Phosphorylation of elongation factor 2 during Ca(2+)-mediated secretion from rat parotid acini

C-terminal Src kinase (Csk)-mediated phosphorylation of eukaryotic elongation factor 2 (eEF2) promotes proteolytic cleavage and nuclear translocation of eEF2

Protein-tyrosine kinase C-terminal Src kinase (Csk) was originally purified as a kinase for phosphorylating Src and other Src family kinases. The phosphorylation of a C-terminal tyrosine residue of Src family kinases suppresses their kinase activity. Therefore, most physiological studies regarding Csk function have been focused on Csk as a negative regulator of Src family tyrosine kinases and as a potential tumor suppressor. Paradoxically, the protein levels of Csk were elevated in some human carcinomas. In this report, we show that eukaryotic elongation factor 2 (eEF2) is a new protein substrate of Csk and could locate in the nucleus. We demonstrate that Csk-mediated phosphorylation of eEF2 has no effect on its cytoplasmic function in regulating protein translation. However, phosphorylation of eEF2 enhances its proteolytic cleavage and the nuclear translocation of the cleaved eEF2 through a SUMOylation-regulated process. Furthermore, we show that cleaved fragments of eEF2 can induce nuclear morphological changes and aneuploidy similar to those in cancer cells, suggesting that there is an additional mechanism for Csk in tumorigenesis through regulation of eEF2 subcellular localization.

Ovocalyxin-36 is a pattern recognition protein in chicken eggshell membranes

The avian eggshell membranes are essential elements in the fabrication of the calcified shell as a defense against bacterial penetration. Ovocalyxin-36 (OCX-36) is an abundant avian eggshell membrane protein, which shares protein sequence homology to bactericidal permeability-increasing protein (BPI), lipopolysaccharide-binding protein (LBP) and palate, lung and nasal epithelium clone (PLUNC) proteins. We have developed an efficient method to extract OCX-36 from chicken eggshell membranes for purification with cation and anion exchange chromatographies. Purified OCX-36 protein exhibited lipopolysaccharide (LPS) binding activity and bound lipopolysaccharide (LPS) from Escherichia coli O111:B4 in a dose-dependent manner. OCX-36 showed inhibitory activity against growth of Staphylococcus aureus ATCC 6538. OCX-36 single nucleotide polymorphisms (SNPs) were verified at cDNA 211 position and the corresponding proteins proline-71 (Pro-71) or serine-71 (Ser-71) were purified from eggs collected from genotyped hens. A significant difference between Pro-71 and Ser-71 OCX-36 for S. aureus lipoteichoic acid (LTA) binding activity was detected. The current study is a starting point to understand the innate immune role that OCX-36 may play in protection against bacterial invasion of both embryonated eggs (relevant to avian reproductive success) and unfertilized table eggs (relevant to food safety).

Colloidal-gold immunocytochemical localization of osteopontin in avian eggshell gland and eggshell

During mineralization of the avian eggshell, there is a sequential and orderly deposition of both matrix and mineral phases. Therefore, the eggshell is an excellent model for studying matrix-mineral relationships and the regulation of mineralization. Osteopontin, as an inhibitor of crystal growth, potently influences the formation of calcium phosphate and calcium carbonate biominerals. The purpose of this study was to characterize matrix-mineral relationships, specifically for osteopontin, in the avian eggshell using high-resolution transmission (TEM) and scanning (SEM) electron microscopy to gain insight into how calcite crystal growth is structured and compartmentalized during eggshell mineralization. Osteopontin was localized at the ultrastructural level by colloidal-gold immunocytochemistry. In EDTA-decalcified eggshell, an extensive matrix network was observed by TEM and SEM throughout all regions and included interconnected fibrous sheets, irregularly shaped aggregates, vesicular structures, protein films, and isolated protein fibers. Osteopontin was associated with protein sheets in the highly mineralized palisades region; some of these features defined boundaries that compartmentalized different eggshell structural units. In fractured and undecalcified eggshell, osteopontin was immunolocalized on the {104} crystallographic faces of calcite-its natural cleavage plane. The specific occlusion of osteopontin into calcite during mineralization may influence eggshell structure to modify its fracture resistance.

Microarray analysis of the rat lacrimal gland following the loss of parasympathetic control of secretion

Previous studies showed that loss of muscarinic parasympathetic input to the lacrimal gland (LG) leads to a dramatic reduction in tear secretion and profound changes to LG structure. In this study, we used DNA microarrays to examine the regulation of the gene expression of the genes for secretory function and organization of the LG. Long-Evans rats anesthetized with a mixture of ketamine/xylazine (80:10 mg/kg) underwent unilateral sectioning of the greater superficial petrosal nerve, the input to the pterygopalatine ganglion. After 7 days, tear secretion was measured, the animals were killed, and structural changes in the LG were examined by light microscopy. Total RNA from control and experimental LGs (n = 5) was used for DNA microarray analysis employing the U34A GeneChip. Three statistical algorithms (detection, change call, and signal log ratio) were used to determine differential gene expression using the Microarray Suite (5.0) and Data Mining Tools (3.0). Tear secretion was significantly reduced and corneal ulcers developed in all experimental eyes. Light microscopy showed breakdown of the acinar structure of the LG. DNA microarray analysis showed downregulation of genes associated with the endoplasmic reticulum and Golgi, including genes involved in protein folding and processing. Conversely, transcripts for cytoskeleton and extracellular matrix components, inflammation, and apoptosis were upregulated. The number of significantly upregulated genes (116) was substantially greater than the number of downregulated genes (49). Removal of the main secretory input to the rat LG resulted in clinical symptoms associated with severe dry eye. Components of the secretory pathway were negatively affected, and the increase in cell proliferation and inflammation may lead to loss of organization in the parasympathectomized lacrimal gland.

Regulation of peptide-chain elongation in mammalian cells

The elongation phase of mRNA translation is the stage at which the polypeptide is assembled and requires a substantial amount of metabolic energy. Translation elongation in mammals requires a set of nonribosomal proteins called eukaryotic elongation actors or eEFs. Several of these proteins are subject to phosphorylation in mammalian cells, including the factors eEF1A and eEF1B that are involved in recruitment of amino acyl-tRNAs to the ribosome. eEF2, which mediates ribosomal translocation, is also phosphorylated and this inhibits its activity. The kinase acting on eEF2 is an unusual and specific one, whose activity is dependent on calcium ions and calmodulin. Recent work has shown that the activity of eEF2 kinase is regulated by MAP kinase signalling and by the nutrient-sensitive mTOR signalling pathway, which serve to activate eEF2 in response to mitogenic or hormonal stimuli. Conversely, eEF2 is inactivated by phosphorylation in response to stimuli that increase energy demand or reduce its supply. This likely serves to slow down protein synthesis and thus conserve energy under such circumstances.

Novel compounds, '1,3-selenazine derivatives' as specific inhibitors of eukaryotic elongation factor-2 kinase

The inhibitory activities of 5,6-dihydro-4H-1,3-selenazine derivatives on protein kinases were investigated. In a multiple protein kinase assay using a postnuclear fraction of v-src-transformed NIH3T3 cells, 4-ethyl-4-hydroxy-2-p-tolyl-5, 6-dihydro-4H-1,3-selenazine (TS-2) and 4-hydroxy-6-isopropyl-4-methyl-2-p-tolyl-5,6-dihydro-4H-1, 3-selenazine (TS-4) exhibited selective inhibitory activity against eukaryotic elongation factor-2 kinase (eEF-2K) over protein kinase A (PKA), protein kinase C (PKC) and protein tyrosine kinase (PTK). In further experiments using purified kinases, TS-2 (IC(50)=0.36 microM) and TS-4 (IC(50)=0.31 microM) inhibited eEF-2K about 25-fold more effectively than calmodulin-dependent protein kinase-I (CaMK-I), and about 6-fold (TS-2) or 33-fold (TS-4) more effectively than calmodulin-dependent protein kinase-II (CaMK-II), respectively. TS-2 and TS-4 showed much weaker inhibitory activity toward PKA and PKC, while TS-4, but not TS-2, moderately inhibited immunoprecipitated v-src kinase. TS-2 (10.7-fold) and TS-4 (12.5-fold) demonstrated more potent and more specific eEF-2K inhibitory activity than rottlerin, a previously identified eEF-2K inhibitor. TS-2 inhibited ATP or eEF-2 binding to eEF-2K in a competitive or non-competitive manner, respectively. In cultured v-src-transformed NIH3T3 cells, TS-2 also decreased phospho-eEF-2 protein level (IC(50)=4.7 microM) without changing the total eEF-2 protein level. Taken together, these results suggest that TS-2 and TS-4 are the first identified selective eEF-2K inhibitors and should be useful tools for studying the function of eEF-2K.

Surviving rat distal tubule bicarbonate reabsorption: effects of chronic AT(1) blockade

To determine the in vivo effects of chronic ANG II type 1 (AT(1))-receptor blockade by losartan (Los) on enhanced unidirectional bicarbonate reabsorption (J(HCO(3))) of surviving distal tubules, nephrectomized rats drank either water or a solution of Los, 7 days before microperfusion. J(HCO(3)) was suppressed by 50% after Los without further reduction by 5 nM concanamycin A (Conc), suggesting that Los suppresses all Conc-sensitive H(+)-ATPase pumping. Indeed, ultrastructural analysis of A-type intercalated cells revealed a 50% reduction of H(+)-ATPase immunogold labeling of the apical plasma membrane, whereas Western blotting showed that H(+)-ATPase protein levels were also reduced by one-half by Los treatment. To identify other transporters sustaining J(HCO(3)), we perfused three inhibitors simultaneously [5-(N, N-dimethyl) amiloride hydrochloride, Conc, Schering 28080] with or without prior Los treatment: J(HCO(3)) was unchanged despite marked reduction of water reabsorption. We conclude enhanced distal tubule J(HCO(3)) of surviving nephrons is largely mediated by AT(1) receptor-dependent synthesis and insertion of apical H(+)-ATPase pumps in A-type intercalated cells.

An examination of the role of increased cytosolic free Ca2+ concentrations in the inhibition of mRNA translation

Mobilization of Ca2+ sequestered by the endoplasmic reticulum (ER) produces the phosphorylation of initiation factor (eIF) 2, whereas an increase in cytosolic free Ca2+ ([Ca2+]i) due to plasmalemmal Ca2+ influx increases the phosphorylation of elongation factor (eEF) 2. In nucleated mammalian cells, depletion of ER Ca2+ stores has been demonstrated to inhibit translational initiation, but evidence that increased [Ca2+]i per se causes slowing of peptide chain elongation is lacking. L-type Ca2+ channel activity of GH3 pituitary cells, which are enriched in calmodulin-dependent eEF-2 kinase, was manipulated such that the impact of [Ca2+]i on eEF-2 phosphorylation and translational rate could be examined for up to 10 min without inhibiting initiation. At 1 mM extracellular Ca2+, resting [Ca2+]i values were high (154-255 nM) and eEF-2 was phosphorylated. The Ca2+ channel antagonist, nisoldipine, lowered [Ca2+]i and reduced eEF-2 phosphorylation by half but had no effect on amino acid incorporation. The Ca2+ channel agonist, Bay K 8644, produced sustained elevations of [Ca2+]i that were associated with 25-50% increases in eEF-2 phosphorylation, but no changes in protein synthetic rates occurred. Larger Ca2+ influxes were achievable with either 25 mM KCl or KCl plus Bay K 8644. These treatments further increased eEF-2 phosphorylation (50-100% above control) and inhibited leucine incorporation by 20-70% but ATP content was reduced by 25-50% and total cell-associated Ca2+ contents rose by 3- to 13-fold. eIF-2alpha was not phosphorylated during these treatments. Addition of low concentrations of ionomycin, which do not lower ATP content, was associated with complex changes in [Ca2+]i that resembled alterations in eEF-2 phosphorylation. The inhibition of leucine incorporation in response to ionomycin, however, coincided only with the phosphorylation of eIF-2alpha, not eEF-2. It is concluded that changes in [Ca2+]i occurring in the absence of ATP depletion alter the phosphorylation state of eEF-2 but are not regulatory for mRNA translation.

K depletion stimulates in vivo HCO3 reabsorption in surviving rat distal tubules

To evaluate whether K depletion enhances in vivo bicarbonate reabsorption (JtCO2) in surviving distal tubules (DT), we compared DT JtCO2 in five-sixths nephrectomized rats (Nx) with and without dietary K depletion (Nx-K). Furthermore, to identify possible mechanisms of increased JtCO2, we perfused inhibitors of proton secretion in both Nx and Nx-K rats. JtCO2 (102 +/- 8 pmol.min-1.mm-1) was significantly increased in Nx-K vs. Nx rats (65 +/- 7 pmol.min-1.mm-1, P < 0.05) but unaffected by 10(-6) M losartan perfusion (94 +/- 6 pmol.min-1.mm-1, P = not significant). Although 10(-5) M Sch-28080 also had no significant effect, 5 x 10(-9) M concanamycin A perfusion significantly decreased JtCO2 in Nx-K rats to 65 +/- 8 pmol.min-1. mm-1 (P < 0.05). Morphometric evaluation and H(+)-ATPase immunogold labeling of Nx-K A-type intercalated cells revealed cellular hypertrophy, elaborated apical microplicae, and enhanced H(+)-ATPase apical polarization. Accordingly, these combined studies confirm that K depletion enhances JtCO2 in surviving DT by stimulating H(+)-ATPase activity, independent of the AT1 receptor.

Glutamate-dependent phosphorylation of elongation factor-2 and inhibition of protein synthesis in neurons

Postischemic delayed neuronal death is attributed to excitotoxic activation of glutamate receptors. It is preceded by a persistent inhibition of protein synthesis, the molecular basis of which is not known. Here we have examined in cortical neurons in culture the regulation by glutamate of phosphorylation of eukaryotic elongation factor-2 (eEF-2) by eEF-2 kinase, a Ca2+/calmodulin-dependent enzyme. Using a phosphorylation state-specific antibody, we show that glutamate, which triggers a large influx of Ca2+, enhances dramatically the phosphorylation of eEF-2. On the basis of kinetic and pharmacological analysis, we demonstrate a close correlation among the increase in cytosolic Ca2+ concentration, the degree of eEF-2 phosphorylation, and the inhibition of protein synthesis. A 30 min treatment with NMDA induced a transient phosphorylation of eEF-2 and delayed neuronal death. However, pharmacological inhibition of protein translation was not neurotoxic by itself and protected neurons against the toxicity evoked by low concentrations of NMDA. Thus, phosphorylation of eEF-2 and the resulting depression of protein translation may have protective effects against excitotoxicity and open new perspectives for understanding long-term effects of glutamate.

Glutamate-dependent phosphorylation of elongation factor-2 and inhibition of protein synthesis in neurons

Postischemic delayed neuronal death is attributed to excitotoxic activation of glutamate receptors. It is preceded by a persistent inhibition of protein synthesis, the molecular basis of which is not known. Here we have examined in cortical neurons in culture the regulation by glutamate of phosphorylation of eukaryotic elongation factor-2 (eEF-2) by eEF-2 kinase, a Ca2+/calmodulin-dependent enzyme. Using a phosphorylation state-specific antibody, we show that glutamate, which triggers a large influx of Ca2+, enhances dramatically the phosphorylation of eEF-2. On the basis of kinetic and pharmacological analysis, we demonstrate a close correlation among the increase in cytosolic Ca2+ concentration, the degree of eEF-2 phosphorylation, and the inhibition of protein synthesis. A 30 min treatment with NMDA induced a transient phosphorylation of eEF-2 and delayed neuronal death. However, pharmacological inhibition of protein translation was not neurotoxic by itself and protected neurons against the toxicity evoked by low concentrations of NMDA. Thus, phosphorylation of eEF-2 and the resulting depression of protein translation may have protective effects against excitotoxicity and open new perspectives for understanding long-term effects of glutamate.

Regulation of translation elongation factor-2 by insulin via a rapamycin-sensitive signalling pathway

It is well established that insulin and serum stimulate gene expression at the level of mRNA translation in animal cells, and previous studies have mainly focused on the initiation process. Here we show that, in Chinese hamster ovary cells expressing the human insulin receptor, insulin causes decreased phosphorylation of elongation factor eEF-2 and that this is associated with stimulation of the rate of peptide-chain elongation. eEF-2 is phosphorylated by a very specific Ca 2+/calmodulin-dependent protein kinase (eEF-2 kinase) causing its complete inactivation. The decrease in eEF-2 phosphorylation induced by insulin reflects a fall in eEF-2 kinase activity. Rapamycin, a macrolide immunosuppressant which blocks the signalling pathway leading to the stimulation of the 70/85 kDa ribosomal protein S6 kinases, substantially blocks the activation of elongation, the fall in eEF-2 phosphorylation and the decrease in eEF-2 kinase activity, suggesting that p7O S6 kinase (p70s6k) and eEF-2 kinase may tie on a common signalling pathway. Wortmannin, an inhibitor of phosphatidylinositide-3-OH kinase, had similar effects. eEF-2 kinase was phosphorylated in vitro by purified p70s6k but this had no significant effect on the in vitro activity of eEF-2 kinase.

Increased expression of BDNF and trkB mRNA in rat facial motoneurons after axotomy

Motoneurons of the adult survive after axotomy even though they are deprived of putative target derived trophic factors. Alternative sources of trophic support may substitute. In this study we test the hypothesis that the immediate environment of the motoneuronal cell body or the cell body itself increases the production of trophic factors after axonal injury. Using in situ hybridization (ISH) and reverse transcription-polymerase chain reaction (RT-PCR), we report that after axotomy, rat facial motoneurons increase the expression of mRNA for brain-derived neurotrophic factor (BDNF) and its receptor trkB. After transection of the facial nerve, we measured a 2- to 4-fold increase in BDNF mRNA expression which had its onset between 3 and 8 h after injury. The BDNF mRNA levels peaked at approximately 1-2 days and gradually declined thereafter to return to contralateral levels within 7 days of injury. Western blotting revealed a several-fold increase in BDNF as early as 24 h, which subsequently reached a maximum in approximately 5-7 days and was still sustained at 2 weeks post-axotomy. Using exon-specific primers, we determined that the increase in BDNF mRNA is largely due to an increased expression from the promoters of exons IV and III, and to a lesser extent from exons I and II. Analysing the mRNA expression for the BDNF receptor, trkB, we found a 2- to 3-fold increase in full-length trkB mRNA expression starting 2 days after axotomy which lasted 2-3 weeks. These findings suggest that BDNF might act locally on axotomized motoneurons in an autocrine fashion, providing support for axotomized motoneurons during the first weeks after axotomy.

Purification and immunochemistry of a soluble matrix protein of the chicken eggshell (ovocleidin 17)

The protein components of biomineralized structures (matrix proteins) are believed to modulate crystal nucleation and growth, and thereby influence the shape and strength of the final structure. The chicken eggshell contains a complex array of distinct matrix proteins. The most abundant of these was purified to homogeneity by a combination of anionic exchange and hydroxyapatite chromatographies. Antibodies to this protein were raised in rabbit, and utilized for Western blotting and immunohistochemistry. These studies indicated that the 17 kDa antigen (ovocleidin 17, OC-17) is found in the shell gland mucosa, and that only the tubular gland cells were positive. Immunohistochemistry with decalcified shell indicated that OC-17 is uniformly distributed throughout the shell matrix, but concentrated in the mammillary bodies. Our results indicate that this protein is secreted during shell formation and becomes incorporated into this structure. It may therefore play a role in the crystallization process and influence the properties of the resulting eggshell.

Cholinergic regulation of amylase gene expression in the rat parotid gland. Inhibition by two distinct post-transcriptional mechanisms

Stimulation of the beta-adrenergic or cholinergic muscarinic receptors are the principal mechanisms by which parotid salivary secretion is regulated in vivo. In this study we have examined the effects of cholinergic stimulation on amylase gene expression in dispersed rat parotid cells. [3H]Leucine incorporation into amylase and total protein was inhibited by carbamylcholine. Within 5 min of its addition, 10 microM carbamylcholine induced a 50-60% reduction in the rate of amylase synthesis which was sustained for more than 2 h. Blockade of the muscarinic receptor with atropine 8 min after addition of 10 microM carbamylcholine reversed the carbamylcholine-induced inhibition of amylase synthesis. When cells were exposed to carbamylcholine for 2 h before addition of atropine, there was only a slight reversal of inhibition. Carbamylcholine had no significant effect on the rate of total RNA synthesis but caused a progressive loss of amylase mRNA. After 2 h, amylase mRNA in cells treated with 10 microM carbamylcholine was 46% of control levels. Actinomycin D (5 micrograms/ml) lowered amylase mRNA by 8%; cycloheximide and phorbol 12-myristate 13-acetate had no effect. Isoprenaline (isoproterenol; at a concentration of 10 microM), which is an inducer of amylase gene transcription, elevated the amylase mRNA content by 30% after 2h. The calcium ionophore A23187 mimicked the effect of carbamylcholine by inhibiting [3H]leucine incorporation into amylase and lowering amylase mRNA content. The results suggest that acute stimulation of the muscarinic cholinergic receptor inhibits amylase biosynthesis in parotid cells not only by rapid attenuation of translation but also by causing a gradual loss of amylase mRNA, apparently by a Ca(2+)-dependent destabilization of the mRNA.

Ovalbumin is a component of the chicken eggshell matrix

The protein components of biomineralized structures (matrix proteins) are believed to modulate crystal nucleation and growth, and thereby influence the shape and strength of the final structure. The chicken eggshell contains a complex array of distinct matrix proteins. One of these was found to have similar molecular weight and chromatographic properties as purified egg ovalbumin. A commercially available antibody to ovalbumin was utilized for western blotting to demonstrate that ovalbumin is one of the matrix proteins this is extracted from decalcified eggshell. Immunohistochemistry revealed that ovalbumin is found only in the mammillary bodies of decalcified shell, and is not distributed throughout the shell matrix. These results indicate that ovalbumin is present during the initial phase of shell formation and becomes incorporated into the protein matrix of the mammillary bodies. However, it is not yet clear whether ovalbumin at this site plays a specific role in shell mineralization.

Elongation factor-2 kinase: effective inhibition by the novel protein kinase inhibitor rottlerin and relative insensitivity towards staurosporine

The elongation factor-2 (eEF-2) is selectively phosphorylated by the eEF-2 kinase (calmodulin-dependent kinase III). This phosphorylation can be inhibited by calmodulin antagonists, such as CGS 9343B (IC50 = 4 microM). The novel protein kinase inhibitor rottlerin is shown to suppress eEF-2 phosphorylation with an IC50 of 5.3 microM. By contrast, the eEF-2 kinase is rather resistant towards the potent but non-selective protein kinase inhibitor staurosporine (IC50 > 50 microM) and thus can be differentiated from most other protein kinases that are suppressed by staurosporine in the nM range.

Cyclic AMP-dependent protein kinase phosphorylates rabbit reticulocyte elongation factor-2 kinase and induces calcium-independent activity

The catalytic subunit of cyclic AMP-dependent protein kinase (PKA) phosphorylated purified calcium/calmodulin-dependent eukaryotic elongation factor-2 (eEF-2) kinase, isolated from rabbit reticulocyte lysates. It maximally incorporated about 1 mol of phosphate/mol of eEF-2 kinase. The Km of eEF-2 kinase for PKA was calculated to be 7 microM. Phosphorylation of eEF-2 kinase by PKA induced calcium-independent activity which amounted to 40-50% of the total activity measured in the presence of calcium. Furthermore, the level of calcium-independent activity induced by phosphorylation by PKA was similar to that induced by the calcium-stimulated autophosphorylation of eEF-2 kinase. Phosphopeptide mapping of eEF-2 kinase labelled by autophosphorylation and by PKA revealed a number of common phosphopeptides. This suggests that PKA may phosphorylate the same site(s) which are phosphorylated autocatalytically and which are responsible for the induction of calcium-independent activity. The possible implications these findings have for the control of translation are discussed.

Purification and phosphorylation of elongation factor-2 kinase from rabbit reticulocytes

Eukaryotic elongation-factor-2 kinase has been purified to homogeneity from rabbit reticulocytes through a seven-step procedure and has been identified as a protein with a molecular mass of approximately 103 kDa as judged by SDS/PAGE. A degradation product of about 95 kDa was also evident in some preparations. The activity of the purified kinase was completely dependent on calcium and calmodulin. The kinase rapidly underwent extensive autophosphorylation, incorporating 1 mol phosphate/mol within 1 min; 5 mol phosphate/mol were incorporated within 1 h. The autophosphorylation was Ca2+/calmodulin-dependent; phosphopeptide mapping revealed multiple phosphopeptides even after just 0.5 min of autophosphorylation, suggesting that a number of sites became rapidly phosphorylated. Autophosphorylation occurred on serine and threonine residues. Preincubation in the presence of Ca2+, Mg2+ and ATP produced a rapid 2-3-fold activation of the kinase and also induced partial Ca(2+)-independent activity. Preincubation in the absence of the ligands showed that all three were required for full activation and induction of Ca(2+)-independent activity.