Glycosylation of the major polar tube protein of Encephalitozoon cuniculi.

To infect their host cells the Microsporidia use a unique invasion organelle, the polar tube complex. During infection, the organism is injected into the host cell through the hollow polar tube formed during spore germination. Currently, three proteins, PTP1, PTP2, and PTP3 have been identified by immunological and molecular techniques as being components of this structure. Genomic data suggests that Microsporidia are capable of O-linked, but not N-linked glycosylation as a post-translational protein modification. Cells were infected with Encephalitozoon cunicuili, labeled with radioactive mannose or glucosamine, and the polar tube proteins were examined for glycosylation. PTP1 was clearly demonstrated to be mannosylated consistent with 0-glycosylation. In addition, it was evident that several other proteins were mannosylated, but no labeling was seen with glucosamine. The observed post-translational mannosylation of PTP1 may be involved in the functional properties of the polar tube, including its adherence to host cells during penetration.

Interactions of Encephalitozoon cuniculi polar tube proteins.

Microsporidia are eukaryotic, obligate intracellular organisms defined by small spores that contain a single invasion organelle, the polar tube, which coils around the interior of the spore. When these parasites infect host cells, the polar tube is discharged from the anterior pole of the spore, pierces the cell, and transfers sporoplasm into the cytoplasm of the host. Three polar tube proteins (PTP1, PTP2, and PTP3) have been identified in this structure. The interactions of these proteins in the assembly and function of the polar tube are not known. This study was undertaken to examine the protein interactions of the Encephalitozoon cuniculi polar tube proteins (EcPTPs). Immunofluorescence and immunoelectron microscopy confirmed the colocalization of EcPTP1, EcPTP2, and EcPTP3 to the polar tube. Experiments using cross-linkers indicated that EcPTP1, EcPTP2, and EcPTP3 form a complex in the polar tube, which was confirmed by immunoprecipitation using EcPTP1 antiserum. Yeast two-hybrid analysis revealed that full-length EcPTP1, EcPTP2, and EcPTP3 interact with each other in vivo. Both the N and C termini of EcPTP1 were involved in these interactions, but the central region of this protein, which contains a repetitive motif, was not. Further studies of polar tube proteins and their structural interactions may help elucidate the formation of the polar tube during the invasion process.

Loss of retinal cadherin facilitates mammary tumor progression and metastasis.

The mammary epithelium is thought to be stabilized by cell-cell adhesion mediated mainly by E-cadherin (E-cad). Here, we show that another cadherin, retinal cadherin (R-cad), is critical for maintenance of the epithelial phenotype. R-cad is expressed in nontransformed mammary epithelium but absent from tumorigenic cell lines. In vivo, R-cad was prominently expressed in the epithelium of both ducts and lobules. In human breast cancer, R-cad was down-regulated with tumor progression, with high expression in ductal carcinoma in situ and reduced expression in invasive duct carcinomas. By comparison, E-cad expression persisted in invasive breast tumors and cell lines where R-cad was lost. Consistent with these findings, R-cad knockdown in normal mammary epithelium stimulated invasiveness and disrupted formation of acini despite continued E-cad expression. Conversely, R-cad overexpression in aggressive cell lines induced glandular morphogenesis and inhibited invasiveness, tumor formation, and lung colonization. R-cad also suppressed the matrix metalloproteinase 1 (MMP1), MMP2, and cyclooxygenase 2 gene expression associated with pulmonary metastasis. The data suggest that R-cad is an adhesion molecule of the mammary epithelium, which acts as a critical regulator of the normal phenotype. As a result, R-cad loss contributes to epithelial suppression and metastatic progression.

Regulation of host cell cyclin D1 by Trypanosoma cruzi in myoblasts.

Infection with the parasite Trypanosoma cruzi causes Chagas disease. In this study we demonstrated that there was an increase in cyclin D1 expression in T. cruzi (Tulahuen strain)-infected myoblasts. To examine a possible mechanism for the increased cyclin D1 expression we transfected L(6)E(9) myoblasts with cyclin D1 luciferase reporter constructs and infected with T. cruzi. There was no evidence of an increase in promoter activity. Additionally, quantitative PCR did not demonstrate any change in cyclin D1 message during infection. Moreover, we demonstrated that the cyclin D1 protein was significantly stabilized after infection. Collectively, these data indicate that infection with T. cruzi increases cyclin D1 protein abundance post-translationally.

Cell cycle regulatory proteins in the liver in murine Trypanosoma cruzi infection.

The liver is an important target of Trypanosoma cruzi infection. Infection of CD-1 mice with T. cruzi (Brazil strain) resulted in parasitism of the liver, primarily in sinusoidal and Kupffer cells. Immunoblot analysis revealed activation of extra cellular signal-regulated kinase (ERK) during the acute and subacute period of infection, but p38 mitogen activated kinase (MAPK) and JNK were not activated. The activity of important cell cycle regulatory genes was also examined in the liver following infection. There was increased expression of cyclin D1, cyclin E and cyclin A as well as proliferating cell nuclear antigen (PCNA) at 45, 60 and 215 days post infection. In addition, the levels of the cyclin-dependent kinase inhibitors p27(KIP1), p21(WAF1) and the tumor suppressor p53 were increased in the livers obtained from infected mice. Quantitative PCR revealed increased abundance of mRNA for cyclins A, D1 and E. Interestingly, cyclin A and E are ordinarily not found in the adult liver. Thus infection caused a reversion to a fetal/neonatal phenotype. These data provide a molecular basis for cell proliferation in the liver following T. cruzi infection.

Trypanosoma cruzi infection induces proliferation of vascular smooth muscle cells.

Trypanosoma cruzi infection causes cardiomyopathy and vasculopathy. Previous studies have demonstrated that infection of human umbilical vein endothelial and smooth muscle cells resulted in activation of extracellular signal-regulated kinase (ERK). In the present study, smooth muscle cells were infected with trypomastigotes, and immunoblot analysis revealed an increase in the expression of cyclin D1 and proliferating cell nuclear antigen (PCNA), important mediators of smooth muscle cell proliferation. Interestingly, after infection, the expression of caveolin-1 was reduced in both human umbilical vein endothelial cells and smooth muscle cells. Immunoblot and immunohistochemical analyses of lysates of carotid arteries obtained from infected mice revealed increased expression of PCNA, cyclin D1, its substrate, phospho-Rb (Ser780), and phospho-ERK1/2. The expression of the cyclin-dependent kinase inhibitor p21(Cip1/Waf1), caveolin-1, and caveolin-3 was reduced in carotid arteries obtained from infected mice. There was an increase in the abundance of pre-pro-endothelin-1 mRNA in the carotid artery and aorta from infected mice. The ET(A) receptor was also elevated in infected arteries. ERK activates endothelin-1, which in turn exerts positive feedback activating ERK, and cyclin D1 is a downstream target of both endothelin-1 and ERK. There was significant incorporation of bromodeoxyuridine into smooth muscle cell DNA when treatment was with conditioned medium obtained from infected endothelial cells. Taken together, these data suggest that T. cruzi infection stimulates smooth muscle cell proliferation and is likely a result of the upregulation of the ERK-cyclin D1-endothelin-1 pathway.

Cyclin and caveolin expression in an acute model of murine Chagasic myocarditis.

Chagas' disease caused by the parasite, Trypanosoma cruzi, is accompanied by an acute myocarditis which can be fatal. Mice (A/J strain) infected with T. cruzi (Tulahuen strain) develop an acute myocarditis associated with high parasitemia and uniform mortality. Examination of the myocardium demonstrated myonecrosis, vasculitis and parasite pseudocysts. Immunoblot analysis and quantitative real time PCR of heart lysates demonstrated an increased expression of cell cycle regulatory proteins such as cyclins B1, D1, A1 and E1 and an increased expression of cdk2 when compared with uninfected controls. Extracellular signal-regulated kinase (ERK) was activated. Proliferating cell nuclear antigen (PCNA), endothelin-1, endothelin receptor type A (ET(A)) and endothelin receptor type B (ET(B)) expression were increased. Caveolin-1 is important in the regulation of ERK and cyclin D1. The expression of caveolin-1 as well as caveolin-2 and caveolin-3 was reduced. These data suggest that acute fatal T. cruzi myocarditis is accompanied by changes in cell cycle proteins such as the cyclins and caveolin and that the upregulation of the endothelin pathway may be important in the myocardial abnormalities and mortality observed in this mouse model.

Risedronate in the treatment of Murine Chagas' disease.

Risedronate, a bisphosphonate, was used to treat CD-1 mice infected with the Brazil strain of Trypanosoma cruzi. When given by subcutaneous injection 3 times/week, there was a significant reduction in mortality, however, the myocardial pathology and right ventricular dilation was unchanged in these mice compared to control animals. In C57BL/6 mice infected with the Tulahuen strain, there was no change in mortality in response to risedronate treatment. These data suggest that this class of compounds has activity against T. cruzi in vivo and illustrate the utility of imaging and pathologic studies as adjuncts in the evaluation of therapeutic compounds as treatments for experimental Chagas' disease. In addition, it underscores the need to use different strains of T. cruzi.

Absence of caveolin-1 sensitizes mouse skin to carcinogen-induced epidermal hyperplasia and tumor formation.

Caveolin-1 is the principal protein component of caveolae membrane domains, which are located at the cell surface in most cell types. Evidence has accumulated suggesting that caveolin-1 may function as a suppressor of cell transformation in cultured cells. The human CAV-1 gene is located at a putative tumor suppressor locus (7q31.1/D7S522) and a known fragile site (FRA7G) that is deleted in a variety of epithelial-derived tumors. Mechanistically, caveolin-1 is known to function as a negative regulator of the Ras-p42/44 MAP kinase cascade and as a transcriptional repressor of cyclin D1, possibly explaining its transformation suppressor activity in cultured cells. However, it remains unknown whether caveolin-1 functions as a tumor suppressor gene in vivo. Here, we examine the tumor suppressor function of caveolin-1 using Cav-1 (-/-) null mice as a model system. Cav-1 null mice and their wild-type counterparts were subjected to carcinogen-induced skin tumorigenesis, using 7,12-dimethylbenzanthracene (DMBA). Mice were monitored weekly for the development of tumors. We demonstrate that Cav-1 null mice are dramatically more susceptible to carcinogen-induced tumorigenesis, as they develop skin tumors at an increased rate. After 16 weeks of DMBA-treatment, Cav-1 null mice showed a 10-fold increase in tumor incidence, a 15-fold increase in tumor number per mouse (multiplicity), and a 35-fold increase in tumor area per mouse, as compared with wild-type littermate mice. Moreover, before the development of tumors, DMBA-treatment induced severe epidermal hyperplasia in Cav-1 null mice. Both the basal cell layer and the suprabasal cell layers were expanded in treated Cav-1 null mice, as evidenced by immunostaining with cell-type specific differentiation markers (keratin-10 and keratin-14). In addition, cyclin D1 and phospho-ERK1/2 levels were up-regulated during epidermal hyperplasia, suggesting a possible mechanism for the increased susceptibility of Cav-1 null mice to tumorigenesis. However, the skin of untreated Cav-1 null mice appeared normal, without any evidence of epidermal hyperplasia, despite the fact that Cav-1 null keratinocytes failed to express caveolin-1 and showed a complete ablation of caveolae formation. Thus, Cav-1 null mice require an appropriate oncogenic stimulus, such as DMBA treatment, to reveal their increased susceptibility toward epidermal hyperplasia and skin tumor formation. Our results provide the first genetic evidence that caveolin-1 indeed functions as a tumor suppressor gene in vivo.

Activation of transcription factors AP-1 and NF-kappa B in murine Chagasic myocarditis.

The myocardium of CD1 mice was examined for the activation of signal transduction pathways leading to cardiac inflammation and subsequent remodeling during Trypanosoma cruzi infection (Brazil strain). The activity of three pathways of the mitogen-activated protein kinases (MAPKs) was determined. Immunoblotting revealed a persistent elevation of phosphorylated (activated) extracellular-signal-regulated kinase (ERK), which regulates cell proliferation. During infection there was a transient activation of p38 MAPK but no activation of Jun N-terminal kinase. Early targets of activated ERK, c-Jun and c-Fos, were elevated during infection, as demonstrated by semiquantitative reverse transcription-PCR. Immunostaining revealed that the endothelium and the interstitial cells were most intensely stained with antibodies to c-Jun and c-Fos. Soon after infection, AP-1 and NF-kappa B DNA binding activity was increased. Protein levels of cyclin D1, the downstream target of ERK and NF-kappa B, were induced during acute infection. Immunostaining demonstrated increased expression of cyclin D1 in the vascular and endocardial endothelium, inflammatory cells, and the interstitial areas. Increased expression of the cyclin D1-specific phosphorylated retinoblastoma protein (Ser780) was also evident. Immunoblotting and immunostaining also demonstrated increased expression of proliferating cellular nuclear antigen that was predominantly present in the inflammatory cells, interstitial areas (i.e., fibroblasts), and endothelium. These data demonstrate that T. cruzi infection results in activation of the ERK-AP-1 pathway and NF-kappa B. Cyclin D1 expression was also increased. These observations provide a molecular basis for the activation of pathways involved in cardiac remodeling in chagasic cardiomyopathy.

Cardioprotective effects of phosphoramidon on myocardial structure and function in murine Chagas' disease.

Chagas' disease is an important cause of cardiomyopathy. Endothelin-1, a vasoactive peptide has been implicated in the pathogenesis of chagasic cardiomyopathy. C57BL/6 x 129sv and CD1 mice were thus, infected with trypomastigotes of Trypanosoma cruzi (Brazil strain) and these infected mice were compared with infected mice treated with phosphoramidon. This compound inhibits endothelin-converting enzyme and neutral endopeptidases and does not affect the growth of the parasite in culture. Phosphoramidon was given in a dose of 10mg/kg for the initial 15 days post-infection None of the C57Bl/6 x 129sv mice died as a result of infection. However, there was marked myocardial inflammation and fibrosis in infected, untreated mice. The hearts of the infected, phosphoramidon-treated mice showed significantly less pathology. Cardiac magnetic resonance imaging of infected mice revealed right ventricular dilation that was less severe in those treated with phosphoramidon. Phosphoramidon-treated CD1 mice survived the acute infection. Transthoracic echocardiography demonstrated left ventricular dilation and reduced percent fractional shortening and relative wall thickness. These alterations were also attenuated as a result of phosphoramidon treatment. These data suggest that endothelin-1 contributes to the pathogenesis of chagasic cardiomyopathy and interventions that inhibit the synthesis of endothelin-1 and/or neutral endopeptidase might have a protective effect on myocardial structure and function in murine Chagas' disease.