SQSTM1/p62 Protein

Overview

SQSTM1/p62 Protein
Symbol	SQSTM1
Full Name	SQSTM1/p62
Type	Protein
UniProt	Search UniProt
Associated Diseases	AD, ADH, ALI, ALS, ALZHEIMER
KG Connections	2520 edges

SQSTM1 (sequestosome-1), commonly called p62, is a multifunctional scaffold protein that couples ubiquitin tagging, autophagosome recruitment, and stress-response signaling.^{1p62/SQSTM1 binds directly to Atg8/LC3 to facilitate degradation of ubiquitinated protein aggregates by autophagy2007 · J Biol Chem · PMID 17580304Open reference}^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference} In neurodegeneration biology, p62 is best interpreted as a flux integrator: it accumulates when degradative systems fail, but it is also required for selective cargo capture and clearance when those systems work.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference} This dual role explains why p62 can appear protective in early stress adaptation yet still mark disease progression in advanced proteinopathy.

In neurons and glia, p62 participates in proteostasis triage across protein aggregation, oxidative stress, and inflammatory signaling axes.^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}^{5p62/SQSTM1 is a target gene for transcription factor NRF2 and creates a positive feedback loop by inducing antioxidant response element-driven gene transcription2010 · J Biol Chem · PMID 20452972Open reference} Mechanistically, it intersects with pathways central to amyotrophic lateral sclerosis (ALS), frontotemporal degeneration (FTD), tauopathies, and related disorders where autophagy-lysosome throughput is rate-limiting.^{6Autophagy and Neurodegeneration: Pathogenic Mechanisms and Therapeutic Opportunities2015 · Neuron · PMID 25914067Open reference}^{7Altered proteostasis in aging and neurodegenerative disease2018 · Int Neurourol J · PMID 30030024Open reference}

Domain Architecture And Functional Consequences

SQSTM1 is a modular protein with architecture that enables simultaneous signaling and cargo trafficking.

PB1 Domain: Oligomerization And Signal Platform

The N-terminal PB1 domain mediates p62 self-assembly and higher-order complex formation. Oligomerization supports cargo clustering and concentrates autophagy machinery around ubiquitinated substrates.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}

LIR Motif: LC3/GABARAP Coupling

The LC3-interacting region (LIR) directly binds Atg8-family proteins, functionally docking p62-cargo complexes to autophagosomal membranes.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}0 This step is required for efficient selective autophagy of ubiquitinated inclusions.

UBA Domain: Ubiquitin Chain Recognition

The C-terminal UBA domain binds polyubiquitin chains and enables cargo selection. Disease-associated changes in p62 function can impair this recognition-to-delivery step and produce apparent “cargo capture without clearance” states.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}1^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}2

KIR Region: KEAP1-NRF2 Redox Interface

A KEAP1-interacting region allows p62 to modulate NRF2 signaling. Under stress, p62 can sequester KEAP1 and enhance antioxidant transcription programs, creating feedback between proteostasis demand and redox defense.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}3^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}4

Core Mechanisms Relevant To Neurodegeneration

1. Selective Autophagy Of Ubiquitinated Cargo

p62 is a canonical selective autophagy receptor: it links ubiquitinated proteins to autophagosomes via LC3 binding.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}5 Experimental disruption of p62 pathways increases aggregate burden and destabilizes cellular quality control.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}6

2. Flux Sensing Versus Cargo Throughput

Static p62 abundance is not equivalent to increased autophagic activity. High p62 may indicate active adaptation or blocked degradation, depending on lysosomal throughput and LC3 flux context.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}7^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}8 For translational studies, p62 should therefore be interpreted with orthogonal flux measurements, not as a standalone endpoint.

3. Ubiquitylation/Phosphoregulation Of Receptor Activity

p62 function is dynamically tuned by post-translational modifications. Ubiquitylation can increase receptor activity for selective autophagy under ubiquitin stress, and phosphorylation-dependent regulation influences redox-signaling crosstalk and condensate behavior under stress.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}9^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}0^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}1

4. Proteostasis-Inflammation Coupling

By integrating stress-signaling inputs with degradative handling, p62 sits at a proteostasis-inflammation interface. In neurodegeneration, this coupling likely contributes to self-reinforcing loops between protein accumulation and tissue injury.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}2^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}3

Human Genetics And Disease Associations

ALS/FTD Spectrum

SQSTM1 variants have been reported in patients with FTD and FTD-ALS phenotypes.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}4^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}5 Functional follow-up studies support a mechanism where mutation-linked p62 dysregulation impairs selective autophagy and anti-oxidative stress buffering.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}6

From an evidence-quality perspective, SQSTM1 is a contributory risk/modifier axis in many cohorts rather than a single dominant driver in most sporadic disease. That distinction matters for trial design: pathway-stratified enrollment and mechanism-proximal endpoints are more defensible than broad unselected populations.

Interaction With TBK1-Centered Autophagy Networks

ALS-linked TBK1 perturbations can reduce p62 phosphorylation dynamics and alter downstream autophagic handling, including effects on pathogenic protein clearance pathways.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}7 This places SQSTM1 within a broader autophagy receptor-kinase network where upstream defects can phenocopy direct receptor dysfunction.

Tauopathy Context

Although SQSTM1 mutations are not primary monogenic causes of classic 4R-tau syndromes, p62 pathway behavior remains biologically relevant because tau aggregation and lysosomal insufficiency converge on selective-autophagy reserve.^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}8^{2p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding2011 · J Cell Biol · PMID 21220506Open reference}9 In this framework, p62 serves as a mechanistic bridge between aggregate burden and degradative capacity.

Translational And Biomarker Implications

Interpreting p62 In Preclinical And Clinical Studies

p62 should be modeled as a state variable, not a binary marker. Interpretation is strongest when combined with:

LC3-II dynamics and validated flux assays.^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}0^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}1
Insoluble/soluble cargo partitioning profiles.^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}2
Oxidative-stress response markers when KEAP1-NRF2 engagement is expected.^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}3^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}4
Disease-context readouts such as TDP-43/tau burden and neuroinflammatory metrics.^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}5^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}6

What A “Good” p62 Shift Looks Like

A therapeutic decrease in p62 can indicate improved clearance, but only if accompanied by evidence of restored substrate turnover. A decrease without cargo movement can also reflect reduced receptor competence. Conversely, a transient increase may occur during effective mobilization of stressed proteomes.

Patient-Selection Logic

Programs targeting p62-adjacent pathways are likely most actionable in cohorts with documented autophagy-lysosome stress signatures, ALS/FTD-related proteostasis phenotypes, or molecular evidence of receptor-kinase network disruption.^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}7^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}8^{3Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice2007 · Cell · PMID 18083104Open reference}9

Therapeutic Strategy Framing

Strategy A: Improve End-To-End Autophagy Throughput

Interventions should prioritize restoration of full cargo-to-lysosome flux, not isolated reduction of p62 signal intensity.^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}0^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}1

Strategy B: Rebalance Receptor Regulation

Targeting phosphorylation/ubiquitylation control points that tune p62 receptor activity may improve selective cargo handling in genetically sensitized contexts.^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}2^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}3^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}4

Strategy C: Couple Proteostasis And Redox Modulation

Because p62 couples degradative stress and NRF2 biology, combination approaches that co-manage aggregate load and oxidative stress may have better mechanistic coherence than single-axis programs.^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}5^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}6^{4Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy2013 · Mol Cell · PMID 24011591Open reference}7

Evidence Boundaries And Open Questions

Which SQSTM1 variant classes map reproducibly to disease-specific phenotypes versus broad proteostasis risk?
Which p62 post-translational states are most predictive of treatment response across ALS/FTD versus tau-first syndromes?
How should p62-centered biomarkers be harmonized across tissue compartments (CSF, blood, and tissue/pathology endpoints)?

These are tractable questions for prospective translational studies that embed mechanism-proximal biomarker panels and predefined flux interpretation rules.

Pathway & Interaction Diagram

Interactive diagram showing SQSTM1 key relationships in the SciDEX knowledge graph (15 connections shown).

flowchart TD
    SQSTM1(["SQSTM1"])
    NFE2L2(["NFE2L2"])
    A["utophagyAutophagy"]
    A["lsAls"]
    C["ancerCancer"]
    T["umorTumor"]
    I["nflammationInflammation"]
    M["torMtor"]
    MTOR(["MTOR"])
    P62(["P62"])

    SQSTM1 -->|"activates"| NFE2L2
    SQSTM1 -->|"regulates"| Autophagy
    SQSTM1 -->|"interacts with"| Autophagy
    SQSTM1 -->|"associated with"| Autophagy
    SQSTM1 -->|"associated with"| Als
    SQSTM1 -->|"regulates"| Cancer
    SQSTM1 -->|"activates"| Autophagy
    SQSTM1 -->|"activates"| Tumor
    SQSTM1 -->|"activates"| Als
    SQSTM1 -.->|"inhibits"| Als
    SQSTM1 -->|"activates"| Inflammation
    SQSTM1 -->|"activates"| Mtor
    SQSTM1 -->|"activates"| MTOR
    SQSTM1 -->|"associated with"| P62
    SQSTM1 -->|"activates"| P62

    style SQSTM1 fill:#006494,stroke:#4fc3f7,stroke-width:3px,color:#e0e0e0

External Links

References

p62/SQSTM1 binds directly to Atg8/LC3 to facilitate degradation of ubiquitinated protein aggregates by autophagy Pankiv S, Clausen TH, Lamark T, et al 2007 · J Biol Chem · PMID 17580304
p62 Targeting to the autophagosome formation site requires self-oligomerization but not LC3 binding Itakura E, Kishi-Itakura C, Mizushima N 2011 · J Cell Biol · PMID 21220506
Homeostatic levels of p62 control cytoplasmic inclusion body formation in autophagy-deficient mice Komatsu M, Waguri S, Koike M, et al 2007 · Cell · PMID 18083104
Phosphorylation of p62 activates the Keap1-Nrf2 pathway during selective autophagy Ichimura Y, Waguri S, Sou YS, et al 2013 · Mol Cell · PMID 24011591
p62/SQSTM1 is a target gene for transcription factor NRF2 and creates a positive feedback loop by inducing antioxidant response element-driven gene transcription Jain A, Lamark T, Sjottem E, et al 2010 · J Biol Chem · PMID 20452972
Autophagy and Neurodegeneration: Pathogenic Mechanisms and Therapeutic Opportunities Menzies FM, Fleming A, Caricasole A, et al 2015 · Neuron · PMID 25914067
Altered proteostasis in aging and neurodegenerative disease Son SM, Song H, Byun J, et al 2018 · Int Neurourol J · PMID 30030024
SQSTM1 mutations in French patients with frontotemporal dementia or frontotemporal dementia with amyotrophic lateral sclerosis Le Ber I, Camuzat A, Guerreiro R, et al 2013 · JAMA Neurol · PMID 24042580
Ubiquitylation of p62/sequestosome1 activates its autophagy receptor function and controls selective autophagy upon ubiquitin stress Pan JA, Sun Y, Jiang YP, et al 2016 · Cell Res · PMID 28322253
Requirement for p62 acetylation in the aggregation of ubiquitylated proteins under nutrient stress Sun D, Wu R, Zheng J, Li P, Yu L 2018 · Nat Commun · PMID 31857589
ALS-FTLD-linked mutations of SQSTM1/p62 disrupt selective autophagy and NFE2L2/NRF2 anti-oxidative stress pathway Goode A, Butler K, Long J, et al 2020 · Autophagy · PMID 31362587
Rare mutations in SQSTM1 modify susceptibility to frontotemporal lobar degeneration Rubino E, Rainero I, Chiò A, et al 2014 · J Neurol Neurosurg Psychiatry · PMID 24899140
ALS-associated TBK1 variant p.G175S is defective in phosphorylation of p62 and impacts TBK1-mediated signalling and TDP-43 autophagic degradation Ye J, Cheung J, Gerbino V, et al 2020 · Hum Mol Genet · PMID 32835772

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