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

Histidine Phosphorylation: Protein Kinases and Phosphatases

Phosphohistidine (pHis) is a reversible protein post-translational modification (PTM) that is currently poorly understood. The P-N bond in pHis is heat and acid-sensitive, making it more challenging to study than the canonical phosphoamino acids pSer, pThr, and pTyr. As advancements in the development of tools to study pHis have been made, the roles of pHis in cells are slowly being revealed. To date, a handful of enzymes responsible for controlling this modification have been identified, including the histidine kinases NME1 and NME2, as well as the phosphohistidine phosphatases PHPT1, LHPP, and PGAM5. These tools have also identified the substrates of these enzymes, granting new insights into previously unknown regulatory mechanisms. Here, we discuss the cellular function of pHis and how it is regulated on known pHis-containing proteins, as well as cellular mechanisms that regulate the activity of the pHis kinases and phosphatases themselves. We further discuss the role of the pHis kinases and phosphatases as potential tumor promoters or suppressors. Finally, we give an overview of various tools and methods currently used to study pHis biology. Given their breadth of functions, unraveling the role of pHis in mammalian systems promises radical new insights into existing and unexplored areas of cell biology.

LHPP expression in triple-negative breast cancer promotes tumor growth and metastasis by modulating the tumor microenvironment

Triple-negative breast cancer (TNBC) is a highly aggressive and metastatic form of breast cancer that lacks an effective targeted therapy. To identify new therapeutic targets, we investigated the phosphohistidine phosphatase, LHPP, which has been implicated in the development of several types of cancer. However, the full significance of LHPP in cancer progression remains unclear due to our limited understanding of its molecular mechanism. We found that levels of the LHPP phosphohistidine phosphatase were significantly increased in human breast cancer patients compared to normal adjacent tissues, with the highest levels in the TNBC subtype. When LHPP was knocked out in the MDA-MB-231 human TNBC cell line, cell proliferation, wound healing capacity, and invasion were significantly reduced. However, LHPP knockout in TNBC cells did not affect the phosphohistidine protein levels. Interestingly, LHPP knockout in MDA-MB-231 cells delayed tumor growth and reduced metastasis when orthotopically transplanted into mouse mammary glands. To investigate LHPP's role in breast cancer progression, we used next-generation sequencing and proximity-labeling proteomics, and found that LHPP regulates gene expression in chemokine-mediated signaling and actin cytoskeleton organization. Depletion of LHPP reduced the presence of tumor-infiltrating macrophages in mouse xenografts. Our results uncover a new tumor promoter role for LHPP phosphohistidine phosphatase in TNBC and suggest that targeting LHPP phosphatase could be a potential therapeutic strategy for TNBC.

Derivatives of the Fungal Natural Product Illudalic Acid Inhibit the Activity of Protein Histidine Phosphatase PHPT1

PHPT1 is a protein histidine phosphatase that has been implicated in several disease pathways, but the chemical tools necessary to study the biological roles of this enzyme and investigate its utility as a therapeutic target have yet to be developed. To this end, the discovery of PHPT1 inhibitors is an area of significant interest. Here, we report an investigation of illudalic acid and illudalic acid analog-based inhibition of PHPT1 activity. Four of the seven analogs investigated had IC50 values below 5 μM, with the most potent compound (IA1-8H2) exhibiting an IC50 value of 3.4±0.7 μM. Interestingly, these compounds appear to be non-covalent, non-competitive inhibitors of PHPT1 activity, in contrast to other recently reported PHPT1 inhibitors. Mutating the three cysteine residues to alanine has no effect on inhibition, indicating that cysteine is not critical for interactions between inhibitor and enzyme.

The histidine phosphatase LHPP: an emerging player in cancer

Cancers continue to have high incidence and mortality rates worldwide. Therefore, cancer control remains the main public health goal. Growing research evidence suggests that phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) plays an important role in inhibiting tumor cell progression. It has been reported in the literature that LHPP is expressed at low levels in tumor tissues and cells and that patients with low LHPP expression have a poorer prognosis. Functional studies have shown that LHPP can inhibit tumor cell proliferation, metastasis, and apoptosis by affecting different target genes. In addition, researchers have used iDPP nanoparticles to deliver LHPP plasmids to treat tumors, demonstrating the great potential of LHPP plasmids for cancer therapy. In our review, we highlight the biological functions and important downstream target genes of LHPP in tumors, providing a theoretical basis for the treatment of human cancers. Although not thoroughly studied in terms of tumor mechanisms, LHPP still represents a promising and effective anticancer drug target.

FBXO32 targets PHPT1 for ubiquitination to regulate the growth of EGFR mutant lung cancer

BACKGROUND

Phosphohistidine phosphatase 1 (PHPT1) is an oncogene that has been reported to participate in multiple tumorigenic processes. As yet, however, the role of PHPT1 in lung cancer development remains uncharacterized.

METHODS

RNA sequencing assay and 18 pairs of tumor and normal tissues from patients were analyzed to reveal the upregulation of PHPT1 in lung cancer, followed by confirming the biological function in vitro and in vivo. Next, Gene Set Enrichment Analysis, lung cancer samples, apoptosis assay, mass spectrometry experiments and western blotting were used to investigate the molecular mechanism underlying PHPT1 driven progression in epidermal growth factor receptor (EGFR)-mutant lung cancer. Finally, we performed cellular and animal experiments to explore the tumor suppressive function of F-box protein 32 (FBXO32).

RESULTS

We found that PHPT1 is overexpressed in lung cancer patients and correlates with a poor overall survival. In addition, we found that the expression of PHPT1 is elevated in EGFR-mutant lung cancer cells and primary patient samples. Inhibition of PHPT1 expression in EGFR mutant lung cancer cells significantly decreased their proliferation and clonogenicity, and suppressed their in vitro tumor growth. Mechanistic studies revealed that activation of the ERK/MAPK pathway is driven by PHPT1. PHPT1 is required for maintaining drug resistance to erlotinib in EGFR mutant lung cancer cells. We found that FBXO32 acts as an E3 ubiquitin ligase for PHPT1, and that knockdown of FBXO32 leads to PHPT1 accumulation, activation of the ERK/MAPK pathway and promotion of the proliferation, clonogenicity and growth of lung cancer cells.

CONCLUSIONS

Our findings indicate that PHPT1 may serve as a biomarker and therapeutic target for acquired erlotinib resistance in lung cancer patients carrying EGFR mutations.

[Roles of Histidine Kinases and Histidine Phosphatases in Cancer]

蛋白磷酸化修饰是最常见、最重要的蛋白质翻译后修饰方式。磷酸化修饰在细胞的增殖、分化、发育和代谢等生物学过程中发挥了重要的调控功能，与肿瘤的发生和发展也密切相关。蛋白激酶和磷酸酶对蛋白磷酸化修饰具有普遍的开/关调控作用。真核生物的蛋白磷酸化主要发生在丝氨酸、苏氨酸和酪氨酸残基，他们在肿瘤发生和发展中的作用已经得到了广泛的研究。但关于组氨酸磷酸化的研究受限于质谱分析和富集技术的发展研究较少。近年来，随着相关技术的快速发展和新的组氨酸磷酸酶的发现，使得研究人员越来越多关注到组氨酸磷酸化在肿瘤中的作用。因此，本文旨在对组氨酸磷酸化调控相关的组氨酸激酶和组氨酸磷酸酶在肿瘤中的作用作一综述。

Differential Membrane Protein Profile in Bovine X- and Y-Sperm

The aim of this study was to understand the molecular mechanisms behind the biological differences of X- and Y-sperm and to screen the sex-specific candidate antigen proteins for sexed semen production. To this end, we investigated differential expression of total membrane proteins of the two sperm types by using high-purity X- and Y-sperm from 20 Holstein bulls and applying the label-free proteomic technique; 1521 proteins were identified. In the X-sperm group, 8 and 23 proteins were significantly up- and down-regulated, respectively. In the X- and the Y-sperm group, 151 and 88 proteins were specifically expressed, respectively. These were overexpressed in the dynamic changes of the actin cytoskeleton, and cell senescence/apoptosis induced by the immune response, and could result in differences in the state, size, and immune sensitivity of the X-/Y-sperm membranes. The prediction of transmembrane structure, subcellular localization, and Western blotting validation results showed that the CLRN3 and SCAMP1 proteins were cell surface specific antigens of X- and Y-sperm, respectively. Our findings help explain the molecular mechanism behind the biological differences of X-/Y-sperm and lay the foundation for application of immunological methods to produce sex-sorted semen and control livestock sex. Data are available via ProteomeXchange with identifier PXD019435.

14-kDa phosphohistidine phosphatase is a potential therapeutic target for liver fibrosis

Liver fibrosis, a major cause of morbidity and mortality worldwide, leads to liver damage, seriously threatening human health. In our previous study, we demonstrated that 14 kDa phosphohistidine phosphatase (PHP14) was upregulated in fibrotic liver tissue and involved in the migration and lamellipodia formation of hepatic stellate cells (HSCs). In this study, we evaluated PHP14 as a therapeutic target for liver fibrosis and investigated the mechanism by which it mediates liver fibrosis. AAV-shPhpt1 administration significantly attenuates CCl₄-induced liver fibrosis in mice. In particular, fibrosis-associated inflammatory infiltration was significantly suppressed after PHP14 knockdown. Mechanistically, PHP14 regulated macrophage recruitment, infiltration, and migration by affecting podosome formation of macrophages. Inhibition of PHP14 decreased the expression of the fibrogenic signature at the early stage of liver fibrogenesis and the activation of HSCs in vivo. Thus, PHP14 can be considered a potential therapeutic target for liver fibrosis.NEW & NOTEWORTHY PHP14 inhibition via adeno-associated virus (AAV)-mediated gene silencing could potently attenuate carbon tetrachloride (CCl₄)-induced liver fibrosis. PHP14 could regulate the migration of macrophages to the site of injury in vivo. PHP14 knockdown in vivo influenced the environment of fibrogenesis and relevant signaling pathways, subsequently affecting myofibroblast activation.

Natural Products Containing 'Rare' Organophosphorus Functional Groups

Phosphorous-containing molecules are essential constituents of all living cells. While the phosphate functional group is very common in small molecule natural products, nucleic acids, and as chemical modification in protein and peptides, phosphorous can form P⁻N (phosphoramidate), P⁻S (phosphorothioate), and P⁻C (e.g., phosphonate and phosphinate) linkages. While rare, these moieties play critical roles in many processes and in all forms of life. In this review we thoroughly categorize P⁻N, P⁻S, and P⁻C natural organophosphorus compounds. Information on biological source, biological activity, and biosynthesis is included, if known. This review also summarizes the role of phosphorylation on unusual amino acids in proteins (N- and S-phosphorylation) and reviews the natural phosphorothioate (P⁻S) and phosphoramidate (P⁻N) modifications of DNA and nucleotides with an emphasis on their role in the metabolism of the cell. We challenge the commonly held notion that nonphosphate organophosphorus functional groups are an oddity of biochemistry, with no central role in the metabolism of the cell. We postulate that the extent of utilization of some phosphorus groups by life, especially those containing P⁻N bonds, is likely severely underestimated and has been largely overlooked, mainly due to the technological limitations in their detection and analysis.

Redox inhibition of protein phosphatase PP2A: Potential implications in oncogenesis and its progression

Cellular processes are dictated by the active signaling of proteins relaying messages to regulate cell proliferation, apoptosis, signal transduction and cell communications. An intricate web of protein kinases and phosphatases are critical to the proper transmission of signals across such cascades. By governing 30–50% of all protein dephosphorylation in the cell, with prominent substrate proteins being key regulators of signaling cascades, the phosphatase PP2A has emerged as a celebrated player in various developmental and tumorigenic pathways, thereby posing as an attractive target for therapeutic intervention in various pathologies wherein its activity is deregulated. This review is mainly focused on refreshing our understanding of the structural and functional complexity that cocoons the PP2A phosphatase, and its expression in cancers. Additionally, we focus on its physiological regulation as well as into recent advents and strategies that have shown promise in countering the deregulation of the phosphatase through its targeted reactivation. Finally, we dwell upon one of the key regulators of PP2A in cancer cells-cellular redox status-its multifarious nature, and its integration into the reactome of PP2A, highlighting some of the significant impacts that ROS can inflict on the structural modifications and functional aspect of PP2A.

Advances in development of new tools for the study of phosphohistidine

Protein phosphorylation is an important post-translational modification that is an integral part of cellular function. The O-phosphorylated amino-acid residues, such as phosphoserine (pSer), phosphothreonine (pThr) and phosphotyrosine (pTyr), have dominated the literature while the acid labile N-linked phosphorylated amino acids, such as phosphohistidine (pHis), have largely been historically overlooked because of the acidic conditions routinely used in amino-acid detection and analysis. This review highlights some misinterpretations that have arisen in the existing literature, pinpoints outstanding questions and potential future directions to clarify the role of pHis in mammalian signalling systems. Particular emphasis is placed on pHis isomerization and the hybrid functionality for both pHis and pTyr of the proposed τ-pHis analogue bearing the triazole residue.

PHP14 regulates hepatic stellate cells migration in liver fibrosis via mediating TGF-β1 signaling to PI3Kγ/AKT/Rac1 pathway

Hepatic fibrosis is characterized by the activation of hepatic stellate cells (HSCs). Migration of the activated HSCs to the site of injury is one of the key characteristics during the wound healing process. We have previously demonstrated that 14 kDa phosphohistidine phosphatase (PHP14) is involved in migration and lamellipodia formation of HSCs. However, the role of PHP14 in liver fibrosis remains unknown. In this study, we first assessed PHP14 expression and distribution in liver fibrotic tissues using western blot, immunohistochemistry, and double immunofluorescence staining. Next, we investigated the role of PHP14 in liver fibrosis and, more specifically, the migration of HSCs by Transwell assay and 3D collagen matrices assay. Finally, we explored the possible molecular mechanisms of the effects of PHP14 on these processes. Our results show that the PHP14 expression is up-regulated in fibrotic liver and mainly in HSCs. Importantly, TGF-β1 can induce PHP14 expression in HSCs accompanied with the activation of HSCs. Consistent with the previous study, PHP14 promotes HSCs migration, especially, promotes 3D floating collagen matrices contraction but inhibits stressed-released matrices contraction. Mechanistically, the PI3Kγ/AKT/Rac1 pathway is involved in migration regulated by PHP14. Moreover, PHP14 specifically mediates the TGF-β1 signaling to PI3Kγ/AKT pathway and regulates HSC migration, and thus participates in liver fibrosis. Our study identified the role of PHP14 in liver fibrosis, particularly HSC migration, and suggested a novel mediator of transducting TGF-β1 signaling to PI3Kγ/AKT/Rac1 pathway.

KEY MESSAGES

PHP14 is up-regulated in fibrotic liver and activated hepatic stellate cells. The expression of PHP14 is induced by TGF-β1. The migration of hepatic stellate cells is regulated by PHP14. PHP14 is a mediator of TGF-β1 signaling to PI3Kγ/AKT/Rac1 pathway in hepatic stellate cells.

pHisphorylation: the emergence of histidine phosphorylation as a reversible regulatory modification

Histidine phosphorylation is crucial for prokaryotic signal transduction and as an intermediate for several metabolic enzymes, yet its role in mammalian cells remains largely uncharted. This is primarily caused by difficulties in studying histidine phosphorylation because of the relative instability of phosphohistidine (pHis) and lack of specific antibodies and methods to preserve and detect it. The recent synthesis of stable pHis analogs has enabled development of pHis-specific antibodies and their use has started to shed light onto this important, yet enigmatic posttranslational modification. We are beginning to understand that pHis has broader roles in protein and cellular function including; cell cycle regulation, phagocytosis, regulation of ion channel activity and metal ion coordination. Two mammalian histidine kinases (NME1 and NME2), two pHis phosphatases (PHPT1 and LHPP), and a handful of substrates were previously identified. These new tools have already led to the discovery of an additional phosphatase (PGAM5) and hundreds of putative substrates. New methodologies are also being developed to probe the pHis phosphoproteome and determine functional consequences, including negative ion mode mass spectroscopy and unnatural amino acid incorporation. These new tools and strategies have the potential to overcome the unique challenges that have been holding back our understanding of pHis in cell biology.

A novel role for 14-kDa phosphohistidine phosphatase in lamellipodia formation

Cell migration involves dynamic regulation of the actin cytoskeleton, which exhibits rapid actin polymerization at the leading edge of migrating cells. This process relies on regulated recruitment of actin nucleators and actin-binding proteins to the leading edge to polymerize new actin filaments. Many of these proteins have been identified, including the actin-related protein (Arp) 2/3 complex, which has emerged as the core player in the initiation of actin polymerization. However, the functional coordination of these proteins is unclear. Previously, we have demonstrated that the 14-kDa phosphohistidine phosphatase (PHP14) is involved in cell migration regulation and affects actin cytoskeleton reorganization. Here, we show that PHP14 may regulate actin remodeling directly and play an important role in dynamic regulation of the actin cytoskeleton. We observed a colocalization of PHP14 with Arp3 and F-actin at the leading edge of migrating cells. Moreover, PHP14 was recruited to the actin remodeling sites in parallel with Arp3 during lamellipodia formation. Furthermore, PHP14 knockdown impaired Arp3 localization at the leading edge of lamellipodia, as well as lamellipodia formation. Most importantly, we found that PHP14 was a novel F-actin-binding protein, displaying an Arp2/3-dependent localization to the leading edge. Collectively, our results indicated a crucial role for PHP14 in the dynamic regulation of the actin cytoskeleton and cell migration.

Differential expression of alternatively spliced transcripts related to energy metabolism in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is one of the most common malignant tumors worldwide. CRC molecular pathogenesis is heterogeneous and may be followed by mutations in oncogenes and tumor suppressor genes, chromosomal and microsatellite instability, alternative splicing alterations, hypermethylation of CpG islands, oxidative stress, impairment of different signaling pathways and energy metabolism. In the present work, we have studied the alterations of alternative splicing patterns of genes related to energy metabolism in CRC.

RESULTS

Using CrossHub software, we analyzed The Cancer Genome Atlas (TCGA) RNA-Seq datasets derived from colon tumor and matched normal tissues. The expression of 1014 alternative mRNA isoforms involved in cell energy metabolism was examined. We found 7 genes with differentially expressed alternative transcripts whereas overall expression of these genes was not significantly altered in CRC. A set of 8 differentially expressed transcripts of interest has been validated by qPCR. These eight isoforms encoded by OGDH, COL6A3, ICAM1, PHPT1, PPP2R5D, SLC29A1, and TRIB3 genes were up-regulated in colorectal tumors, and this is in concordance with the bioinformatics data. The alternative transcript NM_057167 of COL6A3 was also strongly up-regulated in breast, lung, prostate, and kidney tumors. Alternative transcript of SLC29A1 (NM_001078177) was up-regulated only in CRC samples, but not in the other tested tumor types.

CONCLUSIONS

We identified tumor-specific expression of alternative spliced transcripts of seven genes involved in energy metabolism in CRC. Our results bring new knowledge on alternative splicing in colorectal cancer and suggest a set of mRNA isoforms that could be used for cancer diagnosis and development of treatment methods.

Clarification of the molecular pathway of Taiwan local pomegranate fruit juice underlying the inhibition of urinary bladder urothelial carcinoma cell by proteomics strategy

Background

Pomegranate fruit has been shown to exhibit the inhibitory activity against prostate cancer and lung cancer in vitro and in vivo, which might be a resource for chemoprevention and chemotherapy of cancer. Our previous documented findings indicated that treatment of urinary bladder urothelial carcinoma cell with the ethanol extract isolated from the juice of pomegranate fruit grown in Taiwan could inhibit tumor cell. In this study we intended to uncover the molecular pathway underlying anti-cancer efficacy of Taiwan pomegranate fruit juice against urinary bladder urothelial carcinoma.

Methods

We exploited two-dimensional gel electrophoresis coupled with tandem mass spectrometry to find the de-regulated proteins. Western immunoblotting was used to confirm the results collected from proteomics study.

Results

Comparative proteomics indicated that 20 proteins were differentially expressed in ethanol extract-treated T24 cells with 19 up-regulated and 1 down-regulated proteins. These de-regulated proteins were involved in apoptosis, cytoskeleton regulation, cell proliferation, proteasome activity and aerobic glycolysis. Further studies on signaling pathway demonstrated that ethanol extract treatment might inhibit urinary bladder urothelial carcinoma cell proliferation through restriction of PTEN/AKT/mTORC1 pathway via profilin 1 up-regulation. It also might evoke cell apoptosis through Diablo over-expression.

Conclusions

The results of this study provide a global picture to further investigate the anticancer molecular mechanism of pomegranate fruit.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1071-7) contains supplementary material, which is available to authorized users.

Nuclear expression and clinical significance of phosphohistidine phosphatase 1 in clear-cell renal cell carcinoma

OBJECTIVE

To explore expression and clinical relevance of phosphohistidine phosphatase 1 (PHPT1) in clear-cell renal cell carcinoma.

METHODS

Patients with clear-cell renal cell carcinoma who underwent radical or nephron-sparing nephrectomy were enrolled. Correlations between PHPT1 expression and demographic and clinical characteristics were analysed prospectively.

RESULTS

In total, 122 patients (78 male/44 female) were included. In normal kidney tissue, PHPT1 expression was observed only in the proximal tubule. High PHPT1 expression levels were associated with larger tumour size, higher Fuhrman nuclear grade and advanced pathological tumour-node-metastasis (pTNM) stage compared with low PHPT1 expression levels. Patients with low PHPT1 expression showed better overall survival and progression-free survival compared with those with high PHPT1 expression. In addition, multivariate analysis showed that nuclear grade and pTNM stage were independent predictors of progression-free survival and overall survival in patients with clear-cell renal cell carcinoma. PHPT1 expression was also an independent predictor of overall survival but not progression-free survival.

CONCLUSIONS

PHPT1 was expressed in the epithelium of proximal tubuli and nuclei of clear-cell renal cell carcinoma tissue samples. High levels of 14 kDa phosphohistidine phosphatase protein were negatively associated with overall survival and progression-free survival in patients with clear-cell renal cell carcinoma.

The Characteristics and Function of S100A7 Induction in Squamous Cell Carcinoma: Heterogeneity, Promotion of Cell Proliferation and Suppression of Differentiation

S100A7 is highly expressed in squamous cell carcinomas (SCC) and is related to the terminal differentiation of keratinocytes. However, its characteristic and function in SCC is not very known. In this present study, we used immunohistochemistry to examine the expression of S100A7 in 452 SCC specimens, including the lung, esophagus, oral cavity, skin, cervix, bladder, and three SCC cell lines. We found that S100A7-positive staining showed significant heterogeneity in six types of SCC specimen and three SCC cell lines. Further examination found that S100A7-positive cells and its expression at mRNA and protein levels could be induced in HCC94, FaDu, and A-431 cells both in vitro and in vivo using immunohistochemistry, real-time PCR, and Western blotting. Notably, the upregulation of squamous differentiation markers, including keratin-4, keratin-13, TG-1, and involucrin, also accompanied S100A7 induction, and a similar staining pattern of S100A7 and keratin-13 was found in HCC94 cells both in vitro and in vivo. Further study revealed that the overexpression of S100A7 significantly increased proliferation and inhibited squamous differentiation in A-431 cells both in vitro and in vivo. Conversely, silencing S100A7 inhibited cell growth and survival and increased the expression of keratin-4, keratin-13, TG-1, and involucrin in HCC94 cells. Therefore, these results demonstrate that S100A7 displays heterogeneous and inducible characteristic in SCC and also provide novel evidence that S100A7 acts as a dual regulator in promoting proliferation and suppressing squamous differentiation of SCC.

Phosphohistidine phosphatase 1 (PHPT1) also dephosphorylates phospholysine of chemically phosphorylated histone H1 and polylysine

BACKGROUND

Phosphohistidine phosphatase 1 (PHPT1), also named protein histidine phosphatase (PHP), is a eukaryotic enzyme dephosphorylating proteins and peptides that are phosphorylated on a histidine residue. A preliminary finding that histone H1, which lacks histidine, was phosphorylated by phosphoramidate and dephosphorylated by PHPT1 prompted the present investigation.

METHODS

Histone H1 and polylysine were phosphorylated at a low concentration (3.9 mM) of phosphoramidate. Their dephosphorylation by recombinant human PHPT1 was investigated by using a DEAE-Sepharose spin column technique earlier developed by us for studies on basic phosphoproteins and phosphopeptides. Determination of protein-bound, acid-labile phosphate was performed by a malachite green method. Mass spectrometry (MS) was used to investigate the occurrence of N-ε-phospholysine residues in a phosphorylated histone H1.2 preparation, and to measure the activity of PHPT1 against free N-ω-phosphoarginine.

RESULTS

Histone H1.2, which lacks histidine, was phosphorylated by phosphoramidate on several lysine residues, as shown by MS. PHPT1 was shown to dephosphorylate phosphohistone H1 at a rate similar to that previously described for the dephosphorylation of phosphohistidine-containing peptides. In addition, phosphopolylysine was an equally good substrate for PHPT1. However, no dephosphorylation of free phosphoarginine by PHPT1 could be detected.

CONCLUSION

The finding that PHPT1 can dephosphorylate phospholysine in chemically phosphorylated histone H1 and polylysine demonstrates a broader specificity for this enzyme than known so far.

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 14 kDa 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.

A novel high throughput invasion screen identifies host actin regulators required for efficient cell entry by Toxoplasma gondii

Toxoplasma gondii critically relies on cell invasion as a survival strategy to evade immune clearance during infection. Although it was widely thought that Toxoplasma entry is parasite directed and that the host cell is largely a passive victim, recent studies have suggested that host components such as microfilaments and microtubules indeed contribute to entry. Hence to identify additional host factors, we performed a high-throughput siRNA screen of a human siRNA library targeting druggable proteins using a novel inducible luciferase based invasion assay. The top 100 hits from the primary screen that showed the strongest decreases in invasion were subjected to confirmation by secondary screening, revealing 24 proteins that are potentially involved in Toxoplasma entry into host cells. Interestingly, 6 of the hits appear to affect parasite invasion by modifying host cell actin dynamics, resulting in increased deposition of F-actin at the periphery of the cell. These findings support the emerging notion that host actin dynamics are important for Toxoplasma invasion along with identifying several novel host factors that potentially participate in parasite entry.

Mass spectrometry-based proteomics: the road to lung cancer biomarker discovery

Lung cancer is the leading cause of cancer death in men and women in Western nations, and is among the deadliest cancers with a 5-year survival rate of 15%. The high mortality caused by lung cancer is attributable to a late-stage diagnosis and the lack of effective treatments. So, it is crucial to identify new biomarkers that could function not only to detect lung cancer at an early stage but also to shed light on the molecular mechanisms that underlie cancer development and serve as the basis for the development of novel therapeutic strategies. Considering that DNA-based biomarkers for lung cancer showed inadequate sensitivity, specificity, and reproducibility, proteomics could represent a better tool for the identification of useful biomarkers and therapeutic targets for this cancer type. Among the proteomics technologies, the most powerful tool is mass spectrometry. In this review, we describe studies that use mass spectrometry-based proteomics technologies to analyze tumor proteins and peptides, which might represent new diagnostic, prognostic, and predictive markers for lung cancer. We focus in particular on those findings that hold promise to impact significantly on the clinical management of this disease.

Expanded protein expression profile of human placenta using two-dimensional gel electrophoresis

Studying proteins expressed in placenta is important to understand its function in pregnancy and fetal growth. Here, we present protein expression profiling from normal human placenta by 2-D gel - MS/MS approach that resulted in identification of 117 unique proteins. Integration with earlier analyses resulted in a profile of 423 non-redundant proteins, 75 of them being new identifications unique to this study including their isoforms. We present a compilation of placental protein expressions identified by proteomic approaches, their functions and known clinical implications. We believe that our dataset would be a useful resource for studies related to placental dysfunction.

Application of glycoproteomics for the discovery of biomarkers in lung cancer

Lung cancer is the leading cause of cancer-related deaths in the United States. Approximately 40-60% of lung cancer patients present with locally advanced or metastatic disease at the time of diagnosis. Lung cancer development and progression are a multistep process that is characterized by abnormal gene and protein expressions ultimately leading to phenotypic change. Glycoproteins have long been recognized to play fundamental roles in many physiological and pathological processes, particularly in cancer genesis and progression. In order to improve the survival rate of lung cancer patients, the discovery of early diagnostic and prognostic biomarkers is urgently needed. Herein, we reviewed the recent technological developments of glycoproteomics and published data in the field of glycoprotein biomarkers in lung cancer, and discussed their utility and limitations for the discovery of potential biomarkers in lung cancer. Although numerous papers have already acknowledged the importance of the discovery of cancer biomarkers, the systemic study of glycoproteins in lung cancer using glycoproteomic approaches is still suboptimal. Recent development in the glycoproteomics will provide new platforms for identification of potential protein biomarkers in lung cancers.

Influence of protein histidine phosphatase overexpression and down-regulation on human umbilical-vein endothelial cell viability

PHP (protein histidine phosphatase) is expressed by mammalian tissues, particularly in blood vessel walls. We investigated whether PHP plays a significant role in endothelial cells. By Western blot and immunofluorescence analysis PHP was found in HUVEC (human umbilical-vein endothelial cells). Overexpression of PHP by the use of a plasmid vector, pIRES2-AcGFP1-PHP, induced apoptosis in HUVEC. To exclude the possibility that increased cellular protein alone unspecifically caused cell damage, the inactive H53A mutant of PHP was also overexpressed as a control; it did not lead to apoptosis. Down-regulation of PHP by the RNAi (RNA interference) technique did not affect cell viability. In conclusion, HUVEC are damaged by overexpression, but not down-regulation, of PHP, suggesting a pronounced impact of the enzyme on the cells when its activity is increased.

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.

P-N bond protein phosphatases

The current work briefly reviews what is currently known about protein phosphorylation on arginine, lysine and histidine residues, where PN bonds are formed, and the protein kinases that catalyze these reactions. Relatively little is understood about protein arginine and lysine kinases and the role of phosphorylation of these residues in cellular systems. Protein histidine phosphorylation and the two-component histidine kinases play important roles in cellular signaling systems in bacteria, plants and fungi. Their roles in vertebrates are much less well researched and there are no protein kinases similar to the two-component histidine kinases. The main focus of the review however, is to present current knowledge of the characterization, mechanisms of action and biological roles of the phosphatases that catalyze the hydrolysis of these phosphoamino acids. Very little is known about protein phosphoarginine and phospholysine phosphatases, although their existence is well documented. Some of these phosphatases exhibit very broad specificity in terms of which phosphoamino acids are substrates, however there appear to be one or two quite specific protein phospholysine and phosphoarginine phosphatases. Similarly, there are phosphatases with broad substrate specificities that catalyze the hydrolysis of phosphohistidine in protein substrates, including the serine/threonine phosphatases 1, 2A and 2C. However there are two, more specific, protein phosphohistidine phosphatases that have been well characterized and for which structures are available, SixA is a phosphatase associated with two-component histidine kinase signaling in bacteria, and the other is found in a number of organisms, including mammals. This article is part of a Special Issue entitled: Chemistry and mechanism of phosphatases, diesterases and triesterases.

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.

Lung cancer proteomics: recent advances in biomarker discovery

Lung cancer is the most common cause of cancer death in both men and women in Western countries, with a 5-year survival rate of 15%, which is among the lowest of all cancers. The high mortality from lung cancer is due not only to the late stage diagnosis but also to the lack of effective treatments even for patients diagnosed with stage I lung cancer. Therefore, there is an urgent need to identify new markers for early diagnosis and prognosis that could serve to open novel therapeutic avenues. Proteomics can represent an important tool for the identification of biomarkers and therapeutic targets for lung cancer since DNA-based biomarkers did not prove to have adequate sensitivity, specificity, and reproducibility. In this paper we will describe studies focused on the identification of new diagnostic, prognostic, and predictive markers for lung cancer, using proteomics technologies.

Proteomic profile regulated by the anticancer peptide CIGB-300 in non-small cell lung cancer (NSCLC) cells

CIGB-300 is a proapoptotic peptide-based drug that abrogates the CK2-mediated phosphorylation. This peptide has antineoplastic effect on lung cancer cells in vitro and in vivo. To understand the mechanisms involved on such anticancer activity, the NCI-H125 cell line proteomic profile after short-term incubation (45 min) with CIGB-300 was investigated. As determined by 2-DE or 2D-LC-MS/MS, 137 proteins changed their abundances more than 2-fold in response to the CIGB-300 treatment. The expression levels of proteins related to ribosome biogenesis, metastasis, cell survival and proliferation, apoptosis, and drug resistance were significantly modulated by the presence of CIGB-300. The protein translation process was the most affected (23% of the identified proteins). From the proteome analysis of the NCI-H125 cell line, novel potentialities for CIGB-300 as anticancer agent were evidenced.

Regulation of glucose- and mitochondrial fuel-induced insulin secretion by a cytosolic protein histidine phosphatase in pancreatic beta-cells

We report localization of a cytosolic protein histidine phosphatase (PHP; approximately 16 kDa) in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knockdown of PHP markedly reduced glucose- or mitochondrial fuel-induced but not KCl-induced insulin secretion. siRNA-mediated knockdown of PHP also attenuated mastoparan-induced insulin secretion, suggesting its participation in G protein-sensitive signaling steps, leading to insulin secretion. Functional assays revealed that the beta-cell PHP catalyzes the dephosphorylation of ATP-citrate lyase (ACL). Silencing of PHP expression markedly reduced ACL activity, suggesting functional regulation of ACL by PHP in beta-cells. Coimmunoprecipitation studies revealed modest effects of glucose on the interaction between PHP and ACL. Confocal microscopic evidence indicated that glucose promotes association between ACL and nm23-H1, a known kinase histidine kinase, but not between PHP and ACL. Furthermore, metabolic viability of INS 832/13 cells was resistant to siRNA-PHP, suggesting no regulatory roles of PHP in cell viability. Finally, long-term exposure (24 h) of INS 832/13 cells or rat islets to high glucose (30 mM) increased the expression of PHP. Such increases in PHP expression were also seen in islets derived from the Zucker diabetic fatty rat compared with islets from the lean control animals. Together, these data implicate regulatory roles for PHP in a G protein-sensitive step involved in nutrient-induced insulin secretion. In light of the current debate on putative regulatory roles of ACL in insulin secretion, additional studies are needed to precisely identify the phosphoprotein substrate(s) for PHP in the cascade of events leading to nutrient-induced insulin secretion.

Lung cancer proteomics, clinical and technological considerations

The overall survival of lung cancer patients is disappointingly low. This is due to several factors, including the lack of an effective screening strategy to detect tumors at a potentially curable early stage, a marked resistance of lung cancer cells to drug treatment and a still superficial knowledge about the multifactorial cellular networks that are activated or suppressed during cancer progression. Furthermore, the armamentarium of clinicians and researchers in the field does not yet include reliable biomarkers to predict tumor response to treatment and foresee the natural history of the disease. In the present situation, a potential breakthrough is presented by proteomics technologies with the potential to discover relevant biomarkers which can be accurately quantified in multiplexed assays. Proteomics field can also contribute greatly in the understanding of mechanisms in tumor progression and treatment response. In this review we will describe the work that is being done in the field of lung cancer proteomics, focusing on clinically relevant questions that need to be addressed and on the possible applications of novel technologies.