TPR-MET Fusion Expression Plasmid Vectors

The TPR-MET fusion gene is an oncogenic fusion resulting from a chromosomal translocation between the TPR gene (Translocated Promoter Region) and the MET gene (Mesenchymal-Epithelial Transition factor). TPR-MET is a rare but potent oncogenic driver that promotes tumorigenesis through. When the coiled-coil domain of TPR fuses with the kinase domain of MET, the fusion causes MET dimerization which leads to constitutive activation of the MET kinase domain and ligand (HGF)-independent activation. This constitutive MET signaling promotes tumor cell proliferation, survival, and metastasis.

TPR-MET fusion is commonly found in non-small cell lung cancer (NSCLC), gastric cancer, colorectal cancer, etc., accounting for approximately 1% ~ 2% of NSCLC cases, serving as a potential therapeutic target. MET inhibitors are the primary targeted therapy for TPR-MET-driven tumors, including: 1) Small-molecule tyrosine kinase inhibitors (TKIs) such as Crizotinib, Cabozantinib, Tepotinib and Capmatinib. 2) Monoclonal Antibodies, e.g., Onartuzumab. Ongoing research aims to improve targeted therapies and overcome resistance mechanisms.

RGBiotech offers high-quality TPR-MET expression plasmid vectors, designed for robust and reliable gene expression in mammalian systems. These vectors feature the TPR (Tetratricopeptide Repeat) domain fused to the MET receptor tyrosine kinase, enabling precise studies of signaling pathways, and oncogenic mechanisms. Engineered for optimal performance, our plasmids ensure high transfection efficiency, strong promoter-driven expression, and compatibility with standard cloning and purification protocols. Ideal for cancer research, kinase assays, and structural biology applications, our TPR-MET constructs are rigorously validated by sequencing. Contact us at admin@rgbiotech.com to streamline your MET-related research with trusted molecular tools.

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As a significant discovery in the field of tumor molecular biology in recent years, the TPR-MET fusion gene plays a crucial role in the occurrence and development of various malignant tumors.

Molecular Biological Backgrounds of TPR Gene and MET Gene

The TPR gene (Translocated Promoter Region), as a key component of the nuclear pore complex (NPC), was first discovered in a chemically induced human osteosarcoma cell line in 1984, and was identified as part of the oncogenic fusion with the MET gene at that time. The TPR gene is located on human chromosome 1q25, and the encoded protein is mainly localized in the nuclear basket region of the nuclear pore complex, playing an important role in various cellular processes such as nucleocytoplasmic transport, transcriptional regulation, mitosis, and autophagy. As a scaffold protein of the nuclear pore complex, the TPR protein not only participates in the material exchange between the nucleus and cytoplasm but also plays a key role in cell cycle regulation and gene expression. Recent studies have found that TPR is abnormally expressed in various cancer types, including ependymoma, cervical cancer, and colon cancer, indicating that it may have multiple functions in tumor occurrence and development.

The MET gene (mesenchymal-epithelial transition factor) is located on the long arm of human chromosome 7 (7q21-31), and the encoded c-MET protein is a transmembrane receptor tyrosine kinase with autonomous phosphorylation activity. The normal activation of the c-MET pathway promotes tissue differentiation and repair, while its abnormal expression is closely related to tumor cell proliferation, invasion, and metastasis. The natural ligand of MET is hepatocyte growth factor (HGF), also known as "scatter factor" (SF), and both were confirmed to be the same protein in 1991. The HGF/MET signaling pathway is indispensable in physiological processes such as embryonic development, wound healing, and tissue regeneration, and has also been proven to be a key driving factor in the occurrence and development of various cancers.

The abnormal activation mechanisms of the MET gene mainly include three types: MET exon 14 skipping mutation (METex14), MET gene copy number amplification, and MET protein overexpression. Among them, METex14 skipping mutation leads to the deletion of the JM domain encoding segment containing Y1003 and c-Cbl E3 ubiquitin ligase binding sites, resulting in reduced ubiquitination of the receptor, hindered degradation of the MET protein, continuous activation of the signal, and ultimately driving tumorigenesis. MET amplification leads to protein overexpression by increasing the gene copy number, and the incidence of MET amplification in non-small cell lung cancer (NSCLC) is 0.7% to 21% under different detection technologies and positive thresholds.

Formation Mechanism and Biological Characteristics of TPR-MET Fusion Gene

The TPR-MET fusion gene is an oncogenic fusion variant formed by the translocation of the TPR gene and the MET gene, and its formation mechanism involves the breakage and rearrangement of the chromosomal regions 1q25 and 7q21-31. This fusion causes the MET kinase domain to combine with the coiled-coil domain of TPR, forming a chimeric protein with continuous activation ability. Structurally, the TPR-MET fusion protein retains the tyrosine kinase domain of MET but loses the normal regulatory region, while the coiled-coil domain of TPR promotes the dimerization and autonomous phosphorylation of the fusion protein, leading to the constitutive activation of downstream signaling pathways (such as PI3K-AKT, MAPK/ERK, and JAK-STAT).

The oncogenic mechanism of the TPR-MET fusion gene mainly includes three aspects: first, it relieves the normal regulation of MET activation, keeping the kinase activity in a continuous "on" state; second, it changes the subcellular localization, which may affect the efficiency of signal transduction; third, it enhances protein stability and prolongs its half-life. It is worth noting that, unlike wild-type MET, the activation of the TPR-MET fusion protein is not dependent on HGF stimulation, showing ligand-independent activation characteristics, which makes it a highly attractive therapeutic target.

Disease Spectrum and Clinical Characteristics Related to TPR-MET Fusion Gene

The TPR-MET fusion gene has been detected in various malignant tumors, and its disease spectrum and clinical characteristics vary with tumor types. In central nervous system tumors, TPR-MET fusion is mainly seen in high-grade gliomas, especially glioblastoma (GBM) and anaplastic astrocytoma. Such patients usually present with an aggressive clinical course, poor response to conventional treatment, and extremely poor prognosis. In non-small cell lung cancer (NSCLC), MET fusion (including TPR-MET) accounts for approximately 1-2% of all cases, and is more common in special subtypes such as pulmonary sarcomatoid carcinoma. Compared with lung cancers with other driver genes, patients with positive MET fusion often have unique clinicopathological features, such as higher invasiveness and faster disease progression. It is worth noting that MET fusion may be related to the EGFR-TKI resistance mechanism. When patients with EGFR-mutant NSCLC develop resistance to first- or second-generation TKIs, approximately 5-20% will have MET amplification or overexpression. In addition, TPR-MET fusion has also been sporadically reported in solid tumors such as osteosarcoma, gastric cancer, and renal cancer. The exact incidence of TPR-MET fusion in different tumor types still needs to be determined by larger-scale epidemiological studies, but existing data have fully shown that this is a type of molecular variation with important clinical significance.

Current Treatment Status and Challenges of TPR-MET Fusion Gene

Significant progress has been made in the treatment of TPR-MET fusion-positive tumors in recent years, but there are still many challenges. In terms of treatment strategies, targeted drugs for TPR-MET fusion are mainly divided into three categories: small-molecule tyrosine kinase inhibitors (TKIs), monoclonal antibodies, and antibody-drug conjugates (ADCs). Among them, small-molecule TKIs are the most widely used in clinical practice, and they can be further divided into type I (binding to the active conformation) and type II (binding to the inactive conformation) inhibitors based on their binding properties. However, there are still several key difficulties in current treatments: first, the issue of blood-brain barrier penetration, as many MET inhibitors have limited efficacy in central nervous system tumors; second, the complex drug resistance mechanisms, including intra-target mutations (such as G1163R, D1228H/N, Y1230C/H, etc.) and off-target bypass activation (such as KRAS mutations, EGFR/HER3 amplification, etc.); third, the lack of biomarkers for predicting therapeutic efficacy, making it difficult to accurately screen potential benefit populations; fourth, the small sample size of clinical trials, and the level of evidence-based medical evidence needs to be improved. Regarding the problem of drug resistance, studies have found that type II MET inhibitors may overcome part of the resistance to type I inhibitors, and combination therapy strategies (such as MET-TKI combined with MEK inhibitors) have shown synergistic effects in preclinical models. In addition, new therapeutic drugs such as the EGFR/MET bispecific antibody Amivantamab and the MET-ADC drug Telisotuzumab vedotin are under development, which are expected to provide new options for patients with drug resistance.

Future Research Directions of TPR-MET Fusion Gene Research

The future research on TPR-MET fusion gene will focus on several key directions. The innovation of diagnostic technology is the primary task, including the development of more sensitive and specific detection methods, such as RNA-based next-generation sequencing (NGS) technology, to improve the detection rate of fusion genes 3. At the same time, it is also crucial to establish standardized detection procedures and interpretation criteria, especially for the accurate identification of rare fusion variants. The advancement of liquid biopsy technology may enable non-invasive dynamic monitoring of TPR-MET fusion, providing new tools for efficacy evaluation and drug resistance early warning. In terms of treatment strategies, the development of next-generation MET inhibitors will focus on addressing the limitations of existing drugs, especially the issues of blood-brain barrier penetration and drug resistance. New-generation drugs such as brigatinib have shown good central nervous system activity, bringing breakthroughs in the treatment of brain tumors. Combination therapy will be another important direction; for example, the rational combination of MET-TKI with immune checkpoint inhibitors, anti-angiogenic drugs, or chemotherapy may produce synergistic effects and delay the occurrence of drug resistance. In-depth basic research will reveal the precise molecular mechanism of TPR-MET fusion carcinogenesis, including its interaction with the tumor microenvironment, epigenetic regulation, and metabolic reprogramming. The use of organoid models and patient-derived xenograft (PDX) models can more truly simulate the biological characteristics of human tumors and accelerate the drug development process.

Background and Progress of TPR-MET Targeted Drug Research and Development

The research and development history of TPR-MET targeted drugs can be traced back to 1984, when the MET gene was first discovered as part of the fusion with the TPR gene. This accidental discovery opened the prelude to the research on the MET signaling pathway and laid the foundation for the subsequent development of targeted therapy. The early research and development stage mainly focused on the abnormal activation mechanisms of MET in various cancers, and it was not until 2004 that the concept of MET abnormality as a tumor driver was formally established. Since then, the research and development of drugs targeting the MET pathway have gone through an evolution from multi-target inhibitors to highly selective inhibitors. The current research and development progress of TPR-MET targeted drugs is mainly reflected in three aspects: first, the selectivity of inhibitors is continuously improving, evolving from multi-target drugs such as crizotinib to highly selective type Ib inhibitors such as tepotinib and brigatinib; second, the forms of drugs are increasingly abundant, including not only small-molecule TKIs but also new preparations such as bispecific antibodies and ADC drugs; third, the range of indications is gradually expanding, from the initial NSCLC to various solid tumors such as glioma.

Research Methods and Technical Platforms for TPR-MET Inhibitors

Cell models are indispensable platforms for TPR-MET inhibitor research. Among them, the Ba/F3-TPR-MET stable transfectant, due to its IL-3-independent growth characteristic, has become an ideal tool for high-throughput screening. This model can comprehensively evaluate compound activity by detecting cell proliferation inhibition, fusion protein phosphorylation levels, and the activation status of downstream signaling pathways (such as Erk, AKT, etc.).

The BaF3 cell model has become the gold standard system for TPR-MET inhibitor screening. Its core principle lies in introducing the TPR-MET fusion gene into IL-3-dependent BaF3 cells, transforming them into IL-3-independent growth. This transformation is completely dependent on the continuous activation of the TPR-MET fusion protein. Therefore, when effective inhibitors block the MET signaling pathway, cell proliferation will be specifically inhibited, thereby establishing a sensitive and specific drug screening platform. Compared with traditional tumor cell lines, the BaF3-TPR-MET system has multiple technical advantages: first, it has a clear background and a single signaling pathway, eliminating the interference of other oncogenic mutations on result interpretation; second, it has high sensitivity and can detect inhibitor activity at the nanomolar level; third, it has strong specificity and can distinguish between targeted and non-targeted effects through the degree of recovery of IL-3 dependence; fourth, it has high throughput and is suitable for large-scale compound library screening; fifth, it has good cost-effectiveness, is easy to maintain, and has good repeatability.

In terms of application value, the BaF3-TPR-MET model runs through the entire process of drug research and development: in the early stage, it is used for high-throughput primary screening and structure-activity relationship research; in the middle stage, it evaluates the activity spectrum of compounds on specific mutant types (such as drug-resistant mutations); in the later stage, it can be used for exploring combined medication regimens and studying drug resistance mechanisms. In addition, this system can also develop more convenient phenotypic detection methods by introducing various reporter genes (such as luciferase).

It is worth noting that the BaF3 model also has certain limitations. For example, it cannot fully simulate the complex microenvironment and signal network crosstalk of human tumor cells. Therefore, positive results need to be further verified in primary tumor cells or animal models. Nevertheless, as a primary screening tool, the BaF3-TPR-MET system is still widely used due to its efficiency and reliability, greatly accelerating the research and development process of MET inhibitors.

Construction Methods and Procedures of BaF3 Cell Line Stably Expressing TPR-MET

Constructing a BaF3 cell line stably expressing TPR-MET is a systematic and delicate work, and its standard process can be divided into four key steps. Vector construction is the primary link, which requires cloning the TPR-MET fusion gene into a suitable expression vector. Commonly used vectors include lentiviral vectors such as pCDH and pLVX, or plasmid vectors such as pcDNA3.1. Vector design needs to consider factors such as promoter strength (e.g., CMV, EF1α), selection markers (e.g., puromycin resistance gene), and reporter genes (e.g., GFP).

The first step is cell preparation. BaF3 cells in the logarithmic growth phase are selected, as they are in good condition and have strong proliferation ability, which can improve the subsequent transfection efficiency. Replace with fresh medium 24 hours in advance to ensure that the cells are in a good nutritional environment, count the cell density, and adjust to an appropriate concentration for later use.

The second step is transfection operation. Using the liposome transfection method, mix the TPR-MET expression plasmid with liposomes in a certain proportion and incubate at room temperature for 15-20 minutes to form a stable complex. Then slowly add the complex to the prepared BaF3 cells, shake gently, place in a 37°C, 5% CO₂ incubator for 4-6 hours, and then replace with fresh medium to reduce the toxic effect of liposomes on the cells. If viral infection is adopted, add the virus to the cells at an appropriate MOI, and add polybrene to make its final concentration 8 μg/mL. Replace the medium after 12-24 hours. The screening stage after transfection or infection is crucial. Generally, 48-72 hours later, according to the resistance gene carried on the plasmid (such as puromycin resistance), add the corresponding screening drug to the medium. The initial screening concentration needs to be determined through pre-experiments, which should be the minimum concentration that can kill untransfected or uninfected cells. Continue screening for 1-2 weeks, during which the medium containing the screening drug is replaced every 2-3 days to gradually eliminate cells that have not successfully transferred into the plasmid and retain positive cells. Then, culture the cells in a medium without mouse IL3 growth factor to obtain cells with functional TPR-MET.

The final step is monoclonalization and identification. Perform limited dilution on the selected positive cells, inoculate them into 96-well plates, and culture until monoclonal cell clusters are formed. Select monoclonal cells for expansion culture, use Western blot to detect the expression level of TPR-MET protein, RT-PCR to verify the transcription of the target gene, and detect the sensitivity of the cells to MET inhibitors through cell proliferation experiments to ensure that the constructed cell line stably expresses TPR-MET and has corresponding biological functions.

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