose columns. The purified kinase had an apparent molecular mass of 150 kDa with a catalytic subunit of 55 kDa, and it was Ca2+-independent. The purified kinase phosphorylated a recombinant cytochrome c reductase protein, a partial protein of NR, and holo NR, and inactivated NR in the presence of both 14-3-3 protein and Mg2+. The kinase also phosphorylated synthetic peptide substrates designed for sucrose phosphate synthase and 3-hydroxy-3-methylglutaryl-Coenzyme A reductase. Among inhibitors tested, only K252a, a potent and specific serine/threonine kinase inhibitor, completely inhibited the activity of the dark-activated kinase. The activity of the purified kinase was also specifically inhibited by K252a. Taken together with these findings, results obtained suggest that the putative dark-activated protein kinase may be the purified kinase itself, and may be responsible for in vivo phosphorylation of NR and its inactivation during darkness.

Integrin-linked kinase phosphorylates the myosin phosphatase target subunit at the inhibitory site in platelet cytoskeleton

The myosin phosphatase (MP) composed of the catalytic subunit of type 1 protein phosphatase and myosin phosphatase target subunit isoform 1 (MYPT1) was identified as the major serine/threonine phosphatase component in the platelet-cytoskeleton fraction. MYPT1 was phosphorylated by cytoskeletal kinase(s), but the identity of the kinase(s) and the effect of phosphorylation were not established. Incubation of platelet-cytoskeletal fraction with MgATP or MgATP[S] (magnesium adenosine 5'-[gamma-thio]triphosphate) caused a decrease in the 20 kDa light-chain of smooth-muscle myosin (MLC20) phosphatase and phosphorylase phosphatase activities. MYPT1 contains a phosphorylation site, Thr-695, involved in the inhibition of MP in a RhoA/Rho kinase-dependent manner. The cytoskeletal kinase(s) phosphorylated Thr-695 of glutathione S-transferase (GST)-MYPT1, as determined with an antibody specific for phosphorylated Thr-695. The level of Rho kinase was low in the cytoskeletal fraction and was detected primarily in the membrane and cytosolic fractions. The phosphorylation of Thr-695 by the cytoskeletal kinase(s) was not affected by Rho kinase inhibitor, Y-27632, suggesting that kinase(s) other than Rho kinase were involved. In-gel kinase assay identified a kinase at 54-59 kDa that phosphorylated the C-terminal fragment of MYPT1 (GST-MYPT1(667-1004)). Western blots detected both zipper-interacting protein kinase (ZIPK) and integrin-linked kinase (ILK) at 54-59 kDa in the cytoskeleton and membrane fractions. Cytoskeletal ZIPK and ILK were separated and partially purified by chromatography on SP-Sepharose and on MonoQ. ZIPK preferentially phosphorylated MLC20 and had low activity on MYPT1. ILK phosphorylated both MLC20 and MYPT1 and phosphorylation of MYPT1 occured on Thr-695. The above results raise the potential for regulation of MP activity in platelet cytoskeleton by ILK and suggest an alternative to the Rho-linked pathway.

Identification of protein kinase CK2 as a potent kinase of Epstein-Barr virus latent membrane protein 1

The C-terminus of latent membrane protein 1 (LMP1) can be phosphorylated in vivo. However, the protein kinase responsible for LMP1 phosphorylation has not yet been identified. In this study, GST fusion proteins containing the C-terminus of LMP1 were generated and used as substrates to survey the kinases that phosphorylate LMP1. Among several purified protein kinases tested, only protein kinase CK2 (CK2) could specifically phosphorylate LMP1. Using the in-gel kinase assay in the absence and presence of a selective CK2 inhibitor, 4,5,6,7-tetrabromobenzotriazole, CK2 was determined to be the major kinase to phosphorylate LMP1 in lymphoma and epithelial cell lines. This is the first study to show that CK2 is a potent kinase to phosphorylate LMP1 in vitro.

CK2 and GAK/auxilin2 are major protein kinases in clathrin-coated vesicles

Several peripheral membrane proteins associated with clathrin-coated vesicles (CCVs) are reversibly phosphorylated, but it is not clear precisely which protein kinases are involved. In order to address this question directly, we have isolated highly purified CCVs from porcine brain. The peripheral membrane proteins have been removed and assayed for kinase activity using the CCV peripheral membrane proteins as substrate. The major kinase activity identified has a molecular mass of 40 kDa, is inhibited by known specific inhibitors of the protein kinase CK2 and is recognised by an antibody specific to CK2. We show that CK2 is responsible for the phosphorylation of the majority of CCV-associated proteins that are subject to phosphorylation. Intriguingly, CK2 is inactive when associated with CCVs but becomes active once the clathrin coat has been removed. The medium subunit of the AP2 adaptor complex (mu2) is not a substrate for CK2, but is phosphorylated by a second kinase that we show to be cyclin G-associated kinase (GAK/auxilin2). Unlike the situation for the CK2 substrates, mu2 is a substrate for GAK/auxilin2, both in intact CCVs and in solution. In addition, we show that the 'stripped' CCV membranes that remain once the peripheral membrane proteins have been removed from CCVs inhibit CK2 but not GAK/auxilin2 activity.

Analysis of the complexity of protein kinases within the phloem sieve tube system. Characterization of Cucurbita maxima calmodulin-like domain protein kinase 1

In angiosperms, functional, mature sieve elements lack nuclei, vacuoles, ribosomes, and most of the endomembrane network. In this study, the complexity, number, and nature of protein kinases within the phloem sap of Cucurbita maxima were investigated to test the hypothesis that the enucleate sieve tube system utilizes a simplified signal transduction network. Supporting evidence was obtained in that only five putative protein kinases (three calcium-independent and two calcium-dependent protein kinases) were detected within the phloem sap extracted from stem tissues. Biochemical methods were used to purify one such calcium-dependent protein kinase. The gene for this C. maxima calmodulin-like domain protein kinase 1 (CmCPK1), was cloned using peptide microsequences. A combination of mass spectrometry, peptide fingerprinting, and amino-terminal sequencing established that, in the phloem sap, CmCPK1 exists as an amino-terminally cleaved protein. A second highly homologous isoform, CmCPK2, was identified, but although transcripts could be detected in the companion cells, peptide fingerprint analysis suggested that CmCPK2 does not enter the phloem sap. Potential substrates for CmCPK1, within the phloem sap, were also detected using an on-membrane phosphorylation assay. Entry of CmCPK1 into sieve elements via plasmodesmata and the potential roles played by these phloem protein kinases are discussed.

Dysregulation of phosphatidylinositol 3-kinase and downstream effectors in human breast cancer

Phosphatidylinositol 3-kinase (PI3-K) is a growth factor-activated transforming lipid (and protein) kinase, involved in cell motility and invasion, that has multiple effectors. Relatively little is known about its expression and enzymatic activity in human breast cancer. Since growth factor receptors are amplified in breast cancer, and the tumor suppressor PTEN may be mutated in human breast cancer, it was hypothesized that PI3-K and its downstream effectors would be activated in this disease. In 11 resected tumors analyzed for expression of this kinase, a mean 3-fold increase in protein expression was observed over the corresponding adjacent control tissue. Using an in vitro lipid kinase assay of the immunoprecipitated PI3-K protein, a greater than 2-fold increase in activation was observed. These changes were observed in the absence of an activation of either protein kinase B (PKB, akt1) or p70 S6 kinase (p70 S6K). However, p21-activated kinase (Pak), p38 mitogen-activated protein kinase (p38 MAPK) and mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK 2) were all overexpressed and demonstrated increased enzyme activity. It may be concluded that aberrant mitogenic signaling in human breast cancer in vivo involves Pak, p38 MAPK and MAPKAPK2 downstream of PI3-K, but neither of PKB or p70 S6K. It is proposed that this pathway may serve as a useful targeting nexus for investigation of small molecule inhibitors in human breast cancer.

Identification of a light-regulated protein kinase activity from seedlings of Arabidopsis thaliana

Protein kinase transduction pathways are thought to be involved in light signaling in plants, but other than the photoreceptors, no protein kinase activity has been shown to be light-regulated in vivo. Using an in-gel protein kinase assay technique with histone H III SS as an exogenous substrate, we identified a light-regulated protein kinase activity with an apparent molecular weight ca 50 kDa. The kinase activity increased transiently after irradiation of dark-grown seedlings with continuous far red light (FR) and blue light (B) and decreased after irradiation with red light (R). The maximal activation was achieved after 30 min to 1 h with FR or B. After irradiation times longer than 2 h, the kinase activity decreased to below the sensitivity level of the assay. In Arabidopsis mutants lacking either the photoreceptors phytochrome A, phytochrome B or the blue-light receptor cryptochrome 1, kinase activity was undetectable, whereas in the photomorphogenic mutants cop1 and det1 the kinase activity was also observed in the absence of light signals, though still stimulated by B and FR. Interestingly, the R inhibition of the kinase activity was lost in the mutant hy5. Pretreatment with cycloheximide blocked the kinase activity.

The major form of protein tyrosine kinase in the dog prostate is expressed by a 50 kDa polypeptide

We have already reported that the protein tyrosine kinase (PTK) activity in the dog prostate is distributed in cytosolic (75%) and particulate (Triton X-100-solubilized) fractions and that upon gel filtration, both PTKs migrate as entities of Mr 44,000 [(1991) Biochem. Cell. Biol. 69, 146-153]. Herein we demonstrate by immunoprecipitation with anti-phosphotyrosine antibodies that the soluble PTK has the ability to undergo self-phosphorylation. In addition, the polypeptide responsible for that enzymatic activity has been identified by 2 approaches: (1) a two-dimensional electrophoresis, in which the first dimension performed in non-denaturing conditions allowed the localization of the native enzyme, while the second dimension (SDS-PAGE) permitted the analysis of alkali-resistant phosphoproteins corresponding to the activity; (2) protein renaturation after SDS-PAGE followed by in situ phosphorylation (with [gamma-32P]ATP) of polyGT electrophoresed together with the enzyme preparation; the exclusive presence of the radiolabeled phosphotyrosine in the renatured protein confirmed its enzymatic nature. Using these methods, the major form of PTK in the dog prostate was shown to be expressed by a 50 kDa polypeptide which possesses autophosphorylation sites and which is present in the cytosol as an active monomer.

Phosphorylation of cysteine string protein by protein kinase A. Implications for the modulation of exocytosis

Cyclic AMP-dependent protein kinase (PKA) enhances regulated exocytosis in neurons and most other secretory cells. To explore the molecular basis of this effect, known exocytotic proteins were screened for PKA substrates. Both cysteine string protein (CSP) and soluble NSF attachment protein-alpha (alpha-SNAP) were phosphorylated by PKA in vitro, but immunoprecipitation of cellular alpha-SNAP failed to detect (32)P incorporation. In contrast, endogenous CSP was phosphorylated in synaptosomes, PC12 cells, and chromaffin cells. In-gel kinase assays confirmed PKA to be a cellular CSP kinase, with phosphorylation occurring on Ser(10). PKA phosphorylation of CSP reduced its binding to syntaxin by 10-fold but had little effect on its interaction with HSC70 or G-protein subunits. Furthermore, an in vivo role for Ser(10) phosphorylation at a late stage of exocytosis is suggested by analysis of chromaffin cells transfected with wild type or non-phosphorylatable mutant CSP. We propose that PKA phosphorylation of CSP could modulate the exocytotic machinery, by selectively altering its availability for protein-protein interactions.

IgE receptor type I-dependent regulation of a Rab3D-associated kinase: a possible link in the calcium-dependent assembly of SNARE complexes

Following activation through high affinity IgE receptors (FcepsilonRI), mast cells release, within a few minutes, their granule content of inflammatory and allergic mediators. FcepsilonRI-induced degranulation is a SNARE (soluble N-ethylmaleimide attachment protein receptors)-dependent fusion process. It is regulated by Rab3D, a subfamily member of Rab GTPases. Evidence exists showing that Rab3 action is calcium-regulated although the molecular mechanisms remain unclear. To obtain an understanding of Rab3D function we have searched for Rab3D-associated effectors that respond to allergic triggering through FcepsilonRI. Using the RBL-2H3 mast cell line we detected a Ser/Thr kinase activity, termed here Rak3D (from Rab3D-associated kinase), because it was specifically co-immunoprecipitated with anti-Rab3D antibody. Rak3D activity, as measured by its auto- or transphosphorylation, was maximal in resting cells and decreased upon stimulation. The down-regulation of the observed activity was blocked with EGTA, but not with other degranulation inhibitors, suggesting that its activity functions downstream of calcium influx. We found that Rak3D phosphorylates the NH(2)-terminal regulatory domain of the t-SNARE syntaxin 4, but not syntaxin 2 or 3. The phosphorylation of syntaxin 4 decreased its binding to its partner SNAP23. Thus, we propose a novel phosphorylation-dependent mechanism by which Rab3D controls SNARE assembly in a calcium-dependent manner.

T-kininogen inhibits fibroblast proliferation in the G(1) phase of the cell cycle

By using synthetic protease inhibitors, several investigators have demonstrated that cysteine proteinases are required for cell proliferation. Kininogens are potent and specific physiological inhibitors of cysteine proteinases. We have used several mouse fibroblast-derived cell lines that express biologically active T-kininogen under the control of the mouse metallothionein promoter to test its effect on cell proliferation. Our results indicate that expression of T-kininogen results in diminished proliferative capacity, as measured by reduced cell numbers, both in logarithmically growing cultures and in G(0) cells induced to proliferate in response to serum. Furthermore, both fluorescence-activated cell sorting (FACS) analysis and incorporation of radioactive precursors into DNA suggest that the cells are unable to progress from G(0) through the S phase of the cell cycle in response to serum stimulation. However, we find that T-kininogen-expressing cell lines are still capable of responding to growth factors present in the serum, both by activating the ERK pathway and by expressing early genes, such as c-Fos and c-Jun. Thus, our results suggest that inhibition of cysteine proteinases by T-kininogen leads to inhibition of cell proliferation between the G(1) and S phases of the cell cycle.

Lack of Elk-1 phosphorylation and dysregulation of the extracellular regulated kinase signaling pathway in senescent human fibroblast

Replicative senescence is characterized by numerous phenotypic alterations including the loss of proliferative capacity in response to mitogens and numerous changes in gene expression including impaired serum inducibility of the immediate-early genes c-fos and erg-1. Transcription of c-fos in response to mitogens depends on the activation of a multiprotein complex formed on the c-fos serum response element (SRE), which includes the transcription factors SRF (serum response factor) and TCF (ternary complex factor). Our data indicate that at least two defects are responsible for the decreased c-fos transcription in senescent cells, one caused by diminished DNA binding activity of the SRF and another resulting from impaired activation of the TCF, Elk-1. In nuclei isolated from serum stimulated senescent cells the activating phosphorylation of p62(TCF)/Elk-1, which is catalyzed by the members of the extracellular-regulated kinase (ERK) family was strikingly diminished and correlated with a decrease in the abundance of activated ERK proteins. In contrast, in total cell lysates ERK phosphorylation and ERK activity (normalized to total protein) reached similar levels following stimulation of early- and late-passage cells. Interestingly, senescent cells consistently exhibited higher ERK protein abundance. Thus, the proportion of phosphorylated (active) ERK molecules in stimulated senescent cells was lower than in early passage cells. The accumulation of unphosphorylated ERK molecules in senescent cells correlated with the diminished abundance of phosphorylated (active) MEK. These data indicate that in senescent cells there is a general dysregulation in the ERK signaling pathway, which results in the accumulation of inactive ERK molecules, decreased abundance of active ERK in the nucleus of senescent cells, and subsequent lack of activation of the transcription factor TCF(Elk-1). These impairments, together with the impaired DNA binding activity of SRF, could potentially account for the lack of c-fos expression in senescent cells and for multiple other molecular changes dependent upon this pathway.

Enteropathogenic E. coli Tir binds Nck to initiate actin pedestal formation in host cells

Enteropathogenic Escherichia coli (EPEC) is a bacterial pathogen that causes infantile diarrhea worldwide. EPEC injects a bacterial protein, translocated intimin receptor (Tir), into the host-cell plasma membrane where it acts as a receptor for the bacterial outer membrane protein, intimin. The interaction of Tir and intimin triggers a marked rearrangement of the host actin cytoskeleton into pedestals beneath adherent bacteria. On delivery into host cells, EPEC Tir is phosphorylated on tyrosine 474 of the intracellular carboxy-terminal domain, an event that is required for pedestal formation. Despite its essential role, the function of Tir tyrosine phosphorylation has not yet been elucidated. Here we show that tyrosine 474 of Tir directly binds the host-cell adaptor protein Nck, and that Nck is required for the recruitment of both neural Wiskott-Aldrich-syndrome protein (N-WASP) and the actin-related protein (Arp)2/3 complex to the EPEC pedestal, directly linking Tir to the cytoskeleton. Cells with null alleles of both mammalian Nck genes are resistant to the effects of EPEC on the actin cytoskeleton. These results implicate Nck adaptors as host-cell determinants of EPEC virulence.

Agonists of the P2Y(AC)-receptor activate MAP kinase by a ras-independent pathway in rat C6 glioma

We have previously shown that an ecto-NPPase modulates the ATP- and ADP-mediated P2Y(AC)-receptor activation in rat C6 glioma. In the present study, 2MeSADP and Ap(3)A induced no detectable PI turnover and were identified as specific agonists of the P2Y(AC)-receptor with EC(50) values of 250 +/- 37 pM and 1 +/- 0.5 microM, respectively. P2Y(AC)-receptor stimulation increased MAP kinase (ERK1/2) activation that returned to the basal level 4 h after stimulation and was correlated with a gradual desensitization of the P2Y(AC)-purinoceptor. The purinoceptor antagonists DIDS and RB2 blocked MAP kinase activation. An IP(3)-independent Ca(2+)-influx was observed after P2Y(AC)-receptor activation. Inhibition of this influx by Ca(2+)-chelation, did not affect MAP kinase activation. Pertussis toxin, toxin B, selective PKC-inhibitors and a specific MEK-inhibitor inhibited the 2MeSADP- and Ap(3)A-induced MAP kinase activation. In addition, transfection with dominant negative RhoA(Asn19) rendered C6 cells insensitive to P2Y(AC)-receptor-mediated MAP kinase activation whereas dominant negative ras was without effect. Immunoprecipitation experiments indicated a significant increase in the phosphorylation of raf-1 after P2Y(AC)-receptor activation. We may conclude that P2Y(AC)-purinoceptor agonists activate MAP kinase through a G(i)-RhoA-PKC-raf-MEK-dependent, but ras- and Ca(2+)-independent cascade.

P2Y(AC)(-)-receptor agonists enhance the proliferation of rat C6 glioma cells through activation of the p42/44 mitogen-activated protein kinase

1. Extracellularly added P(1),P(3)-di(adenosine-5') triphosphate (Ap(3)A), P(1),P(4)-di(adenosine-5') tetraphosphate (Ap(4)A), ATP, ADP, AMP and adenosine are growth inhibitory for rat C6 glioma cells. Analysis of nucleotide hydrolysis and the use of nucleotidase inhibitors demonstrated that the latter inhibition is due to hydrolysis of the nucleotides to adenosine. 2. Agonists of the P2Y(AC)(-)-receptor enhance the growth of C6 cells if their hydrolysis to adenosine is inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS). In these conditions, the potency to stimulate cell growth parallels the ranking of the receptor agonists, i.e. 2-methylthioadenosine-5'-diphosphate (2MeSADP)>Ap(3)A>Ap(4)A. ATP and ADP are still hydrolysed in the presence of PPADS and have no proliferative effect on C6 cells. 3. The enhanced growth is due to a P2Y(AC)(-)-receptor-mediated activation of p42/44 mitogen-activated protein kinase (MAPK) as shown by immunoblotting and protein kinase assays for active MAPK and the use of the MAPK/extracellular signal-regulated kinase kinase (MEK) inhibitor PD98059. 4. The UTP-induced enhancement of the growth of C6 cells is due to activation of MAPK by a PPADS sensitive nucleotide receptor. 5. In conclusion, the effect of nucleotides on the growth of C6 cells is determined by ecto-nucleotidases and by activation of nucleotide receptors. Hydrolysis of nucleotides to adenosine induces growth inhibition while inhibition of the hydrolysis of agonists of the P2Y(AC)(-)-receptor enhances cell growth by activation of MAPK.

Ten ERK-related proteins in three distinct classes associate with AP-1 proteins and/or AP-1 DNA

We have identified seven ERK-related proteins ("ERPs"), including ERK2, that are stably associated in vivo with AP-1 dimers composed of diverse Jun and Fos family proteins. These complexes have kinase activity. We designate them as "class I ERPs." We originally hypothesized that these ERPs associate with DNA along with AP-1 proteins. We devised a DNA affinity chromatography-based analytical assay for DNA binding, the "nucleotide affinity preincubation specificity test recognition" (NAPSTER) assay. In this assay, class I ERPs do not associate with AP-1 DNA. However, several new "class II" ERPs do associate with DNA. p41 and p44 are ERK1/2-related ERPs that lack kinase activity and associate along with AP-1 proteins with AP-1 DNA. Class I ERPs and their associated kinase activity thus appear to bind AP-1 dimers when they are not bound to DNA and then disengage and are replaced by class II ERPs to form higher order complexes when AP-1 dimers bind DNA. p97 is a class III ERP, related to ERK3, that associates with AP-1 DNA without AP-1 proteins. With the exception of ERK2, none of the 10 ERPs appear to be known mitogen-activated protein kinase superfamily members.

p70S6 kinase signals cell survival as well as growth, inactivating the pro-apoptotic molecule BAD

Cytokines often deliver simultaneous, yet distinct, cell growth and cell survival signals. The 70-kDa ribosomal protein S6 kinase (p70S6K) is known to regulate cell growth by inducing protein synthesis components. We purified membrane-based p70S6K as a kinase responsible for site-specific phosphorylation of BAD, which inactivates this proapoptotic molecule. Rapamycin inhibited mitochondrial-based p70S6K, which prevented phosphorylation of Ser-136 on BAD and blocked cell survival induced by insulin-like growth factor 1 (IGF-1). Moreover, IGF-1-induced phosphorylation of BAD Ser-136 was abolished in p70S6K-deficient cells. Thus, p70S6K is itself a dual pathway kinase, signaling cell survival as well as growth through differential substrates which include mitochondrial BAD and the ribosomal subunit S6, respectively.

Multiple phosphorylation of membrane-associated calcium-dependent protein serine/threonine kinase in Streptomyces fradiae

In Streptomyces fradiae, calcium ions induce alterations in intensity and specificity of the secondary metabolism and stimulate aerial mycelium formation and sporulation. Using in vitro labeling, we demonstrate that in S. fradiae in the late exponential growth phosphorylation of 65-kDa membrane-associated protein is also influenced by Ca(2+) added exogenously. Calcium ions at physiological concentration stimulate intensive Ca(2+)-dependent phosphorylation of 65-kDa protein at multiple sites on serine, threonine, and tyrosine residues. Assay of protein kinases in situ demonstrated in the fraction of membrane-associated proteins the presence of two autophosphorylating protein serine/threonine kinases with molecular masses of 127 kDa and 65 kDa. Autophosphorylation of both proteins is also Ca(2+)-dependent.

Histamine-induced vasoconstriction involves phosphorylation of a specific inhibitor protein for myosin phosphatase by protein kinase C alpha and delta isoforms

Histamine stimulus triggers inhibition of myosin phosphatase-enhanced phosphorylation of myosin and contraction of vascular smooth muscle. In response to histamine stimulation of intact femoral artery, a smooth muscle-specific protein called CPI-17 (for protein kinase C-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa) is phosphorylated and converted to a potent inhibitor for myosin phosphatase. Phosphorylation of CPI-17 is diminished by pretreatment with either or GF109203x, suggesting involvement of multiple kinases (Kitazawa, T., Eto, M., Woodsome, T. P., and Brautigan, D. L. (2000) J. Biol. Chem. 275, 9897--9900). Here we purified and identified CPI-17 kinases endogenous to pig artery that phosphorylate CPI-17. DEAE-Toyopearl column chromatography of aorta extracts separated two CPI-17 kinases. One kinase was protein kinase C (PKC) alpha, and the second kinase was purified to homogeneity as a 45-kDa protein, and identified by sequencing as PKC delta. Purified PKC delta was 3-fold more reactive with CPI-17 compared with myelin basic protein, whereas purified PKC alpha and recombinant RhoA-activated kinases (Rho-associated coiled-coil forming protein Ser/Thr kinase and protein kinase N) showed equal activity with CPI-17 and myelin basic protein. inhibited CPI-17 phosphorylation by purified PKC delta with IC(50) of 0.6 microm (in the presence of 0.1 mm ATP) or 14 microm (2.0 mm ATP). significantly suppressed CPI-17 phosphorylation in smooth muscle cells, and the contraction of permeabilized rabbit femoral artery induced by stimulation with phorbol ester. GF109203x inhibited phorbol ester-induced contraction of rabbit femoral artery by 80%, whereas a PKC alpha/beta inhibitor, Go6976, reduced contraction by 47%. The results imply that histamine stimulation elicits contraction of vascular smooth muscle through activation of PKC alpha and especially PKC delta to phosphorylate CPI-17.

A systematic approach to the complete study of a signaling molecule: ribosomal p90rsk as an example

Ribosomal p90rsk is a kinase of central importance in transducing mitogenic signals from an activated receptor to the cell nucleus and for protein synthesis. Here, we analyze the optimal steps to fully describe this kinase in both normal neutrophils and leukemic cell lines. These are: (i) immunological analyses (immunoblotting and immunoprecipitation); (ii) enzyme activity assays (in vitro and "in-gel"); and (iii) immunobiochemical combination methods (immunoprecipitation/kinase assay, immunoprecipitation/"in-gel" assay and ion exchange chromatography/immunoblotting). For the enzyme assays, we describe a novel method to measure ribosomal p90rsk kinase activity "in-gel", based on a renatured-protein method that allows for the direct quantitation of enzyme activity. Finally, we present an algorithm that can be readily implemented to the quantification of the extent of stimulation of a kinase in response to a particular extracellular stimuli. In our case, it was found that activation of p90rsk was higher in proliferating leukemic cells than in mature neutrophils, indicating that a suppression of key signal transduction links could contribute to the maturational arrest typical of acute leukemia. All the techniques and strategies described here for p90rsk could be easily extrapolated to the study of any signal transduction molecule, provided it has a phosphotransferase activity.

p21-activated protein kinase gamma-PAK suppresses programmed cell death of BALB3T3 fibroblasts

In response to stress stimulants, cells activate opposing signaling pathways for cell survival and programmed cell death. p21-activated protein kinase gamma-PAK is involved in both cell survival and cell death pathways. Many stress stimulants activate gamma-PAK as a full-length enzyme and as a proteolytic fragment. Caspase-mediated proteolytic activation parallels cell death and appears to be a pro-apoptotic factor in stress-induced cell death. Here, we show that activation of full-length gamma-PAK promotes cell survival and suppresses stress-induced cell death. Expression of constitutively active gamma-PAK-T402E, which mimics activated full-length gamma-PAK, stimulates cell survival of BALB3T3 fibroblasts in response to tumor necrosis factor alpha, growth factor withdrawal, and UVC light. This stimulation of cell survival is mainly due to protection of cells from cell death rather than by stimulation of proliferation. Expression of gamma-PAK-T402E increases phosphorylation of the pro-apoptotic Bcl-2 family protein Bad and protects from cell death induced by ectopic expression of Bad. In response to tumor necrosis factor alpha, expression of gamma-PAK-T402E increases the early but reduces the late activation of ERK, JNK, and p38. Our results indicate that the ubiquitous gamma-PAK may have a crucial function in cell survival by regulating the pro-apoptotic activity of Bad and the stress-induced activation of ERK, JNK, and p38 pathways.

Assays of protein kinases using exogenous substrates

In studies of the regulation of specific biochemical events by reversible phosphorylation, assaying the protein kinases themselves can often lead to significant progress in understanding the mechanistic details of a system under study. This unit describes assays for a variety of protein kinases that require different conditions to detect and measure their activities: cyclic nucleotide-dependent kinases, protein kinase C and isoforms, casein kinases, Ca(2+)/calmodulin-dependent kinases, and tyrosine kinase. A protocol for in-gel assays for specific kinase activity is also provided. The unit is not meant to be a catalog of individual protein kinase assays; however, the general principles of these assays should apply to most if not all known protein kinases.

Involvement of mitogen-activated protein kinase activation in the signal-transduction pathways of the soya bean oxidative burst

The oxidative burst constitutes one of the most rapid defence responses characterized in the Plant Kingdom. We have observed that four distinct elicitors of the soya bean oxidative burst activate kinases of masses approximately 44 kDa and approximately 47 kDa. Evidence that these kinases regulate production of reactive oxygen species include: (i) their rapid activation by oxidative burst elicitors, (ii) their tight temporal correlation between activation/deactivation of the kinases and activation/deactivation of the oxidative burst, (iii) the identical pharmacological profile of kinase activation and oxidant production for 13 commonly used inhibitors, and (iv) the autologous activation of both kinases and oxidant production by calyculin A and cantharidin, two phosphatase inhibitors. Immunological and biochemical studies reveal that the activated 44 kDa and 47 kDa kinases are mitogen-activated protein (MAP) kinase family members. The kinases prefer myelin basic protein as a substrate, and they phosphorylate primarily on threonine residues. The kinases are themselves phosphorylated on tyrosine residues, and this phosphorylation is required for activity. Finally, both kinases are recognized by an antibody against activated MAP kinase immediately after (but not before) cell stimulation by elicitors. Based on these and other observations, a preliminary sequence of signalling steps linking elicitor stimulation, kinase activation and Ca(2+) entry, to initiation of oxidant production, is proposed.

Effects of prostaglandin F(2alpha)and carbachol on MAP kinases, cytosolic phospholipase A(2)and arachidonic acid release in cat iris sphincter smooth muscle cells

The signal transduction pathways initiated by Ca(2+)-mobilizing agonists, such as prostaglandin F(2alpha)(PGF(2alpha)) and carbachol (CCh), leading to activation of cytosolic phospholipase A(2)(cPLA(2)) and arachidonic acid (AA) release in a wide variety of tissues remain obscure. To further define the role of protein kinases in receptor mediated stimulation of cPLA(2)and consequently AA release we have investigated the role of mitogen-activated protein (MAP) kinases and protein kinase C (PKC) in PGF(2alpha)- and CCh-induced cPLA(2)phosphorylation and AA release in cat iris sphincter smooth muscle (CISM) cells. The cells were prelabeled with [(3)H]AA for 24 hr and incubated in the absence or presence of the agonist for 5-10 min as indicated. MAP kinases activities and cPLA(2)phosphorylation were determined in immunoprecipitates obtained by using anti-p38 MAP kinase and anti-cPLA(2)antibodies. We found that: (a) PGF(2alpha)and CCh increased p38 MAP kinase activity by 197 and 215%, respectively, and increased p42/p44 MAP kinase activity by 200 and 125%, respectively. (b) SB202190, a p38 MAP kinase specific inhibitor, inhibited PGF(2alpha)- and CCh-induced cPLA(2)phosphorylation by 92 and 85%, respectively, and AA release by 62 and 78%, respectively. (c) PD98059, a p42/p44 MAP kinase inhibitor, inhibited CCh-induced cPLA(2)phosphorylation by 70% and AA release by 71%, but had no effect on that of PGF(2alpha). (d) Inhibition of PKC activity by RO 31-8220 inhibited both PGF(2alpha)- and CCh-stimulation of p38 MAP kinase, p42/p44 MAP kinases and cPLA(2)phosphorylation. We conclude from these results that in CISM cells PGF(2alpha)-induced cPLA(2)phosphorylation and AA release is mediated through p38 MAP kinase, but not through p42/p44 MAP kinases, whereas that of CCh is mediated through both p38 MAP kinase and p42/p44 MAP kinases. These effects of PGF(2alpha)and CCh are regulated by the MAP kinases in a PKC-dependent manner. Studies aimed at elucidating the role of protein kinases in the coupling mechanism between the activation of PGF(2alpha)and muscarinic receptors, and the stimulation of cPLA(2)and AA release in the smooth muscles of the iris-ciliary body will provide important information about the role of protein kinases signaling pathways in smooth muscle function, as well as about the mechanism of the intraocular pressure-lowering effects of PGF(2alpha)and its analog, latanoprost, in glaucoma therapy.

Lysophosphatidic acid- and Gbeta-dependent activation of Dictyostelium MAP kinase ERK2

Exogenous lysophosphatidic acid (LPA) has been shown to evoke a chemotactic response in aggregative cells of the social amoeba Dictyostelium discoideum. In this paper, we demonstrate that extracellular LPA is also able to induce activation of mitogen-activated protein (MAP) kinase DdERK2 (extracellular signal regulated kinase 2) in these cells. This activation is independent of cyclic AMP receptors, yet fully dependent on the single Gbeta subunit, hinting to the presence of functional heptahelical LPA receptors in a primitive eukaryote. We did not observe LPA-dependent cyclic GMP accumulation, which suggests that the pathways for LPA-induced and "classical" chemotaxis of D. discoideum cells are substantially different.

Analysis of R-Ras signalling pathways

R-Ras has a high degree of sequence homology to Ras and to other members of the Ras subfamily including Rap, TC21 and M-Ras. Activated versions of Ras and TC21 are highly transforming in a variety of cell lines and mutated forms of both proteins have been found in human tumours. R-Ras interacts with many of the same proteins as Ras and TC21, including c-Raf1, and can induce transformed foci, although this activity is weak compared to Ras and appears to be cell-type specific. Here, we have investigated R-Ras signalling pathways in a variety of cell types. We find that microinjection of activated R-Ras into quiescent fibroblasts stimulates cell cycle progression through G(1) phase and subsequent DNA synthesis. However, unlike Ras, R-Ras does not activate the ERK MAP kinase pathway nor does it activate the JNK or p38/Mpk2 MAP kinase pathways. Microinjection of R-Ras into PC12 cells does not induce terminal differentiation, but instead causes extensive cell spreading, consistent with R-Ras having a role in integrin activation. Finally, in a macrophage cell line, R-Ras activates the (α)(M)(β)(2)integrin via the small GTPase Rap1, leading to phagocytosis of opsonized red blood cells, whereas Ras does not. These results indicate that R-Ras has an important role in the regulation of cell growth and adhesion, but that this is mediated through downstream signals distinct from those used by Ras.

Interaction of phospholipase D1 with a casein-kinase-2-like serine kinase

Phospholipase D (PLD)1 was phosphorylated in vivo and by an associated kinase in vitro following immunoprecipitation. Both phosphorylation events were greatly reduced in a catalytically inactive point mutant in which the serine residue at position 911 was converted into alanine (S911A). The kinase could be enriched from detergent-extracted brain membranes and bind and phosphorylate PLD1 that was immunoprecipitated from COS-7 cells. Using in-gel kinase assays we determined that the size of the kinase is approximately 40 kDa and that PLD1 is more effective than S911A in binding the kinase. Preliminary analysis of the phosphorylation sites on PLD1 suggested that the kinase belongs to the casein kinase 2 (CK2) family. Consistent with this, we found that the kinase could utilize GTP, and could be inhibited by heparin and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB). Membrane fractions from Chinese hamster ovary (CHO) cell lines that inducibly express PLD1 contained an endogenous kinase activity that phosphorylated PLD1 using GTP and was inhibited by DRB. Direct evidence that the kinase is CK2 came from observations that immunoprecipitates using PLD1 antibodies contained immunoreactive CK2alpha, and immunoprecipitates using CK2alpha antibodies contained immunoreactive PLD1. Co-expression of PLD1 in COS-7 cells with the two recombinant CK2 subunits, alpha or beta, suggests that the association of PLD1 with the kinase is through the beta subunit. Supporting this, phosphorylation of PLD1 by purified recombinant CK2alpha was enhanced by purified recombinant CK2beta. Assays measuring PLD1 catalytic activity following phosphorylation by CK2 suggest that this phosphorylation event does not influence PLD1-mediated hydrolysis of phosphatidylcholine in vitro.

Identification of the endogenous smooth muscle myosin phosphatase-associated kinase

Ca(2+) sensitization of smooth muscle contraction involves inhibition of myosin light chain phosphatase (SMPP-1M) and enhanced myosin light chain phosphorylation. Inhibition of SMPP-1M is modulated through phosphorylation of the myosin targeting subunit (MYPT1) by either Rho-associated kinase (ROK) or an unknown SMPP-1M-associated kinase. Activated ROK is predominantly membrane-associated and its putative substrate, SMPP-1M, is mainly myofibrillar-associated. This raises a conundrum about the mechanism of interaction between these enzymes. We present ZIP-like kinase, identified by "mixed-peptide" Edman sequencing after affinity purification, as the previously unidentified SMPP-1M-associated kinase. ZIP-like kinase was shown to associate with MYPT1 and phosphorylate the inhibitory site in intact smooth muscle. Phosphorylation of ZIP-like kinase was associated with an increase in kinase activity during carbachol stimulation, suggesting that the enzyme may be a terminal member of a Ca(2+) sensitizing kinase cascade.

L-asparaginase of Thermus thermophilus: purification, properties and identification of essential amino acids for its catalytic activity

L-asparaginase EC 3.5.1.1 was purified to homogeneity from Thermus thermophilus. The apparent molecular mass of L-asparaginase by SDS-PAGE was found to be 33 kDa, whereas by its mobility on Sephacryl S-300 superfine column was around 200 kDa, indicating that the enzyme at the native stage acts as hexamer. The purified enzyme showed a single band on acrylamide gel electrophoresis with pI = 6.0. The optimum pH was 9.2 and the Km for L-asparagine was 2.8 mM. It is a thermostable enzyme and it follows linear kinetics even at 77 degrees C. Chemical modification experiments implied the existence ofhistidyl, arginyl and a carboxylic residues located at or near active site while serine and mainly cysteine seems to be necessary for active form.

MAP kinase upregulation after hematopoietic differentiation: role of chemotaxis

Mitogen-activated protein kinase (MAPK) isoform p42 is known to be active in exponentially growing cells at several points of the cell cycle. A high basal activity was present in three cell lines representative of immature myeloid cells tested: uHL-60, AML-14, and MPD. However, DMSO-induced differentiation of HL-60 cells (dHL-60) and subsequent expression of the neutrophilic phenotype occurred with a concomitant reduction on the basal level of MAPK activity. Simultaneously, extracellular stimuli like the cytokine granulocyte/macrophage colony-stimulating factor (GM-CSF) induced a fast (<10 min) and robust response. In terms of MAPK activity, the more mature the cell was, the higher the corresponding activity, in the three differentiation series considered: AML-14 < 3D10; MPD < G-MPD; uHL-60 < dHL-60 < neutrophils. Interestingly, peripheral blood neutrophils expressed the highest (16-fold) MAPK activation level in response to GM-CSF. Finally, using the specific MAPK inhibitor PD-98059, we demonstrated that MAPK activation is needed for neutrophil chemotaxis toward interleukin-8 and its priming by GM-CSF. Since neutrophils are terminally differentiated cells, GM-CSF does not serve a purpose in proliferation, and it must trigger the recruitment of selective signal transduction pathways particular to that final stage that includes enhanced physiological functions such as chemotaxis.

Inactivation of a MAPK-like protein kinase and activation of a MBP kinase in germinating barley embryos

We provide evidence for involvement of two different 45 kDa protein kinases in rehydration and germination of barley embryos. In dry embryos, a myelin basic protein (MBP) phosphorylating kinase was detected, which could be immunoprecipitated with an anti-MAPK (mitogen-activated protein kinase) antibody. Rehydration of the embryo induced a decrease in activity of this 45 kDa MAPK-like protein kinase. In addition, activity of a MBP kinase of the same molecular weight was subsequently found to be induced. This second MBP kinase activity could not be immunoprecipitated with the anti-MAPK antibody and was induced only in germinating embryos, not in dormant embryos.

Close linkage between calcium/calmodulin kinase II alpha/beta and NMDA-2A receptors in the lateral amygdala and significance for retrieval of auditory fear conditioning

The general mechanism underlying memory and learning is an area under intense investigation and debate, yet this mechanism still remains elusive. Auditory fear conditioning (when a tone is paired with a foot shock) is a simple associative form of learning for which many mechanistic details are known. Lesions of the lateral/basolateral nuclei of the amygdala result in the selective impairment of fear conditioning, indicating that this is a key region for this type of learning. Fear conditioning induces a lasting synaptic potentiation in the lateral nuclei of the amygdala. In addition, recent results from several laboratories suggest that N-methyl-D-aspartate (NMDA) receptor activation in the amygdala is required for the acquisition and expression of cue-conditioned fear responses using several kinds of antagonists. Little is known, however, about the signal transduction pathway and molecular substrate underlying fear conditioning. Here we use NMDA receptor-deficient mice to demonstrate that calmodulin-dependent kinase II, CaMKIIbeta, and CaMKIIalpha activation involves the NR2A subunit in the lateral/basolateral amygdala during memory retrieval following auditory fear conditioning. These results suggest that auditory fear conditioning involves a close linkage between NMDA2A receptors and the CaMKII cascade.

Activation of protein kinase Calpha inhibits growth of pancreatic cancer cells via p21(cip)-mediated G(1) arrest

We have analyzed human pancreatic cancer cells to explore the growth regulatory function of protein kinase C (PKC)alpha. PKCalpha subcellular redistribution, activation kinetics and downregulation were examined in detail and correlated to immediate and delayed effects on cell-cycle regulatory pathways. TPA treatment resulted in transient PKC(α) activation accompanied by translocation of the enzyme into membrane and nuclear compartments, and was followed by subsequent downregulation. TPA-induced inhibition of DNA synthesis was prevented by a PKC-antagonist and was reproduced by microinjection of recombinant PKCalpha, indicating that activation of this isoenzyme was required and sufficient for growth inhibitory effects. PKC(α) activation arrested cells in the G(1) phase of the cell cycle as a consequence of selective inhibition of cyclin dependent kinase (CDK)2 activity with concomitant hypophosphorylation of Rb. The inhibition of CDK2 activity resulted from induction of p21(cip1) cyclin-dependent kinase inhibitors. Levels of p21(cip1) remained elevated and CDK2 activity repressed in spite of PKCalpha downregulation, indicating that downstream effectors of PKCalpha are the primary determinants for the duration of PKC-mediated growth inhibition. The PKCalpha-induced block in cell proliferation persisted even though cells were kept in the presence of growth factors, suggesting that induction of PKCalpha results in a permanent withdrawal of pancreatic cancer cells from the cell cycle.

Function of the Mos/MAPK pathway during oocyte maturation in the Japanese brown frog Rana japonica

Fully grown immature oocytes acquire the ability to be fertilized with sperm after meiotic maturation, which is finally accomplished by the formation and activation of the maturation-promoting factor (MPF). MPF is the complex of Cdc2 and cyclin B, and its function in promoting metaphase is common among species. The Mos/mitogen-activated protein kinase (MAPK) pathway is also commonly activated during vertebrate oocyte maturation, but its function seems to be different among species. We investigated the function of the Mos/MAPK pathway during oocyte maturation of the frog Rana japonica. Although MAPK was activated in accordance with MPF activation during oocyte maturation, MPF activation and germinal vesicle breakdown (GVBD) was not initiated when the Mos/MAPK pathway was activated in immature oocytes by the injection of c-mos mRNA. Inhibition of Mos synthesis by c-mos antisense RNA and inactivation of MAPK by CL100 phosphatase did not prevent progesterone-induced MPF activation and GVBD. However, continuous MAPK activation and MAPK inhibition through oocyte maturation accelerated and delayed MPF activation, respectively. Furthermore, Mos induced a low level of cyclin B protein synthesis in immature oocytes without the aid of MAPK. These results suggest that the general function of the Mos/MAPK pathway, which is not essential for MPF activation and GVBD in Rana oocytes, is to enhance cyclin B translation by Mos itself and to stabilize cyclin B protein by MAPK during oocyte maturation.

Inhibition of neuronal nitric oxide synthase activity by 3-[2-[4-(3-chloro-2-methylphenyl)- 1-piperazinyl]ethyl]-5, 6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), a novel neuroprotective agent, in vitro and in cultured neuroblastoma cells in situ

DY-9760e, 3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5, 6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate, a novel calmodulin (CaM) antagonist, possesses neuroprotective activity. In the current study, we examined the effects of DY-9760e on nitric oxide synthase (NOS) activities in vitro and on calcium ionophore-induced NO production in situ. DY-9760e inhibited both neuronal NOS and endothelial NOS activities without affecting inducible NOS activity. It also inhibited purified neuronal NOS activity with a potency similar to that seen for purified CaM kinase II activity in vitro. Furthermore, DY-9760e significantly inhibited Ca(2+) ionophore (A23187)-induced NO production in mouse N1E-115 neuroblastoma cells, at a concentration of less than 1 microM. In contrast, no apparent inhibitory effect on Ca(2+)/CaM-dependent protein kinase II activity was observed in cultured hippocampal neurons up to 5 microM. These results suggest that the inhibitory effect of DY-9760e on CaM-dependent NOS activities underlies neuroprotective effects of the agent.

Detection of a novel quiescence-dependent protein kinase

We have identified a cell quiescence-specific 33-kDa cytoplasmic protein kinase (p33(QIK), Quiescence-Induced Kinase) based on induction of p33(QIK)-specific kinase activity of cells growth-arrested in the quiescent phase and deactivation upon entry into the cell cycle. Blockage of macromolecular synthesis prevents p33(QIK) from deactivation, indicating a requirement of newly synthesized regulators for deactivation of p33(QIK) during G(0)/G(1) transition. Stress shock induces additional increases of p33(QIK) activity in a quiescence-dependent manner that correlates with induction of apoptosis. Using a specific antibody to Krs1/Mst2 protein, we found that p33(QIK) is related to p63(Krs1) and is distinguishable from a 36-kDa protein kinase, which is induced through proteolytic modification of activated p63(Krs1) in proliferating cells undergoing apoptosis. p33(QIK) is constantly expressed in quiescent, proliferating, and apoptotic quiescent cells. Regulation of p33(QIK) activity involves protein phosphorylation/dephosphorylation in a proteolysis-independent manner. Regulation of p33(QIK) and related p63(Krs1) and p36 appears to involve distinct pathways in quiescent and proliferating cells, respectively. Our results illustrate the relevance of p33(QIK) activity for cell quiescence that may provide a new insight into signaling pathways regulated in cells during quiescence and quiescence-related apoptosis.