Beyond Mutations: miR-101a as a Molecular Bridge Linking Ethanolamine, Microbial Dysbiosis, and Inflammation in Obesity-Driven Colorectal Cancer

1. Introduction

Colorectal cancer (CRC) remains a leading cause of cancer mortality worldwide. Widespread screening and advances in systemic treatment have broadly improved survival, the risk of CRC and cancer-related death remains elevated in certain populations. For instance, CRC incidence is rising in patients under 50 years old [1] and is substantially elevated in obese compared to non-obese individuals [2]. The underlying pathobiology of increased cancer incidence in these populations remains unclear, but recent work implicates alterations in the gut microbiome induced by a Western-style diet [3,4,5]. This review outlines a pathway linking diet and the gut microbiome to the regulation of gene expression by MicroRNAs (miRNAs) in the tumor microenvironment and may represent a novel therapeutic target in CRC.

MicroRNAs (miRNAs) are a class of small, non-coding RNAs approximately 20-24 nucleotides in length that function as critical regulators of post-transcriptional gene expression [6]. They primarily exert their effect through base-pairing with complementary sequences in the 3′ untranslated region (3′ UTR) of target messenger RNAs (mRNAs), leading to mRNA degradation or translational repression [7]. By fine-tuning protein expression, miRNAs regulate diverse cellular processes, including cell proliferation, differentiation, apoptosis, immune regulation, and stress adaptation [8,9]. Importantly, aberrant miRNA expression or activity has been recognized as a hallmark of cancer biology, contributing to both tumor initiation and progression. Some miRNAs function as tumor suppressors by restraining oncogenic pathways, while others function as oncomiRs, promoting tumor growth, metastasis, or therapeutic resistance. Notably, certain miRNAs exhibit context-dependent dual roles, functioning as tumor suppressors in one tissue or cellular environment and as tumor promoters in another [10,11,12]. miR-101a, the murine homolog of human miR-101, is encoded within conserved genomic loci and is ubiquitously expressed across several tissues, including the intestinal epithelium, liver, brain, and immune compartments [13,14,15,16,17,18]. Historically, miR-101a has been characterized as a tumor suppressor. One of its canonical targets is Enhancer of Zeste Homolog 2 (EZH2), the catalytic component of the Polycomb Repressive Complex 2 (PRC2), which mediates trimethylation of histone H3 lysine 27 (H3K27me3), leading to transcriptional silencing of tumor suppressor genes [14,19,20,21,22]. Loss or downregulation of miR-101a, therefore, results in EZH2 overexpression, enhanced histone methylation, and widespread suppression of genes critical for maintaining epithelial differentiation and genomic stability [22,23,24,25]. In prostate, breast, liver, and brain cancers, decreased expression of miR-101 has been consistently associated with increased tumor aggressiveness, angiogenesis, and poor prognosis [26,27]. Other validated targets of miR-101a include MCL-1 (myeloid cell leukemia-1), an anti-apoptotic member of the B-cell lymphoma (BCL)-2 family; cyclooxygenase-2 (COX-2), a pro-inflammatory enzyme implicated in carcinogenesis; and DNA methyltransferases (DNMT)3A/B, which regulate DNA methylation patterns in cancer [28,29]. Collectively, these studies have established miR-101a as a guardian against uncontrolled proliferation, epigenetic silencing of tumor suppressors, and evasion of apoptosis, functioning predominantly as a tumor suppressor under physiological conditions.

Despite its well-documented tumor-suppressive role, accumulating evidence suggests that miR-101a can paradoxically promote tumor growth in specific pathological contexts, particularly those characterized by metabolic dysregulation, chronic inflammation, and gut barrier dysfunction [30,31,32,33,34]. A notable example emerges in obesity and/or type-2 diabetes (T2D)-associated colorectal cancer (CRC). Obesity/T2D is characterized by systemic low-grade inflammation, altered lipid metabolism, insulin resistance, and significant changes in gut microbiome composition (dysbiosis) [35,36,37,38,39,40,41,42]. The microenvironment of CRC is saturated with pro-inflammatory lipid mediators and deficient in pro-resolving mediators, creating dysregulated, non-resolving inflammation [39,43]. These alterations collectively create a microenvironment conducive to colorectal initiation and progression. In this context, miR-101a expression has been observed to increase rather than decrease, with downstream effects that deviate markedly from its classical tumor-suppressive functions. The gut microbiota, heavily shaped by dietary patterns, is increasingly recognized as a pivotal regulator of host miRNA expression. Diets enriched in fat and red meat increase luminal ethanolamine concentrations, a membrane phospholipid-derived metabolite that serves as a carbon and nitrogen source for many gut bacteria [44,45]. Elevated intestinal ethanolamine has been identified as a critical inducer of miR-101a expression in the colonic epithelium [33,46]. Mechanistically, ethanolamine may act both directly, through epithelial signaling pathways, and indirectly, by selecting for bacterial taxa that produce metabolites influencing host gene expression [47]. Dysbiotic microbiota in obesity may amplify this effect, establishing an ethanolamine miR-101a axis that links diet, microbial metabolism, and host transcriptomic regulation.

Together, this evidence positions miR-101a as both a guardian and a potential accomplice in tumorigenesis, with its role determined by the surrounding metabolic-microbial landscape. This paradox offers a novel framework connecting obesity, gut dysbiosis, and colorectal cancer pathogenesis.

1.1. Genomic Organization and Sequence Features of the miR-101 Family

In mammals, the miR-101 family is encoded by two conserved loci that produce the same predominant mature effector strands, miR-101-3p/5p (5′-UACAGUACUGUGAUAACUGAA-3′) [48]. In humans, the precursors map to miR-101-1 on chr1p31.3 and miR-101-2 on chr9p24.1; in mice, the orthologues loci correspond to miR-101a on chr4 (negative strand; GRCm39: ~101,204,142-101,204,224) and miR-101b on chr19 (positive strand; ~29,112,679-29,112,775) [49,50,51,52,53]. Within the human genome, miR-101 derives from two primary precursors, miR-101-1 (75 bp) and miR-101-2 (79 bp), both of which are essential for its biogenesis. In mice, miR-101b is embedded within an intron of RNA Terminal Phosphate Cyclase-Like (Rcl)1, whereas miR-101a is intergenic, an arrangement that likely contributes to subtle differences in transcriptional control and co-regulation with host-gene programs [49]. Biogenesis follows the canonical microRNA processing pathway: RNA polymerase II transcription, nuclear cropping by Drosha-DiGeorge Critical Region (DGCR8), cytoplasmic cleavage by Dicer, and Argonaute loading into the RNA-Induced Silencing Complex (RISC) [54,55]. Although both arms are detectable, most tissues preferentially load the 3p arm, establishing miR-101-3p as the principal functional strand for target repression. Sequence variation introduces additional regulatory complexity. Single-nucleotide variants within the hairpin (e.g., basal junction, apical loop, dicer processing sites) can shift microprocessor/dicer efficiency, thereby affecting mature miRNA abundance and 5p/3p arm selection [56,57,58]. Variants within the seed regions (nts 2-8 of miR-101-3p) are especially consequential, as they redefine the targetome, simultaneously extinguishing canonical sites (e.g., in Enhancer of Zeste Homolog [EZH]2 or Post-Transcriptional Gene Silencing [PTGS]2/ Cyclooxygenase [COX]-2) and creating novel interactions in unrelated transcripts [59,60]. Population resources catalog multiple variants in and around miR101-1/-2; some of which have been associated with altered cancer risk, underscoring their potential functional impact [54]. Complementing miRNA-centric variation, 3′-UTR polymorphisms (“miR-eQTLs”) within target genes can gain or lose miR-101 recognition motifs, stratifying repression across individuals, tissues, and life developmental stages.

Expression atlases reveal a broad, developmentally dynamic abundance of miR-101-3p. In the mouse brain, miR-101a/b levels rise from late embryogenesis (~E16) through early postnatal stages (~P12), consistent with roles in neuronal maturation and circuit refinement [61]. In adults, miR-101 is readily detected across epithelial, stromal, and immune compartments, with absolute levels tuned by hormonal, inflammatory, and metabolic cues [53,61,62,63]. Functionally, miR-101-3p converges on regulators of chromatin state, eicosanoid/inflammatory tone, cell survival, and cytoskeletal dynamics-with repeatedly validated targets including EZH2, Myeloid Cell Leukemia (MCL)1, PTGS2/COX-2, and context-dependent effectors such as FBJ Murine Osteosarcoma Viral Oncogene (FOS), Stathmin (STMN)1, DNMT3A, Ras-related C3 botulinum toxin substrate (RAC)1, SRY (Sex-determining Region Y)-Box (SOX)9, and Cyclin-Dependent Kinase (CDK)8 [59,64,65,66,67,68,69]. These interactions typically impose anti-proliferative and anti-inflammatory constraints in epithelial tissues. However, tissue state (e.g., obesity-associated inflammation, cytokine milieu, metabolite availability) can invert net outcomes by reshaping competing RNA networks and transcriptional baselines. Aberrant expression of miR-101a exerts profound influence on genomic stability by targeting multiple classes of genes involved in DNA repair, chromatin regulation, inflammation, and barrier integrity [23,33,70,71,72]. At the level of the DNA damage response (DDR), miR-101a directly represses ataxia-telangiectasia mutated (ATM) and Protein Kinase, DNA-Activated, Catalytic Subunit (PRKDC [DNA-PKcs]), impairing double-strand break repair and thereby sensitizing epithelial cells to DNA damage and mutational accumulation [73,74]. In parallel, miR-101a regulates chromatin modifiers such as EZH2, Disruptor of Telomeric Silencing 1-Like (DOT1L), and DNMT3A/3B, leading to altered histone methylation and DNA methylation landscapes that promote epigenetic instability and oncogenic transcriptional reprogramming [28,75,76,77,78,79]. Cytoskeletal fidelity is also influenced through repression of STMN1, which disrupts microtubule dynamics and predisposes cells to aneuploidy [80,81,82]. In obesity-associated CRC, these molecular effects converge with barrier dysfunction, where miR-101a-driven defects in goblet cell differentiation and mucin secretion reduce Mucin (MUC)2 levels, permitting microbial translocation and activation of Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB)/ Interleukin (IL)-6/ (Signal Transducer and Activator of Transcription) STAT3 signaling [83,84,85,86,87]. This inflammatory loop sustains the production of reactive oxygen and nitrogen species (ROS/RNS), amplifying DNA damage and accelerating the clonal expansion of mutated epithelial cells. Collectively, these findings position miR-101a as a context-dependent regulator of tumorigenesis that does not directly induce point mutations but instead establishes a mutagenic microenvironment by suppressing DNA repair, promoting epigenetic deregulation, driving prostaglandin-mediated inflammation, and disrupting barrier function, ultimately promoting colorectal tumor initiation and progression.

Induction of miR-101a by Metabolic and gut barrier dysregulation

The tumor-promoting role of miR-101a is closely linked to diet and metabolites generated by the gut microbiota [33]. Recent investigations reveal that intestinal ethanolamine, a phospholipid precursor derived from dietary phosphatidylethanolamine and abundant in high-fat and high-meat diets [44,88,89,90,91,92,93], plays a central role in driving miR-101a expression. Ethanolamine is a preferential nutrient source for several gut bacterial taxa, including opportunistic pathogens and dysbiosis-associated organisms enriched during dysbiosis [94,95,96,97,98,99,100,101]. In the context of obesity and metabolic syndrome, dysbiotic microbiota increases the availability of ethanolamine within the colonic lumen [33,96,102,103,104,105]. This metabolite acts as more than a passive nutrient and functions as a signaling molecule linking diet to host transcriptional regulation [33,106]. Elevated ethanolamine stimulates miR-101a upregulation in colonic epithelial cells, thereby altering the delicate balance between epithelial homeostasis and injury responses. Unlike the canonical tumor-suppressive functions of miR-101a observed in non-obese conditions, chronic upregulation in obesity skews epithelial biology toward barrier dysfunction and downstream neoplasia as described below [33]. This metabolic induction of miR-101a positions it as a molecular bridge connecting nutrition, dysbiosis, and tumor initiation.

One of the earliest and most consequential downstream effects of miR-101a upregulation is its interference with goblet cell differentiation and mucin biosynthesis. Goblet cells are specialized epithelial cells responsible for secreting MUC2, the major structural mucin forming the intestinal mucus layer. This mucus barrier functions as the first line of defense, physically separating luminal microbes from the epithelial surface [107,108,109,110]. Overexpression of miR-101a represses transcriptional regulators that orchestrate goblet cell maturation and MUC2 production [67,111,112]. Consequently, MUC2 expression is reduced, leading to a thinner, discontinuous mucus layer. This structural defect compromises mucosal protection and allows bacteria and microbial-associated molecular patterns (MAMPs) to approach the epithelium [113,114,115,116,117]. This barrier disruption, often termed as “leaky gut”, represents a critical initiating event in CRC pathogenesis [118,119,120]. Barrier impairment creates a permissive environment for microbial translocation, allowing endotoxins, such as lipopolysaccharide (LPS), to cross into the lamina propria and the systemic circulation [121,122,123,124,125]. The resulting endotoxemia perpetuates immune activation and contributes to systemic low-grade inflammation, a hallmark of obesity-associated diseases [126,127,128,129,130,131]. The detailed schematic diagram showing obesity-driven colorectal cancer development is shown in Figure 1. Moreover, the loss of mucin alters the spatial distribution of the microbiota, promoting closer interactions between microbes and the epithelium, which further exacerbate dysbiosis [110,125,132,133,134]. Thus, miR-101a-mediated suppression of mucin biosynthesis dismantles a key protective mechanism of the gut, transforming the mucosal interface from a defensive barrier into a zone of persistent microbial challenge.

1.2. Chronic Inflammation as a Driver of Malignant Transformation via miR-101a

The epithelial barrier defects induced by miR-101a create fertile ground for sustained inflammation, which in turn may accelerate tumor initiation and progression. Microbial translocation engages pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs) on epithelial and immune cells, triggering activation of the NF-κB pathway [135,136,137]. This leads to robust transcription of pro-inflammatory cytokines, including Tumor Necrosis Factor (TNF)-α, IL-6, and IL-1β, which amplify local and systemic immune responses [138,139,140]. Likewise, miR-101a overexpression directly interacts with inflammatory mediators by enhancing COX-2 expression, a critical enzyme in prostaglandin synthesis [141,142]. Elevated COX-2 activity promotes angiogenesis, inhibits apoptosis, and fosters immune evasion, thereby contributing to a tumor-permissive environment [143,144]. Furthermore, chronic inflammation stimulates the production of ROS/RNS by infiltrating immune cells [145,146,147]. These reactive ROS/RNS molecules induce DNA damage and mutagenic stress in epithelial cells, thereby accelerating the accumulation of oncogenic mutations [148,149,150,151,152,153,154]. This chronic inflammatory state not only sustains epithelial injury but also promotes cycles of injury and regenerative proliferation, further increasing the probability of malignant transformation [155,156,157,158,159]. Local immune cells experience exhaustion, and populations of anti-tumor cytotoxic T cells decline [160]. Importantly, inflammation-induced activation of STAT3 and related oncogenic pathways promotes survival signaling and resistance to apoptosis in epithelial cells, consolidating the tumor-promoting role of miR-101a in the inflamed gut [161,162,163].

This inflammatory microenvironment promotes cycles of epithelial injury and regenerative proliferation. The colon is a tissue characterized by rapid turnover, with epithelial cells replenished by stem cells located at the base of the crypts. In the presence of persistent barrier stress and inflammation, stem cells undergo hyperproliferation to repair damaged mucosa [164,165]. This process, while initially protective, increases the probability of replication errors, clonal expansion, and selection of mutant populations. Within this hyperproliferative context, canonical oncogenic pathways such as STAT3, NF-κB, COX-2/ Prostaglandin E₂ (PGE2), and Wingless Integration-1 (Wnt)/β-catenin are activated, synergizing with accumulating genetic mutations to drive the transition from normal epithelium to dysplastic adenomas [149,166,167,168]. Importantly, miR-101a acts as an upstream driver of this vicious cycle by compromising the mucus barrier and facilitating microbial translocation, thereby perpetuating the continuous activation of inflammatory and proliferative signaling pathways [33,148,169]. As adenomas develop, miR-101a continues to influence tumor progression by remodeling the tumor microenvironment. The validated gene and protein targets of miR-101a, functionally implicated in diverse disease conditions, are listed in Table 1. Persistent COX-2 activity and cytokine signaling stimulate neovascularization, ensuring adequate oxygen and nutrient supply for expanding lesions [170,171,172]. Inflammatory mediators and pathogenic bacteria remodel the extracellular matrix, weakening cell adhesion and facilitating epithelial invasion into deeper tissue layers.

1.3. Obesity Associated Colorectal Cancer Development via miR-101a

In the colon and mammary epithelium, miR-101 regulates COX-2 signaling and cytoskeletal programs, thereby linking it to barrier integrity, goblet-cell differentiation, mucus production, and epithelial restitution [32,173,174,175]. In parallel, its developmental trajectory and neuronal expression support roles in synaptic maturation and activity-dependent plasticity. Together, genomic organization, sequence features, and variant landscapes position the miR-101 family as a precision node through which diet-microbe-host signals (e.g., ethanolamine-driven transcriptional shifts) can recalibrate target accessibility and pathway flux, with implications for context-dependent phenotypes in health and disease. Chronic inflammation further recruits immunosuppressive cells, such as regulatory T cells and myeloid-derived suppressor cells, which dampen anti-tumor immunity and create a permissive environment for malignant clones [159,176]. This shift from immune surveillance to immune evasion marks a critical step in tumor progression, allowing adenomas to evolve into invasive carcinomas.

The role of miR-101a in CRC is highly context-dependent, which explains its paradoxical classification as both a tumor suppressor and a tumor promoter. In many non-obese contexts, loss of miR-101a contributes to tumorigenesis by relieving repression of oncogenes such as EZH2, MCL-1, and DNMT3A. In contrast, in the obese, dysbiotic colon, overexpression of miR-101a acts through an entirely different mechanism: weakening epithelial barrier defenses, fueling chronic inflammation, and potentiating oncogenic signaling. This duality highlights the importance of considering metabolic, microbial, and inflammatory contexts when assessing miRNA function in cancer biology. In the framework of the adenoma carcinoma sequence, miR-101a does not operate as a classical genetic driver mutation but rather as a facilitator of tumor-promoting conditions. Barrier dysfunction increases stem cell exposure to microbial ligands and mutagens, inflammation sustains proliferative and survival signaling, and microenvironmental remodeling accelerates progression. In this way, miR-101a integrates into the canonical CRC model as a non-genetic but essential regulator that increases the likelihood of malignant transformation in metabolically stressed environments.

A significant tumor-promoting effect of elevated miR-101a in this context is the disruption of mucosal barrier integrity [33]. Normally, colonic goblet cells secrete MUC2, the predominant mucin that forms the mucus layer protecting epithelial surfaces from microbial encroachment [110]. Upregulation of miR-101a interferes with goblet cell differentiation and represses the transcriptional machinery required for mucin biosynthesis. This results in decreased MUC2 production and a thinner or disrupted mucus barrier. The immediate consequence is exposure of the intestinal epithelium to luminal bacteria and their associated components, such as LPS. This condition facilitates microbial translocation into the lamina propria and systemic circulation by increasing the gut permeability [106]. The barrier defects initiated by miR-101a overexpression propagate a cycle of chronic low-grade inflammation. In summary, elevated miR-101a acts as a tumor-promoting factor in obesity associated CRC by disrupting goblet cell maturation and mucin biosynthesis, leading to MUC2 depletion and compromised mucus barrier integrity. The resulting weakening of the gut barrier permits microbial translocation and sustained low-grade inflammation, establishing a pro-carcinogenic environment.

2. Conclusions

Taken together, the evidence indicates that miR-101a serves as a central mediator of tumor initiation and progression in obesity-associated CRC. Its contribution lies not in direct oncogene activation but in ecological disruption: destabilizing mucosal defenses, perpetuating inflammation, and shaping a tumor-permissive, immune-privileged niche. By linking dietary metabolites, such as ethanolamine, to microbial dysbiosis and host epithelial regulation, miR-101a exemplifies the intricate interactions that drive cancer development beyond genetic mutations alone. Importantly, this understanding underscores the need for context-specific investigation in miRNA biology, as the same molecule may serve as a tumor suppressor in one tissue or metabolic state and a tumor promoter in another. In obesity-associated CRC, miR-101a emerges as a crucial molecular bridge linking diet, microbiota, and tumorigenesis, offering both mechanistic insight and a potential therapeutic target.