RHEB-CSF1R signaling, autophagy, and metastatic plasticity in pancreatic cancer: Current advances, controversies, and translational opportunities

Abstract

A recent study comprehensively described an autophagy-related mechanism in pancreatic cancer in which ras homolog enriched in brain (RHEB) interacts with and upregulates colony stimulating factor 1 receptor (CSF1R), thereby increasing phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin phosphorylation, attenuating autophagy-associated readouts, and promoting epithelial-mesenchymal transition and metastatic behavior. By integrating patient cohorts, public datasets, cell-based assays, co-immunoprecipitation, and an in vivo liver metastasis model, the study advances a potentially actionable biomarker framework and therapeutic hypothesis. In this article, we place these findings within the broader biological context of pancreatic ductal adenocarcinoma and discuss how RHEB-centered signaling may intersect with CSF1R-associated biology, autophagy regulation, and metastatic plasticity. We further highlight key unresolved issues, including validation of tumor-cell CSF1R expression and subcellular localization, rigorous assessment of autophagy flux beyond static markers, and external validation of prognostic performance. Addressing these questions may clarify the biological scope and translational potential of the proposed RHEB-CSF1R-phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin-autophagy axis in pancreatic cancer metastasis.

Key Words: Pancreatic cancer; Ras homolog enriched in brain; Colony stimulating factor 1 receptor; Autophagy; Phosphatidylinositol 3-kinase/protein kinase B/mammalian pathway; Epithelial-mesenchymal transition; Metastasis; Tumor microenvironment

Core Tip: A recent study comprehensively summarized that a tumor-cell ras homolog enriched in brain-colony stimulating factor 1 receptor complex promotes pancreatic cancer metastasis by increasing phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin phosphorylation, suppressing autophagy, and inducing epithelial-mesenchymal transition. Building on this work, the present article discusses how ras homolog enriched in brain-centered signaling may connect tumor-cell metabolic adaptation, macrophage-associated biology, autophagy regulation, and metastatic plasticity in pancreatic ductal adenocarcinoma. We emphasize current advances, major controversies, and translational opportunities, with particular focus on tumor-cell colony stimulating factor 1 receptor, autophagic flux, and biomarker-guided therapeutic development.

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) is among the most aggressive human malignancies and remains defined by early dissemination, profound therapeutic resistance, and a dismal prognosis[1]. Across disease stages, median overall survival has been reported to be as short as 4 months[2]. Globally, PDAC ranks among the leading causes of cancer-related death despite being less common than many other solid tumors[3,4]. Although historically regarded as relatively rare because of its lower incidence[5], it is projected to become one of the major causes of cancer mortality by 2050[6].

Autophagy-related regulatory networks have emerged as an important component of PDAC biology[7-9]. Multi-omics analyses have identified ras homolog enriched in brain (RHEB) among the leading hub genes within autophagy-centered signaling networks and have linked it to broader mRNA/miRNA/transcription factor/immune-cell regulatory programs[10,11]. Consistent with this view, RHEB is overexpressed in pancreatic cancer, correlates with adverse prognosis, and promotes proliferation, migration, and metastatic phenotypes in experimental systems[12]. A prognostic model incorporating five autophagy-related genes, including RHEB, has likewise suggested potential relevance to immune-related stratification and therapeutic targeting[13].

The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway is a central regulator of cell growth, survival, proliferation, metabolism, and motility, and it is among the most frequently dysregulated signaling pathways in human cancer[14-19]. In PDAC, aberrant PI3K/AKT/mTOR activity has been linked to tumor progression, survival signaling, and metabolic adaptation[20-22]. Against this background, the recent report by Deng et al[23] has drawn attention to a potentially important signaling interface that links RHEB, colony stimulating factor 1 receptor (CSF1R), PI3K/AKT/mTOR activation, autophagy-associated changes, and metastatic progression. In our view, the significance of this work extends beyond a single mechanistic observation because it prompts a broader reconsideration of how tumor-cell signaling and macrophage-associated biology may converge during PDAC progression.

RHEB SIGNALING IN PANCREATIC CANCER PROGRESSION

Deng et al[23] propose that the RHEB-CSF1R complex promotes pancreatic cancer metastasis by enhancing PI3K/AKT/mTOR activation, suppressing autophagy-associated programs, and facilitating epithelial-mesenchymal transition (EMT) and metastatic dissemination. More broadly, their study supports the concept that RHEB is not simply a generic growth-associated GTPase but a functionally relevant regulator of aggressive PDAC behavior. The reported integration of patient-derived tissues, transcriptomic analyses, functional assays across multiple cell lines, and in vivo validation lends coherence to this model and places RHEB within a clinically relevant metastatic framework.

This point is conceptually important. Rather than functioning solely as a proliferation-associated molecule, RHEB may act as an interface between metabolic signaling, autophagy control, invasive-state transitions, and adaptation to microenvironmental stress. Seen in this light, recent RHEB-centered observations may help explain why autophagy exerts context-dependent effects during pancreatic cancer progression[24].

CSF1R: FROM MACROPHAGE BIOLOGY TO A POSSIBLE TUMOR-CELL SIGNALING NODE

The RHEB-CSF1R axis is especially provocative because CSF1R has classically been studied as a macrophage-centered regulator of immune suppression, stromal crosstalk, and disease progression in PDAC. Recent data suggest that the RHEB-CSF1R complex may inhibit autophagy and promote metastasis through PI3K/AKT/mTOR signaling, while a large body of prior work has already established that CSF1R regulates tumor-associated macrophage (TAM)-mediated immune responses and contributes to malignant progression in pancreatic cancer[25-28]. CSF1R is a receptor tyrosine kinase that regulates myeloid-cell differentiation, proliferation, migration, and survival[29]. It’s signaling is indispensable for the development of the mononuclear phagocyte system and for macrophage differentiation and survival[30]. As a class III receptor tyrosine kinase encoded by the proto-oncogene c-fms[31], CSF1R therefore occupies a well-established position within macrophage biology.

The central conceptual advance introduced by the recent RHEB-CSF1R model is not that CSF1R suddenly becomes relevant to pancreatic cancer - its relevance is already firmly established - but that tumor-cell-intrinsic CSF1R signaling may coexist with, and potentially intersect with, its canonical macrophage-centered functions. If validated, this interpretation would recast CSF1R not only as a microenvironmental regulator but also as a tumor-cell signaling node linked to metastatic plasticity. Representative studies relevant to this concept are summarized in Table 1.

Table 1 Representative studies supporting the ras homolog enriched in brain-colony stimulating factor 1 receptor-phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin-autophagy framework in pancreatic ductal adenocarcinoma.

Ref.	Study type	Molecule/pathway	Principal finding	Relevance to PDAC progression/metastasis	Translational implication
Tan et al[12], 2021	Bioinformatics + cell assays	RHEB	RHEB is overexpressed in PDAC and promotes proliferation, migration, and invasion, with additional links to cell-cycle regulation and Wnt signaling	Supports RHEB as a pro-aggressive signaling node in PDAC	Potential prognostic biomarker and pathway target
Deng et al[23], 2026	Tissue, cell, and in vivo study	RHEB-CSF1R/PI3K/AKT/mTOR	Proposed a tumor-cell RHEB-CSF1R complex that enhances PI3K/AKT/mTOR phosphorylation, suppresses autophagy-associated programs, and promotes EMT and metastasis	Directly links RHEB-centered signaling to metastatic behavior	Provides a biomarker-driven and combination-targeting hypothesis
Zhu et al[25], 2014	Preclinical PDAC model	CSF1/CSF1R-TAM axis	CSF1R blockade reprograms TAMs and improves the response to T-cell checkpoint immunotherapy	Demonstrates macrophage-driven support of progression and immune escape	Supports CSF1R-directed microenvironmental therapy
Mitchem et al[26], 2013	Preclinical PDAC model	CSF1R-TAM axis	Targeting TAMs reduces tumor-initiating cells, relieves immunosuppression, and enhances response to chemotherapy	Supports a metastasis-promoting role of macrophage-rich microenvironments	Supports combining CSF1R/TAM-directed therapy with cytotoxic treatment
Chen et al[10], 2023	Multi-omics analysis	Autophagy-related genes, including RHEB	Constructed an autophagy-related mRNA/miRNA/transcription factor/immune-cell network and identified RHEB among key autophagy-related hub genes	Supports the prognostic and regulatory relevance of autophagy-associated signaling in PDAC	Suggests candidate autophagy-modulator targets
Deng et al[13], 2025	Bioinformatics	Five autophagy-related genes, including RHEB	Developed a five-gene autophagy-related prognostic model with potential relevance to immune targeting	Supports the association between RHEB-centered signatures and immune infiltration	Suggests potential immunotherapy-oriented biomarker development

RHEB: Ras homolog enriched in brain; CSF1R: Colony stimulating factor 1 receptor; PDAC: Pancreatic ductal adenocarcinoma; AKT: Protein kinase B; PI3K: Phosphatidylinositol 3-kinase; mTOR: Mammalian target of rapamycin; TAM: Tumor-associated macrophage; EMT: Epithelial-mesenchymal transition.

PI3K/AKT/MTOR SIGNALING AND AUTOPHAGY IN METASTATIC ADAPTATION

Autophagy is a conserved lysosomal degradation process that clears damaged or aged cellular components and thereby supports cellular homeostasis[32,33]. In cancer, however, its role is inherently context-dependent. By recycling intracellular constituents, autophagy can provide substrates that sustain tumor-cell survival under stress, yet by removing toxic cellular material, it may also restrain tumor initiation or progression under selected conditions[34]. It can, therefore, promote survival in one context and contribute to cell death in another[35]. The autophagic process is orchestrated through the phagophore, autophagosome, and autolysosome and is controlled by a broad set of autophagy-related genes[36]. Mechanistically, adenosine monophosphate-activated protein kinase and mTOR exert opposing control over autophagy via Unc-51 like kinase 1 phosphorylation: MTOR complex 1 (mTORC1) inhibits autophagy, whereas adenosine monophosphate-activated protein kinase suppresses mTORC1 and activates the Unc-51 like kinase 1 complex. In parallel, the class III phosphatidylinositol 3-kinase complex containing PIK3C3 cooperates with ATG9 to regulate phagophore formation and maturation[37].

Both pancreatic cancer cell lines and patient tumor tissues exhibit high basal autophagy[38]. Experimental inhibition of autophagy, whether genetic or pharmacologic, can induce reactive oxygen species accumulation, DNA damage, and metabolic dysfunction, thereby suppressing PDAC progression in vitro and in vivo and suggesting that enhanced autophagy may support tumor growth in particular settings[39]. At the same time, other observations indicate that autophagy may also restrain progression under selected biological conditions. Collectively, these data support a dual, context-dependent role for autophagy in PDAC, as summarized in Table 2.

Table 2 Representative small molecules that modulate autophagy-and epithelial-mesenchymal transition-related pathways in pancreatic ductal adenocarcinoma.

Agent/target	Signaling pathway	Effect on autophagy	Principal phenotypic effect	Ref.
Umbelliprenin	AKT/mTOR, Notch1	Induces autophagy	Inhibits cancer stemness and induces apoptosis	[42]
Alisertib	PI3K/AKT/mTOR, p38 MAPK, ERK1/2, Sirtuin 1	Induces autophagy	Suppresses EMT and induces cell-cycle arrest	[55]
Qingyihuaji formula	MAPK/ERK, PI3K/AKT/mTOR	Induces autophagy	Induces apoptosis	[44]
Tetrandrine	ROS-related signaling	Inhibits autophagy	Promotes ROS accumulation and enhances therapeutic efficacy	[46]
Rhus coriaria	Not specified	Induces autophagy	Induces apoptosis	[47]
Hernandezine	ROS/AMPK	Induces autophagic cell death	Promotes cancer-cell death	[48]
G6PD	AMPK-mTOR axis	Modulates autophagy	Promotes ferroptosis resistance	[43]
PITPNC1	KRAS-MYC axis	Inhibits autophagy	Links KRAS to MYC and restrains autophagy	[45]

AKT: Protein kinase B; PI3K: Phosphatidylinositol 3-kinase; mTOR: Mammalian target of rapamycin; EMT: Epithelial-mesenchymal transition; MAPK: Mitogen-activated protein kinase; Notch1: Notch homolog 1 (translocation-associated); ERK: Extracellular signal-regulated kinase; ROS: Reactive oxygen species; AMPK: Adenosine monophosphate-activated protein kinase; KRAS: Kirsten rat sarcoma viral oncogene homolog; MYC: Myelocytomatosis viral oncogene homolog.

Within this framework, the RHEB-CSF1R axis can be viewed as part of a broader metastatic stress-adaptation program. The association among RHEB activation, PI3K/AKT/mTOR phosphorylation, attenuation of autophagy-associated programs, and induction of EMT suggests that PDAC cells may exploit this signaling module to preserve survival, motility, and phenotypic plasticity under nutrient limitation, immune pressure, and dissemination-associated stress.

THERAPEUTIC IMPLICATIONS, EMT, AND RATIONAL COMBINATION STRATEGIES

The therapeutic implications of this framework are noteworthy. CSF1R inhibitors are already being explored in oncology[40], predominantly through reprogramming of TAMs[41], and autophagy modulation has entered clinical testing in pancreatic cancer. Multiple small-molecule agents influence PDAC biology by modulating autophagy and apoptosis through pathways that include epidermal growth factor receptor/Ras/Raf/mitogen-activated protein kinase and PI3K/AKT/mTOR. Representative examples include direct autophagy inducers such as rapamycin, indirect autophagy modulators such as resveratrol, and inhibitors such as chloroquine. Additional agents that perturb autophagy-related signaling in PDAC include Umbelliprenin[42], glucose-6-phosphate dehydrogenase-related redox control[43], the Qingyihuaji formula[44], PITPNC1[45], tetrandrine[46], Rhus coriaria[47], and Hernandezine[48]. Their principal mechanisms in relation to autophagy and EMT, are summarized in Table 3.

Table 3 Context-dependent roles of autophagy in pancreatic ductal adenocarcinoma progression.

Context	Functional role of autophagy	Mechanistic basis	Biological consequence	Ref.
Basal PDAC state	Tumor-promoting	High basal autophagic activity in PDAC cell lines and patient tissues	Supports tumor growth and metabolic fitness	[38]
Genetic inhibition (ATG7 or HMGB1 knockout)	Functionally tumor-supportive under basal conditions	Autophagy blockade induces ROS accumulation, DNA damage, and metabolic abnormalities	Suppresses PDAC progression	[39]
Pharmacological inhibition (chloroquine)	Functionally tumor-supportive under basal conditions	Pharmacologic blockade disrupts autophagic recycling and promotes oxidative/metabolic stress	Suppresses PDAC progression	[39]
Environmental stress (hypoxia or nutrient deprivation)	Pro-survival	Provides metabolic sub strates and stress adaptation	Supports tumor-cell survival under hostile microenvironmental conditions	[35,72]

PDAC: Pancreatic ductal adenocarcinoma; ROS: Reactive oxygen species.

Combination strategies are particularly attractive. In preclinical models, combining CSF1R inhibition with programmed death 1 blockade produced marked tumor regression[49]. In PDAC mouse models, inhibition of myeloid growth factor receptor CSF1R signaling functionally reprogrammed macrophages, enhanced antigen presentation, and promoted an anti-tumor T-cell response[25]. Given that TAMs are consistently associated with tumor progression and poor prognosis[25,50,51], the possibility that tumor-cell CSF1R may cooperate with RHEB signaling broadens the translational scope of this pathway.

The relevance of this signaling framework becomes even more apparent when viewed through the lens of EMT and metastatic plasticity. EMT is a prerequisite for invasion and dissemination and is shaped by both cell-intrinsic signaling and the tumor microenvironment[52-54]. In PDAC, EMT contributes not only to metastatic spread but also to therapeutic resistance and disease recurrence[55,56]. Increasingly, EMT is recognized as one manifestation of broader lineage plasticity, encompassing acinar-to-ductal metaplasia, cancer stem-cell regeneration, and molecular subtype rewiring during disease progression[57,58].

Mechanistically, the PI3K/AKT/mTOR pathway serves as a central node linking autophagy and EMT-associated phenotypes. Yang et al[59] reviewed these interactions from a cellular perspective and emphasized invasion as a survival behavior of PDAC cells. Wang et al[55] showed that the Aurora kinase A inhibitor Alisertib induces cell-cycle arrest and autophagy while suppressing EMT in human pancreatic cancer cells through pathways that include PI3K/AKT/mTOR, p38 mitogen-activated protein kinase, extracellular signal-regulated kinase 1, and Sirtuin 1 signaling[55]. These findings support the idea that coordinated targeting of multiple nodes within this network may concurrently modulate EMT and autophagy.

Recent studies have further connected metastasis, cell plasticity, and EMT to therapeutic resistance in PDAC. Guo et al[60] highlighted that EMT in PDAC arises from altered molecular interactions and contributes to both metastasis and chemoresistance. Key pathways involved - including signal transducer and activator of transcription 3, phosphatase and tensin homolog (deleted on chromosome 10), PI3K/AKT, and Wnt - remain attractive therapeutic targets. The tumor microenvironment further amplifies this process, with macrophages, neutrophils, and cancer-associated fibroblasts reshaping both disease progression and treatment response[60]. At the level of organ colonization, Rademaker et al[61] identified proprotein convertase subtilisin/kexin type 9 as a determinant of liver vs lung metastatic tropism in PDAC and linked differential cholesterol metabolism to mTORC1 activation at the lysosome. This observation directly reinforces the relevance of metabolic rewiring to the signaling model discussed here.

Therapeutic strategies targeting EMT and metastatic plasticity are evolving rapidly. Ling et al[62] emphasized the role of epithelial-mesenchymal plasticity, alternative splicing, ras-related C3 botulinum toxin substrate 1 (RAC1)/ras-related C3 botulinum toxin substrate 1 isoform B, and context-dependent transforming growth factor-β signaling in tumor differentiation and therapy. Zahid Hosen et al[63] showed that selective urokinase inhibition combined with chemotherapy reduced primary tumor growth, decreased EMT and stemness, and eliminated visible distant metastases in PDAC mouse models. Taken together, these data argue for mechanism-driven combinations that target macrophage biology, tumor-cell stress adaptation, and metastatic plasticity in parallel.

If tumor-cell CSF1R is confirmed as a functional partner of RHEB, it will be important to determine whether clinically relevant CSF1R inhibitors or PI3K/AKT/mTOR inhibitors can suppress the metastatic phenotypes associated with this axis and how such interventions interact with immune contexture in immunocompetent models[64]. Mapping the binding domains and nucleotide-state dependence of the RHEB-CSF1R interaction may also provide a foundation for structure-guided inhibitor development.

FUTURE DIRECTIONS AND UNRESOLVED QUESTIONS

Several unresolved issues should shape the next phase of this field. First, the cellular source and spatial biology of CSF1R require deeper clarification. CSF1R is highly expressed in pancreatic cancer tissues and contributes to an inhibitory tumor microenvironment[65]. Although current data show CSF1R regulation and functional rescue in tumor cell lines, orthogonal confirmation of tumor-cell CSF1R in human specimens - using multiplex immunofluorescence, RNAscope in situ hybridization, or single-cell RNA sequencing - would help exclude confounding by myeloid infiltration, particularly in metastatic lesions.

Second, the autophagy-related conclusions would be strengthened by rigorous flux-based assessment. Because autophagy is intrinsically dynamic[66], complementary approaches such as LC3-II turnover in the presence and absence of lysosomal inhibitors, as well as p62/SQSTM1 degradation kinetics, may improve mechanistic interpretability in future studies. Static readouts such as LC3 abundance are difficult to interpret in isolation, especially when lysosomotropic agents are used as perturbation tools.

Third, the prognostic component is promising but would benefit from additional methodological refinement. The institutional cohort remains relatively small, and follow-up windows should be harmonized to reduce potential bias. Independent external validation, together with time-dependent receiver operating characteristic analysis, Harrell’s C-index, calibration plots, and multivariable Cox models that incorporate clinicopathological covariates, would increase confidence that RHEB-based risk stratification is clinically robust.

Fourth, future work should distinguish more clearly between class I and class III PI3K signaling. Class I PI3K-driven AKT/mTOR activation is frequently discussed alongside autophagy biology, yet class III PI3K/vacuolar protein sorting 34 is indispensable for autophagosome nucleation. Failure to distinguish these classes risks oversimplifying the mechanism under discussion. Fifth, next-generation validation should incorporate tissue-level and spatially resolved analyses in clinically annotated cohorts and translational models that reflect liver metastatic biology and immune contexture. The principal controversies and prioritized future directions are summarized in Table 4.

Table 4 Major controversies and priority future directions in the ras homolog enriched in brain-colony stimulating factor 1 receptor-autophagy field.

Key question	Current evidence	Major limitation	Why it matters	Priority next step
Is tumor-cell CSF1R broadly reproducible in PDAC	Recent work suggests that tumor-cell CSF1R may participate in metastatic signaling	CSF1R is classically macrophage-enriched, and tissue-level reproducibility remains uncertain	Determines whether this reflects a tumor-cell mechanism, a microenvironmental signal, or both	Spatially resolved validation using multiplex IF, RNAscope, or scRNA-seq[65]
Is autophagy suppressive or permissive for PDAC metastasis	Available evidence supports a context-dependent dual role of autophagy in PDAC progression[34,35]	Stage, treatment context, and model system can alter interpretation	Directly affects therapeutic strategy	Phenotype-linked, context-aware autophagy studies
Are class I and class III PI3K being conceptually conflated	Class I PI3K–AKT–mTOR signaling is generally linked to autophagy suppression, whereas class III PI3K/VPS34 is required for autophagosome initiation	Many studies refer broadly to PI3K without class-specific clarification	Prevents mechanistic overstatement and improves pathway precision	Class-specific wording and validation
Can RHEB-based signatures improve risk stratification	RHEB is associated with poor prognosis in PDAC datasets and functional models[12]	Existing cohorts remain limited and require independent confirmation	Essential for biomarker development and clinical risk stratification	External validation with C-index, calibration, and time-dependent ROC analysis
What is the most rational translational strategy	CSF1R/TAM, PI3K/mTOR, and autophagy are all targetable in principle	Single-pathway strategies may be insufficient in a highly adaptive tumor	Guides clinical trial design	Evaluate mechanism-driven combinations, including CSF1R-directed therapy with chemotherapy, immunotherapy, or pathway-targeted agents[25,63]

RHEB: Ras homolog enriched in brain; CSF1R: Colony stimulating factor 1 receptor; PDAC: Pancreatic ductal adenocarcinoma; AKT: Protein kinase B; PI3K: Phosphatidylinositol 3-kinase; mTOR: Mammalian target of rapamycin; TAM: Tumor-associated macrophage; IF: Immunofluorescence; VPS34: Vacuolar protein sorting 34; scRNA-seq: Single cell RNA sequencing; ROC: Receiver operating characteristic.

CONCLUSION

Recent work has linked RHEB to metastatic behavior in pancreatic cancer through a CSF1R-associated PI3K/AKT/mTOR-autophagy-EMT axis. This framework is conceptually attractive because it integrates tumor-cell metabolic signaling, macrophage-associated biology, autophagy regulation, and invasive-state transitions within a single translational narrative.

At the mechanistic level, targeting the PI3K/AKT/mTOR pathway[67], accounting for the dual functions of autophagy[68], and considering non-canonical roles of RHEB[24] together provide a rationale for deeper interrogation of this axis. Likewise, therapeutic strategies that modulate TAMs through CSF1R[40,69,70] and experimental approaches that rigorously assess autophagic flux[71] provide important tools for future translational development.

In our view, the main value of the recent RHEB-CSF1R literature is not simply that it adds another pathway component but that it forces a reconsideration of how tumor-cell signaling and macrophage-associated biology intersect in pancreatic cancer. The RHEB-CSF1R axis may ultimately prove most relevant not as a universal PDAC mechanism, but as a context-specific metastatic adaptation program. Its clinical significance will therefore depend on rigorous validation of cell-type specificity, careful interpretation of autophagy biology, and biomarker-guided evaluation of mechanism-driven combination strategies.