Novel regulatory network of the TGF-β/ZEB1/LMO7 axis in colorectal cancer metastasis

Abstract

Colorectal cancer remains a leading cause of cancer-related morbidity and mortality worldwide and is characterized by high genetic heterogeneity and poor prognosis. Bai et al report a significant finding in the World Journal of Gastroenterology: LIM domain only protein 7 (LMO7), transcriptionally activated by the transforming growth factor-β/zinc finger E-box binding homeobox 1 axis, promotes colorectal cancer metastasis by regulating cell adhesion and epithelial-mesenchymal transition. The primary strength of this study lies in the identification of LMO7 as an important downstream effector of this key pathway. However, while the study establishes a regulatory hierarchy, it does not deeply interrogate the underlying molecular mechanisms, such as the precise control of LMO7 by zinc finger E-box binding homeobox 1 or the functional consequences for adhesion molecules like E-cadherin. This research provides a solid conceptual foundation, but its translational promise hinges on future studies that move beyond correlation to offer mechanistic validation and functional insights that establish causality.

Key Words: LIM domain only protein 7; Colorectal cancer; Epithelial-mesenchymal transition; Transforming growth factor-β; Zinc finger E-box binding homeobox 1

Core Tip: Bai et al identified the transforming growth factor-β/zinc finger E-box binding homeobox 1/LIM domain only protein 7 (LMO7) axis in colorectal cancer. Their work establishes LMO7 as a key downstream effector of this axis, showing that it significantly promotes colorectal cancer cell proliferation, migration, invasion, and metastasis in vivo. Significantly, LMO7 expression correlates positively with adverse clinicopathological features. Based on this foundational discovery, future research should further investigate the functional implications of LMO7’s subcellular localization, the regulatory dynamics of this pathway, and the identity of its downstream effector molecules. Such efforts are crucial for constructing a more comprehensive molecular framework.

This editorial refers to “LIM domain only protein 7 promotes metastasis in colorectal cancer by TGF-β/ZEB1 pathway” by Bai et al, 2026; https://dx.doi.org/10.3748/wjg.v32.i11.115393.

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INTRODUCTION

Colorectal cancer (CRC) is one of the leading causes of cancer-related death globally, ranking third in incidence and second in mortality among all malignancies[1]. A significant proportion of patients experience a poor prognosis, which is driven by delayed diagnosis, marked intratumoral heterogeneity, and a high propensity for therapeutic resistance[2,3]. Metastasis remains the leading cause of CRC-related mortality. It has been reported that the overall 5-year survival rate for CRC is around 64%, but it sharply drops to 12% for metastatic CRC[4]. For instance, in patients diagnosed with locally advanced rectal cancer, treatment failure is primarily attributed to distant metastasis[5]. As metastasis represents a critical event in CRC progression, elucidating its molecular drivers may lead to the identification of novel therapeutic strategies.

The transforming growth factor-β (TGF-β) signaling pathway is increasingly recognized as a critical regulator of the progression of CRC. Activation of the TGF-β pathway inhibits the proliferation of normal colonic epithelial cells and exhibits tumor-suppressive properties in the early stage of tumorigenesis[6]. However, the pro-tumorigenic role of TGF-β is further enhanced during the progression of CRC. Epithelial-mesenchymal transition (EMT) enables cells to lose their epithelial characteristics and acquire invasive phenotypes[6,7]. TGF-β typically signals through the canonical SMAD pathway; following ligand binding, TGF-β receptor II recruits and phosphorylates TGF-β receptor I, which in turn phosphorylates SMAD2 and SMAD3[8]. Once phosphorylated, SMAD2/3 form a complex with SMAD4, and together they translocate to the nucleus to regulate the transcription of genes related to EMT[8]. TGF-β-induced EMT involves a critical effector downstream of the zinc finger E-box binding homeobox 1 (ZEB1), which represses epithelial markers[9-11]. The role of ZEB1 in transcriptional changes in cancer cells is supported by the evidence that ZEB1 directly binds to E-boxes in the E-cadherin promoter, inducing the cooperative recruitment of histone deacetylases, histone 3 lysine 27 methyltransferases, and DNA methyltransferases. This results in epigenetic remodeling that silences E-cadherin expression and enables tumor cells to acquire invasive and metastatic properties[12]. ZEB1 is regulated by a complex network of signaling pathways, including Wnt/β-catenin, TGF-β, nuclear factor-κB, and hypoxia-inducible factor-1α. These pathways enhance its transcriptional activity, thereby positioning ZEB1 as an integrator of extracellular signals and epigenetic reprogramming in CRC metastasis[13,14]. Reciprocally, ZEB1 induces TGF-β ligand expression, contributing to the formation of a positive feedback loop[8]. Therefore, identifying the downstream effector molecules that interact with ZEB1 to promote its pro-metastatic functions is essential.

A recent study by Bai et al[15] published in the World Journal of Gastroenterology revealed that LIM domain only protein 7 (LMO7) is a direct transcriptional target of ZEB1, thus acting as a crucial downstream effector of the TGF-β/ZEB1 pathway. They demonstrated that LMO7 expression is significantly elevated in CRC tissues, lymph nodes, and blood samples. Moreover, they identified that ZEB1 directly binds to the LMO7 promoter, leading to increased transcriptional activation of LMO7. Thus, this study identifies LMO7 as both a new nodal point in the TGF-β-driven metastatic network and a potential therapeutic target downstream of ZEB1 (Figure 1).

Figure 1 The transforming growth factor-β/zinc finger E-box binding homeobox 1/LIM domain only protein 7 signaling axis orchestrates the epithelial-mesenchymal transition in colorectal cancer. Extracellular transforming growth factor-β from the tumor microenvironment binds to its receptors on the cancer cell membrane, activating the canonical SMAD signaling pathway. This activation leads to the upregulated expression of the transcription factor zinc finger E-box binding homeobox 1 within the nucleus. Zinc finger E-box binding homeobox 1 directly binds to the promoter region of the LIM domain only protein 7 gene and drives its transcriptional expression, thereby promoting tumor metastasis. TGFβ: Transforming growth factor β; TGFβRI: Transforming growth factor beta receptor 1; TGFβRII: Transforming growth factor beta receptor 2; LMO7: LIM domain only protein 7; ZEB1: Zinc finger E-box binding homeobox 1; EMT: Epithelial-mesenchymal transition.

RESEARCH PROGRESS ON LMO7 IN CANCER

The LIM domain protein family is involved in cell differentiation, migration, and adhesion of cells[16,17]. The E3 ubiquitin ligase activity of LMO7 plays critical roles in tumor chemosensitivity as well as in fibrotic and inflammatory responses[18]. Previous studies have reported the upregulation of LMO7 expression in various tumor types, where higher LMO7 levels correlate with adverse clinical outcomes and poor prognosis in several cancer types[19,20]. LMO7 links the nectin and E-cadherin adhesion systems by interacting with afadin and α-actinin[21]. By influencing the membrane localization of E-cadherin, LMO7 contributes to the structural integrity of epithelial cells and the stability of intercellular junctions[21]. Recently, the role of LMO7 as an E3 ubiquitin ligase has obtained considerable attention[22]. Additionally, LMO7 promotes the K48-linked polyubiquitination and proteasomal degradation of the DNA repair protein MGMT by directly binding to it through its F-box domain, subsequently increasing the chemosensitivity of non-small cell lung cancer cells to temozolomide[23]. Notably, temozolomide treatment enhances the interaction between LMO7 and MGMT[23]. Studies have also found that LMO7 targets the TGF-β negative regulator SMAD7 for K70-linked ubiquitination and degradation[24]. This action stabilizes TGF-β receptor 1, increases SMAD2/3 phosphorylation, and activates pro-fibrotic genes[24]. Consequently, it drives fibroblast-to-myofibroblast differentiation and excessive deposition of the extracellular matrix[24]. Analysis of clinical data suggests that lung cancer patients with low LMO7 and high MGMT expression have a significantly shorter overall survival, indicating that LMO7 may play an important role in regulating chemoresistance[23].

In cancer immune regulation, the LIM domain of LMO7 directly binds to the Foxp1 transcription factor, promoting its K48-linked polyubiquitination and proteasomal degradation[25]. Foxp1 functions as a transcriptional repressor of TGF-β and chemokine (C-C motif) ligand 5 (CCL5). Its degradation relieves the transcriptional repression of these two molecules, leading to their upregulation[25]. According to a recent study, CCL5 mediates the chemotactic recruitment of Tregs while TGF-β induces Treg differentiation. Collectively, these factors promote the enrichment of Treg cells in the tumor microenvironment, suppress the cytotoxic functions of CD8+ T cells and natural killer cells, and ultimately create an immunosuppressive microenvironment[25]. Beyond immune regulation, LMO7 is implicated in various other biological processes. LMO7 regulates the STING signaling pathway, which in turn affects the ubiquitination status of STING[26]. Additionally, LMO7 modulates the innate immune response through phosphorylation[26]. In CRC, LMO7 expression is associated with elevated levels of cullin4A, an essential component of the CRL4 E3 ubiquitin ligase complex, which promotes the migration and invasion of CRC cells by regulating the ubiquitination of its various substrates[27].

THE TGF-β/ZEB1/LMO7 AXIS IN CRC METASTASIS

To identify the potential key genes involved in CRC initiation and progression, Bai et al[15] conducted an in-depth proteomic analysis of 78 pairs of CRC tissues and their matched normal tissues and identified LMO7 as a significantly altered gene. Cross-validation was then performed using publicly available genomic resources, including The Cancer Genome Atlas and The Human Protein Atlas. Independent quantitative polymerase chain reaction and immunohistochemistry assays confirmed that LMO7 was increased at both the mRNA and protein levels in CRC tissues and metastatic lymph nodes. This up-regulation was significantly positively correlated with tumor-node-metastasis stage, lymph node metastasis (N stage), and distant metastasis (M stage). Subsequently, in in vitro experiments, the authors demonstrated the expression of LMO7 mRNA and protein in normal colon epithelial cells and five colon cancer epithelial cell lines. Compared with the normal colon epithelial cells, the expression of both LMO7 mRNA and protein was increased in the colon cancer cell lines (CaCo2, SW480, LoVo, and HT29). In contrast, the expression of LMO7 mRNA in the HCT116 cell line showed no significant difference compared with human normal intestinal epithelial cells. Importantly, knockdown of LMO7 inhibited subcutaneous tumor formation and lung metastasis. These results indicate that LMO7 likely promotes CRC progression and is associated with distant metastasis of the disease.

During the EMT, polarized epithelial cells with established intercellular connections lose their epithelial characteristics, enabling tumor cells to acquire metastatic capabilities[28]. Bai et al[15] reported that Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that the functions of LMO7 are largely associated with cell junctions, cell structure, and adhesion-related processes. Similar studies have also shown that LMO7 is required by fibroblasts to establish front-rear polarity and directed migration[29]. Chromatin immunoprecipitation analysis demonstrated that ZEB1 binds to the LMO7 promoter, indicating that LMO7 is a direct downstream target gene of ZEB1. Furthermore, dual-luciferase reporter assays confirmed the interaction of ZEB1 with the LMO7 promoter and showed that ZEB1 increased luciferase activity driven by the LMO7 promoter. A previous study indicated that TGF-β induces the expression of ZEB1 and LMO7[30,31]. Bai et al[15] treated SW480 and LoVo cells with increasing concentrations of TGF-β, which resulted in upregulated LMO7 mRNA levels. This regulatory effect was abolished by ZEB1 knockdown. These findings demonstrate that TGF-β induces both ZEB1 and LMO7 expression concurrently and that this induction depends on ZEB1. To our knowledge, this study is the first to reveal the “TGF-β/ZEB1/LMO7” regulatory axis in CRC and identifies LMO7 as a novel downstream effector of the TGFβ/ZEB1 pathway.

STRENGTHS AND LIMITATIONS OF THE STUDY

The strength of the study by Bai et al[15] lies in the diversity of its experimental approaches. The authors employed a multi-level strategy that included screening of clinical samples for independent validation through proteomics, public databases, and validation with independent cohorts. This comprehensive approach clearly showed elevated expression of LMO7 and its pro-metastatic role in mouse and cellular models of CRC. Furthermore, high LMO7 expression was positively associated with tumor-node-metastasis stage, lymph node metastasis, and distant metastasis, supporting its potential as a prognostic marker[15]. In addition, molecular techniques such as chromatin immunoprecipitation and luciferase reporter assays were used to demonstrate, for the first time, that LMO7 is a downstream effector of the TGF-β/ZEB1 axis, linking this pathway to CRC metastasis. These findings expand current understanding of the TGF-β-driven metastatic network and may facilitate the development of targeted anti-metastatic strategies against CRC.

While this study provides the first evidence for a critical role of LMO7 in CRC metastasis, several issues remain to be addressed. First, LMO7 was found to be enriched in the nucleus of cells within a subset of metastatic lymph nodes, suggesting context-dependent specificity. However, the functional consequences of LMO7 nuclear translocation have not been investigated. LMO7 can interact with nuclear proteins such as emerin and function as a transcriptional regulator[32]. Future studies should perform nuclear-cytoplasmic fractionation followed by co-immunoprecipitation coupled with mass spectrometry to identify nuclear interactors of LMO7 and elucidate its regulatory functions in the nucleus. Furthermore, Bai et al[15] observed that LMO7 overexpression did not alter E-cadherin expression in HCT116 cells. However, the underlying mechanism remains unclear. Other studies suggest that LMO7 promotes migration and invasion in an EMT-independent manner[33,34]. Future research should consider differences in genetic backgrounds between cell lines and examine whether LMO7 affects E-cadherin membrane localization.

Second, this study identified ZEB1 as a direct transcriptional activator of LMO7; however, the epigenetic regulatory functions of ZEB1 itself have not been thoroughly investigated. It has been demonstrated that ZEB1 drives epigenetic silencing of epithelial tumor suppressor genes through the coordinated mechanisms involving histone deacetylation, histone methylation, and DNA methylation[12,35]. Therefore, future investigations should further explore whether ZEB1 regulates the transcriptional activity of LMO7 by modulating histone modifications in the LMO7 promoter region. Furthermore, it is important to determine whether ZEB1 serves as an epigenetic regulatory platform that recruits distinct chromatin-modifying complexes to the LMO7 promoter. Intervening in the ZEB1-LMO7 signaling axis using epigenetic drugs, such as histone deacetylase inhibitors, and evaluating their potential efficacy in suppressing CRC metastasis, could provide a novel theoretical basis for therapeutic strategies targeting this axis. Based on the unresolved issues discussed above, we summarize the recommended experimental strategies for future investigation of LMO7 in CRC metastasis in Table 1.

Table 1 Knowledge gaps and future research directions for LIM domain only protein 7 in colorectal cancer.

Research area	Unresolved issues	Suggested approach
Clinical expression and prognosis	Lack of large-scale, multi-center, independent cohort validation	Conduct a multi-center retrospective study; perform single-cell sequencing to analyze the expression heterogeneity of LMO7 in cell subpopulations
Upstream regulatory mechanism	Does ZEB1 regulate LMO7 through epigenetic modification?	Perform ChIP-qPCR for histone modifications at the LMO7 promoter; validate using HDAC inhibitor intervention
Cellular function and molecular mechanism	Does LMO7 affect the membrane localization of E-cadherin? Downstream interacting proteins are unknown	Use immunofluorescence to observe membrane localization and Co-IP-MS to identify interacting proteins; generate LIM domain-deletion mutants to define its function
Subcellular localization and function	What triggers LMO7 nuclear translocation? What are its nuclear functions?	Perform nuclear-cytoplasmic fractionation combined with immunofluorescence and DNA pull-down-MS to identify nuclear binding complexes

Co-IP-MS: Co-immunoprecipitation mass spectrometry; ChIP-seq: Chromatin immunoprecipitation sequencing; LMO7: LIM domain only protein 7; ZEB1: Zinc finger E-box binding homeobox 1; ChIP-qPCR: Chromatin immunoprecipitation quantitative polymerase chain reaction; HDAC: Histone deacetylase.

FUTURE DIRECTIONS

Based on Bai et al’s identification of LMO7[15] as a critical mediator of CRC metastasis, future studies should address three interlinked aims: Demonstrating its function in vivo, determining its protein structure, and advancing therapeutic development. It is still not completely understood how LMO7 promotes metastasis beyond the TGF-β/ZEB1 axis. Additionally, the precise role of maleic acid in living systems has yet to be confirmed. Mouse models of CRC lacking LMO7, such as APC-Min models, will be valuable for clarifying its role in tumor metastasis and colonization. The structural information on LMO7 is currently limited. The absence of high-resolution data for both the LIM and PDZ domains hinders structure-based drug design. The interaction surfaces that mediate binding to transcriptional regulators and cytoskeletal proteins can be mapped using X-ray crystallography and cryo-electron microscopy. This structural insight will facilitate the design of inhibitors targeting LMO7. Since LMO7 functions primarily through protein-protein interactions, a promising strategy would be to develop small molecules that disrupt these interactions. Candidate compounds can benefit from enhanced binding affinity and cellular uptake through structure-based approaches. The efficacy of inhibitors should be evaluated using three-dimensional spheroid invasion assays and patient-derived organoids to determine their ability to reverse the EMT or reduce invasive behavior. By integrating structural, mechanistic, and pharmacological approaches, this framework aims to transform LMO7 from a correlative marker into a validated oncogenic target. Ultimately, this may lead to novel anti-metastatic therapeutic options for CRC.

CONCLUSION

Through multi-omics validation and functional assays performed in vitro and in vivo, the study of Bai et al demonstrates that LMO7 is a key downstream effector of the TGF-β/ZEB1 axis. Elevated expression of LMO7 correlates with advanced tumor stage and metastasis and directly promotes malignant cellular phenotypes. This study reveals a novel pro-metastatic signaling axis in CRC, namely TGF-β/ZEB1/LMO7, providing deeper insights into the molecular basis of CRC metastasis. However, several mechanistic questions remain unresolved. It remains unclear whether metastatic lesions exhibit more specificity than primary tumors. In particular, decisive rescue experiments to confirm phenotypic specificity were not performed, and the significance of LMO7 nuclear enrichment in metastatic lesions remains an open question. Despite these limitations, these findings suggest potential directions for future research.