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Tuberculosis is a chronic bacterial disease with a complex pathogenesis. An effective immunity against Mycobacterium tuberculosis requires both the innate and adaptive immune responses, including proper T helper (Th) type 1 cell function. FURIN is a proprotein convertase subtilisin/kexin (PCSK) enzyme, which is highly expressed in Th1 type cells. FURIN expression in T cells is essential for maintaining peripheral immune tolerance, but its role in the innate immunity and infections has remained elusive. Here, we utilized Mycobacterium marinum infection models in zebrafish (Danio rerio) to investigate how furin regulates host responses against mycobacteria. In steady-state furinAtd204e/+ fish reduced furinA mRNA levels associated with low granulocyte counts and elevated Th cell transcription factor expressions. Silencing furin genes reduced the survival of M. marinum-infected zebrafish embryos. A mycobacterial infection upregulated furinA in adult zebrafish, and infected furinAtd204e/+ mutants exhibited a proinflammatory phenotype characterized by elevated tumor necrosis factor a (tnfa), lymphotoxin alpha (lta) and interleukin 17a/f3 (il17a/f3) expression levels. The enhanced innate immune response in the furinAtd204e/+ mutants correlated with a significantly decreased bacterial burden in a chronic M. marinum infection model. Our data show that upregulated furinA expression can serve as a marker for mycobacterial disease, since it inhibits early host responses and consequently promotes bacterial growth in a chronic infection., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Background: Subtilisin/kexin-like proprotein convertase (PCSK) enzymes have important regulatory function in a wide variety of biological processes. PCSKs proteolytically process at a target sequence that contains basic amino acids arginine and lysine, which results in functional maturation of the target protein. In vitro assays have showed significant biochemical redundancy between the seven family members, but the phenotypes of PCSK deficient mice and patients carrying an inactive PCSK allele argue for a specific biological function. Modeling the structures of individual PCSK enzymes has offered little insights into the specificity determinants. However, previous studies have shown that there can be a coordinated expression between a PCSK and its target molecule. Here, we have surveyed the putative PCSK target proteins using genome-wide expression correlation analysis and cleavage site prediction algorithms., Results: We first performed a gene expression correlation analysis over the whole genome for all PCSK enzymes. PCSKs were found to cluster differently based on the strength of correlations. The screen for putative PCSK target proteins showed a significant enrichment (p-values from 1.2e-4 to < 1.0e-10) of putative targets among the most positively correlating genes for most PCSKs. Interestingly, there was no enrichment in putative targets among the genes that correlated positively with the biologically redundant PCSK7, whereas PCSK5 showed an inverse correlation. PCSKs also showed a highly variable degree of shared target genes that were identified by expression correlation and cleavage site prediction. Multiple alignments were used to evaluate the putative targets to pinpoint the important residues for the substrate recognition. Finally, we validated our approach and identified biochemically PAPPA1 and ADAMTS6 as novel targets for FURIN proteolytic activity., Conclusions: Most PCSK enzymes display strong positive expression correlation with predicted target proteins in our genome-wide analysis. We also show that expression correlation screen combined with a cleavage site-prediction analysis can be used to identify novel bona fide target molecules for PCSKs. Exploring the positively correlating genes can thus offer additional insights into the biology of proprotein convertases., (© 2011 Turpeinen et al; licensee BioMed Central Ltd.)

Proprotein convertase subtilisin/kexin (PCSK) enzymes cleave and convert their immature substrates into biologically active forms. Polymorphisms in the PCSK genes have been reported to associate with human diseases and phenotypes, including hypercholesterolemia and blood pressure (BP), and targeting PCSKs is considered a promising future form of drug therapy. PCSK processing is readily induced upon upregulation of the enzyme, but the genetic factors contributing to PCSK expression have not been thoroughly characterized. To gain a comprehensive understanding of the genetic regulation of PCSK expression, we performed, for the first time, a genome-wide expression quantitative trait loci (eQTL) analysis using mRNA expression in >1400 human peripheral blood samples from the Cardiovascular Risk in Young Finns Study and ca. ten million single-nucleotide polymorphisms (SNPs). The expression data showed clear expression for FURIN, PCSK5, PCSK7 and MBTPS1 (membrane-bound transcription factor peptidase, site 1) mRNAs in virtually all tested samples. A discovery analysis demonstrated a genome-wide significant ( p < 5 × 10) association with the selected PCSK probes for 1024 variants, which were located at ten independent loci. Of these loci, 5/10 could be confirmed to regulate PCSK expression in two additional and independent sample sets. Finally, a phenotypic analysis demonstrated that a novel cis-eQTL SNP rs4702 for FURIN is strongly associated with both diastolic ( p = 0.012) and systolic ( p = 0.035) BP levels, as well as peripheral vascular resistance ( p = 0.003). These findings indicate that the expression of the PCSK enzymes is regulated by genetic factors, which have biological roles in health and disease. [ABSTRACT FROM AUTHOR]

Proprotein convertase subtilisin/kexin (PCSK) enzymes convert proproteins into bioactive end products. Although other PCSK enzymes are known to be essential for biological processes ranging from cholesterol metabolism to host defense, the in vivo importance of the evolutionarily ancient PCSK7 has remained enigmatic. Here, we quantified the expressions of all pcsk genes during the 1st week of fish development and in several tissues. pcsk7 expression was ubiquitous and evident already during the early development. To compare mammalian and zebrafish PCSK7, we prepared homology models, which demonstrated remarkable structural conservation. When the PCSK7 function in developing larvae was inhibited, we found that PCSK7-deficient fish have defects in various organs, including the brain, eye, and otic vesicle, and these result in mortality within 7 days postfertilization. A genome-wide analysis of PCSK7-dependent gene expression showed that, in addition to developmental processes, several immune system-related pathways are also regulated by PCSK7. Specifically, the PCSK7 contributed to the mRNA expression and proteolytic cleavage of the cytokine TGFβ1a. Consequently, tgfβ1a morphant fish displayed phenotypical similarities with pcsk7 morphants, underscoring the importance of this cytokine in the zebrafish development. Targeting PCSK activity has emerged as a strategy for treating human diseases. Our results suggest that inhibiting PCSK7 might interfere with normal vertebrate development. [ABSTRACT FROM AUTHOR]