Protein-Protein Interaction Assay to Analyze NOX4/p22(phox) Heterodimerization

Advances in luminescence-based technologies for drug discovery

INTRODUCTION

Luminescence-based technologies, specifically bioluminescence and chemiluminescence, are powerful tools with extensive use in drug discovery. Production of light during chemiluminescence and bioluminescence, unlike fluorescence, doesn't require an excitation light source, resulting in high signal-to-noise ratio, less background interference, and no issues from phototoxicity and photobleaching. These characteristics of luminescence technologies offer unique advantages for experimental designs, allowing for greater flexibility to target a wide range of proteins and biological processes for drug discovery at different stages.

AREAS COVERED

This review provides a basic overview of luciferase-based technologies and details recent advances and use cases of luciferase and luciferin variations and their applicability in the drug discovery toolset. The authors expand upon specific applications of luciferase technologies, including chemiluminescent and bioluminescent-based microscopy. Finally, the authors lay out forward-looking statements on the field of luminescence and how it may shape the translational scientists' work moving forward.

EXPERT OPINION

The demand for improved luciferase and luciferin pairs correlates strongly with efforts to improve the sensitivity and robustness of high-throughput assays. As luminescent reporter systems improve, so will the expansion of use cases for luminescence-based technologies in early-stage drug discovery. With the synthesis of novel, non-enzymatic chemiluminescence-based probes, which previously were restrained to only basic research applications, they may now be readily implemented in drug discovery campaigns.

Connexin32 ameliorates epithelial-to-mesenchymal-transition in diabetic renal tubular via inhibiting NOX4

Renal tubulointerstitial fibrosis (RIF), characterized by epithelial-to-mesenchymal transition (EMT) of renal tubular epithelial cells (TECs), is the main cause of diabetic renal fibrosis. Oxidative stress plays a pivotal role in the development of diabetic RIF. Connexin32 (Cx32), prominently expressed in renal TECs, has emerged as an important player in the regulation of oxidative stress. However, the role of Cx32 in diabetic RIF has not been explored yet. Here, we showed that adenovirus-mediated Cx32 overexpression suppressed EMT to ameliorate RIF and renal function in STZ-induced diabetic mice, while knockout (KO) of Cx32 exacerbated RIF in diabetic mice. Moreover, overexpression of Cx32 inhibited EMT and the production of extra cellular matrix (ECM) in high glucose (HG) induced NRK-52E cells, whereas knockdown of Cx32 showed the opposite effects. Furthermore, we showed that NOX4, the main source of ROS in renal tubular, was down-regulated by Cx32. Mechanistically, Cx32 down-regulated the expression of PKC alpha in a carboxyl-terminal-dependent manner, thereby inhibiting the phosphorylation at Thr147 of p22phox triggered by PKC alpha, which ultimately repressed the formation of the p22phox-NOX4 complex to reduce the protein level of NOX4. Thus, we establish Cx32 as a novel target and confirm the protection mechanism in RIF.

Bioluminescence-Based Complementation Assay to Correlate Conformational Changes in Membrane-Bound Complexes with Enzymatic Function

The proteomics field has undergone tremendous development with the introduction of many innovative methods for the identification and characterization of protein-protein interactions (PPIs). Sensitive and quantitative protein association-based techniques represent a versatile tool to probe the architecture of receptor complexes and receptor-ligand interactions and expand the drug discovery toolbox by facilitating high-throughput screening (HTS) approaches. These novel methodologies will be highly enabling for interrogation of structural determinants required for the activity of multimeric membrane-bound enzymes with unresolved crystal structure and for HTS assay development focused on unique characteristics of complex assembly instead of common catalytic features, thereby increasing specificity. We describe here an example of a binary luciferase reporter assay (NanoBiT®) to quantitatively assess the heterodimerization of the catalytically active NADPH oxidase 4 (NOX4) enzyme complex. The catalytic subunit NOX4 requires association with the protein p22^phox for stabilization and enzymatic activity, but the precise manner by which these two membrane-bound proteins interact to facilitate hydrogen peroxide (H₂O₂) generation is currently unknown. The NanoBiT complementation reporter quantitatively determined the accurate, reduced, or failed complex assembly, which can then be confirmed by determining H₂O₂ release, protein expression, and heterodimer trafficking. Multimeric complex formation differs between NOX enzyme isoforms, facilitating isoform-specific, PPI-based drug screening in the future.

NADPH oxidases: Pathophysiology and therapeutic potential in age-associated pulmonary fibrosis

Oxidative stress has been associated with a number of human fibrotic diseases, including idiopathic pulmonary fibrosis (IPF). Although oxidative stress is associated with both fibrosis and aging, the precise cellular sources(s) of reactive oxygen species (ROS) that contribute to the disease pathogenesis remain poorly understood. NADPH oxidase (Nox) enzymes are an evolutionarily conserved family, where their only known function is the production of ROS. A growing body of evidence supports a link between excessive Nox-derived ROS and numerous chronic diseases (including fibrotic disease), which is most prevalent among the elderly population. In this review, we examine the evidence for Nox isoforms in the pathogenesis of IPF, and the potential to target this enzyme family for the treatment of IPF and related fibrotic disorders. A better understanding of the Nox-mediated redox imbalance in aging may be critical to the development of more effective therapeutic strategies for age-associated fibrotic disorders. Strategies aimed at specifically blocking the source(s) of ROS through Nox inhibition may prove to be more effective as anti-fibrotic therapies, as compared to antioxidant approaches. This review also discusses the potential of Nox-targeting therapeutics currently in development.