Mechanism of interaction of the 85B secreted protein of Mycobacterium bovis with fibronectin

Fusion Protein Vaccine Based on Ag85B and STEAP1 Induces a Protective Immune Response against Prostate Cancer

(1) Background: There are currently limited treatments for castration-resistant prostate cancer. Immunotherapy involving Sipuleucel-T has increasingly drawn attention for prostate cancer management. BCG plays a vital role in treating bladder cancer, mainly by inducing immune activation, but is rarely used for prostate cancer. (2) Methods: The TCGA database, PCR, and Western blotting were used to analyze the expression of STEAP1 in mouse and human tissues. Then, we constructed a fusion protein vaccine with Mycobacterium tuberculosis Ag85B and three repeated octapeptide epitopes of a six-transmembrane epithelial antigen of the prostate 1 (STEAP1_186-193), Ag85B-3×STEAP1_186-193. The uptake of the fusion protein vaccine by DCs was evaluated by confocal microscopy, and DC markers were detected using flow cytometry after incubation with the fusion protein. The immune response against prostate cancer was evaluated by the LDH assay and xenografts in vitro and in vivo. Then, the tumor microenvironment was determined using IHC and ELISA. In addition, the epitope was mutated using CRISPR-Cas9 to illustrate that the fusion protein elicited immunization against STEAP1. (3) Results: The TCGA database analysis, PCR, and Western blotting showed that STEAP1 was highly expressed in human and murine prostate cancer. After the uptake of the purified fusion protein vaccine by DCs, CD11c, CD80, CD86, and MHC II were upregulated and triggered a cytotoxic T lymphocyte (CTL) response against TRAMP-C1 and RM1 cells in vitro. Furthermore, the fusion protein vaccine inhibited tumor growth and improved the tumor microenvironment in vivo, with more CD3⁺ cells and fewer FOXP3⁺ cells in the tumor. Serum IFN-γ and IL-2 were significantly higher than in the control group, while IL-4 expression was lower, indicating that the fusion protein vaccine activated Th1 immunity. The immune response against prostate cancer was greatly suppressed when the antigen targets were knocked out using CRISPR-Cas9. (4) Conclusion: In summary, our results provide the first evidence that a vaccine based on a fusion protein consisting of Ag85B and a prostate cancer octapeptide epitope with complete Freund’s adjuvant (CFA), triggers a robust immune response and inhibits tumor growth in murine prostate cancer.

Features of the biochemistry of Mycobacterium smegmatis, as a possible model for Mycobacterium tuberculosis

An alternate host for mycobacteria is Mycobacterium smegmatis which is used frequently. It is a directly budding eco-friendly organism not emulated as human infection. It is mainly useful for the investigation of various microorganisms in the sort of Mycobacteria in cell culture laboratories. Some Mycobacterium species groups that is normal, unsafe ailments, likely to Mycobacterium leprae, Mycobacterium tuberculosis and Mycobacterium bovis. At present, various laboratories are clean and culture this type of species to make an opinion that fascinating route of harmful Mycobacteria. This publication provides aggregate data on cell shape, genome studies, ecology, pathology and utilization of M. smegmatis.

Fibronectin and Its Role in Human Infective Diseases

Fibronectin is a multidomain glycoprotein ubiquitously detected in extracellular fluids and matrices of a variety of animal and human tissues where it functions as a key link between matrices and cells. Fibronectin has also emerged as the target for a large number of microorganisms, particularly bacteria. There are clear indications that the binding of microorganism’ receptors to fibronectin promotes attachment to and infection of host cells. Each bacterium may use different receptors which recognize specific fibronectin domains, mostly the N-terminal domain and the central cell-binding domain. In many cases, fibronectin receptors have actions over and above that of simple adhesion: In fact, adhesion is often the prerequisite for invasion and internalization of microorganisms in the cells of colonized tissues. This review updates the current understanding of fibronectin receptors of several microorganisms with emphasis on their biochemical and structural properties and the role they can play in the onset and progression of host infection diseases. Furthermore, we describe the antigenic profile and discuss the possibility of designing adhesion inhibitors based on the structure of the fibronectin-binding site in the receptor or the receptor-binding site in fibronectin.

Evaluation of a temperature-restricted, mucosal tuberculosis vaccine in guinea pigs

Tuberculosis (TB) is currently the leading cause of death in humans by a single infectious agent, Mycobacterium tuberculosis. The Bacillus Calmette-Guérin (BCG) vaccine prevents pulmonary TB with variable efficacy, but can cause life-threatening systemic infection in HIV-infected infants. In this study, TBvac85, a derivative of Mycobacterium shottsii expressing M. tuberculosis Antigen 85B, was examined as a safer alternative to BCG. Intranasal vaccination of guinea pigs with TBvac85, a naturally temperature-restricted species, resulted in serum Ag85B-specific IgG antibodies. Delivery of the vaccine by this route also induced protection equivalent to intradermal BCG based on organ bacterial burdens and lung pathology six weeks after aerosol challenge with M. tuberculosis strain Erdman. These results support the potential of TBvac85 as the basis of an effective TB vaccine. Next-generation derivatives expressing multiple M. tuberculosis immunogens are in development.

Protective efficacy of recombinant BCG over-expressing protective, stage-specific antigens of Mycobacterium tuberculosis

Tuberculosis (TB) remains a major cause of mortality and morbidity worldwide, yet current control strategies, including the existing BCG vaccine, have had little impact on disease control. CysVac2, a fusion protein comprising stage-specific Mycobacterium tuberculosis antigens, provided superior protective efficacy against chronic M. tuberculosis infection in mice, compared to BCG. To determine if the delivery of CysVac2 in the context of BCG could improve BCG-induced immunity and protection, we generated a recombinant strain of BCG overexpressing CysVac2 (rBCG:CysVac2). Expression of CysVac2 in BCG was facilitated by the M. tuberculosis hspX promoter, which is highly induced inside phagocytic cells and induces strong cellular immune responses to antigens expressed under its regulation. Intradermal vaccination with rBCG:CysVac2 resulted in increased monocyte/macrophage recruitment and enhanced antigen-specific CD4⁺ T cell priming compared to parental BCG, indicating CysVac2 overexpression had a marked effect on rBCG induced-immunity. Further, rBCG:CysVac2 was a more potent inducer of antigen-specific multifunctional CD4⁺ T cells (CD4⁺IFN-γ⁺TNF⁺IL-2⁺) than BCG after vaccination of mice. This improved immunogenicity however did not influence protective efficacy, with both BCG and rBCG:CysVac2 affording comparable level of protection aerosol infection with M. tuberculosis. Boosting either BCG or rBCG:CysVac2 with the CysVac2 fusion protein resulted in a similar improvement in protective efficacy. These results demonstrate that the expression of protective antigens in BCG can augment antigen-specific immunity after vaccination but does not alter protection against infection, further highlighting the challenge of developing effective vaccines to control TB.

The Ag85B protein of the BCG vaccine facilitates macrophage uptake but is dispensable for protection against aerosol Mycobacterium tuberculosis infection

Defining the function and protective capacity of mycobacterial antigens is crucial for progression of tuberculosis (TB) vaccine candidates to clinical trials. The Ag85B protein is expressed by all pathogenic mycobacteria and is a component of multiple TB vaccines under evaluation in humans. In this report we examined the role of the BCG Ag85B protein in host cell interaction and vaccine-induced protection against virulent Mycobacterium tuberculosis infection. Ag85B was required for macrophage infection in vitro, as BCG deficient in Ag85B expression (BCG:(Δ85B)) was less able to infect RAW 264.7 macrophages compared to parental BCG, while an Ag85B-overexpressing BCG strain (BCG:(oex85B)) demonstrated improved uptake. A similar pattern was observed in vivo after intradermal delivery to mice, with significantly less BCG:(Δ85B) present in CD64(hi)CD11b(hi) macrophages compared to BCG or BCG:(oex85B). After vaccination of mice with BCG:(Δ85B) or parental BCG and subsequent aerosol M. tuberculosis challenge, similar numbers of activated CD4(+) and CD8(+) T cells were detected in the lungs of infected mice for both groups, suggesting the reduced macrophage uptake observed by BCG:(Δ85B) did not alter host immunity. Further, vaccination with both BCG:(Δ85B) and parental BCG resulted in a comparable reduction in pulmonary M. tuberculosis load. These data reveal an unappreciated role for Ag85B in the interaction of mycobacteria with host cells and indicates that single protective antigens are dispensable for protective immunity induced by BCG.

Mycobacterial laminin-binding histone-like protein mediates collagen-dependent cytoadherence

When grown in the presence of exogenous collagen I, Mycobacterium bovis BCG was shown to form clumps. Scanning electron microscopy examination of these clumps revealed the presence of collagen fibres cross-linking the bacilli. Since collagen is a major constituent of the eukaryotic extracellular matrices, we assayed BCG cytoadherence in the presence of exogenous collagen I. Collagen increased the interaction of the bacilli with A549 type II pneumocytes or U937 macrophages, suggesting that BCG is able to recruit collagen to facilitate its attachment to host cells. Using an affinity chromatography approach, we have isolated a BCG collagen-binding protein corresponding to the previously described mycobacterial laminin-binding histone-like protein (LBP/Hlp), a highly conserved protein associated with the mycobacterial cell wall. Moreover, Mycobacterium leprae LBP/Hlp, a well-characterized adhesin, was also able to bind collagen I. Finally, using recombinant fragments of M. leprae LBP/Hlp, we mapped the collagen-binding activity within the C-terminal domain of the adhesin. Since this protein was already shown to be involved in the recognition of laminin and heparan sulphate-containing proteoglycans, the present observations reinforce the adhesive activities of LBP/Hlp, which can be therefore considered as a multifaceted mycobacterial adhesin, playing an important role in both leprosy and tuberculosis pathogenesis.

Surface proteome of "Mycobacterium avium subsp. hominissuis" during the early stages of macrophage infection

"Mycobacterium avium subsp. hominissuis" is a robust and pervasive environmental bacterium that can cause opportunistic infections in humans. The bacterium overcomes the host immune response and is capable of surviving and replicating within host macrophages. Little is known about the bacterial mechanisms that facilitate these processes, but it can be expected that surface-exposed proteins play an important role. In this study, the selective biotinylation of surface-exposed proteins, streptavidin affinity purification, and shotgun mass spectrometry were used to characterize the surface-exposed proteome of M. avium subsp. hominissuis. This analysis detected more than 100 proteins exposed at the bacterial surface of M. avium subsp. hominissuis. Comparisons of surface-exposed proteins between conditions simulating early infection identified several groups of proteins whose presence on the bacterial surface was either constitutive or appeared to be unique to specific culture conditions. This proteomic profile facilitates an improved understanding of M. avium subsp. hominissuis and how it establishes infection. Additionally, surface-exposed proteins are excellent targets for the host adaptive immune system, and their identification can inform the development of novel treatments, diagnostic tools, and vaccines for mycobacterial disease.

Attempted immunotherapy for Mycobacterium tuberculosis with viral and protein vaccines based on Ag85B-ESAT6 in a mouse model

The increasing threat of drug-resistant strains of Mycobacterium tuberculosis (M. tb) and co-infection with human immunodeficiency virus (HIV) has worsened the international public health crisis and challenged conventional chemotherapy. Therapeutic vaccines, which possess the capacity to stimulate the immune system and affect the disease progression, deserve reconsideration to aid chemotherapy. Vaccines based on Ag85B-ESAT6 fusion protein were tested as potential immunotherapeutic vaccines against ongoing intravenous infection in a mouse model. Therapeutic efficacy was evaluated by enumeration of bacilli in infected tissues and by histological examination of the lungs. Ag85B-ESAT6 with the adjuvant dimethyl dioctadecylammonium bromide (DDA) - monophosphoryl lipid A (MPL) did not reduce bacterial load, however induced a sharp weight loss and worsened pathology. Recombinant virus-based vaccines failed to protect mice against tuberculosis either. More efforts should be taken to search for protective candidates and elucidate the mechanism for immunotherapy.

Novel mycobacteria antigen 85 complex binding motif on fibronectin

The members of the antigen 85 protein family (Ag85), consisting of members Ag85A, Ag85B, and Ag85C, are the predominantly secreted proteins of mycobacteria and possess the ability to specifically interact with fibronectin (Fn). Because Fn-binding proteins are likely to be important virulence factors of Mycobacterium spp., Ag85 may contribute to the adherence, invasion, and dissemination of organisms in host tissue. In this study, we reported the Fn binding affinity of Ag85A, Ag85B, and Ag85C from Mycobacterium avium subsp. paratuberculosis (MAP) (K(D) values were determined from 33.6 to 68.4 nm) and mapped the Ag85-binding motifs of Fn. Fn14, a type III module located on the heparin-binding domain II (Hep-2) of Fn, was discovered to interact with Ag85 from MAP. The peptide inhibition assay subsequently demonstrated that a peptide consisting of residues 17-26 from Fn14 ((17)SLLVSWQPPR(26), termed P17-26) could interfere with Ag85B binding to Fn (73.3% reduction). In addition, single alanine substitutions along the sequence of P17-26 revealed that the key residues involved in Ag85-Fn binding likely contribute through hydrophobic and charge interactions. Moreover, binding of Ag85 on Fn siRNA-transfected Caco2 cells was dramatically reduced (44.6%), implying the physiological significance of the Ag85-Fn interaction between mycobacteria and host cells during infection. Our results indicate that Ag85 binds to Fn at a novel motif and plays a critical role in mycobacteria adherence to host cells by initiating infection. Ag85 might serve as an important colonization factor potentially contributing to mycobacterial virulence.

Bacterial virulence in the moonlight: multitasking bacterial moonlighting proteins are virulence determinants in infectious disease

Men may not be able to multitask, but it is emerging that proteins can. This capacity of proteins to exhibit more than one function is termed protein moonlighting, and, surprisingly, many highly conserved proteins involved in metabolic regulation or the cell stress response have a range of additional biological actions which are involved in bacterial virulence. This review highlights the multiple roles exhibited by a range of bacterial proteins, such as glycolytic and other metabolic enzymes and molecular chaperones, and the role that such moonlighting activity plays in the virulence characteristics of a number of important human pathogens, including Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Helicobacter pylori, and Mycobacterium tuberculosis.

Phenylalanine-rich peptides potently bind ESAT6, a virulence determinant of Mycobacterium tuberculosis, and concurrently affect the pathogen's growth

Background

The secretory proteins of Mycobacterium tuberculosis (M. tuberculosis) have been known to be involved in the virulence, pathogenesis as well as proliferation of the pathogen. Among this set, many proteins have been hypothesized to play a critical role at the genesis of the onset of infection, the primary site of which is invariably the human lung.

Methodology/Principal Findings

During our efforts to isolate potential binding partners of key secretory proteins of M. tuberculosis from a human lung protein library, we isolated peptides that strongly bound the virulence determinant protein Esat6. All peptides were less than fifty amino acids in length and the binding was confirmed by in vivo as well as in vitro studies. Curiously, we found all three binders to be unusually rich in phenylalanine, with one of the three peptides a short fragment of the human cytochrome c oxidase-3 (Cox-3). The most accessible of the three binders, named Hcl1, was shown also to bind to the Mycobacterium smegmatis (M. smegmatis) Esat6 homologue. Expression of hcl1 in M. tuberculosis H37Rv led to considerable reduction in growth. Microarray analysis showed that Hcl1 affects a host of key cellular pathways in M. tuberculosis. In a macrophage infection model, the sets expressing hcl1 were shown to clear off M. tuberculosis in much greater numbers than those infected macrophages wherein the M. tuberculosis was not expressing the peptide. Transmission electron microscopy studies of hcl1 expressing M. tuberculosis showed prominent expulsion of cellular material into the matrix, hinting at cell wall damage.

Conclusions/Significance

While the debilitating effects of Hcl1 on M. tuberculosis are unrelated and not because of the peptide's binding to Esat6–as the latter is not an essential protein of M. tuberculosis–nonetheless, further studies with this peptide, as well as a closer inspection of the microarray data may shed important light on the suitability of such small phenylalanine-rich peptides as potential drug-like molecules against this pathogen.

Study on enhancement of fibronectin-mediated bacillus Calmette-Guérin attachment to urinary bladder wall in rabbits

To clarify whether intravesical usage of fibrin clot stabilizer epsilon-aminocaproic acid (EACA) or p-aminomethyl benzoic acid (PAMBA) and different injuries enhance fibronectin (FN)-mediated bacillus Calmette-Guérin (BCG) attachment to bladder wall. Thirty New Zealand male white rabbits were randomly divided into five groups and the bladder wall of each rabbit was injured by electrocautery, cryocautery or knife cutting on left lateral wall, right lateral wall and posterior wall in different groups, respectively. Different drug was instilled into the bladder: Group A: pure PBS; B: PBS and radiolabeled BCG ((3)H-BCG); C: EACA and (3)H-BCG; D: PAMBA and (3)H-BCG; E: heparin and (3)H-BCG. After instillation, each injured and non-injured bladder wall were surgically harvested and digested. The quantity of BCG attachment was detected by liquid scintillation counter (scintillation times per min, STPM). Quantity of BCG attachment to injured bladder wall was significantly (P < 0.01) greater than that of non-injured one, no matter which injury was performed. The BCG attachment to bladder wall in Group C or Group D was significantly (P < 0.05) greater than that of Group B. The quantity of BCG attachment to bladder of Group E was significantly (P < 0.05) less than that of Group B, C and D, respectively. Intravesical instillation of fibrin clot stabilizer (PAMBA, EACA) enhances FN-mediated BCG attachment to bladder wall while heparin inhibits this process. Injuries; e.g., cutting, cryocautery or electrocautery of bladder wall can significantly increase BCG attachment to the bladder wall.

Ag85B of mycobacteria elicits effective CTL responses through activation of robust Th1 immunity as a novel adjuvant in DNA vaccine

CD4+ T cells play a crucial role in CTL generation in a DNA vaccination strategy. Several studies have demonstrated the requirement of CD4+ T cells for the induction of a sufficient immune response by coadministrating DNAs. In the present study we investigated the effectiveness of Ag85B of mycobacteria, which is known to be one of the immunogenic proteins for Th1 development, as an adjuvant of a DNA vaccine. HIV gp120 DNA vaccine mixed with Ag85B DNA as an adjuvant induced HIV gp120-specific Th1 responses, as shown by delayed-type hypersensitivity, cytokine secretion, and increasing HIV-specific CTL responses. Moreover, these responses were enhanced in mice primed with Mycobacterium bovis bacillus Calmette-Guérin before immunization of HIV DNA vaccine mixed with Ag85B DNA. Furthermore, these immunized mice showed substantial reduction of HIV gp120-expressing recombinant vaccinia virus titers compared with the titers in other experimental mice after recombinant vaccinia virus challenge. Because most humans have been sensitized by spontaneous infection or by vaccination with mycobacteria, these findings indicate that Ag85B is a promising adjuvant for enhancing CTL responses in a DNA vaccination strategy.

FbpA-Dependent biosynthesis of trehalose dimycolate is required for the intrinsic multidrug resistance, cell wall structure, and colonial morphology of Mycobacterium smegmatis

Ligation of mycolic acids to structural components of the mycobacterial cell wall generates a hydrophobic, impermeable barrier that provides resistance to toxic compounds such as antibiotics. Secreted proteins FbpA, FbpB, and FbpC attach mycolic acids to arabinogalactan, generating mycolic acid methyl esters (MAME) or trehalose, generating alpha,alpha'-trehalose dimycolate (TDM; also called cord factor). Our studies of Mycobacterium smegmatis showed that disruption of fbpA did not affect MAME levels but resulted in a 45% reduction of TDM. The fbpA mutant displayed increased sensitivity to both front-line tuberculosis-targeted drugs as well as other broad-spectrum antibiotics widely used for antibacterial chemotherapy. The irregular, hydrophobic surface of wild-type M. smegmatis colonies became hydrophilic and smooth in the mutant. While expression of M. smegmatis fbpA restored defects of the mutant, heterologous expression of the Mycobacterium tuberculosis fbpA gene was less effective. A single mutation in the M. smegmatis FbpA esterase domain inactivated its ability to provide antibiotic resistance. These data show that production of TDM by FbpA is essential for the intrinsic antibiotic resistance and normal colonial morphology of some mycobacteria and support the concept that FbpA-specific inhibitors, alone or in combination with other antibiotics, could provide an effective treatment to tuberculosis and other mycobacterial diseases.

Characterization of the secreted chorismate mutase from the pathogen Mycobacterium tuberculosis

The gene encompassing ORF Rv1885c with weak sequence similarity to AroQ chorismate mutases (CMs) was cloned from the genome of Mycobacterium tuberculosis and expressed in Escherichia coli. The gene product (*MtCM) complements a CM-deficient E. coli strain, but only if produced without the predicted N-terminal signal sequence typical of M. tuberculosis. The mature *MtCM, which was purified by exploiting its resistance to irreversible thermal denaturation, possesses high CM activity in vitro. The enzyme follows simple Michaelis-Menten kinetics, having a k(cat) of 50 s(-1) and a K(m) of 180 microM (at 30 degrees C and pH 7.5). *MtCM was shown to be a dimer by analytical ultracentrifugation and size-exclusion chromatography. Secondary-structure prediction and CD spectroscopy confirmed that *MtCM is a member of the all-alpha-helical AroQ class of CMs, but it seems to have a topologically rearranged AroQ fold. Because CMs are normally intracellular metabolic enzymes required for the biosynthesis of phenylalanine and tyrosine, the existence of an exported CM in Gram-positive M. tuberculosis is puzzling. The observation that homologs of *MtCM with a predicted export sequence are generally only present in parasitic or pathogenic organisms suggests that secreted CMs may have evolved to participate in some aspect of parasitism or pathogenesis yet to be unraveled.

Mycobacterium tuberculosis antigen 85A and 85C structures confirm binding orientation and conserved substrate specificity

The maintenance of the highly hydrophobic cell wall is central to the survival of Mycobacterium tuberculosis within its host environment. The antigen 85 proteins (85A, 85B, and 85C) of M. tuberculosis help maintain the integrity of the cell wall 1) by catalyzing the transfer of mycolic acids to the cell wall arabinogalactan and 2) through the synthesis of trehalose dimycolate (cord factor). Additionally, these secreted proteins allow for rapid invasion of alveolar macrophages via direct interactions between the host immune system and the invading bacillus. Here we describe two crystal structures: the structure of antigen 85C co-crystallized with octylthioglucoside as substrate, resolved to 2.0 A, and the crystal structure of antigen 85A, which was solved at a resolution of 2.7 A. The structure of 85C with the substrate analog identifies residues directly involved in substrate binding. Elucidation of the antigen 85A structure, the last of the three antigen 85 homologs to be solved, shows that the active sites of the three antigen 85 proteins are virtually identical, indicating that these share the same substrate. However, in contrast to the high level of conservation within the substrate-binding site and the active site, surface residues disparate from the active site are quite variable, indicating that three antigen 85 enzymes are needed to evade the host immune system.

Interaction of Mycobacterium tuberculosis with human respiratory mucosa

OBJECTIVE

Endobronchial infection is associated with pulmonary tuberculosis in the majority of cases. We have investigated the adherence of Mycobacterium tuberculosis to the human respiratory mucosa.

DESIGN

Organ cultures constructed with human tissue were infected with M. tuberculosis in the presence or absence of mycobacterial fibronectin attachment cell surface proteins and examined by scanning electron microscopy.

RESULTS

M. tuberculosis adhered mainly to extracellular matrix (ECM) in areas of mucosal damage, but not to ciliated mucosa, intact extruded cells, basement membrane or collagen fibres. Bacteria also adhered to fibrous but not globular mucus and occasionally to healthy unciliated mucosa, open tight junctions and to extruded cells that had degenerated, exposing their contents. There was a significant reduction (p<0.05) in the number of bacteria adhering to ECM after pre-incubation of bacteria with fibronectin and after pre-incubation of the tissue with M. avium fibronectin attachment protein (FAP) and M. bovis antigen 85B protein, in a concentration dependent manner. The combined effect of FAP and antigen 85B protein was significantly greater than either protein alone. Bacterial adherence to fibrous mucus was not influenced by fibronectin.

CONCLUSION

We conclude that M. tuberculosis adheres to ECM in areas of mucosal damage at least in part via FAP and antigen 85B protein.

Secreted intestinal surfactant-like particles interact with cell membranes and extracellular matrix proteins in rats

Surfactant-like particles (SLP) are secreted from enterocytes basolaterally into the lamina propria, and reach the apical surface through the intercellular tight junctions. Interactions of SLP with apical and basolateral membranes and with extracellular matrix proteins were measured using a solid-phase binding assay and gel overlays. Small-intestinal SLP bound to basolateral membranes much more than to apical membranes, and more tightly to fibronectin than to laminin (affinity constant K(a) = 1.23 x 10(-2) microg vs. 0.67 x 10(-2) microg; maximal number of binding sites 4.1 microg x ml(-1) vs. 0.32 microg x ml(-1)), but did not bind to collagen types I or IV. Small-intestinal SLP bound fibronectin more than colonic or gastric SLP. Binding to fibronectin was inhibited only partially by RGD peptide and gelatin, but not by heparin. An antibody against alpha(v) integrin also identified the fibronectin-binding component in SLP at approximately 220 kDa, which is the expected size for integrin heterodimers. SLP binding to apical microvillous membranes was weaker and was inhibited by heparin. SLP bound more strongly to heparin itself, and this binding was inhibited by glucuronic acid and chondroitin sulfate. These data are consistent with the hypothesis that the time spent by secreted SLP in the lamina propria is prolonged by strong interactions with proteins in the basolateral membranes, and in the intestinal lumen by weaker interactions with apical membrane components, including heparin. These interactions may allow SLP the time to exert their functions in each tissue compartment.

Fibronectin facilitates Mycobacterium tuberculosis attachment to murine alveolar macrophages

Mycobacterium tuberculosis remains a major cause of pulmonary infection worldwide. Attachment of M. tuberculosis organisms to alveolar macrophages (AMs) represents the earliest phase of primary infection in pulmonary tuberculosis. In this study fibronectin (Fn), an adhesive protein, is shown to bind M. tuberculosis organisms and facilitates attachment of M. tuberculosis to murine AMs. A monoclonal antibody (MAb) specific to the heparin binding domain (HBD) of Fn decreases (125)I-Fn binding to M. tuberculosis; whereas MAbs specific to either the cell binding domain (CBD) or the gelatin binding domain (GBD) have no effect on Fn binding to M. tuberculosis. In the presence of exogenous Fn (10 microg/ml) M. tuberculosis attachment to AMs increased significantly from control levels (means +/- standard errors of the means) of 11.5% +/- 1.1% to 44.2% +/- 4.2% (P < 0.05). Fn-enhanced attachment was significantly decreased from 44.2% +/- 4.2% to 10.8% +/- 1.2% (P < 0.05) in the presence of anti-Fn polyclonal antibodies. The attachment is also inhibited in the presence of MAbs specific for the HBD and CBD, whereas MAbs specific to GBD did not affect the attachment. Further, an Fn cell binding peptide, Arg-Gly-Asp-Ser (RGDS), decreased the attachment from 44.2% +/- 4.2% to 15.3% +/- 1.2% (P < 0.05), whereas addition of a control peptide, Arg-Gly-Glu-Ser (RGES) did not affect the attachment (40.5% +/- 1.8%). These results suggest that Fn-mediated attachment of M. tuberculosis can occur through the binding of Fn to the AM via the CBD and to M. tuberculosis organisms via the HBD.

Fibronectin attachment protein homologue mediates fibronectin binding by Mycobacterium avium subsp. paratuberculosis

Attachment of Mycobacterium avium subsp. paratuberculosis to host tissue and penetration of mucosal surfaces are pivotal events in the pathogenesis of Johne's disease. Fibronectin (FN) binding is required for attachment and internalization of several mycobacteria by epithelial cells in vitro. The objective of this study was to further characterize the FN binding activity of M. avium subsp. paratuberculosis. Although the bacteria bound FN poorly at pH above 7, brief acid pretreatment greatly enhanced FN binding within the pH range (3 to 10) studied. A 4.6-kbp fragment from an M. avium subsp. paratuberculosis genomic library was found to contain a 1,107-bp open reading frame that shows very high nucleotide sequence identity with that of the FN attachment protein (FAP) gene of M. avium subsp. avium. Pretreatment of FN with an FN-binding peptide from M. avium subsp. avium FAP abolished FN binding, indicating that M. avium subsp. paratuberculosis binds FN in a FAP-dependent manner. Pretreatment of M. avium subsp. paratuberculosis with anti-FAP immunoglobulin G did not abrogate FN binding; blocking occurred only when anti-FAP was added together with FN. FAP was detected by immunofluorescence only in lipid-extracted M. avium subsp. paratuberculosis. Western blotting and immunoelectron microscopy revealed that FAP is located near the interior of the cell envelope of M. avium subsp. paratuberculosis. The results indicate that a FAP homologue mediates the attachment of FN to M. avium subsp. paratuberculosis. Further, given the subcellular location of FAP, it is considered that this protein operates at the terminus of a coordinated FN binding system in the cell envelope of M. avium subsp. paratuberculosis.

Epitope focus, clonal composition and Th1 phenotype of the human CD4 response to the secretory mycobacterial antigen Ag85

Lymphoproliferation of healthy donors was tested against mycobacterial antigens (PPD, Ag85, Ag85 peptides). All PPD responders recognized the secretory antigen Ag85 and the peptide specificity for Ag85B was defined. Peptide 91-108 was recognized by 85% of donors. In addition, all CD4 T cell lines generated from 12 donors against PPD or Ag85 responded to 91-108. When this peptide was used to generate T cell lines, the cells responded also to tuberculins from atypical mycobacterial species. Thus the cross-reactive peptide behaved as quasi-universal. The analysis of TCR-BV gene usage by cell lines showed that most Ag85-specific T cells correspond to 91-108-specific clonotypes. Intracytoplasmic staining of cell lines after phorbol myristate acetate stimulation resulted in dominance of interferon-gamma (IFN-gamma)-IL-4 double-positive cells, whereas antigen stimulation resulted in production of IFN-gamma only. The data show that peptide 91-108 is the major focus of the CD4 response to mycobacterial antigens in peripheral blood mononuclear cells and in T cell lines from PPD responders.

The role of Mycobacterium avium complex fibronectin attachment protein in adherence to the human respiratory mucosa

Mycobacterium avium complex (MAC) are opportunistic respiratory pathogens that infect non-immunocompromised patients with established lung disease, although they can also cause primary infections. The ability to bind fibronectin is conserved among many mycobacterial species. We have investigated the adherence of a sputum isolate of MAC to the mucosa of organ cultures constructed with human tissue and the contribution of M. avium fibronectin attachment protein (FAP) to the process. MAC adhered to fibrous, but not globular mucus, and to extracellular matrix (ECM) in areas of epithelial damage, but not to intact extruded cells and collagen fibres. Bacteria occasionally adhered to healthy unciliated epithelium and to cells that had degenerated exposing their contents, but never to ciliated cells. The results obtained with different respiratory tissues were similar. Two ATCC strains of MAC gave similar results. There was a significant reduction (P < 0.05) in the number of bacteria adhering to ECM after preincubation of bacteria with fibronectin and after preincubation of the tissue with M. avium FAP in a concentration-dependant manner. The number of bacteria adhering to fibrous mucus was unchanged. Immunogold labelling demonstrated fibronectin in ECM as well as in other areas of epithelial damage, but only ECM bound FAP. A Mycobacterium smegmatis strain had the same pattern of adherence to the mucosa as MAC. When the FAP gene was deleted, the strain demonstrated reduced adherence to ECM, and adherence was restored when the strain was transfected with an M. avium FAP expression construct. We conclude that MAC adheres to ECM in areas of epithelial damage via FAP and to mucus with a fibrous appearance via another adhesin. Epithelial damage exposing ECM and poor mucus clearance will predispose to MAC airway infection.

The domains of human fibronectin mediating the binding of alpha antigen, the most immunopotent antigen of mycobacteria that induces protective immunity against mycobacterial infection

We have recently shown that alpha antigen (alpha-Ag), the immunodominant antigen of mycobacteria, has a novel fibronectin (FN)-binding motif that is unique among mycobacteria [Naito, Ohara, Matsumoto and Yamada (1998) J. Biol. Chem. 273, 2905-2909]. In this study, we examined the domains of human FN that interacted with alpha-Ag. Fragments of FN generated by either proteolysis or recombinant DNA techniques were compared for their ability to bind to alpha-Ag. Fragments containing either the C-terminal heparin-binding domain or the central cell-binding domain consistently bound to alpha-Ag. The fragment of the C-terminal heparin-binding domain, upon mutation that resulted in the loss of its heparin-binding activity, could not bind with alpha-Ag. These findings suggested that the mutated site, i.e. the main heparin-binding site of FN, was also the principal site for binding to alpha-Ag. The alpha-Ag-binding domains of FN could bind whole mycobacterial bacilli, suggesting that these two domains are important contributors to mycobacterial infection.

Role of fibronectin-binding MSCRAMMs in bacterial adherence and entry into mammalian cells

Most bacterial infections are initiated by the adherence of microorganisms to host tissues. This process involves the interaction of specific bacterial surface structures, called adhesins, with host components. In this review, we discuss a group of microbial adhesins known as Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) which recognize and bind FN. The interaction of bacteria with FN is believed to contribute significantly to the virulence of a number of microorganisms, including staphylococci and streptococci. Several FN-binding MSCRAMMs of staphylococci and streptococci exhibit a similar structural organization and mechanism of ligand recognition. The ligand-binding domain consists of tandem repeats of a approximately 45 amino acid long unit which bind to the 29-kDa N-terminal region of FN. The binding mechanism is unusual in that the repeat units are unstructured and appear to undergo a conformational change upon ligand binding. Apart from supporting bacterial adherence, FN is also involved in bacterial entry into non-phagocytic mammalian cells. A sandwich model has been proposed in which FN forms a molecular bridge between MSCRAMMs on the bacterial surface and integrins on the host cell. However, the precise mechanism of bacterial invasion and the roles of FN and integrins in this process have yet to be fully elucidated.

Characterization of the fibronectin binding motif for a unique mycobacterial fibronectin attachment protein, FAP

Studies were performed to define the fibronectin binding motif of the previously identified Mycobacterium avium fibronectin attachment protein (FAP-A). Using synthetic peptides of a previously identified fibronectin binding region (amino acids 269-292), the minimal binding sequence was determined to be 12 amino acids, 269-280 (FAP-A-(269-280)). Synthetic peptides were prepared in which each amino acid in the 269-280 sequence was substituted with Ala. Assessment of the effect of Ala substitution on fibronectin binding showed that the presence of Ala at amino acids 273-276 (RWFV) completely abrogated fibronectin binding activity. Furthermore, the ability to inhibit the attachment of viable Mycobacterium bovis BCG to fibronectin was abrogated by Ala substitution at the RWFV sites. To validate the function of RWFV, further studies were performed with recombinant FAP-A in which single Ala mutations were generated for the RWFV sites and as controls at amino acids 269 and 280. Mutant FAP-A containing single Ala substitutions at the RWFV sites (amino acids 273, 274, 275, or 276) showed significant abrogation of fibronectin binding function. Recombinant FAP-A with Ala substitutions at either 269 or 280 showed wild type activity. When the four essential amino acids (RWFV) were either substituted en bloc with Ala or were all deleted, complete loss of fibronectin binding function was observed. Control recombinant proteins with en bloc Ala substitutions or deletions at four positions outside the fibronectin binding region (amino acids 255-257) retained functional activity. These data show that the RWFV sequence is necessary for fibronectin binding function of FAP-A. Furthermore, the data suggest that mycobacterial FAP proteins, all of which share the RWFV binding motif, constitute a family of highly homologous proteins that bind fibronectin in a unique manner.

Identification of a 47 kDa fibronectin-binding protein expressed by Borrelia burgdorferi isolate B31

The attachment of pathogenic microorganisms to host cells and tissues is often mediated through the expression of surface receptors recognizing components of the extracellular matrix (ECM). Here, we investigate the ability of Borrelia spirochaetes to bind the ECM constituent, fibronectin. Borrelia lysates were separated by SDS-PAGE, transferred to nitrocellulose and probed with alkaline phosphatase-labelled fibronectin (fibronectin-AP). Five of six Borrelia species and four of eight B. burgdorferi sensu lato isolates expressed one or more fibronectin-binding proteins. Borrelia burgdorferi isolate B31 expressed a 47 kDa (P47) fibronectin-binding protein that was localized to the outer envelope based on susceptibility to proteinase K. The interaction of P47 with fibronectin was specific, and the region of fibronectin bound by P47 mapped to the gelatin/collagen binding domain. P47 was purified by affinity chromatography, digested with endoproteinase Lys-C, and the peptide fragments analysed by liquid chromatography/tandem mass spectroscopy. A search of protein databases disclosed that the P47 peptide mass profile matched that predicted for the bbk32 gene product of B. burgdorferi isolate B31. The bbk32 gene was cloned into Escherichia coli, and the ability of recombinant BBK32 to bind fibronectin and inhibit the attachment of B. burgdorferi was demonstrated. The identification of BBK32 as a receptor for fibronectin binding may enhance our understanding of the pathogenesis and chronic nature of Lyme disease.

Stable overexpression of TGFbeta1 in a transitional carcinoma cell line: impact on fibronectin production

INTRODUCTION

TGFbeta1 is a potent modulator of the biology of both benign and neoplastic cells. Exocrine TGFbeta1 has been shown to alter fibronectin expression of bladder carcinoma cell lines. The present study describes the development of a stable TGFbeta1 overexpressing transitional carcinoma cell line, and evaluates the impact of autocrine TGFbeta1 production on fibronectin expression.

MATERIALS AND METHODS

The human transitional carcinoma cell line 253J was transfected using the pcDNA3/hTGFbeta1 expression vector under control of the CMV promoter. TGFbeta1 mRNA expression was determined by Northern analysis. TGFbeta1 protein levels were analyzed by biological assay. Subsequently, the effect of TGFbeta1 autocrine production on fibronectin expression at both the mRNA and protein level was determined. Results were compared to cells transfected with the pcDNA3/CAT and non-transfected 253J cells.

RESULTS

Two 253J clones which uniformly expressed TGFbeta1 mRNA at 22 and four-fold increases relative to controls were identified. mRNA overexpression correlated with marked increase in biologically active TGFbeta1 protein production. Autocrine production of cellular TGFbeta1 showed a positive correlation with fibronectin expression at both the mRNA and protein levels.

CONCLUSIONS

Autocrine expression of TGFbeta1 increases cellular fibronectin production in a human transitional carcinoma cell line. Therapeutic strategies altering urothelial production of TGFbeta1 and fibronectin may be a potential strategy to potentiate intravesical BCG activity.

Identification of a gene unique to Mycobacterium avium subspecies paratuberculosis and application to diagnosis of paratuberculosis

Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) is the etiologic agent of paratuberculosis (Johne's disease), a chronic granulomatous enteritis in ruminants. Currently, there is a need for improved diagnostic tests because of the lack of methods for accurate, rapid and reliable detection of M. paratuberculosis infection. A M. paratuberculosis gene (hspX) was cloned, sequenced, and a 30 bp species-specific oligonucleotide was synthesized. As an internal control to identify mycobacterial strains, a 33 bp Mycobacterium genus-specific oligonucleotide was synthesized based on the conserved 5' terminus of the mycobacterial recA gene. Dioligonucleotide hybridization (dOH) analysis identified 28/28 (100%) mycobacterial strains and specifically identified 14/14 (100%) reference (ATCC 19698), bovine, ovine and human isolates of M. paratuberculosis. The M. paratuberculosis-specific oligonucleotide distinguished M. paratuberculosis isolates from related mycobacteria, including all closely related members of the Mycobacterium avium complex (MAC) tested in this study. The members of MAC tested in this study included Mycobacterium avium subspecies avium (M. paratuberculosis, Mycobacterium avium subspecies silvaticum (M. silvaticum) and Mycobacterium intracellulare strains. Hybridization was not observed with DNA extracted from a selected group of other bacterial pathogens. The experiments indicate that the dOH analysis is a useful diagnostic tool to detect mycobacterial infection, specifically M. paratuberculosis. The dOH method could be a good alternative to existing assays and will be adapted for specific identification of M. paratuberculosis from faecal samples, mixed bacteriologic cultures, tissue specimens and whole blood.

The novel fibronectin-binding motif and key residues of mycobacteria

The binding motifs of the immunodominant antigen (Ag) alpha-Ag (Ag 85 complex B) of Mycobacterium kansasii for human fibronectin were examined using digested fragments. We defined two fibronectin-binding epitopes on 27 amino acids from 84 to 110 and on 20 amino acids from 211 to 230. The epitopes were almost conserved in the closely related Ag 85 complex of other mycobacteria species. Inhibition of fibronectin binding to intact alpha-Ag molecules was observed with peptide-(84-110), but not with peptide-(211-230). Peptide-(84-110) could also inhibit fibronectin binding to all components of the Ag 85 complex of Bacillus Calmette-Guérin (Ag 85A, Ag 85B, and Ag 85C). Further study with synthetic peptides defined 11 residues from 98 to 108 as the minimum motif. Six residues (98FEWYYQ103) were critical for interacting with fibronectin. The motif revealed no homology to other known prokaryotic and eukaryotic fibronectin-binding proteins. The defined motif of alpha-Ag is novel and unique for mycobacteria.

A matrix form of fibronectin mediates enhanced binding of Streptococcus pyogenes to host tissue

The pathogenic Gram-positive bacterium Streptococcus pyogenes (group A streptococcus) binds to fibronectin via protein F. In this study, we have investigated the binding properties of protein F to various multimeric tissue forms of fibronectin that appear on cell surfaces and in the extracellular matrix. We show that binding of S. pyogenes through protein F is more efficient to an in vitro-derived polymerized form of fibronectin (superfibronectin) than to soluble fibronectin immobilized in a solid phase. In addition, Chinese hamster ovary cells overexpressing the alpha5beta1 integrin produced an increased amount of a fibronectin matrix and consequently bound a higher number of S. pyogenes cells. Inhibition and direct binding assays using purified proteins demonstrated that binding to a fibronectin matrix involved both domains of protein F (UR and RD2) that have previously been implicated in interactions with fibronectin. Using intact S. pyogenes bacteria in which various domains of protein F were expressed as hybrids with the surface-exposed region of an unrelated protein, we revealed that, in contrast to the predominantly UR-mediated binding to soluble fibronectin, the maximal binding to the fibronectin matrix required RD2 in addition to UR. Since in some infections S. pyogenes may initially encounter a matrix form of fibronectin, these results suggest that UR and RD2 may be important for the initiation of streptococcal infectious processes.

Cloning of the antigen 85A from Mycobacterium gordonae and its use for the specific PCR identification of these mycobacteria

The complete nucleotide sequence of 85A antigen of Mycobacterium gordonae was determined. This gene encodes 339 amino acids, including 43 amino acids for the signal peptide, followed by a mature protein of 296 amino acids. A polymerase chain reaction (PCR) assay for the rapid detection of M. gordonae DNA using two pairs of oligonucleotide primers, derived from our sequence, is described. This one-step PCR has been used successfully to amplify 38 strains of M. gordonae. Conversely, the primers did not amplify DNA from any of the 25 mycobacterial species tested. The results suggest that this PCR assay could be a good alternative to existing commercial assays for the specific identification of M. gordonae on early culture on solid medium or on early BACTEC broth culture.

Induction of monocyte expression of tumor necrosis factor alpha by the 30-kD alpha antigen of Mycobacterium tuberculosis and synergism with fibronectin

Native 30-kD antigen, also known as alpha antigen, is a fibronectin-binding protein that is secreted by live Mycobacterium tuberculosis. This antigen may play an important biological role in the host-parasite interaction since it elicits delayed type hypersensitivity response and protective immunity in vivo and T lymphocyte blastogenesis and IFN-gamma production in vitro. In the present study, we show that, TNF-alpha protein is produced in monocyte culture supernatants in response to 30-kD antigen and the level is as high as that to purified protein derivative of M. tuberculosis. This stimulatory effect was not due to contamination with either bacterial lipopolysaccharide or mycobacterial lipoarabinomannan. The preincubation of monocytes with plasma fibronectin significantly enhanced the release of TNF-alpha into the culture supernatants in response to 30-kD antigen. This effect was blocked by polygonal antibody to plasma fibronectin. In contrast, the monocytic cell line U937 failed to release TNF-alpha protein in the culture supernatants in response to 30-kD antigen with or without preincubation with plasma fibronectin. To determine whether this observation was due to differential binding of the 30-kD to fibronectin on these cells, a cell based ELISA was used. Pretreatment of monocytes with fibronectin enhanced their binding of the 30-kD antigen. U937 cells bound the 30-kD antigen weakly with or without fibronectin pretreatment. These results indicate that 30-kD antigen which is a known secretary antigen of M. tuberculosis is a stimulus for human monocytes to express TNF-alpha and that stimulatory effect may be mediated through plasma fibronectin.

Characterization of the gene encoding the MPB51, one of the major secreted protein antigens of Mycobacterium bovis BCG, and identification of the secreted protein closely related to the fibronectin binding 85 complex

The secreted protein MPB51 is one of the major proteins in the culture filtrate of Mycobacterium bovis BCG (BCG) and is a protein immunologically cross-reacting with the fibronectin binding 85 complex secreted by this bacterium. The gene encoding MPB51 (mpb51) was cloned, sequenced, and expressed in Escherichia coli. The mpb51 gene was mapped downstream of the gene for 85A component with 179 bp spaces. The mpb51 gene encoded 299 amino acids, including 33 amino acids for the signal peptide, followed by 266 amino acids for the mature protein with a molecular mass of 27807.37 Da. This is the first complete sequence of MPB51. MPB51 showed 37-43% homology to the components of 85 complex. Two-dimensional electrophoresis of culture fluids of BCG and Western blotting indicated the existence of the other novel protein(s) which strongly cross-reacted with the alpha antigen (85B) and MPB51.

IgG humoral response against the antigen 85 complex homologues in leprosy

Antigen 85 complex is the major protein component present in M. bovis BCG culture filtrate (CF). It consists of a family of three proteins: 85A, 85B and 85C. Combining isoelectric focusing and Western blot analysis, we have previously identified different antigenically related proteins present in the CF of other mycobacteria (M. tuberculosis, M. kansasii, M. avium, M. gordonae, M. fortuitum and M. phlei) using monoclonal antibodies (MoAbs) directed against the antigen 85 complex of M. bovis BCG. Humoral immune response directed against these cross-reactive homologues was analysed in sera from 20 patients with multibacillary leprosy (BL/LL), from 20 patients with paucibacillary leprosy (BT/TT) and from 15 healthy leprosy contacts. All the antigen 85 homologues identified in the seven CFs by MoAbs were also recognized by IgG present in sera from multibacillary leprosy patients, but not or very faintly in sera from paucibacillary leprosy patients or from healthy subjects. These results suggest that some of the M. leprae epitopes inducing a significant humoral response in multibacillary leprosy are common to the various 85 antigenically related proteins present in all mycobacterial species.

T-cell determinants and antibody binding sites on the major mycobacterial secretory protein MPB59 of Mycobacterium bovis

Among the first proteins encountered by the host immune system upon infection or vaccination with mycobacteria are those secreted by the bacillus during growth. The antigen 85 complex of Mycobacterium bovis bacillus Calmette-Gúerin (BCG) is composed of three closely related members. The mature 85B protein of M. bovis (MPB59) has a high degree of amino acid identity with the M. bovis 85A protein (76%) and the Mycobacterium tuberculosis 85B (99%) and 85A (76%) proteins. We have examined the regions of MPB59 which stimulate human T- and B-cell responses by use of a set of 28 synthetic peptides, 20 amino acids (aa) in length and overlapping by 10 aa. Initial proliferative assays with recombinant MPB59 demonstrated that peripheral blood mononuclear cells from 95% of BCG vaccinees and 52% of tuberculosis patients responded to the whole mature protein. Peripheral blood mononuclear cells from MPB59 responders, but not nonresponders, were stimulated by peptides in a dose-dependent fashion. Five peptides were reactive in more than half of the MPB59 responders. The T-cell-reactive regions were essentially identical in the M. bovis and M. tuberculosis 85B proteins. Subjects with a variety of HLA-DR phenotypes responded to a number of these peptides. The dominant T-cell-reactive regions were distinct from the peptides recognized by sera from tuberculosis patients (aa 71 to 100) and the murine monoclonal antibody HYT27 (aa 61 to 90). The region reactive with antibodies overlapped part of the MPB59 sequence recently shown to participate in the binding of MPB59 to fibronectin.

Microbial adhesins recognizing extracellular matrix macromolecules

Microorganisms express a family of cell-surface adhesins that specifically recognize and bind components of the extracellular matrix. Adhesion of microorganisms to host tissues represents a critical phase in the development of many types of infections. Recent studies have focused on the mechanisms of microbial attachment at a molecular level, including the identification of ligand-binding domains in several cell-surface adhesins from Gram-positive bacteria and the construction of adhesin-deficient isogenic mutants.

Gene for an extracellular matrix receptor protein from Pneumocystis carinii

An initial and crucial step in the establishment of many microbial infections is the attachment of the pathogen to the host cells. Thus, adherence of Pneumocystis carinii (Pc) to type I pneumocytes is believed to be important in the induction of Pc pneumonia. Little is known about the nature of the attachment of Pc to type I cells, although extracellular matrix (ECM) proteins, such as fibronectin and laminin, have been implicated in the process. We report here the isolation of a Pc gene encoding a receptor protein that binds both fibronectin and laminin in vitro. A cDNA clone encoding the Pc ECM receptor was isolated from a Pc cDNA library and identified on the basis of sequence homology to the human colon carcinoma laminin receptor. Southern blot analysis of Pc genomic DNA confirmed that the cDNA was of Pc origin. Northern blot analysis of Pc total RNA showed a predominant mRNA of approximately 1400 nucleotides that hybridized to the ECM receptor gene. The ECM receptor predicted from the cDNA sequence is 295 amino acid residues long, with a molecular mass of 32.8 kDa. The C-terminal third of the polypeptide is highly negatively charged, whereas the N-terminal two-thirds contains hydrophobic segments that may play a role in membrane association. Sequence analysis and alignment of the N terminus with the laminin receptor cDNA sequence of human colon carcinoma support the conclusion that the Pc ECM receptor cDNA clone is a full-length clone. A Western blot of the overexpressed ECM receptor protein bound both laminin and fibronectin in vitro. Antibodies raised to the overexpressed receptor protein interacted with a 33-kDa protein in total Pc cell lysates. These findings raise the possibility that the Pc ECM receptor protein may mediate the organism's attachment to type I pneumocytes and, thus, may play a crucial role in Pc pathogenesis.

Mechanisms of persistence of mycobacteria

Pathogenic mycobacteria use a variety of mechanisms to survive and replicate within mononuclear phagocytic cells, including avoidance of early direct activation of macrophages, interference with gamma-interferon-mediated activation and inhibition of bactericidal products. Developments in genetic manipulation should allow the genes involved in mycobacterial virulence and intracellular survival to be identified. Understanding these mechanisms may lead to more effective treatment and prevention of mycobacterial infections.