Calmodulin-dependent multifunctional protein kinase in Aspergillus nidulans

Involvement of Ca2+/calmodulin-dependent protein kinases in mycelial growth of the basidiomycetous mushroom, Coprinus cinereus

Although multifunctional Ca(2+)/calmodulin-dependent protein kinases (CaM-kinases) are widely distributed in animal cells, the occurrence of CaM-kinases in the basidiomycetous mushroom has not previously been documented. When the extracts from various developmental stages from mycelia to the mature fruiting body of Coprinus cinereus were analyzed by Western blotting using Multi-PK antibodies, which had been generated to detect a wide variety of protein serine/threonine kinases (Ser/Thr kinases), a variety of stage-specific Ser/Thr kinases was detected. Calmodulin (CaM) overlay assay using digoxigenin-labeled CaM detected protein bands of 65 kDa, 58 kDa, 46 kDa, 42 kDa, and 38 kDa only in the presence of CaCl(2), suggesting that these bands were CaM-binding proteins. When the CaM-binding fraction was prepared from mycelial extract of C. cinereus by CaM-Sepharose and analyzed with Multi-PK antibodies, two major immunoreactive bands corresponding to 65 kDa and 46 kDa were detected. CaM-binding fraction, thus obtained, exhibited Ca(2+)/CaM-dependent protein kinase activity toward protein substrates such as histones. These CaM-kinases were found to be highly expressed in the actively growing mycelia, but not in the resting mycelial cells. Mycelial growth was enhanced by the addition of CaCl(2) in the culture media, but inhibited by the addition of EGTA or trifluoperazine, a potent CaM inhibitor. This suggested that CaM-dependent enzymes including CaM-kinases play crucial roles in mycelial growth of basidiomycete C. cinereus.

Biochemical characterization of Ca2+/calmodulin dependent protein kinase from Candida albicans

A multifunctional Ca2+/calmodulin dependent protein kinase was purified approximately 650 fold from cytosolic extract of Candida albicans. The purified preparation gave a single band of 69 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis with its native molecular mass of 71 kDa suggesting that the enzyme is monomeric. Its activity was dependent on calcium, calmodulin and ATP when measured at saturating histone IIs concentration. The purified Ca2+/CaMPK was found to be autophosphorylated at serine residue(s) in the presence of Ca2+/calmodulin and enzyme stimulation was strongly inhibited by W-7 (CaM antagonist) and KN-62 (Ca2+/CaM dependent PK inhibitor). These results confirm that the purified enzyme is Ca2+/CaM dependent protein kinase of Candida albicans. The enzyme phosphorylated a number of exogenous and endogenous substrates in a Ca2+/calmodulin dependent manner suggesting that the enzyme is a multifunctional Ca2+/calmodulin-dependent protein kinase of Candida albicans.

Influence of W-7, a calmodulin antagonist on phospholipid biosynthesis in Candida albicans

AIM

This study was undertaken to investigate the role of calmodulin in phospholipid biosynthesis in Candida albicans using W-7, a calmodulin antagonist.

METHODS

Cells were grown as shake cultures in the absence and presence of W-7 at different concentrations. Changes in cell mass, phospholipid content and incorporation of labelled precursor into phospholipid and activities of respective enzymes have been studied.

RESULTS

Decreased incorporation of labelled acetate into total lipids and phospholipids was observed in the presence of 40 microm of W-7 which was not as a consequence of altered growth of Candida in the presence of calmodulin antagonist. Further, a significant decrease in the levels of calmodulin and CaM dependent protein kinase activity was observed in cells grown with different concentrations of W-7. This was accompanied by decreased/increased activity of phosphatidic acid phosphatase and phospholipase A, respectively in W-7 grown cells as compared to controls.

CONCLUSIONS

These findings suggest definite involvement of calmodulin in the regulation of phospholipid metabolism in Candida albicans.

Augmentation of apoptosis by the combination of bleomycin with trifluoperazine in the presence of mutant p53

A variety of anticalmodulin drugs can increase the cytotoxicity of bleomycin, a DNA damaging cancer chemotherapeutic. The combination has been shown to produce greater than expected DNA damage compared wot what was observed with either drug alone. Promising preclinical results led to Phase I and Phase II trials of trifluoperazine and bleomycin, which revealed activity in non-Hodgkin's lymphoma. Despite the unique activity of the combination, the mechanism underlying the DNA damaging effect remained poorly understood. In several systems, DNA damage leads to the induction of programmed cell death or apoptosis, which is characterized by interoligonucleosomal cleavage of DNA. To determine whether the activity of the combination of bleomycin with trifluoperazine was due to induction of apoptosis, we exposed L1210 leukemic lymphocytes to bleomycin in the presence or absence of trifluoperazine. The combination produced DNA laddering, cellular shrinkage, and chromatin condensation typical of programmed cell death. Cell cycle analyses revealed a blockade of cells in G2/M, suggesting the presence of mutant p53, which was confirmed by immunoanalysis. In addition, L1210 cells were found not to overexpress Bcl-2 in the presence or absence of drugs. These results indicate that the enhancement of bleomycin induced DNA damage by trifluoperazine is mediated, at least in part, through the induction of apoptosis.

Possible involvement of Ca2+/calmodulin-dependent protein kinase in the regulation of phospholipid biosynthesis in Microsporum gypseum

The mechanism of action of Ca2+/calmodulin on phospholipid synthesis in Microsporum gypseum has been studied. These second messengers were observed to mediate their function through phosphorylation mechanism as altered protein kinase activity was seen in calcium/trifluoperazine (calmodulin antagonist) grown cells. The activity of protein kinase was dependent on calcium (200 microm) and calmodulin (1 microm). In vitro studies of phosphorylation and dephosphorylation in relation to phospholipid synthesis in Microsporum gypseum have been carried out. Addition of KN-62 (a specific inhibitor of Ca2+/calmodulin-dependent protein kinases) and polyclonal antibodies raised against purified Ca2+/calmodulin-kinase (CaMPK) of M. gypseum in the cell extract, leads to the inhibition in the incorporation of labelled acetate into total phospholipids in this fungus. These results suggest a possible involvement of Ca2+/calmodulin via Ca2+/calmodulin-dependent phosphorylation in phospholipid synthesis in M. gypseum.

Calcium/calmodulin-dependent phosphorylation and activation of human Cdc25-C at the G2/M phase transition in HeLa cells

The human tyrosine phosphatase (p54(cdc25-c)) is activated by phosphorylation at mitosis entry. The phosphorylated p54(cdc25-c) in turn activates the p34-cyclin B protein kinase and triggers mitosis. Although the active p34-cyclin B protein kinase can itself phosphorylate and activate p54(cdc25-c), we have investigated the possibility that other kinases may initially trigger the phosphorylation and activation of p54(cdc25-c). We have examined the effects of the calcium/calmodulin-dependent protein kinase (CaM kinase II) on p54(cdc25-c). Our in vitro experiments show that CaM kinase II can phosphorylate p54(cdc25-c) and increase its phosphatase activity by 2.5-3-fold. Treatment of a synchronous population of HeLa cells with KN-93 (a water-soluble inhibitor of CaM kinase II) or the microinjection of AC3-I (a specific peptide inhibitor of CaM kinase II) results in a cell cycle block in G2 phase. In the KN-93-arrested cells, p54(cdc25-c) is not phosphorylated, p34(cdc2) remains tyrosine phosphorylated, and there is no increase in histone H1 kinase activity. Our data suggest that a calcium-calmodulin-dependent step may be involved in the initial activation of p54(cdc25-c).

Chimeric calcium/calmodulin-dependent protein kinase in tobacco: differential regulation by calmodulin isoforms

cDNA clones of chimeric Ca2+/calmodulin-dependent protein kinase (CCaMK) from tobacco (TCCaMK-1 and TCCaMK-2) were isolated and characterized. The polypeptides encoded by TCCaMK-1 and TCCaMK-2 have 15 different amino acid substitutions, yet they both contain a total of 517 amino acids. Northern analysis revealed that CCaMK is expressed in a stage-specific manner during anther development. Messenger RNA was detected when tobacco bud sizes were between 0.5 cm and 1.0 cm. The appearance of mRNA coincided with meiosis and became undetectable at later stages of anther development. The reverse polymerase chain reaction (RT-PCR) amplification assay using isoform-specific primers showed that both of the CCaMK mRNAs were expressed in anther with similar expression patterns. The CCaMK protein expressed in Escherichia coli showed Ca2+-dependent autophosphorylation and Ca2+/calmodulin-dependent substrate phosphorylation. Calmodulin isoforms (PCM1 and PCM6) had differential effects on the regulation of autophosphorylation and substrate phosphorylation of tobacco CCaMK, but not lily CCaMK. The evolutionary tree of plant serine/threonine protein kinases revealed that calmodulin-dependent kinases form one subgroup that is distinctly different from Ca2+-dependent protein kinases (CDPKs) and other serine/threonine kinases in plants.

Role of Ca++/calmodulin binding proteins in Aspergillus nidulans cell cycle regulation

The goal of this review is to summarise the current knowledge concerning the targets of Ca++/calmodulin that are essential for cell cycle progression in lower eukaryotes. Emphasis is placed on Aspergillus nidulans since this is the only organism to date shown to posses essential Ca++ dependent calmodulin activated enzymes. Two such enzymes are the calmodulin activated protein phosphatase, calcineurin and the calmodulin dependent protein kinase. These proteins, each the product of a unique gene, are required for progression of quiescent spores into the proliferative cycle and also for execution of the nuclear division cycle in exponentially growing germlings.

Characterization of calcium/calmodulin-dependent protein kinase II activity in the nervous system of the lobster, Panulirus interruptus

Nervous system tissue from Panulirus interruptus has an enzyme activity that behaves like calcium/calmodulin-dependent protein kinase II (CaM KII) This activity phosphorylates known targets of CaM KII, such as synapsin I and autocamtide 3. It is inhibited by a CaM KII-specific autoinhibitory domain peptide. In addition, this lobster brain activity displays calcium-independent activity after autophosphorylation, another characteristic of CaM KII. A cDNA from the lobster nervous system was amplified using polymerase chain reaction. The fragment was cloned and found to be structurally similar to CaM KII. Serum from rabbits immunized with a fusion protein containing part of this sequence immunoprecipitated a CaM KII enzyme activity and a family of phosphoproteins of the appropriate size for CaM KII subunits. Lobster CaM KII activity is found in the brain and stomatogastric nervous system including the commissural ganglia, commissures, stomatogastric ganglion and stomatogastric nerve. Immunoblot analysis of these same regions also identifies bands at an apparent molecular weight characteristic of CaM KII.

Expression of a constitutively active Ca2+/calmodulin-dependent kinase in Aspergillus nidulans spores prevents germination and entry into the cell cycle

The unique gene for Ca2+/calmodulin-dependent protein kinase (CaMK) has been shown to be essential in Aspergillus nidulans. Disruption of the gene prevents entry of spores into the nuclear division cycle. Here we show that expression of a constitutively active form of CaMK also prevents spores from entering the first S phase in response to a germinating stimulus. Expression of the constitutively active kinase induces premature activation of NIMEcyclin B/NIMXcdc2 in G0/G1. As NIMXcdc2 is present in spores, the elevation of maturation promotion factor activity may be secondary to the early production of NIMEcyclin B or post-translation modification of maturation promotion factor. The expression of the constitutively active CaMK also results in the appearance of NIMA kinase activity within 1 h of the germinating signal. These results support the contention that the activities of maturation promotion factor and NIMA are coincidentally regulated in A. nidulans and suggest that the unscheduled appearance of one or both of these activities may be sufficient to prevent A. nidulans spores from entering into DNA synthesis.

Ca(2+)/calmodulin-dependent kinase is essential for both growth and nuclear division in Aspergillus nidulans

The calmodulin gene has been shown to be essential for cell cycle progression in a number of eukaryotic organisms. In vertebrates and Aspergillus nidulans the calmodulin dependence also requires calcium. We demonstrate that the unique gene encoding a multifunctional calcium/calmodulin-dependent protein kinase (CaMK) is also essential in A. nidulans. This enzyme is required both for the nuclear division cycle and for hyphal growth, because spores containing the disrupted gene arrest with a single nucleus and fail to extend a germ tube. A strain conditional for the expression of CaMK was created. When grown under conditions that resulted in a 90% decrease in the enzyme, both nuclear division and growth were markedly slowed. The CaMK seems to be important for progression from G2 to mitosis.

Calcium, calmodulin and cell cycle regulation

Calcium and its ubiquitous intracellular receptor calmodulin are required for cell proliferation. Studies in a variety of model systems are beginning to identify components of the calcium/calmodulin cascade required for movement of quiescent cells into the cell cycle as well as for proliferating cells to move from G1 to S, G2 to M and through mitosis. Two calcium/calmodulin-dependent enzymes, the multifunctional calcium/calmodulin-dependent protein kinase and the protein phosphatase 2B (calcineurin) as well as a spindle pole body protein that binds calmodulin in the absence of calcium have been shown to be essential at specific phases of the cell cycle. In addition, the status of the intracellular calcium pools is critical for normal traverse of the cell cycle.

Trypanosoma cruzi epimastigote forms possess a Ca(2+)-calmodulin dependent protein kinase

Trypanosoma cruzi epimastigote forms showed a tightly bound Ca(2+)-calmodulin-dependent protein kinase activity, which could be partially extracted from membranes and axonemes. The enzyme is constituted by subunits which were autophosphorylated in the absence of exogenous substrates. An antibody against CaM kinase II recognized a Ca(2+)- or Ca(2+)-CaM-dependent conformational epitope in these fractions. The detected bands were of molecular weights similar to the alpha and beta subunits of the corresponding bovine brain enzyme (60 and 50 kDa). Studies using [125I]CaM revealed the presence of a CaM-binding domain. These experiments confirm that the parasite possesses a particulate CaM kinase with characteristics similar to the bovine brain enzyme.

Ca2+ calmodulin-dependent protein kinase activity in the ascomycetes Neurospora crassa

DEAE-cellulose column chromatography of Neurospora crassa soluble mycelial extracts leads to the resolution of three major protein kinase activity peaks designated PKI, PKII, and PKIII. PKII activity is stimulated by Ca2+ and Neurospora or brain calmodulin. Maximal stimulation was observed at 2 microM-free Ca2+ and 1 microgram/ml of the modulator. The stimulatory effect of the Ca(2+)-calmodulin complex was blocked by EGTA and by some calmodulin antagonists such as phenothiazine drugs or compound 48/80. PKII phosphorylates different proteins, among which histone II-A at a low concentration and CDPKS, the synthetic peptide specific for Ca(2+-)-calmodulin dependent protein kinase, are the best substrates. Some phosphorylation can be detected in the absence of any exogenous acceptor. PKII activity assayed in the presence of histone II-A or in the absence of exogenous phosphate acceptor (autophosphorylation) co-elute in a DEAE-cellulose column at 0.28 NaCl. As result of the autophosphorylation reaction of the purified enzyme a main phosphorylated component of 70 kDa was resolved by SDS-polyacrylamide gel electrophoresis. It is possible that this component is an active part of this enzyme.

Calcium/calmodulin-dependent protein kinase II

There is a great deal known about the in vitro properties of CaM kinase II, both in terms of its substrate specificity and its regulation by calmodulin and autophosphorylation. Much of this characterization is based on experiments performed with the rat brain isozyme of CaM kinase II, although in the aspects examined to date isozymes of the kinase from other tissues appear to behave in a broadly similar manner in vitro. However, relatively little is known about the functions of the kinase in vivo. The proteins phosphorylated by the kinase (with the probable exception of synapsin I and tyrosine hydroxylase) and the role of kinase autophosphorylation in vivo remain largely unknown. Investigation of the physiological role of the kinase in brain and other tissues will be a particularly exciting area for future work. The current knowledge of the in vitro properties and the availability of cDNA clones will hopefully expedite this research.

Calcium/calmodulin-dependent protein kinase II

Images