GO:0031929 TOR signaling: Nutrient-Sensing Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0031929 TOR signaling describes the molecular signaling cascade mediated by TOR (Target of rapamycin) serine/threonine kinases, which belong to the phosphoinositide 3-kinase related kinase (PIKK) family.
• TOR kinases integrate nutrient availability and growth factor cues to control cell growth, proliferation, metabolism, and autophagy.
• TOR functions in two distinct multiprotein complexes, TORC1 and TORC2, which have separate substrates and biological outputs.
• The pathway is conserved from yeast and fungi to plants and humans, making model organisms valuable for mechanistic studies.
• Dysregulated TOR signaling is implicated in cancer, metabolic disorders, neurodegeneration, and aging.
• CRISPR-based knockout, point mutation, knock-in, and overexpression models enable causal dissection of TOR pathway genes.
Description
TOR signaling (GO:0031929) is the series of molecular signals mediated by TOR (Target of rapamycin) proteins, which are serine/threonine kinases of the phosphoinositide 3-kinase related kinase (PIKK) family that respond to nutrient availability or growth factors. This pathway is a central hub that coordinates cell growth, proliferation, metabolism, and survival with environmental cues. Because TOR signaling is conserved across eukaryotes, it has been studied extensively in yeast, fungi, plants, and mammals, revealing both shared and organism-specific features. In humans, the mTOR kinase nucleates two complexes, mTORC1 and mTORC2, which phosphorylate distinct substrates to control anabolic and catabolic processes. Dysregulation of TOR signaling contributes to cancer, metabolic disease, and aging, making it a major therapeutic target. Understanding the precise molecular steps, key genes, and regulatory inputs of TOR signaling is therefore essential for basic and translational research.
TOR signaling At A Glance
| GO ID | GO:0031929 |
|---|---|
| GO term | TOR signaling |
| Ontology | biological_process |
| Synonym | target of rapamycin signaling pathway; TOR signaling cascade; TOR signal transduction |
| Major function | Serine/threonine kinase signaling in response to nutrients and growth factors to control cell growth and metabolism |
| Key complexes | TORC1 and TORC2 |
| Conservation | Present in yeast, fungi, plants, and mammals |
| Major upstream inputs | Amino acids, glucose, growth factors, energy status |
| Major downstream outputs | Protein synthesis, autophagy, lipid synthesis, ribosome biogenesis |
What Is GO:0031929?
TOR signaling (GO:0031929) is defined as the series of molecular signals mediated by TOR (Target of rapamycin) proteins, members of the phosphoinositide (PI) 3-kinase related kinase (PIKK) family that act as serine/threonine kinases in response to nutrient availability or growth factors. In practice, this term encompasses the upstream sensing of nutrients and growth factors, the activation of TOR kinase within TORC1 and TORC2 complexes, and the downstream phosphorylation of effector proteins that reprogram transcription, translation, metabolism, and autophagy.
Why Is TOR signaling Important in Cell Biology?
TOR signaling is important because it serves as a master integrator of nutrient and growth factor signals that determine whether a cell grows, divides, or enters a quiescent state. Its dysregulation is directly linked to major human diseases, including cancer, where hyperactive mTOR promotes uncontrolled proliferation and survival. In plants and fungi, TOR signaling controls photosynthesis, differentiation, and stress responses, affecting agriculture and biotechnology. Because TOR signaling is central to so many processes, it is a prime target for pharmacological and genetic interventions.
• Controls cell growth and proliferation in response to nutrients and growth factors.
• Regulates protein synthesis, autophagy, and lipid metabolism.
• Hyperactive mTOR signaling is common in many cancers.
• mTOR inhibitors are used clinically in cancer and transplantation.
• TOR signaling modulates aging and age-related diseases.
• In plants, TOR signaling influences photosynthesis and nutrient use.
• In fungi, TOR controls differentiation and virulence.
• TORC2 regulates cytoskeletal organization and cell survival.
• The pathway is highly conserved, enabling cross-species studies.
• CRISPR screens can identify novel TOR pathway components.
What Happens During TOR signaling?
Nutrient and Growth Factor Sensing
In simple terms: The cell first checks whether nutrients and growth signals are available.
TOR signaling begins with the sensing of nutrient availability and growth factors. Amino acids, glucose, and energy status are detected by upstream sensors that converge on the TOR kinase complexes. Growth factors activate PI3K/AKT signaling, which in turn phosphorylates and inhibits TSC2, relieving inhibition of the small GTPase Rheb and allowing TORC1 activation. This integration ensures that TOR signaling is only active when conditions favor growth.
Activation of TORC1 and TORC2
In simple terms: The TOR kinase turns on two different molecular machines, TORC1 and TORC2.
TOR exists in two structurally and functionally distinct complexes: TORC1 and TORC2. TORC1 is acutely sensitive to rapamycin and nutrients, and it phosphorylates substrates such as S6K1 and 4E-BP1 to promote translation and inhibit autophagy. TORC2 is rapamycin-insensitive and phosphorylates AKT and PKC to regulate cytoskeletal dynamics and cell survival. The assembly and localization of these complexes are tightly controlled by accessory proteins.
Downstream Effector Phosphorylation
In simple terms: Once active, TOR adds phosphate groups to target proteins that switch cell processes on or off.
Activated TORC1 phosphorylates downstream effectors including S6K1 and 4E-BP1, leading to increased cap-dependent translation and ribosome biogenesis. It also phosphorylates ULK1 and ATG13 to suppress autophagy under nutrient-rich conditions. TORC2 phosphorylates AKT at Ser473, contributing to full AKT activation and downstream survival signaling. These phosphorylation events reprogram gene expression and metabolism.
Feedback Regulation and Crosstalk
In simple terms: The pathway has built-in brakes and cross-talk with other signals.
TOR signaling is subject to negative feedback loops; for example, S6K1 phosphorylates IRS-1 to dampen PI3K/AKT signaling. This crosstalk prevents excessive pathway activation and integrates inputs from multiple signaling networks. Dysregulation of these feedback mechanisms can contribute to disease.
Key Genes Involved in GO:0031929 TOR signaling
The following genes and proteins are core components or regulators of TOR signaling (GO:0031929) and are frequently studied using genetic and pharmacological approaches.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MTOR | Serine/threonine kinase catalytic subunit of TORC1 and TORC2 | Central target for cancer and metabolic research |
| RPTOR | Scaffold protein of TORC1, essential for substrate recruitment | Knockout studies define TORC1-specific functions |
| RICTOR | Scaffold protein of TORC2, required for AKT Ser473 phosphorylation | Key for dissecting TORC2 biology |
| MLST8 | Common subunit of both TORC1 and TORC2 | Structural and functional studies |
| DEPTOR | Endogenous inhibitor of mTOR | Regulation of mTOR activity |
| AKT1 | Upstream activator and downstream substrate of TORC2 | Cancer signaling research |
| TSC1 | Tumor suppressor, inhibits Rheb to suppress TORC1 | Hamartoma syndromes and cancer |
| TSC2 | Tumor suppressor, partner of TSC1 | Tuberous sclerosis complex research |
| RHEB | Small GTPase activator of TORC1 | Growth control studies |
| RPS6KB1 | S6K1, downstream effector of TORC1 | Translation and metabolism research |
| EIF4EBP1 | 4E-BP1, downstream effector of TORC1 | Translation control studies |
| ULK1 | Autophagy initiator inhibited by TORC1 | Autophagy research |
| ATG13 | Autophagy component phosphorylated by TORC1 | Autophagy regulation |
| PIK3CA | PI3K catalytic subunit upstream of AKT/mTOR | Cancer genomics |
| PTEN | Lipid phosphatase that opposes PI3K signaling | Tumor suppressor studies |
| STK11 | LKB1 kinase that activates AMPK to inhibit mTOR | Metabolic and cancer research |
| PRKAA1 | AMPK catalytic subunit, energy sensor inhibiting TORC1 | Energy stress studies |
How Is TOR signaling Regulated?
TOR signaling is regulated by a complex network of upstream inputs and feedback loops. Nutrient availability, particularly amino acids and glucose, is sensed by mechanisms that converge on TORC1. Growth factors activate PI3K/AKT, which inhibits TSC1/TSC2 and activates Rheb, leading to TORC1 activation. Energy stress activates AMPK, which phosphorylates TSC2 and Raptor to inhibit TORC1. TORC2 is regulated by growth factor signals and interacts with the cytoskeleton. Negative feedback from S6K1 to IRS-1 modulates PI3K/AKT activity. These regulatory layers ensure appropriate cellular responses to changing conditions.
TOR signaling and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MTOR | Cancer, metabolic disorders | Kinase-dead or constitutively active knock-in |
| TSC1 | Tuberous sclerosis complex | Knockout mouse or cell lines |
| TSC2 | Tuberous sclerosis complex | Knockout organoids |
| PTEN | Cancer predisposition | Conditional knockout |
| PIK3CA | Breast and other cancers | Point mutation knock-in |
Cancer
Hyperactivation of TOR signaling is a hallmark of many cancers. Mutations in upstream regulators such as PIK3CA, PTEN, and TSC1/2 lead to constitutive mTORC1 activity, promoting proliferation and survival. mTOR inhibitors, including rapamycin analogs, are used in the clinic for certain cancers, though resistance mechanisms exist. Targeting TOR signaling remains a major therapeutic strategy.
Metabolic Disorders and Aging
Dysregulated TOR signaling contributes to obesity, type 2 diabetes, and age-related diseases. mTOR integrates nutrient signals to control metabolism, and its chronic overactivation is associated with insulin resistance and aging. Caloric restriction and rapamycin extend lifespan in model organisms, highlighting the role of TOR in aging.
Neurological and Developmental Disorders
Mutations in TSC1 or TSC2 cause tuberous sclerosis complex, characterized by benign tumors and neurological symptoms due to mTORC1 hyperactivation. Dysregulated mTOR signaling has also been implicated in neurodegeneration and neurodevelopmental disorders.
From TOR signaling-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of MTOR abolish TORC1 and TORC2 signaling? | CRISPR knockout of MTOR in cell lines |
| What is the effect of a specific kinase-dead mutation in MTOR? | Point mutation knock-in |
| How does a disease-associated mutation in TSC1 affect TORC1 activity? | Knock-in of mutant TSC1 |
| Where is mTOR localized in cells? | Tagged knock-in with fluorescent protein |
| Does overexpression of RHEB activate TORC1? | Overexpression of wild-type or mutant RHEB |
| Which genes are essential for TOR signaling? | Genome-wide CRISPR knockout library screening |
How to Study the TOR signaling Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Western blot | Phosphorylation of TOR substrates | Assessing TORC1/TORC2 activity |
| Phosphoproteomics | Global phosphorylation changes | Identifying novel TOR substrates |
| RNA-seq | Transcriptional changes | Gene expression profiling upon TOR inhibition |
| Ribo-seq | Translation efficiency | mTOR-dependent translation control |
| CRISPR knockout | Gene function loss | Testing essentiality of TOR pathway genes |
| CRISPR knock-in | Precise mutation introduction | Modeling disease-associated variants |
| Live-cell imaging | Protein localization and dynamics | Visualizing TOR complex assembly |
Genetic Perturbation and Phenotyping
CRISPR-Cas9 knockout, point mutation, and knock-in approaches allow precise manipulation of TOR pathway genes to assess their roles in signaling and cellular phenotypes. Overexpression models can test gain-of-function effects.
Phosphoproteomics and Signaling Assays
Phosphoproteomics and immunoblotting for phosphorylated substrates such as S6K1, 4E-BP1, and AKT are standard methods to measure TORC1 and TORC2 activity.
Transcriptomics and Translation Profiling
RNA-seq and Ribo-seq reveal how TOR signaling rewires gene expression and translation, particularly for growth-related genes.
Imaging and Localization Studies
Fluorescence microscopy of tagged TOR components and substrates provides spatial and dynamic information about pathway activation.
How CRISPR Can Be Used to Study GO:0031929 TOR signaling
Knockout
CRISPR knockout of MTOR, RPTOR, or RICTOR completely abolishes TORC1 or TORC2 function, enabling researchers to dissect their specific contributions to cell growth and metabolism.
Point Mutation
Point mutations can be introduced into the MTOR kinase domain to create kinase-dead or constitutively active alleles, allowing precise structure-function studies.
Knock-in
Knock-in of disease-associated mutations in TSC1, TSC2, or PIK3CA creates isogenic models to study how these lesions affect TOR signaling and cellular behavior.
Overexpression
Overexpression of wild-type or mutant RHEB, AKT1, or other pathway components can activate TOR signaling and test gain-of-function phenotypes.
How EDITGENE Supports TOR signaling Research
Researchers studying TOR signaling-related genes often need to determine whether a candidate gene is causally involved in pathway regulation or disease. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models for such functional studies.
Contact EDITGENE today to design your custom CRISPR model for TOR signaling research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| RPS6KB2 Knockout HEK293 Cell Line | EDJ-KQ125 | Human | 6199 | Details Get a Quote |
| RPS6KB1 Knockout HEK293 Cell Line | EDJ-KQ398 | Human | 6198 | Details Get a Quote |
| AKT1 Knockout HEK293 Cell Line | EDJ-KQ446 | Human | 207 | Details Get a Quote |
| GATA3 Knockout HEK293 Cell Line | EDJ-KQ1017 | Human | 2625 | Details Get a Quote |
| EIF4EBP1 Knockout HEK293 Cell Line | EDJ-KQ1177 | Human | 1978 | Details Get a Quote |
| CCDC88A Knockout HEK293 Cell Line | EDJ-KQ2314 | Human | 55704 | Details Get a Quote |
| LARP1 Knockout HEK293 Cell Line | EDJ-KQ2425 | Human | 23367 | Details Get a Quote |
| EIF4EBP2 Knockout HEK293 Cell Line | EDJ-KQ4512 | Human | 1979 | Details Get a Quote |
| RHEBL1 Knockout HEK293 Cell Line | EDJ-KQ7917 | Human | 121268 | Details Get a Quote |
| DISC1 Knockout HEK293 Cell Line | EDJ-KQ8712 | Human | 27185 | Details Get a Quote |
| IGBP1C Knockout HEK293 Cell Line | EDJ-KQ13809 | Human | 645545 | Details Get a Quote |
| MEAK7 Knockout HEK293 Cell Line | EDJ-KQ14228 | Human | 57707 | Details Get a Quote |
| AKT1 Knockout HCT 116 Cell Line | EDJ-KQ18004 | Human | 207 | Details Get a Quote |
| AKT1 Knockout A-549 Cell Line | EDC90037 | Human | 207 | Details Get a Quote |
| GATA3 Knockout A-549 Cell Line | EDJ-KQ20091 | Human | 2625 | Details Get a Quote |
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Frequently Asked Questions About TOR signaling
What is TOR signaling?
TOR signaling (GO:0031929) is the series of molecular signals mediated by TOR kinases, which respond to nutrients and growth factors to control cell growth and metabolism.
What genes are involved in TOR signaling?
Key genes include MTOR, RPTOR, RICTOR, TSC1, TSC2, RHEB, AKT1, RPS6KB1, and EIF4EBP1.
What is the difference between TORC1 and TORC2?
TORC1 is rapamycin-sensitive and controls translation and autophagy, while TORC2 is rapamycin-insensitive and regulates AKT and cytoskeletal dynamics.
How is TOR signaling regulated?
It is regulated by nutrient availability, growth factors, energy status, and feedback loops involving AMPK, PI3K/AKT, and S6K1.
What diseases are associated with TOR signaling?
Cancer, tuberous sclerosis complex, metabolic disorders, and aging-related diseases are linked to dysregulated TOR signaling.
How can I study TOR signaling using CRISPR?
CRISPR knockout, point mutation, knock-in, and overexpression models allow precise manipulation of TOR pathway genes in cells.
What methods measure TOR activity?
Western blot for phosphorylated S6K1, 4E-BP1, and AKT, as well as phosphoproteomics and Ribo-seq, are commonly used.
Is TOR signaling conserved in plants?
Yes, TOR signaling is conserved in plants and regulates photosynthesis, nutrient sensing, and growth.
What are the clinical inhibitors of TOR signaling?
Rapamycin and its analogs (rapalogs) inhibit TORC1 and are used in cancer and transplantation.
How does EDITGENE support TOR signaling research?
EDITGENE provides CRISPR knockout, point mutation, knock-in, overexpression, library screening, and bioinformatics services for TOR pathway studies.
Conclusion
TOR signaling (GO:0031929) is a fundamental biological process that integrates nutrient and growth factor signals to control cell growth, metabolism, and survival. Its dysregulation underlies major human diseases, making it a prime target for therapeutic intervention. Advances in CRISPR-based genome editing and functional genomics continue to illuminate the precise molecular mechanisms and disease relevance of this pathway. EDITGENE's comprehensive services empower researchers to dissect TOR signaling with precision and efficiency.
References
- 1. Glaviano A et al.. 2023. PI3K/AKT/mTOR signaling transduction pathway and targeted therapies in cancer.. Mol Cancer 22(1):138 PMID: 37596643
- 2. Song Y et al.. 2021. Contributions of TOR Signaling on Photosynthesis.. Int J Mol Sci 22(16) PMID: 34445664
- 3. Dobrenel T et al.. 2016. TOR Signaling and Nutrient Sensing.. Annu Rev Plant Biol 67:261-85 PMID: 26905651
- 4. Liu GY et al.. 2020. mTOR at the nexus of nutrition, growth, ageing and disease.. Nat Rev Mol Cell Biol 21(4):183-203 PMID: 31937935
- 7. Cybulski N et al.. 2009. TOR complex 2: a signaling pathway of its own.. Trends Biochem Sci 34(12):620-7 PMID: 19875293
- 8. Rohde JR et al.. 2004. Nutrient signaling through TOR kinases controls gene expression and cellular differentiation in fungi.. Curr Top Microbiol Immunol 279:53-72 PMID: 14560951
