Mouse p53 represses the rat brain creatine kinase gene but activates the rat muscle creatine kinase gene

CKB affects human osteosarcoma progression by regulating the p53 pathway

This study aimed to explore the role of the creatine kinase B (CKB) gene in the development of human osteosarcoma (OS). Western blotting and qRT-PCR were performed to detect CKB expression in tissues and cells. CCK-8, colony formation, flow cytometry, Transwell, and cell scratch assays were performed to detect OS cell viability, proliferation, apoptosis, invasion, and migration. Gene set enrichment analysis (GSEA) was used to conduct signal pathway enrichment. CKB expression was higher in OS tissues and cells than that in normal tissues and cells. Silencing CKB expression reduced cell proliferation, migration, and invasion, and improved cell apoptosis in HOS cells, while overexpressing CKB increased cell proliferation, migration, and invasion, and decreased apoptosis in U2-OS cells. GSEA showed that CKB affected the p53 signaling pathway. Overexpression of CKB inhibited the protein expression of p53, p21, and Bax and promoted the expression of Bcl-2 and MDM2 in U2-OS cells. Conversely, silencing CKB promoted the protein expression of p53, p21, and Bax, and inhibited the expression of Bcl-2 and MDM2 in HOS cells. Silencing p53 could reverse the effect of the silencing CKB in HOS cells, and overexpressing p53 could reverse the effect of overexpressing CKB in U2-OS cells. Taken together, CKB affects the development of OS by regulating the activity of the p53 signaling pathway.

Mitochondrial Proteolipid Complexes of Creatine Kinase

Isoforms of creatine kinase (CK) generate and use phosphocreatine, a concentrated and highly diffusible cellular "high energy" intermediate, for the main purpose of energy buffering and transfer in order to maintain cellular energy homeostasis. The mitochondrial CK isoform (mtCK) localizes to the mitochondrial intermembrane and cristae space, where it assembles into peripherally membrane-bound, large cuboidal homooctamers. These are part of proteolipid complexes wherein mtCK directly interacts with cardiolipin and other anionic phospholipids, as well as with the VDAC channel in the outer membrane. This leads to a stabilization and cross-linking of inner and outer mitochondrial membrane, forming so-called contact sites. Also the adenine nucleotide translocator of the inner membrane can be recruited into these proteolipid complexes, probably mediated by cardiolipin. The complexes have functions mainly in energy transfer to the cytosol and stimulation of oxidative phosphorylation, but also in restraining formation of reactive oxygen species and apoptosis. In vitro evidence indicates a putative role of mtCK in mitochondrial phospholipid distribution, and most recently a role in thermogenesis has been proposed. This review summarizes the essential structural and functional data of these mtCK complexes and describes in more detail the more recent advances in phospholipid interaction, thermogenesis, cancer and evolution of mtCK.

Identification of differentially expressed proteins in retinoblastoma tumors using mass spectrometry-based comparative proteomic approach

In India, retinoblastoma is among the top five childhood cancers. Children mostly present with extraocular extension and high risk features that results in unsatisfactory treatment and low survival rate. In addition, lack of potential therapeutic and prognostic targets is another challenge in the management of retinoblastoma. We studied comparative proteome of retinoblastoma patients (HPV positive and negative (n=4 each) and controls (n=4), in order to identify potential retinoblastoma-specific protein targets. 2D-DIGE coupled MALDI-TOF/TOF mass spectrometry identified 39 unique proteins. Highly deregulated proteins were GFAP,RBP3,APOA1,CRYAA,CRABP1,SAG and TF. Gene ontology (Panther 7.0) revealed majority of proteins to be associated with metabolic processes (26%) and catalytic activity (38%). 8 proteins were significantly upregulated in HPV positive vis-a-vis HPV negative cases. Patient group exhibited 12 upregulated and 18 downregulated proteins compared to controls. Pathway and network analysis (IPA software) revealed CTNNB1 as most significantly regulated signalling pathway in HPV positive than HPV negative retinoblastoma. The trends in transcriptional change of 9 genes were consistent with those at proteomic level. The Western blot analysis confirmed the expression pattern of RBP3,GFAP and CRABP1. We suggest GFAP,RBP3,CRABP1,CRYAAA,APOA1 and SAG as prospective targets that could further be explored as potential candidates in therapy and may further assist in studying the disease mechanism.

SIGNIFICANCE

In this study we evaluated tumor tissue specimens from retinoblastoma patients and identified 39 differentially regulated proteins compared to healthy retina. From these, we propose RBP3, CRABP1, GFAP, CRYAA, APOA1 and SAG as promising proteomic signatures that could further be explored as efficient prognostic and therapeutic targets in retinoblastoma. The present study is not only a contribution to the ongoing endeavour for the discovery of proteomic signatures in retinoblastoma, but, may also act as a starting point for future studies aimed at uncovering novel targets for further therapeutic interventions and improving patient outcomes.

Moderately increased maternal dietary energy intake delays foetal skeletal muscle differentiation and maturity in pigs

OBJECTIVES

This study aimed to evaluate the effects of moderately increased maternal dietary energy intake during gestation on foetal skeletal muscle development and metabolism with pig as a model.

METHODS

Twelve primiparous purebred Large White sows (initial body weight 135.5 ± 1.6 kg) were allocated to one of two energy intake treatments: normal-energy-intake group (Con, 30.96 MJ DE/day) as recommended by the National Research Council (NRC; 2012) and high-energy-intake group (HE, 34.15 MJ DE/day). The nutritional treatments were introduced from mating to day 90 of gestation. On day 90 of gestation, foetuses were examined by morphological, biochemical and molecular analysis of the longissimus muscle. Umbilical vein serum hormones were measured.

RESULTS

Sow body weight was increased in HE group compared with Con group (P < 0.05), whereas foetal myofibre density was decreased (P < 0.05). Meanwhile, protein concentration, creatine kinase and lactate dehydrogenase activities and umbilical vein serum triiodothyronine (T3) concentration were decreased in HE foetuses (P < 0.05). Maternal HE diets decreased the mRNA abundance of muscle growth-related genes, myosin heavy-chain (MYH/MyHC) genes (MYH2 and MYH1) and insulin-like growth factor 1 and insulin growth factor-binding protein 5 (P < 0.05). Furthermore, the protein expressions of myogenic differentiation factor 1, myogenin and fast-MyHC isoforms were reduced in HE foetuses (P < 0.05).

CONCLUSION

Our results suggest that moderately increased maternal dietary energy intake delays the differentiation and maturation in skeletal muscle of the foetus on day 90 of gestation.

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.

The expression of p53-regulated genes in human cultured lymphoblastoid TSCE5 and WTK1 cell lines during spaceflight

PURPOSE

The space environment contains two major biologically significant influences; space radiations and microgravity. The 53 kDa tumour suppressor protein (p53) plays a role as a guardian of the genome through the activity of p53-centered signal transduction pathways. The aim of this study was to clarify the biological effects of space radiations, microgravity, and the space environment on the gene expression of p53-regulated genes.

MATERIALS AND METHODS

Space experiments were performed with two human cultured lymphoblastoid cell lines; one line (TSCE5) bears a wild-type p53 gene status, and another line (WTK1) bears a mutated p53 gene status. Under one gravity or microgravity conditions, the cells were grown in the cell biology experimental facility (CBEF) of the International Space Station for 8 days without experiencing stress during launching and landing because the cells were frozen during these periods. Ground control samples also were cultured for 8 days in the CBEF on the ground during the spaceflight. Gene expression was analysed using an Agilent Technologies 44 k whole human genome microarray DNA chip.

RESULTS

p53-dependent up-regulated gene expression was observed for 111, 95, and 328 genes and p53-dependent down-regulated gene expression was found for 177, 16, and 282 genes after exposure to space radiations, to microgravity, and to both, respectively.

CONCLUSIONS

The data provide the p53-dependent regulated genes by exposure to radiations and/or microgravity during spaceflight. Our expression data revealed genes that might help to advance the basic space radiation biology.

ASB9 interacts with ubiquitous mitochondrial creatine kinase and inhibits mitochondrial function

BACKGROUND

The ankyrin repeat and suppressor of cytokine signalling (SOCS) box proteins (Asbs) are a large protein family implicated in diverse biological processes including regulation of proliferation and differentiation. The SOCS box of Asb proteins is important in a ubiquitination-mediated proteolysis pathway. Here, we aimed to evaluate expression and function of human Asb-9 (ASB9).

RESULTS

We found that a variant of ASB9 that lacks the SOCS box (ASB9DeltaSOCS) was naturally detected in human cell lines but not in peripheral blood mononuclear cells or normal hepatocytes. We also identified ubiquitous mitochondrial creatine kinase (uMtCK) as a new target of ASB9 in human embryonic kidney 293 (HEK293) cells. The ankyrin repeat domains of ASB9 can associate with the substrate binding site of uMtCK in a SOCS box-independent manner. The overexpression of ASB9, but not ASB9DeltaSOCS, induces ubiquitination of uMtCK. ASB9 and ASB9DeltaSOCS can interact and colocalise with uMtCK in the mitochondria. However, only expression of ASB9 induced abnormal mitochondrial structure and a decrease of mitochondrial membrane potential. Furthermore, the creatine kinase activities and cell growth were significantly reduced by ASB9 but not by ASB9DeltaSOCS.

CONCLUSIONS

ASB9 interacts with the creatine kinase system and negatively regulates cell growth. The differential expression and function of ASB9 and ASB9DeltaSOCS may be a key factor in the growth of human cell lines and primary cells.

p53 and Metabolism: The GAMT Connection

In this issue of Molecular Cell, Ide et al. (2009) have identified the enzyme guanidinoacetate methyltransferase (GAMT) that regulates creatine metabolism as a p53 target involved in apoptosis, reactive oxygen species (ROS), and fatty acid metabolism.

GAMT, a p53-inducible modulator of apoptosis, is critical for the adaptive response to nutrient stress

The p53 tumor suppressor protein has a well-established role in cell-fate decision-making processes. However, recent discoveries indicate that p53 has a non-tumor-suppressive role. Here we identify guanidinoacetate methyltransferase (GAMT), an enzyme involved in creatine synthesis, as a p53 target gene and a key downstream effector of adaptive response to nutrient stress. We show that GAMT is not only involved in p53-dependent apoptosis in response to genotoxic stress but is important for apoptosis induced by glucose deprivation. Additionally, p53-->GAMT upregulates fatty acid oxidation (FAO) induced by glucose starvation, utilizing this pathway as an alternate ATP-generating energy source. These results highlight that p53-dependent regulation of GAMT allows cells to maintain energy levels sufficient to undergo apoptosis or survival under conditions of nutrient stress. The p53-->GAMT pathway represents a new link between cellular stress responses and processes of creatine synthesis and FAO, demonstrating a further role of p53 in cellular metabolism.

Discovering multiple realistic TFBS motifs based on a generalized model

BACKGROUND

Identification of transcription factor binding sites (TFBSs) is a central problem in Bioinformatics on gene regulation. de novo motif discovery serves as a promising way to predict and better understand TFBSs for biological verifications. Real TFBSs of a motif may vary in their widths and their conservation degrees within a certain range. Deciding a single motif width by existing models may be biased and misleading. Additionally, multiple, possibly overlapping, candidate motifs are desired and necessary for biological verification in practice. However, current techniques either prohibit overlapping TFBSs or lack explicit control of different motifs.

RESULTS

We propose a new generalized model to tackle the motif widths by considering and evaluating a width range of interest simultaneously, which should better address the width uncertainty. Moreover, a meta-convergence framework for genetic algorithms (GAs), is proposed to provide multiple overlapping optimal motifs simultaneously in an effective and flexible way. Users can easily specify the difference amongst expected motif kinds via similarity test. Incorporating Genetic Algorithm with Local Filtering (GALF) for searching, the new GALF-G (G for generalized) algorithm is proposed based on the generalized model and meta-convergence framework.

CONCLUSION

GALF-G was tested extensively on over 970 synthetic, real and benchmark datasets, and is usually better than the state-of-the-art methods. The range model shows an increase in sensitivity compared with the single-width ones, while providing competitive precisions on the E. coli benchmark. Effectiveness can be maintained even using a very small population, exhibiting very competitive efficiency. In discovering multiple overlapping motifs in a real liver-specific dataset, GALF-G outperforms MEME by up to 73% in overall F-scores. GALF-G also helps to discover an additional motif which has probably not been annotated in the dataset. http://www.cse.cuhk.edu.hk/%7Etmchan/GALFG/

Characterization of Molecular Markers Indicative of Cervical Cancer Progression

Cervical cancer originates with human papillomavirus (HPV) infection and progresses via histologically-defined premalignant stages. Here we compare normal cervical epithelium and patient-matched high grade squamous intraepithelial lesions (HSIL) with cervical carcinoma tissue from the same patient population (n=10 per group). Specimens were analyzed by combined laser capture microdissection and 2D-DIGE. Significant expression changes were seen with 53 spots resulting in identification of 23 unique proteins at the molecular level. These include eight that uniquely distinguish normal epithelium and HSIL and four that uniquely distinguish HSIL and carcinoma. In addition, one protein, cornulin, distinguishes all three states. Other identified proteins included differentiation markers, oncogene DJ-1, serpins, stress and interferon-responsive proteins, detoxifying enzymes, and serum transporters. A literature review, performed for all identified proteins, allowed most changes to be assigned to one of three causes: direct or indirect HPV oncoprotein interactions, growth selection during latency, or interactions in the lesion microenvironment. Selected findings were confirmed by immunohistochemistry using either frozen sections from the same cohort or formalin fixed paraffin embedded samples from a tissue microarray. Novel markers described here have potential applications for increasing the predictive value of current screening methods.

Ankyrin repeat and suppressors of cytokine signaling box protein asb-9 targets creatine kinase B for degradation

The suppressors of cytokine signaling (SOCS) proteins inhibit cytokine action by direct interaction with Janus kinases or activated cytokine receptors. In addition to the N-terminal and Src homology 2 domains that mediate these interactions, SOCS proteins contain a C-terminal SOCS box. DNA data base searches have identified a number of other protein families that possess a SOCS box, of which the ankyrin repeat and SOCS box-containing (Asb) proteins constitute the largest. Although it is known that the SOCS proteins are involved in the negative regulation of cytokine signaling, the biological and biochemical functions of the Asbs are largely undefined. Using a proteomics approach, we demonstrate that creatine kinase B (CKB) interacts with Asb-9 in a specific, SOCS box-independent manner. This interaction increases the polyubiquitylation of CKB and decreases total CKB levels within the cell. The targeting of CKB for degradation by Asb-9 was primarily SOCS box-dependent and suggests that Asb-9 acts as a specific ubiquitin ligase regulating levels of this evolutionarily conserved enzyme.

Brain-type creatine kinase BB-CK interacts with the Golgi Matrix Protein GM130 in early prophase

Creatine kinase (CK) isoenzymes are essential for storing, buffering and intracellular transport of "energy-rich" phosphate compounds in tissues with fluctuating high energy demand such as muscle, brain and other tissues and cells where CK is expressed. In brain and many non-muscle cells, ubiquitous cytosolic "brain-type" BB-CK and ubiquitous mitochondrial CK (uMtCK) act as components of a phosphocreatine shuttle to maintain cellular energy pools and distribute energy flux. To date, still relatively little is known about direct coupling of functional dimeric BB-CK with other partner proteins or enzymes that are important for cell function. Using a global yeast two-hybrid (Y2H) screen with monomeric B-CK as bait and a representative brain cDNA library to search for interaction partners of B-CK with proteins of the brain, we repeatedly identified the cis-Golgi Matrix protein (GM130) as recurrent interacting partner of B-CK. Since HeLa cells also express both BB-CK and GM130, we subsequently used this cellular model system to verify and characterize the BB-CK-GM130 complex by GST-pulldown experiments, as well as by in vivo co-localization studies with confocal microscopy. Using dividing HeLa cells, we report here for the first time that GM130 and BB-CK co-localize specifically in a transient fashion during early prophase of mitosis, when GM130 plays an important role in Golgi fragmentation that starts also at early prophase. These data may shed new light on BB-CK function for energy provision for Golgi-fragmentation that is initiated by cell signalling cascades in the early phases of mitosis.

Increased creatine kinase BB activity and CKB mRNA expression in patients with hematologic disorders: relation to methylation status of the CKB promoter

BACKGROUND

We encountered 2 patients with increased activities of the creatine kinase (CK)-BB isoenzyme in their sera. Here we examined the relation among CK-BB activity, expression of CKB mRNA in peripheral blood, and hypermethylation of the CKB.

METHODS

The 2 patients and other 26 patients with hematologic malignancies, and some cancer cell lines were subjected to measurement of serum CK activity, CK isoenzyme analysis, CKB mRNA expression analysis by RT-PCR, and methylation analysis of the CKB promoter region.

RESULTS

CK-BB activity and proportion of leukemia blasts were correlated in the 2 patients. CKB mRNA was increased in peripheral blood during an increase in leukemia blast numbers. In contrast, none of the other 26 patients showed CK-BB activity or expression of CKB mRNA. In all of the patients with hematologic disorders, the analyzed region of CKB promoter was mostly unmethylated. However, some of cancer cell lines showed the methylated pattern. CKB mRNA was expressed at higher levels in cells with an unmethylated CKB promoter than in cells with a methylated promoter.

CONCLUSIONS

Expression of CKB mRNA and CK-B sometimes occurred in blastic transformation of the hematopoietic system. A relation between CKB mRNA expression and methylation of the CKB promoter was suggested.

Elevated creatine kinase activity in primary hepatocellular carcinoma

Background

Inconsistent findings have been reported on the occurrence and relevance of creatine kinase (CK) isoenzymes in mammalian liver cells. Part of this confusion might be due to induction of CK expression during metabolic and energetic stress.

Methods

The specific activities and isoenzyme patterns of CK and adenylate kinase (AdK) were analysed in pathological liver tissue of patients undergoing orthotopic liver transplantation.

Results

The brain-type, cytosolic BB-CK isoenzyme was detected in all liver specimens analysed. Conversely, CK activity was strongly increased and a mitochondrial CK (Mi-CK) isoenzyme was detected only in tissue samples of two primary hepatocellular carcinomas (HCCs).

Conclusion

The findings do not support significant expression of CK in normal liver and most liver pathologies. Instead, many of the previous misconceptions in this field can be explained by interference from AdK isoenzymes. Moreover, the data suggest a possible interplay between p53 mutations, HCC, CK expression, and the growth-inhibitory effects of cyclocreatine in HCC. These results, if confirmed, could provide important hints at improved therapies and cures for HCC.

Mitochondrial-dependent regulation of myoblast proliferation

The aim of the present study was to determine whether mitochondrial activity could regulate myoblast proliferation. We demonstrate that an increase in mitochondrial activity of L6E9 myoblasts can be easily obtained by simply raising extracellular pyruvate concentration in the culture dish. Under this condition, L6E9 myoblasts underwent a rapid growth arrest in G1 + S phases concomitant to a marked cellular hypertrophy. No sign of myoblast fusion was evident. This was accompanied by the down-regulation of proliferating cell nuclear antigen expression and an increase in p21 expression. Mitochondrial biogenesis was also stimulated, as indicated by a twofold increase in mitochondrial content. These cells exhibited a large increase in the production of reactive oxygen species that could contribute to the observed phenotypic alterations. However, exposure of pyruvate-treated cells to antioxidants did not reverse growth arrest. Similarly, exposure of control cells to oxidants did not induce growth arrest. Our observations suggest that mitochondrial activity appears to play a central role in regulating myoblast proliferation. They also argue strongly in favor of a retrograde communication establishing a mitochondrial control of nuclear gene expression that could be modulated by mitochondrial activity.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Comparative analysis of brain proteins from p53-deficient mice by two-dimensional electrophoresis

p53 is a tumor suppressor protein that regulates many cellular processes including the cell cycle, DNA repair, and apoptosis. It also serves as a critical regulator of neuronal apoptosis in the central nervous system (CNS). To elucidate the role of p53 in the CNS, brain proteins of p53 knock-out mice (p53-/-) were analyzed by two-dimensional gel electrophoresis (2-DE) and compared with those from p53 wild type (p53+/+) mice. Six types of brain tissue (temporal cortex, cerebellum, hippocampus, striatum, olfactory bulb, and cervical spinal cord) and other control tissues (lung and blood) from 18-week-old non-stress-induced mice were analyzed. The morphology of brains from p53-/- mice appeared to be normal and identical to that of p53+/+ mice, although lungs showed diffuse tumors that may have been caused by p53 deficiency. Comparative 2-D gel analysis showed that, on average, 7 of 886 spots from brain tissue were p53-/- specific, whereas 12 of 1008 spots from lung tissue were p53-/- specific. N-terminal amino acid sequence was determined for p53-/- specific proteins. In all brain tissues from p53-/- mice, a newly identified mouse mitochondrial NADH-ubiquinone oxidoreductase 24 kDa subunit showed decreased expression, and apolipoprotein A1 acidic forms showed increased expression. In addition, brain-type creatine kinase B chain and tubulin beta-5 N-terminal fragment were increased in the p53-/- cerebellum, and a new protein in mouse, hydroxyacylglutathione hydrolase (glyoxalase II) was decreased in the temporal cortex of p53-/- mice. The alterations in protein expression identified in this study may imply a p53-related brain function. This is the first proteomic analysis on the p53-/- mouse brain, and further information based on this study will provide new insights into the p53 function in the CNS.

A complete system for identifying inhibitors of creatine kinase B

We have developed a complete system for discovery of lead compounds as inhibitors of creatine kinase B. In this article, we describe production and purification of the recombinant protein, conditions and features of an optimized high-throughput screening assay, and results of our implementation of the system using a diverse compound library.

Crystal structure of brain-type creatine kinase at 1.41 A resolution

Excitable cells and tissues like muscle or brain show a highly fluctuating consumption of ATP, which is efficiently regenerated from a large pool of phosphocreatine by the enzyme creatine kinase (CK). The enzyme exists in tissue--as well as compartment-specific isoforms. Numerous pathologies are related to the CK system: CK is found to be overexpressed in a wide range of solid tumors, whereas functional impairment of CK leads to a deterioration in energy metabolism, which is phenotypic for many neurodegenerative and age-related diseases. The crystal structure of chicken cytosolic brain-type creatine kinase (BB-CK) has been solved to 1.41 A resolution by molecular replacement. It represents the most accurately determined structure in the family of guanidino kinases. Except for the N-terminal region (2-12), the structures of both monomers in the biological dimer are very similar and closely resemble those of the other known structures in the family. Specific Ca2+-mediated interactions, found between two dimers in the asymmetric unit, result in structurally independent heterodimers differing in their N-terminal conformation and secondary structure. The high-resolution structure of BB-CK presented in this work will assist in designing new experiments to reveal the molecular basis of the multiple isoform-specific properties of CK, especially regarding different subcellular locations and functional interactions with other proteins. The rather similar fold shared by all known guanidino kinase structures suggests a model for the transition state complex of BB-CK analogous to the one of arginine kinase (AK). Accordingly, we have modeled a putative conformation of CK in the transition state that requires a rigid body movement of the entire N-terminal domain by rms 4 A from the structure without substrates.

Regulation of p53 mediated transactivation by the beta-subunit of protein kinase CK2

The growth suppressor protein p53 plays a main part in cellular growth control. Two of its key functions are sequence specific DNA binding and transactivation. Functions of p53 in growth control are regulated at least in part by its interaction with protein kinases. p53 binds to protein kinase CK2, formerly known as casein kinase 2, and it is phosphorylated by this enzyme. CK2 is composed of two regulating beta-subunits and two catalytic alpha- or alpha'-subunits and the interaction with p53 is mediated by the regulatory beta-subunit of CK2. Recently we showed that the beta-subunit could inhibit the sequence specific DNA binding activity of p53 in vitro. Based on this finding, we asked if a coexpression of the beta-subunit of CK2 with p53 in mammalian cells could inhibit the DNA binding activity of p53 in a physiological context. We found that the coexpression of the beta-subunit showed the same inhibitory effect as in the previous assays with purified proteins. Then, we investigated the effects of the coexpression of the beta-subunit of CK2 on the transactivation and transrepression activity of p53. We found that transactivation of the mdm2, p21(WAF1/CIP1) and cyclin G promoter was inhibited in three different cell lines whereas transactivation of the bax promoter was not affected in COS1 cells but down-regulated in MCO1 and SaosS138V21 cells. p53 mediated transrepression of the fos promoter was not influenced by coexpression of the CK2 beta-subunit. Taken together we propose a cell type dependent fine regulation of the p53 transactivation function by the CK2 beta-subunit in vivo, which does not affect p53 mediated transrepression.

Creatine and cyclocreatine treatment of human colon adenocarcinoma xenografts: 31P and 1H magnetic resonance spectroscopic studies

Creatine (Cr) and cyclocreatine (cyCr) have been shown to inhibit the growth of a variety of human and murine tumours. The purpose of this study was to evaluate the anti-tumour effect of these molecules in relation to drug accumulation, energy metabolism, tumour water accumulation and toxicity. Nude mice carrying a human colon adenocarcinoma (LS174T) with a creatine kinase (CK) activity of 2.12 units mg(-1) protein were fed Cr (2.5% or 5%) or cyCr (0.025%, 0.1% or 0.5%) for 2 weeks and compared with controls fed standard diet. Cr concentrations of 2.5% and 5% significantly inhibited tumour growth, as did 0.1% and 0.5% cyCr. In vivo 31P magnetic resonance spectroscopy (MRS) after 2 weeks of treatment showed an increase in [phosphocreatine (PCr)+phosphocyclocreatine (PcyCr)]/nucleoside triphosphate (NTP) with increasing concentrations of dietary Cr and cyCr, without changes in absolute NTP contents. The antiproliferative effect of the substrates of CK was not related to energy deficiency but was associated with acidosis. Intratumoral substrate concentrations (measured by 1H-MRS) of 4.8 micromol g(-1) wet weight Cr (mice fed 2.5% Cr) and 6.2 micromol g(-1) cyCr (mice fed 0.1% cyCr) induced a similar decrease in growth rate, indicating that both substrates were equally potent in tumour growth inhibition. The best correlant of growth inhibition was the total Cr or (cyCr+Cr) concentrations in the tissue. In vivo, these agents did not induce excessive water accumulation and had no systemic effects on the mice (weight loss, hypoglycaemia) that may have caused growth inhibition.

Thymidine dinucleotide mimics the effect of solar simulated irradiation on p53 and p53-regulated proteins

The tumor suppressor protein p53 participates in DNA repair and cell cycle regulation in response to injuries like ultraviolet (UV) irradiation. We have previously reported that the thymidine dinucleotide (pTpT), a common target for DNA photoproduct formation by UV light, mimics many effects of UV irradiation in cultured skin-derived cells, at least in part through the activation of p53. In this report we compare the effects of solar-simulated irradiation and pTpT on p53 and p53-regulated proteins involved in cellular growth arrest and DNA repair in cultured human dermal fibroblasts. We find that, like UV irradiation, pTpT increases the levels of p53, p21, and proliferating-cell nuclear antigen. The magnitude and time course of the inductions are UV dose dependent and consistent with known regulatory interactions among these nuclear proteins. These data confirm and expand previous studies of UV effects on nuclear proteins involved in cell cycle regulation and DNA repair. Our observations suggest that such protective effects can also be induced by pTpT in the absence of initial DNA damage, rendering cells more capable of responding to subsequent DNA damage.

Cyclocreatine inhibits stimulated motility in tumor cells possessing creatine kinase

Cyclocreatine (1-carboxymethyl-2-iminoimidazolidine), an analog of creatine and a substrate for creatine kinase (EC 2.7.3.2), inhibits the stimulated motility of tumor cells which possess creatine kinase. A2058-055 human melanoma cells, transfected with a creatine kinase gene, showed an 80-90% reduction in chemotactic response to type IV collagen when incubated overnight in the presence of 10 mM cyclocreatine (p < 0.0001 for n = 8 experiments). This inhibitory effect of cyclocreatine can be partially reversed by addition of creatine to the overnight cell treatment. Non-transfected cells, with very low levels of creatine kinase, were not significantly inhibited. Further experiments utilizing type IV collagen as attractant demonstrated that cyclocreatine inhibited the chemokinetic (91%) and the haptotactic (73%) responses and the in vitro invasion of A2058-055 cells through Matrigel-coated membranes (88%). In addition, motility stimulation of A2058-055 cells by either autotaxin or fibronectin was markedly inhibited by cyclocreatine. DU-145 prostatic tumor cells, which express endogenous creatine kinase, also have a reduced motility response to either autotaxin or epidermal growth factor induced motility in the presence of cyclocreatine.

p53 suppresses cytokine induced, Stat5 mediated activation of transcription

p53 is a tumor suppressor which exerts its function through the regulation of genes mediating cell cycle arrest and the induction of apoptosis. Cellular survival and proliferation can be positively regulated through the action of cytokines. These signals act through the activation of cell surface receptors, and the phosphorylation of intracellular signaling components, e.g. members of the Stat family (signal transducers and activators of transcription). The signaling effects of p53 and the cytokine receptors on the cellular phenotype are counteracting. We investigated the influence of p53 on the transactivation potential of Stat5. p53 repressed the prolactin induction of the Stat5 mediated transcription of the beta-casein promoter-luciferase reporter gene, but did not affect IFN-gamma induced, Stat1 dependent transcription of the IRF-1 promoter. The inhibition was not due to a decrease in the cellular concentration of Stat5 or to interference with its specific DNA binding activity. No repression of the basal transcriptional activity of the beta-casein promoter was observed. p53 mutants defective in their DNA binding or oligomerization functions had only weak inhibitory effects, but a mutant of p53 in the transactivation domain, efficiently repressed Stat5 dependent induction. The repressive function of p53 on Stat5 activity is independent of the amino-terminal transactivation domain, but requires a functional DNA binding domain and the carboxyl-terminal domain. Our experiments show that p53 counteracts Stat5 mediated cytokine induction of gene transcription. The effect is specific for Stat5 and independent of p53 induced apoptosis.

Molecular characterization of the creatine kinases and some historical perspectives

Over the last 15 years, molecular characterization of the creatine kinase (CK) gene family has paralleled the molecular revolution of understanding gene structure, function, and regulation. In this review, we present a summary of advances in molecular analysis of the CK gene family with a few vignettes of historical interest. We describe how the muscle CK gene provided an essential model system to examine myogenic regulatory mechanisms, leading to the discovery of the binding site for the MyoD family of basic helix-loop-helix transcription factors essential in skeletal myogenesis and the characterization of the MEF2 family of factors with an A/T rich consensus binding site essential in skeletal myogenesis and cardiogenesis. Cloning and characterization of the four mRNAs and nuclear genes encoding the cytosolic CKs, muscle and brain CKs, and the mitochondrial (Mt) CKs, sarcomeric MtCK and ubiquitous MtCK, has allowed intriguing study of tissue-specific and cell-specific expression of the different CKs and analysis of structural, functional, regulatory, and evolutionary relationships among both the four CK proteins and genes. Current and future studies focus on understanding both cellular energetics facilitated by the CK enzymes, especially energy channelling from the site of production, the mitochondrial matrix and inner membrane, to various cytosolic foci of utilization, and regulation of MtCK gene expression at the cell and tissue-specific level as models of regulation of energy producing genes.

Differential effects of creatine kinase isoenzymes and substrates on regeneration in livers of transgenic mice

Creatine kinase (CK) has been implicated in affecting cell growth, and the CK substrates creatine (Cr) and cyclocreatine (CyCr) have been shown to have anti-tumor activity. The influence of Cr and CyCr on liver regeneration following major hepatectomy was evaluated in normal and transgenic mice expressing the human ubiquitous mitochondrial isoform of CK (CK-mit) or the brain isoform of CK (CK-B) or livers expressing both CK-mit and CK-B (CK-comb). Expression of CK isoenzymes had little effect on liver regeneration in the absence of dietary supplementation with Cr or CyCr as assayed by the increase in liver mass. Dietary supplementation with Cr and CyCr significantly reduced liver growth in normal mice. Liver regeneration was almost completely inhibited in mice expressing CK-mit in the presence of Cr. Livers expressing CK-mit regenerated better than normal livers in the presence of CyCr. In mice expressing CK-B, Cr and CyCr had opposite effects from those found in CK-mit mice. In the presence of CyCr, regeneration was inhibited in livers expressing CK-B, and, in the presence of Cr, CK-B-expressing livers regenerated better than normal livers. The amount of DNA synthesized 2 days after hepatectomy confirmed the results obtained from measurements of liver mass for all groups. Growth and DNA synthesis were completely abolished by Cr in CK-mit mice, whereas CyCr mainly affected growth 2 days after hepatectomy in CK-B-expressing mice. Coexpression of the CK isoforms in CK-comb mice ameliorated the effects detected with either isoform alone. Inhibition of growth by Cr and CyCr was not correlated to water accumulation. These results clearly demonstrate isoenzyme and substrate-specific effects of CK on cell growth.

Inhibition of mouse thymidylate synthase promoter activity by the wild-type p53 tumor suppressor protein

The p53 tumor suppressor protein is an important negative regulator of the G1 to S transition in mammalian cells. We have investigated the effect of p53 on the expression of the mouse thymidylate synthase (TS) gene, which normally increases as cells enter S phase. A luciferase indicator gene that was driven by the wild-type or various modified forms of the TATA-less mouse TS promoter was transiently cotransfected with a p53 expression plasmid into TS-deficient hamster V79 cells and the level of luciferase activity was determined. We found that wild-type p53 inhibited TS promoter activity by greater than 95% but had a strong stimulatory effect on an artificial promoter that contained multiple p53-binding sites. In contrast, an expression plasmid that encodes a mutant form of p53 or a wild-type retinoblastoma tumor suppressor protein had little effect on TS promoter activity. Deletion of sequences upstream or downstream of the TS essential promoter region, or inactivation of each of the known elements within the essential promoter region, had no effect on the ability of wild-type p53 to inhibit TS promoter activity. Our observations indicate that the inhibition of TS promoter activity by p53 is not due to the presence of a specific p53 negative response element in the TS promoter. Rather, it appears that p53 inhibits the TS promoter by sequestering ("squelching") one or more general transcription factors.

p53 stimulates promoter activity of the sgk. serum/glucocorticoid-inducible serine/threonine protein kinase gene in rodent mammary epithelial cells

sgk is a novel member of the serine/threonine protein kinase gene family that is transcriptionally regulated by serum and glucocorticoids in mammary epithelial cells. To functionally determine if the sgk promoter is regulated by the p53 tumor suppressor protein in mammary cells, a series of sgk promoter fragments with 5'-deletions were linked to the bacterial chloramphenicol acetyltransferase gene (sgk-CAT) and transiently co-transfected into nontumorigenic NMuMG or transformed Con8Hd6 mammary epithelial cells with p53 expression plasmids. Wild-type p53, but not mutant p53, strongly stimulated sgk promoter activity in both mammary epithelial cell lines. These effects were mediated by specific regions within the sgk promoter containing p53 DNA-binding sites. The sgk p53 sequence at-1380 to-1345 (site IV) was sufficient to confer p53-dependent transactivation to a heterologous promoter, and p53 was capable of binding to this sequence in vitro as assessed by gel shift analysis. In the nontumorigenic NMuMG epithelial cell line, cotransfection of wild-type p53 strongly stimulated the activities of both the sgk promoter and the well characterized p53-responsive p21/Waf1 promoter, whereas in Rat-2 fibroblasts, wild-type p53 repressed the basal activities of both promoters, revealing that sgk and p21/Waf1 are similarly regulated in a cell type-specific manner. Taken together, these results demonstrate that sgk is a new transcriptional target of p53 in mammary epithelial cells and represent the first example of a hormone-regulated protein kinase gene with a functionally defined p53 promoter recognition element.

Expression of brain-type creatine kinase and ubiquitous mitochondrial creatine kinase in the fetal rat brain: evidence for a nuclear energy shuttle

To test the hypothesis that embryonic brain cells utilize a creatine phosphate energy shuttle, we examined the pattern of creatine kinase (CK) isoform expression and localization in the fetal rat brain. Moderate levels of CK activity are present at embryonic day 14 (7 U/mg protein) and decrease slightly until 3 days postpartum followed by a rapid, fourfold up-regulation to adult levels by 1 month (18 U/mg protein). In parallel with changes in enzyme activity, there is a biphasic and coordinate pattern of expression of brain-type CK (BCK) and ubiquitous mitochondrial CK (uMtCK) determined by nondenaturing electrophoresis and immunoblot analysis. The localization of CK isoforms was examined by immunocytochemistry, and, during the fetal period, BCK and uMtCK immunoreactivity was detected throughout the central and peripheral nervous system, especially in neuroepithelial regions of the cerebral vesicles and spinal cord. In large cells within the olfactory neuroepithelium and ventral spinal cord, differential compartmentation of CK isoforms was evident, with BCK localized primarily in cell nuclei, whereas uMtCK immunoreactivity was present in the cell body (but not within nuclei). In olfactory bulb neuroepithelium, both isoforms were expressed in the middle zone of the germinal layer associated with DNA synthesis. In embryonic skeletal and cardiac muscle, which also express BCK, the same compartmentation of BCK was seen, with BCK localized primarily in the cell nucleus of cardiac and skeletal myoblasts. These results demonstrate a coordinate pattern of expression and compartmentation of BCK and uMtCK isoforms in the fetal brain that, in some cells, provides the anatomic basis for a nuclear energy shuttle.

Two distinct signaling pathways activate the latent DNA binding function of p53 in a casein kinase II-independent manner

Post-translational modification of a carboxyl-terminal negative regulatory domain in vitro by either casein kinase II or protein kinase C allosterically activates the latent sequence-specific DNA binding function of p53. Reported here is a biochemical approach to determine the types of signaling pathways and enzymes that are involved in p53 activation in cells. Using a novel chromatographic method, we have been able to separate three distinct biochemical forms of p53 that have been synthesized in vivo; two are in an activated state, and one is in a latent state for sequence-specific DNA binding. The two activated forms of p53 appear to be controlled individually by either a constitutive or a UV-inducible signaling pathway. p53 lacking the COOH-terminal casein kinase II site (p53 delta 4) was characterized biochemically and used to determine the affects of deletion of the casein kinase II motif on the production of the two activated forms of p53 in vivo. As observed with full-length p53, the production of two distinct chromatographic forms of activated p53 delta 4 occurs in vivo, indicating that p53 activation can occur through a casein kinase II-independent pathway and suggesting that two other factors are involved in activation of p53 in vivo.