Subcellular localization of creatine kinase in Torpedo electrocytes: association with acetylcholine receptor-rich membranes

Proteomic analysis reveals energy metabolic dysfunction and neurogenesis in the prefrontal cortex of a lipopolysaccharide-induced mouse model of depression

Substantial evidence from previous studies has suggested an association between major depressive disorder (MDD) and inflammation, and previous studies have associated prefrontal cortex (PFC) dysfunction with MDD. Systemic administration of bacterial lipopolysaccharide has been used to study inflammation-associated behavioral changes in rodents. However, proteomic studies investigating PFC protein expression in an LPS-induced mouse model of depression have yet to be conducted. Using two-dimensional electrophoresis coupled with matrix-assisted laser desorption ionization-time of flight-tandem mass spectrometry, PFC proteomes were comparatively assessed in LPS-induced acute inflammation reaction mice, LPS-induced depressive-like behavior mice (Dep), and control mice. A total of 26 differentially expressed proteins were identified, two of which were selected for western blot analysis, the results of which revealed a significant increase in the expression levels of creatine kinase B and dihydropyrimidinase-like 3 in Dep mice, suggesting that changes in energy metabolism and neuro-genesis occur in the PFC of Dep mice. Further investigation on these processes and on the proteins of the PFC are required in order to elucidate the pathophysiological mechanism underlying MDD.

Small leucine zipper protein (sLZIP) negatively regulates skeletal muscle differentiation via interaction with α-actinin-4

The small leucine zipper protein (sLZIP) plays a role in transcriptional regulation in various types of cells. However, the role of sLZIP in myogenesis is unknown. We identified α-actinin-4 (ACTN4) as a sLZIP-binding protein. ACTN4 functions as a transcriptional regulator of myocyte enhancer factor (MEF)2, which plays a critical role in expression of muscle-specific genes during skeletal muscle differentiation. We found that ACTN4 translocates to the nucleus, induces myogenic gene expression, and promotes myotube formation during myogenesis. The myogenic process is controlled by an association between myogenic factors and MEF2 transcription factors. ACTN4 increased expression of muscle-specific proteins via interaction with MEF2. However, sLZIP decreased myogenic gene expression and myotube formation during myogenesis via disruption of the association between ACTN4 and MEF2. ACTN4 increased the promoter activities of myogenic genes, whereas sLZIP abrogated the effect of ACTN4 on transcriptional activation of myogenic genes in myoblasts. The C terminus of sLZIP is required for interaction with the C terminus of ACTN4, based on deletion mutant analysis, and sLZIP plays a role in regulation of MEF2 transactivation via interaction with ACTN4. Our results indicate that sLZIP negatively regulates skeletal muscle differentiation via interaction with ACTN4 and that sLZIP can be used as a therapeutic target molecule for treatment of muscle hypertrophy and associated diseases.

Energy dysfunction in Huntington's disease: insights from PGC-1α, AMPK, and CKB

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a CAG trinucleotide expansion in the Huntingtin (Htt) gene. When the number of CAG repeats exceeds 36, the translated polyglutamine-expanded Htt protein interferes with the normal functions of many types of cellular machinery and causes cytotoxicity. Clinical symptoms include progressive involuntary movement disorders, psychiatric signs, cognitive decline, dementia, and a shortened lifespan. The most severe brain atrophy is observed in the striatum and cortex. Besides the well-characterized neuronal defects, recent studies showed that the functions of mitochondria and several key players in energy homeostasis are abnormally regulated during HD progression. Energy dysregulation thus is now recognized as an important pathogenic pathway of HD. This review focuses on the importance of three key molecular determinants (peroxisome proliferator-activated receptor-γ coactivator-1α, AMP-activated protein kinase, and creatine kinase B) of cellular energy homeostasis and their possible involvement in HD pathogenesis.

Besides Huntington's disease, does brain-type creatine kinase play a role in other forms of hearing impairment resulting from a common pathological cause?

Hearing impairment following cochlear damage due to noise trauma, ototoxicity caused by aminoglycoside antibiotics, or age-related cochlear degeneration was linked to a common pathogenesis involving the formation of reactive oxygen species (ROS). Cochleae are more vulnerable to oxidative stress than other organs because of the high metabolic demands of their mechanosensory hair cells in response to sound stimulation. We recently showed that patients and mice with Huntington's disease (HD) have hearing impairment and that the dysregulated phosphocreatine (PCr)-creatine kinase (CK) system may account for this auditory dysfunction. Given the importance of noninvasive biomarkers and the easy access of hearing tests, the symptom of hearing loss in HD patients may serve as a useful clinical indicator of disease onset and progression of HD. We also showed that dietary creatine supplementation rescued the impaired PCr-CK system and improved the expression of cochlear brain-type creatine kinase (CKB) in HD mice, thereby restoring their hearing. Because creatine is an antioxidant, we postulated that creatine might enhance expression of CKB by reducing oxidative stress. In addition to HD-related hearing impairment, inferior CKB expression and/or an impaired PCr-CK system may also play an important role in other hearing impairments caused by elevated levels of ROS. Most importantly, dietary supplements may be beneficial to patients with these hearing deficiencies.

An organelle proteomic method to study neurotransmission-related proteins, applied to a neurodevelopmental model of schizophrenia

Limited information is currently available on molecular events that underlie schizophrenia-like behaviors in animal models. Accordingly, we developed an organelle proteomic approach enabling the study of neurotransmission-related proteins in the prefrontal cortex (PFC) of postpubertal (postnatal day 60 (PD60)) neonatally ventral hippocampal (nVH) lesioned rats, an extensively used neurodevelopmental model of schizophrenia-like behaviors. The PFC was chosen because of its purported role in the etiology of the disease. Statistical analysis of 392 reproducible spots on 2-D organelle proteomic patterns revealed significant changes in intensity of 18 proteinous spots in plasma membrane-enriched fractions obtained from postpubertal nVH lesioned rats compared to controls. Mass spectrometric analysis and database searching allowed the identification of a single protein in each of the nine differential spots, including proteins of low abundance, such as neurocalcin delta. Most of the identified dysregulated proteins, including clathrin light chain B, syntaxin binding protein 1b and visinin-like protein 1 are known to be linked to various neurotransmitter systems and to play key roles in plasma membrane receptor expression and recycling as well as synaptic vesicle exocytosis/recycling. Organelle proteomic approaches have hence proved to be most useful to identify key proteins linked to a given behavior in animal models of brain diseases.

Effect of coenzyme Q10 and vitamin E on brain energy metabolism in the animal model of Huntington's disease

The neuropathological and clinical symptoms of Huntington's disease (HD) can be simulated in animal model with systemic administration of 3-nitropropionic acid (3-NP). Energy defects in HD could be ameliorated by administration of coenzyme Q(10) (CoQ(10)), creatine, or nicotinamid. We studied the activity of creatine kinase (CK) and the function of mitochondrial respiratory chain in the brain of aged rats administered with 3-NP with and without previous application of antioxidants CoQ(10)+vitamin E. We used dynamic and steady-state methods of in vivo phosphorus magnetic resonance spectroscopy ((31)P MRS) for determination of the pseudo-first order rate constant (k(for)) of the forward CK reaction, the phosphocreatine (PCr) to adenosinetriphosphate (ATP) ratio, intracellular pH(i) and Mg(i)(2+) content in the brain. The respiratory chain function of isolated mitochondria was assessed polarographically; the concentration of CoQ(10) and alpha-tocopherol by HPLC. We found significant elevation of k(for) in brains of 3-NP rats, reflecting increased rate of CK reaction in cytosol. The function of respiratory chain in the presence of succinate was severely diminished. The activity of cytochromeoxidase and mitochondrial concentration of CoQ(10) was unaltered; tissue content of CoQ(10) was decreased in 3-NP rats. Antioxidants CoQ(10)+vitamin E prevented increase of k(for) and the decrease of CoQ(10) content in brain tissue, but were ineffective to prevent the decline of respiratory chain function. We suppose that increased activity of CK system could be compensatory to decreased mitochondrial ATP production, and CoQ(10)+vitamin E could prevent the increase of k(for) after 3-NP treatment likely by activity of CoQ(10) outside the mitochondria. Results of our experiments contributed to elucidation of mechanism of beneficial effect of CoQ(10) administration in HD and showed that the rate constant of CK is a sensitive indicator of brain energy disorder reflecting therapeutic effect of drugs that could be used as a new in vivo biomarker of neurodegenerative diseases.

Over-expression, purification and characterization of the oligomerization dynamics of an invertebrate mitochondrial creatine kinase

Mitochondrial creatine kinase (MtCK) plays a central role in energy homeostasis within cells that display high and variable rates of ATP turnover. Vertebrate MtCKs exist primarily as octamers but readily dissociate into constituent dimers under a variety of circumstances. MtCK is an ancient protein that is also found in invertebrates including sponges, the most primitive of all multi-cellular animals. We have cloned, expressed, and purified one of these invertebrate MtCKs from a marine polychaete worm, Chaetopterus variopedatus (CVMtCK). Size exclusion chromatography and dynamic light scattering (DLS) were used to characterize oligomeric state in comparison with that of octameric chicken sarcomeric isoform (SarMtCK). At protein concentrations >1 mg/ml, CVMtCK was predominantly octameric (>90%). When diluted to 0.1 mg/ml, CVMtCK dissociated into dimers much more rapidly than SarMtCK when observed under identical conditions. The rate of dissociation for both MtCKs increased as temperature rose from 2 to 28 degrees C, and in CVMtCK, fell at higher incubation temperatures. The fraction of octameric CVMtCK at equilibrium increased with temperature and then fell. Temperature transition studies showed that octamers and dimers were rapidly interconvertible on a similar time scale. Importantly, when CVMtCK was converted to the transition state analog complex (TSAC), both size exclusion chromatography and DLS showed that there was minimal dissociation of octamers into dimers while SarMtCK octamers were highly unstable as the TSAC. These results clearly show distinct differences in octamer stability between CVMtCK and SarMtCK, which could impact function under physiological circumstances. Furthermore, the large yield of recombinant protein and high stability of CVMtCK in the TSAC suggest that this protein might be a good target for crystallization efforts.

Effects of creatine treatment on survival and differentiation of GABA-ergic neurons in cultured striatal tissue

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder, characterized by a prominent loss of GABA-ergic medium-sized spiny neurons in the caudate putamen. There is evidence that impaired energy metabolism contributes to neuronal death in HD. Creatine is an endogenous substrate for creatine kinases and thereby supports cellular ATP levels. This study investigated the effects of creatine supplementation (5 mm) on cell survival and neuronal differentiation in striatal cultures. Chronic creatine treatment resulted in significant increased densities of GABA-immunoreactive (-ir) neurons, although total neuronal cell number and general viability were not affected. Similar effects were seen after short-term treatment, suggesting that creatine acted as a differentiation factor. Inhibitors of transcription or translation did not abolish the creatine-mediated effects, nor did omission of extracellular calcium, whereas inhibition of mitogen-activated protein kinase and phosphatidylinositol-3-kinase significantly attenuated the creatine induced increase in GABA-ir cell densities. Creatine exhibited significant neuroprotection against toxicity instigated either by glucose- and serum deprivation or addition of 3-nitropropionic acid. In sum, the neuroprotective properties in combination with promotion of neuronal differentiation suggest that creatine has potential as a therapeutic drug in the treatment of neurodegenerative diseases, like HD.

Transcription of brain creatine kinase in U87-MG glioblastoma is modulated by factor AP2

Our previous studies established in U87-MG glioblastoma cells that elevated cAMP increased transcription of the endogenous as well as a transiently-transfected brain creatine kinase (CKB) gene, despite the absence of a cAMP response element (CRE) in the CKB proximal promoter. This report employed transfection to show that the transcription of CKB in U87 cells is induced by transcription factor AP2alpha, which is known to be activated by cAMP. Dominant-negative forms of AP2alpha not only prevented the AP2alpha-mediated activation of CKB but also blocked the cAMP-mediated increase in CKB transcription caused by forskolin treatment. The mutation of the four potential AP2 elements within the CKB proximal promoter showed that induction of CKB by AP2 was mediated principally through the AP2 element located at -50 bp in the promoter. Electromobility shift assays revealed a protein in U87 nuclear extracts that bound to a consensus AP2alpha element as well as to the (-50) AP2 element in CKB. Interestingly, the CKB (-50) AP2 element contains GCCAATGGG which also bound NF-Y, the CCAAT-binding protein, suggesting that interplay between AP2 and NF-Y may modulate CKB transcription. This is the first report of a role for AP2 in the regulation of CKB transcription and of an AP2 element within which an NF-Y site is located.

Expression of creatine kinase isoenzyme genes during postnatal development of rat brain cerebellum: evidence for transcriptional regulation

Transcription and accumulation of brain-type creatine kinase (CKB) mRNA and its protein was examined during postnatal development of rat brain cerebellum, the brain region containing highest CKB mRNA in the adult. CKB protein was extremely low at day 1, increased about 10-fold until week 4 and remained constant until week 10. This time course was paralleled by cerebellar CKB mRNA, which was also extremely low at day 1 and increased 5-fold during the first 3 weeks and then remained constant. High levels of CKB protein were also detected in cultured primary cerebellar granular neurons. Nuclear run-on assays directly showed that CKB mRNA accumulation during postnatal cerebellar development was due to increased transcription. When compared with cerebrum and whole brain, cerebellar CKB mRNA accumulation during postnatal development was temporally delayed. Analysis of myocyte enhancer factor (MEF)-2 and Sp1, factors known to initiate or sustain CKB transcription in tissues other than brain, revealed that MEF-2 in cerebellum was low at week 1 but increased 3.5-fold by week 7, while Sp1 remained unchanged. The increase in CKB protein during cerebellar postnatal development was coincident with that of the ubiquitous mitochondrial CK protein and mRNA, indicating that a functional phosphocreatine energy shuttle probably exists for efficient ATP regeneration in the cerebellum. This should be beneficial for the many energy-demanding requirements during cerebellar development, as indicated by the observed temporal co-expression of CKB with myelin basic protein, which is involved in axon myelination by oligodendrocytes.

Conditions providing enhanced transfection efficiency in rat pheochromocytoma PC12 cells permit analysis of the activity of the far-upstream and proximal promoter of the brain creatine kinase gene

While brain creatine kinase (CKB) is expressed at highest levels in the brain, where it functions in regenerating ATP, the gene elements and protein factors regulating CKB transcription in neuronal and glial cells have not been identified. To investigate the regulation of CKB in neuronal cells, we examined the expression of the promoter proximal and 5' far-upstream regions of the rat CKB gene transiently transfected into rat PC12 pheochromocytoma cells. Initially, these experiments were hampered by the extremely low transfection efficiency of PC12 cells. We increased efficiency by greater than 200-fold by employing CaPO4-precipitated DNA transfection into PC12 cells which were optimized for transient transfection by: (i) culturing cells in polylysine-coated dishes to insure attachment throughout transfection; (ii) exposing cells to transfected DNA for an optimal time and employing a glycerol shock; and, most importantly, (iii) dissociating the characteristic self-adhesive clumps of PC12 into mostly single cells. Use of the plasmid expressing green fluorescent protein allowed identification of the transfected cells that averaged 10-20% of the total. Analyses of CKB promoter-CAT gene constructs showed that in PC12 cells expression of the proximal (0.2 kb) CKB promoter was low while expression of the 1.4 kb promoter was three fold higher and the 2.9 kb promoter was ten fold higher, suggesting the presence of at least two upstream cis-acting, positive regulatory elements. In agreement, the steady-state CKB mRNA level was higher in PC12 than in other neuronal cell lines examined, possibly reflecting the effects of positive upstream factors. The results are discussed in relation to how this economical and straightforward transfection procedure may be useful in identify factors regulating the transcription of CKB and other genes expressed in neuronal cells.

Kinetics of cyclocreatine and Na(+) cotransport in human breast cancer cells: mechanism of activity

The growth-inhibitory effect of cyclocreatine (CCr) and the kinetics of CCr and Na(+) cotransport were investigated in MCF7 human breast cancer cells and its adriamycin-resistant subline with use of (31)P- and (23)Na-NMR spectroscopy. The growth-inhibitory effect in the resistant line occurred at a lower CCr concentration and was more pronounced than in the wild-type line. This correlated with an approximately 10-fold higher affinity of CCr to the transporter in the resistant line. The passive diffusion coefficient of CCr was also higher in the resistant line by three- to fourfold. The transport of CCr was accompanied by a rapid increase in intracellular Na(+). This increase was found to depend on the rate of CCr transport and varied differently with CCr concentration in the two cell lines. It is proposed that the cotransport of CCr and Na(+) followed by increased Na(+) concentration, together with the accumulation of the highly charged phosphocyclocreatine, are responsible for cell swelling and death.

Proximal promoter of the rat brain creatine kinase gene lacks a consensus CRE element but is essential for the cAMP-mediated increased transcription in glioblastoma cells

Our previous studies have shown that transcription of brain creatine kinase (CKB) mRNA in U87-MG glioblastoma cells is stimulated by a forskolin-mediated increase in cyclic AMP (cAMP) via a pathway involving protein kinase A (PKA) and the activation of Galphas proteins. In this report, we have employed transient transfection to investigate the rat CKB gene elements essential for the cAMP-mediated induction of rat CKB transcription in human U87 cells and have mapped the transcription start site of the induced CKB transcripts. We found that the level of induced transcription from the transfected genomic rat CKB gene was the same whether transcription was driven by 2.9 kb of CKB promoter plus 5' flanking sequence or the 0.2 kb CKB promoter, suggesting that the proximal CKB promoter was essential. Also, the level of induced transcription of the chloramphenicol acetyl transferase (CAT) reporter gene driven by the 2.9 kb CKB promoter was the same as with the 0.2 kb CKB promoter. Analyses of a series of 5' deletions of the 0.2 kb proximal CKB promoter showed that the sequences between -80 bp and +1 bp were essential for the cAMP-mediated induction of CKB transcription, despite the absence of a consensus cAMP response element (CRE) sequence in that region. In agreement, gel mobility shift assays showed that nuclear extracts from U87 cells contained a protein(s) which bound specifically to a [32P]CKB DNA probe containing the -60 bp to +1 bp sequence. Mapping the 5' end of the CKB transcripts showed that the initiation of the cAMP-induced transcription occurred almost exclusively from the downstream transcription start site, apparently under the initiation direction of the nonconsensus (-28) TTAA element and not the consensus (-60) TATAAATA element. The results are discussed with regard to nuclear protein factors which may be involved, and the possible cAMP-mediated increase in CKB transcription during myelinogenesis, since the differentiation of oligodendrocytes has previously been shown to be accelerated by increased intracellular cAMP.

Oligomeric state and membrane binding behaviour of creatine kinase isoenzymes: implications for cellular function and mitochondrial structure

The membrane binding properties of cytosolic and mitochondrial creatine kinase isoenzymes are reviewed in this article. Differences between both dimeric and octameric mitochondrial creatine kinase (Mi-CK) attached to membranes and the unbound form are elaborated with respect to possible biological function. The formation of crystalline mitochondrial inclusions under pathological conditions and its possible origin in the membrane attachment capabilities of Mi-CK are discussed. Finally, the implications of these results on mitochondrial energy transduction and structure are presented.

Amyloid beta-peptide (1-40)-mediated oxidative stress in cultured hippocampal neurons. Protein carbonyl formation, CK BB expression, and the level of Cu, Zn, and Mn SOD mRNA

Mechanism of amyloid beta-peptide (A beta) toxicity in cultured neurons involves the development of oxidative stress in the affected cells. A significant increase in protein carbonyl formation was detected in cultured hippocampal neurons soon after the addition of preaggregated A beta(1-40), indicating oxidative damage of proteins. We report that neurons, subjected to A beta(1-40), respond to A beta oxidative impact by activation of antioxidant defense mechanisms and alternative ATP-regenerating pathway. The study demonstrates an increase of Mn SOD gene expression and the restoration of Cu, Zn SOD gene expression to a normal level after temporary suppression. Partial loss of creatine kinase (CK) BB activity, which is the key enzyme for functioning of the creatine/phosphocreatine shuttle, was compensated in neurons surviving the A beta oxidative attack by increased production of the enzyme. As soon as the oxidative attack triggered by the addition of preaggregated A beta (1-40) to rat hippocampal cell cultures has been extinguished, CK BB expression and SOD isoenzyme-specific mRNA levels in surviving neurons return to normal. We propose that the maintenance of a constant level of CK function by increased CK BB production together with the induction of antioxidant enzyme gene expression in A beta-treated hippocampal neurons accounts for at least part of their adaptation to A beta toxicity.

The expression of creatine kinase isoenzymes in neocortex of patients with neurodegenerative disorders: Alzheimer's and Pick's disease

Creatine kinase (CK) activity was found decreased in the brains of patients with Alzheimer's disease (AD) and Pick's disease (PD). However, the decrease of total CK activity in AD was more pronounced than in PD. Analysis of the activity of two CK isoforms, BCK and ubiquitous mitochondrial CK, demonstrated that the decrease of total CK activity in AD and PD was related to the decrease of BCK activity. The decline of CK activity both in AD and PD correlated well with the decline of the content of immunoreactive BCK in brain extracts. The BCK mRNA level in AD and PD was not significantly different from control patients and could not be the primary reason for decreases in CK content and activity. The decreased level of BCK in AD and PD brains might be caused by posttranscriptional events, which could affect the translation of BCK mRNA and/or lead to the inactivation and degradation of the enzyme. Because CK is sensitive to oxidative modification, it is possible that the changes observed in this study result from free radical damage.

Transcription of the brain creatine kinase gene in glial cells is modulated by cyclic AMP-dependent protein kinase

The brain creatine kinase (CKB) gene is expressed in a variety of tissues with highest expression seen in the brain. We have previously shown in primary rat brain cell cultures that CKB mRNA levels are high in oligodendrocytes and astrocytes and low in neurons (Molloy et al.: J Neurochem 59:1925-1932, 1992). In this report we show that treatment of human U87 glioblastoma cells with forskolin and IBMX, to elevate intracellular cAMP, induces expression of CKB mRNA from the transiently transfected rat CKB gene by 14-fold and also increases expression from the endogenous human CKB gene. This induction of CKB mRNA i) is due to increased transcription; ii) occurs rapidly (with maximal induction after 6 hr; iii) requires the activity of protein kinase A (PKA), but iv) does not require de novo protein synthesis and, in fact, is superinduced in the presence of cycloheximide. Given the role of oligodendrocytes in the energy-demanding process of myelination and of astrocytes in ion transport, these results have physiological significance, since they suggest that changes in cellular energy requirements in the brain during events, such as glial cell differentiation and increased neuronal activity, may in part be met by a cAMP-mediated modulation of CKB gene expression. Of particular importance is the possible modulation of CKB gene expression during myelinogenesis, since oligodendrocyte differentiation has been shown previously to be stimulated by increases in cAMP.

Compartmentation of ATP synthesis and utilization in smooth muscle: roles of aerobic glycolysis and creatine kinase

The phosphocreatine content of smooth muscle is of similar magnitude to ATP. Thus the function of the creatine kinase system in this tissue cannot simply be regarded as an energy buffer. Thus an understanding of its role in smooth muscle behavior can point to CK function in other systems. From our perspective CK function in smooth muscle is one example of a more general phenomenon, that of the co-localization of ATP synthesis and utilization. In an interesting and analogous fashion distinct glycolytic cascades are also localized in regions of the cell with specialized energy requirements. Similar to CK, glycolytic enzymes are known to be localized on thin filaments, sarcoplasmic reticulum and plasma membrane. In this chapter we will describe the relations between glycolysis and smooth muscle function and compare and contrast to that of the CK system. Our goal is to more fully understand the significance of the compartmentation of distinct pathways for ATP synthesis with specific functions in smooth muscle. This organization of metabolism and function seen most clearly in smooth muscle is likely representative of many other cell types.

Creatine kinase in non-muscle tissues and cells

Over the past years, a concept for creatine kinase function, the 'PCr-circuit' model, has evolved. Based on this concept, multiple functions for the CK/PCr-system have been proposed, such as an energy buffering function, regulatory functions, as well as an energy transport function, mostly based on studies with muscle. While the temporal energy buffering and metabolic regulatory roles of CK are widely accepted, the spatial buffering or energy transport function, that is, the shuttling of PCr and Cr between sites of energy utilization and energy demand, is still being debated. There is, however, much circumstantial evidence, that supports the latter role of CK including the distinct, isoenzyme-specific subcellular localization of CK isoenzymes, the isolation and characterization of functionally coupled in vitro microcompartments of CK with a variety of cellular ATPases, and the observed functional coupling of mitochondrial oxidative phosphorylation with mitochondrial CK. New insight concerning the functions of the CK/PCr-system has been gained from recent M-CK null-mutant transgenic mice and by the investigation of CK localization and function in certain highly specialized non-muscle tissues and cells, such as electrocytes, retina photoreceptor cells, brain cells, kidney, salt glands, myometrium, placenta, pancreas, thymus, thyroid, intestinal brush-border epithelial cells, endothelial cells, cartilage and bone cells, macrophages, blood platelets, tumor and cancer cells. Studies with electric organ, including in vivo 31P-NMR, clearly reveal the buffer function of the CK/PCr-system in electrocytes and additionally corroborate a direct functional coupling of membrane-bound CK to the Na+/K(+)-ATPase. On the other hand, experiments with live sperm and recent in vivo 31P-NMR measurements on brain provide convincing evidence for the transport function of the CK/PCr-system. We report on new findings concerning the isoenzyme-specific cellular localization and subcellular compartmentation of CK isoenzymes in photoreceptor cells, in glial and neuronal cells of the cerebellum and in spermatozoa. Finally, the regulation of CK expression by hormones is discussed, and new developments concerning a connection of CK with malignancy and cancer are illuminated. Most interesting in this respect is the observed upregulation of CK expression by adenoviral oncogenes.

Rat brain creatine kinase messenger RNA levels are high in primary cultures of brain astrocytes and oligodendrocytes and low in neurons

Rat brain creatine kinase (CKB) gene expression is highest in the brain but is also detectable at lower levels in some other tissues. In the brain, the CKB enzyme is thought to be involved in the regeneration of ATP necessary for transport of ions and neurotransmitters. To understand the molecular events that lead to high CKB expression in the brain, we have determined the steady-state levels of CKB mRNA in homogeneous cultures of primary rat brain astrocytes, oligodendrocytes, and neurons. Northern blot analysis showed that whereas the 1.4-kb CKB mRNA was detectable in neurons, the level was about 17-fold higher in oligodendrocytes and 15-fold higher in astrocytes. The blots were hybridized with a CKB-specific 32P-antisense RNA probe, complementary to the 3' untranslated sequence of CKB, which hybridizes to CKB mRNA but not CKM mRNA. Also, the 5' and 3' ends of CKB mRNA from the glial cells were mapped, using exon-specific antisense probes in the RNase-protection assay, and were found to be the same in astrocytes and oligodendrocytes. This indicated that (a) the site of in vivo transcription initiation in astrocytes and oligodendrocytes was directed exclusively by the downstream, nonconcensus TTAA sequence at -25 bp in the CKB promoter that is also utilized by all other cell types that express CKB and (b) the 3' end of mature CKB mRNA was the same in astrocytes and oligodendrocytes. In addition, there was no detectable alternate splicing in exon 1, 2, or 8 of CKB mRNA in rat astrocytes and oligodendrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular compartmentation, structure and function of creatine kinase isoenzymes in tissues with high and fluctuating energy demands: the 'phosphocreatine circuit' for cellular energy homeostasis

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Identification of creatine kinase isoenzymes in the guinea-pig. Presence of mitochondrial creatine kinase in smooth muscle

Isoenzymes of creatine kinase (CK, EC 2.7.3.2) in guinea-pig smooth, cardiac and skeletal muscles as well as in brain were analyzed by cellulose acetate electrophoresis and FPLC gel permeation chromatography. In crude tissue extracts of smooth muscles brain type BB-CK and the hybrid form MB-CK were detected, but in enriched mitochondrial fractions from different guinea-pig smooth muscles, mitochondrial type Mi-CK was unambiguously identified. Smooth muscle Mi-CK displayed the same electrophoretic mobility as Mi-CK from brain, which migrates slower than cardiac Mi-CK. Identical to parallel experiments with Mi-CK from cardiac muscle and brain, smooth muscle Mi-CK could be resolved into dimeric and octameric species, the latter being remarkably stable. In contrast to guinea-pig smooth muscles, Mi-CK was not detected in chicken gizzard tissue extracts nor in enriched mitochondrial fractions thereof. The presence of Mi-CK, predominantly in octameric form, in guinea-pig smooth muscles, but not in chicken gizzard, may represent a clue for the different physiological properties of these muscles and may provide the molecular basis for the dependence of the PCr production on oxidative metabolism observed in the guinea-pig taenia caeci.

Differential expression and localization of brain-type and mitochondrial creatine kinase isoenzymes during development of the chicken retina: Mi-CK as a marker for differentiation of photoreceptor cells

The expression and the cellular- as well as subcellular-distribution of brain-type B-CK and mitochondrial Mi-CK during development of the chicken retina was studied by immunoblotting, immunofluorescence and immunogold methods. B-CK expression and accumulation in retina was high from early stages of embryonic development on, decreased slightly around hatching and remained high again during adulthood. At early stages of development (days 2-5), B-CK was more or less evenly distributed over the entire retina with the exception of ganglion cells, which were stained more strongly for B-CK than other retinal precursor cells. Then, at around day 10, the beginning of stratified immunostaining by anti-B-CK antibody was noted concomitant with progressing differentiation. Finally, a dramatic increase in staining of the differentiating photoreceptor cells was seen before hatching (day 18) with weaker staining of other cell types. At hatching, as in the adult state, most of the B-CK was localized within rods and cones. Thus, during retinal development marked changes in the immunostaining pattern for B-CK were evident. By contrast, Mi-CK expression was low during development in ovo and rose just before hatching with a predominant accumulation of this isoenzyme within the ellipsoid portion of the inner photoreceptor cell segments. Mi-CK accumulation in the retina coincided with functional maturation of photoreceptors and therefore represents a good marker for terminal differentiation of these cells. B-CK, present from early stages of retina development, seems to be relevant for the energetics of retinal cell proliferation, migration and differentiation, whereas the simultaneous expression of both B- and Mi-CK around the time of hatching indicates a coordinated function of the two CK isoforms as constituents of a PCr-circuit involved in the energetics of vision, which, in autophagous birds, has to be operational at this point in time.

Phosphorylation of chicken brain-type creatine kinase affects a physiologically important kinetic parameter and gives rise to protein microheterogeneity in vivo

In addition to the two monomer subunits of chicken brain-type creatine kinase (B-CK, EC, 2.7.3.2), termed Bb (basic) and Ba (acidic), another subspecies called Bb* was identified by chromatofocussing in the presence of 8 M urea (Quest et al., ). The latter low abundance protein species, isolated from tissue extracts, comigrated on 2D-gels with three minor species (Bb1-3), initially identified in immunoprecipitated, [35S]methionine labeled in vitro translation products of cDNA coding for the basic monomer Bb. During in vitro translation experiments in the presence of [32P]-gamma-ATP, Bb1-3 were labeled while phosphatase treatment eliminated these minor species. It is concluded that Bb* is identical to Bb1-3 and represents phosphorylated derivatives of Bb. B-CK dimer populations from different tissues were separated by ion-exchange chromatography and the Km values of the resulting fractions were determined under phospho-creatine (CP)-limiting conditions. In fractions containing only Bb and Bb* two kinetically different enzyme species were detected (Km values for CP = 1.6 mM and 0.8 mM), while fractions containing B-CK dimers composed of the major Ba and Bb monomers, but no Bb*, were homogeneous in this respect (Km for CP = 1.6 mM). Phosphorylation of Bb to yield Bb* is concluded to reduce the Km of B-CK dimers for CP by about 50%. This Km shift is within the range of CP concentrations found in tissues expressing the B-CK isoform and may therefore be of physiological relevance.

Two different B-type creatine kinase subunits dimerize in a tissue-specific manner

Brain-type creatine kinase B-CK (EC 2.7.3.2) was purified from several chicken tissues, e.g. cardiac muscle, brain, gizzard and retina. Two major monomeric chicken B-CK subunits, designated Bb (basic) and Ba (acidic), which differ in isoelectric point, were separated by chromatofocusing in the presence of 8 M urea on a MonoP column. The two subunits were shown by peptide mapping, amino acid analysis and partial sequencing, as well as by immunological criteria, to be distinct B-CK polypeptides. The N-terminal sequence of 30 amino acid residues of Bb correspond entirely to data derived from a B-CK c-DNA clone termed H4 [(1986) Nucleic Acids Res. 14, 1449-1463], whereas the N-terminus of the acidic Ba species was blocked. Native dimeric B-CK isoenzymes obtained from these tissues were separated by ion exchange chromatography on a MonoQ column yielding two B-CK dimer populations, type-I and type-II B-CK, varying in relative proportions. Quantitation of the CK activity peak ratios of these two populations revealed the existence of a tissue-specific, post-translational mechanism regulating B-CK dimerization in neural tissues. Tissue-specific dimerization of the two distinct B-CK monomer species may represent a means of specifying the intracellular distribution of the dimeric B-CK subspecies.

The upstream muscle-specific enhancer of the rat muscle creatine kinase gene is composed of multiple elements

A series of constructs that links the rat muscle creatine kinase promoter to the bacterial chloramphenicol acetyltransferase gene was generated. These constructs were introduced into differentiating mouse C2C12 myogenic cells to localize sequences that are important for up-regulation of the creatine kinase gene during myogenic differentiation. A muscle-specific enhancer element responsible for induction of chloramphenicol acetyltransferase expression during myogenesis was localized to a 159-base-pair region from 1,031 to 1,190 base pairs upstream of the transcription start site. Analysis of transient expression experiments using promoters mutated by deletion indicated the presence of multiple functional domains within this muscle-specific regulatory element. A DNA fragment spanning this region was used in DNase I protection experiments. Nuclear extracts derived from C2 myotubes protected three regions (designated E1, E2, and E3) on this fragment from digestion, which indicated there may be three or more trans-acting factors that interact with the creatine kinase muscle enhancer. Gel retardation assays revealed that factors able to bind specifically to E1, E2, and E3 are present in a wide variety of tissues and cell types. Transient expression assays demonstrated that elements in regions E1 and E3, but not necessarily E2, are required for full enhancer activity.

The upstream muscle-specific enhancer of the rat muscle creatine kinase gene is composed of multiple elements

A series of constructs that links the rat muscle creatine kinase promoter to the bacterial chloramphenicol acetyltransferase gene was generated. These constructs were introduced into differentiating mouse C2C12 myogenic cells to localize sequences that are important for up-regulation of the creatine kinase gene during myogenic differentiation. A muscle-specific enhancer element responsible for induction of chloramphenicol acetyltransferase expression during myogenesis was localized to a 159-base-pair region from 1,031 to 1,190 base pairs upstream of the transcription start site. Analysis of transient expression experiments using promoters mutated by deletion indicated the presence of multiple functional domains within this muscle-specific regulatory element. A DNA fragment spanning this region was used in DNase I protection experiments. Nuclear extracts derived from C2 myotubes protected three regions (designated E1, E2, and E3) on this fragment from digestion, which indicated there may be three or more trans-acting factors that interact with the creatine kinase muscle enhancer. Gel retardation assays revealed that factors able to bind specifically to E1, E2, and E3 are present in a wide variety of tissues and cell types. Transient expression assays demonstrated that elements in regions E1 and E3, but not necessarily E2, are required for full enhancer activity.

Identification of a novel TA-rich DNA binding protein that recognizes a TATA sequence within the brain creatine kinase promoter

The rat brain creatine kinase gene possesses a structurally complex promoter with multiple potential regulatory elements. Two CCAAT sequences, a TATAAATA sequence and a TTAA sequence are found within the first one hundred base pairs. We present evidence that favors the allocation of the downstream TTAA sequence as the potential TATA box. We show that the CCAAT sequences and the upstream TATAAATA sequence are binding sites for potential regulatory factors and that sequences in this region are capable of regulating expression from the downstream TTAA sequence. We suggest that the protein that binds to the upstream TATAAATA sequence is not a classical TFIID factor but rather may serve to block the binding of TFIID and/or to promote transcription from the downstream start site. We have been able to define conditions in vitro under which binding to this upstream TATAAATA sequence does not occur. Under these conditions we are able to detect transcription from both potential TATA sequences, a situation which we have been unable to detect in vivo. Our experiments suggest the existence in HeLa and brain nuclei of a protein that recognizes the concensus TATAAATA sequence, that is distinct from TFIID, and that may function in part to deny access of TFIID to this potential promoter element.

Localization of brain type creatine kinase in kidney epithelial cell subpopulations in rat

Immunoperoxidase studies of rat kidney using antibody to brain type isoenzyme of creatine kinase (BB) revealed a specific staining in the epithelial cells of the thick ascending limb of the Henle's loop and collecting tubule. Occasional epithelial cells in cortical tubules that lack brush border were also positive for BB. Renal glomeruli and proximal tubules showed no immunoreactivity to this enzyme.

Isolation of four rat creatine kinase genes and identification of multiple potential promoter sequences within the rat brain creatine kinase promoter region

Rat genes encoding muscle creatine kinase (gene ckm) and brain creatine kinase (gene ckb) have been cloned. The two genes have an identical intron-exon distribution, although introns of the ckb gene are much smaller than those for ckm. The complete nucleotide sequence has been determined for the ckb gene. 5'-Flanking sequences have been compared for both ckm and ckb. The ckb gene has a structurally complex 5'-flanking region with multiple TATA and CAAT sequences suggesting that the gene may contain overlapping promoter elements. Examination of ckb RNA from brain tissue provides no evidence for the existence of more than one set of transcriptional start points. The ckm and ckb genes show little homology in the 5'-flanking regions, although we observed some sequence conservation in the regions immediately surrounding the CAAT and TATA sequences. The rat genome also contains two other creatine kinase-like sequences which may represent processed pseudogenes or mitochondrial creatine kinase.

Creatine kinase immunoreactivity: localization in nerve terminals in the hypothalamic area and superior colliculus of the mouse brain

Immunoperoxidase studies of mouse brain using antibody to creatine kinase (CK) revealed the presence of immunoreactive neuronal varicosities in the zona incerta, lateral hypothalamic area, arcuate nucleus and superior colliculus. In the zona incerta and lateral hypothalamic area, the varicosities were distributed among the distinctive CK-immunoreactive neurons and some varicosities apparently emerged from these neurons. In the arcuate nucleus, the varicosities were concentrated in the periventricular region and occasionally clustered around unstained neurons. In serial sections, a portion of varicosities could be traced from the lateral hypothalamic area to the arcuate nucleus. In the superior colliculus, CK immunoreactivity formed a network pattern, which was mainly confined to the stratum zonale and stratum griseum superficiale.

Energy metabolism and quantal acetylcholine release: effects of botulinum toxin, 1-fluoro-2,4-dinitrobenzene, and diamide in the Torpedo electric organ

In the Torpedo electric organ, a modified nerve-muscle system, type A botulinum toxin blocked the release of acetylcholine (ACh) quanta, both neurally evoked and spontaneous. At the same time, the toxin increased the release of a class of small miniature potentials (the subminiature potentials), reduced the ATP and more the creatine phosphate content of the tissue, and impaired the activity of creatine kinase (CK). Thus, we compared this pattern of changes with those provoked by 1-fluoro-2,4-dinitrobenzene (FDNB), an efficient inhibitor of CK. As expected, FDNB rapidly inactivated CK, which resulted in a profound depletion of ATP whereas the stores of creatine phosphate were preserved. In addition, FDNB caused conspicuous morphological alterations of nerve endings and ACh depletion. This agent also suppressed evoked and spontaneous quantal release whereas the occurrence of subminature potentials was markedly increased. Diamide, a penetrating thiol oxidizing substance, provoked first a transient rise in quantal ACh release and then blockade of transmission with, again, production of a large number of subminiature potentials. Creatine phosphate was depleted in the tissue by diamide, the ATP content reduced, and CK activity partly inhibited. The morphology of nerve terminals did not show obvious changes with either diamide or botulinum toxin at the stage of transmission failure. Although the three poisons acted by different mechanisms, this resulted in a rather similar pattern of physiological changes: failure of quantal release and enhancement of subquantal release. These results and experiments on synaptosomes indicated that CK inhibition was probably a crucial mechanism for FDNB but not for diamide or botulinum intoxication.(ABSTRACT TRUNCATED AT 250 WORDS)

Botulinum toxin inhibits quantal acetylcholine release and energy metabolism in the Torpedo electric organ

1. Type A Botulinum toxin (BoTX) blocked nerve-electroplaque transmission in small fragments of Torpedo marmorata electric organ incubated in vitro. The effect was observed either with the crystalline toxin complex (associated with haemagglutinin) or with the purified neurotoxin (molecular weight approximately 150,000). 2. The quantal content of the evoked post-synaptic response was reduced by BoTX but the quantum size remained unchanged till complete blockade of the evoked response. 3. Spontaneous electroplaque potentials were composed of two populations: one with a bell-shaped amplitude distribution (miniature potentials or quanta) and a population of small events with a skewed distribution (subminiatures). In BoTX-poisoned tissue, the bell-distributed miniatures progressively disappeared, but the subminiatures kept on occurring. Occasionally, larger spontaneous potentials with a slow time course were recorded; they were also BoTX resistant. 4. A biochemical assay showed that evoked acetylcholine (ACh) release was impaired by BoTX. During the period when evoked transmission was blocked, spontaneous ACh release transiently increased. 5. At the time of transmission blockade, there was no significant change of ACh content, of ACh turnover, of ACh repartition in the vesicle-bound and free compartments, or of the number of synaptic vesicles. 6. The amount of ATP was reduced to 50% by BoTX, and that of creatine phosphate (CrP) to less than 20%. The ATP-CrP-converting enzyme, creatine kinase, was inhibited in BoTX-poisoned tissue. 7. Thus, the electrophysiological effects of BoTX are very similar at the nerve-electroplaque and the neuromuscular junctions. The present work suggests in addition that suppression of quantal release by BoTX is related to marked alterations of the energy metabolism in the tissue.

Isolation and sequence analysis of a full-length cDNA for human M creatine kinase

A full length cDNA for human M creatine kinase has been isolated and sequenced. The cDNA contains 77 bp of 5' untranslated, 338 bp of 3' untranslated sequence and the entire coding region (1146 bp) for human M creatine kinase. The M creatine kinases from different species share considerable sequence homology within the coding region (77-91%) and in amino acid sequence (82-97%). Little or no sequence homology is observed in the 3' untranslated sequence of the mammalian M creatine kinases, although canine and human creatine kinase share overall 80% sequence homology in 5' untranslated sequence. A unique 8 bp sequence was identified in the 5' untranslated regions of mammalian M creatine kinase but is not present in B creatine kinase cDNA. The degree of sequence conservation observed implies an evolutionary constraint on M creatine kinase structure beyond that which would be expected for the maintenance of enzymatic function.

High content of creatine kinase in chicken retina: compartmentalized localization of creatine kinase isoenzymes in photoreceptor cells

Two isoforms of creatine kinase (CK; ATP:creatine N-phosphotransferase, E.C. 2.7.3.2), brain type (BB-CK) and mitochondrial type (MiMi-CK), but not the muscle types (MM- or hybrid MB-CK), were identified by cellulose polyacetate electrophoresis and immunoblots in retina from adult chickens. Indirect immunofluorescence labeling of cryosections of retinas revealed high concentrations of BB-CK in both rod and cone photoreceptor cells. Most of the fluorescence staining with anti-B-CK antibodies was found within the myoid and the ellipsoid portions of inner segments and the peripheral region of the outer segments. Significant staining with anti-B-CK antibodies was also found in horizontal cells and in the optical nerve fibers, with additional stratified staining in the inner plexiform layer. MiMi-CK was solely demonstrated in the ellipsoid portion of the photoreceptor cells. The presence of high concentrations of compartmentalized CK isoenzymes within photoreceptor cells (approximately equal to 30 enzyme units/mg) as well as the relatively high concentration of total creatine in these cells (approximately equal to 10-15 mM) indicates an important physiological function for CK and phosphocreatine in the energy transduction of vision.

Creatine kinase isoenzymes in Torpedo californica: absence of the major brain isoenzyme from nicotinic acetylcholine receptor membranes

Creatine kinase, actin, and nu 1 are three proteins of Mr 43 000 associated with membranes from electric organ highly enriched in nicotinic acetylcholine receptor. High levels of creatine kinase are required to maintain adequate ATP levels, while actin may play a role in maintaining the synaptic cytoskeleton. Previous investigations have prompted the conclusion that postsynaptic specializations at the receptor-enriched membrane domains in electroplax contain the brain form of creatine kinase rather than the form of creatine kinase predominantly found in muscle. We have examined this conclusion by purifying Torpedo brain creatine kinase to virtual homogeneity in order to examine its immunochemical, molecular, and electrophoretic properties. On the basis of immunological cross-reactivity and isozyme analysis, the receptor-associated creatine kinase is identified to be of the muscle type. When the molecular characteristics of Torpedo brain and muscle creatine kinase are compared, the brain enzyme is positioned at a more basic pH during chromatofocusing and on two-dimensional gel electrophoresis (pI = 7.5-7.9). Furthermore, electrophoretic mobilities of the brain and muscle forms of creatine kinase differ in sodium dodecyl sulfate electrophoresis: the brain isozyme of creatine kinase has lower apparent molecular weight (Mr 41 000) when compared with the muscle enzyme (Mr 43 000). On the basis of the results of our current investigations, the hypothesis that the brain isozyme of creatine kinase is a component of the postsynaptic specializations of the Torpedo californica electroplax must be abandoned. Recent sequence data have established close homology between Torpedo and mammalian muscle creatine kinases. On the basis of electrophoretic criteria, our results indicate that a lower degree of homology exists between the brain isozymes.