Invasive mucinous adenocarcinoma mimicking organizing pneumonia associated with Mycobacterium fortuitum infection.

We herein report the case of a 68-year-old man diagnosed with invasive mucinous adenocarcinoma of the lungs. Chest computed tomography showed subpleural ground-glass opacity and small nodules with cavitation. A culture of the bronchoalveolar lavage fluid resulted in the detection of Mycobacterium fortuitum. The patient's lung consolidation rapidly progressed; however, repeated bronchoscopy showed no atypical cells, thus suggesting a diagnosis of organizing pneumonia associated with M. fortuitum infection. However, the surgical biopsy specimen was diagnostic for adenocarcinoma, with no mycobacterial infection. Invasive mucinous adenocarcinoma should not be excluded in the differential diagnosis of patients with clinical features of organizing pneumonia and nontuberculous mycobacterium infection, even if a transbronchial biopsy confirms the absence of malignancy.

Cathepsin E deficiency impairs autophagic proteolysis in macrophages.

Cathepsin E is an endosomal aspartic proteinase that is predominantly expressed in immune-related cells. Recently, we showed that macrophages derived from cathepsin E-deficient (CatE(-/-)) mice display accumulation of lysosomal membrane proteins and abnormal membrane trafficking. In this study, we demonstrated that CatE(-/-) macrophages exhibit abnormalities in autophagy, a bulk degradation system for aggregated proteins and damaged organelles. CatE(-/-) macrophages showed increased accumulation of autophagy marker proteins such as LC3 and p62, and polyubiquitinated proteins. Cathepsin E deficiency also altered autophagy-related signaling pathways such as those mediated by the mammalian target of rapamycin (mTOR), Akt, and extracellular signal-related kinase (ERK). Furthermore, immunofluorescence microscopy analyses showed that LC3-positive vesicles were merged with acidic compartments in wild-type macrophages, but not in CatE(-/-) macrophages, indicating inhibition of fusion of autophagosome with lysosomes in CatE(-/-) cells. Delayed degradation of LC3 protein was also observed under starvation-induced conditions. Since the autophagy system is involved in the degradation of damaged mitochondria, we examined the accumulation of damaged mitochondria in CatE(-/-) macrophages. Several mitochondrial abnormalities such as decreased intracellular ATP levels, depolarized mitochondrial membrane potential, and decreased mitochondrial oxygen consumption were observed. Such mitochondrial dysfunction likely led to the accompanying oxidative stress. In fact, CatE(-/-) macrophages showed increased reactive oxygen species (ROS) production and up-regulation of oxidized peroxiredoxin-6, but decreased antioxidant glutathione. These results indicate that cathepsin E deficiency causes autophagy impairment concomitantly with increased aberrant mitochondria as well as increased oxidative stress.

(-)-Xanthatin induces the prolonged expression of c-Fos through an N-acetyl-L-cysteine (NAC)-sensitive mechanism in human breast cancer MDA-MB-231 cells.

We reported that (-)-xanthatin, a xanthanolide sesquiterpene lactone present in the Cocklebur plant, exhibited potent anti-proliferative effects on human breast cancer cells, in which GADD45γ, a novel tumor suppressor gene, was induced. Mechanistically, topoisomerase IIα (Topo IIα) inhibition by (-)-xanthatin was shown to be the upstream trigger that stimulated the expression of GADD45γ mRNA and concomitantly produced reactive oxygen species (ROS) to maintain this expression. Since the anti-cancer drug etoposide, a selective Topo IIα inhibitor, has also been shown to induce intracellular ROS, (-)-xanthatin may exert its anti-proliferative effects on cancer cells in a similar manner to those of etoposide. In the present study, to generalize its applicability to cancer therapy, we further investigated the biological activities of (-)-xanthatin by comparing its activities to those of the established anti-cancer drug etoposide. After the exposure of breast cancer cells to (-)-xanthatin or etoposide, a prolonged and marked up-regulation in the expression of c-fos, a proapoptotic molecule, was detected together with GADD45γ; and the expression of these molecules was stabilized by ROS and abrogated by the pretreatment with N-acetyl-L-cysteine (NAC), a potent ROS scavenger. (-)-Xanthatin in particular exhibited stronger anti-proliferative potential than that of etoposide, which underlies the marked induction of c-fos/GADD45γ and ROS production.

Δ(9)-Tetrahydrocannabinol disrupts estrogen-signaling through up-regulation of estrogen receptor ß (ERß).

Δ(9)-Tetrahydrocannabinol (Δ(9)-THC) has been reported as possessing antiestrogenic activity, although the mechanisms underlying these effects are poorly delineated. In this study, we used the estrogen receptor α (ERα)-positive human breast cancer cell line, MCF-7, as an experimental model and showed that Δ(9)-THC exposures markedly suppresses 17ß-estradiol (E2)- induced MCF-7 cell proliferation. We demonstrate that these effects result from Δ(9)-THC's ability to inhibit E2-liganded ERα activation. Mechanistically, the data obtained from biochemical analyses revealed that (i) Δ(9)-THC up-regulates ERß, a repressor of ERα, inhibiting the expression of E2/ERα-regulated genes that promote cell growth and that (ii) Δ(9)-THC induction of ERß modulates E2/ERα signaling in the absence of direct interaction with the E2 ligand binding site. Therefore, the data presented support the concept that Δ(9)-THC's antiestrogenic activities are mediated by the ERß disruption of E2/ERα signaling.

Induction of the fatty acid 2-hydroxylase (FA2H) gene by Δ(9)-tetrahydrocannabinol in human breast cancer cells.

To investigate gene(s) being regulated by ∆(9)-tetrahydrocannabinol (∆(9)-THC), we performed DNA microarray analysis of human breast cancer MDA-MB-231 cells, which are poorly differentiated breast cancer cells, treated with ∆(9)-THC for 48 hr at an IC50 concentration of approximately 25 µM. Among the highly up-regulated genes (> 10-fold) observed, fatty acid 2-hydroxylase (FA2H) was significantly induced (17.8-fold). Although the physiological role of FA2H has not yet been fully understood, FA2H has been shown to modulate cell differentiation. The results of Oil Red O staining after ∆(9)-THC exposure showed the distribution of lipid droplets (a sign of the differentiated phenotype) in cells. Taken together, the results obtained here indicate that FA2H is a novel ∆(9)-THC-regulated gene, and that ∆(9)-THC induces differentiation signal(s) in poorly differentiated MDA-MB-231 cells.

(-)-Xanthatin up-regulation of the GADD45γ tumor suppressor gene in MDA-MB-231 breast cancer cells: role of topoisomerase IIα inhibition and reactive oxygen species.

Previously, we reported that (-)-xanthatin, a naturally occurring xanthanolide present in the Cocklebur plant, exhibits potent anti-proliferative effects on human breast cancer cells, accompanied by an induction of the growth arrest and DNA damage-inducible gene 45γ (GADD45γ), recognized recently as a novel tumor suppressor gene. However, the mechanisms mediating this activation were unknown. Topoisomerase IIα (Topo IIα) inhibition has been reported to produce a cell death response accompanied by an atypical DNA laddering fragmentation profile, similar to that noted previously for (-)-xanthatin. Therefore we hypothesized that (-)-xanthatin's GADD45γ activation was mediated through the Topo IIα pathway. Here, we identify that (-)-xanthatin does function as a catalytic inhibitor of Topo IIα, promoting DNA damage. In addition, reactive oxygen species (ROS) were elevated in cells treated with this agent. Mechanistically, it was determined that the induced levels of GADD45γ mRNA resulting from (-)-xanthatin exposures were stabilized by coordinately produced ROS, and that the consequent induction of GADD45γ mRNA, GADD45γ protein and ROS generation were abrogated by co-treatment with N-acetyl-l-cysteine. Taken together, the data support the concept that Topo IIα inhibition by (-)-xanthatin is a trigger that stimulates expression of DNA damage-inducible GADD45γ mRNA and that concomitantly produced ROS act downstream to further enhance the GADD45γ mRNA/GADD45γ protein induction process, resulting in breast cancer cell death.

Cannabidiolic acid, a major cannabinoid in fiber-type cannabis, is an inhibitor of MDA-MB-231 breast cancer cell migration.

Cannabidiol (CBD), a major non-psychotropic constituent of fiber-type cannabis plant, has been reported to possess diverse biological activities, including anti-proliferative effect on cancer cells. Although CBD is obtained from non-enzymatic decarboxylation of its parent molecule, cannabidiolic acid (CBDA), few studies have investigated whether CBDA itself is biologically active. Results of the current investigation revealed that CBDA inhibits migration of the highly invasive MDA-MB-231 human breast cancer cells, apparently through a mechanism involving inhibition of cAMP-dependent protein kinase A, coupled with an activation of the small GTPase, RhoA. It is established that activation of the RhoA signaling pathway leads to inhibition of the mobility of various cancer cells, including MDA-MB-231 cells. The data presented in this report suggest for the first time that as an active component in the cannabis plant, CBDA offers potential therapeutic modality in the abrogation of cancer cell migration, including aggressive breast cancers.

Role of the transcription factor Sp1 in regulating the expression of the murine cathepsin E gene.

Cathepsin E (CE) is an intracellular aspartic proteinase that is exclusively expressed in cells of the gastrointestinal tracts, lymphoid tissues, urinary organs and red blood cells. However, the molecular mechanism by which CE is predominantly expressed in these cells remains unknown. Here, we report the identification of several transcription start sites of the CE gene and their regulatory factors in gastric adenosarcoma cells. We first identified several unique transcription start sites in mouse CE genes by an oligo cap method. Their analysis also revealed the existence of a non-coding region ∼24-kb upstream of exon 1 in the CE gene and also the existence of two transcripts for CE. Luciferase analyses in upstream of exon 1 revealed that this site contained putative binding regions for the transcription factors Sp1, AP-1 and cEts-1 essential for the expression of CE gene. Moreover, electrophoretic mobility shift assays revealed that the protein-oligonucleotides complex of the Sp1 site were supershifted by an anti-Sp1 antibody. The chromatin immunoprecipitation assay showed that Sp1 bound to the CE promoter region. In addition, overexpression of the Sp1 protein increased the expression of the CE protein. Altogether, these results suggest that Sp1 binding plays a particularly important role in the regulation of CE gene expression.

[Signet ring cell carcinoma of the bile duct: a case report].

A 72-year-old man was admitted with obstructive jaundice. Computed tomography revealed a 4cm tumor with multiple cystic components obstructing the common bile duct. Endoscopic ultrasonography, endoscopic retrograde cholangiopancreatography and intraductal ultrasonography demonstrated the tumor, which derived from the lower bile duct, grew into the bile duct lumen. Peroral cholangioscopy revealed distended tumor vessels on the surface of the tumor. Signet ring cell carcinoma of the bile duct was diagnosed by biopsy. The patient died 3 months after the first hospital admission despite chemotherapy.

Cannabidiol-2',6'-dimethyl ether as an effective protector of 15-lipoxygenase-mediated low-density lipoprotein oxidation in vitro.

15-Lipoxygenase (15-LOX) is one of the key enzymes responsible for the formation of oxidized low-density lipoprotein (ox-LDL), a major causal factor for atherosclerosis. Both enzymatic (15-LOX) and non-enzymatic (Cu(2+)) mechanisms have been proposed for the production of ox-LDL. We have recently reported that cannabidiol-2',6'-dimethyl ether (CBDD) is a selective and potent inhibitor of 15-LOX-catalyzed linoleic acid oxygenation (Takeda et al., Drug Metab. Dispos., 37, 1733-1737 (2009)). In the LDL, linoleic acid is present as cholesteryl linoleate, the major fatty acid esterified to cholesterol, and is susceptible to oxidative modification by 15-LOX or Cu(2+). In this investigation, we examined the efficacy of CBDD on i) 15-LOX-catalyzed oxygenation of cholesteryl linoleate, and ii) ox-LDL formation catalyzed by 15-LOX versus Cu(2+)-mediated non-enzymatic generation of this important mediator. The results obtained demonstrate that CBDD is a potent and selective inhibitor of ox-LDL formation generated by the 15-LOX pathway. These studies establish CBDD as both an important experimental tool for characterizing 15-LOX-mediated ox-LDL formation, and as a potentially useful therapeutic agent for treatment of atherosclerosis.

(--)-Xanthatin selectively induces GADD45γ and stimulates caspase-independent cell death in human breast cancer MDA-MB-231 cells.

exo-Methylene lactone group-containing compounds, such as (--)-xanthatin, are present in a large variety of biologically active natural products, including extracts of Xanthium strumarium (Cocklebur). These substances are reported to possess diverse functional activities, exhibiting anti-inflammatory, antimalarial, and anticancer potential. In this study, we synthesized six structurally related xanthanolides containing exo-methylene lactone moieties, including (--)-xanthatin and (+)-8-epi-xanthatin, and examined the effects of these chemically defined substances on the highly aggressive and farnesyltransferase inhibitor (FTI)-resistant MDA-MB-231 cancer cell line. The results obtained demonstrate that (--)-xanthatin was a highly effective inhibitor of MDA-MB-231 cell growth, inducing caspase-independent cell death, and that these effects were independent of FTase inhibition. Further, our results show that among the GADD45 isoforms, GADD45γ was selectively induced by (--)-xanthatin and that GADD45γ-primed JNK and p38 signaling pathways are, at least in part, involved in mediating the growth inhibition and potential anticancer activities of this agent. Given that GADD45γ is becoming increasingly recognized for its tumor suppressor function, the results presented here suggest the novel possibility that (--)-xanthatin may have therapeutic value as a selective inducer of GADD45γ in human cancer cells, in particular in FTI-resistant aggressive breast cancers.

The role of cathepsin E in terminal differentiation of keratinocytes.

Cathepsin E (CatE) is predominantly expressed in the rapidly regenerating gastric mucosal cells and epidermal keratinocytes, in addition to the immune system cells. However, the role of CatE in these cells remains unclear. Here we report a crucial role of CatE in keratinocyte terminal differentiation. CatE deficiency in mice induces abnormal keratinocyte differentiation in the epidermis and hair follicle, characterized by the significant expansion of corium and the reduction of subcutaneous tissue and hair follicle. In a model of skin papillomas formed in three different genotypes of syngeneic mice, CatE deficiency results in significantly reduced expression and altered localization of the keratinocyte differentiation induced proteins, keratin 1 and loricrin. Involvement of CatE in the regulation of the expression of epidermal differentiation specific proteins was corroborated by in vitro studies with primary cultures of keratinocytes from the three different genotypes of mice. In wild-type keratinocytes after differentiation inducing stimuli, the CatE expression profile was compatible to those of the terminal differentiation marker genes tested. Overexpression of CatE in mice enhances the keratinocyte terminal differentiation process, whereas CatE deficiency results in delayed differentiation accompanying the reduced expression or the ectopic localization of the differentiation markers. Our findings suggest that in keratinocytes CatE is functionally linked to the expression of terminal differentiation markers, thereby regulating epidermis formation and homeostasis.

Quantum chemical molecular dynamics simulation of single-walled carbon nanotube cap nucleation on an iron particle.

The atomic scale details of single-walled carbon nanotube (SWNT) nucleation on metal catalyst particles are elusive to experimental observations. Computer simulation of metal-catalyzed SWNT nucleation is a challenging topic but potentially of great importance to understand the factors affecting SWNT diameters, chirality, and growth efficiency. In this work, we use nonequilibrium density functional tight-binding molecular dynamics simulations and report nucleation of sp(2)-carbon cap structures on an iron particle consisting of 38 atoms. One C(2) molecule was placed every 1.0 ps around an Fe(38) cluster for 30 ps, after which a further 410 ps of annealing simulation without carbon supply was performed. We find that sp(2)-carbon network nucleation and annealing processes occur in three sequential and repetitive stages: (A) polyyne chains on the metal surface react with each other to evolve into a Y-shaped polyyne junction, which preferentially form a five-membered ring as a nucleus; (B) polyyne chains on the first five-membered ring form an additional fused five- or six-membered ring; and (C) pentagon-to-hexagon self-healing rearrangement takes place with the help of short-lived polyyne chains, stabilized by the mobile metal atoms. The observed nucleation process resembles the formation of a fullerene cage. However, the metal particle plays a key role in differentiating the nucleation process from fullerene cage formation, most importantly by keeping the growing cap structure from closing into a fullerene cage and by keeping the carbon edge "alive" for the addition of new carbon material.

Impaired chemotaxis and cell adhesion due to decrease in several cell-surface receptors in cathepsin E-deficient macrophages.

Cathepsin E is an endo-lysosomal aspartic proteinase exclusively present in immune system cells. Previous studies have shown that cathepsin E-deficient (CatE(-/-)) mice display aberrant immune responses such as atopic dermatitis and higher susceptibility to bacterial infection. However, the mechanisms underlying abnormal immune responses induced by cathepsin E deficiency are still unclear. In this study, we found that the cell-surface levels of chemotactic receptors, including chemokine receptor (CCR)-2 and N-formyl peptide receptors (FPRs), were clearly diminished in CatE(-/-)macrophages compared with those in wild-type cells. Consistently, chemotaxis of CatE(-/-)macrophages to MCP-1 and N-formyl-methionyl-leucyl-phenylalanine was also decreased. Similar to the chemotactic receptors, the surface expressions of the adhesion receptors CD18 (integrin beta(2)) and CD 29 (integrin beta(1)) in CatE(-/-) macrophages were significantly decreased, thereby reducing cell attachment of CatE(-/-) macrophages. These results indicate that the defects in chemotaxis and cell adhesion are likely to be involved in the imperfect function of CatE(-/-)macrophages.

Direct metagenomic detection of viral pathogens in nasal and fecal specimens using an unbiased high-throughput sequencing approach.

With the severe acute respiratory syndrome epidemic of 2003 and renewed attention on avian influenza viral pandemics, new surveillance systems are needed for the earlier detection of emerging infectious diseases. We applied a "next-generation" parallel sequencing platform for viral detection in nasopharyngeal and fecal samples collected during seasonal influenza virus (Flu) infections and norovirus outbreaks from 2005 to 2007 in Osaka, Japan. Random RT-PCR was performed to amplify RNA extracted from 0.1-0.25 ml of nasopharyngeal aspirates (N = 3) and fecal specimens (N = 5), and more than 10 microg of cDNA was synthesized. Unbiased high-throughput sequencing of these 8 samples yielded 15,298-32,335 (average 24,738) reads in a single 7.5 h run. In nasopharyngeal samples, although whole genome analysis was not available because the majority (>90%) of reads were host genome-derived, 20-460 Flu-reads were detected, which was sufficient for subtype identification. In fecal samples, bacteria and host cells were removed by centrifugation, resulting in gain of 484-15,260 reads of norovirus sequence (78-98% of the whole genome was covered), except for one specimen that was under-detectable by RT-PCR. These results suggest that our unbiased high-throughput sequencing approach is useful for directly detecting pathogenic viruses without advance genetic information. Although its cost and technological availability make it unlikely that this system will very soon be the diagnostic standard worldwide, this system could be useful for the earlier discovery of novel emerging viruses and bioterrorism, which are difficult to detect with conventional procedures.

Rapid growth of a single-walled carbon nanotube on an iron cluster: density-functional tight-binding molecular dynamics simulations.

Continued growth of a single-walled carbon nanotube (SWNT) on an Fe cluster at 1500 K is demonstrated using quantum chemical molecular dynamics simulations based on the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. In order to deal with charge transfer between carbon and metal particles and the multitude of electronic states, a finite electronic temperature approach is applied. We present trajectories of 45 ps length, where a continuous supply of carbon atoms is directed toward the C-Fe boundary between a 7.2 A long armchair (5,5) SWNT fragment and an attached Fe(38) cluster. The incident carbon atoms react readily at the C-Fe interface to form C- and C(2)-extensions on the tube rim that attach to the Fe cluster. These bridging sp-hybridized carbon fragments are vibrationally excited and highly mobile and, therefore, become engaged in frequent bond formation and breaking processes between their constituent C and the Fe atoms. The sp-hybridized carbon bridge dynamics and their reactions with the Fe-attached nanotube end bring about formations of new five-, six-, and seven-membered carbon rings extending the tube sidewall, resulting in overall continued growth of the nanotube on the Fe cluster up to nearly twice its length. Due to the random nature of new polygon formation, sidewall growth is observed as an irregular process without clear SWNT chirality preference. Compared to fullerene formation, heptagon formation is considerably promoted.

Cathepsin E prevents tumor growth and metastasis by catalyzing the proteolytic release of soluble TRAIL from tumor cell surface.

The aspartic proteinase cathepsin E is expressed predominantly in cells of the immune system and highly secreted by activated phagocytes, and deficiency of cathepsin E in mice results in a phenotype affecting immune responses. However, because physiologic substrates for cathepsin E have not yet been identified, the relevance of these observations to the physiologic functions of this protein remains speculative. Here, we show that cathepsin E specifically induces growth arrest and apoptosis in human prostate carcinoma tumor cell lines without affecting normal cells by catalyzing the proteolytic release of soluble tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) from the cell surface. The antitumor activity of cathepsin E was corroborated by in vivo studies with mice bearing human and mouse tumor transplants. Administration of purified cathepsin E into human tumor xenografts in nude mice dose-dependently induced apoptosis in the tumor cells to inhibit tumor growth. The growth, viability, and metastasis of mouse B16 melanoma cells were also more profound in cathepsin E-deficient mice compared with those in the syngeneic wild-type and transgenic mice overexpressing cathepsin E. Taken together, the number of apoptotic tumor cells, as well as tumor-infiltrating activated macrophages, was apparently reduced in cathepsin E-deficient mice compared with those in the other two groups, implying the positive correlation of endogenous cathepsin E levels with the extent of tumor suppression in vivo. These results thus indicate that cathepsin E plays a substantial role in host defense against tumor cells through TRAIL-dependent apoptosis and/or tumor-associated macrophage-mediated cytotoxicity.

[The program of Founding Research Centers for Emerging and Reemerging Infectious Diseases: the present status and future prospects].

The program of Founding Research Centers for Emerging and Reemerging Infectious Diseases was commenced in 2005 with an outline for Japanese universities and research institutions to establish bilateral collaboration research bases in countries where emerging and reemerging infections are breaking out or will likely break out. So far, six universities and two institutions are participating in the program and ten collaboration bases have been established in six countries (five in Asia and one in Africa). Each research base aims to contribute to the security and safety of the partner and own countries by facilitating better understanding of infectious diseases, technology innovation in diagnosis, therapy and prevention, and human resources development. The experiences of the Reseau International des Instituts Pasteur (RIIP), France, and the Wellcome Trust Southeast Asian Tropical Medicine Research Units (Oxford Network), United Kingdom, which appear to share similar missions, suggest that infectious diseases research that is based on overseas research bases can produce first-time results through the building of long-term mutual trust with the counterparts. By referring to these networks as models, Japan's program should be implemented over the long run but not be based on a short-time perspective. Thus, secure funding is a major issue.

Cathepsin E deficiency induces a novel form of lysosomal storage disorder showing the accumulation of lysosomal membrane sialoglycoproteins and the elevation of lysosomal pH in macrophages.

Cathepsin E, an endolysosomal aspartic proteinase predominantly expressed in cells of the immune system, has an important role in immune responses. However, little is known about the precise roles of cathepsin E in this system. Here we report that cathepsin E deficiency (CatE(-/-)) leads to a novel form of lysosome storage disorder in macrophages, exhibiting the accumulation of the two major lysosomal membrane sialoglycoproteins LAMP-1 and LAMP-2 and the elevation of lysosomal pH. These striking features were also found in wild-type macrophages treated with pepstatin A and Ascaris inhibitor. Whereas there were no obvious differences in their expression, biosynthesis, and trafficking between wild-type and CatE(-/-) macrophages, the degradation rates of these two membrane proteins were apparently decreased as a result of cathepsin E deficiency. Because there was no difference in the vacuolar-type H(+)-ATPase activity in both cell types, the elevated lysosomal pH in CatE(-/-) macrophages is most likely due to the accumulation of these lysosomal membrane glycoproteins highly modified with acidic monosaccharides, thereby leading to the disruption of non-proton factors controlling lysosomal pH. Furthermore, the selective degradation of LAMP-1 and LAMP-2, as well as LIMP-2, was also observed by treatment of the lysosomal membrane fraction isolated from wild-type macrophages with purified cathepsin E at pH 5. Our results thus suggest that cathepsin E is important for preventing the accumulation of these lysosomal membrane sialoglycoproteins that can induce a new form of lysosomal storage disorder.

Cathepsin E-deficient mice show increased susceptibility to bacterial infection associated with the decreased expression of multiple cell surface Toll-like receptors.

Cathepsin E, an intracellular aspartic proteinase, is predominantly localized in the endosomal compartments of immune system cells. In the present study, we investigated the role of cathepsin E in immune defense systems against bacterial infection. Cathepsin E-deficient (CatE(-/-)) mice showed dramatically increased susceptibility to infection with both the Gram-positive bacterium Staphyrococcus aureus, and the Gram-negative bacterium Porphyromonas gingivalis when compared with syngeneic wild-type mice, most likely due to impaired regulation of bacterial elimination. Peritoneal macrophages from CatE(-/-) mice showed significantly impaired tumor necrosis factor-alpha and IL-6 production in response to S. aureus and decreased bactericidal activities toward this bacterium. Moreover, the cell surface levels of Toll-like receptor-2 (TLR2) and TLR4, which recognize specific components of Gram-positive and -negative bacteria, respectively, were decreased in CatE(-/-) macrophages, despite no significant difference in the total cellular expression levels of these receptors between the wild-type and CatE(-/-) macrophages, implying trafficking defects in these surface receptors in the latter. These results indicate an essential role of cathepsin E in immune defense against invading microorganisms, most probably due to regulation of the cell surface expression of TLR family members required for innate immune responses.