PDZ domains: fundamental building blocks in the organization of protein complexes at the plasma membrane

The differential role of HTRA1 in HPV-positive and HPV-negative cervical cell line proliferation

BACKGROUND

High-risk human papillomaviruses (HPVs) are strongly associated with the development of some malignancies. The E6 and E7 viral oncoproteins are the primary proteins responsible for cell homeostasis alteration and immortalization. Furthermore, the E6 protein from high-risk HPVs can interact with the PDZ (PSD-90/Dlg/ZO-1) domains of cellular proteins, triggering cell transformation. One protein that is associated with pathological conditions and has a PDZ domain is the protease HTRA1 (high temperature requirement 1). This protein is poorly expressed in some cancers, suggesting a tumor suppressor role. The aim of this study was to evaluate the effect of HTRA1 overexpression in HPV16-positive (CasKi) and HPV-negative (C33) cervical cell lines.

METHODS

The cells were transfected with a vector containing the HTRA1 ORF or an empty vector. HTRA1 overexpression was confirmed by qRT-PCR. The cells were subjected to cell proliferation, colony formation, apoptosis and cell cycle assays.

RESULTS

C33 cells expressing HTRA1 grew significantly fewer colonies and showed less proliferation than cells without HTRA1 expression. In contrast, in the CasKi cells overexpressing HTRA1, there was an increase in the cell growth rate and in the colonies density compared to cells expressing low levels of HTRA1. An apoptosis assay showed that HTRA1 does not interfere with the apoptosis rate in these cells. A cell cycle immunofluorescence assay revealed more CasKi cells overexpressing HTRA1 in the S phase and more C33 HTRA1-transfected cells in the G0/G1 phase, suggesting that HTRA1 plays different roles in the cell cycle progression of these cells.

CONCLUSIONS

HTRA1 overexpression prevents cell proliferation in the HPV-negative cell line and increases cell proliferation in the HPV-positive cell line. Although the E6/HTRA1 interaction has already been described in the literature, more studies are required to confirm whether the present functional findings are a result of this interaction.

MAGI3 negatively regulates Wnt/β-catenin signaling and suppresses malignant phenotypes of glioma cells

Gliomas are the most common primary brain malignancies and are associated with a poor prognosis. Here, we showed that the PDZ domain-containing protein membrane-associated guanylate kinase inverted 3 (MAGI3) was downregulated at the both mRNA and protein levels in human glioma samples. MAGI3 inhibited proliferation, migration, and cell cycle progression of glioma cells in its overexpression and knockdown studies. By using GST pull-down and co-immunoprecipitation assays, we found that MAGI3 bound to β-catenin through its PDZ domains and the PDZ-binding motif of β-catenin. MAGI3 overexpression inhibited β-catenin transcriptional activity via its interaction with β-catenin. Consistently, MAGI3 overexpression in glioma cells C6 suppressed expression of β-catenin target genes including Cyclin D1 and Axin2, whereas MAGI3 knockdown in glioma cells U373 and LN229 enhanced their expression. MAGI3 overexpression decreased growth of C6 subcutaneous tumors in mice, and inhibited expression of β-catenin target genes in xenograft tumors. Furthermore, analysis based on the Gene Expression Omnibus (GEO) glioma dataset showed association of MAGI3 expression with overall survival and tumor grade. Finally, we demonstrated negative correlation between MAGI3 expression and activity of Wnt/β-catenin signaling through GSEA of three public glioma datasets and immunohistochemical staining of clinical glioma samples. Taken together, these results identify MAGI3 as a novel tumor suppressor and provide insight into the pathogenesis of glioma.

Impact of Tight Junction Protein ZO-1 and TWIST Expression on Postoperative Survival of Patients with Hepatocellular Carcinoma

BACKGROUND

Epithelial-mesenchymal transition (EMT) is considered to play a critical role in cancer progression and metastasis. However, the impact of EMT on the prognosis of hepatocellular carcinoma (HCC) is still elusive. In this study, we examined the relationship between the expression of EMT markers and recurrence-free survival (RFS) and overall survival (OS) in HCC patients after hepatic resection.

SUMMARY

The mRNA expression of 15 genes related to EMT was assessed by quantitative real-time polymerase chain reaction in cancerous tissues from 72 patients who underwent hepatic resection of HCC between January 2005 and December 2010 at our hospital. The upregulation of TWIST and the downregulation of tight junction protein ZO-1 (TJP1) were significantly associated with shorter RFS as well as OS. Increased levels of TWIST and decreased levels of TJP1 should be predictive markers for poor prognosis in patients with HCC after hepatectomy; those could serve as potential biomarkers for the treatment of HCC. Key Messages: A low level of TJP1 and high level of TWIST expression were prognostic factors predicting HCC after hepatic resection.

Characterization of novel human papillomavirus types 157, 158 and 205 from healthy skin and recombination analysis in genus γ-Papillomavirus

Gammapapillomavirus (γ-PV) is a diverse and rapidly expanding genus, currently consisting of 79 fully characterized human PV (HPV) types. In this study, three novel types, HPV157, HPV158 and HPV205, obtained from healthy sun-exposed skin of two immunocompetent individuals, were amplified by the "Hanging droplet" long PCR technique, cloned, sequenced and characterized. HPV157, HPV158 and HPV205 genomes comprise 7154-bp, 7192-bp and 7298-bp, respectively, and contain four early (E1, E2, E6 and E7) and two late genes (L1 and L2). Phylogenetic analysis of the L1 ORF placed all novel types within the γ-PV genus: HPV157 was classified as a new member of species γ-12 while HPV158 and HPV205 belong to species γ-1. We then explored potential recombination events in genus γ-PV with the RDP4 program in a dataset of 74 viruses (71 HPV types with available full-length genomes and the 3 novel types). Two events, both located in the E1 ORF, met the inclusion criterion (p-values <0.05 with at least four methods) and persisted in different ORF combinations: an inter-species recombination in species γ-8 (major and minor parents: species γ-24 and γ-11, respectively), and an intra-species recombination in species γ-7 (recombinant strain: HPV170; major and minor parents: HPV-109 and HPV-149, respectively). These findings were confirmed by phylogenetic tree incongruence analysis. An additional incongruence was found in members of species γ-9 but it was not detected by the RDP4. This report expands our knowledge of the family Papillomaviridae and provides for the first time in silico evidence of recombination in genus γ-PV.

Intestinal epithelial barrier function and tight junction proteins with heat and exercise

A single layer of enterocytes and tight junctions (intercellular multiprotein complexes) form the intestinal epithelial barrier that controls transport of molecules through transcellular and paracellular pathways. A dysfunctional or "leaky" intestinal tight junction barrier allows augmented permeation of luminal antigens, endotoxins, and bacteria into the blood stream. Various substances and conditions have been shown to affect the maintenance of the intestinal epithelial tight junction barrier. The primary focus of the present review is to analyze the effects of exertional or nonexertional (passive hyperthermia) heat stress on tight junction barrier function in in vitro and in vivo (animals and humans) models. Our secondary focus is to review changes in tight junction proteins in response to exercise or hyperthermic conditions. Finally, we discuss some pharmacological or nutritional interventions that may affect the cellular mechanisms involved in maintaining homeostasis of the intestinal epithelial tight junction barrier during heat stress or exercise.

Expression of claudin-5, -7, -8 and -9 in cervical carcinoma tissues and adjacent non-neoplastic tissues

Recent data indicate that the tight junction proteins are abnormally regulated in several human cancers and the expression of these proteins is involved in the etiology and progression of cancer. To explore the expression distinction of the tight junction proteins claudin-5, -7, -8 and -9 in the adjacent non-neoplastic tissues and cervical carcinoma tissues, 72 cervical carcinoma tissues and the samples of non-neoplastic tissues adjacent to the tumors were examined for expression of claudin-5, -7, -8 and -9 by streptavidin-perosidase immunohistochemical staining method. The positive expression rates of claudin-5 in cervical carcinoma tissues and adjacent non-neoplastic tissues were 31.9% (23/72) and 51.4% (37/72) respectively (P < 0.05). The positive expression rates of claudin-7 in cervical carcinoma tissues and adjacent non-neoplastic tissues were 47.2% and 50.0% respectively (P = 1.000). The positive expression rates of claudin-8 in cervical carcinoma tissues and adjacent non-neoplastic tissues were 54.2 % and 27.8% respectively (P < 0.01). The positive expression rates of claudin-9 in cervical carcinoma tissues and adjacent non-neoplastic tissues were 38.9% and 56.9% respectively (P < 0.05). Thus in our study, the expression of claudin-5 and claudin-9 was down-regulated while the expression of claudin-8 was up-regulated in cervical carcinoma tissues compared with adjacent non-neoplastic tissues. The expression of claudin-7 has no obviously difference between cervical carcinoma tissues and adjacent non-neoplastic tissues. In addition, correlations between claudin-5, -8 and -9 expression with lymphatic metastasis were observed. Our study reveals that the expression of claudin-5, -8 and -9 altered between in cervical carcinoma tissues and adjacent non-neoplastic tissues.

Evolutionary trajectories and diagnostic challenges of potentially zoonotic avian influenza viruses H5N1 and H9N2 co-circulating in Egypt

In Egypt, since 2006, descendants of the highly pathogenic avian influenza virus (HP AIV) H5N1 of clade 2.2 continue to cause sharp losses in poultry production and seriously threaten public health. Potentially zoonotic H9N2 viruses established an endemic status in poultry in Egypt as well and co-circulate with HP AIV H5N1 rising concerns of reassortments between H9N2 and H5N1 viruses along with an increase of mixed infections of poultry. Nucleotide sequences of whole genomes of 15 different isolates (H5N1: 7; H9N2: 8), and of the hemagglutinin (HA) and neuraminidase (NA) encoding segments of nine further clinical samples (H5N1: 2; H9N2: 7) from 2013 and 2014 were generated and analysed. The HA of H5N1 viruses clustered with clade 2.2.1 while the H9 HA formed three distinguishable subgroups within cluster B viruses. BEAST analysis revealed that H9N2 viruses are likely present in Egypt since 2009. Several previously undescribed substituting mutations putatively associated with host tropism and virulence modulation were detected in different proteins of the analysed H9N2 and H5N1 viruses. Reassortment between HP AIV H5N1 and H9N2 is anticipated in Egypt, and timely detection of such events is of public health concern. As a rapid tool for detection of such reassortants discriminative SYBR-Green reverse transcription real-time PCR assays (SG-RT-qPCR), targeting the internal genes of the Egyptian H5N1 and H9N2 viruses were developed for the rapid screening of viral RNAs from both virus isolates and clinical samples. However, in accordance to Sanger sequencing, no reassortants were found by SG-RT-qPCR. Nevertheless, the complex epidemiology of avian influenza in poultry in Egypt will require sustained close observation. Further development and continuing adaptation of rapid and cost-effective screening assays such as the SG-RT-qPCR protocol developed here are at the basis of efforts for improvement the currently critical situation.

Syntenin is involved in the bacteria clearance response of kuruma shrimp (Marsupenaeus japonicus)

Syntenin is a multifunctional cytosolic adaptor protein that contributes to cell migration, proliferation, attachment, and apoptosis, as well as immune response to virus, in vertebrates. However, the functions of syntenin in the antibacterial response of invertebrates remain unclear. In this study, we identified a syntenin-like gene (MjSyn) from the kuruma shrimp (Marsupenaeus japonicus) and detected its function in the antibacterial immunity of shrimp. The full-length MjSyn was 1223 bp with a 963 bp open reading frame that encodes 320 amino acids. The deduced MjSyn proteins contained two atypical PDZ domains (sequence repeat that was first reported in the postsynaptic density protein or PSD-95, DlgA, and ZO-1 protein), an N-terminal domain, and a C-terminal domain. Reverse transcription (RT)-PCR results showed that MjSyn was expressed in all tested tissues. Quantitative real-time PCR analysis revealed that MjSyn transcripts in the hemocyte, gill, and intestine were significantly induced at various time points after infection with Staphylococcus aureus and Vibrio anguillarum. The knockdown of the expression of MjSyn by RNA interference resulted in a significant decrease in the phagocytic ability and increased bacteria number in vivo of shrimp. Moreover, the expression of MjCnx, a cytoplasma and membrane location lectin chaperone protein, was inhibited in the MjSyn-knocked down shrimp, which indicated a possible calnexin-related way. Thus, the MjSyn participates in the bacterial clearance response of kuruma shrimp, thereby providing new insight into the function of this kind of important adaptor protein.

Application of wavelet transform for PDZ domain classification

PDZ domains have been identified as part of an array of signaling proteins that are often unrelated, except for the well-conserved structural PDZ domain they contain. These domains have been linked to many disease processes including common Avian influenza, as well as very rare conditions such as Fraser and Usher syndromes. Historically, based on the interactions and the nature of bonds they form, PDZ domains have most often been classified into one of three classes (class I, class II and others - class III), that is directly dependent on their binding partner. In this study, we report on three unique feature extraction approaches based on the bigram and trigram occurrence and existence rearrangements within the domain's primary amino acid sequences in assisting PDZ domain classification. Wavelet packet transform (WPT) and Shannon entropy denoted by wavelet entropy (WE) feature extraction methods were proposed. Using 115 unique human and mouse PDZ domains, the existence rearrangement approach yielded a high recognition rate (78.34%), which outperformed our occurrence rearrangements based method. The recognition rate was (81.41%) with validation technique. The method reported for PDZ domain classification from primary sequences proved to be an encouraging approach for obtaining consistent classification results. We anticipate that by increasing the database size, we can further improve feature extraction and correct classification.

The C-terminal tail of tetraspanin proteins regulates their intracellular distribution in the parasite Trichomonas vaginalis

The parasite Trichomonas vaginalis is the causative agent of trichomoniasis, a prevalent sexually transmitted infection. Here, we report the cellular analysis of T.vaginalis tetraspanin family (TvTSPs). This family of membrane proteins has been implicated in cell adhesion, migration and proliferation in vertebrates. We found that the expression of several members of the family is up-regulated upon contact with vaginal ectocervical cells. We demonstrate that most TvTSPs are localized on the surface and intracellular vesicles and that the C-terminal intracellular tails of surface TvTSPs are necessary for proper localization. Analyses of full-length TvTSP8 and a mutant that lacks the C-terminal tail indicates that surface-localized TvTSP8 is involved in parasite aggregation, suggesting a role for this protein in parasite : parasite interaction.

Effects of interleukin-13 and montelukast on the expression of zonula occludens-1 in human podocytes

PURPOSE

The aim of this study was to investigate whether pathologic changes in zonula occludens-1 (ZO-1) are induced by interleukin-13 (IL-13) in the experimental minimal-change nephrotic syndrome (MCNS) model and to determine whether montelukast, a leukotriene receptor antagonist, has an effect on ZO-1 restoration in cultured human podocytes.

MATERIALS AND METHODS

Human podocytes cultured on bovine serum albumin-coated plates were treated with different doses of IL-13 and montelukast and then examined for distribution using confocal microscopy and for ZO-1 protein levels using Western blotting.

RESULTS

ZO-1 was internalized and shown to accumulate in the cytoplasm of human podocytes in an IL-13 dose-dependent manner. High doses (50 and 100 ng/mL) of IL-13 decreased the levels of ZO-1 protein at 12 and 24 h (both p<0.01; n=3), which were significantly reversed by a high dose (0.5 μM) montelukast treatment (p<0.01; n=3).

CONCLUSION

Our results suggest that IL-13 alters the expression of ZO-1, and such alterations in the content and distribution of ZO-1 may be relevant in the pathogenesis of proteinuria in the MCNS model.

The mechanism and implications of hScrib regulation of ERK

Scribble is a potential tumor suppressor protein, whose loss is a frequent event in late stage cancer development. In both Drosophila and mammalian model systems, Scribble has been shown capable of regulating cell polarity, cell proliferation and apoptosis. Although several interacting partners, including βPiX, have been identified that help to explain how Scribble can regulate cell polarity and migration, little is known about how Scribble can control cell proliferation. Recent work from our laboratory has shown that Scribble can directly regulate the ERK signaling pathway. This is mediated by a direct protein-protein interaction between Scribble and ERK, which has two components. In the first, Scribble appears to anchor ERK at membrane-bound sites, with the loss of Scribble enhancing ERK nuclear translocation. In the second, Scribble can decrease the levels of active phosphorylated ERK, a function that is dependent upon the ability of Scribble to bind ERK directly. One of the consequences of this activity of Scribble is the inhibition of EJ-ras induced cell transformation. These results provide some of the first direct mechanistic information on how Scribble can regulate cell proliferation and, furthermore, they provide indications as to the identity of other signaling intermediates that may be recruited by Scribble to directly regulate mitogenic signaling pathways.

PTEN hamartoma tumor syndrome: clinical risk assessment and management protocol

The tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is an important phosphatase that counteracts one of the most critical cancer pathways: the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathways. Clinically, deregulation of PTEN function resulting in reduced PTEN expression and activity is implicated in human diseases. Cowden syndrome (CS) is an autosomal dominant disorder characterized by benign and malignant tumors. CS-related individual features occur commonly in the general population. Approximately 25% of patients diagnosed with CS have pathogenic germline PTEN mutations, which increase lifetime risks of breast, thyroid, uterine, renal and other cancers. PTEN testing and intensive cancer surveillance allow for early detection and treatment of these cancers for mutation positive patients and their relatives. In this review, we highlight our current knowledge of germline PTEN mutations in relation to human disease. We review current clinical diagnosis and management recommendations for PHTS including recent discoveries in understanding PTEN function regulation and how this can be exploited therapeutically.

Differential association of the Na+/H+ Exchanger Regulatory Factor (NHERF) family of adaptor proteins with the raft- and the non-raft brush border membrane fractions of NHE3

BACKGROUND/AIMS

Trafficking, brush border membrane (BBM) retention, and signal-specific regulation of the Na+/H+ exchanger NHE3 is regulated by the Na+/H+ Exchanger Regulatory Factor (NHERF) family of PDZ-adaptor proteins, which enable the formation of multiprotein complexes. It is unclear, however, what determines signal specificity of these NHERFs. Thus, we studied the association of NHE3, NHERF1 (EBP50), NHERF2 (E3KARP), and NHERF3 (PDZK1) with lipid rafts in murine small intestinal BBM.

METHODS

Detergent resistant membranes ("lipid rafts") were isolated by floatation of Triton X-incubated small intestinal BBM from a variety of knockout mouse strains in an Optiprep step gradient. Acid-activated NHE3 activity was measured fluorometrically in BCECF-loaded microdissected villi, or by assessment of CO2/HCO3(-) mediated increase in fluid absorption in perfused jejunal loops of anethetized mice.

RESULTS

NHE3 was found to partially associate with lipid rafts in the native BBM, and NHE3 raft association had an impact on NHE3 transport activity and regulation in vivo. NHERF1, 2 and 3 were differentially distributed to rafts and non-rafts, with NHERF2 being most raft-associated and NHERF3 entirely non-raft associated. NHERF2 expression enhanced the localization of NHE3 to membrane rafts. The use of acid sphingomyelinase-deficient mice, which have altered membrane lipid as well as lipid raft composition, allowed us to test the validity of the lipid raft concept in vivo.

CONCLUSIONS

The differential association of the NHERFs with the raft-associated and the non-raft fraction of NHE3 in the brush border membrane is one component of the differential and signal-specific NHE3 regulation by the different NHERFs.

Molecular characterization of avian influenza H5N1 virus in Egypt and the emergence of a novel endemic subclade

Clade 2.2 highly pathogenic H5N1 viruses have been in continuous circulation in Egyptian poultry since 2006. Their persistence caused significant genetic drift that led to the reclassification of these viruses into subclades 2.2.1 and 2.2.1.1. Here, we conducted full-genome sequence and phylogenetic analyses of 45 H5N1 isolated during 2006-2013 through systematic surveillance in Egypt, and 53 viruses that were sequenced previously and available in the public domain. Results indicated that H5N1 viruses in Egypt continue to evolve and a new distinct cluster has emerged. Mutations affecting viral virulence, pathogenicity, transmission, receptor-binding preference and drug resistance were studied. In light of our findings that H5N1 in Egypt continues to evolve, surveillance and molecular studies need to be sustained.

Family-wide investigation of PDZ domain-mediated protein-protein interactions implicates β-catenin in maintaining the integrity of tight junctions

β-catenin is a multifunctional protein that plays a critical role in cell-cell contacts and signal transduction. β-catenin has previously been shown to interact with PDZ-domain-containing proteins through its C terminus. Using protein microarrays comprising 206 mouse PDZ domains, we identified 26 PDZ-domain-mediated interactions with β-catenin and confirmed them biochemically and in cellular lysates. Many of the previously unreported interactions involved proteins with annotated roles in tight junctions. We found that four tight-junction-associated PDZ proteins-Scrib, Magi-1, Pard3, and ZO-3-colocalize with β-catenin at the plasma membrane. Disrupting these interactions by RNA interference, overexpression of PDZ domains, or overexpression of the β-catenin C terminus altered localization of the full-length proteins, weakened tight junctions, and decreased cellular adhesion. These results suggest that β-catenin serves as a scaffold to establish the location and function of tight-junction-associated proteins.

The distinct expression patterns of claudin-10, -14, -17 and E-cadherin between adjacent non-neoplastic tissues and gastric cancer tissues

BACKGROUND

Recent data indicate that the cell adhesion proteins are abnormally regulated in several human cancers and the expression of the cell adhesion proteins E-cadherin and claudin proteins is involved in the etiology and progression of cancer. It is clear that these protein represent promising targets for cancer detection, diagnosis, and therapy.

METHODS

To explore the expression distinction of the cell adhesion proteins claudin-10,-14,-17 and E-cadherin in the adjacent non-neoplastic tissues and gastric cancer tissues, 50 gastric cancer tissues and 50 samples of adjacent non-neoplastic tissues adjacent to the tumors were examined for expression of claudin-10,-14,-17 and E-cadherin by streptavidin-perosidase immunohistochemical staining method.

RESULTS

The positive expression rates of E-cadherin in gastric cancer tissues and adjacent non-neoplastic tissues were 32% and 74% respectively (P < 0.01). The positive expression rates of claudin-10 in gastric cancer tissues and adjacent non-neoplastic tissues were 24% and 72% respectively (P < 0.01). The positive expression rates of claudin-17 in gastric cancer tissues and adjacent non-neoplastic tissues were 18% and 70% (P < 0.01). In contrast, the positive expression rates of claudin-14 in gastric cancer tissues and adjacent non-neoplastic tissues were 58% and 24% respectively (P = 0.015 < 0.05) Thus in our study, the expression of E-cadherin, claudin-10, and claudin-17 was down-regulated in gastric cancer tissue while the expression of claudin-14 was up-regulated. Correlations between claudins and E-cadherin expression with lymphatic metastasis were observed.

CONCLUSION

Our study reveals that the expression of E-cadherin, claudin-10, and claudin-17 were down-regulated in gastric cancer tissue while the expression of claudin-14 was up-regulated and correlation between claudins and E-cadherin expression with lymphatic metastasis were observed.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1475928069111326.

Roles of the PDZ domain-binding motif of the human papillomavirus type 16 E6 on the immortalization and differentiation of primary human foreskin keratinocytes

A number of PDZ domain-containing proteins have been identified as binding partners for the oncoprotein E6 of the high-risk type human papillomaviruses (HPVs). These include hDlg, hScrib, MAGI1, MAGI2, and MAGI3, MUPP1, 14-3-3zeta, Na/H exchange regulatory factor 1, PTPN13, TIP-2/GIPC, Tip-1, and PATJ. The PDZ domain-binding motif (-X-T-X-V) at the carboxy terminus of E6 is essential for targeting PDZ proteins for proteasomal degradation. However, contribution of degradation of PDZ proteins by E6 to HPV-induced oncogenesis is still controversial. In order to clarify potential roles of molecular interactions between high-risk HPV E6 and one of best characterized PDZ proteins, hDlg in HPV-induced transformation, we used a retroviral infection system to overexpress HPV16 E7 gene alone or together with either HPV16 E6 wild type or E6 mutant gene lacking the PDZ domain-binding motif and investigated the effect of mutating the PDZ domain-binding motif of E6 on the immortalization and differentiation of human foreskin keratinocytes (HFKs) by the high-risk type HPV E6 and E7. Although the PDZ domain-binding motif of E6 was found to be required for the efficient growth of HFKs, it was not necessary for the E6 and E7-induced immortalization of HFKs. Furthermore, the overexpression of E6 and E7 neither induced degradation nor altered cellular localization of hDlg in undifferentiated or differentiated HFKs. These data indicate that the PDZ domain-binding motif of E6 contributes to the efficient cellular growth through mechanisms other than degradation and changes in the subcellular localizations of hDlg.

Immunoglobulin superfamily protein Dscam exhibited molecular diversity by alternative splicing in hemocytes of crustacean, Eriocheir sinensis

Be absent of adaptive immunity which have both specificity and memory, invertebrates seem to have evolved alternative adaptive immune strategies to resist various intruding pathogens. Whereas vertebrates could generate a wide range of immunological receptors with somatic rearrangement, invertebrates possibly depend on alternative splicing of pattern-recognition receptors (PRRs). Recently, it has been suggested that a member of the immunoglobulin superfamily (IgSF), Down syndrome cell adhesion molecule (Dscam), plays a crucial role in the alternative adaptive immune system of invertebrates. At present, we successfully isolated and characterized the first crab Dscam from Eriocheir sinensis. EsDscam has typical domain architecture compared with other Dscam orthologs, including one signal-peptide, 10 immunoglobulin (Ig) domains, 6 fibronectin type III domains (FNIII), one transmembrane domain (TM) and one cytoplasmic tail. We had detected four hypervariable regions of EsDscam in the N-terminal halves of Ig2 (25) and Ig3 domain (30), the complete Ig7 (18) and also the transmembrane domain (2), potentially generate 27,000 unique isoforms at least. Transcription of EsDscam were both a) detected in all tissues, especially in immune system, digestive system and nerve system; b) significantly induced in hemocytes post lipopolysaccharides (LPS), peptidoglycans (PG) and β-1, 3-glucans (Glu) injection. Importantly, we had detected membrane-bound and secreted Dscam isoforms in E. sinensis, and showed that secreted isoforms were extensively transcribed post different PAMPs challenge respectively. Results from immuno-localization assay revealed that EsDscam evenly distributed in the cell surface of hemocytes. These findings indicated that EsDscam is a hypervariable PRR in the innate immune system of the E. sinensis.

Syntrophin proteins as Santa Claus: role(s) in cell signal transduction

Syntrophins are a family of cytoplasmic membrane-associated adaptor proteins, characterized by the presence of a unique domain organization comprised of a C-terminal syntrophin unique (SU) domain and an N-terminal pleckstrin homology (PH) domain that is split by insertion of a PDZ domain. Syntrophins have been recognized as an important component of many signaling events, and they seem to function more like the cell's own personal 'Santa Claus' that serves to 'gift' various signaling complexes with precise proteins that they 'wish for', and at the same time care enough for the spatial, temporal control of these signaling events, maintaining overall smooth functioning and general happiness of the cell. Syntrophins not only associate various ion channels and signaling proteins to the dystrophin-associated protein complex (DAPC), via a direct interaction with dystrophin protein but also serve as a link between the extracellular matrix and the intracellular downstream targets and cell cytoskeleton by interacting with F-actin. They play an important role in regulating the postsynaptic signal transduction, sarcolemmal localization of nNOS, EphA4 signaling at the neuromuscular junction, and G-protein mediated signaling. In our previous work, we reported a differential expression pattern of alpha-1-syntrophin (SNTA1) protein in esophageal and breast carcinomas. Implicated in several other pathologies, like cardiac dys-functioning, muscular dystrophies, diabetes, etc., these proteins provide a lot of scope for further studies. The present review focuses on the role of syntrophins in membrane targeting and regulation of cellular proteins, while highlighting their relevance in possible development and/or progression of pathologies including cancer which we have recently demonstrated.

Biogenesis of β-barrel integral proteins of bacterial outer membrane

Gram-negative bacteria are enveloped by two membranes, the inner (cytoplasmic) (CM) and the outer (OM). The majority of integral outer membrane proteins are arranged in β-barrels of cylindrical shape composed of amphipathic antiparallel β-strands. In bacteria, β-barrel proteins function as water-filled pores, active transporters, enzymes, receptors, and structural proteins. Proteins of bacterial OM are synthesized in the cytoplasm as unfolded polypeptides with an N-terminal sequence that marks them for transport across the CM. Precursors of membrane proteins move through the aqueous medium of the cytosol and periplasm under the protection of chaperones (SecB, Skp, SurA, and DegP), then cross the CM via the Sec system composed of a polypeptide-conducting channel (SecYEG) and ATPase (SecA), the latter providing the energy for the translocation of the pre-protein. Pre-protein folding and incorporation in the OM require the participation of the Bam-complex, probably without the use of energy. This review summarizes current data on the biogenesis of the β-barrel proteins of bacterial OM. Data on the structure of the proteins included in the multicomponent system for delivery of the OM proteins to their destination in the cell and on their complexes with partners, including pre-proteins, are presented. Molecular models constructed on the basis of structural, genetic, and biochemical studies that describe the mechanisms of β-barrel protein assembly by this molecular transport machinery are also considered.

CXCR2 macromolecular complex in pancreatic cancer: a potential therapeutic target in tumor growth

The signaling mediated by the chemokine receptor CXC chemokine receptor 2 (CXCR2) plays an important role in promoting the progression of many cancers, including pancreatic cancer, one of the most lethal human malignancies. CXCR2 possesses a consensus PSD-95/DlgA/ZO-1 (PDZ) motif at its carboxyl termini, which might interact with potential PDZ scaffold/adaptor proteins. We have previously reported that CXCR2 PDZ motif-mediated protein interaction is an important regulator for neutrophil functions. Here, using a series of biochemical assays, we demonstrate that CXCR2 is physically coupled to its downstream effector phospholipase C-β3 (PLC-β3) that is mediated by PDZ scaffold protein Na(+)/H(+) exchange regulatory factor 1 (NHERF1) into a macromolecular signaling complex both in vitro and in pancreatic cancer cells. We also observe that disrupting the CXCR2 complex, by gene delivery or peptide delivery of exogenous CXCR2 C-tail, significantly inhibits the biologic functions of pancreatic cancer cells (i.e., proliferation and invasion) in a PDZ motif-dependent manner. In addition, using a human pancreatic tumor xenograft model, we show that gene delivery of CXCR2 C-tail sequence (containing the PDZ motif) by adeno-associated virus type 2 viral vector potently suppresses human pancreatic tumor growth in immunodeficient mice. In summary, our results suggest the existence of a physical and functional coupling of CXCR2 and PLC-β3 mediated through NHERF1, forming a macromolecular complex that is critical for efficient and specific CXCR2 signaling in pancreatic cancer progression. Disrupting this CXCR2 complex could represent a novel and effective treatment strategy against pancreatic cancer.

Diet, microbiome, and the intestinal epithelium: an essential triumvirate?

The intestinal epithelium represents a critical barrier protecting the host against diverse luminal noxious agents, as well as preventing the uncontrolled uptake of bacteria that could activate an immune response in a susceptible host. The epithelial monolayer that constitutes this barrier is regulated by a meshwork of proteins that orchestrate complex biological function such as permeability, transepithelial electrical resistance, and movement of various macromolecules. Because of its key role in maintaining host homeostasis, factors regulating barrier function have attracted sustained attention from the research community. This paper will address the role of bacteria, bacterial-derived metabolism, and the interplay of dietary factors in controlling intestinal barrier function.

PEX7 and EBP50 target iNOS to the peroxisome in hepatocytes

iNOS localizes to both the cytosol and peroxisomes in hepatocytes in vitro and in vivo. The structural determinants for iNOS localization are not known. One plausible mechanism for iNOS localization to the peroxisome is through the interaction with peroxisomal import proteins PEX5 or PEX7. siRNA knockdown of PEX7 reduced iNOS colocalization with the peroxisomal protein PMP70. Proteomic studies using MALDI-MS identified iNOS association with the 50-kD ezrin binding PDZ protein (EBP50). Confocal microscopy studies and immunoelectron microscopy confirmed iNOS association with EBP50, with greatest colocalization occurring at 8h of cytokine exposure. EBP50 associated with peroxisomes in a PEX5 and PEX7-dependent manner. iNOS localization to peroxisomes was contingent on EBP50 expression in LPS-treated mice. Thus, iNOS targeting to peroxisomes in hepatocytes involves interaction with PEX7 and EBP50. The targeting of iNOS protein to the peroxisome may shift the balance of metabolic processes that rely on heme proteins susceptible to modification by radical oxygen and nitrogen radicals.

Identification of human papillomavirus type 156, the prototype of a new human gammapapillomavirus species, by a generic and highly sensitive PCR strategy for long DNA fragments

This study developed a hanging-droplet long PCR, a generic and highly sensitive strategy to facilitate the identification of new human papillomavirus (HPV) genomes. This novel procedure used for the first time the hanging-droplet PCR technique for the amplification of long DNA fragments with generic primers targeting the L1 and E1 regions. It was first applied to the amplification of types belonging to the highly divergent genus Gammapapillovirus (γ-PV). The hanging-droplet long PCR was 100-fold more sensitive than a simple long PCR procedure, detecting as few as ten copies of HPV-4. Nineteen skin samples, potentially containing putative HPV types from the γ-PV genus, were also screened. The method identified four γ-PV genomic halves from new and previously described putative types, and made the full characterization of HPV-156 possible. This novel virus meets the criteria for a new species within the γ-PV genus, with nucleotide identities in the L1 ORF ranging from 58.3 to 67.3 % compared with representative types of the current γ-PV species. HPV-156 showed the highest identity to HPV-60 (67.3 %) from species γ-4, and was consistently closely related to it in both late- and early-gene-derived phylogenies. In conclusion, this report provides a versatile and highly sensitive approach that allowed identification of the prototype of a new species within the γ-PV genus. Its application with primers targeting the different genera in which both human and non-human PVs are distributed may facilitate characterization of the missing members of the family Papillomaviridae.

Human T-cell leukemia virus type 1 Tax protein interacts with and mislocalizes the PDZ domain protein MAGI-1

Human T-cell leukemia virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia (ATL). HTLV-1 encodes the oncoprotein Tax1, which is essential for immortalization of human T-cells and persistent HTLV-1 infection in vivo. Tax1 has a PDZ binding motif (PBM) at its C-terminus. This motif is crucial for the transforming activity of Tax1 to a T-cell line and persistent HTLV-1 infection. Tax1 through the PBM interacts with PDZ domain proteins such as Dlg1 and Scribble, but it has not been determined yet, which cellular PDZ proteins mediate the functions of Tax1 PBM. Here we demonstrate that Tax1 interacts with the PDZ domain protein MAGI-1 in a PBM-dependent manner, and the interaction mislocalizes MAGI-1 from the detergent-soluble to the detergent-insoluble cellular fraction in 293T cells and in HTLV-1-infected T-cells. In addition, Tax1-transformation of a T-cell line from interleukin (IL)-2-dependent to IL-2-independent growth selects cells with irreversibly reduced expression of MAGI-1 at mRNA level. These findings imply that Tax1, like other viral oncoproteins, targets MAGI-1 as a mechanism to suppress its anti-tumor functions in HTLV-1-infected cells to contribute to the transforming activity of T-cells and persistent HTLV-1 infection.

Polarity protein complex Scribble/Lgl/Dlg and epithelial cell barriers

The Scribble polarity complex or module is one of the three polarity modules that regulate cell polarity in multiple epithelia including blood-tissue barriers. This protein complex is composed of Scribble, Lethal giant larvae (Lgl) and Discs large (Dlg), which are well conserved across species from fruitflies and worms to mammals. Originally identified in Drosophila and C. elegans where the Scribble complex was found to work with the Par-based and Crumbs-based polarity modules to regulate apicobasal polarity and asymmetry in cells and tissues during embryogenesis, their mammalian homologs have all been identified in recent years. Components of the Scribble complex are known to regulate multiple cellular functions besides cell polarity, which include cell proliferation, assembly and maintenance of adherens junction (AJ) and tight junction (TJ), and they are also tumor suppressors. Herein, we provide an update on the Scribble polarity complex and how this protein complex modulates cell adhesion with some emphasis on its role in Sertoli cell blood-testis barrier (BTB) function. It should be noted that this is a rapidly developing field, in particular the role of this protein module in blood-tissue barriers, and this short chapter attempts to provide the information necessary for investigators studying reproductive biology and blood-tissue barriers to design future studies. We also include results of recent studies from flies and worms since this information will be helpful in planning experiments for future functional studies in the testis to understand how Scribble-based proteins regulate BTB dynamics and spermatogenesis.

Sequence and phylogenetic analysis of highly pathogenic avian influenza H5N1 viruses isolated during 2006-2008 outbreaks in Pakistan reveals genetic diversity

BACKGROUND

Since the first outbreak recorded in northern areas of Pakistan in early 2006, highly pathogenic avian influenza H5N1 viruses were isolated from commercial poultry and wild/domestic birds from different areas of Pakistan up to July 2008. Different isolates of H5N1 were sequenced to explore the genetic diversity of these viruses.

RESULTS

Phylogenetic analysis revealed close clustering and highest sequence identity in all 8 genes to HPAI H5N1 isolates belonging to unified H5 clade 2.2, sub-lineage EMA-3 recovered from Afghanistan during the same time period. Two subgroups within Pakistani H5N1 viruses, from domestic and wild birds, were observed on the basis of their sequence homology and mutations. HPAI motif, preferred receptor specificity for α-(2, 3) linkages, potential N-linked glycosylation sites and an additional glycosylation site at the globular head of HA protein of four Pakistani H5N1 isolates. While, the amino acids associated with sensitivities to various antiviral drugs (Oseltamivir, Zanamivir, Amantadine) were found conserved for the Pakistani H5N1 isolates. Conspicuously, some important mutations observed at critical positions of antigenic sites (S141P, D155S, R162I & P181S) and at receptor binding pocket (A185T, R189K & S217P) of HA-1. A high sequence similarity between Pakistani HP H5N1 and LP H9N2 viruses was also observed. Avian like host specific markers with the exception of E627K in PB2, K356R in PA, V33I in NP, I28V in M2 and L107F in NS2 proteins were also observed.

CONCLUSIONS

Various point mutations in different genes of H5 viruses from Pakistan were observed during its circulation in the field. The outbreaks started in Khyber Pakhtoon Khawa (North West) province in 2006 and spread to the Southern regions over a period of time. Though migratory birds may have a role for this continued endemicity of clade 2.2 H5N1 viruses during 2006-2008 in Pakistan, the possibility of their transmission through legal or illegal poultry trade across the borders cannot be ignored.

KIF14 negatively regulates Rap1a-Radil signaling during breast cancer progression

The kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules.

The small GTPase Rap1 regulates inside-out integrin activation and thereby influences cell adhesion, migration, and polarity. Several Rap1 effectors have been described to mediate the cellular effects of Rap1 in a context-dependent manner. Radil is emerging as an important Rap effector implicated in cell spreading and migration, but the molecular mechanisms underlying its functions are unclear. We report here that the kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules. The depletion of KIF14 led to increased cell spreading, altered focal adhesion dynamics, and inhibition of cell migration and invasion. We also show that Radil is important for breast cancer cell proliferation and for metastasis in mice. Our findings provide evidence that the concurrent up-regulation of Rap1 activity and increased KIF14 levels in several cancers is needed to reach optimal levels of Rap1–Radil signaling, integrin activation, and cell–matrix adhesiveness required for tumor progression.

Comparing proteins by their internal dynamics: exploring structure-function relationships beyond static structural alignments

The growing interest for comparing protein internal dynamics owes much to the realisation that protein function can be accompanied or assisted by structural fluctuations and conformational changes. Analogously to the case of functional structural elements, those aspects of protein flexibility and dynamics that are functionally oriented should be subject to evolutionary conservation. Accordingly, dynamics-based protein comparisons or alignments could be used to detect protein relationships that are more elusive to sequence and structural alignments. Here we provide an account of the progress that has been made in recent years towards developing and applying general methods for comparing proteins in terms of their internal dynamics and advance the understanding of the structure-function relationship.

Involvement of nuclear NHERF1 in colorectal cancer progression

NHERF1 (Na+/H+ exchanger regulatory factor 1) is expressed in the luminal membrane of many epithelia, and associated with proteins involved in tumor progression. Alterations of NHERF1 expression in different sites of metastatic colorectal cancer (mCRC) suggest a dynamic role of this protein in colon carcinogenesis. We focused on the observation of the altered expression of NHERF1 from non-neoplastic tissues to metastatic sites by immunohistochemistry. Moreover, we studied, by immunofluorescence, the colocalization between NHERF1 and the epidermal growth factor receptor (EGFR), whose overexpression is implicated in CRC progression. NHERF1 showed a different localization and expression in the examined sites. The distant non-neoplastic tissues showed NHERF1 mostly expressed at the apical membrane, while in surrounding non-neoplastic tissue decreased the apical membrane and increased cytoplasmic immunoreactivity. In adenomas a shift from apical membrane to cytoplasmic localization and nuclear expression were observed. Cytoplasmic staining in the tumor, and metastatic sites was stronger than surrounding non-neoplastic tissue. Furthermore, nuclear NHERF1 expression was noted in 80% of all samples and surprisingly, it appeared already in adenoma lesions, suggesting that NHERF1 represents an early marker of pre-morphological triggering of colorectal carcinogenesis. Then, in few tumors a positive direct correlation between membrane NHERF1 and EGFR expression was evidenced by their colocalization. Nuclear NHERF1 expression, present in the early stages of carcinogenesis and related with poor prognosis, may contribute to the onset of malignant phenotype. Specifically, we hypothesize the direct involvement of nuclear NHERF1 in both carcinogenesis and progression and its role as a potential colorectal cancer marker.

Biochemical and cellular implications of a dual lipase-GEF function of phospholipase D2 (PLD2)

PLD2 plays a key role in cell membrane lipid reorganization and as a key cell signaling protein in leukocyte chemotaxis and phagocytosis. Adding to the large role for a lipase in cellular functions, recently, our lab has identified a PLD2-Rac2 binding through two CRIB domains in PLD2 and has defined PLD2 as having a new function, that of a GEF for Rac2. PLD2 joins other major GEFs, such as P-Rex1 and Vav, which operate mainly in leukocytes. We explain the biochemical and cellular implications of a lipase-GEF duality. Under normal conditions, GEFs are not constitutively active; instead, their activation is highly regulated. Activation of PLD2 leads to its localization at the plasma membrane, where it can access its substrate GTPases. We propose that PLD2 can act as a "scaffold" protein to increase efficiency of signaling and compartmentalization at a phagocytic cup or the leading edge of a leukocyte lamellipodium. This new concept will help our understanding of leukocyte crucial functions, such as cell migration and adhesion, and how their deregulation impacts chronic inflammation.

The PDZ-adaptor protein syntenin-1 regulates HIV-1 entry

Syntenin-1 is recruited to the human immunodeficiency virus (HIV)-induced capping area but vanishes once the viral particles have entered the cell. Syntenin-1 limits HIV-1 infection. Moreover, syntenin-1 depletion specifically increases the HIV-1 entry step without affecting viral attachment to the cell surface. Silencing of syntenin-1 expression blocks actin polymerization triggered by HIV-1 contact and enhances phosphatidylinositol 4,5-bisphosphate production.

Syntenin-1 is a cytosolic adaptor protein involved in several cellular processes requiring polarization. Human immunodeficiency virus type 1 (HIV-1) attachment to target CD4⁺ T-cells induces polarization of the viral receptor and coreceptor, CD4/CXCR4, and cellular structures toward the virus contact area, and triggers local actin polymerization and phosphatidylinositol 4,5-bisphosphate (PIP₂) production, which are needed for successful HIV infection. We show that syntenin-1 is recruited to the plasma membrane during HIV-1 attachment and associates with CD4, the main HIV-1 receptor. Syntenin-1 overexpression inhibits HIV-1 production and HIV-mediated cell fusion, while syntenin depletion specifically increases HIV-1 entry. Down-regulation of syntenin-1 expression reduces F-actin polymerization in response to HIV-1. Moreover, HIV-induced PIP₂ accumulation is increased in syntenin-1–depleted cells. Once the virus has entered the target cell, syntenin-1 polarization toward the viral nucleocapsid is lost, suggesting a spatiotemporal regulatory role of syntenin-1 in actin remodeling, PIP₂ production, and the dynamics of HIV-1 entry.

A chemokine receptor CXCR2 macromolecular complex regulates neutrophil functions in inflammatory diseases

Inflammation plays an important role in a wide range of human diseases such as ischemia-reperfusion injury, arteriosclerosis, cystic fibrosis, inflammatory bowel disease, etc. Neutrophilic accumulation in the inflamed tissues is an essential component of normal host defense against infection, but uncontrolled neutrophilic infiltration can cause progressive damage to the tissue epithelium. The CXC chemokine receptor CXCR2 and its specific ligands have been reported to play critical roles in the pathophysiology of various inflammatory diseases. However, it is unclear how CXCR2 is coupled specifically to its downstream signaling molecules and modulates cellular functions of neutrophils. Here we show that the PDZ scaffold protein NHERF1 couples CXCR2 to its downstream effector phospholipase C (PLC)-β2, forming a macromolecular complex, through a PDZ-based interaction. We assembled a macromolecular complex of CXCR2·NHERF1·PLC-β2 in vitro, and we also detected such a complex in neutrophils by co-immunoprecipitation. We further observed that the CXCR2-containing macromolecular complex is critical for the CXCR2-mediated intracellular calcium mobilization and the resultant migration and infiltration of neutrophils, as disrupting the complex with a cell permeant CXCR2-specific peptide (containing the PDZ motif) inhibited intracellular calcium mobilization, chemotaxis, and transepithelial migration of neutrophils. Taken together, our data demonstrate a critical role of the PDZ-dependent CXCR2 macromolecular signaling complex in regulating neutrophil functions and suggest that targeting the CXCR2 multiprotein complex may represent a novel therapeutic strategy for certain inflammatory diseases.

The regulation of N-methyl-D-aspartate receptors by Src kinase

Src family kinases (SFKs) play critical roles in the regulation of many cellular functions by growth factors, G-protein-coupled receptors and ligand-gated ion channels. Recent data have shown that SFKs serve as a convergent point of multiple signaling pathways regulating N-methyl-d-aspartate (NMDA) receptors in the central nervous system. Multiple SFK molecules, such as Src and Fyn, closely associate with their substrate, NMDA receptors, via indirect and direct binding mechanisms. The NMDA receptor is associated with an SFK signaling complex consisting of SFKs; the SFK-activating phosphatase, protein tyrosine phosphatase α; and the SFK-inactivating kinase, C-terminal Src kinase. Early studies have demonstrated that intramolecular interactions with the SH2 or SH3 domain lock SFKs in a closed conformation. Disruption of the interdomain interactions can induce the activation of SFKs with multiple signaling pathways involved in regulation of this process. The enzyme activity of SFKs appears 'graded', exhibiting different levels coinciding with activation states. It has also been proposed that the SH2 and SH3 domains may stimulate catalytic activity of protein tyrosine kinases, such as Abl. Recently, it has been found that the enzyme activity of neuronal Src protein is associated with its stability, and that the SH2 and SH3 domain interactions may act not only to constrain the activation of neuronal Src, but also to regulate the enzyme activity of active neuronal Src. Collectively, these findings demonstrate novel mechanisms underlying the regulation of SFKs.

The cation diffusion facilitator proteins MamB and MamM of Magnetospirillum gryphiswaldense have distinct and complex functions, and are involved in magnetite biomineralization and magnetosome membrane assembly

Magnetotactic bacteria form chains of intracellular membrane-enclosed, nanometre-sized magnetite crystals for navigation along the earth's magnetic field. The assembly of these prokaryotic organelles requires several specific polypeptides. Among the most abundant proteins associated with the magnetosome membrane of Magnetospirillum gryphiswaldense are MamB and MamM, which were implicated in magnetosomal iron transport because of their similarity to the cation diffusion facilitator family. Here we demonstrate that MamB and MamM are multifunctional proteins involved in several steps of magnetosome formation. Whereas both proteins were essential for magnetite biomineralization, only deletion of mamB resulted in loss of magnetosome membrane vesicles. MamB stability depended on the presence of MamM by formation of a heterodimer complex. In addition, MamB was found to interact with several other proteins including the PDZ1 domain of MamE. Whereas any genetic modification of MamB resulted in loss of function, site-specific mutagenesis within MamM lead to increased formation of polycrystalline magnetite particles. A single amino acid substitution within MamM resulted in crystals consisting of haematite, which coexisted with magnetite crystals. Together our data indicate that MamM and MamB have complex functions, and are involved in the control of different key steps of magnetosome formation, which are linked by their direct interaction.

PDlim2 selectively interacts with the PDZ binding motif of highly pathogenic avian H5N1 influenza A virus NS1

The multi-functional NS1 protein of influenza A virus is a viral virulence determining factor. The last four residues at the C-terminus of NS1 constitute a type I PDZ domain binding motif (PBM). Avian influenza viruses currently in circulation carry an NS1 PBM with consensus sequence ESEV, whereas human influenza viruses bear an NS1 PBM with consensus sequence RSKV or RSEV. The PBM sequence of the influenza A virus NS1 is reported to contribute to high viral pathogenicity in animal studies. Here, we report the identification of PDlim2 as a novel binding target of the highly pathogenic avian influenza virus H5N1 strain with an NS1 PBM of ESEV (A/Chicken/Henan/12/2004/H5N1, HN12-NS1) by yeast two-hybrid screening. The interaction was confirmed by in vitro GST pull-down assays, as well as by in vivo mammalian two-hybrid assays and bimolecular fluorescence complementation assays. The binding was also confirmed to be mediated by the interaction of the PDlim2 PDZ domain with the NS1 PBM motif. Interestingly, our assays showed that PDlim2 bound specifically with HN12-NS1, but exhibited no binding to NS1 from a human influenza H1N1 virus bearing an RSEV PBM (A/Puerto Rico/8/34/H1N1, PR8-NS1). A crystal structure of the PDlim2 PDZ domain fused with the C-terminal hexapeptide from HN12-NS1, together with GST pull-down assays on PDlim2 mutants, reveals that residues Arg16 and Lys31 of PDlim2 are critical for the binding between PDlim2 and HN12-NS1. The identification of a selective binding target of HN12-NS1 (ESEV), but not PR8-NS1 (RSEV), enables us to propose a structural mechanism for the interaction between NS1 PBM and PDlim2 or other PDZ-containing proteins.

Regulation of tight junction permeability by intestinal bacteria and dietary components

The human intestinal epithelium is formed by a single layer of epithelial cells that separates the intestinal lumen from the underlying lamina propria. The space between these cells is sealed by tight junctions (TJ), which regulate the permeability of the intestinal barrier. TJ are complex protein structures comprised of transmembrane proteins, which interact with the actin cytoskeleton via plaque proteins. Signaling pathways involved in the assembly, disassembly, and maintenance of TJ are controlled by a number of signaling molecules, such as protein kinase C, mitogen-activated protein kinases, myosin light chain kinase, and Rho GTPases. The intestinal barrier is a complex environment exposed to many dietary components and many commensal bacteria. Studies have shown that the intestinal bacteria target various intracellular pathways, change the expression and distribution of TJ proteins, and thereby regulate intestinal barrier function. The presence of some commensal and probiotic strains leads to an increase in TJ proteins at the cell boundaries and in some cases prevents or reverses the adverse effects of pathogens. Various dietary components are also known to regulate epithelial permeability by modifying expression and localization of TJ proteins.

Interaction energy based protein structure networks

The three-dimensional structure of a protein is formed and maintained by the noncovalent interactions among the amino-acid residues of the polypeptide chain. These interactions can be represented collectively in the form of a network. So far, such networks have been investigated by considering the connections based on distances between the amino-acid residues. Here we present a method of constructing the structure network based on interaction energies among the amino-acid residues in the protein. We have investigated the properties of such protein energy-based networks (PENs) and have shown correlations to protein structural features such as the clusters of residues involved in stability, formation of secondary and super-secondary structural units. Further we demonstrate that the analysis of PENs in terms of parameters such as hubs and shortest paths can provide a variety of biologically important information, such as the residues crucial for stabilizing the folded units and the paths of communication between distal residues in the protein. Finally, the energy regimes for different levels of stabilization in the protein structure have clearly emerged from the PEN analysis.

Analysis of the PDZ binding specificities of Influenza A virus NS1 proteins

The Influenza A virus non-structural protein 1 (NS1) is a multifunctional virulence factor with several protein-protein interaction domains, involved in preventing apoptosis of the infected cell and in evading the interferon response. In addition, the majority of influenza A virus NS1 proteins have a class I PDZ-binding motif at the C-terminus, and this itself has been shown to be a virulence determinant.

In the majority of human influenza NS1 proteins the consensus motif is RSxV: in avian NS1 it is ESxV. Of the few human strains that have the avian motif, all were from very high mortality outbreaks of the disease. Previous work has shown that minor differences in PDZ-binding motifs can have major effects on the spectrum of cellular proteins targeted. In this study we analyse the effect of these differences upon the binding of Influenza A virus NS1 protein to a range of cellular proteins involved in polarity and signal transduction.

Local signals with global impacts and clinical implications: lessons from the plasma membrane calcium pump (PMCA4)

Calcium has been unequivocally regarded as a key signal messenger in almost every cell type. Calcium regulates a number of important cellular functions including cell growth, myofilament contraction, cell survival and apoptosis as well as gene transcription. A complex regulatory mechanism of cellular calcium is needed to fine tune the precise calcium concentration in each subcellular location and also to transmit the signals carried by the calcium pool to the correct end target. In this article we will review the recently emerging role of the plasma membrane calcium/calmodulin dependent ATPase isoform 4 (PMCA4) in regulating calcium signalling. We will then focus on the function of this molecule in cardiomyocytes, in which PMCA4 forms protein-protein interactions with several key signalling molecules. Recent evidence has shown in vivo physiological functionalities and possible clinical implications of the PMCA4 signalling complex. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Pdlim7 is required for maintenance of the mesenchymal/epidermal Fgf signaling feedback loop during zebrafish pectoral fin development

Background

Vertebrate limb development involves a reciprocal feedback loop between limb mesenchyme and the overlying apical ectodermal ridge (AER). Several gene pathways participate in this feedback loop, including Fgf signaling. In the forelimb lateral plate mesenchyme, Tbx5 activates Fgf10 expression, which in turn initiates and maintains the mesenchyme/AER Fgf signaling loop. Recent findings have revealed that Tbx5 transcriptional activity is regulated by dynamic nucleocytoplasmic shuttling and interaction with Pdlim7, a PDZ-LIM protein family member, along actin filaments. This Tbx5 regulation is critical in heart formation, but the coexpression of both proteins in other developing tissues suggests a broader functional role.

Results

Knock-down of Pdlim7 function leads to decreased pectoral fin cell proliferation resulting in a severely stunted fin phenotype. While early gene induction and patterning in the presumptive fin field appear normal, the pectoral fin precursor cells display compaction and migration defects between 18 and 24 hours post-fertilization (hpf). During fin growth fgf24 is sequentially expressed in the mesenchyme and then in the apical ectodermal ridge (AER). However, in pdlim7 antisense morpholino-treated embryos this switch of expression is prevented and fgf24 remains ectopically active in the mesenchymal cells. Along with the lack of fgf24 in the AER, other critical factors including fgf8 are reduced, suggesting signaling problems to the underlying mesenchyme. As a consequence of perturbed AER function in the absence of Pdlim7, pathway components in the fin mesenchyme are misregulated or absent, indicating a breakdown of the Fgf signaling feedback loop, which is ultimately responsible for the loss of fin outgrowth.

Conclusion

This work provides the first evidence for the involvement of Pdlim7 in pectoral fin development. Proper fin outgrowth requires fgf24 downregulation in the fin mesenchyme with subsequent activation in the AER, and Pdlim7 appears to regulate this transition, potentially through Tbx5 regulation. By controlling Tbx5 subcellular localization and transcriptional activity and possibly additional yet unknown means, Pdlim7 is required for proper development of the heart and the fins. These new regulatory mechanisms may have important implications how we interpret Tbx5 function in congenital hand/heart syndromes in humans.