transfection of 293ft cells with pcmv5-nanoluc-craf and pcmv5-14-3-3&#950;-halo expression constructs

使用基于 BRET 的方法在活细胞中进行 CRAF-14-3-3 相互作用分析

RAF kinases (ARAF, BRAF, and CRAF) are the direct effectors of RAS GTPases and the initiating members of the pro-proliferative/pro-survival RAF-MEK-ERK kinase cascade. Recent studies have shown that CRAF expression plays a key role in the tumorigenesis of several KRAS-driven cancers, including non-small cell lung cancer and pancreatic ductal adenocarcinoma1,2,3,4,5. Moreover, germline CRAF mutations cause a particularly severe form of the RASopathy, Noonan syndrome6,7. Understanding CRAF regulation is critical for developing successful therapeutic approaches that target its function in cells.
All RAF kinases can be divided into two functional domains, a C-terminal catalytic (CAT) domain and an N-terminal regulatory (REG) domain, that controls its activity (Figure 1A)8. The REG domain encompasses the RAS binding domain (RBD), the cysteine-rich domain (CRD), and a serine/threonine-rich region (S/T-rich). Notably, the S/T-rich region contains the N&#39; site, which binds to 14-3-3 in a phosphorylation-dependent manner (S259 in CRAF; Figure 1A)8. The CAT domain encompasses the kinase domain, along with a second high-affinity 14-3-3 docking site, referred to as the C&#39; site (S621 in CRAF; Figure 1A)8. The differential binding of dimeric 14-3-3 proteins to the N&#39; and C&#39; sites, along with the CRD, plays critical roles in both RAF activation and inhibition9,10,11,12,13. Under normal signaling conditions, RAF activation is initiated by its recruitment to the plasma membrane by RAS, allowing it to form active dimers, of which the BRAF-CRAF heterodimer is the predominant active form14,15. Biochemical assays with BRAF and CRAF, along with cryogenic electron microscopy (Cryo-EM) structures of dimeric BRAF, indicate that a 14-3-3 dimer stabilizes active RAF dimers by binding simultaneously to the C&#39; site of both RAF protomers (Figure 1B)9,13,16,17. Conversely, studies have shown that under quiescent conditions, RAF adopts a cytosolic, autoinhibited confirmation, where the REG domain binds to the CAT domain and inhibits its activity12,18,19,20. This closed state is stabilized by a 14-3-3 dimer bound to the CRD and N&#39; site in the REG domain and to the C&#39; site in the CAT domain (Figure 1B)10,13,21. In BRAF, this model is supported by recent Cryo-EM structures of autoinhibited BRAF monomers and by our previous biochemical studies10,12,13,21,22. However, while 14-3-3 is shown to play an inhibitory role in CRAF regulation23, a BRAF-like autoinhibited state may play a lesser role in CRAF regulation12; therefore further studies are required to clarify the mechanisms by which 14-3-3 proteins regulate CRAF activity. The 14-3-3-mediated regulation of RAF kinases requires a plethora of RAF phosphorylation and de-phosphorylation events, the binding to various regulatory proteins, and interactions with the plasma membrane8. Therefore, it is critical that 14-3-3-RAF interactions are measured under physiologically relevant conditions and in the presence of an intact lipid bilayer.
To address this issue, NanoBRET (from here on referred to as N-BRET; see Table of Materials for kit details) technology was utilized to develop a proximity-based assay for measuring the interactions of CRAF with 14-3-3 proteins in live cells (Figure 1C). This BRET-based system measures the interactions of two proteins of interest (POI), where one protein is tagged with a nanoluciferase (Nano) donor and the other with a Halo tag, for labeling with the Halo618 energy acceptor ligand22,24. Interaction of the proteins of interest results in donor to acceptor energy transfer, which in turn generates the BRET signal (Figure 1C). The extremely bright Nano donor protein (emission (em) 460 nm) and the Halo618 ligand (em 618 nm) provide greater spectral separation and sensitivity over conventional BRET, making it an ideal platform for studying weaker interactions and detecting subtle changes in binding24. Indeed, we previously developed a N-BRET-based assay for measuring the autoinhibitory interactions of the RAF REG and CAT domains, which was essential for the characterization of a panel of RASopathy mutations in the BRAF CRD and demonstrated the critical importance of this domain for maintaining autoinhibition and preventing constitutive BRAF activation12.
The assay described here measures the interactions of CRAF, fused to an N-terminal Nano tag (Nano-CRAF), and the zeta isoform of 14-3-3 fused to C-terminal Halo tag (14-3-3&#950;-Halo; Figure 1C). We show that the interactions of Nano-CRAF with 14-3-3&#950;-Halo generates a robust BRET signal, which can in turn be disrupted by mutations which prevent 14-3-3 binding to the N&#39; site (S259A) and/or the C&#39; site (S621A). The following protocol provides detailed steps for performing, optimizing, and troubleshooting this assay.

作者聚焦：整合基于 BRET 的检测和罕见突变分析以破译活细胞中的 RAF 激酶调控

基于生物发光共振能量转移 （BRET） 的测定法，用于测量 CRAF 与活细胞中 14-3-3 蛋白的相互作用

The primary focus of our research is to uncover new vulnerabilities in the Ras-MAPK kinase pathway through the study of rare disease associated mutations within. We recently developed another BRET-based assay for measuring the auto inhibitory activities of RAF kinases in live cells. Importantly, this assay was essential for characterizing a group of rare germline mutations in the BRAF cysteine rich domain, which demonstrated the critical importance of this domain for maintaining BRAF auto inhibition and for preventing constitutive BRAF biological activity.This assay measures the interactions of 1433 proteins with the RAF kinase CRAF, and these interactions play essential roles in mediating RAF function in both development and disease. In addition, this assay combined with previously established assays for measuring RAF auto inhibition and the RAF-RAF interaction form the basis of a toolkit for dissecting the regulatory mechanisms of RAF kinases in live cells.

用 pCMV5-NanoLuc-CRAF 和 pCMV5-14-3-3ζ-Halo 表达构建体转染 293FT 细胞

首先，取在 10 厘米培养皿中培养的 293FT 细胞，并吸出培养基。用 5 毫升 PBS 洗涤细胞。然后加入 1 毫升胰蛋白酶 EDTA，在 37 摄氏度下孵育 3-5 分钟，以将细胞从培养皿中分离出来。孵育后，向细胞中加入 9 mL 完全 DMEM 以中和胰蛋白酶。反复上下移液以产生均匀的单细胞悬液，并将细胞转移到 15 mL 试管中。立即将 20 μL 细胞转移到 1.7 mL 试管中，并与 20 μL 台盼蓝染色剂混合。使用自动细胞计数仪或血细胞计数器对细胞进行计数。将适当体积的细胞转移到 50 mL 试管中，并在完整的 DMEM 中稀释。向 6 孔板的每个孔中加入 2 毫升细胞悬液。将细胞在 37 摄氏度和 10% 二氧化碳下孵育过夜。转染前，在 TE 缓冲液中稀释纳米荧光素酶 CRAF 和 1433 zeta 晕质粒以及 pCDNA3 空载体。标记一组无菌 1.7 毫升试管。向每个试管中加入 100 μL 转染培养基以及表达构建体。现在加入 2 μL 转染试剂，轻轻涡旋混合。在微量离心机中脉冲旋转试管，然后在 25 摄氏度左右孵育试管 15 分钟，以形成转染复合物。然后，向细胞中逐滴添加转染复合物，并在 37 摄氏度下孵育 16-20 小时，以表达 halo 和纳米标记蛋白。

transfection-293ft-cells-with-pcmv5-nanoluc-craf-pcmv5-14-3-3-halo

Research

JoVE Journal

Biochemistry

Transfection of 293FT Cells with pCMV5-NanoLuc-CRAF and pCMV5-14-3-3&#950;-Halo Expression Constructs

62 次观看. 首先，取在 10 厘米培养皿中培养的 293FT 细胞，并吸出培养基。用 5 毫升 PBS 洗涤细胞。然后加入 1 毫升胰蛋白酶 EDTA，在 37 摄氏度下孵育 3-5 分钟，以将细胞从培养皿中分离出来。孵育后，向细胞中加入 9 mL 完全 DMEM 以中和胰蛋白酶。反复上下移液以产生均匀的单细胞悬液，并将细胞转移到 15 mL 试管中。立即将 20 μL 细胞转移到 1.7 mL 试管中，并与 20 μL 台盼蓝染色剂混...

视频: 用 pCMV5-NanoLuc-CRAF 和 pCMV5-14-3-3ζ-Halo 表达构建体转染 293FT 细胞

Bioluminescence Resonance Energy Transfer (BRET)-Based Assay for Measuring Interactions of CRAF with 14-3-3 Proteins in Live Cells

CRAF is a primary effector of RAS GTPases and plays a critical role in the tumorigenesis of several KRAS-driven cancers. In addition, CRAF is a hotspot for germline mutations, which are shown to cause the developmental RASopathy, Noonan syndrome. All RAF kinases contain multiple phosphorylation-dependent binding sites for 14-3-3 regulatory proteins. The differential binding of 14-3-3 to these sites plays essential roles in the formation of active RAF dimers at the plasma membrane under signaling conditions and in maintaining RAF autoinhibition under quiescent conditions. Understanding how these interactions are regulated and how they can be modulated is critical for identifying new therapeutic approaches that target RAF function. Here, I describe a bioluminescence resonance energy transfer (BRET)-based assay for measuring the interactions of CRAF with 14-3-3 proteins in live cells. Specifically, this assay measures the interactions of CRAF fused to a Nano luciferase donor and 14-3-3 fused to a Halo tag acceptor, where the interaction of RAF and 14-3-3 results in donor-to-acceptor energy transfer and the generation of the BRET signal. The protocol further shows that this signal can be disrupted by mutations shown to prevent 14-3-3 binding to each of its high-affinity RAF docking sites. This protocol describes the procedures for seeding, transfecting, and replating the cells, along with detailed instructions for reading BRET emissions, performing data analysis, and confirming protein expression levels. In addition, example assay results, along with optimization and troubleshooting steps, are provided.

This protocol describes a BRET-based assay for measuring the interactions of the CRAF kinase with 14-3-3 proteins in live cells. The protocol outlines steps for preparing the cells, reading BRET emissions, and data analysis. An example result with identification of appropriate controls and troubleshooting for assay optimization is also presented.

CRAF is a primary effector of RAS GTPases and plays a critical role in the tumorigenesis of several KRAS-driven cancers. In addition, CRAF is a hotspot ...

科研

生物化学

To begin, take 293FT cells cultured in a 10 centimeter dish, and aspirate the media. Wash cells with five milliliters of PBS. Then add one milliliter of trypsin EDTA, and incubate for 3-5 minutes at 37 degrees Celsius to detach cells from the dish.After incubation, add nine milliliters of complete DMEM to the cells to neutralize the trypsin. Pipette up and down repeatedly to generate a homogenous single cell suspension, and transfer the cells to a 15 milliliter tube. Immediately transfer 20 microliters of cells to a 1.7 milliliter tube, and mix with 20 microliters of trypan blue stain.Count cells using either an automated cell counter or a hemocytometer. Transfer the appropriate volume of cells to a 50 milliliter tube, and dilute in complete DMEM. Add two milliliters of cell suspension to each well of a six-well plate.Incubate cells at 37 degrees Celsius and 10%carbon dioxide overnight. Prior to transfection, dilute nanoluciferase CRAF and 1433 zeta halo plasmids, along with a pCDNA3 empty vector in TE buffer. Label a set of sterile 1.7 milliliter tubes.Add 100 microliters of transfection media to each tube, along with the expression constructs. Now add two microliters of transfection reagent, and vortex gently to mix. Pulse spin the tubes briefly in a microcentrifuge, and then incubate the tubes at around 25 degrees Celsius for 15 minutes to allow transfection complexes to form.Afterwards, add transfection complexes to cells dropwise, and incubate at 37 degrees Celsius for 16-20 hours to express the halo and nanotagged proteins.

Preparing 293FT Cells Transfected with pCMV5-NanoLuc-CRAF and pCMV5-14-3-3&#950;-Halo for BRET Emission Assay

To begin, label three sets of sterile 1.7-milliliter tubes and one set of sterile 15-milliliter conical bottom tubes. Prepare a swing bucket centrifuge with 15-milliliter tube inserts and pre-cool to four degrees Celsius. Take the six-well cell culture plate with transfected 293FT cells.Aspirate the media from the wells. Add 250 microliters of trypsin-EDTA and incubate at 37 degrees until cells begin to detach. Then add one milliliter of 10%FBS supplemented assay media to each well and pipette vigorously to create a single-cell suspension.Transfer one milliliter of cell suspension to pre-labeled 15-milliliter tubes. Add one milliliter of 10%FBS supplemented assay media to each of these tubes and invert five times to mix. Then immediately transfer 20 microliters of cell suspension to tube set one.Now centrifuge the 15 milliliter tubes for five minutes at 250 g in a pre-cooled centrifuge. Mix 20 microliters of trypan blue cell stain with cells in set one and count using a cell counter or hemocytometer. After removing the 15-milliliter tubes from the centrifuge, aspirate media from cell pellets and resuspend pellets in serum-free assay media to create a single-cell suspension.To reflate cells in 384-well and six-well plates, invert the 15-milliliter tubes several times for a homogenous cell suspension and transfer 500 microliters to 1.7 milliliter tubes in set two and set three. Add 0.5 microliters of DMSO to set two and 0.5 microliters of Halo 618 ligand to tube set three and mix well. Transfer the DMSO and ligand-positive cell suspensions to separate wells of reagent reservoirs.Use a multi-channel pipette to transfer 40 microliters of each suspension to the 384-well culture plate. Transfer the remaining cells to fresh six-well culture plates for subsequent western blot analysis and incubate both 384-well and six-well plates overnight at 37 degrees Celsius and 5%carbon dioxide. Take serum-free assay media prewarmed at 37 degrees Celsius.Dilute the thawed nanoluciferase substrate 1:100 in serum-free assay media and transfer it to a reagent reservoir. Using a multi-channel pipette, transfer 10 microliters of substrate mixture to each well of the 384-well culture plate. Gently rotate the plate for one minute.Insert the 384-well plate into a multi-mode plate reader and record the 460 and 618 nanometers emissions from all wells with cells. Calculate the raw BRET ratios for vehicle-positive and ligand-positive in milliBRET units using the given equation. Calculate the corrected BRET ratio by subtracting the vehicle-positive BRET ratio from that of the ligand-positive.The nano-CRAFS259A mutant reduces the BRET signal by approximately 45%and the nano-CRAFS621A mutant by around 25%The double mutant nearly eliminates the BRET signal.