Alcohol-associated liver disease (ALD) is a major contributor to liver-related morbidity and mortality worldwide, encompassing a broad pathological continuum that spans simple steatosis, steatohepatitis, and progressive fibrosis to cirrhosis, as well as hepatocellular carcinoma [
1]. In the United States, approximately 3.8% of all deaths are attributable to heavy alcohol consumption, thus implicating the substantial public health and socioeconomic burden imposed by alcohol-related disorders [
2,
3]. Excessive alcohol consumption triggers numerous pathogenic processes, including oxidative stress, inflammation activation, toxic acetaldehyde generation, disruption of the gut barrier integrity, profibrotic tissue remodeling, and mitochondrial dysfunction [
4,
5]. Multiple pathophysiological processes in ALD have been increasingly characterized; however, these mechanisms collectively only explain a limited part of the biological networks involved in ALD progression. Consequently, despite decades of intensive investigation, the molecular mechanisms underlying ALD remain incompletely understood.
A growing body of evidence has highlighted the critical role of endoplasmic reticulum (ER) stress in alcohol-associated hepatocellular injury. ER stress is a potent trigger of hepatic inflammation via unfolded protein response (UPR)-driven cytokine release [
6]. Furthermore, excessive alcohol consumption can directly promote the accumulation of unfolded and misfolded proteins within the ER lumen through the three canonical ER stress sensors PKR-like ER kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 [
7]. Activation of these UPR pathways facilitates the reestablishment of protein homeostasis and initiates inflammatory signaling cascades. In particular, the PERK-mediated phosphorylation of eukaryotic translation initiation factor 2 subunit alpha (eIF2α) promotes the selective translation of ATF4, which is a key transcription factor that links ER stress to inflammatory signaling, while IRE1α facilitates c-Jun N-terminal kinase (JNK) signaling and enhances the production of pro-inflammatory cytokines [
8,
9]. As a result, ER stress is a crucial upstream promoter of hepatic inflammation in ALD, thereby linking disrupted of protein homeostasis to cytokine production, hepatocyte injury, and innate immune activation. However, the inhibition of these classical UPR sensors does not fully mitigate the ER stress-mediated hepatic injury, which suggests that additional, noncanonical ER stress mechanisms further contribute to ER stress signaling during alcohol-induced liver pathology.
The newly published study in
Clinical and Molecular Hepatology by Liu et al. [
10] addresses this issue in a tour de force article that mechanistically demonstrated a novel signaling axis, RAB25/GCN1, which promotes ER stress via a noncanonical pathway, thereby reshaping our understanding of how alcohol disrupts hepatic homeostasis. RAB proteins, as small GTPases, are most well-known for their roles in vesicular transport but have only recently been implicated in organelle stress responses [
11]. Single-cell RNA sequencing consistently exhibited that
RAB25 expression was markedly elevated in hepatocytes exposed to alcohol and in liver tissues from patients with ALD. Immunohistochemical analysis further demonstrated that elevated RAB25 and ATF4 levels were correlated with ALD severity, thus supporting the concept that the expression of
RAB25 significantly participates in ER stress regulation. The enrichment of RAB25 to the ER further implicated that RAB25 may act as a trigger of ER stress, positioning it as a potential pathophysiological mediator that connects intracellular trafficking pathways with cellular stress-response signaling, which has previously been recognized as largely independent. Building on these observations, the authors also identified hypoxia-inducible factor 1α (HIF1A) as a key transcriptional regulator that promotes
RAB25 expression under alcohol-associated cellular stress conditions. This finding further provided an important mechanistic bridge between hypoxic conditions and metabolic stress, which also suggested that the HIF1A-RAB25 axis may function as an integrative signaling pathway that coordinates oxygen-sensing mechanisms with ER stress responses during the progression of ALD. Furthermore, co-immunoprecipitation and mass spectrometry analyses identified GCN1 as a major RAB25-binding partner. GCN1 is a well-established activator of GCN2, which is an eIF2α kinase that is involved in amino acid-responsive stress signaling. Subsequent analyses confirmed that RAB25-GCN1 binding suppresses its K33-linked ubiquitination and degradation, thereby enhancing the phosphorylation of GCN2 and triggering the downstream ATF4-dependent ER stress signaling. This cascade ultimately contributed to the progression of ALD by facilitating the dysregulation in lipid metabolism, mitochondrial homeostasis, and inflammatory responses. This notable finding revealed additional PERK-independent mechanisms of ATF4 activation, refining our understanding of alternative ATF4 regulatory pathways. By situating RAB25 upstream of GCN1-GCN2-ATF4 signaling, the authors delineated a noncanonical ER stress pathway that functions parallel to, but also independent of, the classic PERK-eIF2α axis. The mechanistic clarity offered by this study provides a framework for revisiting earlier assumptions that PERK is the exclusive upstream kinase for ATF4 activation in alcohol-associated hepatic stress.
Furthermore, a key strength of this study is its clear demonstration of cross-organelle communication between the ER and mitochondria during ALD progression. ER stress has previously been associated with impaired mitochondrial function, enhanced inflammatory signaling, and increased lipid accumulation in individuals with ALD. Alcohol-fed mice exhibited significant ER dilation and membrane disruption, as well as swelling and cristae rupture in mitochondria, both of which are structural abnormalities that collectively indicated concurrent ER stress and mitochondrial injury. These findings emphasized the tight functional interplay between the ER stress pathways and mitochondrial dysfunction during alcohol-induced liver pathology, which ultimately culminates in oxidative stress, impaired β-oxidation, and lipid accumulation. RAB25 suppression markedly attenuated alcohol-induced mitochondrial abnormalities, thereby preserving mitochondrial morphology and cristae integrity, normalizing oxygen consumption rates, and reducing aberrant ER-mitochondria interaction and calcium flux. Collectively, these findings identified RAB25 as a key regulator of ER-mitochondria crosstalk in ALD, alleviating mitochondrial dysfunction and attendant metabolic derangements. Therefore, the RAB25-GCN1 axis is implicated as a key integrative pathway connecting ER stress with mitochondrial metabolism and lipid synthesis in the context of ALD progression.
Hepatic inflammation is promoted by alcohol-exposed hepatocytes via the release of cytokines, chemokines, and damage-associated molecular patterns. Single-cell transcriptomic analysis revealed that
RAB25 expression was strongly associated with the activation of cytokine and chemokine pathways, thereby identifying hepatocytes as major producers of inflammatory mediators such as IL-1, CCL2, CXCL10, and CXCL12. Integrative cell-cell communication analysis highlighted CXCL12 as a downstream effector chemokine which links ER stress to immune cell recruitment, suggesting that therapeutic modulation of this axis could mitigate inflammatory injury in ALD. Mechanistically, RAB25 promoted CXCL12 induction via the ER stress-NLRP3 inflammatory axis, as evidenced by the finding that RAB25 suppression reduced NLRP3 protein levels—an established downstream effector of the ATF4-CHOP pathway—and attenuated caspase-1 activation, thereby mitigating hepatocyte inflammatory responses [
12]. Collectively, these findings also clearly demonstrated that RAB25 functions as a key amplifier of hepatocyte-driven inflammation in ALD by linking ER stress to NLRP3 activation and the subsequent CXCL12-mediated inflammatory signaling.
In summary, this study reframes our understanding of ALD progression by revealing that RAB25, as a membrane-trafficking GTPase, can accelerate ER stress through a ubiquitination-dependent mechanism. This insight challenges the traditional view of ALD as a disorder that is primarily driven by oxidative injury, lipid peroxidation, and inflammation, and rather suggests that this disease is a failure of coordinated organelle communication. By establishing the RAB25-GCN1-GCN2-ATF4 axis as a central driver of noncanonical ER stress, Liu et al. [
10] provide a new conceptual view through which hepatocyte vulnerability to metabolic injury can be interpreted. Their work highlights RAB25 as a molecular bridge connecting ER signaling, mitochondrial dysfunction, and immune activation, which is an integrative framework that aligns with emerging paradigms that emphasize organelle crosstalk as the foundation of metabolic homeostasis. Beyond its mechanistic depth, elevated levels of RAB25 could serve as a biomarker of active ER stress in alcohol-induced hepatic injury, while therapeutic strategies aimed at disrupting RAB25-GCN1 signaling or modulating USP5-mediated deubiquitination may provide novel avenues for intervention. The identification of this noncanonical ER stress pathway expands the therapeutic landscape of ALD and emphasizes the importance of investigating cellular stress networks.
FOOTNOTES
-
Authors’ contribution
Seol Hee Park: Writing draft. WonhyoSeo: Conceptualization, critical revision of the manuscript and supervision.
-
Acknowledgements
This study was supported by the National Research Foundation of Korea (2021R1A6C101A442, 2022R1C1C1008912, RS-2023-00262969), the Supporting Program of The Korean Association for the Study of the Liver and the Korean Liver Foundation, and the Research Support Project for Young Medical Scientists funded by the Daewoong Foundation.
-
Conflicts of Interest
The authors have no conflicts to disclose.
Abbreviations
alcohol-associated liver disease
eukaryotic translation initiation factor 2 subunit alpha
hypoxia-inducible factor 1α
inositol-requiring enzyme 1α
unfolded protein response
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Citations
Citations to this article as recorded by
- Correspondence to editorial on “RAB25/GCN1 signaling promotes endoplasmic reticulum stress to mediate alcohol-associated liver disease progression”
Xue-Wen Liu, Zi-Bin Zhan, Yu Gong, Ze-Hua Li, Kun-Hao Bai, Jun Weng
Clinical and Molecular Hepatology.2026; 32(3): e349. CrossRef - Reply to correspondence on “RAB25/GCN1 signaling promotes endoplasmic reticulum stress to mediate alcohol-associated liver disease progression”
Seol Hee Park, Wonhyo Seo
Clinical and Molecular Hepatology.2026; 32(3): e432. CrossRef
