AMPK–SQSTM1/p62 Feedback Links Metabolic Stress to Antioxidant Defense

Metabolic stress can activate overlapping survival programs in cancer cells, but the connections between energy sensing and antioxidant defense are not fully explained by examining AMPK or NRF2 alone. In a 2024 study in Autophagy, Choi and colleagues describe a feedback circuit in which AMPK and SQSTM1/p62 reinforce one another, enabling coordinated activation of AMPK and NFE2L2/NRF2. The work provides a mechanistic account of how lysosomal changes under nutrient stress may support both metabolic adaptation and antioxidant responses.

The study’s central contribution is not simply that p62 participates in stress signaling. It proposes that p62 is a shared regulatory node: it promotes NRF2 activation by facilitating KEAP1 degradation and supports AMPK activation by helping assemble an AXIN–STK11/LKB1–AMPK complex at lysosomes. AMPK, in turn, is required for the stress-induced rise in p62 expression and phosphorylation. The authors report these relationships in the reference study.

Study Background and Research Question

In a tumor microenvironment, limited nutrient availability and reactive oxygen species (ROS) can occur together. Glucose limitation may reduce the availability of metabolites needed to sustain NADPH production, while oxidative damage to mitochondrial respiration can further impair ATP generation. The resulting energy and redox pressures create a survival challenge for cancer cells.

STK11/LKB1–AMPK signaling is one route by which cells respond to energy stress. AMPK helps rebalance energy use and production; NRF2, encoded by NFE2L2, regulates antioxidant defenses. KEAP1 normally restrains NRF2, while mutations affecting KEAP1 or STK11 can alter the balance of these stress-response pathways. The authors frame their work around a consequential question: how might metabolic stress connect STK11–AMPK signaling with KEAP1–NRF2 signaling, particularly in the context of co-occurring mutations in non-small cell lung cancer (NSCLC)?

Rather than treating the pathways as independent responses, the study asks whether a stress-responsive factor can coordinate both. Its findings place SQSTM1/p62 at that intersection and propose that lysosomal changes provide an upstream signal linking nutrient stress to the feedback loop.

Key Innovation from the Reference Study

The key innovation is the proposed double-positive feedback between AMPK and p62. Under metabolic stress, p62 expression and phosphorylation increase. p62 then contributes to activation of both AMPK and NRF2 through distinguishable mechanisms. For NRF2, p62 promotes autophagic degradation of KEAP1, reducing a constraint on NRF2 activity. For AMPK, p62 facilitates formation of the AXIN–STK11–AMPK complex at the lysosomal membrane. The resulting AMPK activity is also needed for the stress-induced increase in p62, completing the feedback relationship.

This model integrates two outputs that are often discussed separately: adaptation to energy stress through AMPK and antioxidant defense through NRF2. The paper further assigns upstream steps to lysosomal deacidification, transcription factors TFEB and TFE3, the phosphatase PP2A, ROS-responsive MAP3K7/TAK1, and lysosomal calcium release. These connections provide a proposed sequence from metabolic and lysosomal disturbance to p62 regulation and downstream pathway activation. The authors report that p62 phosphorylation at S24 and S226 is important for activation of AMPK and NRF2, distinguishing modification of p62 from a simple change in its abundance.

Methods and Experimental Design Insights

The study’s experimental logic is organized around testing dependencies in the proposed pathway. It examines metabolic stress conditions, including low-nutrient conditions, and relates changes in p62 expression and phosphorylation to AMPK and NRF2 activity. The reported mechanistic conclusions address whether p62 is required for these responses, how KEAP1 turnover and lysosomal complex formation contribute, and whether upstream regulators such as TFEB/TFE3, PP2A, and TAK1 are involved. The authors also report that protons supplied by lactic acid abrogated stress-induced effects, which helps connect lysosomal pH changes to the signaling model.

For researchers interpreting the work, the important design principle is to separate pathway output from pathway mechanism. Measuring AMPK activation alone would not establish NRF2 engagement; likewise, NRF2 target responses alone would not show how energy sensing is involved. A useful replication or extension would therefore pair pathway activity measurements with p62 abundance and phosphorylation, KEAP1 turnover, and evidence for lysosomal AXIN–STK11–AMPK assembly. The full article should be consulted for the exact models, reagents, assay conditions, and controls; the condensed findings summarized here do not specify all experimental parameters.

Protocol Parameters

• Stress comparison: Compare low-nutrient conditions with an appropriate nutrient-replete control; treat this as a design principle from the study rather than a prescribed duration or nutrient concentration.
• Pathway readouts: Where feasible, assess AMPK and NRF2 responses alongside p62 expression and phosphorylation so that coordinated activation can be distinguished from a change in only one pathway.
• Mechanism checks: To test the proposed branches, examine KEAP1 turnover and lysosomal AXIN–STK11–AMPK complex formation, consulting the full paper for the specific assays and controls.
• Reproduction details: The findings summarized here do not provide validated reagent concentrations, treatment times, or dosing schedules. Use the full methods and optimize conditions for the chosen model rather than inferring numeric settings.

Core Findings and Why They Matter

First, metabolic stress increased p62 expression and phosphorylation, and p62 was necessary for effective activation of both AMPK and NRF2 in the reported system. This supports a model in which p62 functions as an active signaling organizer rather than only as an autophagy-associated cargo receptor.

Second, the study separates p62’s downstream effects into two branches. Its role in promoting autophagic KEAP1 degradation offers a route to NRF2 activation. Its contribution to lysosomal AXIN–STK11–AMPK complex formation offers a route to AMPK activation. These branches help explain how one stress-responsive protein could coordinate redox defense and energy adaptation.

Third, the authors describe how metabolic stress may regulate p62 itself. Lysosomal deacidification, associated in the paper with low-glucose metabolism and AMPK-dependent proton reduction, promotes PP2A-dependent dephosphorylation of TFEB and TFE3 and increased p62 expression. In parallel, ROS and pH-dependent lysosomal calcium release are linked to TAK1 activation and p62 phosphorylation. The reported importance of p62 S24 and S226 gives this regulatory sequence specific molecular features that can be tested in follow-up work.

Finally, the observation that protons provided by lactic acid abrogated the reported stress effects makes lysosomal pH a relevant experimental variable. It cautions against treating nutrient deprivation as a single, uniform stimulus: the resulting signaling may depend on the associated cellular and lysosomal environment. The overall findings offer a plausible explanation for why enhanced NRF2 signaling could compensate for altered STK11–AMPK activity in some cancer contexts, but they do not establish that this feedback is the sole explanation for co-occurring mutations or tumor behavior.

Comparison with Existing Internal Articles

The internal overview “AMPK–SQSTM1 Feedback Enhances Antioxidant Responses in Stress” summarizes the same central relationship between AMPK and p62. The reference study supplies the more detailed mechanistic framework: it links p62 to KEAP1 degradation and lysosomal AMPK-complex formation, and identifies upstream contributions from lysosomal pH regulation, TFEB/TFE3, PP2A, and TAK1. These details are useful when translating the broad feedback concept into experimentally distinguishable hypotheses.

Limitations and Transferability

The findings support a mechanistic model in the experimental systems used by the authors; they do not by themselves demonstrate that the same dependencies hold across all tumor types, nutrient environments, or stages of disease. The proposed relevance to STK11- and KEAP1-altered NSCLC is biologically important, but the work should not be read as proof that the feedback loop explains every instance of mutation co-occurrence or predicts patient response to a particular therapy.

Several parts of the pathway also warrant context-specific testing. Lysosomal pH, ROS, calcium signaling, and nutrient availability can vary with cell type and culture conditions. A result obtained under low-nutrient stress may not transfer directly to a different stressor or tissue. In addition, p62 has multiple cellular roles, so changes in its abundance may affect processes beyond the specific signaling branches highlighted here. Follow-up studies can test whether the S24/S226 phosphorylation dependence and the proposed lysosomal steps are conserved across relevant models, while retaining controls that distinguish pathway activation from general cellular injury.

Research Support Resources

Why this cross-domain matters, maturity, and limitations

The reference study concerns cancer-cell metabolic stress, not calcineurin inhibition or immune suppression. For separate transplantation immunology research, cytokine signaling pathway modulation, or an autoimmune disease model, Tacrolimus (FK506) (SKU B2143) can support studies of FKBP12–calcineurin-dependent T-cell signaling and immune response suppression. It is a distinct experimental perturbation and should not be treated as evidence for, or a direct tool to reproduce, the AMPK–p62–NRF2 mechanism described above.