Fibroblast activation protein (FAP) is best known for its heightened expression in tumour stroma. This atypical serine protease has both dipeptidyl peptidase and endopeptidase activities, cleaving substrates at a post-proline bond. FAP expression is difficult to detect in non-diseased adult organs, but is greatly upregulated in sites of tissue remodelling, which include liver fibrosis, lung fibrosis, atherosclerosis, arthritis, tumours and embryonic tissues. Due to its restricted expression pattern and dual enzymatic activities, FAP is emerging as a unique therapeutic target. However, methods to exploit and target this protease are advancing more rapidly than knowledge of the fundamental biology of FAP. This review highlights this imbalance, emphasising the need to better define the substrate repertoire and expression patterns of FAP to elucidate its role in biological and pathological processes.

Glucocorticoid and other adipogenic hormones are secreted in mammals in circadian oscillations. Loss of this circadian oscillation pattern correlates with obesity in humans, raising the intriguing question of how hormone secretion dynamics affect adipocyte differentiation. Using live, single-cell imaging of the key adipogenic transcription factors CEBPB and PPARG, endogenously tagged with fluorescent proteins, we show that pulsatile circadian hormone stimuli are rejected by the adipocyte differentiation control system. In striking contrast, equally strong persistent signals trigger maximal differentiation. We identify the mechanism of how hormone oscillations are filtered as a combination of slow and fast positive feedback centered on PPARG. Furthermore, we confirm in mice that flattening of daily glucocorticoid oscillations significantly increases the mass of subcutaneous and visceral fat pads. Together, our study provides a molecular mechanism for why stress, Cushing's disease, and other conditions for which glucocorticoid secretion loses its pulsatility may lead to obesity.

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Common laboratory strains of Bacillus subtilis encode two glutamate dehydrogenases: the enzymatically active protein RocG and the cryptic enzyme GudB that is inactive due to a duplication of three amino acids in its active center. The inactivation of the rocG gene results in poor growth of the bacteria on complex media due to the accumulation of toxic intermediates. Therefore, rocG mutants readily acquire suppressor mutations that decryptify the gudB gene. This decryptification occurs by a precise deletion of one part of the 9-bp direct repeat that causes the amino acid duplication. This mutation occurs at the extremely high frequency of 10 ؊4 . Mutations affecting the integrity of the direct repeat result in a strong reduction of the mutation frequency; however, the actual sequence of the repeat is not essential. The mutation frequency of gudB was not affected by the position of the gene on the chromosome. When the direct repeat was placed in the completely different context of an artificial promoter, the precise deletion of one part of the repeat was also observed, but the mutation frequency was reduced by 3 orders of magnitude. Thus, transcription of the gudB gene seems to be essential for the high frequency of the appearance of the gudB1 mutation. This idea is supported by the finding that the transcription-repair coupling factor Mfd is required for the decryptification of gudB. The Mfd-mediated coupling of transcription to mutagenesis might be a built-in precaution that facilitates the accumulation of mutations preferentially in transcribed genes.A s the central amino group donor for nearly all biosynthetic pathways in any living cell, glutamate plays a key role in the biochemistry and physiology of all organisms (15). Investigations with Escherichia coli demonstrate that glutamate is by far the most abundant metabolite in these bacteria, accounting for ca. 40% of the internal metabolite pool (60). Moreover, glutamate is one of the most highly embedded metabolites. In the Gram-positive soil bacterium Bacillus subtilis, at least 37 reactions make use of this amino acid (42).In B. subtilis, glutamate is exclusively synthesized from 2-oxoglutarate and glutamine by the activity of glutamate synthase in the absence of exogenous glutamate or other sources of glutamate. 2-Oxoglutarate is replenished in the citric acid cycle, whereas glutamine can be synthesized with ammonium as the nitrogen source and one of the two molecules of glutamate that are generated by glutamate synthase as the acceptor. Glutamate does also serve as a precursor for proline biosynthesis and, under conditions of osmotic stress, molar concentrations of proline have to be produced (28). Thus, it is not surprising that glutamate synthesis has to be a highly efficient process and, indeed, interactions between enzymes of the branch of the citric acid cycle that generates 2-oxoglutarate and glutamate synthase have been reported (39). Glutamate can also serve as source of carbon and nitrogen. Its utilization is initiated by an oxidative deamination...

Numerous studies highlight the fact that concerted proteolysis is essential for skin morphology and function. The cysteine protease cathepsin L (Ctsl) has been implicated in epidermal proliferation and desquamation, as well as in hair cycle regulation. In stark contrast, mice deficient in cathepsin B (Ctsb) do not display an overt skin phenotype. To understand the systematic consequences of deleting Ctsb or Ctsl, we determined the protein abundances of >1300 proteins and proteolytic cleavage events in skin samples of wild-type, Ctsb ؊/؊ , and Ctsl ؊/؊ mice via mass-spectrometry-based proteomics. Both protease deficiencies revealed distinct quantitative changes in proteome composition. Ctsl Cathepsins B and L are ubiquitously expressed papain-like cysteine proteases belonging to the C1a papain family (clan CA), with 11 members in humans (1) and 18 members in mice (2). Most cysteine cathepsins like cathepsin L are endopeptidases, whereas cathepsin B shows both endopeptidase and carboxydipeptidase activity (3). Mainly localized in the endosomal/lysosomal compartment, cathepsins have traditionally been thought to play important roles in lysosomal protein turnover. Additional specific functions have been postulated that link cathepsins to different physiological and pathological processes.Studies using cathepsin L (Ctsl)-gene-deficient mice 1 revealed an important role of Ctsl in cardiac homeostasis (4 -6) and a contribution of Ctsl to MHC II-mediated antigen presentation (7, 8) and prohormone processing (9, 10). In a mouse model of pancreatic neuroendocrine cancer, Ctsl promoted tumor growth and invasiveness (11,12). In stark contrast, Ctsl was found to attenuate tumor progression in mouse models of skin cancer, highlighting the context-specific function of this protease (13,14).The most prominent phenotype of Ctsl-deficient mice is periodic hair loss together with epidermal hyperplasia, acanthosis, and hyperkeratosis (15). These alterations in skin morphology are assumed to be keratinocyte specific, as controlled re-expression of Ctsl under a keratin 14 promoter Research

The endolysosomal cysteine endoprotease cathepsin L is secreted from cells in a variety of pathological conditions such as cancer and arthritis. We compared the secretome composition and extracellular proteolytic cleavage events in cell supernatants of cathepsin L-deficient and wild-type mouse embryonic fibroblasts (MEFs). Quantitative proteomic comparison of cell conditioned media indicated that cathepsin L deficiency affects, albeit in a limited manner, the abundances of extracellular matrix (ECM) components, signaling proteins, and further proteases as well as endogenous protease inhibitors. Immunodetection corroborated that cathepsin L deficiency results in decreased abundance of the ECM protein periostin and elevated abundance of matrix metalloprotease (MMP)-2. While mRNA levels of MMP-2 were not affected by cathepsin L ablation, periostin mRNA levels were reduced, potentially indicating a downstream effect. To characterize cathepsin L contribution to extracellular proteolysis, we performed terminal amine isotopic labeling of substrates (TAILS), an N-terminomic technique for the identification and quantification of native and proteolytically generated protein N-termini. TAILS identified >1500 protein N-termini. Cathepsin L deficiency predominantly reduced the magnitude of collagenous cleavage sites C-terminal to a proline residue. This contradicts cathepsin L active site specificity and indicates altered activity of further proteases as a result of cathepsin L ablation.

Proteolysis shapes proteomes by protein degradation or restricted proteolysis, which generates stable cleavage products. Proteolytic (in-)activation of enzymes and cytokines is an essential aspect of the functional proteome status. Proteome-wide identification and quantification of proteolytic processing is accessible by complementary techniques for the focused analysis of protein termini. These innovative strategies are now widely applied and have transformed protease research. Pioneering studies portrayed apoptotic and caspase-dependent cleavage events. Protease-centric investigations focused predominantly on matrix metalloproteinases (MMPs), granzymes and aspartyl and cysteine cathepsins. The first in vivo degradomic studies were performed with mice lacking either cysteine cathepsins or matrix metalloproteinases. Process-centric degradomic analyses investigated infectious processes and mitochondrial import. Peptidomic analyses yielded disease biomarkers representing cleavage fragments from bodily fluids. The diversity of degradomic endeavors illustrates the importance of portraying proteolytic processing in health and disease. The present review provides an overview of the current status of degradomic studies.