Volume 396, Issue 3

The peptidome represents the array of endogenous peptides that are present in both the intracellular and extracellular space of the body. Peptides are constantly generated in vivo by active synthesis, and by proteolytic processing of larger precursor proteins, often yielding protein fragments that mediate a variety of physiological functions. Given that aberrant proteolysis is a hallmark of various pathological diseases, many studies have now turned to the peptidome. Differential regulation of endogenous peptides may play a role in many pathological conditions. Mass spectrometry (MS) -based investigation of peptides in a system-wide manner is currently facilitating the identification of potential biomarkers. Furthermore, peptidomic approaches have provided major contributions to the identification of protease-substrate relationships; representing one of the major challenges in understanding and therapeutically exploiting protease function in health and disease. As such, degradomic studies looking for cleavage products via peptidomics in particular, have warranted a significant research interest in recent years. Given that substantial studies are accumulating in the field of peptidomics, this review highlights recent advances of MS-based peptidomic strategies in facilitating the identification of potential peptides as novel clinical markers and protease-substrate profiling.

The innate immune system represents the first line of defence against infectious agents, and co-ordinates cellular and molecular mechanisms that result in effective inflammatory and anti-microbial responses against pathogens. Infection and cellular stress trigger assembly of canonical and noncanonical inflammasome complexes that activate the inflammatory caspases-1 and -11, respectively. These inflammatory caspases play key roles in innate immune responses by inducing pyroptosis to halt intracellular replication of pathogens, and by engaging the extracellular release of pro-inflammatory cytokines and danger signals. In addition, the inflammatory caspases-4, -5 and -11 were recently shown to directly bind microbial components. Although the immune roles of caspase-12 are debated, it was proposed to dampen inflammatory responses by interfering with caspase-1 activation and other innate immune pathways. Here, we recapitulate the reported roles of inflammatory caspases with an emphasis on recent insights into their biological functions.

Tumor cells are characterized by uncontrolled cell growth at a primary site that is caused by genetic alterations. Tumor cells that metastasize from their primary site to distant locations are commonly referred to as malignant. Cell migration is a critical step in this process. The ability of tumor cells to migrate and invade is partly controlled by proteolytic enzymes. These enzymes are secreted by either the tumor cells themselves or adjacent cells. They represent all classes of proteases, including serine and cysteine proteases. Serine proteases, in particular urokinase plasminogen activator (uPA), initiate a proteolytic cascade that culminates in degrading components of the extracellular matrix (ECM). Some serine proteases are controlled by a superfamily of proteins known as serpins. This minireview provides an overview of serpins that are vital in regulating tumor cell migration and progressing cancer.

Abstract: The large proregions of cystine knot growth factors exert several important biological functions. Previous results have shown that the proregion of BMP2 retards the activity of the mature growth factor. Hitherto, no information exists about the function of the BMP2 proregion during the biogenesis of the mature growth factor. Here, evidence is presented that the proregion is required for the secretion of BMP2 when present in covalent linkage to the mature domain. In trans complementation, i.e., with the proregion encoded by a separate plasmid, does not result in secretion of homodimeric mature growth factor. An extended variant of a previously in vitro characterized subdomain of the proregion, when being present in covalent linkage to the mature growth factor, restores secretion of mature BMP2, albeit at a reduced level.

Lung cancer is the second most commonly diagnosed neoplasm, and represents the leading cause of tumour death worldwide. As patients are often diagnosed at a late stage, current therapeutic strategies have limited effectiveness and the prognosis remains poor. Successful treatment depends on early diagnosis and knowledge concerning molecular mechanisms underlying lung carcinogenesis. In the present study, we focused on nicotinamide N-methyltransferase (NNMT), which is overexpressed in several malignancies. First, we analysed NNMT expression in a cohort of 36 patients with non-small cell lung cancer (NSCLC) by immunohistochemistry. Subsequently, we examined NNMT expression levels in the human lung cancer cell line A549 by Real-Time PCR, Western blot and catalytic activity assay, and evaluated the effect of NNMT knockdown on cell proliferation and anchorage-independent cell growth by MTT and soft agar colony formation assays, respectively. NSCLC displayed higher NNMT expression levels compared to both tumour-adjacent and surrounding tissue. Moreover, shRNA-mediated gene silencing of NNMT led to a significant inhibition of cell proliferation and colony formation ability on soft agar. Our results show that the downregulation of NNMT significantly reduced in vitro tumorigenicity of A549 cells and suggest that NNMT could represent an interesting molecular target for lung cancer therapy.

MicroRNAs are small non-coding RNAs that partially bind to the 3’ untranslated (3’UTR) regions of target genes in animals and regulate protein production of the target transcripts. MiR-103 has been confirmed to play a critical role in lipid metabolism, however, the target genes and signaling pathway regulated by miR-103 is still unclear. In our experiment, we observed a positive function of miR-103 on the adipogenic differentiation of 3T3-L1 pre-adipocyte. Furthermore, we proved that this function of miR-103 worked through activating AKT/mTOR signal pathway and impairing target gene MEF2D . By inhibiting and over-expressing the MEF2D gene, we found that MEF2D had a negative role in regulating adipocyte key genes, and this function of MEF2D could be impaired by miR-103. In conclusion, we found that miR-103 can promote 3T3-L1 cells differentiation by targeting MEF2D and activating AKT/mTOR signal pathway. These results will shed a light on further study of microRNAs.

Vascularization plays an important role in tissue engineering applications. It is known that implantation of differentiated endothelial cells or endothelial progenitor cells (EPCs) from cord blood (cbEPCs) gives rise to the formation of a complex functional neovasculature, whereas EPCs isolated from peripheral blood (pbEPCs) have a limited capability to form blood vessels upon implantation. MicroRNA-126 (miR-126) has been shown to have pro-angiogenic effects in vivo . In this study, we investigated whether modulation of miR-126 expression in pbEPCs may alter their angiogenic properties. Gain of function and loss of function experiments revealed that miR-126 has anti-angiogenic effects in pbEPCs. Overexpression of miR-126 resulted in decreased proliferation, migration, invasion and tube formation, while inhibition of miR-126 induced the opposite effects. However, modulation of miR-126 expression did not influence apoptotic susceptibility of pbEPCs. This study provides evidence that inhibition of miR-126 improves angiogenesis-related growth parameters in pbEPCs and may represent a therapeutic option to ameliorate the angiogenic and vasculogenic properties of pbEPCs.

Vascularization is essential in bone tissue engineering and recent research has focused on interactions between osteoblasts (hOBs) and endothelial cells (ECs). It was shown that cocultivation increases the stability of osteoblastic alkaline phosphatase (ALP) mRNA. We investigated the mechanisms behind this observation, focusing on mRNA binding proteins. Using a luciferase reporter assay, we found that the 3′-untranslated region (UTR) of ALP mRNA is necessary for human umbilical vein endothelial cells (HUVEC)-mediated stabilization of osteoblastic ALP mRNA. Using pulldown experiments and nanoflow-HPLC mass spectrometry, vimentin was identified to bind to the 3′-UTR of ALP mRNA. Validation was performed by Western blotting. Functional experiments inhibiting intermediate filaments with iminodipropionitrile and specific inhibition of vimentin by siRNA transfection showed reduced levels of ALP mRNA and protein. Therefore, ALP mRNA binds to and is stabilized by vimentin. This data add to the understanding of intracellular trafficking of ALP mRNA, its function, and have possible implications in tissue engineering applications.

The genome of Tannerella forsythia , an etiological factor of chronic periodontitis, contains several genes encoding putative proteases. Here, we characterized a subtilisin-like serine protease of T . forsythia referred to as mirolase. Recombinant full-length latent promirolase [85 kDa, without its signal peptide (SP)] processed itself through sequential autoproteolytic cleavages into a mature enzyme of 40 kDa. Mirolase latency was driven by the N-terminal prodomain (NTP). In stark contrast to almost all known subtilases, the cleaved NTP remained non-covalently associated with mirolase, inhibiting its proteolytic, but not amidolytic, activity. Full activity was observed only after the NTP was gradually, and fully, degraded. Both activity and processing was absolutely dependent on calcium ions, which were also essential for enzyme stability. As a consequence, both serine protease inhibitors and calcium ions chelators inhibited mirolase activity. Activity assays using an array of chromogenic substrates revealed that mirolase specificity is driven not only by the substrate-binding subsite S1, but also by other subsites. Taken together, mirolase is a calcium-dependent serine protease of the S8 family with the unique mechanism of activation that may contribute to T. forsythia pathogenicity by degradation of fibrinogen, hemoglobin, and the antimicrobial peptide LL-37.

Cathepsin B has been demonstrated to be involved in several proteolytic processes that support tumor progression and metastasis and neurodegeneration. To further clarify its role, defined monoclonal antibodies are needed. As the primary structure of human cathepsin B is almost identical to that of the mouse, cathepsin B-deficient mice were used in a novel approach for generating such antibodies, providing the chance of an increased immune response to the antigen, human cathepsin B. Thirty clones were found to produce cathepsin B-specific antibodies. Seven of these antibodies were used to detect cathepsin B in MCF10-DCIS human breast cancer cells by immunocytochemistry and immunoblotting. Five different binding sites were identified by epitope mapping giving the opportunity to combine these antibodies in oligoclonal antibody mixtures for an improved detection of cathepsin B.