STAT3 is considered to play an oncogenic role in several malignancies including lung cancer; consequently, targeting STAT3 is currently proposed as therapeutic intervention. Here we demonstrate that STAT3 plays an unexpected tumour-suppressive role in KRAS mutant lung adenocarcinoma (AC). Indeed, lung tissue-specific inactivation of Stat3 in mice results in increased KrasG12D-driven AC initiation and malignant progression leading to markedly reduced survival. Knockdown of STAT3 in xenografted human AC cells increases tumour growth. Clinically, low STAT3 expression levels correlate with poor survival and advanced malignancy in human lung AC patients with smoking history, which are prone to KRAS mutations. Consistently, KRAS mutant lung tumours exhibit reduced STAT3 levels. Mechanistically, we demonstrate that STAT3 controls NF-κB-induced IL-8 expression by sequestering NF-κB within the cytoplasm, thereby inhibiting IL-8-mediated myeloid tumour infiltration and tumour vascularization and hence tumour progression. These results elucidate a novel STAT3–NF-κB–IL-8 axis in KRAS mutant AC with therapeutic and prognostic relevance.

Upon stable cell line generation, chromosomal integration site of the vector DNA has a major impact on transgene expression. Here we apply an active gene environment, rather than specified genetic elements, in expression vectors used for random integration. We generated a set of Bacterial Artificial Chromosome (BAC) vectors with different open chromatin regions, promoters and gene regulatory elements and tested their impact on recombinant protein expression in CHO cells. We identified the Rosa26 BAC as the most efficient vector backbone showing a nine-fold increase in both polyclonal and clonal production of the human IgG-Fc. Clonal protein production was directly proportional to integrated vector copy numbers and remained stable during 10 weeks without selection pressure. Finally, we demonstrated the advantages of BAC-based vectors by producing two additional proteins, HIV-1 glycoprotein CN54gp140 and HIV-1 neutralizing PG9 antibody, in bioreactors and shake flasks reaching a production yield of 1 g/l.

Human chymotrypsin C (CTRC) is a pancreatic protease that participates in the regulation of intestinal digestive enzyme activity. Other chymotrypsins and elastases are inactive on the regulatory sites cleaved by CTRC, suggesting that CTRC recognizes unique sequence patterns. To characterize the molecular determinants underlying CTRC specificity, we selected high affinity substrate-like small protein inhibitors against CTRC from a phage library displaying variants of SGPI-2, a natural chymotrypsin inhibitor from Schistocerca gregaria. On the basis of the sequence pattern selected, we designed eight inhibitor variants in which amino acid residues in the reactive loop at P1 (Met or Leu), P2 (Leu or Asp), and P4 (Glu, Asp, or Ala) were varied. Binding experiments with CTRC revealed that (i) inhibitors with Leu at P1 bind 10-fold stronger than those with P1 Met; (ii) Asp at P2 (versus Leu) decreases affinity but increases selectivity, and (iii) Glu or Asp at P4 (versus Ala) increase affinity 10-fold. The highest affinity SGPI-2 variant (K D 20 pM) bound to CTRC 575-fold tighter than the parent molecule. The most selective inhibitor variant exhibited a K D of 110 pM and a selectivity ranging from 225-to 112,664-fold against other human chymotrypsins and elastases. Homology modeling and mutagenesis identified a cluster of basic amino acid residues (Lys 51 , Arg 56 , and Arg 80 ) on the surface of human CTRC that interact with the P4 acidic residue of the inhibitor. The acidic preference of CTRC at P4 is unique among pancreatic proteases and might contribute to the high specificity of CTRC-mediated digestive enzyme regulation.Digestion of dietary proteins in the small intestine is catalyzed by proteases secreted from the pancreas. These proteases are produced as inactive proenzymes (zymogens) and their activation is spatially restricted to the duodenum and proceeds in a cascade-like manner. The membrane-localized serine protease enteropeptidase (enterokinase) activates trypsinogens to active trypsins, which, in turn, activate all other proteolytic proenzymes; in the human these include chymotrypsinogens B1, B2, C, and L1, proelastases 2A, 3A, and 3B, and procarboxypeptidases A1, A2, and B1. This classic textbook paradigm of digestive enzyme activation has been recently revised by the discovery of interactions between digestive proteases that can modulate the ultimate levels of active enzymes. In this regard, we demonstrated that human chymotrypsin C (CTRC) 4 regulates activation and degradation of human cationic trypsinogen and trypsin (1, 2). CTRC facilitates trypsin-mediated activation (autoactivation) of cationic trypsinogen by processing the trypsinogen activation peptide, at the Phe 18 -Asp 19 peptide bond, to a shorter form that is more readily cleaved by trypsin (1). Mutation A16V in the trypsinogen activation peptide stimulates CTRC-mediated processing and subjects with this mutation are at increased risk of developing chronic pancreatitis (1, 3). CTRC can also promote degradation of human cationic trypsinogen a...

Vector engineering approaches are commonly used to increase recombinant protein production in mammalian cells, and among various concepts, bacterial artificial chromosomes (BAC) have been proposed to serve as open chromatin regions to omit chromosome positional effects. For proof of concept, we developed stable recombinant Chinese hamster ovary (CHO) cell lines using different expression vector systems: the plasmid vectors contained the identical expression cassette as the BAC constructs. Two anti-HIV1 antibody derivates served as model proteins (3D6scFc and 2F5scFc) for generation of four stable recombinant CHO cell lines. The BAC-derived clones showed three to four times higher specific productivity, and therefore, gene copy numbers and transcript level were quantified. The active chromatin region provided with the BAC environment significantly improved transcription evidenced with both model proteins. Specific transcription was approximately six times higher from BAC-based vectors compared to the corresponding plasmid vectors for both single-chain fragment crystallizable (scFc) proteins. Our accurate investigations elucidated also differences between translational activities related to the protein of choice. 3D6scFc expressed specifically three to four times more product than 2F5scFc indicating that the product by itself also contributes to enhanced productivity. This study indicated comparable increase of transcription level for both scFc proteins when using the BAC system, but translation, maturation, and secretion of individual proteins seem to be protein specific.

Background and Purpose Sodium channel inhibitors can be used to treat hyperexcitability‐related diseases, including epilepsies, pain syndromes, neuromuscular disorders and cardiac arrhythmias. The applicability of these drugs is limited by their nonspecific effect on physiological function. They act mainly by sodium channel block and in addition by modulation of channel kinetics. While channel block inhibits healthy and pathological tissue equally, modulation can preferentially inhibit pathological activity. An ideal drug designed to target the sodium channels of pathological tissue would act predominantly by modulation. Thus far, no such drug has been described. Experimental Approach Patch‐clamp experiments with ultra‐fast solution exchange and photolabeling‐coupled electrophysiology were applied to describe the unique mechanism of riluzole on Nav1.4 sodium channels. In silico docking experiments were used to study the molecular details of binding. Key Results We present evidence that riluzole acts predominantly by non‐blocking modulation. We propose that, being a relatively small molecule, riluzole is able to stay bound to the binding site, but nonetheless stay off the conduction pathway, by residing in one of the fenestrations. We demonstrate how this mechanism can be recognized. Conclusions and Implications Our results identify riluzole as the prototype of this new class of sodium channel inhibitors. Drugs of this class are expected to selectively prevent hyperexcitability, while having minimal effect on cells firing at a normal rate from a normal resting potential.