Reply to correspondence 2 on “MET promotes hepatocellular carcinoma development through the promotion of TRIB3-mediated FOXO1 degradation”

Dear Editor,

We sincerely appreciate the insightful response from Dr. Wang and colleagues regarding our editorial on “Uncovering the MET–TRIB3–FOXO1 axis: A novel target in MET-driven hepatocellular carcinoma.” [1]

Their thoughtful clarification further emphasizes the significance of their findings and contributes valuable insight into the molecular mechanism of MET-driven hepatocellular carcinoma (HCC) [2]. We commend their comprehensive approach, which illuminates MET-driven oncogenesis and convincingly demonstrated the pivotal role of Tribbles Pseudokinase 3 (TRIB3) as a downstream effector of the MET signaling pathway.

We were particularly intrigued by the elucidation of a self-reinforcing oncogenic loop of MET-driven HCC, in which TRIB3 promotes the proteasomal degradation of the tumor suppressor FOXO1, leading to consequent activation of oncogenic drivers such as MET, CCND1, and TWIST1. In turn, activated MET signaling enhances TRIB3 expression via the ERK–SP1 pathway, thus establishing a positive feedback circuit that amplifies tumor-promoting signaling in HCC.

The authors’ in vivo therapeutic model using hepatocyte-specific AAV8-shTRIB3 was noteworthy, underscoring the translational potential of liver-directed gene therapy [3,4]. The observed molecular changes, reduced expression of TRIB3, MET, CCND1, and TWIST1, along with restored FOXO1 expression, offering robust preclinical evidence that TRIB3 silencing could disrupt MET-driven oncogenic feedback loops and contribute to effective tumor suppression in HCC.

Importantly, the authors demonstrated that the TRIB3–COP1–FOXO1 axis, characterized in HCC, is also functionally engaged in vitro colorectal and breast cancer models. However, TRIB3’s functional role appears to be highly context-dependent, with its binding partners determining whether it exerts oncogenic or tumor-suppressive effects across tumor types: in endometrial cancer, TRIB3 has been shown to suppress the AKT pathway and inhibit cellular proliferation and invasion [5]; in acute promyelocytic leukemia, it facilitates PML-RARα degradation and contributes to therapeutic resistance; and in breast cancer, it enhances tumor stemness and progression by interfering with the AKT–FOXO1 axis [6]. These findings underscore the tumor type–specific duality of TRIB3, which may act either as an oncogene or tumor suppressor depending on cellular context and signaling environment. Therefore, systemic TRIB3 inhibition carries the potential risk of unintended tumorigenesis in non-hepatic tissues. Therefore, we agree that organ-specific targeting strategies, such as AAV8-mediated hepatic delivery, represent an essential consideration in clinical translation.

As the authors pointed out, the tumor microenvironment (TME) in HCC is notoriously heterogeneous, and MET alteration alone may not fully capture the complex biological landscape across different subtypes of HCC. In this context, their efforts to validate the MET-TRIB3-FOXO1 axis in patient-derived xenograft (PDX) models and across different etiologies, including non-viral HCC, are especially commendable and necessary. Models such as MET/β-catenin-driven HCC are known to exhibit immune escape and resistance to immune checkpoint inhibitors [7]. Thus, it remains essential to validate the therapeutic efficacy of TRIB3 inhibition not only in immune-cold tumors, but also in immune-infiltrated hot tumors. To determine whether TRIB3-targeted therapies exert antitumor effects beyond MET–β-catenin-driven HCC, further studies using diverse PDX models, including those induced by non-MET pathway, are warranted. In particular, given that TRIB3 is implicated in metabolic regulation and cellular stress responses, the use of MASLD-associated HCC models−such as the STAM model, CDAHFD-induced model, or Western diet plus DEN/CCl4 model−may help elucidate its broader therapeutic potential in various TME [8].

In our editorial, we briefly mentioned the importance of investigating TRIB3’s potential role in modulating response to immunotherapies [9]. We are pleased to see that the authors are actively considering this, as the immune evasion in TME are now recognized as central components of HCC progression and therapeutic resistance. Targeting TRIB3− through its role in FOXO1 degradation and immune suppression− may represent a novel strategy to improve the efficacy of immune checkpoint blockade, possibly by reprogramming tumor microenvironment.

Moreover, previous studies show that VEGF inhibition can activate MET signaling as a compensatory mechanism, even in the absence hypoxia, especially in non-small cell lung cancer [10]. In addition, MET inhibitors have been shown to stabilize PD-L1 expression, thereby impairing T-cell– mediated anti-tumor responses [11]. Building on these findings, combining c-MET inhibitors with immune checkpoint inhibitors has demonstrated synergistic antitumor effects by converting immunologically “cold” tumors into “hot” tumors [12,13]. These findings support the hypothesis that targeting MET-related pathways, either at the level of the receptor (e.g., MET inhibitors) or downstream effectors such as TRIB3, could sensitize tumors to immunotherapy and broaden the population of HCC patients who benefit from combination treatments.

Beyond immunologic synergy, some MET-targeted therapies may also offer clinical benefit in specific molecular subtypes of HCC. HCCs harboring MET alterations have been associated with primary resistance to first-line tyrosine kinase inhibitors (TKIs) and anti-angiogenic agents such as sorafenib, lenvatinib and bevacizumab-based regimens. In such cases, MET-driven signaling may sustain oncogenic proliferation despite VEGF pathway blockade [14]. These observations underscore the need for biomarker-guided treatment strategies and still support the rationale for incorporating MET inhibitors as a potential first-line therapy in selected patients with MET-driven HCC [15,16].

In addition, the role of FOXO1 dysregulation in therapy resistance warrants further investigation. FOXO1 is a critical transcription factor that orchestrates cell cycle arrest, apoptosis, DNA repair, and oxidative stress responses [17]. As a key transcription factor regulating cell cycle arrest, apoptosis, DNA repair, and oxidative stress responses, FOXO1 is frequently inactivated through phosphorylation by upstream kinases such as EGFR, PI3K/AKT, and mTORC2. This inactivation results in cytoplasmic sequestration or proteasomal degradation, contributing to radio- and chemoresistance in various cancers [18]. Therapeutic strategies aimed at restoring FOXO1 activity, including SIRT1 activators, AKT inhibitors, or direct FOXO1 stabilizers, either alone or in combination with conventional chemotherapy or radiotherapy, may re-sensitize resistant HCC to standard treatments.

From this perspective, we fully agree that future studies focusing on small-molecule inhibitors of TRIB3, or stabilizers of FOXO1, may offer promising avenues for patients with MET-dysregulated HCC not as direct substitutes for MET inhibitors, but as complementary strategies that intercept downstream oncogenic feedback circuits. This approach may be particularly valuable given the limited efficacy and safety concerns of direct MET inhibitors other than cabozantinib in HCC, which have been hampered by off-target toxicities and incomplete pathway suppression in clinical trials. Additionally, we acknowledge that direct MET inhibition may still hold clinical value for certain subsets of HCC characterized by MET amplification or overexpression with resistant to TKIs, while targeting downstream effectors such as TRIB3 or stabilizing FOXO1 represents a promising alternative approach.

To our knowledge, this study is among the first to experimentally define a self-sustaining feedback loop underlying MET-driven HCC. The identification of the MET–TRIB3–FOXO1 axis as a closed oncogenic circuit offers novel mechanistic insight into how MET signaling may be sustained and amplified in certain molecular subtypes of HCC, with significant implications for therapeutic targeting.

Abbreviations

HCC

hepatocellular carcinoma

HTVi

hydrodynamic tail vein injection

MAPK

mitogen-activated protein kinase

PDX

patient-derived xenograft

TME

tumor microenvironment

TKIs

Tyrosine kinase inhibitors

TRIB3

Tribbles Pseudokinase 3