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Research Report: Functional Annotation of rat Mapk1 (ERK2) — UniProt P63086

1. Target verification (critical disambiguation)

A native rat inner medullary collecting duct (IMCD) phosphoproteomics study explicitly maps UniProt P63086 to Mapk1 (Mitogen‑activated protein kinase 1; ERK2), and distinguishes it from Mapk3/ERK1 using closely related ERK-family TEY-motif phosphopeptides. In this dataset, Mapk1/ERK2 carries TEY-region phosphorylation at T179 and Y185 (rat numbering) (chou2025phosphoproteomicresponseto pages 34-40, chou2025phosphoproteomicresponseto pages 30-34).

2. Key concepts and definitions (current understanding)

2.1 What Mapk1/ERK2 is

ERK1/2 (MAPK3/MAPK1) are described as terminal kinases in the canonical RAS→RAF→MEK→ERK cascade downstream of many membrane receptors, with outputs that include proliferation, differentiation, epithelial–mesenchymal transition (EMT), senescence, and cell death; these outcomes depend on signal strength, duration, context, and spatial localization (deschenessimard2023extracellularsignalregulatedkinases pages 1-2, deschenessimard2023extracellularsignalregulatedkinases pages 4-6).

2.2 Signal decoding: amplitude, duration, and location

A 2023 review emphasizes that ERK signaling “fates” are shaped by activation intensity and duration (“Goldilocks”/non‑monotonic behavior), and by where ERK activity occurs within the cell (e.g., plasma membrane vs Golgi, cytosolic vs nuclear pools), with transcriptional outcomes often requiring nuclear ERK (deschenessimard2023extracellularsignalregulatedkinases pages 1-2, deschenessimard2023extracellularsignalregulatedkinases pages 4-6, deschenessimard2023extracellularsignalregulatedkinases pages 6-8).

2.3 Localization control as a core regulatory principle

The same review highlights nuclear import/export and cytoplasmic sequestration as biologically important control points. In particular, PEA‑15 binds ERK and (i) contains a nuclear export sequence, and (ii) can prevent nuclear accumulation of ERK; disabling PEA‑15 increases proliferation, while blocking ERK nuclear translocation reduces melanoma cell survival (deschenessimard2023extracellularsignalregulatedkinases pages 4-6, deschenessimard2023extracellularsignalregulatedkinases pages 2-4, deschenessimard2023extracellularsignalregulatedkinases pages 13-14). Consistently, the rat IMCD dataset detects PEA15 as an ERK-binding regulator in an EGF-driven ERK network (chou2025phosphoproteomicresponseto pages 45-46, chou2025phosphoproteomicresponseto pages 18-21).

3. Biochemical function: reaction type, activation mechanism, and substrate specificity

3.1 Enzymatic activity in cell signaling (what reaction is performed)

In the rat IMCD phosphoproteomic resource, ERK family proteins are annotated under a serine/threonine kinase domain category (“Ser/Thr_kinase_AS”), consistent with the expected enzymatic class of MAPKs (chou2025phosphoproteomicresponseto pages 30-34, chou2025phosphoproteomicresponseto pages 34-40). (Note: the explicit EC number 2.7.11.24 was not present in the retrieved full-text excerpts and therefore cannot be directly cited from them.)

3.2 Activation mechanism: TEY motif phosphorylation and MEK→ERK axis

Dual phosphorylation in the TEY activation segment region is directly observed for rat Mapk1/ERK2:
- Mapk1 phosphopeptide sequence includes pTEpY (e.g., VADPDHDHTGFLpTEpYVATR) (chou2025phosphoproteomicresponseto pages 30-34).
- The rat dataset explicitly lists Mapk1 sites T179;Y185 and reports a quantitative EGF response (log2(EGF/Control)=0.354; P=0.083) (chou2025phosphoproteomicresponseto pages 34-40).

Upstream, the same rat IMCD network links Map2k2 (MEK2) activity to Mapk1 phosphorylation (“Mapk1 (T179;Y185)”), and concludes that EGF activates the canonical MAPK pathway in this native rat tissue context (chou2025phosphoproteomicresponseto pages 43-45, chou2025phosphoproteomicresponseto pages 46-48).

3.3 Substrate specificity (consensus motif evidence)

A 2024 Cell Reports mechanistic study explicitly states that ERK1/2 substrates contain a Ser/Thr‑Pro consensus (“Ser/Thr‑Pro”), and it uses an antibody recognizing the phosphorylated Ser/Thr‑Pro “ERK1/2 substrate signature” to test candidate phosphorylation sites (becker2024erk12interactionwith pages 5-6). This provides direct evidence for the commonly used ERK substrate motif at the experimental/assay level.

3.4 Numbering differences across species/constructs (important for annotation)

The 2024 Cell Reports study provides explicit residue correspondences for the TEY activation loop between rat and human ERK2 constructs, stating that rat ERK2 Thr183/Tyr185 correspond to human Thr185/Tyr187 (becker2024erk12interactionwith pages 5-6). Such differences matter when mapping sites across organisms and databases.

4. Biological processes, pathways, and cellular localization (rat-focused where possible)

4.1 Pathways in native rat tissue: EGFR→ERK signaling and downstream processes

In native rat IMCD cells stimulated with EGF, pathway enrichment confirms engagement of RAF–MEK–ERK signaling and also highlights translation-related regulation (chou2025phosphoproteomicresponseto pages 18-21). The dataset reports broad-scale phosphorylation remodeling (see quantitative section) and identifies enrichment terms including “nucleocytoplasmic transport” (chou2025phosphoproteomicresponseto pages 30-34), consistent with the importance of ERK localization dynamics.

4.2 Membrane-associated scaffolding and local signaling pools

The rat IMCD study reports that NHE1/Slc9a1 can act as a membrane scaffold for ERK2 and that “ERK2 phosphorylates NHE1,” with increased phosphorylation observed at Ser727 and Ser730 after EGF stimulation (chou2025phosphoproteomicresponseto pages 18-21). This supports a model in which ERK2 signaling is not purely nuclear, but also organized via membrane/cytoplasmic scaffolds.

4.3 Cytosol↔nucleus shuttling and sequestration (PEA‑15)

In the rat IMCD resource, PEA15 is presented as an ERK-binding regulator that can increase binding to ERKs and prevent their nuclear localization, consistent with the broader mechanistic consensus that localization is tightly controlled (chou2025phosphoproteomicresponseto pages 45-46). The 2023 review frames ERK nuclear translocation as necessary for growth factor-driven proliferation/DNA synthesis and discusses PEA‑15 as a key mediator of cytoplasmic sequestration and export (deschenessimard2023extracellularsignalregulatedkinases pages 4-6, deschenessimard2023extracellularsignalregulatedkinases pages 13-14).

5. Recent developments (prioritizing 2023–2024) and expert analysis

5.1 “Goldilocks” quantitative view of ERK output requirements

The 2023 review argues that ERK signaling can be non‑monotonic with respect to proliferation, and summarizes quantitative observations relevant to interpreting phospho‑ERK readouts in real systems:
- In colorectal cancer cells, phospho‑ERK was reported at <10% (deschenessimard2023extracellularsignalregulatedkinases pages 2-4).
- In “drug‑addicted” tumor cells, mass spectrometry reportedly found ~2–3% phospho‑ERK supporting proliferation (deschenessimard2023extracellularsignalregulatedkinases pages 2-4).
- The review further notes that achieving antiproliferative effects may require suppression of >85% of pathway output (deschenessimard2023extracellularsignalregulatedkinases pages 2-4).
These points collectively inform experimental design: small fractions of active ERK may be biologically sufficient, and bulk phospho‑ERK levels can be misleading without context.

5.2 New mechanistic biology: ERK functions beyond phosphorylation

A 2024 Cell Reports paper describes ERK1/2 forming a regulated interaction with DHPS affecting eIF5A deoxyhypusination, and provides quantitative binding evidence that metabolic state can tune this interaction:
- NAD lowers the DHPS–ERK2 interaction Kd by ~5‑fold, and NAD + spermidine further decreases Kd to ~1 μM (becker2024erk12interactionwith pages 5-6).
- Importantly for functional annotation, the same study demonstrates ERK1/2 can regulate protein interactions in ways that are not simply “ERK phosphorylates X”: they show “ERK1/2 do not phosphorylate DHPS” despite DHPS containing Ser/Thr‑Pro motifs, using multiple assays including an in vitro kinase assay with active TEY-phosphorylated ERK2 and an ATPγS analog (becker2024erk12interactionwith pages 5-6).

5.3 New therapeutic strategy class: targeting ERK protein–protein interactions (PPI)

A 2024 Nature Communications study reports a small molecule (EI‑52) that disrupts the ERK–MYD88 interaction via ERK’s docking region (DRS), with a key mechanistic distinction: EI‑52 does not reduce ERK phosphorylation and does not compromise phosphorylation of an ERK substrate (RSK), consistent with preserved ERK kinase activity (virard2024targetingerkmyd88interaction pages 4-5). Yet it causes “activated ERK” mislocalization (phospho‑ERK accumulation in cytoplasm after 6 h) and triggers an integrated stress response and apoptosis in transformed cells (virard2024targetingerkmyd88interaction pages 4-5, virard2024targetingerkmyd88interaction pages 10-11). This represents a real-world implementation of “functional rewiring” by targeting ERK interaction networks rather than ATP-site inhibition.

6. Current applications and real-world implementations

6.1 Rat-native signaling resources

The 2025 AJP Renal Physiology study provides a large-scale, native rat phosphoproteomic dataset and associated public resources (reported in the paper abstract): EGF-phospho database and network map resources are provided as a community data resource for signaling modeling in collecting duct cells (chou2025phosphoproteomicresponseto pages 30-34). Within the accessible excerpts, the dataset quantifies thousands of proteins and tens of thousands of phosphosites and directly observes Mapk1 TEY phosphorylation (chou2025phosphoproteomicresponseto pages 30-34, chou2025phosphoproteomicresponseto pages 34-40).

6.2 Oncology drug development: beyond ATP-competitive inhibition

The EI‑52 study includes in vivo and translational components: it reports EI‑52 anti-tumor activity in mice and activity in patient-derived tumor organoids/sections, while also reporting pharmacokinetic measures for intraperitoneal dosing (bioavailability and AUC) (virard2024targetingerkmyd88interaction pages 4-5, virard2024targetingerkmyd88interaction pages 10-11). This demonstrates an emerging “PPI-targeting” approach to ERK pathway intervention.

7. Quantitative data highlights from recent studies

7.1 Native rat IMCD EGF phosphoproteomics (resource-level statistics)

In rat IMCD suspensions treated with EGF, the study reports:
- 29,881 unique phosphorylation sites detected across 5,457 proteins (chou2025phosphoproteomicresponseto pages 30-34).
- Under stringent statistical selection, 135 sites increased and 119 sites decreased (chou2025phosphoproteomicresponseto pages 30-34).
- For site selection, the excerpt specifies thresholds P < 0.1 and |log2(EGF/Control)| > 0.3428 (chou2025phosphoproteomicresponseto pages 18-21).
- For Mapk1/ERK2 specifically (UniProt P63086), TEY-region phosphosites T179;Y185 have log2(EGF/Control)=0.354 with P=0.083 (chou2025phosphoproteomicresponseto pages 34-40).

7.2 Quantitative binding and pharmacology in 2024 mechanistic/therapeutic studies

• DHPS–ERK2 binding modulation: NAD lowers Kd ~5×; NAD+spermidine yields Kd ~1 μM (becker2024erk12interactionwith pages 5-6).
• EI‑52 cancer model metrics: LLC apoptosis IC50 = 4 μM; intraperitoneal PK reported as bioavailability 52.9% and AUC 1129 ng/mL/h (~3 μmol/L/h) (virard2024targetingerkmyd88interaction pages 4-5).

8. Evidence map table (for rapid functional annotation)

The following table consolidates identity, activation, localization, substrates/outputs, and key quantitative findings with dates and URLs.

Table: This table summarizes verified identity, activation, localization, representative outputs, quantitative findings, and recent mechanistic developments for rat Mapk1/ERK2 (UniProt P63086). It provides a compact evidence map for functional annotation with direct citation IDs, dates, and URLs.

9. Summary functional annotation (rat Mapk1 / ERK2; UniProt P63086)

Mapk1 encodes ERK2, a serine/threonine MAP kinase in the canonical RAS→RAF→MEK→ERK cascade. In rat-native tissue signaling (IMCD), ERK2 is activated downstream of EGF with dual TEY-region phosphorylation (T179/Y185) and connects to translation control nodes and membrane-associated scaffolding (NHE1/Slc9a1) while being subject to cytoplasmic sequestration and nucleo-cytoplasmic regulation (PEA‑15). Beyond canonical substrate phosphorylation, recent 2024 work expands ERK2 functional understanding to include regulated protein–protein interactions that can be tuned by cofactors (e.g., NAD effects on DHPS–ERK2 binding) and therapeutically perturbed via docking-region PPI inhibitors that alter ERK complex composition and localization without suppressing ERK phosphorylation (chou2025phosphoproteomicresponseto pages 34-40, chou2025phosphoproteomicresponseto pages 43-45, chou2025phosphoproteomicresponseto pages 18-21, chou2025phosphoproteomicresponseto pages 45-46, deschenessimard2023extracellularsignalregulatedkinases pages 4-6, becker2024erk12interactionwith pages 5-6, virard2024targetingerkmyd88interaction pages 4-5).

10. Notes on limitations of this tool-based literature extraction

• The provided excerpts did not contain a directly citable statement of the EC number (2.7.11.24) for ERK2/MAPK1; although this EC assignment is widely used in databases, it is not asserted here without direct excerpt support.
• Substrate specificity evidence here is limited to an explicit Ser/Thr‑Pro consensus statement and assay usage; more detailed docking-site consensus sequences (e.g., D‑site/DEF-site) were not present in the retrieved full-text excerpts and would require targeted retrieval of ERK substrate-recognition literature.

References

1. (chou2025phosphoproteomicresponseto pages 34-40): Chung-Lin Chou, Nipun U. Jayatissa, Elena T. Kichula, Shuo-Ming Ou, Kavee Limbutara, and Mark A. Knepper. Phosphoproteomic response to epidermal growth factor in native rat inner medullary collecting duct. Jan 2025. URL: https://doi.org/10.1152/ajprenal.00182.2024, doi:10.1152/ajprenal.00182.2024. This article has 0 citations and is from a peer-reviewed journal.

2. (chou2025phosphoproteomicresponseto pages 30-34): Chung-Lin Chou, Nipun U. Jayatissa, Elena T. Kichula, Shuo-Ming Ou, Kavee Limbutara, and Mark A. Knepper. Phosphoproteomic response to epidermal growth factor in native rat inner medullary collecting duct. Jan 2025. URL: https://doi.org/10.1152/ajprenal.00182.2024, doi:10.1152/ajprenal.00182.2024. This article has 0 citations and is from a peer-reviewed journal.

3. (deschenessimard2023extracellularsignalregulatedkinases pages 1-2): Xavier Deschênes-Simard, Mohan Malleshaiah, and Gerardo Ferbeyre. Extracellular signal-regulated kinases: one pathway, multiple fates. Cancers, 16:95, Dec 2023. URL: https://doi.org/10.3390/cancers16010095, doi:10.3390/cancers16010095. This article has 24 citations.

4. (deschenessimard2023extracellularsignalregulatedkinases pages 4-6): Xavier Deschênes-Simard, Mohan Malleshaiah, and Gerardo Ferbeyre. Extracellular signal-regulated kinases: one pathway, multiple fates. Cancers, 16:95, Dec 2023. URL: https://doi.org/10.3390/cancers16010095, doi:10.3390/cancers16010095. This article has 24 citations.

5. (deschenessimard2023extracellularsignalregulatedkinases pages 6-8): Xavier Deschênes-Simard, Mohan Malleshaiah, and Gerardo Ferbeyre. Extracellular signal-regulated kinases: one pathway, multiple fates. Cancers, 16:95, Dec 2023. URL: https://doi.org/10.3390/cancers16010095, doi:10.3390/cancers16010095. This article has 24 citations.

6. (deschenessimard2023extracellularsignalregulatedkinases pages 2-4): Xavier Deschênes-Simard, Mohan Malleshaiah, and Gerardo Ferbeyre. Extracellular signal-regulated kinases: one pathway, multiple fates. Cancers, 16:95, Dec 2023. URL: https://doi.org/10.3390/cancers16010095, doi:10.3390/cancers16010095. This article has 24 citations.

7. (deschenessimard2023extracellularsignalregulatedkinases pages 13-14): Xavier Deschênes-Simard, Mohan Malleshaiah, and Gerardo Ferbeyre. Extracellular signal-regulated kinases: one pathway, multiple fates. Cancers, 16:95, Dec 2023. URL: https://doi.org/10.3390/cancers16010095, doi:10.3390/cancers16010095. This article has 24 citations.

8. (chou2025phosphoproteomicresponseto pages 45-46): Chung-Lin Chou, Nipun U. Jayatissa, Elena T. Kichula, Shuo-Ming Ou, Kavee Limbutara, and Mark A. Knepper. Phosphoproteomic response to epidermal growth factor in native rat inner medullary collecting duct. Jan 2025. URL: https://doi.org/10.1152/ajprenal.00182.2024, doi:10.1152/ajprenal.00182.2024. This article has 0 citations and is from a peer-reviewed journal.

9. (chou2025phosphoproteomicresponseto pages 18-21): Chung-Lin Chou, Nipun U. Jayatissa, Elena T. Kichula, Shuo-Ming Ou, Kavee Limbutara, and Mark A. Knepper. Phosphoproteomic response to epidermal growth factor in native rat inner medullary collecting duct. Jan 2025. URL: https://doi.org/10.1152/ajprenal.00182.2024, doi:10.1152/ajprenal.00182.2024. This article has 0 citations and is from a peer-reviewed journal.

10. (chou2025phosphoproteomicresponseto pages 43-45): Chung-Lin Chou, Nipun U. Jayatissa, Elena T. Kichula, Shuo-Ming Ou, Kavee Limbutara, and Mark A. Knepper. Phosphoproteomic response to epidermal growth factor in native rat inner medullary collecting duct. Jan 2025. URL: https://doi.org/10.1152/ajprenal.00182.2024, doi:10.1152/ajprenal.00182.2024. This article has 0 citations and is from a peer-reviewed journal.

11. (chou2025phosphoproteomicresponseto pages 46-48): Chung-Lin Chou, Nipun U. Jayatissa, Elena T. Kichula, Shuo-Ming Ou, Kavee Limbutara, and Mark A. Knepper. Phosphoproteomic response to epidermal growth factor in native rat inner medullary collecting duct. Jan 2025. URL: https://doi.org/10.1152/ajprenal.00182.2024, doi:10.1152/ajprenal.00182.2024. This article has 0 citations and is from a peer-reviewed journal.

12. (becker2024erk12interactionwith pages 5-6): Andrew E. Becker, Paweł Kochanowski, Pui-Kei Wu, Elżbieta Wątor, Wenjing Chen, Koushik Guchhait, Artur P. Biela, Przemysław Grudnik, and Jong-In Park. Erk1/2 interaction with dhps regulates eif5a deoxyhypusination independently of erk kinase activity. Cell reports, 43:114831-114831, Oct 2024. URL: https://doi.org/10.1016/j.celrep.2024.114831, doi:10.1016/j.celrep.2024.114831. This article has 5 citations and is from a highest quality peer-reviewed journal.

13. (virard2024targetingerkmyd88interaction pages 4-5): François Virard, Stéphane Giraud, Mélanie Bonnet, Léa Magadoux, Laetitia Martin, Thuy Ha Pham, Najwa Skafi, Sophie Deneuve, Rita Frem, Bruno O. Villoutreix, Nawal Hajj Sleiman, Jonathan Reboulet, Samir Merabet, Vincent Chaptal, Cédric Chaveroux, Nader Hussein, Nicolas Aznar, Tanguy Fenouil, Isabelle Treilleux, Pierre Saintigny, Stéphane Ansieau, Serge Manié, Serge Lebecque, Toufic Renno, and Isabelle Coste. Targeting erk-myd88 interaction leads to erk dysregulation and immunogenic cancer cell death. Nature Communications, Aug 2024. URL: https://doi.org/10.1038/s41467-024-51275-z, doi:10.1038/s41467-024-51275-z. This article has 10 citations and is from a highest quality peer-reviewed journal.

14. (virard2024targetingerkmyd88interaction pages 10-11): François Virard, Stéphane Giraud, Mélanie Bonnet, Léa Magadoux, Laetitia Martin, Thuy Ha Pham, Najwa Skafi, Sophie Deneuve, Rita Frem, Bruno O. Villoutreix, Nawal Hajj Sleiman, Jonathan Reboulet, Samir Merabet, Vincent Chaptal, Cédric Chaveroux, Nader Hussein, Nicolas Aznar, Tanguy Fenouil, Isabelle Treilleux, Pierre Saintigny, Stéphane Ansieau, Serge Manié, Serge Lebecque, Toufic Renno, and Isabelle Coste. Targeting erk-myd88 interaction leads to erk dysregulation and immunogenic cancer cell death. Nature Communications, Aug 2024. URL: https://doi.org/10.1038/s41467-024-51275-z, doi:10.1038/s41467-024-51275-z. This article has 10 citations and is from a highest quality peer-reviewed journal.

15. (becker2024erk12interactionwith pages 6-8): Andrew E. Becker, Paweł Kochanowski, Pui-Kei Wu, Elżbieta Wątor, Wenjing Chen, Koushik Guchhait, Artur P. Biela, Przemysław Grudnik, and Jong-In Park. Erk1/2 interaction with dhps regulates eif5a deoxyhypusination independently of erk kinase activity. Cell reports, 43:114831-114831, Oct 2024. URL: https://doi.org/10.1016/j.celrep.2024.114831, doi:10.1016/j.celrep.2024.114831. This article has 5 citations and is from a highest quality peer-reviewed journal.

Artifacts

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Citations

1. chou2025phosphoproteomicresponseto pages 30-34
2. chou2025phosphoproteomicresponseto pages 34-40
3. chou2025phosphoproteomicresponseto pages 18-21
4. chou2025phosphoproteomicresponseto pages 45-46
5. deschenessimard2023extracellularsignalregulatedkinases pages 2-4
6. deschenessimard2023extracellularsignalregulatedkinases pages 1-2
7. deschenessimard2023extracellularsignalregulatedkinases pages 4-6
8. deschenessimard2023extracellularsignalregulatedkinases pages 6-8
9. deschenessimard2023extracellularsignalregulatedkinases pages 13-14
10. chou2025phosphoproteomicresponseto pages 43-45
11. chou2025phosphoproteomicresponseto pages 46-48
12. https://doi.org/10.1152/ajprenal.00182.2024
13. https://doi.org/10.1152/ajprenal.00182.2024;
14. https://doi.org/10.3390/cancers16010095
15. https://doi.org/10.1038/s41467-024-51275-z;
16. https://doi.org/10.1016/j.celrep.2024.114831
17. https://doi.org/10.1152/ajprenal.00182.2024,
18. https://doi.org/10.3390/cancers16010095,
19. https://doi.org/10.1016/j.celrep.2024.114831,
20. https://doi.org/10.1038/s41467-024-51275-z,