Bacterial Outer Membrane Protein OmpX Regulates ß1 Integrin and Epidermal Growth Factor Receptor (EGFR) Involved in Invasion of M-HeLa Cells by Serratia proteamaculans.

Opportunistic pathogen Serratia proteamaculans are able to penetrate the eukaryotic cells. The penetration rate can be regulated by bacterial surface protein OmpX. OmpX family proteins are able to bind to host cell surface to the epidermal growth factor receptor (EGFR) and the extracellular matrix protein fibronectin, whose receptors are in return the α5 ß1 integrins. Here we elucidated the involvement of these host cell proteins in S. proteamaculans invasion. We have shown that, despite the absence of fibronectin contribution to S. proteamaculans invasion, ß1 integrin was directly involved in invasion of M-HeLa cells. Herewith ß1 integrin was not the only receptor that determines sensitivity of host cells to bacterial invasion. Signal transfer from EGFR was also involved in the penetration of these bacteria into M-HeLa cells. However, M-HeLa cells have not been characterized by large number of these receptors. It turned out that S. proteamaculans attachment to the host cell surface resulted in an increment of EGFR and ß1 integrin genes expression. Such gene expression increment also caused Escherichia coli attachment, transformed with a plasmid encoding OmpX from S. proteamaculans. Thus, an OmpX binding to the host cell surface caused an increase in the EGFR and ß1 integrin expression involved in S. proteamaculans invasion.

The Serratia grimesii outer membrane vesicles-associated grimelysin triggers bacterial invasion of eukaryotic cells.

Serratia grimesii are facultative pathogenic bacteria that can penetrate a wide range of host cells and cause infection, especially in immunocompromised patients. Previously, we have found that bacterial metalloprotease grimelysin is a potential virulence determinant of S. grimesii invasion (E. S. Bozhokina et al., (2011). Cell Biology International, 35(2), 111-118). Protease is characterized as an actin-hydrolyzing enzyme with a narrow specificity toward other cell proteins. It is not known, however, whether grimelysin is transported into eukaryotic cells. Here, we show, for the first time, that S. grimesii can generate outer membrane vesicles (OMVs) displayed specific proteolytic activity against actin, characteristic of grimelysin. The presence of grimelysin was also confirmed by the Western blot analysis of S. grimesii OMVs lysate. Furthermore, confocal microscopy analysis revealed that the S. grimesii grimelysin-containing OMVs attached to the host cell membrane. Finally, pretreatment of HeLa cells with S. grimesii OMVs before the cells were infected with bacteria increased the bacterial penetration several times. These data strongly suggest that protease grimelysin promotes S. grimesii internalization by modifying bacterial and/or host molecule(s) when it is delivered as a component of OMVs.

Bacterial Actin-Specific Endoproteases Grimelysin and Protealysin as Virulence Factors Contributing to the Invasive Activities of Serratia.

The article reviews the discovery, properties and functional activities of new bacterial enzymes, proteases grimelysin (ECP 32) of Serratia grimesii and protealysin of Serratia proteamaculans, characterized by both a highly specific "actinase" activity and their ability to stimulate bacterial invasion. Grimelysin cleaves the only polypeptide bond Gly42-Val43 in actin. This bond is not cleaved by any other proteases and leads to a reversible loss of actin polymerization. Similar properties were characteristic for another bacterial protease, protealysin. These properties made grimelysin and protealysin a unique tool to study the functional properties of actin. Furthermore, bacteria Serratia grimesii and Serratia proteamaculans, producing grimelysin and protealysin, invade eukaryotic cells, and the recombinant Escherichia coli expressing the grimelysin or protealysins gene become invasive. Participation of the cellular c-Src and RhoA/ROCK signaling pathways in the invasion of eukaryotic cells by S. grimesii was shown, and involvement of E-cadherin in the invasion has been suggested. Moreover, membrane vesicles produced by S. grimesii were found to contain grimelysin, penetrate into eukaryotic cells and increase the invasion of bacteria into eukaryotic cells. These data indicate that the protease is a virulence factor, and actin can be a target for the protease upon its translocation into the host cell.

The Genome-Wide Analysis of Carcinoembryonic Antigen Signaling by Colorectal Cancer Cells Using RNA Sequencing.

Сarcinoembryonic antigen (CEA, CEACAM5, CD66) is a promoter of metastasis in epithelial cancers that is widely used as a prognostic clinical marker of metastasis. The aim of this study is to identify the network of genes that are associated with CEA-induced colorectal cancer liver metastasis. We compared the genome-wide transcriptomic profiles of CEA positive (MIP101 clone 8) and CEA negative (MIP 101) colorectal cancer cell lines with different metastatic potential in vivo. The CEA-producing cells displayed quantitative changes in the level of expression for 100 genes (over-expressed or down-regulated). They were confirmed by quantitative RT-PCR. The KEGG pathway analysis identified 4 significantly enriched pathways: cytokine-cytokine receptor interaction, MAPK signaling pathway, TGF-beta signaling pathway and pyrimidine metabolism. Our results suggest that CEA production by colorectal cancer cells triggers colorectal cancer progression by inducing the epithelial- mesenchymal transition, increasing tumor cell invasiveness into the surrounding tissues and suppressing stress and apoptotic signaling. The novel gene expression distinctions establish the relationships between the existing cancer markers and implicate new potential biomarkers for colorectal cancer hepatic metastasis.

Contribution of α-smooth muscle actin and extracellular matrix to the in vitro reorganization of cardiomyocyte contractile system.

Cardiomyocytes in culture undergo reversible rearrangement of their contractile apparatus with the conversion of typical myofibrils into the structures of non-muscle type and the loss of contractility. Along with these transformations, the cardiomyocytes gain the capacity to synthesize extracellular matrix. Here we show that during cultivation of rat neonatal cardiomyocytes, the inherent α-cardiac actin isoform is transiently replaced by α-smooth-muscle actin, whose expression is accompanied by transformation of myofibrils into stress-fiber-like structures. The following down-regulation of α-smooth muscle actin parallels restoration of myofibrillar system and correlates with the accumulation of extracellular collagen and laminin, initially missing from the cardiomyocytes culture.

Dihydrolipoic but not alpha-lipoic acid affects susceptibility of eukaryotic cells to bacterial invasion.

Sensitivity of eukaryotic cells to facultative pathogens can depend on physiological state of host cells. Previously we have shown that pretreatment of HeLa cells with N-acetylcysteine (NAC) makes the cells 2-3-fold more sensitive to invasion by the wild-type Serratia grimesii and recombinant Escherichia coli expressing gene of actin-specific metalloprotease grimelysin [1]. To evaluate the impact of chemically different antioxidants, in the present work we studied the effects of α-Lipoic acid (LA) and dihydrolipoic acid (DHLA) on efficiency of S. grimesii and recombinant E. coli expressing grimelysin gene to penetrate into HeLa and CaCo cells. Similarly to the effect of NAC, pretreatment of HeLa and CaCo cells with 0.6 or 1.25 mM DHLA increased the entry of grimelysin producing bacteria by a factor of 2.5 and 3 for the wild-type S. grimesii and recombinant E. coli, respectively. In contrast, pretreatment of the cells with 0.6 or 1.25 mM LA did not affect the bacteria uptake. The increased invasion of HeLa and CaCo cells correlated with the enhanced expression of E-cadherin and ß-catenin genes, whereas expression of these genes in the LA-treated cells was not changed. Comparison of these results suggests that it is sulfhydryl group of DHLA that promotes efficient modification of cell properties assisting bacterial uptake. We assume that the NAC- and DHLA-induced stimulation of the E-cadherin-catenin pathway contributes to the increased internalization of the grimelysin producing bacteria within transformed cells.

Virulence factors contributing to invasive activities of Serratia grimesii and Serratia proteamaculans.

Previously, we have shown that facultative pathogens Serratia grimesii and Serratia proteamaculans are capable to invade eukaryotic cells provided that they synthesize intracellular metalloprotease grimelysin or protealysin, respectively (Bozhokina et al. in Cell Biol Int 35(2):111-118, 2011). Noninvasive Escherichia coli transformed with grimelysin or protealysin gene became invasive, indicating that the protease is a virulence factor. Here we elucidated involvement of other virulence factors in the invasion of S. grimesii and S. proteamaculans. Under similar experimental conditions, the amount of S. proteamaculans internalized within human carcinoma HeLa cells was fivefold higher than that of S. grimesii. In accord with this, in S. proteamaculans, high activities of pore-forming hemolysin ShlA and extracellular metalloprotease serralysin were detected. In S. grimesii, activity of toxin ShlA was not detected, and the serralysin activity of the bacterial growth medium was very low. We also show that iron depletion strongly enhanced invasive activity of S. proteamaculans, increasing activities of hemolysin ShlA and serralysin, but did not affect S. grimesii properties. These results show that the invasive activity of S. proteamaculans is maintained, along with protealysin, by hemolysin and serralysin. On the other hand, grimelysin is so far the only known invasion factor of S. grimesii.

N-acetylcysteine increases susceptibility of HeLa cells to bacterial invasion.

Serratia grimesii are non-pathogenic bacteria capable, however, to invade eukaryotic cells provided that they synthesize intracellular metalloprotease grimelysin (Bozhokina et al. [2011] Cell. Biol. Int. 35: 111-118). To elucidate how invasion of grimelysin containing bacteria depends on physiological state of host cells, we studied the effect of N-acetylcysteine (NAC) on susceptibility of HeLa cells to invasion by the wild-type S. grimesii and recombinant E. coli expressing grimelysin gene. Incubation of HeLa cells with 10 mM NAC resulted in changes of cell morphology and disassembly of actin cytoskeleton that were reversed when NAC was removed from the culture medium. Both in the presence of NAC and upon its removal, the entry of grimelysin producing bacteria increased by a factor of 1.5-2 and 3-3.5 for wild-type S. grimesii and recombinant E. coli, respectively. This effect does not correlate with cytoskeleton rearrangements but may be due to the NAC-induced up-regulation of cell surface receptors playing a role in cell adhesion and cell-cell junctions. A twofold difference in the efficiency of S. grimesii and recombinant E. coli to enter the NAC-treated cells suggests that the entry of the wild-type and recombinant bacteria occurs via different receptors which activity is differently affected by NAC.

Bacterial invasion of eukaryotic cells can be mediated by actin-hydrolysing metalloproteases grimelysin and protealysin.

Earlier, we have shown that spontaneously isolated non-pathogenic bacteria Serratia grimesii and Serratia proteamaculans invade eukaryotic cells, provided that they synthesize thermolysin-like metalloproteases ECP32/grimelysin or protealysin characterized by high specificity towards actin. To address the question of whether the proteases are active players in entry of these bacteria into host cells, in this work, human larynx carcinoma Hep-2 cells were infected with recombinant Escherichia coli expressing grimelysin or protealysin. Using confocal and electron microscopy, we have found that the recombinant bacteria, whose extracts limitedly cleaved actin, were internalized within the eukaryotic cells residing both in vacuoles and free in cytoplasm. The E. coli-carrying plasmids without inserts of grimelysin or protealysin gene did not enter Hep-2 cells. Moreover, internalization of non-invasive E. coli was not observed in the presence of protealysin introduced into the culture medium. These results are consistent with the direct participation of ECP32/grimelysin and protealysin in entry of bacteria into the host cells. We assume that ECP32/grimelysin and protealysin mediate invasion being injected into the eukaryotic cell and that the high specificity of the enzyme towards actin may be a factor contributed to the bacteria internalization.

Grimelysin, a novel metalloprotease from Serratia grimesii, is similar to ECP32.

Limited actin proteolysis is the hallmark of bacterial metalloprotease ECP32. While ECP32 has long been considered an Escherichia coli protein, the N-terminal amino acid sequence of the active enzyme described previously, could not been retrieved in the E. coli genome. We cloned, sequenced and characterized Serratia grimesii protease grimelysin and show that grimelysin is similar to the previously described protease ECP32.