ras-mapk

RAS–RAF–MEK–ERK MAPK signaling pathway

The RAS–MAPK cascade (also called the ERK pathway) is the canonical mitogenic signaling route that transduces extracellular growth signals — from receptor tyrosine kinases (RTKs) such as EGFR, FGFR, and PDGFR — through the small GTPase RAS, the RAF family kinases, dual-specificity kinases MEK1/2 (MAP2K1/2), and finally ERK1/2 (MAPK3/MAPK1) to nuclear transcription factors (ELK1, FOS, MYC) that drive cell proliferation, survival, and differentiation.

In the context of aging, the pathway occupies a pivotal dual role: physiological RAS-MAPK signaling drives growth and tissue maintenance, while oncogenic or hyperactivated RAS-MAPK is a primary trigger of oncogene-induced senescence (OIS) — a tumor-suppressive program that underlies cellular senescence accumulation in aged tissues. Pharmacological attenuation of ERK output (e.g., with the MEK inhibitor trametinib) extends lifespan in Drosophila, making this pathway a qualified longevity drug target.

Naming note: This page is the canonical [[ras-mapk]] wikilink target — it covers the pathway. Individual component protein pages (RAS GTPases, RAF kinases, MEK1/2, ERK1/2) are implicit stubs until seeded; link via [[ras]], [[raf]], [[mek]], [[erk1-2]]. The grb2 adaptor protein has a dedicated seeded page.

Cascade architecture

The canonical four-tier kinase cascade:

RTK (EGFR, FGFR, IGF1R, PDGFR,...) — ligand-activated → autophosphorylation
  ↓  [[grb2]] (SH2 domain binds pY on RTK)
  ↓  [[sos1]] (GEF, recruited by GRB2 SH3 domain)
  ↓  RAS (HRAS / KRAS / NRAS): GDP → GTP exchange (activated)
  ↓  RAF (BRAF / CRAF / ARAF): RAS:GTP recruits RAF to membrane; dimerization → activation
  ↓  MEK1/2 (MAP2K1/2): phosphorylated by RAF on Ser218/Ser222 (MEK1) → active dual-specificity kinase
  ↓  ERK1/2 (MAPK3/MAPK1): phosphorylated by MEK on Thr202/Tyr204 (ERK1), Thr185/Tyr187 (ERK2)
  ↓  Nuclear targets: ELK1, FOS, MYC, RSK1/2, MNK1/2 → proliferation, survival, differentiation output

The step from RAS to RAF is the critical regulatory switch: RAS·GTP physically recruits RAF to the plasma membrane, enabling dimerization-driven RAF trans-autophosphorylation and full activation. ERK1 and ERK2 are >85% identical in catalytic domain and largely functionally redundant, though isoform-specific functions in development and possibly aging have been proposed ¹. needs-replication (ERK1 vs ERK2 isoform-specific aging roles)

RAS family

GTPase	Gene	Key oncogenic codons	Predominant cancer context	Aging relevance
HRAS	HRAS	G12V, G12S, Q61L	Bladder, skin carcinomas	OIS prototype (Serrano 1997) 2
KRAS	KRAS	G12C, G12D, G12V, Q61H	Lung, colorectal, pancreatic	Most frequently mutated RAS; KRAS-G12C inhibitor sotorasib FDA-approved 2021
NRAS	NRAS	Q61K, Q61R	Melanoma, AML	Clonal hematopoiesis-associated NRAS mutations accumulate with age

All three are ~189 aa GTPases; oncogenic mutations impair intrinsic GTPase activity, locking RAS in the GTP-bound (active) state and driving constitutive downstream signaling. GAPs (NF1/neurofibromin, RASA1) accelerate GTP hydrolysis normally and are tumor suppressors ¹.

Upstream activators

Beyond RTKs, RAS-MAPK receives mitogenic inputs from:

• Insulin signaling — IGF1R → IRS-1 → GRB2/SOS1 → RAS; and separately IGF1R → PI3K → PI3K-AKT (parallel arm). Both RTK classes converge on GRB2/SOS1.
• GPCRs — via βγ subunits activating SRC, which transactivates RTKs, or directly via RAS-GEFs (RASGRP1/2).
• Integrins — via FAK/SRC → GRB2/SOS1 → RAS; contributes to contact-dependent growth regulation.
• Cytokines (EGF, FGF, PDGF, NGF, HGF) — via cognate RTKs.

Negative feedback loops

Sustained ERK activity triggers at least four negative feedback circuits that attenuate pathway output — essential for ensuring transient mitogenic pulses rather than chronic growth signaling ³:

1. ERK → SOS1 phosphorylation — ERK directly phosphorylates SOS1 on multiple sites, reducing GRB2 binding affinity and cytosol retention → diminished RAS-GEF activity. This is the most proximal (fastest) feedback.
2. ERK → RAF phosphorylation — ERK and RSK phosphorylate CRAF on Ser289/Ser296/Ser301 → CRAF inactivation and dissociation from RAS:GTP.
3. SPRY proteins — Sprouty 1/2/4 are ERK-transcriptional targets; they act as decoy substrates for GRB2, competing with SOS1 for GRB2 SH3 binding and sequestering RTK-proximal adaptor complexes.
4. DUSPs / MKPs — Dual-specificity phosphatases (DUSP6/MKP-3, DUSP1/MKP-1, DUSP4/MKP-2) are ERK-induced transcriptional targets that dephosphorylate both pThr and pTyr on ERK1/2, directly terminating kinase activity. DUSP6 is cytoplasmic and ERK1/2-selective; DUSP1 is nuclear and stress-activated ³.

Failure of these feedback mechanisms — due to oncogenic RAS mutations, receptor overexpression, or DUSP/SPRY loss-of-function — produces chronic ERK hyperactivation that paradoxically arrests proliferation via OIS rather than driving it (see below).

Cross-talk with other pathways

Interaction	Mechanism	Functional consequence
RAS → PI3K-AKT	RAS:GTP directly binds PI3Kγ/δ p110 catalytic subunit	Parallel survival signaling; explains incomplete efficacy of single-agent MAPK inhibitors
ERK → TSC2 → mTORC1	ERK phosphorylates TSC2 (inhibitory), relieving mTORC1 brake	Nutrient-sensing cross-activation; MAPK-driven mTOR promotes anabolic growth
S6K1 → IRS-1 (negative feedback via mTOR)	mTORC1/S6K1 phosphorylates IRS-1 Ser636, reducing PI3K/RAS input	Reduces IGF-1-driven RAS activation; connects MAPK, PI3K, and mTOR in a regulatory triangle
AKT → CRAF	AKT phosphorylates CRAF Ser259 → 14-3-3 binding → CRAF cytosolic sequestration	PI3K-AKT cross-inhibits CRAF; partially explains tissue-specific RAS output
ERK → NF-κB	RSK2 (ERK substrate) phosphorylates IKKα	MAPK couples mitogenic signals to inflammatory gene programs; relevant to inflammaging

Aging biology

Oncogene-induced senescence (OIS)

Hyperactivated RAS-MAPK is the founding trigger of oncogene-induced senescence (OIS). Serrano et al. 1997 demonstrated that expression of oncogenic HRAS-G12V in normal human diploid fibroblasts (IMR90) induced irreversible growth arrest — not transformation — accompanied by accumulation of p53 and p16INK4a ². This was the seminal demonstration that oncogene activation in cells with intact tumor-suppressor circuitry causes senescence rather than proliferation.

The mechanistic sequence: oncogenic RAS → ERK hyperactivation → p16INK4a↑ → CDK4/6 inhibition → RB hypophosphorylation → E2F repression → G1 arrest; and in parallel RAS → p53↑ → p21↑ → CDK2 inhibition → reinforcing arrest. The two arms are induced independently (p53 levels increase even in p16⁻/⁻ MEFs; p16 levels increase in p53⁻/⁻ MEFs). Species-specific escape requirement: in rodent MEFs and REF52 cells, disruption of either p53 alone OR the p16/Rb pathway alone is sufficient to prevent RAS-induced arrest and permit transformation. In primary human fibroblasts (IMR90, WI38), disruption of p53 alone or the p16/Rb pathway alone is NOT sufficient to bypass arrest — only combined disruption of both (as achieved by adenovirus E1A) circumvents the block. This species difference underlies the difficulty of immortalizing primary human fibroblasts ².

Extrapolation table — OIS:

Dimension	Status
Pathway conserved in humans?	yes
Phenotype conserved in humans?	yes
Replicated in humans?	yes

OIS is well-documented in human fibroblasts, melanocytes, and benign nevi (which harbor BRAF-V600E but are stably senescent). The pathway → p16/p53 dual-arm mechanism is conserved across mammalian species.

RASopathies and accelerated aging

Germline gain-of-function RAS-MAPK mutations cause RASopathies (Noonan syndrome, Costello syndrome, cardio-facio-cutaneous syndrome) — developmental syndromes featuring premature aging phenotypes including short stature, facial dysmorphism, cardiac hypertrophy, and cognitive deficits. These provide human genetic evidence that chronic RAS-MAPK hyperactivation drives tissue deterioration resembling accelerated aging, consistent with OIS-driven senescence accumulation. needs-replication — no systematic comparison of senescent cell burden in RASopathy tissues vs. age-matched controls has been published.

Trametinib extends lifespan in Drosophila

Slack et al. 2015 (Cell) showed that the MEK inhibitor trametinib (an FDA-approved oncology drug) extended median lifespan in adult Drosophila melanogaster females in a dose-dependent manner: +8% at 1.56 µM (p = 2.65 × 10⁻⁴) and +12% at 15.6 µM (p = 1.92 × 10⁻¹⁰) ⁴. The longevity effect was mediated by attenuation of RAS-ERK-ETS transcriptional output through the ETS-family transcription factor Aop (Anterior open) — a transcriptional repressor that is de-repressed when Erk activity is reduced, and is both necessary and sufficient for the lifespan extension downstream of Ras inhibition. Aop is the Drosophila ortholog of mammalian Etv6/Tel. The ETS activator Pointed (Pnt) counteracts Aop and its overexpression blocks longevity; the paper identifies Aop (not Pointed) as the key pro-longevity effector. The effect was independent of stem-cell proliferation changes in the gut. needs-human-replication

Extrapolation table — trametinib lifespan extension:

Dimension	Status
Pathway conserved in humans?	partial (ERK-ETS axis conserved; ETS targets differ)
Phenotype conserved in humans?	unknown
Replicated in humans?	no

The Drosophila result has not been replicated in mice or humans. Mechanistic extrapolation is complicated by: (a) Drosophila ETS targets differ from mammalian ETS targets in the context of aging; (b) trametinib at oncology doses causes substantial toxicity in humans (dermatitis, retinal events, cardiomyopathy); (c) optimal geroprotective dose in any mammal is not defined. dose-response-unclear needs-human-replication

Age-related accumulation of RAS pathway somatic mutations

Clonal hematopoiesis of indeterminate potential (CHIP) is enriched for mutations in RAS pathway genes (NRAS, KRAS, CBL, PTPN11/SHP2), suggesting that RAS-MAPK-activating mutations confer a proliferative advantage to hematopoietic stem cells during aging-driven stem cell competition. This connects RAS-MAPK to stem cell exhaustion via a clonal selection mechanism. unsourced — dedicated citation needed for CHIP-RAS mutation frequency; link to CHIP literature when a page is seeded.

Pharmacology

Inhibitor class	Examples	Target	FDA status	Aging context
KRAS-G12C inhibitor	Sotorasib (AMG 510), adagrasib (MRTX849)	KRAS-G12C (covalent)	Approved (NSCLC, 2021/2022)	Oncology only; aging application not explored
BRAF-V600E inhibitor	Vemurafenib, dabrafenib	BRAF-V600E (ATP-competitive)	Approved (melanoma, 2011/2012)	Combined with MEK inhibitors; OIS-related
MEK1/2 inhibitor	Trametinib, cobimetinib, binimetinib	MEK1/2 (allosteric)	Approved (melanoma, NSCLC, 2013–2018)	Trametinib extends Drosophila median lifespan +8% (1.56 µM) to +12% (15.6 µM) via Aop ETS TF 4
ERK1/2 inhibitor	Ulixertinib (BVD-523)	ERK1/2 (ATP-competitive)	Phase 1/2 (oncology)	Overcomes paradoxical ERK re-activation from RAF/MEK inhibitors
SOS1 inhibitor	BI-3406, BI 1701963	SOS1 (RAS-GEF)	Phase 1/2 (KRAS-mutant cancers)	Disrupts GRB2/SOS1/RAS nexus; in combination trials
Pan-RAS inhibitor	RMC-6236 (RAS(ON) inhibitor)	RAS-GTP (multiple isoforms)	Phase 1	Next-generation approach for KRAS-G12X, NRAS, HRAS

No RAS-MAPK inhibitor is currently being evaluated in an aging or geroprotection context in humans. Clinical use is restricted to oncology indications. needs-human-replication

Limitations and gaps

• No human geroprotection trials for RAS-MAPK inhibitors. The Slack 2015 Drosophila trametinib result is the strongest longevity-specific data, but has not been tested in mammalian aging models at sub-oncology doses. needs-human-replication
• OIS vs. chronic low-level activation: the aging-relevant mode of RAS-MAPK activation (sporadic somatic mutations + paracrine RTK signaling from SASP) is quantitatively different from the acute oncogenic HRAS-G12V overexpression used in Serrano 1997; whether the same p16/p53 mechanisms mediate senescence in aged tissues at low-level MAPK activation is less established. needs-replication
• BRAF paradox: CRAF/BRAF inhibitors at low doses cause paradoxical ERK activation in RAS-wild-type cells (via dimerization-driven transactivation of the uninhibited RAF partner); this complicates use as aging interventions in cells without oncogenic RAS.
• Isoform specificity: BRAF vs. CRAF vs. ARAF have tissue-specific expression and substrate preferences; the aging-relevant RAF isoform is not defined. unsourced
• WikiPathways ID WP4223 listed in frontmatter — identity flagged for verification; the canonical MAPK/ERK pathway WP ID varies by curation version. needs-canonical-id (WikiPathways ID)

Cross-references

• grb2 — adaptor protein; bridges pY-RTK to SOS1; seeded page
• sos1 — RAS-GEF; implicit stub
• ras — RAS GTPase family (HRAS/KRAS/NRAS); implicit stub
• raf — RAF kinase family (BRAF/CRAF/ARAF); implicit stub
• mek — MEK1/2 (MAP2K1/2); implicit stub
• erk1-2 — ERK1/ERK2 (MAPK3/MAPK1); implicit stub
• egfr — upstream RTK; implicit stub
• fgfr1 — upstream RTK; implicit stub
• cellular-senescence — downstream hallmark (OIS); seeded hallmark page
• p16-rb-pathway — senescence effector arm; seeded pathway page
• p53 — senescence effector arm; seeded protein page
• p21 — senescence effector arm; seeded protein page
• pi3k-akt-pathway — parallel RAS effector arm; seeded pathway page
• insulin-igf1 — upstream growth factor; seeded pathway page
• mtor — downstream cross-talk via ERK→TSC2; seeded pathway page
• nf-kb — inflammatory cross-talk via RSK2→IKKα; seeded pathway page
• chronic-inflammation — downstream inflammaging connection; seeded hallmark page
• deregulated-nutrient-sensing — hallmark; seeded hallmark page
• stem-cell-exhaustion — CHIP-RAS connection; seeded hallmark page

Footnotes

Footnotes

1. doi:10.1016/j.phrs.2012.04.005 · Roskoski R Jr · Pharmacological Research 2012 · review · model: human ERK1/2 biochemistry, crystallographic + kinetic analysis · covers structure, activation mechanism, substrate specificity, 150+ inhibitors; cited >1,600 times · note: closed-access, no local PDF ↩ ↩²

2. doi:10.1016/s0092-8674(00)81902-9 · Serrano M, Lin AW, McCurrach ME, Beach D, Lowe SW · Cell 1997 · in-vitro + in-vivo · n=IMR90 human diploid fibroblasts (in vitro); nude mouse xenograft (in vivo) · model: normal human fibroblasts expressing oncogenic HRAS-G12V; also mouse embryo fibroblasts · p16INK4a and p53 both required for stable OIS; loss of either allows escape to transformation · local PDF: ↩ ↩² ↩³

3. doi:10.1007/s00018-016-2297-8 · Lake D, Corrêa SAL, Müller J · Cell Mol Life Sci 2016 · review · model: ERK1/2 negative feedback circuits (SOS1, RAF, SPRY, DUSP families) · covers kinetics and molecular mechanisms of each feedback arm; cited >490 times · note: OA hybrid; PDF pending download ↩ ↩²

4. doi:10.1016/j.cell.2015.06.023 · Slack C, Alic N, Foley A, Cabecinha M, Hoddinott MP, Partridge L · Cell 2015 · in-vivo · model: Drosophila melanogaster · trametinib at ~1 µM diet concentration extended median lifespan ~8%; effect mediated via RAS-ERK-ETS axis (ETS transcription factor Pointed); did not extend additively with dietary restriction; no mammalian validation · note: OA hybrid; PDF pending download ↩ ↩²