TO THE EDITOR
Colorectal cancer (CRC) is a major global health concern that begins in the colon or rectum, often resulting from polyps. GLOBOCAN predicts around 1.87 million new cases and 0.88 million deaths from colon and rectal cancers by 2022[1]. Beyond its epidemiological implications, CRC development is now recognized as a complex, microenvironment driven phenomenon[2]. Exosomes are small extracellular vesicles speed up CRC progression by transporting bioactive cargo including miRNAs/LncRNAs, DNA, proteins, and lipids that promotes epithelial mesenchymal transmission, invasion, angiogenesis, immunological reprogramming, hepatic pre-metastatic niche creation, and therapy resistance[3]. In this regard, I read with great interest the recent article published in the World Journal of Gastrointestinal Oncology entitled "Exosomal miR-191 promotes colorectal cancer progression by inducing M2 macrophage polarization and inhibiting ferroptosis" by Zhao and Wei[4]. In this study, the authors concluded that the inhibition of exosomal miR-191 mitigated CRC development by triggering ferroptosis in macrophages. This work uncovered a novel mechanism by which exosomal miR-191 influences the tumor microenvironment. Here in I will shed light on the mechanist pathway regarding these findings by using of the bioinformatic analysis of The Cancer Genomic Atlas (TCGA) datasets. Emerging evidence suggests that miR-191 activates NF-κB, a transcriptional regulator of inflammatory and pro-tumor pathways. In endothelial/angiogenesis models, miR-191 increased NF-κB activation and the expression of NF-κB-responsive genes. Hence, the application of Bay11-7082, an NF-κB inhibitor, abolished these effects, confirming a causal miR-191-NF-κB pathway[5]. In airway inflammation, miR-191-enriched extracellular vesicles activate NF-κB in bronchial epithelial cells, leading to increased interlukin-8 production[6]. Significantly, whereas the miR-191–NF-κB axis has predominantly been elucidated in endothelium and inflammatory epithelial models, the proposal is directly applicable to CRC patients, in which NF-κB signaling serves as a pivotal regulator of macrophage polarization and tumor–immune interactions. In this notion, NF-κB activation is dysregulated in many cancers, leading to immune evasion and aggressive behaviour. Prolonged NF-κB signaling leads to increased cytokine production, survival, angiogenesis, metastasis, and resistance to treatment. Inhibitors of the miR-191-NF-κB axis can slow cancer growth and reduce inflammation[7]. A previous study has confirmed that the activation of the NF-κB pathway increases the production of vascular endothelial growth factor-A in CRC and promotes angiogenesis[8]. Cancer cell-released exosomes interact with macrophages by internalizing and transferring cargo such as proteins and microRNAs, which can impair macrophages functions[9]. Tumor-associated macrophages (TAMs) in CRC produce both anti-tumor "M1-like”, and pro-tumor "M2-like" responses. M1-like macrophages (pro-inflammatory and cytotoxic) had a better prognosis in CRC, but M2-like TAMs promote immunosuppression, angiogenesis, invasion, and therapy resistance[10]. Tumor immune estimation resource, version 3 (TIMER3) is an integrated bioinformatics platform for systematic analysis of immune infiltration across diverse cancer types. In TIMER3, gene expression data are normalized using standardized RNA-sequencing processing pipelines, primarily based on transcripts per million values with log2 transformation[11]. Using TIMER3, a bioinformatic tool for immune infiltrate analysis, the gene module was employed to analyse the infiltration of M2 macrophages in CRC patients to examine the impact of NF-κB1 on their infiltration within the tumor microenvironment. Spearman's rank correlation analysis was used to find relationships between NF-κB1 and M2 macrophages infiltration with tumor purity adjustment. The mutation module was used to analyse the influence of NF-κB1 on M2 macrophage infiltration based on four hundred sixty-one TCGA patients. TIMER3 shows a log-fold difference in M2 macrophage infiltration levels between CRC patients with the NF-κB1 mutation and tumors in the wild-type and a P value < 0.05 was indicated statistically significance[11]. Substantially, the bioinformatic analysis of TCGA datasets utilizing TIMER3 demonstrated a significant positive correlation between NF-κB and M2 macrophages infiltration in CRC tissues (Figure 1A). Besides, the findings indicated that the NF-κB mutation significantly reduced macrophage infiltration in CRC patients compared to wild-type NF-κB (Figure 1B). Next, I used TIMER3's outcome module to investigate the impact of M2 macrophages and NF-κB1 expression on disease-free interval (DFI), with the ability to adjust for numerous factors in a multivariable cox proportional hazard model. The hazard ratio and P value for Kaplan-Meier curve were estimated among four hundred sixty-one TCGA patients and a P value < 0.05 was considered statistically significant[11]. Interestingly, in case of NF-κB1 expression; a significant difference in DFI (HR = 6.34, P = 0.00312) between high and low M2 macrophages. On the other hand, the analysis showed that there was no significant difference in DFI between high and low M2 when NF-κB1 expression was low (HR = 0.56, P = 0.333). This reveals that M2 macrophages' impact on DFI appears to be context-dependent; they have a significant negative effect on the high NF-κB expression group but no significant change in the low NF-κB1 expression group (Figure 1C). Overall, miR-191 is a promising therapeutic target for NF-κB-driven inflammation and tumor progression because it can boost NF-κB activation and NF-κB-responsive cytokine/angiogenic programs. This could make CRC where this pathway is chronically dysregulated more resistant to treatment, more likely to spread, and more likely to suppress the immune system[12]. In addition, the analyses show that NF-κB1 changes the immunosuppressive environment of CRC by encouraging M2 macrophages infiltration. Changes in NF-κB1 were connected to macrophages infiltration, which suggests that this pathway plays a role in recruiting as well as macrophages polarization. In tumors with high NF-κB expression, a lot of M2 was linked to a shorter disease-free time, but not when NF-κB1 was low. In the present proposal, the primary focus is the miR-191/NF-κB/M2 macrophage axis; however, macrophage fate in CRC is also influenced by convergent signaling pathways. Notably, STAT3–driven inflammatory and immunosuppressive programs, together with HIF-1α–mediated hypoxic responses, can further modulate macrophage polarization states and functional outputs within the tumor microenvironment[13,14]. Increased NF-κB1 activity leads to an inflammatory and immunosuppressive environment, promoting tumor development and worsening the prognosis for CRC patients. Consequently, exosomal miR-191 promotes CRC progression by activating NF-κB1 to induce M2 macrophages polarization. Furthermore, the miR-191/NF-κB/M2 macrophage axis serves as a pivotal mediator of tumor immune regulation and is a prospective therapeutic target in CRC patients. However, as these conclusions are largely based on bioinformatic analyses of TCGA datasets, additional experimental studies are required to validate these findings and clarify the underlying mechanisms (Figure 2).
Figure 1 NF-κB correlates with M2 macrophages infiltration and disease-free interval in colorectal cancer (The cancer genomic atlas; tumor immune estimation resource version 3).
A: Correlation plots from the tumor immune estimation resource version 3 Gene module comparing NF-κB1 expression (log2 transcripts per million) vs tumor purity (left) and vs inferred M2 macrophage infiltration (right; CIBERSORT-ABS), with Spearman’s rho and P values displayed; B: Violin/box plots showing how M2 macrophages infiltration differs between wild-type and mutant NF-κB1 tumors (log2 FC = -0.93; Wilcoxon P = 0.011); C: Kaplan–Meier disease-free interval (DFI) curves categorized by NF-κB1 expression (high/Low) and M2 macrophage level (high/Low; quanTIseq). A high M2 Level only predicts a worse DFI in the NF-κB1-high group (HR = 6.34, P = 0.00312). When NF-κB1 is low, there is no significant difference (HR = 0.56, P = 0.333). TPM: Transcripts per million.
Figure 2 The colorectal cancer microenvironment exhibits an exosomal miR-191/NF-κB/M2 macrophage axis.
Colorectal cancer cells secrete exosomes containing miR-191 into the tumor microenvironment, where interact with macrophages by being taken in and carrying cargo including miR-191, which can change macrophages polarizations. Exosomal miR-191 stimulates NF-κB activation, shifting macrophages polarization towards an M2 macrophages, (pro-tumor phenotype). Enhanced M2 macrophages activity facilitates an immunosuppressive microenvironment that promotes tumor cell survival, proliferation, and cancer progression. Created in BioRender (Supplementary material). CRC: Colorectal cancer.
