A plant oxysterol, 28-homobrassinolide binds HMGCoA reductase catalytic cleft: stereoselective avidity affects enzyme function

Understanding the influence of ubiquitously present plant steroids on mammalian cell biology is currently of interest. Feedback inhibition of HMGCoA reductase (HMGCR) catalytic activity in the transformation of HMG-CoA to mevalonate is a significant regulatory step in sterol biosynthetic pathway. To assess the role of dietary steroids in this biochemical transformation, the phytosteroid isoform 28-homobrassinolide (28-HB), 90 % pure, obtained from Godrej Agrovet (India) was used to determine its effect on mammalian HMG-CoA reductase. Photometric assay of pure human and select rat tissue HMGCR post 28-HB oral feed, PCR-HMGCR gene expression, and in silico docking of 28-HB and HMGCoA on HMGCR protein template were carried out. Using an oral feed regimen of pure 28-HB, we noted a decrease of 16 % in liver, 17.1 % in kidney and 9.3 % in testicular HMGCR enzyme activity, 25 % in HMGCR gene expression and 44 % in the activity of pure human HMGCR due to this plant oxysterol. In silico docking studies yielded binding metrics for 28-HB-HMGCR lower than for HMGCoA-HMGCR, indicating stronger binding of HMGCR by this ligand. 28-HB exerts differential effects on rat tissue HMGCR, down regulates liver HMGCR gene expression and significantly inhibits HMGCR activity.

Calcium calmodulin dependent kinase kinase 2 - a novel therapeutic target for gastric adenocarcinoma

Gastric cancer is one of the most common gastrointestinal malignancies and is associated with poor prognosis. Exploring alterations in the proteomic landscape of gastric cancer is likely to provide potential biomarkers for early detection and molecules for targeted therapeutic intervention. Using iTRAQ-based quantitative proteomic analysis, we identified 22 proteins that were overexpressed and 17 proteins that were downregulated in gastric tumor tissues as compared to the adjacent normal tissue. Calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) was found to be 7-fold overexpressed in gastric tumor tissues. Immunohistochemical labeling of tumor tissue microarrays for validation of CAMKK2 overexpression revealed that it was indeed overexpressed in 94% (92 of 98) of gastric cancer cases. Silencing of CAMKK2 using siRNA significantly reduced cell proliferation, colony formation and invasion of gastric cancer cells. Our results demonstrate that CAMKK2 signals in gastric cancer through AMPK activation and suggest that CAMKK2 could be a novel therapeutic target in gastric cancer.

Silencing of high-mobility group box 2 (HMGB2) modulates cisplatin and 5-fluorouracil sensitivity in head and neck squamous cell carcinoma

Dysregulation of protein expression is associated with most diseases including cancer. MS-based proteomic analysis is widely employed as a tool to study protein dysregulation in cancers. Proteins that are differentially expressed in head and neck squamous cell carcinoma (HNSCC) cell lines compared to the normal oral cell line could serve as biomarkers for patient stratification. To understand the proteomic complexity in HNSCC, we carried out iTRAQ-based MS analysis on a panel of HNSCC cell lines in addition to a normal oral keratinocyte cell line. LC-MS/MS analysis of total proteome of the HNSCC cell lines led to the identification of 3263 proteins, of which 185 proteins were overexpressed and 190 proteins were downregulated more than twofold in at least two of the three HNSCC cell lines studied. Among the overexpressed proteins, 23 proteins were related to DNA replication and repair. These included high-mobility group box 2 (HMGB2) protein, which was overexpressed in all three HNSCC lines studied. Overexpression of HMGB2 has been reported in various cancers, yet its role in HNSCC remains unclear. Immunohistochemical labeling of HMGB2 in a panel of HNSCC tumors using tissue microarrays revealed overexpression in 77% (54 of 70) of tumors. The HMGB proteins are known to bind to DNA structure resulting from cisplatin-DNA adducts and affect the chemosensitivity of cells. We observed that siRNA-mediated silencing of HMGB2 increased the sensitivity of the HNSCC cell lines to cisplatin and 5-FU. We hypothesize that targeting HMGB2 could enhance the efficacy of existing chemotherapeutic regimens for treatment of HNSCC. All MS data have been deposited in the ProteomeXchange with identifier PXD000737 (http://proteomecentral.proteomexchange.org/dataset/PXD000737).

Phosphotyrosine profiling identifies ephrin receptor A2 as a potential therapeutic target in esophageal squamous-cell carcinoma

Esophageal squamous‐cell carcinoma (ESCC) is one of the most common malignancies in Asia. Currently, surgical resection of early‐stage tumor is the best available treatment. However, most patients present late when surgery is not an option. Data suggest that chemotherapy regimens are inadequate for clinical management of advanced cancer. Targeted therapy has emerged as one of the most promising approaches to treat several malignancies. A prerequisite for developing targeted therapy is prior knowledge of proteins and pathways that drive proliferation in malignancies. We carried out phosphotyrosine profiling across four different ESCC cell lines and compared it to non‐neoplastic Het‐1A cell line to identify activated tyrosine kinase signaling pathways in ESCC. A total of 278 unique phosphopeptides were identified across these cell lines. This included several tyrosine kinases and their substrates that were hyperphosphorylated in ESCC. Ephrin receptor A2 (EPHA2), a receptor tyrosine kinase, was hyperphosphorylated in all the ESCC cell lines used in the study. EPHA2 is reported to be oncogenic in several cancers and is also known to promote metastasis. Immunohistochemistry‐based studies have revealed EPHA2 is overexpressed in nearly 50% of ESCC. We demonstrated EPHA2 as a potential therapeutic target in ESCC by carrying out siRNA‐based knockdown studies. Knockdown of EPHA2 in ESCC cell line TE8 resulted in significant decrease in cell proliferation and invasion, suggesting it is a promising therapeutic target in ESCC that warrants further evaluation.

Molecular and computational approaches to characterize thermostable laccase gene from two xerophytic plant species

Laccases are blue multicopper oxidases that carry out single electron transfers in the oxidation of phenols to quinones. In plants, they confer structural stability to the cell wall. Thermostable laccases were identified in xerophytes Cereus pterogonus and Opuntia vulgaris that could be used in biotechnology and industrial processes. Polyclonal anti-laccase antibodies were generated against purified laccase enzyme isoforms capable of 98-99% inhibition of the catalytic activity. Antibodies raised against lower molecular weight isoforms inhibited 70% of the catalytic activity of higher molecular forms. Only 20% inhibition was noted when assayed in reverse. A partial gene sequence of thermostable xerophytic laccase comprising 712 and 880 bp was identified employing cDNA as template. The nucleotide sequence was submitted to GenBank. The gene sequence was in silico translated into protein sequence and a 3-D structure was predicted using I-Tasser and Genesilico online servers that justified the experimental observations. Anti-laccase antibodies and nucleotide gene sequence of this thermostable plant laccase can be utilized for predicting laccase antigenic sequences and for cloning and expression of the thermostable eukaryotic laccase.

A phytooxysterol, 28-homobrassinolide modulates rat testicular steroidogenesis in normal and diabetic rats

Steroidogenesis in testicular cells depends upon the availability of cholesterol within testicular mitochondria besides the activities of 3β-hydroxysteroid dehydrogenase (3β-HSD, 17β-hydroxysteroid dehydrogenase [17b-HSD]), and the tissue levels of steroidogenic acute regulatory protein (StAR), androgen-binding protein (ABP), and testosterone (T). Cellular cholesterol biosynthesis is regulated by endogenous oxycholesterols acting through nuclear hormone receptors. Plant oxysterols, such as 28-homobrassinolide (28-HB), available to human through diet, was shown to exhibit antihyperglycemic effect in diabetic male rat. Its role in rat testicular steroidogenesis and lipid peroxidation (LPO) was therefore assessed using normal and streptozotocin-induced diabetic male rats. Administration of 28-HB (333 µg/kg body weight) by oral gavage for 15 consecutive days to experimental rats diminished LPO, increased antioxidant enzyme, 3β-HSD and 17β-HSD activities, and elevated StAR and ABP expression and T level in rat testis. We report that 28-HB induced steroidogenesis in normal and diabetic rat testis.

Purification and characterization of thermophilic xylanase isolated from the xerophytic-Cereus pterogonus sp

A thermo stable xylanase was purified and characterized from the cladodes of Cereus pterogonus plant species. The enzyme was purified to homogeneity by ammonium sulfate (80%) fractionation, ion exchange and size exclusion chromatography. The enzyme showed a final specific activity of 216.2 U/mg and the molecular mass of the protein was 80 KDa. The optimum pH and temperature for xylanase activity were 5.0 and 80 °C, respectively. With oat spelt xylan as a substrate the enzyme yielded a Km value of 2.24 mg/mL and a Vmax of 5.8 μmol min(-1) mg(-1). In the presence of metal ions (1 mM) such as Co(2+),Mn(2+), Ni(2+), Ca(2+) and Fe(3+) the activity of the enzyme increased, where as strong inhibition of the enzyme activity was observed with the use of Hg(2+), Cd(2+), Cu(2+), while partial inhibition was noted with Zn(2+) and Mg(2+). The substrate specificity of the xylanase yielded maximum activity with oat spelt xylan.

Thermophilic laccase from xerophyte species Opuntia vulgaris

Two laccase temperature isoforms capable of oxidizing phenolic compounds to quinones were isolated and purified to homogeneity from the cladodes of the xerophyte species Opuntia vulgaris. These catalytically active proteins exhibit apparent molecular masses of 137 and 90 kDa. Under reducing conditions, both isoforms yielded a subunit molecular mass of 43 kDa, suggesting that the enzyme is a multimer of the 43 kDa subunit. The 137 kDa isoform when heated at 80°C for 3 min generated three polypeptide bands on activity stained polyacrylamide gels exhibiting 137, 90 and 43 kDa molecular forms. All isoforms of the enzyme exhibited an optimum pH of 10 when 2,6-dimethoxyphenol was used as a substrate. The optimum temperature of the 137 kDa enzyme form was noted to be 80°C and that of the 90 kDa enzyme form was 70°C. Denaturation kinetics of both the laccase isoforms carried out at their respective optimum temperatures for 30 min exhibited enzyme activity in excess of their t(1/2) values throughout the assay period. The K(m) for the 137 kDa form was determined to be 2.2 ± 0.3 mm and the V(max) was 2.8 ± 0.2 IU/mL. These high temperature stable laccase isoforms having alkaline pH optima can find significant industrial use.

Induction of hexokinase I expression in normal and diabetic rats by a brassinosteroid isoform

This study aimed to investigate the effect of the plant growth regulator 28-homobrassinolide (HB) on the hexokinase I (HK I) enzyme gene expression in the tissues of normal and streptozotocin-induced diabetic rats. Normal and diabetic rats were administered 50 microg of HB for 15 consecutive days. The tissues level of HK I mRNA expression was quantitated by PCR and densitometry analysis, HK I protein expression was quantitated by Western blot and densitometry analysis, localization of HK I was done by immunohistochemistry and HK enzyme activity was determined by coupled enzyme assay. Subchronic treatment of rats with HB enhanced HK I enzyme expression in diabetic rat compared to the control rat. From these experimental evidences, we came to the conclusion that HK I played a vital role in the regulation of blood sugar in streptozotocin-induced diabetic rats. A direct role for hexokinase enzyme activity in the control of diabetes is presented.

Alterations in beta-islets of Langerhans in alloxan-induced diabetic rats by marine Spirulina platensis

Marine Spirulina platensis may potentially influence the metabolic process in animal cells, and the effect of marine Spirulina platensis in normal and alloxan-induced diabetic rats was therefore investigated. Normal and diabetic rats (albino Wistar strain) were orally administered marine Spirulina platensis for 30 days and their blood levels of glucose and insulin and body weight changes were determined. Pancreatic histopathology was also noted. Treatment with marine Spirulina platensis caused significant alterations in the content of these indicators and therefore in the antidiabetic capacity of the treated animals compared to control rats.

Metabolic dysregulation and inhibition of spermatogenesis by gibberellic acid in rat testicular cells

Enzymatic and histological change in the testicular cells of rats treated orally and intradermally for 45 days with gibberellic acid (GBA) in independent studies is reported. Assay of hexokinase (HK), acid phosphatase (AcP) and alkaline phosphatase (AkP) in rat testicular tissue homogenate preparations yielded results that suggested changes in these enzyme activities relative to their respective controls. Histological studies showed loss of germ cells, derangement of the germinal cells, and reduction in the size of the seminiferous tubules and dystrophy of Leydig cells. More importantly decreased sperm count in the lumen was observed. A dysregulatory role is thus established for GBA in rat testicular cell function. This compound may serve as an inhibitor of testicular cell function.

Effect of gastrointestinal proteases on purified human intrinsic factor-vitamin B12 (IF-B12) complex

Intrinsic factor (IF) from human gastric juice was purified and complexed with vitamin B12 (IF-B12 complex) on Sepharose-vitamin B12 affinity matrix. By labeling studies, using [(57)Co] vitamin B12 and (125)I, the specific B12 binding activity of IF was found to be 23 microg B12/mg protein, and the molecular size by gel filtration 60 kDa. Proteolysis of the IF-B12 complex by sequential treatment with pepsin, trypsin, alpha-chymotrypsin and carboxypeptidase A, followed by chromatography of proteolysed complex and IF-B12 showed higher mobility of proteolysed fraction. Gel filtration, however, showed same molecular size for both proteolysed and the IF-B12 complex. On SDS-PAGE, purified IF-B12 appeared as a single band of 60 kDa. The proteolysed complex had higher mobility on SDS-PAGE and did not bind to zirconium phosphate gel. Immunodiffusion with rabbit antisera had positive reaction with IF-B12, but there was no reaction with the proteolysed sample.

Long-term marrow cultures: human and murine systems

The intramedullary control of marrow cell production has been a difficult area to approach experimentally. The introduction by Dr. Dexter and colleagues of long-term stromal dependent culture systems for murine marrow and the adaptation of these systems to human marrow growth have allowed for in-vitro studies of stromal dependent hemopoiesis. Despite some controversy in this area, most studies appear to show that adherent murine or human stromal cells are capable of producing a relatively large number of hemopoietic growth factors including G-CSF, GM-CSF, CSF-1, IL-6 and, at least by PCR analysis, IL-3. Other work indicates that the most primitive hemopoietic cells which appear to be multifactor responsive adhere directly to these stromal cells presumably through mediation of various adherence proteins. An early acting, multilineage factor termed hemolymphopoietic growth factor-1 (HLGF-1) has been isolated from a murine stromal cell line and may be identical to the recently described ligand for the c-kit receptor. This may represent an important early survival/maintenance factor for stem cells in this system. Studies on primitive stem cells, especially the high proliferative potential colony forming cell (HPP-CFC), indicate that they are responsive to varying combinations of growth factors and that with increasing numbers of growth factors, as studied in serum-free systems, decreasing concentrations of the factors may be biologically active. These observations altogether suggest that intramedullary hemopoiesis may be regulated by the positioning of early multifactor responsive stem cells via adherent proteins in juxtaposition to synergistically acting combinations of growth factors attached to stromal cell surfaces or the extracellular matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

Colony-stimulating factor-1 modulates alpha 2-macroglobulin receptor expression in murine bone marrow macrophages

Primary cultures of murine bone marrow macrophages (BMMs) were prepared from marrow cell suspensions. These cells expressed specific receptors that recognized the transformed conformation of human alpha 2-macroglobulin (alpha 2M) generated by reaction with CH3NH2. alpha 2M receptor expression was regulated by colony-stimulating factor-1 (CSF-1). The BMMs were deprived of CSF-1 for 6 h and then treated with different concentrations of the purified cytokine. After 18 h, binding of 125I-alpha 2M-CH3NH2 was examined at 4 degrees C. Analysis of the saturation isotherms and Scatchard transformations indicated that the KD was not affected by CSF-1 (1.9-2.4 nM), whereas the maximum specific radioligand binding capacity (Bmax) was increased from 5.6 x 10(4) receptors/cell in the absence of CSF-1 to 2.2 x 10(5) and 2.6 x 10(5) receptors/cell for BMMs treated with 1,000 and 10,000 units/ml CSF-1, respectively. The difference in total cellular protein after exposure to different levels of CSF-1 for 18 h was small (1.50-1.92 ng/cell) and not statistically significant. A 6-12-h lag phase was identified between the time of CSF-1 exposure and increased alpha 2M receptor expression. Cycloheximide completely blocked the increase in alpha 2M receptor expression when added simultaneously with the CSF-1; greater than 50% inhibition was observed when the cycloheximide was added up to 8 h later. The RNA synthesis inhibitors, actinomycin D and daunomycin, prevented increased alpha 2M receptor expression when added up to 4 h after the CSF-1, but had no effect at 8 h. At 37 degrees C, uptake and digestion of 125I-alpha 2M-CH3NH2 was increased in BMMs treated with 1,000 units/ml CSF-1 for 18 h compared with untreated cells. These studies demonstrate that CSF-1 increases the expression of alpha 2M receptors in BMMs through a pathway that requires new RNA and protein synthesis. We hypothesize that increased alpha 2M receptor expression may play an important role in cellular growth and differentiation.

The role of selenium-dependent and selenium-independent glutathione peroxidases in the formation of prostaglandin F2 alpha

In recent years, growing evidence suggests that glutathione peroxidases (GSH-Pxs), both selenium-dependent GSH-Px (Se-GSH-Px) and selenium-independent GSH-Px (non-Se-GSH-Px) play an important role in the biosynthesis of prostaglandins and leukotrienes and in the regulation of key enzymes associated with the arachidonic acid cascade. The precise nature of their involvement in eicosanoid metabolism, however, is not yet completely understood. In the study reported here, we have systematically determined the catalytic efficiencies of Se-GSH-Px and non-Se-GSH-Px toward prostaglandin (PG) G2 (PGG2) and PGH2. Se-GSH-Px exhibited high catalytic activity for the reduction of PGG2 as indicated by Km and Vmax values of 12 microM and 78 mumol/min/mg, respectively, whereas PGH2 was found to be a poor substrate, an indication that Se-GSH-Px reduces the hydroperoxide moiety but not the endoperoxide moiety of PGG2. The kinetic constants of Se-GSH-Px toward PGG2 were comparable to those determined for such classical substrates as H2O2 and cumene hydroperoxide. In contrast to Se-GSH-Px, non-Se-GSH-Px associated with cationic isozyme II of glutathione S-transferases (GSTs) from sheep lung cytosol was very active in the conversion of PGH2 to PGF2 alpha with a Vmax of 960 nmol/min/mg and a Km of 77 microM. This study shows that PGF2 alpha formation by non-Se-GSH-Px occurred in a GSH-dependent reduction of either PGG2 or PGH2. When PGG2 was used as the substrate for non-Se-GSH-Px, a novel intermediate compound appeared and was later identified by several methods of structural analysis as 15-hydroperoxy PGF2 alpha. Thus, the reductive cleavage of the endoperoxide occurs faster than the 15-hydroperoxide reduction allowing 15-hydroperoxy PGF2 alpha to accumulate briefly. A study of GSTs from several different tissues and species indicated that the transformation of PG endoperoxides to PGF2 alpha is catalyzed specifically by GST isozymes, which contain Ya size subunits. This specificity of GST isozymes in PG biosynthesis, coupled with their tissue-specific expression, may be a mechanism by which the body modulates the type of PGs produced in these tissues. Also, these results suggest a possible interaction of Se-GSH-Px and non-Se-GSH-Px in the biosynthesis of PGF2 alpha.

Aggregation and thermo-inactivation of glutamine synthetase from an extreme thermophile, Bacillus caldolyticus

The extreme thermophile, Bacillus caldolyticus, contains two regulatory isoforms of glutamine synthetase (glutamate-ammonia ligase, EC 6.3.1.2), E-I and E-II, produced as separate gene products. Light scattering and electron microscopy data indicate that these thermophilic enzymes aggregate to higher molecular weight species in two stages: initial polymerization of native dodecamers, followed by 'melting' of the aggregated species to produce amorphous denatured protein. The initial stages of the aggregation occurred at temperatures below those for time-dependent denaturation, especially for E-II. In contrast, mesophilic (B. subtilis) enzyme showed no evidence of temperature-dependent aggregation. Thus, aggregation may be a stabilizing mechanism for the thermophilic systems. Bound metal ions and substrates caused dramatic increases in the temperatures at which aggregation and loss of activity occurred for thermophilic enzymes. Certain combinations of ligands (e.g., MnATP + L-glutamate) acted synergistically, so that these complexes denatured only above 90 degrees C. Various models were considered for heat-driven aggregation followed by denaturation, plus ligand stabilization. Taken together, the data are most consistent with unfolding of subunits within the dodecameric unit, rather than unfolding to monomers prior to aggregation.

Immunological and sequence interrelationships between multiple human liver and rat glutathione S-transferases

The 13 forms of human liver glutathione S-transferases (GST) (Vander Jagt, D. L., Hunsaker, L. A., Garcia, K. B., and Royer, R. E. (1985) J. Biol. Chem. 260, 11603-11610) are composed of subunits in two electrophoretic mobility groups: Mr = 26,000 (Ha) and Mr = 27,500 (Hb). Preparations purified from the S-hexyl GSH-linked Sepharose 4B affinity column revealed three additional peptides at Mr = 30,800, Mr = 31,200, and Mr = 32,200. Immunoprecipitation of human liver poly(A) RNAs in vitro translation products revealed three classes of GST subunits and related peptides at Mr = 26,000, Mr = 27,500, and Mr = 31,000. The Mr = 26,000 species (Ha) can be precipitated with antisera against a variety of rat liver GSTs containing Ya, Yb, and Yc subunits, whereas the Mr = 27,500 species (Hb) can be immunoprecipitated most efficiently by antiserum against the anionic isozymes as well as a second Yb-containing isozyme (peak V) from the rat liver. The Mr = 31,000 band can be immunoprecipitated by antisera preparations against sheep liver, rat liver, and rat testis isozymes. Human liver GSTs do not have any subunits of the rat liver Yc mobility. Antiserum against the human liver GSTs did not cross-react with the Yc subunits of rat livers or brains in immunoblotting experiments. The human liver GST cDNA clone, pGTH1, selected human liver poly(A) RNAs for the Ha subunit(s) in the hybrid-selected in vitro translation experiments. Southern blot hybridization results revealed cross-hybridization of pGTH1 with the Ya, Yb, and Yc subunit cDNA clones of rat liver GSTs. This sequence homology was substantiated further in that immobilized pGTH1 DNA selected rat liver poly(A) RNAs for the Ya, Yb, and Yc subunits with different efficiency as assayed by in vitro translation and immunoprecipitation. Therefore, we have demonstrated convincingly that sequence homology as well as immunological cross-reactivity exist between GST subunits from several rat tissues and the human liver. Also, the multiple forms of human liver GSTs are most likely encoded by a minimum of three different classes of mRNAs. These results suggest a genetic basis for the subunit heterogeneity of human liver GSTs.