Phosphohistidine Phosphatase Research Articles

A splice variant of the human phosphohistidine phosphatase 1 (PHPT1) is degraded by the proteasome

Regulation of protein activity by phosphorylation is central in many cellular processes. Phosphorylation of serine, threonine and tyrosine residues is well documented and studied. In addition, other amino acids, like histidine can be phosphorylated, but neither the mechanism nor the function of this modification is well understood. Nevertheless, there is a 14kDa enzyme with phosphohistidine phosphatase activity, named PHPT1, found in most animals, but not in bacteria, plant or fungi. There are a few splice variant transcripts formed from the human PHPT1 locus and some of them are predicted to form variant proteins, but studies of these proteins are lacking. In order to get insight into the possible function of the variant transcripts encoded at the PHPT1 locus, ectopic expression of PHPT1 transcript variant 6, predicted to be degraded by the non-sense mediated mRNA decay pathway, in HeLa cells was undertaken. In HeLa cells the splice variant protein was degraded by the proteasome, unlike the wild type protein. Using an in silico modeling approach the variant C-terminal end of the proteins were predicted to form different secondary structures that might explain the different properties of the two proteins. The specific degradation of the PHPT1 splice variant indicates that at least for the PHPT1 protein, the quality control and the self-guarding of the cellular system works at two levels, first at the RNA level, aberrant transcripts are degraded by the non-sense mediated mRNA decay pathway, and the small amount of proteins that are formed will be degraded by the proteasome.

Nucleoside diphosphate kinase as protein histidine kinase.

Like phosphorylation of serine, threonine, and tyrosine residues in many organisms, reversible histidine phosphorylation is a well-known regulatory signal in prokaryotes and lower eukaryotes. In vertebrates, phosphohistidine has been mainly described as a phosphorylated intermediate in enzymatic reactions, and it was believed that regulatory histidine phosphorylation is of minor importance. During the last decade, it became evident however, that nucleoside diphosphate kinase (NDPK), an ubiquitously expressed enzyme required for nucleotide homeostasis, can additionally act as a protein histidine kinase. Especially for the isoform NDPK B, at least three defined substrates, the β subunit of heterotrimeric G proteins (Gβ), the intermediate conductance potassium channel KCa3.1, and the Ca(2+)-conducting TRP channel family member, TRPV5, have been identified. In all three proteins, the phosphorylation of a specific histidine residue is of regulatory importance for protein function, and these phosphohistidines are cleaved by a counteracting 14kDa phosphohistidine phosphatase (PHP). This article will therefore give an overview of our current knowledge on protein histidine phosphorylation in prokaryotes and lower eukaryotes and compare it with the regulatory phosphorylation and dephosphorylation of histidine residues in vertebrates by NDPK and PHP, respectively.

Inducible Expression of Arabidopsis Response Regulator 22 (ARR22), a Type-C ARR, in Transgenic Arabidopsis Enhances Drought and Freezing Tolerance

The Arabidopsis two-component signaling system, which is comprised of sensor histidine kinases, histidine phosphotransfer proteins, and response regulators, mediates cytokinin response as well as various other plant responses including abiotic stress responses. Arabidopsis response regulators (ARRs) are classified into type-A, -B, and -C. Although the roles of type-A and -B ARRs are well established in Arabidopsis plant signaling, roles of type-C ARRs, ARR22 and ARR24, remain elusive. ARR22, a preferentially cytosolic protein, interacts with certain Arabidopsis histidine phosphotransfer proteins (AHPs) and displays phosphatase activity on AHP5. ARR22 is induced by cold and dehydration. Here, we show that inducible overexpression of ARR22 in Arabidopsis enhanced dehydration, drought, and cold tolerance in a dexamethasone-dependent manner, whereas mutation of the putative phospho-accepting Asp to Asn in ARR22 (ARR22D74N) abolished these tolerance phenotypes. Overexpression of ARR22 decreased electrolyte leakage in dehydration-, drought-, or cold-stressed transgenic Arabidopsis plants compared with that of ARR22D74N or compared with wild-type plants. Transpiration rates and stomatal apertures were not affected by ARR22 overexpression. No significant difference in both dehydration and freezing tolerance was observed between wild-type and arr22 mutants with or without cytokinin preincubation, consistent with the lack of phenotypes of arr22 mutants in their vegetative development. Meta-profile analyses of the microarray data on ARR22-responsive genes indicate that ARR22 modulates expression of a variety of abiotic stress-responsive genes, which might contribute to increasing drought and freezing tolerance. Taken together, these results suggest that ARR22 plays a positive role in the stress tolerance response in part via enhancing cell membrane integrity and that phospho-histidine phosphatase activity of ARR22 may be required for this function.

106P PROTEOMIC ANALYSIS SHOWED HEAT SHOCK 70 KDA PROTEIN AND 78 KDA GLUCOSE-REGULATED PROTEIN WERE UP-REGULATED IN HUMAN MALIGNANT PLEURAL MESOTHELIOMA CELLS

Malignant pleural mesothelioma (MPM) is a malignant neoplasm arising from mesothelial cells existing in pleura. It is difficult to identify a crucial symptom in patients with MPM, and there is no standard curative therapy for this malignancy. The incidence of MPM is increasing worldwide, and many patients can not survive more than one year after diagnosis. MPM is an asbestos-related disease, and it is believed that the incidence is closely related to the amount and time of exposure to asbestos. Since the latency period after exposure to asbestos is very long, the incidence may increase over the next two decades. Therefore, it is important to understand the biology of MPM, and to find a molecular target for its therapy. Three of human malignant pleural mesothelioma (MPM) cell lines (NCIH28, NCI-H2052, NCI-H2452) and a human pleural mesothelial cell line (MeT-5A) were analyzed by proteomics with the use of twodimensional gel electrophoresis (2-DE) and liquid chromatographytandem mass spectrometry (LC-MS/MS). From the results of 2-DE between MeT-5A and three MPM cell lines, 9 protein spots showed increased expression levels in MPM cells compared to MeT-5A. These spots were analyzed by LC-MS/MS analysis, and identified by a peptide sequence tag. Identified increased spots included 78 kDa glucose regulated protein (GRP78), heat shock 70 kDa protein (HSP70), protein disulfide isomerase A3, annexin A3, peroxiredoxin-2 and 14 kDa phosphohistidine phosphatase. Western blotting using specific antibodies against GRP78 and HSP70 confirmed the elevated expression level of GRP78 and HSP70 in MPM cell lines compared to MeT-5A cells. These results suggest that GRP78 and HSP70 expression is likely to be associated with the tumorigenesis of MPM, and they may be expectable as biomarkers or therapeutic targets for MPM. Disclosure: All authors have declared no conflicts of interest.

107P IMPACT OF PREINTERVENTIONAL PLASMA FIBRINOGEN AS A PROGNOSTIC MARKER IN MALIGNANT PLEURAL MESOTHELIOMA

Malignant pleural mesothelioma (MPM) is a malignant neoplasm arising from mesothelial cells existing in pleura. It is difficult to identify a crucial symptom in patients with MPM, and there is no standard curative therapy for this malignancy. The incidence of MPM is increasing worldwide, and many patients can not survive more than one year after diagnosis. MPM is an asbestos-related disease, and it is believed that the incidence is closely related to the amount and time of exposure to asbestos. Since the latency period after exposure to asbestos is very long, the incidence may increase over the next two decades. Therefore, it is important to understand the biology of MPM, and to find a molecular target for its therapy. Three of human malignant pleural mesothelioma (MPM) cell lines (NCIH28, NCI-H2052, NCI-H2452) and a human pleural mesothelial cell line (MeT-5A) were analyzed by proteomics with the use of twodimensional gel electrophoresis (2-DE) and liquid chromatographytandem mass spectrometry (LC-MS/MS). From the results of 2-DE between MeT-5A and three MPM cell lines, 9 protein spots showed increased expression levels in MPM cells compared to MeT-5A. These spots were analyzed by LC-MS/MS analysis, and identified by a peptide sequence tag. Identified increased spots included 78 kDa glucose regulated protein (GRP78), heat shock 70 kDa protein (HSP70), protein disulfide isomerase A3, annexin A3, peroxiredoxin-2 and 14 kDa phosphohistidine phosphatase. Western blotting using specific antibodies against GRP78 and HSP70 confirmed the elevated expression level of GRP78 and HSP70 in MPM cell lines compared to MeT-5A cells. These results suggest that GRP78 and HSP70 expression is likely to be associated with the tumorigenesis of MPM, and they may be expectable as biomarkers or therapeutic targets for MPM. Disclosure: All authors have declared no conflicts of interest.

14-kDa Phosphohistidine phosphatase plays an important role in hepatocellular carcinoma cell proliferation

14-kDa Phosphohistidine phosphatase (PHP14), the first histidine phosphatase protein identified in vertebrates, was recently revealed to play an essential role in lung cancer. The function of this gene in other tumors is unclear; however, in this study, we demonstrate that PHP14 is highly expressed in hepatocellular carcinoma (HCC) tissues and cell lines compared with adjacent non-cancerous human liver tissues and cells (P<0.05). We used lentivirus-mediated delivery of small interfering RNA (siRNA) to knockdown the expression of PHP14 in an HCC cell line and investigate the effects of PHP14 on cell growth in vitro. Cell proliferation was inhibited and cell apoptosis was significantly increased. PHP14-siRNA affected the cell cycle and promoted G1→S phase transition in HCC cells. These results demonstrate that the knockdown of PHP14 expression by lentivirus-delivered siRNA may be a useful therapeutic approach for the treatment of HCC.

The phosphoramidase competency of prototypical phosphatase motifs

The discovery that phosphorylation of proteins occurs on nitrogen by particular kinases raises the question of whether a separate class of phosphoramidases also exists, or, if known phosphatases carry out the hydrolysis of phosphoramidates. The phosphoramidase activity of a number of phosphatases with different catalytic motifs was studied using the substrates N‐phenylphosphoramidate (N‐PhPAM) and phosphoryl imidazole (PIm). The phosphatases assayed were: the protein tyrosine phosphatase YopH; alkaline phosphatase; the dual‐specificity phosphatase VHR; PHPT1, the only known phosphohistidine phosphatase; and, the serine/threonine phosphatase PP1. The catalytic efficiencies, kcat/Km (s−1M−1), were compared for the respective phosphoramidase and phosphatase activities for each enzyme. Ratios of catalytic efficiencies (kcat/Km)/(kcat/Km) of phosphoester (pNPP or phenyl phosphate) over PIm are: YopH – 43; AP – 4.1; VHR – 0.23; and PHPT1 – 0.0065. PP1 exhibited no phosphoramidase activity. The results show that most phosphatase catalytic motifs display catalytic promiscuity by cleaving both phosphoesters and phosphoramidates, but with a pronounced preference for one substrate type versus the other. (Funding from NIH GM47297)

Design and Synthesis of an Fmoc-SPPS-Compatible Amino Acid Building Block Mimicking the Transition State of Phosphohistidine Phosphatase

The synthesis of a sulfonamide-based transition-state (TS) analogue of enzymatic phosphohistidine dephosphorylation as an amino acid building block is presented, together with the proof-of-concept of its incorporation into peptides. Key features include final global acidolytic protective group removal as well as full compatibility with standard Fmoc solid-phase peptide synthesis (SPPS). The peptides are designed as inhibitors of phosphohistidine phosphatase and as a pull-down probe for identification of phosphohistidine phosphatases, respectively.

Arabitol Metabolism of Corynebacterium glutamicum and Its Regulation by AtlR

Expression profiling of Corynebacterium glutamicum in comparison to a derivative deficient in the transcriptional regulator AtlR (previously known as SucR or MtlR) revealed eight genes showing more than 4-fold higher mRNA levels in the mutant. Four of these genes are located in the direct vicinity of the atlR gene, i.e., xylB, rbtT, mtlD, and sixA, annotated as encoding xylulokinase, the ribitol transporter, mannitol 2-dehydrogenase, and phosphohistidine phosphatase, respectively. Transcriptional analysis indicated that atlR and the four genes are organized as atlR-xylB and rbtT-mtlD-sixA operons. Growth experiments with C. glutamicum and C. glutamicum ΔatlR, ΔxylB, ΔrbtT, ΔmtlD, and ΔsixA derivatives with sugar alcohols revealed that (i) wild-type C. glutamicum grows on D-arabitol but not on other sugar alcohols, (ii) growth in the presence of D-arabitol allows subsequent growth on D-mannitol, (iii) D-arabitol is cometabolized with glucose and preferentially utilized over D-mannitol, (iv) RbtT and XylB are involved in D-arabitol but not in D-mannitol metabolism, (v) MtlD is required for D-arabitol and D-mannitol metabolism, and (vi) SixA is not required for growth on any of the substrates tested. Furthermore, we show that MtlD confers D-arabitol and D-mannitol dehydrogenase activities, that the levels of these and also xylulokinase activities are generally high in the C. glutamicum ΔatlR mutant, whereas in the parental strain, they were high when cells were grown in the presence of D-arabitol and very low when cells were grown in its absence. Our results show that the XylB, RbtT, and MtlD proteins allow the growth of C. glutamicum on D-arabitol and that D-arabitol metabolism is subject to arabitol-dependent derepression by AtlR.

A screening method for phosphohistidine phosphatase 1 activity

Introduction. Research in the field of protein-bound phosphohistidine phosphorylation has been hampered by the difficulties in analysis and detection of phosphohistidine. Therefore a screening method was developed primarily for the analysis of phosphohistidine phosphatase 1 (PHPT1) activity.Methods. A highly positively charged substrate, Ac-Val-Arg-Leu-Lys-His-Arg-Lys-Leu-Arg-pNA, containing the peptide surrounding the phosphorylated histidine in ion channel KCa3.1 was chemically phosphorylated using phosphoramidate. Excess phosphoramidate was removed by anion exchange chromatography using a micro spin column. After incubation of the eluate with PHPT1, the removed phosphate was bound on a consecutive anion exchange spin column. The eluate was assayed in a micro plate format for remaining phosphate in the substrate Ac-Val-Arg-Leu-Lys-His(P)-Arg-Lys-Leu-Arg-pNA. Histone H4, also highly positive in charge, was subjected to the same procedure to explore the possibility to use other substrates to PHPT1 in this assay format.Results. It was found that Ac-Val-Arg-Leu-Lys-His(P)-Arg-Lys-Leu-Arg-pNA and phosphohistone H4 were dephosphorylated by PHPT1. The apparent Km for Ac-Val-Arg-Leu-Lys-His(P)-Arg-Lys-Leu-Arg-pNA was in the order of 10 μM.Using this method, phosphohistidine phosphatase activity was detected in mouse liver cell sap with Ac-Val-Arg-Leu-Lys-His(P)-Arg-Lys-Leu-Arg-pNA as substrate.Discussion. The described method for determination of PHPT1 activity is comparably much easier and faster than presently used methods for detection of phosphohistidine phosphatase activity. It is also sensitive, since the lower activity limit was 5 pmol phosphate released per min. It has the potential to be used both for more rapid screening for inhibitors and activators to phosphohistidine phosphatases and for screening of histidine kinases.

14-kDa phosphohistidine phosphatase and its role in human lung cancer cell migration and invasion

14-kDa phosphohistidine phosphatase (PHP14) was the first protein histidine phosphatase to be discovered, but its biological function remains unclear. In our previous study, we found that it was associated with tumor invasion. Here, we investigated its role in lung cancer cell migration and invasion. Knockdown of PHP14 expression in highly metastatic lung cancer CL1-5 cells inhibited migration and invasion in vitro, but did not alter cell proliferation rates. Overexpression of PHP14 in NCI H1299 cells promoted migration and invasion in vitro, but again did not alter cell proliferation. To evaluate the metastatic properties of PHP14 in vivo, an experimental metastasis assay was performed. Experimental metastasis in vivo was extensively inhibited by PHP14 knockdown. To further examine the mechanism underlying the involvement of PHP14 in cell migration, invasion, and metastasis, a comparative proteomics analysis was performed. The differential protein expression profiles revealed that PHP14 was probably involved in cytoskeletal reorganization; this was further supported by actin filament (F-actin) staining. These results demonstrate for the first time that PHP14 may be functionally important in lung cancer cell migration and the invasion of lung cancer cells, mediated partly through modulation of actin cytoskeleton rearrangement.

Immunohistochemical localization of phosphohistidine phosphatase PHPT1 in mouse and human tissues

Protein histidine phosphorylation accounts for about 6% of the total protein phosphorylation in eukaryotic cells; still details concerning histidine phosphorylation and dephosphorylation are limited. A mammalian 14-kDa phosphohistidine phosphatase, also denominated PHPT1, was found 6 years ago that provided a new tool in the study of phosphohistidine phosphorylation. The localization of PHPT1 mRNA by Northern blot analysis revealed high expression in heart and skeletal muscle. The main object of the present study was to determine the PHPT1 expression on protein level in mouse tissues in order to get further information on the physiological role of the enzyme. Tissue samples from adult mice and 14.5-day-old mouse embryos were processed for immunostaining using a PHPT1-specific polyclonal antibody. The same antibody was also provided to the Swedish human protein atlas project (HPR) (http://www.proteinatlas.org/index.php). The results from both studies were essentially consistent with the previously reported expression of mRNA of a few human tissues. In addition, several other tissues, including testis, displayed a high protein expression. A salient result of the present investigation was the ubiquitous expression of the PHPT1 protein and its high expression in continuously dividing epithelial cells.

The Arabidopsis thaliana response regulator ARR22 is a putative AHP phospho-histidine phosphatase expressed in the chalaza of developing seeds

BackgroundThe Arabidopsis response regulator 22 (ARR22) is one of two members of a recently defined novel group of two-component system (TCS) elements. TCSs are stimulus perception and response modules of prokaryotic origin, which signal by a His-to-Asp phosphorelay mechanism. In plants, TCS regulators are involved in hormone response pathways, such as those for cytokinin and ethylene. While the functions of the other TCS elements in Arabidopsis, such as histidine kinases (AHKs), histidine-containing phosphotransfer proteins (AHPs) and A-type and B-type ARRs are becoming evident, the role of ARR22 is poorly understood.ResultsWe present evidence that ARR22 is a preferentially cytoplasmic protein, exclusively expressed in the chalaza of developing seeds. ARR22 specifically interacts with AHP2, AHP3 and AHP5 in yeast and living plant cells. Two new loss-of-function alleles, arr22-2 and arr22-3, were isolated and characterized. With respect to their morphology and metabolite status, no significant difference in the developing seeds of the arr22 mutants was observed compared to wild type. The genetic complementation of the arr22 mutants with a genomic ARR22 fragment resulted in plants (arr22/gARR22) with a pleiotropic phenotype of different penetrance. This phenotype was not observed when the phosphorylatable Asp74 of ARR22 was changed to either a dominant-active Glu or a dominant-inactive Asn. The phenotype of the arr22/gARR22 plants was comparable to that of multiple ahk, ahp and B-type arr mutants.ConclusionOur results favor the model that ARR22 acts as a phospho-histidine phosphatase on specific AHPs in the cytoplasm of Arabidopsis chalaza cells. The lack of any aberrant morphological and metabolite phenotype in the seeds of the arr22 mutants indicates that ARR22 is probably primarily responsible for the fine tuning of specific branches of chalaza-based TCS signalling. Even when slightly mis-expressed, ARR22 interferes with hormone homeostasis in non-chalaza tissues. Our data indicate that the chromatin status might play a crucial role in maintaining the chalaza-restricted expression of ARR22.

1H, 13C and 15N assignments of a New Phosphohistidine Phosphatase Protein PHPT1 from Homo sapiens

1H, 13C and 15N assignments of a New Phosphohistidine Phosphatase Protein PHPT1 from Homo sapiens

1H, 13C, and 15N resonance assignments of human phosphohistidine phosphatase 1 (PHPT1)

Phosphohistidine phosphatase 1 (PHPT1) is the first protein histidine phosphatase identified in vertebrates. The NMR assignments of human PHPT1 are essential for solution structure determination and NMR study of the protein interactions of PHPT1 with its potential substrates.

G Proteins

See related article, pages 1191–1199 Signaling through the activation of G proteins represents the most widely used signaling pathway in mammalian biology.1,2 Classically, a transmembrane receptor comprising seven transmembrane domains (G protein-coupled receptor, GPCR) is activated by an extracellular stimulus and transduces this information to heterotrimeric G proteins through a conformational change of the receptor protein. Throughout evolution, a large variety of GPCRs has evolved to detect a wide spectrum of signals ranging from photons and odorants to endogenous neurotransmitters and hormones such as the catecholamines. Consequently, the majority of currently used drugs act on GPCRs. On receptor-mediated activation of the G protein α-subunit, the bound GDP is exchanged against GTP and both the GTP-bound α-subunit as well as the βγ-subunits may activate downstream targets (Figure). As a GTPase, the α-subunit then rapidly initiates its own inactivation through GTP-hydrolysis. This GTPase cycle of G protein activation and deactivation is subject to regulation by the RGS family of proteins (regulators of G protein signaling) that activate the GTPase function and thereby negatively regulate signaling of GPCRs.3,4 G protein dependent signaling in the cardiovascular system. Classically G proteins are activated through agonist occupied G protein-coupled receptors (GPCRs). In the inactive state, the G protein α-subunit is bound to GDP, with a rapid exchange against GTP on activation. Both the α-subunit and the βγ-subunits can then activate diverse downstream signaling cascades. In addition G protein dependent signaling can be regulated independent from GPCR-activation through activators of G protein signaling (AGS) and nucleoside diphosphate kinase (NDPK). Membrane-bound NDPK B transfers a high energy phosphate onto G β-subunits, which is then transferred onto GDP to form GTP. It thereby localizes GTP-supply to the vincinity of G protein α-subunits and mediates local, receptor-independent activation of G protein α-subunits. It remains to be determined, …

First Structure of a Eukaryotic Phosphohistidine Phosphatase

Phosphatases are a diverse group of enzymes that regulate numerous cellular processes. Much of what is known relates to the tyrosine, threonine, and serine phosphatases, whereas the histidine phosphatases have not been studied as much. The structure of phosphohistidine phosphatase (PHPT1), the first identified eukaryotic-protein histidine phosphatase, has been determined to a resolution of 1.9A using multiple-wavelength anomalous dispersion methods. This enzyme can dephosphorylate a variety of proteins (e.g. ATP-citrate lyase and the beta-subunit of G proteins). A putative active site has been identified by its electrostatic character, ion binding, and conserved protein residues. Histidine 53 is proposed to play a major role in histidine dephosphorylation based on these observations and previous mutational studies. Models of peptide binding are discussed to suggest possible mechanisms for substrate recognition.

Changes in the muscle proteome after compensatory growth in pigs

Sixteen female pigs (Duroc x Landrace x Large White) were divided into 2 groups, which had either free access to the diet (control group) or were feed-restricted from d 28 to 80 and then had free access to the diet (compensatory growth group). The sensory analysis showed that the pigs exhibiting compensatory growth produced meat with increased tenderness compared with control pigs (P < 0.05). To gain further knowledge of the influence of compensatory growth on meat tenderness, the sarcoplasmic protein fraction of muscle tissue was studied at the time of slaughter and 48 h postmortem using proteome analysis. At slaughter, 7 different proteins were found to be affected by compensatory growth: HSC70, HSP27, enolase 3, glycerol-3-phosphate dehydrogenase, aldehyde dehydrogenase E2, aldehyde dehydrogenase E3, and biphosphoglycerate mutase. The HSC70 and HSP27 both belong to the heat shock family and are known to play a role during muscle development. Hence, they may be affected by compensatory growth and increased protein turnover. Forty-eight hours after slaughter, 8 different proteins were found to be affected by compensatory growth: myosin light chain (MLC) II, MLC III, sulfite oxidase, chloride intracellular channel 1, 14-3-3 protein gamma, elongin B, and phosphohistidine phosphatase 14. The changes observed on MLC II and MLC III could be a consequence of enzymatic cleavage in the neck region of the globular myosin head domain that causes the release of MLC II and MLC III from the actomyosin complex. It has previously been hypothesized that compensatory growth results in an increased postmortem proteolysis; thus it was presumed that the intensity of some protein fragments would be affected by compensatory growth. However, the peptides that were found to be affected at 48 h postmortem were all full-length proteins. The 14-3-3 protein gamma has been proposed to play a role in the contraction of muscle during rigor and may thereby have an effect on meat tenderness. This study reveals some very interesting changes in the muscle proteome affected by compensatory growth, which may be useful in understanding the relationship among compensatory growth, protein turnover, and meat tenderness.

Mutational study of human phosphohistidine phosphatase: Effect on enzymatic activity

Although protein histidine phosphorylation is estimated to account for about 6% of total protein phosphorylation in eukaryotes, knowledge on histidine phosphorylation and dephosphorylation is still limited. Recently, a few reports have appeared on a mammalian 14-kDa phosphohistidine phosphatase, also named protein histidine phosphatase. Molecular cloning of the protein has opened possibilities for exploring its properties and physiological role. In the present work, we have searched for potential active site residues in the human phosphohistidine phosphatase by point mutations of conserved histidine and arginine residues to alanine. When assayed by the phosphohistidine-containing peptide succinyl-Ala-His(P)-Pro-Phe- p-nitroanilide, mutants H53A and H102A showed no detectable activity. Compared to the wild-type recombinant enzyme, the specific activity of mutant R45A was decreased by one order of magnitude, that of mutant R78A was decreased by about 30%, while that of mutant H81A was essentially unchanged. These results will facilitate future studies of the reaction mechanism, substrate binding, and molecular structure of the phosphohistidine phosphatase.

Differential protein expression of etoposide-treated CaSki cervical carcinoma cells

Objective: This study was designed to examine the pharmaco-dynamic pattern of proteomic expression in cervical carcinoma cells (CaSki cell line; HPV-16 positive) after in vitro treatment by the etoposide. Methods: We analyzed proteomic profiling in cervical carcinoma cells after etoposide treatment using two-dimensional gel electrophoresis (2-DE) with MALDI-TOF-MS used for protein identification. Then, we tested the several experimental methods for verification and functional identification, including MTT assay, PI staining, DNA fragmentation assay, FDA, FACS and Western blot analysis. Results: Etoposide inhibited the CaSki cervical cancer cell growth in a dose-dependent manner and the optimal concentration of etoposide is 2microM () in the CaSki cervical cancer cells. The etoposide induced apoptosis, as determined by DNA fragmentation assay, FACS, and Western blot. The etoposide increased the protein expression of Fas (Apo-1/CD95), p53, pRb and caspase-3, but decreased the level of Bcl-2 and caspase-3 precursor and subsequently triggered the mitochondrial apoptotic pathway (release of cytochrome c and activation of caspase-9). To this end, we analyzed CaSki cancer cells using 2-DE. Eight proteins (XAP-5, HXC-36, serine/threonine protein phosphatase 2B catalytic subunit, G2/mitotic-specific cyclin B1, T-box transcription factor TBX20, diacylglycerol kinase, amiloride-sensitive amine oxidase, HEF-like protein, ras-related protein Rab-20) were down-regulated and nine proteins (RNA 3’-terminal phosphate cyclase-like protein, late endosomal/lysosomal Mp1 interacting protein, glia maturation factor, replication protein A 14 kDa subunit, mago sashi protein homolog, 14 kDa phosphohistidine phosphatase, protein C14 or f48, cyclin-dependent kinase 4 inhibitior A, retinoic acid-binding protein II) were up-regulated in etoposide-treated CaSki cells when compared with non-treated cells. Conclusion: Our results clearly indicate that etoposide induced cell death by apoptosis. These findings may provide insights into the mechanisms underlying the apparent anti-tumoral effects of etoposide.