Split Luciferase Complementation Assay Research Articles

Relationship of anti-proliferative activity of TAS-108, a steroid anti-estrogen, and high expression of ERα in MCF7 cells.

e11566 Background: TAS-108 is an anti-estrogen that binds to both ERα and ERβ and has potent anti-proliferative activity in vitro and in vivo assay. Recently, the phase II clinical study of TAS-108 showed that it has competitive clinical benefic with lower level of adverse effects. However, the effect of TAS-108 on molecular mechanism, including ER dimerization, remains largely uninvestigated. Methods: The plasmids containing ERα or ERβ fused with N- and C-terminal fragments of firefly luciferase were constructed for split luciferase complementation assays. The resulting plasmids were transfected in HEK293 cells for 24 hr and TAS-108 was added to the media for 6 hr. For RT-qPCR of AREG and TFF1 and proliferation assay, ERβ was transfected in MCF7 cells for 24hr. The proliferation level was determined by measuring the fluorescent level induced by Prestoblue reagent. Results: Using split luciferase complementation assay, we determined that TAS-108 induced ERα/β heterodimerization about 100-fold more potently than ERα/α homodimerization. Increasing the ERβ level by transfection in MCF7 cells (MCF7-ERβ), potency of TAS-108 was increased significantly; 30nM TAS-108 was suitable to block the E2 mediated increase of AREG and TFF1 expression and significantly decrease proliferation of MCF7-ERβ. Conclusions: Taken together, these data suggest that TAS-108 has a higher affinity for ERα/β heterodimerization than ERα/α homodimerization and TAS-108 shows more effective anti-proliferative activity by blocking the expression of E2-induced proliferative genes when coupled with increased levels of ERβ. These findings also underscore the molecular role of ERβ in the biology and suggest the possibility of the compound inducing ERα/β heterodimerization as anti-breast cancer drugs.

A split luciferase complementation assay for studying in vivo protein–protein interactions in filamentous ascomycetes

Protein-protein interactions play important roles in controlling many cellular events. To date, several techniques have been developed for detection of protein-protein interactions in living cells, among which split luciferase complementation has been applied in animal and plant cells. Here, we examined whether the split luciferase assay could be used in filamentous ascomycetes, such as Gibberella zeae and Cochliobolus heterostrophus. The coding sequences of two strongly interacting proteins (the F-box protein, FBP1, and its partner SKP1) in G. zeae, under the control of the cryparin promoter from Cryphonectria parasitica, were translationally fused to the C- and N-terminal fragments of firefly luciferase (luc), respectively. Each fusion product inserted into a fungal transforming vector carrying the gene for resistance to either geneticin or hygromycin B, was transformed into both fungi. We detected complementation of split luciferase proteins driven by interaction of the two fungal proteins with a high luminescence intensity-to-background ratio only in the fungal transformants expressing both N-luc and C-luc fusion constructs. Using this system, we also confirmed a novel protein interaction between transcription factors, GzMCM1 and FST12 in G. zeae, which could hardly be proven by the yeast two-hybrid method. This is the first study demonstrating that monitoring of split luciferase complementation is a sensitive and efficient method of studying in vivo protein-protein interactions in filamentous ascomycetes.

Bioluminescence Methodology for the Detection of Protein–Protein Interactions Within the Voltage-Gated Sodium Channel Macromolecular Complex

Protein-protein interactions are critical molecular determinants of ion channel function and emerging targets for pharmacological interventions. Yet, current methodologies for the rapid detection of ion channel macromolecular complexes are still lacking. In this study we have adapted a split-luciferase complementation assay (LCA) for detecting the assembly of the voltage-gated Na+ (Nav) channel C-tail and the intracellular fibroblast growth factor 14 (FGF14), a functionally relevant component of the Nav channelosome that controls gating and targeting of Nav channels through direct interaction with the channel C-tail. In the LCA, two complementary N-terminus and C-terminus fragments of the firefly luciferase were fused, respectively, to a chimera of the CD4 transmembrane segment and the C-tail of Nav1.6 channel (CD4-Nav1.6-NLuc) or FGF14 (CLuc-FGF14). Co-expression of CLuc-FGF14 and CD4-Nav1.6-NLuc in live cells led to a robust assembly of the FGF14:Nav1.6 C-tail complex, which was attenuated by introducing single-point mutations at the predicted FGF14:Nav channel interface. To evaluate the dynamic regulation of the FGF14:Nav1.6 C-tail complex by signaling pathways, we investigated the effect of kinase inhibitors on the complex formation. Through a platform of counter screenings, we show that the p38/MAPK inhibitor, PD169316, and the IκB kinase inhibitor, BAY 11-7082, reduce the FGF14:Nav1.6 C-tail complementation, highlighting a potential role of the p38MAPK and the IκB/NFκB pathways in controlling neuronal excitability through protein-protein interactions. We envision the methodology presented here as a new valuable tool to allow functional evaluations of protein-channel complexes toward probe development and drug discovery targeting ion channels implicated in human disorders.

Characterization of Oligomer Formation of Amyloid-β Peptide Using a Split-luciferase Complementation Assay

Amyloid-β peptide (Aβ) is the amyloid component of senile plaques in Alzheimer disease (AD) brains. Recently a soluble oliomeric form of Aβ in Aβ precursor protein transgenic mouse brains and AD brains was identified as a potential causative molecule for memory impairment, suggesting that soluble Aβ oligomers cause neurodegeneration in AD. Further characterization of this species has been hampered, however, because the concentrations are quite small and it is difficult to monitor Aβ oligomers specifically. Here we developed a novel method for monitoring Aβ oligomers using a split-luciferase complementation assay. In this assay, the N- and C-terminal fragments of Gaussia luciferase (Gluc) are fused separately to Aβ. We found that conditioned media from both N- and C-terminal fragments of Gluc-tagged Aβ1-42 doubly transfected HEK293 cells showed strong luminescence. We used gel filtration analyses to analyze the size of oligomers formed by the luciferase complementation assay, and found that it matched closely with oligomers formed by endogenous Aβ in Tg2576 neurons. Large oligomers (24-36-mers), 8-mers, trimers, and dimers predominate. In both systems, Aβ formed oligomers intracellularly, which then appear to be secreted as oligomers. We then evaluated several factors that might impact oligomer formation. The level of oligomerization of Aβ1-40 was similar to that of Aβ1-42. Homodimers formed more readily than heterodimers. The level of oligomerization of murine Aβ1-42 was similar to that of human Aβ1-42. As expected, the familial AD-linked Arctic mutation (E22G) significantly enhanced oligomer formation. These data suggest that Gluc-tagged Aβ enables the analysis of Aβ oligomers.

Application of a split luciferase complementation assay for the detection of viral protein–protein interactions

Intraviral protein-protein interactions are critical for virus survival in the host. Discovery of such interactions is important to understand molecular mechanisms of viral replication and pathogenesis. The development of a cell-based assay that can be employed to examine systematically viral protein interactions is described. The method, known as the split luciferase complementation assay (SLCA), is based on the principle that N- and C-terminal domains of luciferase alone do not emit luminescence; however, if fused to interacting proteins the two non-functional halves can be brought into close enough proximity through a specific protein-protein interaction to restore the functions of the enzyme and emit detectable light. The well-studied influenza B polymerase acidic protein (PA) and basic protein 1 (PB1) interaction was used as a model system to develop the assay. Consistent with previous studies, a strong PA-PB1 interaction was demonstrated in the assay. The PA-PB1 interaction was also disrupted by single amino acid mutations in the N-terminal domain of PB1 that is responsible for binding PA. The described SLCA is highly specific and easy to perform, and thus may be useful for studying protein-protein interactions in viral diseases.

Luminescence detection of SNARE–SNARE interaction in Arabidopsis protoplasts

Membrane associated proteins SNAREs (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors) provide the minimal fusion machinery necessary for cellular vesicles to fuse to target organelle membranes in eukaryotic cells. Despite the conserved nature of the fusion machinery in all eukaryotes, it still remains challenging to identify functional SNARE pairs in higher plants. We developed a method based on a split-luciferase complementation assay for detecting changes in SNARE-SNARE interaction by luminescence within Arabidopsis protoplasts that express recombinant proteins at physiological levels in 96-well plates. The reliability of the assay was confirmed by three experiments. First, reduction of the SNARE-SNARE interaction caused by a single amino acid substitution adjacent to the SNARE motif in endosome-localized AtVAM3/SYP22 (syntaxin of plant 22) was detected by a reduction of luminescence. Second, reduction of the interaction between plasma-membrane localized SYP121 and VAMP722 in response to sodium azide was detected in real-time. Third, the results of 21 SNARE pairs investigated by this method largely agreed with the results from previously reported co-immunoprecipitation assays. Using the method, we newly identified the interaction between SYP121 and VAMP722 was significantly increased when the protoplasts were incubated in the light. Microscopic observation of transgenic Arabidopsis expressing GFP-SYP121 (green fluorescent protein tagged SYP121) from its own promoter suggested that the plasma-membrane localization of GFP-SYP121 is maintained by light. These suggested that the vesicle trafficking pathway mediated by SYP121 might be regulated by light in Arabidopsis. In general, this article demonstrated the method that can generate new biological insight of the SNARE protein interactions in plant cells.

Kinetics of EGF receptor dimer formation

The EGF receptor is thought to exist in the membrane as a monomer that dimerizes in response to ligand binding. Studies on the relationship between ligand binding and dimer formation have been hampered by the lack of an assay that can follow receptor dimerization in living cells in real time. Here we report the use of a split‐luciferase enzyme complementation assay to study the kinetics of EGF receptor dimerization in intact cells. For the assay, the EGF receptor was C‐terminally fused to the N‐terminal or C‐terminal half of firefly luciferase and both constructs transfected into CHO cells. In the absence of ligand, significant basal light production was observed. Addition of EGF led to a rapid decrease in light production during the first two minutes, followed by a rebound in light production over the ensuing 3 to 5 min. The data suggest that under resting conditions, the C‐terminal tails of the EGF receptor are in proximity to each other, possibly in pre‐formed dimers, and that ligand binding induces a conformational change that disrupts these interactions but ultimately allows the formation of an alternative oligomeric state of the receptor.This work is supported by NIH grant GM64491to LJP.

TECHNICAL ADVANCE: Split luciferase complementation assay to study protein–protein interactions in Arabidopsis protoplasts

SummaryWe developed a split luciferase complementation assay to study protein–protein interactions in Arabidopsis protoplasts. In this assay, the N‐ and C‐terminal fragments of Renilla reniforms luciferase are translationally fused to bait and prey proteins, respectively. When the proteins interact, split luciferase becomes activated and emits luminescence that can be measured by a microplate luminometer. Split luciferase activity was measured by first transforming protoplasts with a DNA vector in a 96‐well plate. DNA vector expressing both bait and prey genes was constructed through two independent in vitro DNA recombinant reactions, Gateway and Cre‐loxP. As proof of concept, we detected the protein–protein interactions between the nuclear histones 2A and 2B, as well as between membrane proteins SYP (syntaxin of plant) 51 and SYP61, in Arabidopsis protoplasts.

Split Luciferase Complementation Assay for Studying Interaction of Proteins X and Y in Cells

This protocol describes a split luciferase complementation assay used to study the interaction of proteins in cells. In the "split protein" strategy, a single reporter protein/enzyme (in this case, firefly luciferase [Fluc]) is cleaved into amino-terminal and carboxy-terminal halves; each half is fused to one of two interacting proteins, X and Y. Physical interactions between the two proteins, X and Y, reconstitute the functional reporter protein, leading to enzymatic activities that can be measured by in vitro or in vivo assays. It is important to perform the assay initially in cell culture before proceeding with animal imaging, not only to conserve animals, but also to establish the sensitivity of the assay.

Split Luciferase Complementation Assay for Studying Interaction of Proteins X and Y in Living Mice

This protocol describes a split luciferase complementation assay that can be used to repetitively and noninvasively study the interaction of proteins in small living animals. After the expression of the appropriate vectors has been checked in cell culture in vivo, studies can be performed either by implanting transiently transfected cells for short-term analysis (maximum of 7 days), as described below, or with tumor models grown from tumor cells stably expressing the complete reporter system. For optical imaging, the number of cells implanted can be relatively low (~1-5 × 10(6)), and imaging can begin even before the tumors are palpable. When using a regulated reporter gene, it may be necessary to perform a dose-dependent pilot experiment with the inducer or repressor before performing the primary experiments. Animal models other than mice can be used, including rats and, in theory, transgenic animals in which the reporter constructs have been stably integrated into the genome. Animals larger than the rat would be difficult to image due to poor penetration of light. For these larger-animal models, the use of other imaging technologies such as microPET should be considered.