The kinetics of inhibition of Vigna catjang cotyledon and buffalo liver arginase by L-proline and branched-chain amino acids

The effect of proline, isoleucine, leucine, valine, lysine and ornithine under standard physiological conditions, on purified Vigna catjang cotyledon and buffalo liver arginases was studied. The results showed that V. catjang cotyledon arginase is inhibited by proline at a lower concentration than buffalo liver arginase and the inhibition was found to be linear competitive for both enzymes. Buffalo liver arginase was more sensitive to inhibition by branched-chain amino acids than V. catjang cotyledon. Leucine, lysine, ornithine and valine are competitive inhibitors while isoleucine is a mixed type of inhibitor of liver arginase. We have also studied the effect of manganese concentration which acts as a cofactor and leads to activation of arginase. The optimum Mn^{2 +} concentration for Vigna catjang cotyledon arginase is 0.6 mM and liver arginase is 2.0 mM. The preincubation period required for liver arginase is 20 min at 55°C, the preincubation period and temperature required for activation of cotyledon arginase was found to be 8 min at 35°C. The function of cotyledon arginase in polyamine biosynthesis and a possible role of branched chain amino acids in hydrolysis of arginine in liver are discussed.     

The cell recognition model in chlorolichens involving a fungal lectin binding to an algal ligand can be extended to cyanolichens

Leptogium corniculatum, a cyanolichen containing Nostoc as photobiont, produces and secretes arginase to culture medium containing arginine. This secreted arginase was pre‐purified by affinity chromatography on beads of activated agarose to which a polygalactosylated urease, purified from Evernia prunastri, was attached. Arginase was eluted from the beads with 50 mm α‐d ‐galactose. The eluted arginase binds preferentially to the cell surface of Nostoc isolated from this lichen thallus, although it is also able to bind, to some extent, to the cell surface of the chlorobiont isolated from E. prunastri. Previous studies in chlorolichens have shown that a fungal lectin that develops subsidiary arginase activity can be a factor in recognition of compatible algal cells through binding to a polygalactosylated urease, which acts as a lectin ligand in the algal cell wall. Our experiments demonstrate that this model can now be extended to cyanolichens.     

Distribution and properties of arginase in the salivary glands of four species of laboratory mammals

Important progress in arginine metabolism includes the discovery of widespread expression of two isoforms of arginase, arginase I and II, not only in hepatic cells but also in non-hepatic cells, and the formation of nitric oxide, a widely distributed signal-transducing molecule, from arginine by nitric oxide synthase. Possible physiological roles of arginase may therefore include regulation of nitric oxide synthesis through arginine availability for nitric oxide synthase. In this paper, arginase was investigated in the submandibular, sublingual, and parotid glands of rat, mouse, guinea pig, and rabbit. From their arginase contents, the salivary glands of these species were divided into two groups. Variable levels of arginase activity were detected in the salivary glands of mouse and rat. However, salivary glands of rabbit and guinea pig had almost no arginase activity. The presence of nitric oxide synthase has been reported in all the salivary glands used in this study. Therefore, one of the important findings was the presence of species specificity in the co-localization of arginase and nitric oxide synthase in the salivary glands of the four species. The highest specific activity of arginase was found in mouse parotid gland. In rat, considerable arginase activity was detected in all three glands, at 3.6–7.3% of that in rat liver. In rat submandibular gland, arginase was detected in both cytosolic and particulate fractions. In addition, arginase was detected in isolated acinar cells, but not in duct cells. Experiments on the intracellular distribution and the effects of the arginase inhibitors ornithine and N-hydroxy-L-arginine (NOHA), suggested the presence of both arginase I and arginase II in rat submandibular gland.Abbreviations cGMP cyclic guanosine 3,5-monophosphate - NO nitric oxide - NOHA N-hydroxy-L-arginine - NOS nitric oxide synthase Communicated by I.D. Hume     

Inhibition of arginase I activity by RNA interference attenuates IL-13-induced airways hyperresponsiveness

Increased arginase I activity is associated with allergic disorders such as asthma. How arginase I contributes to and is regulated by allergic inflammatory processes remains unknown. CD4+ Th2 lymphocytes (Th2 cells) and IL-13 are two crucial immune regulators that use STAT6-dependent pathways to induce allergic airways inflammation and enhanced airways responsiveness to spasmogens (airways hyperresponsiveness (AHR)). This pathway is also used to activate arginase I in isolated cells and in hepatic infection with helminths. In the present study, we show that arginase I expression is also regulated in the lung in a STAT6-dependent manner by Th2-induced allergic inflammation or by IL-13 alone. IL-13-induced expression of arginase I correlated directly with increased synthesis of urea and with reduced synthesis of NO. Expression of arginase I, but not eosinophilia or mucus hypersecretion, temporally correlated with the development, persistence, and resolution of IL-13-induced AHR. Pharmacological supplementation with l-arginine or with NO donors amplified or attenuated IL-13-induced AHR, respectively. Moreover, inducing loss of function of arginase I specifically in the lung by using RNA interference abrogated the development of IL-13-induced AHR. These data suggest an important role for metabolism of l-arginine by arginase I in the modulation of IL-13-induced AHR and identify a potential pathway distal to cytokine receptor interactions for the control of IL-13-mediated bronchoconstriction in asthma.     

The Effect of NADP+ on Electrophoretic Behavior of Glucose 6-Phosphate Dehydrogenase from Sweet Potato

The gene from Bacillus brevis TT02–8 encoding arginase was cloned into Escherichia coli, and its nucleotide sequence was identified. The nucleotide sequence contained an open reading frame that encoded a polypeptide of 298 amino acid residues with a predicted molecular weight of 31,891, which was consistent with that previously calculated for arginase purified from this bacterium. Comparison of the deduced amino acid sequence of the B. brevis TT02–8 arginase with that of the prokaryotic and eukaryotic arginases of Bacillus caldovelox, Bacillus subtilis, Agrobacterium Ti plasmid C58, Saccharomyces cerevisiae, Coccidioides immitis, Xenopus laevis, Rana catesbeiana, rat liver, and human liver, showed 33–66% of the sequences to be similar; there were several highly conserved regions. Arginase activity was detected in Escherichia coli cells transformed with an expression plasmid of the cloned arginase gene.     

Effect of the Mammalian Arginase Inhibitor 2(<Emphasis Type="Italic">S</Emphasis>)-Amino-6-Boronohexanoic Acid on <Emphasis Type="Italic">Bacillus anthracis</Emphasis> Arginase

Macrophages, upon phagocytosing endospores of Bacillus anthracis, up-regulate the expression of the immunological isoform of nitric oxide synthase, NOS 2, concomitant with production of nitric oxide (NO•) from metabolism of l-arginine. We have previously demonstrated that macrophages that secrete NO• kill the bacilli of B. anthracis. To circumvent this microbicidal activity of NO•, B. anthracis has evolved pathways that include the enzyme arginase, which metabolizes l-arginine to ornithine and urea. Compounds that inhibit arginase might, therefore, offer a therapeutic approach to controlling B. anthracis infection. 2(S)-Amino-6-boronohexanoic acid (ABH) has been reported to be an inhibitor of mammalian arginase. In this study, we explore the inhibitory effect of ABH against B. anthracis arginase and its potential for future development, as an effective therapeutic agent against microbial infection. We found that ABH is an inhibitor of bacterial arginase in several different endospore strains of B. anthracis. Further, ABH inhibits neither the phagocytosis of these endospores nor the up-regulation of NOS 2 concomitant with secretion of NO•. These findings set the stage to determine how efficacious ABH will be in promoting NO•-mediating killing of B. anthracis.     

Arginase Activity - A Marker of Disease Status in Patients with Visceral Leishmaniasis in Ethiopia

The underlying mechanisms resulting in the profound immune suppression characteristic of human visceral leishmaniasis (VL) are not fully understood.Here, we tested the hypothesis that arginase, an enzyme associated with immunosuppression, is higher in patients with VL and contributes to impaired T cell responses. We recruited patients with VL before and after treatment and healthy controls and measured the arginase metabolism in the blood of these individuals. Our results show that arginase activity is significantly higher in the blood of patients with active VL as compared to controls. These high levels of arginase decline considerably once the patients are successfully treated. We identified the phenotype of arginase-expressing cells among PBMCs as neutrophils and show that their frequency was increased in PBMCs of patients before treatment; this coincides with reduced levels of L-arginine in the plasma and decreased expression levels of CD3ζ in T cells.     

Indospicine combined with arginine deprivation triggers cancer cell death via caspase-dependent apoptosis

Arginine-deprivation therapy is a rapidly developing metabolic anticancer approach. To overcome the resistance of some cancer cells to this monotherapy, rationally designed combination modalities are needed. In this report, we evaluated for the first time indospicine, an arginine analogue of Indigofera plant genus origin, as potential enhancer compound for the metabolic therapy that utilizes recombinant human arginase I. We demonstrate that indospicine at low micromolar concentrations is selectively toxic for human colorectal cancer cells only in the absence of arginine. In arginine-deprived cancer cells indospicine deregulates some prosurvival pathways (PI3K-Akt and MAPK) and activates mammalian target of rapamycin, exacerbates endoplasmic reticulum stress and triggers caspase-dependent apoptosis, which is reversed by the exposure to translation inhibitors. Simultaneously, indospicine is not degraded by recombinant human arginase I and does not inhibit this arginine-degrading enzyme at its effective dose. The obtained results emphasize the potential of arginine structural analogues as efficient components for combinatorial metabolic targeting of malignant cells.     

Regulation of MAP kinase-mediated endothelial dysfunction in hyperglycemia via arginase I and eNOS dysregulation

Emerging evidence suggests that arginase contributes to endothelial dysfunction in diabetes. Intracellular signaling pathways, which interplay between arginase and eNOS enzyme activity leading to the development of endothelial dysfunction in hyperglycemia are not fully understood. Here, we analyzed the possible involvement of hyperglycemia (HG) induced arginase expression in eNOS protein regulation and activity and also the impact of arginase inhibition on eNOS activity. Furthermore, the roles of p38 MAPK and Erk1/2 phosphorylation in upregulation of arginase expression and eNOS dysregulation in endothelial cells (ECs) under hyperglycemia were evaluated. Protein analysis showed a concurrent increase in arginase I expression and decrease in eNOS expression and phosphorylation at Ser¹¹⁷⁷ under HG conditions. There was no simultaneous change in phosphorylation of eNOS at Thr⁴⁹⁵ in HG. Arginase inhibition prevented increased arginase activity, restored impaired NO bioavailability and reduced superoxide anion generation. Inhibition of MAP-kinases demonstrated that, unlike Erk1/2, p38 MAPK is an upstream activator in a signaling cascade leading to increased arginase I in HG conditions. P38 MAPK protein expression and phosphorylation were increased in response to HG. In the presence of a p38 MAPK inhibitor, HG-induced arginase expression was blunted. Although Erk1/2 was activated in HG, increased arginase expression was not blocked by co-treatment with an Erk1/2 inhibitor. Activation of both, p38 MAPK and Erk1/2 in HG, induced a downregulation in eNOS activity. Hence, applying MAPK inhibitors increased eNOS phosphorylation in HG.In conclusion, these findings demonstrate contributions of arginase I in the development of endothelial cell dysfunction under HG conditions via impaired eNOS regulation, which maybe mediated by p38 MAPK.     

Cancer cell sensitivity to arginine deprivation in vitro is not determined by endogenous levels of arginine metabolic enzymes

Single amino acid Arg (arginine) deprivation is currently considered as a therapeutic approach to treat certain types of tumours; the molecular mechanisms that underlie tumour cell sensitivity or resistance to Arg restriction are still little understood. Here, we address the question of whether endogenous levels of key Arg metabolic enzymes [catabolic: arginases, ARG1 (arginase type 1) and ARG2 (arginase type 2), and anabolic: OTC (ornithine transcarbamylase) and ASS (argininosuccinate synthetase)] affect cellular responses to arginine deprivation in vitro. Human epithelial cancer cells of different organs of origin exhibiting variable sensitivity to Arg deprivation provided the experimental models. Neither the basal expression status of the analysed enzymes, nor their changes upon arginine withdrawal correlated with cancer cell sensitivity to arginine deprivation. However, the ability to utilize exogenous Arg precursors (ornithine and citrulline) for growth in Arg‐deficient medium strongly correlated with expression of the corresponding enzymes, OTC and ASS. We also observed that OTC expression was below the level of detection in all the types of tumour cells analysed, suggesting that in vitro, at least for them, Arg is an essential amino acid.     

Boronic acid-based arginase inhibitors in cancer immunotherapy

Arginase is an enzyme that converts l-arginine to l-ornithine and urea in the urea cycle. There are two isoforms of arginase in mammals: ARG-1 and ARG-2. l-Arginine level changes occur in patients with various types of affliction. An overexpression of arginase leads to the depletion of arginine and then to inhibition of the growth of T and NK cells, and in effect to the tumor escape of the immune response. Based on those observations, an inhibition of arginase is proposed as a method to improve anti-tumor immune responses (via an activation and proliferation of T and NK cells). Boronic acid derivatives as arginase inhibitors are leading, potential therapeutic agents for the treatment of several diseases. All these compounds are derived from the original 2-(S)-amino-6-boronohexanoic acid (ABH), the first boronic acid arginase inhibitor proposed by Christianson et al. This article focuses on the review of such sub-class of arginase inhibitors and highlights their SAR and PK properties. It covers molecules published until early 2020, including patent applications.     

Arginase I: a limiting factor for nitric oxide and polyamine synthesis by activated macrophages?

Because arginase hydrolyzes arginine to produce ornithine and urea, it has the potential to regulate nitric oxide (NO) and polyamine synthesis. We tested whether expression of the cytosolic isoform of arginase (arginase I) was limiting for NO or polyamine production by activated RAW 264.7 macrophage cells. RAW 264.7 cells, stably transfected to overexpress arginase I or beta-galactosidase, were treated with interferon-gamma to induce type 2 NO synthase or with lipopolysaccharide or 8-bromo-cAMP (8-BrcAMP) to induce ornithine decarboxylase. Overexpression of arginase I had no effect on NO synthesis. In contrast, cells overexpressing arginase I produced twice as much putrescine after activation than did cells expressing beta-galactosidase. Cells overexpressing arginase I also produced more spermidine after treatment with 8-BrcAMP than did cells expressing beta-galactosidase. Thus endogenous levels of arginase I are limiting for polyamine synthesis, but not for NO synthesis, by activated macrophage cells. This study also demonstrates that it is possible to alter arginase I levels sufficiently to affect polyamine synthesis without affecting induced NO synthesis.     

Purification and properties of Pinus taeda arginase from germinated seedlings

In germinated loblolly pine (Pinus taeda L.) seeds arginine accumulates in the seedling during its growth immediately following germination. The enzyme arginase (L-arginine amidinohydrolase, EC 3.5.3.1) is responsible for hydrolyzing this arginine into ornithine and urea. Loblolly pine arginase was purified to homogeneity from seedling cotyledons by chromatographic separation on DE-52 cellulose, Matrex Green and arginine-linked Sepharose 4B. The enzyme was purified 148-fold and a single polypeptide band was identified as arginase. The molecular mass was determined to be 140 kDa by FPLC, while the subunit size was shown to be 37 kDa by SDS-PAGE, predicting a homotetramer holoprotein. Removal of manganese from the enzyme abolishes catalytic activity, which can be restored by incubating the protein with Mn²⁺. Antibodies, raised against the arginase subunit, are able to immunotitrate arginase activity and are monospecific for arginase on immunoblots.     

Arginase expression and modulation of IL-1β-induced nitric oxide generation in rat and human islets of Langerhans

Proinflammatory cytokine induction of NO synthesis may contribute to the destruction of pancreatic beta cells leading to type 1 diabetes. The NO synthase substrate arginine can also be metabolized to ornithine and urea in a reaction catalyzed by cytosolic (AI) or mitochondrial (AII) isoforms of arginase. Recent evidence suggests that the rate of NO generation is dependent on the relative activities of NO synthase and arginase. The objectives of this study were (i) to identify the arginase isoforms expressed in rat and human islets of Langerhans and a rat beta cell line, RINm5F and (ii) to investigate the competition for arginine between NO synthase and arginase in IL-1β-treated rat islets. Arginase activity was detected in rat islets (fresh tissue, 346 mU/mg protein; cultured, 587 mU/mg), cultured human islets (56 mU/mg), RINm5F cells (376 mU/mg), rat kidney (238 mU/mg), and rat liver (6119 mU/mg). Using Western blots, AI was shown to be the predominant isoform expressed in rat islets and in RINm5F cells while human islets expressed far more AII than AI. Rat islets were cultured in medium containing 1.14, 0.1, and 0.01 mM arginine and treated with IL-1β and the arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH). IL-1β-induced NO generation was unaffected by ABH at 1.14 mM arginine, but significantly increased at 0.1 and 0.01 mM arginine. These findings suggest that the level of islet arginase activity can regulate the rate of induced NO generation and this may be relevant to the insulitis process leading to beta cell destruction in type 1 diabetes.     

Relationship between synovial fluid and plasma manganese,arginase, and nitric oxide in patients with rheumatoid arthritis

Nitric oxide (NO) participates in the pathogenesis of inflammatory reactions in many autoimmune diseases such as rheumatoid arthritis (RA). There is a reciprocal pathway between arginase and nitric oxide synthese (NOS) for NO production, and Mn is required for arginase activity and stability. To investigate whether NO production related with the arginine-nitric oxide pathway in patients with RA, we measured synovial fluid and plasma nitrite (NO_x) levels, arginase activities, and its cofactor manganese (Mn) concentrations in 21 RA patients and 13 healthy control subjects. Plasma albumin levels were measured as an index of nutritional status. NO_x levels were determined after the reduction of nitrates to nitrites using the Griess reaction. Whereas, synovial fluid arginase activities and Mn levels were found to be significantly lower (p<0.001, p<0.001, respectively), plasma arginase activities and Mn levels were similar in patients with RA when compared to the control subjects. Plasma and synovial fluid NO levels were similar in patients with RA and in healthy subjects (p>0.05, p>0.05, respectively). There were significantly positive correlations between synovial fluid and plasma arginase activities vs Mn content (r=0.543, p=0.011; r=0.516, p=0.017, respectively) and significantly negative correlations between synovial fluid and plasma NO levels vs arginase activities (r=−0.497, p=0.022; r=−0.508, p=0.019 respectively) in the patients group. Our results indicate that the lower concentration of synovial fluid Mn could cause lower arginase activity and this could also upregulate NO production by increasing L-arginine content in patients with RA.     

Regulation of loblolly pine (Pinus taeda L.) arginase in developing seedling tissue during germination and post-germinative growth

After seed germination, hydrolysis of storage proteins provides a nitrogen source for the developing seedling. In conifers the majority of these reserves are located in the living haploid megagametophyte tissue. In the developing loblolly pine (Pinus taeda L.) seedling an influx of free amino acids from the megagametophyte accompanies germination and early seedling growth. The major component of this amino acid pool is arginine, which is transported rapidly and efficiently to the seedling without prior conversion. This arginine accounts for nearly half of the total nitrogen entering the cotyledons and is likely a defining factor in early seedling nitrogen metabolism. In the seedling, the enzyme arginase is responsible for liberating nitrogen, in the form of ornithine and urea, from free arginine supplied by the megagametophyte. In this report we investigate how the seedling uses arginase to cope with the large arginine influx. As part of this work we have cloned an arginase cDNA from a loblolly pine expression library. Analysis of enzyme activity data, accumulation of arginase protein and mRNA abundance indicates that increased arginase activity after seed germination is due to de novo synthesis of the enzyme. Our results suggest that arginase is primarily regulated at the RNA level during loblolly pine seed germination and post-germinative growth.     

Proteomic Identification of Mitochondrial Targets of Arginase in Human Breast Cancer

We have previously reported arginase expression in human breast cancer cells and demonstrated that the inhibition of arginase by N^ω hydroxy L-arginine (NOHA) in MDA-MB-468 cells induces apoptosis. However, arginase expression and its possible molecular targets in human breast tumor samples and potential clinical implications have not been fully elucidated. Here, we demonstrate arginase expression in human breast tumor samples, and several established breast cancer cell lines, in which NOHA treatment selectively inhibits cell proliferation. The over-expression of Bcl2 in MDA-MB-468 cells abolished NOHA-induced apoptosis, suggesting that the mitochondria may be the main site of NOHA’s action. We, therefore, undertook a proteomics approach to identify key mitochondrial targets of arginase in MDA-MB-468 cells. We identified 54 non-mitochondrial and 13 mitochondrial proteins that were differentially expressed in control and NOHA treated groups. Mitochondrial serine hydroxymethyltransferase (mSHMT) was identified as one of the most promising targets of arginase. Both arginase II (Arg II) and mSHMT expressions were higher in human breast tumor tissues compared to the matched normal and there was a strong correlation between Arg II and mSHMT protein expression. MDA-MB-468 xenografts had significant upregulation of Arg II expression that preceded the induction of mSHMT expression. Small inhibitory RNA (siRNA)-mediated inhibition of Arg II in MDA-MB-468 and HCC-1806 cells led to significant inhibition of both the mSHMT gene and protein expression. As mSHMT is a key player in folate metabolism, our data provides a novel link between arginine and folate metabolism in human breast cancer, both of which are critical for tumor cell proliferation.     

Arginase activity in the frog urinary bladder epithelial cells and its involvement in regulation of nitric oxide production

The activity of arginase converting arginine into ornithine and urea is of particular interest among many factors regulating NO production in the cells. It is known that by competing with NO-synthase for common substrate, arginase can affect the NO synthesis. In the present work, the properties of arginase from the frog Rana temporaria L. urinary bladder epithelial cells possessing the NO-synthase activity were characterized, and possible contribution of arginase to regulation of NO production by epithelial cells was studied. It has been shown that the enzyme had the temperature optimum in the range of 55-60 degrees C, K(m) for arginine 23 mM, and V(max) about 10 nmol urea/mg protein/min, and its activity was effictively inhibited by (S)-(2-boronoethyl)-L-cysteine (BEC), an inhibitor of arginase, at concentrations from 10(-6) to 10(-4) M. The comparison of arginase activity in various frog tissues revealed the following pattern: liver > kidney > brain > urinary bladder (epithelium) > heart > testis. The arginase activity in the isolated urinary bladder epithelial cells was 3 times higher than that in the intact urinary bladder. To evaluate the role of arginase in the regulation of NO production, epithelial cells were cultivated in the media L-15 or 199 containing different amounts of arginine; the concentration of NO2-, the stable NO metabolite, was determined in the culture fluid after 18-20 h of cells incubation. The vast majority of the produced nitrites are associated with the NOS activity, as L-NAME, the NOS-inhibitor, decreased their accumulation by 77.1% in the L-15 medium and by 80% in 199 medium. BEC (10(-4) M) increased the nitrite production by 18.0 % +/- 2.7 in the L-15 medium and by 24.2 +/- 3.5 in the 199 medium (p < 0.05). The obtained data indicate a relatively high arginase activity in the frog urinary bladder epithelium and its involvement in regulation of NO production by epithelial cells.     

Arginine metabolism of the Antarctic Bivalve <Emphasis Type="Italic">Laternula elliptica</Emphasis> (King &; Broderip, 1831): an ecophysiological approach

The potential aerobic ATP-generating pathway and the argininolytic capacity of the Antarctic bivalve Laternula elliptica in its main tissues were measured by the specific activity of the enzymes malate dehydrogenase (MDH), citrate synthase (CS) and arginase. The kidney showed the major potential for aerobic ATP-generating pathway and argininolytic capacity. High levels of CS and MDH activities indicated that renal tissue can be involved in activities that require a lot of energy such as excretion of metabolic end products, amino acids catabolism or even gluconeogenic activities related to inter-tissue metabolism. The fact that kidneys are the main site for arginase activity is very unusual for mollusks and could be related to the living habits of L. elliptica. Genetic expression of the L. elliptica renal arginase could be controlling the levels of l-arginine and forming urea in the excretory organ, which may not have its physiological functions directly affected by the seasonal retraction of its siphons. Compared to the bivalve Dreissena polymorpha, renal arginase of L. elliptica is more resistant to inhibition by copper and cadmium. This could be related to naturally high levels of these metals in the Antarctic marine environment and its bioaccumulation in the renal tissue of L. elliptica, as a probable advantage to its environmental adaptation. Different from other Antarctic animals that feed on Krill, the arginase of L. elliptica is much more sensitive to fluoride inhibition. However, diet composition of L. elliptica would be expected to be variable site to site and its high sensitivity to fluoride inhibition may be a matter of concern in areas near ornithogenic soils subjected to ice-melting processes.     

Extracellular Signal-regulated Kinase Mediates Expression of Arginase II but Not Inducible Nitric-oxide Synthase in Lipopolysaccharide-stimulated Macrophages

The mitogen-activated protein kinases (MAPK) have been shown to participate in iNOS induction following lipopolysaccharide (LPS) stimulation, while the role of MAPKs in the regulation of arginase remains unclear. We hypothesized that different MAPK family members are involved in iNOS and arginase expression following LPS stimulation. LPS-stimulated RAW 264.7 cells exhibited increased protein and mRNA levels for iNOS, arginase I, and arginase II; although the induction of arginase II was more robust than that for arginase I. A p38 inhibitor completely prevented iNOS expression while it only attenuated arginase II induction. In contrast, a MEK1/2 inhibitor (ERK pathway) completely abolished arginase II expression while actually enhancing iNOS induction in LPS-stimulated cells. Arginase II promoter activity was increased by ∼4-fold following LPS-stimulation, which was prevented by the ERK pathway inhibitor. Arginase II promoter activity was unaffected by a p38 inhibitor or JNK pathway interference. Transfection with a construct expressing a constitutively active RAS mutant increased LPS-induced arginase II promoter activity, while transfection with a vector expressing a dominant negative ERK2 mutant or a vector expressing MKP-3 inhibited the arginase II promoter activity. LPS-stimulated nitric oxide (NO) production was increased following siRNA-mediated knockdown of arginase II and decreased when arginase II was overexpressed. Our results demonstrate that while both the ERK and p38 pathways regulate arginase II induction in LPS-stimulated macrophages, iNOS induction by LPS is dependent on p38 activation. These results suggest that differential inhibition of the MAPK pathway may be a potential therapeutic strategy to regulate macrophage phenotype.