Isozymes of creatine kinase in mammalian cell cultures

Fam96b recruits brain-type creatine kinase to fuel mitotic spindle formation

Mitosis is a complicated and ordered process with high energy demands and metabolite fluxes. Cytosolic creatine kinase (CK), an enzyme involved in ATP homeostasis, has been shown to be essential to chromosome movement during mitotic anaphase in sea urchin. However, it remains elusive for the molecular mechanism underlying the recruitment of cytosolic CK by the mitotic apparatus. In this study, Fam96b/MIP18, a component of the MMXD complex with a function in Fe/S cluster supply, was identified as a brain-type CK (CKB)-binding protein. The binding of Fam96b with CKB was independent of the presence of CKB substrates and did not interfere with CKB activity. Fam96b was prone to oligomerize via the formation of intermolecular disulfide bonds, while the binding of enzymatically active CKB could modulate Fam96b oligomerization. Oligomerized Fam96b recruited CKB and the MMXD complex to associate with the mitotic spindle. Depletion of Fam96b or CKB by siRNA in the HeLa cells led to mitotic defects, which further resulted in retarded cell proliferation, increased cell death and aberrant cell cycle progression. Rescue experiments indicated that both Fam96b oligomerization and CKB activity were essential to the proper formation of mitotic spindle. These findings suggest that Fam96b may act as a scaffold protein to coordinate the supply and homeostasis of ATP and Fe/S clusters during mitosis.

Creatine kinase in cell cycle regulation and cancer

The phosphocreatine-creatine kinase (CK) shuttle system is increasingly recognized as a fundamental mechanism for ATP homeostasis in both excitable and non-excitable cells. Many intracellular processes are ATP dependent. Cell division is a process requiring a rapid rate of energy turnover. Cell cycle regulation is also a key point to understanding the mechanisms underlying cancer progression. It has been known for about 40 years that aberrant CK levels are associated with various cancers and for over 30 years that CK is involved in mitosis regulation. However, the underlying molecular mechanisms have not been investigated sufficiently until recently. By maintaining ATP at sites of high-energy demand, CK can regulate cell cycle progression by affecting the intracellular energy status as well as by influencing signaling pathways that are essential to activate cell division and cytoskeleton reorganization. Aberrant CK levels may impair cell viability under normal or stressed conditions and induce cell death. The involvement of CK in cell cycle regulation and cellular energy metabolism makes it a potential diagnostic biomarker and therapeutic target in cancer. To understand the multiple physiological/pathological functions of CK, it is necessary to identify CK-binding partners and regulators including proteins, non-coding RNAs and participating endogenous small molecular weight chemical compounds. This review will focus on molecular mechanisms of CK in cell cycle regulation and cancer progression. It will also discuss the implications of recent mechanistic studies, the emerging problems and future challenges of the multifunctional enzyme CK.

Reduced creatine kinase as a central and peripheral biomarker in Huntington's disease

A major goal of current clinical research in Huntington's disease (HD) has been to identify preclinical and manifest disease biomarkers, as these may improve both diagnosis and the power for therapeutic trials. Although the underlying biochemical alterations and the mechanisms of neuronal degeneration remain unknown, energy metabolism defects in HD have been chronicled for many years. We report that the brain isoenzyme of creatine kinase (CK-BB), an enzyme important in buffering energy stores, was significantly reduced in presymptomatic and manifest disease in brain and blood buffy coat specimens in HD mice and HD patients. Brain CK-BB levels were significantly reduced in R6/2 mice by approximately 18% to approximately 68% from 21 to 91 days of age, while blood CK-BB levels were decreased by approximately 14% to approximately 44% during the same disease duration. Similar findings in CK-BB levels were observed in the 140 CAG mice from 4 to 12 months of age, but not at the earliest time point, 2 months of age. Consistent with the HD mice, there was a grade-dependent loss of brain CK-BB that worsened with disease severity in HD patients from approximately 28% to approximately 63%, as compared to non-diseased control patients. In addition, CK-BB blood buffy coat levels were significantly reduced in both premanifest and symptomatic HD patients by approximately 23% and approximately 39%, respectively. The correlation of CK-BB as a disease biomarker in both CNS and peripheral tissues from HD mice and HD patients may provide a powerful means to assess disease progression and to predict the potential magnitude of therapeutic benefit in this disorder.

The neuroprotective role of creatine

Significant progress has been made in identifying neuroprotective agents and their translation to patients with neurological disorders. While the direct causative pathways of neurodegeneration remain unclear, they are under great clinical and experimental investigation. There are a number of interrelated pathogenic mechanisms triggering molecular events that lead to neuronal death. One putative mechanism reported to play a prominent role in the pathogenesis of neurological diseases is impaired energy metabolism. If reduced energy stores play a role in neuronal loss, then therapeutic strategies that buffer intracellular energy levels may prevent or impede the neurodegenerative process. Recent studies suggest that impaired energy production promotes neurological disease onset and progression. Sustained ATP levels are critical to cellular homeostasis and may have both direct and indirect influence on pathogenic mechanisms associated with neurological disorders. Creatine is a critical component in maintaining cellular energy homeostasis, and its administration has been reported to be neuroprotective in a wide number of both acute and chronic experimental models of neurological disease. In the context of this chapter, we will review the experimental evidence for creatine supplementation as a neurotherapeutic strategy in patients with neurological disorders, including Huntington's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Alzheimer's disease, as well as in ischemic stroke, brain and spinal cord trauma, and epilepsy.

The therapeutic role of creatine in Huntington's disease

Huntington's disease (HD) is an autosomal dominant and fatal neurological disorder characterized by a clinical triad of progressive choreiform movements, psychiatric symptoms, and cognitive decline. HD is caused by an expanded trinucleotide CAG repeat in the gene coding for the protein huntingtin. No proven treatment to prevent the onset or to delay the progression of HD currently exists. While a direct causative pathway from the gene mutation to the selective neostriatal neurodegeneration remains unclear, it has been hypothesized that interactions of the mutant huntingtin protein or its fragments may result in a number of interrelated pathogenic mechanisms triggering a cascade of molecular events that lead to the untimely neuronal death observed in HD. One putative pathological mechanism reported to play a prominent role in the pathogenesis of HD is mitochondrial dysfunction and the subsequent reduction of cellular energy. Indeed, if mitochondrial impairment and reduced energy stores play roles in the neuronal loss in HD, then a therapeutic strategy that buffers intracellular energy levels may ameliorate the neurodegenerative process. Sustained ATP levels may have both direct and indirect importance in ameliorating the severity of many of the pathogenic mechanisms associated with HD. Creatine, a guanidino compound produced endogenously and acquired exogenously through diet, is a critical component in maintaining much needed cellular energy. As such, creatine is one of a number of ergogens that may provide a relatively safe and immediately available therapeutic strategy to HD patients that may be the cornerstone of a combined treatment necessary to delay the relentless progression of HD.

Variations of muscle mitochondrial creatine kinase activity in mitochondrial diseases

Mitochondrial creatine kinase (mtCK) activity has been measured in the mitochondria isolated from the muscle of 69 patients suspected of mitochondrial diseases. The isolated mitochondria did not contain significant amounts of the muscle isoform of creatine kinase, as checked by an immunoassay performed after electrophoretic separation of the various isoforms. Hence, the enzyme assay reliably represented the mtCK activity. Therefore, a simple measurement of CK activity in isolated mitochondria permitted the measurement of mtCK activity. An absence of mtCK activity in muscle was never observed. The lowest activities were not associated to defined mitochondrial diseases linked to defects of respiratory chain complexes or to defects of citric cycle enzymes. On the contrary, mtCK activity was significantly increased in the muscle of patients exhibiting ragged red fibers. This increase was generally associated to an increase of citrate synthase activity. Since ragged-red fibers and elevated mtCK activities were generally not found in children younger than 3 years, even in cases of characteristic oxidative phosphorylation deficiency, it is suggested that the increase in mtCK activity as well as the appearance of ragged-red fibers are not the first events which occur during the evolution of mitochondrial diseases but would rather be long-term secondary processes which slowly develop in deficient mitochondria.

Thyroxine-induced redistribution of creatine kinase isoenzymes in rat cardiomyocyte cultures

The present study demonstrates a change occurring in the creatine-kinase isoenzyme profile of cardiomyocyte cultures induced by a chronic administration of excessive amounts of thyroid hormones (TH). This change is manifested by an increased level of the CK-BB isoenzyme, generally at the expense of CK-MM isoenzyme. The elevation of CK-BB is probably a result of a specific effect of TH through activation of gene expression, rather than a contribution of an increased number of non-myocardial cells. The implications of these results in the diagnosis of heart failures are discussed.

Cultured heart cell reaggregates: a model for studying relationships between aging and lipid composition

Cultured heart cells serve as a common model for studying the electronphysiology and pharmacology of intact cells of the myocardium from which they are derived (Sperelakis, N. (1982) in Cardiovascular Toxicology (Van Stel, E.W., ed.), pp. 57-108, Raven Press, New York). In this study, heart cell reaggregates were used for investigating the relationship between lipid composition and aging of the heart cells. Spherical reaggregates were prepared from newborn, 3- and 18-month-old rats, respectively. They were grown for 6 days in culture and then analyzed for their lipid composition and creatine phosphokinase levels. There was an age-related increase in total phospholipids and cholesterol level per unit of cell protein. Due to a relatively greater increase in the cholesterol, the mole ratio of cholesterol to phospholipids increased with animal age. The phospholipid composition was also affected. Thus, sphingomyelin levels increased, while those of phosphatidylcholine decreased; these alterations became much more pronounced with increasing animal age. All these changes could be affected by adding small unilamellar vesicles composed of egg phosphatidylcholine to the growth medium on the 5th day after seeding. Such treatment resulted in a lesser ratio of cholesterol to phospholipid as well as sphingomyelin to phosphatidylcholine, without reducing the total phospholipid per unit protein; the level of creatine phosphokinase was also reduced. This study demonstrated that cultured heart reaggregates can serve as a model for studying aging of the whole animal. Its main advantage is the ability to employ cells from rats of any desired age. Currently this is not possible for cultured heart monolayers.

Insulin-independent controlled physiological morphogenesis of chick muscle from fusion-capable myoblasts

Thigh myogenic cells from 11-12-day-old chick embryos were cultured continuously in the presence of medium containing no chick embryo extract (CEE). It is known that CEE contains a muscle-inducing protein of 35,000 daltons. In spite of the absence of embryo extract and provided that calcium, starting at a concentration as low as 3 X 10(-4) M, was present in the tested media, typically aligned myotubes with 20 or more nuclei per fiber or abnormal myosymplasts were produced at will. In the first case, the result was systematically obtained when the media were unchanged. Consequently, the cell microenvironment remained undisturbed and therefore was autoconditioned throughout the 7 days of culture. In the second case, the result depended on the feeding schedules. Conversely, no myotubes were formed in cultures in embryo extract-free medium without calcium, irrespective of the frequency of medium changes. Insulin, a serum factor believed to be involved in syncytium formation process in vitro, was present in all tested media. Undialyzed or dialyzed fetal calf serum (FCS), used for the preparation of the media, contained 11 mu units of insulin per milliliter. The insulin content in all tested media was diluted, however, to one tenth the physiological serum concentration. The hormone did not promote any kind of myoblast fusion in any experiment in which calcium was deleted as a component of the tested media, regardless of the feeding schedule followed.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen consumption of mammalian myocardial cells in culture: measurements in beating cells attached to the substrate of the culture dish

A Lucite attachment which permitted the measurement of oxygen consumption in cells in culture without manipulating the cells was constructed. The attachment fit over commercially available dishes for cell culture and had an oxygen electrode built into it. Oxygen uptake of cells in culture was thus measured. Cells were attached to the substrate of the culture dish during the measurements and could be observed in an inverted phase microscope. Cells did not show any morphological changes, e.g., cell shapes or beating rate in case of myocardial cells, before and after the measurements of oxygen consumption. Using this method the rate of oxygen consumption was determined in rat myocardial and heart non-muscle cells in culture and also in HeLa and L6 cell lines. Myocardial cells in culture had an approximately four times higher rate of oxygen uptake compared with heart non-muscle, HeLa, and L6 cells. The oxygen uptake of beating myocardial cells was higher by about 50% compared with quiescent myocardial cells.

Cardiomyocytes cultured in serum-free medium. Growth and creatine kinase activity

Primary cultures of newborn rat heart cells were grown for up to 3 weeks in serum-free medium supplemented by insulin, hydrocortisone, transferrin and fetuin. The cells resumed spontaneous beating at 20 h post plating. Mean rates of beating on the second and third day were 79.5 and 94 beats per min, respectively. Cell proliferation occurred during the first 3 days of culture with maximal rates of DNA and protein synthesis on the second day. The highest values of creatine kinase activity were observed on days 2-5 and the three cytoplasmic isozymes, MM, MB and BB, were present in the cultures in proportions similar to those of the newborn heart, indicating stability of the differentiated state of the cells. The relative amount of each isozyme remained unchanged throughout the experiments, MM constituted 70-90% of enzyme activity, MB contributed up to 30% and BB did not exceed 15% of activity. The very low proportion of BB and the lack of increase in this isozyme with age of culture support our earlier morphological observations that non-myocytes do not overgrow the culture.