Regulation of cyclooxygenase-2 expression by small GTPase Rac2 in bone marrow macrophages

Macrophages inhibit extracellular hyphal growth of A. fumigatus through Rac2 GTPase signaling

Macrophages act as a first line of defense against pathogens. Against Aspergillus fumigatus, a fungus with pathogenic potential in immunocompromised patients, macrophages can phagocytose fungal spores and inhibit spore germination to prevent the development of tissue-invasive hyphae. However, the cellular pathways that macrophages use to accomplish these tasks and any roles macrophages have later in infection against invasive forms of fungi are still not fully known. Rac-family Rho GTPases are signaling hubs for multiple cellular functions in leukocytes, including cell migration, phagocytosis, reactive oxygen species (ROS) generation, and transcriptional activation. We therefore aimed to further characterize the function of macrophages against A. fumigatus in an in vivo vertebrate infection model by live imaging of the macrophage behavior in A. fumigatus-infected rac2 mutant zebrafish larvae. While Rac2-deficient zebrafish larvae are susceptible to A. fumigatus infection, Rac2 deficiency does not impair macrophage migration to the infection site, interaction with and phagocytosis of spores, spore trafficking to acidified compartments, or spore killing. However, we reveal a role for Rac2 in macrophage-mediated inhibition of spore germination and control of invasive hyphae. Re-expression of Rac2 under a macrophage-specific promoter rescues the survival of A. fumigatus-infected rac2 mutant larvae through increased control of germination and hyphal growth. Altogether, we describe a new role for macrophages against extracellular hyphal growth of A. fumigatus and report that the function of the Rac2 Rho GTPase in macrophages is required for this function.

Small G protein Rac GTPases regulate the maintenance of glioblastoma stem-like cells in vitro and in vivo

Glioblastoma is the most common and aggressive malignant brain tumor in adults. The existence of glioblastoma stem cells (GSCs) or stem-like cells (stemloids) may account for its invasiveness and high recurrence. Rac proteins belong to the Rho small GTPase subfamily which regulates cell movement, proliferation, and survival. To investigate whether Rac proteins can serve as therapeutic targets for glioblastoma, especially for GSCs or stemloids, we examined the potential roles of Rac1, Rac2 and Rac3 on the properties of tumorspheres derived from glioblastoma cell lines. Tumorspheres are thought to be glioblastoma stem-like cells. We showed that Rac proteins promote the STAT3 and ERK activation and enhance cell proliferation and colony formation of glioblastoma stem-like cells. Knockdown of Rac proteins reduces the expression of GSC markers, such as CD133 and Sox2. The in vivo effects of Rac proteins in glioblastoma were further studied in zebrafish and in the mouse xenotransplantation model. Knocking-down Rac proteins abolished the angiogenesis effect induced by the injected tumorspheres in zebrafish model. In the CD133+-U373-tumorsphere xenotransplanted mouse model, suppression of Rac proteins decreased the incidence of tumor formation and inhibited the tumor growth. Moreover, knockdown of Rac proteins reduced the sphere forming efficiency of cells derived from these tumors. In conclusion, not only Rac1 but also Rac2 and 3 are important for glioblastoma tumorigenesis and can serve as the potential therapeutic targets against glioblastoma and its stem-like cells.

Rac2 Functions in Both Neutrophils and Macrophages To Mediate Motility and Host Defense in Larval Zebrafish

Leukocyte motility is required for host defense responses. Rac-family Rho GTPases are implicated in leukocyte function; however, the distinct roles of different Rac isoforms in host defense in vivo have remained unclear. In this study, we generated Rac2-deficient zebrafish using transcription activator-like effector nucleases to directly compare the role of Rac2 in vivo in neutrophils and macrophages in motility and the response to infection. This zebrafish larval model is highly amenable to live imaging of leukocyte behavior, and we report that in rac2-/- larvae both neutrophils and macrophages are defective in basic motility, leading to impaired responses to localized wounds or infections. rac2-/- larvae are highly susceptible to infection with Pseudomonas aeruginosa, which can be almost fully rescued by ectopic expression of either Rac2 or Rac1 specifically in neutrophils, indicating that these isoforms have partially overlapping functions in vivo. Rescue of Rac2 expression specifically in macrophages also confers resistance to Pseudomonas infection, highlighting an important role for Rac2 in this leukocyte population as well. Surprisingly, in contrast to neutrophils expressing a Rac2 dominant inhibitory human disease mutation, rac2-/- neutrophils do not have altered polarity or mobilization from hematopoietic tissue, suggesting that a different Rac isoform, such as Rac1, also contributes to these phenotypes in vivo.

Induction of cyclooxygenase-2 signaling by Stomatococcus mucilaginosus highlights the pathogenic potential of an oral commensal

Stomatococcus mucilaginosus is an oral commensal that has been occasionally reported to cause severe infections in immunocompromised patients. There is no information about the pathogenic role of S. mucilaginosus in airway infections. In a cohort of 182 subjects with bronchiectasis, we found that 9% were colonized with S. mucilaginosus in their lower airways by culture growth from bronchoalveolar lavage. To address the pathogenic potential of S.mucilaginosus, we developed a murine model of S. mucilaginosus lung infection. Intratracheal injection of S. mucilaginosus in C57BL/6 mice resulted in a neutrophilic influx with production of proinflammatory cytokines, chemokines, and lipid mediators, mainly PGE₂ with induction of cyclooxygenase-2 (COX-2) in the lungs. Presence of TLR2 was necessary for induction of COX-2 and production of PGE₂ by S. mucilaginosus. TLR2-deficient mice showed an enhanced clearance of S. mucilaginosus compared with wild-type mice. Administration of PGE₂ to TLR2(-/-) mice resulted in impaired clearance of S. mucilaginosus, suggesting a key role for COX-2-induced PGE₂ production in immune response to S. mucilaginosus. Mechanistically, induction of COX-2 in macrophages was dependent on the p38-ERK/MAPK signaling pathway. Furthermore, mice treated with S. mucilaginosus and Pseudomonas aeruginosa showed an increased mortality compared with mice treated with PA103 or S. mucilaginosus alone. Inhibition of COX-2 significantly improved survival in mice infected with PA103 and S. mucilaginosus. These data provide novel insights into the bacteriology and personalized microbiome in patients with bronchiectasis and suggest a pathogenic role for S. mucilaginosus in patients with bronchiectasis.

Pivotal role of reactive oxygen species in differential regulation of lipopolysaccharide-induced prostaglandins production in macrophages

Gram-negative bacterial endotoxin lipopolysaccharide (LPS) triggers the production of inflammatory cytokines, reactive oxygen species (ROS), and prostaglandins (PGs) by pulmonary macrophages. Here, we investigated if ROS influenced PGs production in response to LPS treatment in mouse bone marrow-derived macrophages (BMDM). We observed that pretreatment of BMDM with two structurally unrelated ROS scavengers, MnTMPyP and EUK-134, not only prevented LPS-induced ROS accumulation, but also attenuated the LPS-induced PGD(2), but not PGE(2), production. Conversely LPS-induced PGD(2), but not PGE(2), production, was potentiated with the cotreatment of BMDM with H(2)O(2). These data suggest that ROS differentially regulate PGD(2) and PGE(2) production in BMDM. In addition, selective inhibition of the ROS generator NADPH oxidase (NOX) using either pharmacologic inhibitors or its p47(phox) subunit deficient mouse BMDM also attenuated LPS-induced PGD(2), but not PGE(2) production, suggesting the critical role of NOX-generated ROS in LPS-induced PGD(2) production in BMDM. We further found that both hematopoietic PGD synthase (H-PGDS) siRNA and its inhibitor HQL-79, but not lipocalin PGDS (L-PGDS) siRNA and its inhibitor AT-56, significantly attenuated LPS-induced PGD(2) production, suggesting that H-PGDS, but not L-PGDS, mediates LPS-induced PGD(2) production in BMDM. Furthermore, data from our in vitro cell-free enzymatic studies showed that coincubation of the recombinant H-PGDS with either MnTMPyP, EUK-134, or catalase significantly decreased PGD(2) production, whereas coincubation with H(2)O(2) significantly increased PGD(2) production. Taken together, our results show that LPS-induced NOX-generated ROS production differentially and specifically regulates the H-PGDS-mediated production of PGD(2), but not PGE(2), in mouse BMDM.

Inhibition of Rac activity alleviates lipopolysaccharide-induced acute pulmonary injury in mice

BACKGROUND

Rac small GTPases play important roles in cytoskeleton and many cell functions including cell cycle, cell growth, cell adhesion and gene transcription. Here, we investigated the roles of Rac including Rac1 and Rac2 in lipopolysaccharide (LPS)-induced pulmonary injury.

METHODS

After LPS was intratracheally instilled to lungs in mice, Rac, CDC42 and RhoA activation assay by pull-down and West blot, inflammatory cell infiltration assay by counting cell numbers and lung histological examination, pro-inflammatory mediator mRNA expression assay by quantitative RT-PCR, measurement of myeloperoxidase (MPO) activity, Evans Blue and albumin accumulation by spectrophotometry were performed to evaluate the roles of Rac in pulmonary injury by using its specific inhibitor, NSC23766.

RESULTS

LPS challenge led to increases of both Rac1 and Rac2, but not CDC42 or RhoA activities in lungs, and intraperitoneal administration with NSC23766 inhibited both Rac1 and Rac2, but not CDC42 or RhoA activities. Treatment with NSC23766 at 1 or 3mg/kg not only reduced the inflammatory cells infiltration and MPO activities, but also inhibited pro-inflammatory mediators, tumor necrosis factor-α and interleukin-1β, mRNA expression. Moreover, in vitro neutrophil migration assay and in vivo microvascular permeability assay indicated that NSC23766 not only inhibited neutrophil transwell migration toward a chemoattractant, fMLP, but also reduced Evans Blue and albumin accumulation in LPS-challenged lungs. LPS activated both Rac1 and Rac2, but not CDC42 or RhoA activities in lungs, and specific inhibition of Rac activities by NSC23766 effectively alleviated LPS-induced injury.

GENERAL SIGNIFICANCE

Rac could be a potential target for therapeutic intervention of pulmonary inflammation.

Synthetic cannabinoid receptor agonists inhibit tumor growth and metastasis of breast cancer

Cannabinoids have been reported to possess antitumorogenic activity. Not much is known, however, about the effects and mechanism of action of synthetic nonpsychotic cannabinoids on breast cancer growth and metastasis. We have shown that the cannabinoid receptors CB1 and CB2 are overexpressed in primary human breast tumors compared with normal breast tissue. We have also observed that the breast cancer cell lines MDA-MB231, MDA-MB231-luc, and MDA-MB468 express CB1 and CB2 receptors. Furthermore, we have shown that the CB2 synthetic agonist JWH-133 and the CB1 and CB2 agonist WIN-55,212-2 inhibit cell proliferation and migration under in vitro conditions. These results were confirmed in vivo in various mouse model systems. Mice treated with JWH-133 or WIN-55,212-2 showed a 40% to 50% reduction in tumor growth and a 65% to 80% reduction in lung metastasis. These effects were reversed by CB1 and CB2 antagonists AM 251 and SR144528, respectively, suggesting involvement of CB1 and CB2 receptors. In addition, the CB2 agonist JWH-133 was shown to delay and reduce mammary gland tumors in the polyoma middle T oncoprotein (PyMT) transgenic mouse model system. Upon further elucidation, we observed that JWH-133 and WIN-55,212-2 mediate the breast tumor-suppressive effects via a coordinated regulation of cyclooxygenase-2/prostaglandin E2 signaling pathways and induction of apoptosis. These results indicate that CB1 and CB2 receptors could be used to develop novel therapeutic strategies against breast cancer growth and metastasis.

Neutrophil chemokines and their role in IL-18-mediated increase in neutrophil O2- production and intestinal edema following alcohol intoxication and burn injury

We examined the role of interleukin (IL)-18 and cytokine-induced neutrophil chemokines (CINC)-1 and CINC-3 in the neutrophil release of superoxide anion (O2-) and elastase following alcohol/ethanol (EtOH) and burn injury. Male rats (approximately 250 g) were gavaged with EtOH to achieve a blood EtOH level of approximately 100 mg/dl before approximately 12.5% total body surface area burn or sham injury. Immediately after injury, rats were administered with anti-rat IL-18 antibody (80 microg/kg) or isotype control. After 20 min, anti-IL-18 antibody-treated rats were given either recombinant (r) rat CINC-1 or CINC-3. On day 1 after injury, the combined insult of EtOH and burn injury caused a significant increase in neutrophil elastase and O2- production as well as an increase in neutrophil accumulation, myeloperoxidase activity, and edema in the intestine. Treatment of rats with anti-IL-18 antibody normalized the above parameters. However, administration of rCINC-1 in anti-IL-18 antibody-treated rats increased the above parameters to levels similar to those observed following EtOH and burn injury. In contrast, administration of rCINC-3 did not influence the above parameters except neutrophil elastase. These findings indicate that IL-18 and CINC-1 may independently modulate neutrophil tissue-damaging actions following EtOH and burn injury. However, the finding that the treatment of rats with anti-IL-18 antibodies inhibits CINC-1 and CINC-3 supports the notion that IL-18 plays a critical role in increased neutrophil tissue-damaging action following a combined insult of EtOH intoxication and burn injury.

Heme oxygenase-1 protects against neutrophil-mediated intestinal damage by down-regulation of neutrophil p47phox and p67phox activity and O2- production in a two-hit model of alcohol intoxication and burn injury

Heme oxygenase-1 (HO-1) has been demonstrated to protect against tissue injury. Furthermore, HO-1 is also shown to be antioxidant. Our recent findings indicate that acute alcohol (EtOH) intoxication exacerbates postburn intestinal and lung tissue damage, and this was found to be neutrophil dependent. Because neutrophil-mediated tissue injury involves the release of superoxide anions (O(2)(-)), the present study examined the role of HO-1 in neutrophil O(2)(-) production following EtOH and burn injury. Furthermore, we investigated whether HO-1 antioxidant properties are mediated via modulation of p47(phox) and/or p67(phox) proteins. Male rats (approximately 250 g) were gavaged with EtOH to achieve a blood EtOH level of approximately 100 mg/dL before burn or sham injury (approximately 12.5% total body surface area). Some rats were treated with HO-1 activator cobalt protoporphyrin IX chloride (Copp; 25 mg/kg body weight) at the time of injury. On day 1 after injury, we found that EtOH combined with burn injury significantly increased neutrophil O(2)(-) production and p47(phox) and p67(phox) activation and decreased caspase-3 activity and apoptosis. This was accompanied with a decrease in neutrophil HO-1 levels. The treatment of animals with HO-1 activator Copp normalized neutrophil HO-1, O(2)(-), p47(phox), and p67(phox) following EtOH and burn injury. The expression of caspase-3, however, was further decreased in Copp-treated sham and EtOH plus burn groups. Moreover, Copp treatment also prevented the increase in intestinal edema and permeability following EtOH and burn injury. Altogether, these findings provide a new insight into the mechanism by which HO-1 regulates neutrophil O(2)(-) production and protect the intestine from damage following EtOH and burn injury.