AMPK–SQSTM1 Positive Feedback: Dual Activation of AMPK and NRF2 in Metabolic Stress

Study Background and Research Question

Metabolic stress—characterized by nutrient depletion and reactive oxygen species (ROS) accumulation—forces cancer cells to adapt for continued survival and proliferation. Two fundamental pathways govern cellular adaptation to these stresses: the STK11/LKB1–AMPK metabolic sensor pathway and the KEAP1–NFE2L2/NRF2 antioxidant response axis. In non-small cell lung cancer (NSCLC), co-occurring mutations in KEAP1 and STK11/LKB1 disrupt these canonical pathways. Yet, the molecular crosstalk and compensatory mechanisms enabling tumor cells to maintain energy homeostasis and redox balance under such conditions remain incompletely understood. The reference study (Cho et al., 2024) investigates how cells integrate metabolic and oxidative stress signals via feedback between AMP-activated protein kinase (AMPK) and the autophagy adaptor protein SQSTM1/p62, and how this impacts the activation of both AMPK and NFE2L2/NRF2.

Key Innovation from the Reference Study

The pivotal contribution of this work is the identification of a double-positive feedback loop between AMPK and SQSTM1/p62 during metabolic stress. This loop simultaneously drives the activation of both AMPK (a central energy sensor) and NFE2L2/NRF2 (master regulator of antioxidant defenses), thereby synergistically enhancing cellular resistance to metabolic and oxidative insults. Importantly, this dual activation is mediated by the dynamic regulation of SQSTM1 at the transcriptional and post-translational level, establishing a molecular bridge that coordinates lysosomal, metabolic, and redox signaling.

Methods and Experimental Design Insights

To dissect this regulatory network, the authors used a combination of molecular genetics, biochemical assays, and cellular imaging in both mouse embryonic fibroblasts (MEFs) and human cancer cell lines. Key methodological approaches included:

• Genetic manipulation (e.g., knockdown and overexpression) of SQSTM1, KEAP1, STK11, and other pathway components.
• Induction of metabolic stress through glucose deprivation and lysosomal deacidification, mimicking tumor microenvironmental conditions.
• Immunoprecipitation and immunoblotting to assess protein–protein interactions and post-translational modifications such as phosphorylation of SQSTM1 at serine residues S24 and S226.
• Assessment of antioxidant defense via measurement of NFE2L2 target gene expression and ROS levels.
• Functional assays to determine cellular growth and viability under stress conditions.

The experimental workflow allowed precise mapping of the sequence and interdependence of signaling events, as well as identification of key phosphorylation sites necessary for feedback amplification.

Core Findings and Why They Matter

The study’s main findings can be summarized as follows (Cho et al., 2024):

• Metabolic stress upregulates and phosphorylates SQSTM1/p62: Stress conditions increased both the expression and phosphorylation of SQSTM1, which was essential for activating NFE2L2 and AMPK.
• Dual activation of NFE2L2 and AMPK by SQSTM1: SQSTM1 promoted NFE2L2 activation through autophagic degradation of KEAP1 and facilitated the assembly of the AXIN–STK11–AMPK complex at the lysosome, boosting AMPK activation.
• AMPK is required for stress-induced SQSTM1 regulation: AMPK activity was itself necessary for the metabolic stress-driven expression and phosphorylation of SQSTM1, establishing the double-positive feedback circuit.
• Mechanistic underpinnings: SQSTM1 expression was increased via PPP2/PP2A-dependent dephosphorylation of TFEB and TFE3, both regulated by lysosomal pH alterations. Phosphorylation of SQSTM1 at S24 and S226 was mediated by MAP3K7/TAK1, itself activated by ROS and lysosomal Ca²⁺ secretion.
• Functional importance of specific SQSTM1 phosphorylation: Phosphorylation at S24 and S226 was critical for the dual activation of AMPK and NFE2L2. Mutation of these residues abrogated feedback and antioxidant defense.
• Feedback is context-dependent: Acidification via lactic acid, which restores lysosomal proton gradients, disrupted the feedback loop, highlighting the importance of microenvironmental pH.

This work advances our understanding of how metabolic and oxidative stress responses are intertwined in cancer biology. The identification of this feedback loop provides a plausible explanation for the frequent co-occurrence of STK11 and KEAP1 mutations in NSCLC, suggesting that tumor cells harness this mechanism to maintain metabolic and redox homeostasis under adverse conditions.

Comparison with Existing Internal Articles

Whereas the reference study focuses on intrinsic cancer cell adaptation to metabolic and oxidative stress, several internal articles explore related themes in immune modulation and signal transduction. For example, Tacrolimus (FK506): Optimizing Immunosuppression Assays provides guidance on harnessing the immunosuppressant FK506 for precise T-cell activation and cytokine signaling pathway modulation in transplantation immunology research and autoimmune disease models. This is mechanistically relevant, as FK506 targets calcineurin signaling—another key phosphatase in immune response suppression—paralleling the stress signaling and feedback control described for AMPK and SQSTM1 in the current study.

Additionally, Tacrolimus (FK506) in Modern Immune Assays discusses the application of the FK506 macrolide immunosuppressant in cellular workflows, offering practical insight into assay optimization and signal inhibition. These articles complement the reference study by illustrating how precise modulation of phosphatase activity (e.g., calcineurin inhibition by FK506) can be leveraged to dissect T-cell signaling and stress response pathways in experimental settings.

Limitations and Transferability

While the reference study provides robust mechanistic insight using both mouse and human cell models, several limitations should be considered:

• Model system specificity: Most findings were derived from in vitro or ex vivo systems; in vivo validation in tumor models, particularly in immunocompetent hosts, remains necessary to fully establish physiological relevance.
• Genetic background and context: The interplay between AMPK and SQSTM1 may differ in non-cancerous settings or in tissues with distinct metabolic demands.
• Therapeutic translation: While the feedback loop offers a rationale for targeting these pathways in NSCLC with co-occurring mutations, the systemic effects of manipulating AMPK, NFE2L2, or autophagy require careful evaluation.
• Microenvironmental factors: The observed feedback is sensitive to pH and metabolic milieu, highlighting the need for precise modeling of tumor microenvironmental conditions.

Thus, while the mechanisms are compelling, further studies are warranted to determine how these findings translate to complex in vivo and therapeutic scenarios.

Protocol Parameters

• Glucose deprivation: 24–48 h of low-glucose medium to induce metabolic stress and promote AMPK/SQSTM1 activation in cell models.
• SQSTM1 phosphorylation assays: Detect S24 and S226 phosphorylation by immunoblotting and mutational analysis for functional studies.
• AMPK activation measurements: Assess via phosphorylation status (Thr172) and downstream target analysis (e.g., ACC phosphorylation).
• Autophagy flux monitoring: Use LC3 lipidation and p62 turnover assays to evaluate pathway engagement under stress conditions.
• KEAP1–NFE2L2 pathway interrogation: Employ qPCR or reporter assays for NFE2L2 target gene induction (e.g., NQO1, HO-1).
• Practical tip: When transitioning protocols to immune or transplantation models, incorporate specific immunosuppressants (e.g., FK506) as needed to study T-cell activation and cytokine signaling in parallel with metabolic stress assays.

Research Support Resources

Researchers aiming to study immune signaling, T-cell activation, or cytokine pathway modulation in the context of metabolic or oxidative stress can incorporate selective tools such as Tacrolimus (FK506) (SKU B2143) from APExBIO. This macrolide immunosuppressant is a potent inhibitor of calcineurin, and is widely applied in both in vitro and in vivo models for immune response suppression and transplantation immunology research. For optimal results, Tacrolimus can be used at 2–4 μM in cell culture or 1–4 mg/kg in animal studies, as supported by the product information. Its reliable inhibition of cytokine signaling pathways makes it a valuable component for dissecting cellular crosstalk under stress and in immune disease models.