Bioprospecting Red Sea Coastal Ecosystems for Culturable Microorganisms and Their Antimicrobial Potential

Microorganisms that inhabit unchartered unique soil such as in the highly saline and hot Red Sea lagoons on the Saudi Arabian coastline, represent untapped sources of potentially new bioactive compounds. In this study, a culture-dependent approach was applied to three types of sediments: mangrove mud (MN), microbial mat (MM), and barren soil (BS), collected from Rabigh harbor lagoon (RHL) and Al-Kharrar lagoon (AKL). The isolated bacteria were evaluated for their potential to produce bioactive compounds. The phylogenetic characterization of 251 bacterial isolates based on the 16S rRNA gene sequencing, supported their assignment to five different phyla: Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Planctomycetes. Fifteen putative novel species were identified based on a 16S rRNA gene sequence similarity to other strain sequences in the NCBI database, being ≤98%. We demonstrate that 49 of the 251 isolates exhibit the potential to produce antimicrobial compounds. Additionally, at least one type of biosynthetic gene sequence, responsible for the synthesis of secondary metabolites, was recovered from 25 of the 49 isolates. Moreover, 10 of the isolates had a growth inhibition effect towards Staphylococcus aureus, Salmonella typhimurium and Pseudomonas syringae. We report the previously unknown antimicrobial activity of B. borstelensis, P. dendritiformis and M. salipaludis against all three indicator pathogens. Our study demonstrates the evidence of diverse cultured microbes associated with the Red Sea harbor/lagoon environments and their potential to produce antimicrobial compounds.

Mammary tumor regression elicited by Wnt signaling inhibitor requires IGFBP5

Wnt ligand-driven tumor growth is inhibited by the soluble Wnt inhibitor Fzd8CRD, but the mechanism through which this effect is mediated is unknown. In the MMTV-Wnt1 mouse model, regression of mammary tumors by Fzd8CRD treatment coincides with an acute and strong induction of insulin-like growth factor (IGF)-binding protein IGFBP5, an antagonist of IGF signaling that mediates involution of mammary gland in females after offspring are weaned. In this study, we show that repression of this IGF inhibitory pathway is crucial for Wnt-driven growth of mammary tumors. We found that IGFBP5 regulation was mediated by the β-catenin-dependent Wnt pathway. Wnt, in addition to IGF ligands, facilitated tumor growth by paracrine communication among tumor cells. In addition, Fzd8CRD caused precocious induction of IGFBP5 in normal mammary glands undergoing involution, implying an acceleration of the involution process by inhibition of Wnt signaling. The molecular and phenotypic parallel between tumor regression and mammary gland involution suggests that Wnt-driven mammary tumors use the same growth mechanism as proliferating normal mammary glands.

Stromal cell-derived factor-1/CXCL12 contributes to MMTV-Wnt1 tumor growth involving Gr1+CD11b+ cells

Background

Histological examinations of MMTV-Wnt1 tumors reveal drastic differences in the tumor vasculature when compared to MMTV-Her2 tumors. However, these differences have not been formally described, nor have any angiogenic factors been implicated to be involved in the Wnt1 tumors.

Methodology/Principal Findings

Here, we show that MMTV-Wnt1 tumors were more vascularized than MMTV-Her2 tumors, and this correlated with significantly higher expression of a CXC chemokine, stromal cell-derived factor-1 (SDF1/CXCL12) but not with VEGFA. Isolation of various cell types from Wnt1 tumors revealed that SDF1 was produced by both tumor myoepithelial cells and stromal cells, whereas Her2 tumors lacked myoepithelial cells and contained significantly less stroma. The growth of Wnt1 tumors, but not Her2 tumors, was inhibited by a neutralizing antibody to SDF1, but not by neutralization of VEGFA. Anti-SDF1 treatment decreased the proportion of infiltrating Gr1⁺ myeloid cells in the Wnt1 tumors, which correlated with a decrease in the percentage of endothelial cells. The involvement of Gr1⁺ cells was evident from the retardation of Wnt1 tumor growth following in vivo depletion of these cells with an anti-Gr1-specific antibody. This degree of inhibition on Wnt1 tumor growth was comparable, but not additive, to the effect observed with anti-SDF1, indicative of overlapping mechanisms of inhibition. In contrast, Her2 tumors were not affected by the depletion of Gr1⁺ cells.

Conclusions/Significance

We demonstrated that SDF1 is important for Wnt1, but not for HER2, in inducing murine mammary tumor and the role of SDF1 in tumorigenesis involves Gr1⁺ myeloid cells to facilitate growth and/or angiogenesis.

Repressor roles for TCF-4 and Sfrp1 in Wnt signaling in breast cancer

Mutations in Wnt pathway genes are rare in human breast cancer, yet activation of the pathway is evident from the misolocalization of beta-catenin. We searched for relationships in the expression of Wnt pathway genes and found that both secreted frizzled related protein 1 (Sfrp1) and TCF-4 transcripts were all highly downregulated in a common subset of breast cancers relative to normal breast tissue. Sfrp1 has been previously characterized as a Wnt inhibitor, and we found that interfering with its expression in the human mammary epithelial cell line MCF10A activated Wnt signaling. Reduction of TCF-4 levels in breast cancer was surprising as it is a transcription factor that is responsive to Wnt signaling. Therefore, we investigated a possible inhibitory role for TCF-4 in human breast cells as well as further characterizing Sfrp1. We identified CD24 as a Wnt target in MCF10A cells and used its expression a marker of Wnt signaling. Interfering with either Sfrp1 or TCF-4 in this cell line enhanced CD24 expression. Furthermore, removal of TCF/LEF binding sites in a CD24-luciferase reporter resulted in elevated reporter gene expression. Our results indicate that both Sfrp1 and TCF-4 repress Wnt signaling in breast tissue and their downregulation contributes to the activation of Wnt signaling.

Synergistic induction of tumor antigens by Wnt-1 signaling and retinoic acid revealed by gene expression profiling

Novel drug targets can be identified by differential analysis of RNA transcripts isolated from cancer cell lines and tissues. We have extended this approach by analyzing differences in gene expression resulting from the drug treatment of transformed and nontransformed cells. A mouse mammary epithelial cell line (C57MG), which conditionally expresses the Wnt-1 proto-oncogene, was left untreated or treated with retinoic acid in the presence or absence of Wnt-1 expression. The experiment was performed in triplicate, and RNA extracted from the four samples was analyzed by hybridization to over 12,000 unique oligonucleotide probe sets. Reproducible alterations in gene expression that occurred in response to retinoic acid, Wnt-1, or retinoic acid plus Wnt-1 relative to untreated cells were identified. Greater attention was given to genes encoding cell surface antigens that were selectively up-regulated by the combination of Wnt-1 and retinoic acid. These genes included the tumor necrosis factor family 4-1BB ligand, ephrin B1, stra6, autotaxin, and ISLR. Administration of retinoic acid to mice bearing tumors driven by activation of the Wnt-1/beta-catenin pathway resulted in increased expression of stra6 in the tumors but not in normal tissue. In principal, the therapeutic index of antibodies directed against these antigens should be enhanced by co-administration of retinoic acid.

Activation of the Wnt pathway interferes with serum response element-driven transcription of immediate early genes

Mutational activation of the Wnt signaling pathway is a common early event in colorectal tumorigenesis, and the identification of target genes regulated by this pathway will provide a better understanding of tumor progression. Gene expression profiling on oligonucleotide microarrays revealed reduced expression of the immediate early genes fos and fosB following stimulation of cells by Wnt-1. Further analysis demonstrated that serum or 12-O-tetradecanoylphorbol-13-acetate activation of several immediate early genes including fos, fosB, junB, and egr1 was inhibited by Wnt signaling. Wnt signaling inhibited transcriptional activation driven by the serum response element without altering the activation of the extracellular signal-regulated kinase cascade or ternary complex formation at the fos serum response element promoter. The Wnt-mediated repression of c-Fos, FosB, and JunB expression was consistent with a decrease in their binding to an AP-1 promoter element and decreased target gene transcription. The expression of fos, fosB, junB, and egr1 was also repressed in human colon tumors relative to patient matched normal tissue. By contrast, the fos family member fra-1 was up-regulated in the human colon tumors, suggesting a compensatory mechanism for the reduction in fos and fosB expression. The results indicate that Wnt signaling can repress the expression of certain immediate early genes, and that this effect is consistent with changes in gene expression observed in human colorectal tumors.