Heterogenous expression and putative structure of human monocyte/macrophage serine esterase 1

Evidence of a novel immune responsive protein in the Hymenoptera

Honeybee populations are severely threatened by parasites and diseases. Recent outbreaks of Colony Collapse Disorder (CCD) has caused loss of more than 35% of bee colonies in the USA, and this is thought to at least in part be due to parasites and/or disease. Interestingly, the honeybee possesses of a limited set of immune genes compared to other insects. Non-canonical immune genes of honeybee are of interest because they may provide greater insights into the peculiar nature of the immune system of this social insect. Previous analyses of bee haemolymph upon bacterial challenge identified a novel leucine-rich repeat protein termed IRP30. Here we show that IRP30 behaves as a typical secreted immune protein. It is expressed simultaneously with carboxylesterase upon treatment with bacteria or other elicitors of immune response. Furthermore we characterize the gene and the mRNA encoding this protein and the IRP30 protein itself. Its regulation and evolution reveal that IRP30 belongs to a protein family, distributed broadly among Hymenoptera, suggesting its ancient function in immune response. We document an interesting case of a recent IRP30 loss in the ant Atta cephalotes and hypothesize that a putative IRP30 homolog of Nasonia emerged by convergent evolution rather than diverged from a common ancestor.

Comprehensive evaluation of carboxylesterase-2 expression in normal human tissues using tissue array analysis

Carboxylesterases play an important role in the hydrolytic biotransformation of a number of structurally diverse endogenous compounds and medications. Several distinct carboxylesterase isoforms have been described in human liver, brain, and placenta. Carboxylesterase-2 has been identified as the key enzyme in the metabolic activation of the irinotecan, a topoisomerase I inhibitor commonly used in the treatment of many solid tumors. The tissue distribution and intensity of protein expression of carboxylesterase-2 have not been defined in any organ or tissue. This study used a carboxylesterase-2-specific antibody and tissue array analysis to detect carboxylesterase-2 expression in human normal tissues by immunohistochemistry. Carboxylesterase-2 is present in a wide variety of organs and tissues. The highest carboxylesterase-2 expression occurs in hepatocyte, small intestine mucosa, kidney proximal convoluted tubule, and adrenal cortex cells. The results suggest that liver and gastrointestinal tract with carboxylesterase-2 are likely the most important sites of conversion of irinotecan to the active metabolite SN-38, but carboxylesterase-2 within the other tissues may be contributive to this process. In the central nervous system, carboxylesterase-2 expression was confined to capillary endothelial cells, consistent with the enzyme having a role to protect the central nervous system from toxic esters and perhaps being a component of a blood-brain barrier system.

Concentration-dependent effects of the esterase inhibitor BNPP on macrophage migration and myelin phagocytosis

Wallerian degeneration of a peripheral nerve is mainly characterized by axon and myelin degradation and is paralleled by a massive invasion of peripheral macrophages into the nerve. These cells enter the nerve attracted by a cascade of chemokines and cytokines but require proteolytic and enzymatic factors which enables them to cross the blood-nerve barrier. Here we investigated whether alpha-naphthyl (alpha-NA) esterases -- which have been shown to be exclusively expressed in human monocytes -- play a role during Wallerian degeneration. These enzymes were blocked by the specific inhibitor bis(4-nitrophenyl)-phosphate (BNPP) in an established in vitro model of Wallerian degeneration. Sciatic nerve segments of mice were co-cultured with peritoneal macrophages and BNPP was added to the cultures in various concentrations and at different timepoints. The macrophage numbers and myelin density in the nerve segments and the myelin load of macrophages were evaluated. After BNPP treatment the macrophage number within the nerve was significantly diminished and the myelin load within the macrophages was decreased, resulting in elevated levels of preserved myelin within the nerves. These experiments clearly showed a double effect of the alphaNA esterase inhibitor BNPP on macrophages. First, it suggests a role for alphaNA esterases on the migratory potential of macrophages since their invasion into the nerves was diminished. Second, the reduced myelin uptake is due to the inhibition of phagocytic capacity of these cells by BNPP. The therapeutical use of this inhibitor for treatment of autoimmune diseases such as multiple sclerosis or Guillain-Barré syndrome remains to be investigated.

Biology of monocyte-specific esterase

The monocyte-specific (carboxyl)esterase (MSE) is a marker enzyme which is well-known to hematologists as its detection is part of the traditional cytochemical stainings of leukemia cells. There are a variety of synonyms for MSE among hematologists and biochemists. Biochemically, MSE is well-characterized, but should be discerned from other esterases with similar or identical substrate specificities and other features. Intensive analysis of normal and malignant hematopoietic cells and leukemia-lymphoma cell lines using isoelectric focusing established the specificity of this enzyme for monocytes and related cells, hence its designation as monocyte-specific esterase. Cloning of the gene led to its molecular characterization and provided new opportunities to examine MSE expression also at the RNA level which confirmed the monocyte/macrophage specificity. The availability of the gene sequences of various serine esterases and lipases which also hydrolyze ester bonds allowed for the identification of identical isolates from different tissues and the construction of an unrooted dendrogram based on sequence homologies of 22 enzymes. The detailed regulation of the gene and the functional role of MSE have remained largely unknown as of yet. However, DNA binding sites for various transcription factors have already been detected. Some evidence suggests involvement in physiological detoxification processes and in the immune defense against tumor cells. A more thorough understanding of the in vivo function of this truly unique enzyme should be helped by characterizing the signals and signal transduction mechanisms which lead to MSE expression.

Induction of carboxylesterase isozymes in Bombyx mori by E. coli infection

Many proteins, including antibacterial peptides in the hemolymph, are induced by bacterial infections. We found two bacterially inducible carboxylesterases (CEs) in the hemolymph of the silkworm, Bombyx mori. CEs Est-1 and 2 were induced by lipopolysaccharide injection after 6 hours as well as E. coli infection. We found that bacterially inducible CEs clearly differed from noninducible CEs, including juvenile hormone esterases, in pI values, migration on analytical native PAGE, and inhibitor sensitivity. We are now studying the features and functions of these CEs.

The mammalian carboxylesterases: from molecules to functions

Multiple carboxylesterases (EC 3.1.1.1) play an important role in the hydrolytic biotransformation of a vast number of structurally diverse drugs. These enzymes are major determinants of the pharmacokinetic behavior of most therapeutic agents containing ester or amide bonds. Carboxylesterase activity can be influenced by interactions of a variety of compounds either directly or at the level of enzyme regulation. Since a significant number of drugs are metabolized by carboxylesterase, altering the activity of this enzyme class has important clinical implications. Drug elimination decreases and the incidence of drug-drug interactions increases when two or more drugs compete for hydrolysis by the same carboxylesterase isozyme. Exposure to environmental pollutants or to lipophilic drugs can result in induction of carboxylesterase activity. Therefore, the use of drugs known to increase the microsomal expression of a particular carboxylesterase, and thus to increase associated drug hydrolysis capacity in humans, requires caution. Mammalian carboxylesterases represent a multigene family, the products of which are localized in the endoplasmic reticulum of many tissues. A comparison of the nucleotide and amino acid sequence of the mammalian carboxylesterases shows that all forms expressed in the rat can be assigned to one of three gene subfamilies with structural identities of more than 70% within each subfamily. Considerable confusion exists in the scientific community in regards to a systematic nomenclature and classification of mammalian carboxylesterase. Until recently, adequate sequence information has not been available such that valid links among the mammalian carboxylesterase gene family or evolutionary relationships could be established. However, sufficient basic data are now available to support such a novel classification system.

Esterase isoenzyme profiles of 255 leukemia-lymphoma cell lines from all hematopoietic cell lineages

Carboxylic esterase isoenzymes isolated from a panel of well-characterized continuous human leukemia-lymphoma cell lines were separated by isoelectric focusing. Typical isoenzyme patterns designated Mono 1/Mono 2 (for monocyte-associated), My 1/My 2 (for myeloid or myeloma), Lym 1/Lym 2 (for lymphoid) and Und (for undifferentiated) could be reproducibly discerned. The Mono patterns contained one unique isoenzyme encoded by the monocyte-specific esterase gene. This comparative analysis of 255 leukemia-lymphoma cell lines covered the major cell lineage that are affected by hematological neoplasias. The results showed that (except for myelomas) lymphoid-derived malignancies, both leukemias and lymphomas, expressed primarily the Und and Lym esterase isoenzyme profiles. In contrast, myeloid leukemia cells and the related erythroid and megakaryocytic cell lines displayed mainly the My patterns. The Mono patterns were detected predominantly in monocyte-derived leukemias. As the B-lymphocytic hierarchy progresses from pre B-cells via B-cells to plasma cells, number and intensity of the isoenzymes increased as well from the Und pattern to the My isoenzyme profile. Hodgkin's disease and anaplastic large cell lymphoma lines displayed heterogenous isoenzyme profiles consistent with their heterogenous cellular origin. The present study using continuous leukemia-lymphoma cell lines as model systems provides a biochemical characterization of different hematopoietic cell lineages and stages of differentiation.

Subcellular fractionation studies indicate an intracellular localization for human monocyte specific esterase (MSE)

Human monocyte-specific esterase (MSE) is one of the few haemopoietic cell enzymes that show absolute lineage restriction. Although the function of MSE has yet to be deduced, its potential role in tumour cell killing has stimulated particular interest. Knowledge of subcellular localization of MSE is fundamental to understanding its function and, in this context, it is widely believed that MSE is expressed as a plasma membrane ectoenzyme; a contention that is largely based upon experiments which examined fixed cells by ultrastructural cytochemistry. However, as recent molecular studies of human MSE indicate, a number of inconsistencies between its structure and a membrane localization, we applied the techniques of phase separation in the non-ionic detergent Triton X-114 and differential centrifugation to further investigate whether this particular esterase species is membrane-bound or associated with an intracellular organelle. These studies provide strong evidence that MSE is in fact a soluble intracellular enzyme that is almost certainly located within the lumen of the endoplasmic reticulum.