Introduction
Oral squamous cell carcinoma (OSCC) is one of the most common head and neck malignant tumors, with a high incidence of 350,000 new cases and 170,000 deaths [
1]. The Asian region has the highest OSCC morbidity and mortality among all other countries, which various etiological factors may cause. The risk factors of OSCC recognized by researchers include smoking [
2], drinking [
3], chewing betel nut [
4], periodontal disease [
5], gene mutation [
6], and so on. However, periodontal diseases represented by periodontitis (PD) have played an increasingly significant role in the occurrence and development of OSCC [
7,
8].
There is a convincing correlation between inflammation and the occurrence and development of many cancers [
9‐
11]. The role of inflammation in tumors can also be observed in the oral environment [
12]. PD also is strongly associated with a variety of tumors, including breast cancer [
13], pancreatic cancer [
14], gastric cancer [
15], and colorectal cancer [
16]. To date, PD is considered one of the most common inflammatory conditions affecting the oral cavity and one of the risk factors for OSCC [
17]. Systematic reviews have confirmed the previous association between OSCC and PD [
18], but further mechanism study of the shared connotation still needs to be completed. In particular, little is known about the possible epigenetic mechanisms of OSCC and PD.
MicroRNA (miRNAs) are small RNAs that play vital roles in regulating gene expression. miRNAs regulate cellular physiological processes by regulating expression and play a crucial role in mediating diseases [
19]. The molecular mechanism of disease occurrence and development can be further grasped by studying disease-related miRNAs and their expression patterns. In addition, miRNAs can serve as biomarkers of two diseases (OSCC and PD) or key targets for therapeutic drugs [
20].
This study aimed to comprehensively analyze differentially expressed miRNAs (DEmiRNAs) in OSCC and PD to identify candidate CO-DEmiRNAs, their associated hub genes, signaling pathways and related compounds. Thereby promoting the understanding of the shared molecular mechanisms between closely related tumors and non-neoplastic diseases. And providing a theoretical basis for driving future basic research and clinical practice.
In more than 20 years of clinical work by our group, we found that almost all patients with OSCC suffer from periodontitis while burdening the tumor. Based on our previous translational studies on inflammation-precancerous lesion cancer, we sought to explore whether the presence of crucial genetic molecules could serve as a connecting key for PD and OSCC. Recent studies have revealed numerous noncoding RNAs (ncRNAs) roles in cancer and various diseases, highlighting the biological significance of these previously “neglected” RNA species. In particular, microRNAs (miRNAs) are involved in many biological processes that affect cell homeostasis. MiRNAs are considered post-transcriptional gene regulators that can achieve translational repression, mRNA degradation, and gene silencing and play a significant role in gene expression. We sought to explore and determine whether there are co-expressed key miRNAs and transcription factors present in PD and OSCC by bioinformatics methods, thus providing a solid basis for our subsequent target findings. This helps us in a series of studies in stomatitis-cancer transformation. We promote an understanding of the shared molecular mechanisms between closely related tumors and non-neoplastic diseases. We provide a theoretical basis for future basic research and clinical practice.
Discussion
The miRNA is an essential intermediate hub of host physiological and pathophysiological activities [
33]. We know that the microbiota changes host miRNA using self-virulence factors, reducing the host immune response-ability, and achieving the final effect of pathogenicity [
34‐
36]. Oral pathogens are important risk factors for periodontitis (PD) and oral squamous cell carcinoma (OSCC) [
18,
37]. In recent years, it has been gradually discovered that PD-related pathogenic microorganisms, mainly
Porphyromonas gingivalis (
P. gingivalis) and
Fusobacterium nucleatum (
F. nucleatum), have played an essential role in oral cancer occurrence [
38], which revealed to us that PD might also be the cause of OSCC or a key step in the malignant transformation process of oral disease. Overall, there may have a homologous genetic and molecular link between OSCC and PD.
Our current study explored the epigenetic mechanism of CO-DEmiRNA mediated the association between OSCC and PD by screening and identifying Co-DEmiRNA common in the two diseases. The network architecture was applied to determine DEmiRNA-related hub genes and TF, which could be used as the linkage mechanism of differential expression and further function of DEmiRNA. In addition, functional enrichment analysis was conducted on them to determine key pathways, molecular functions, and cell components. In addition, the small molecule compounds associated with Co-DEmiRNA were analyzed, and the key junction compounds between OSCC and PD were explored. The key Co-DEmiRNAs identified in this study may provide more effective guidance in the future study of inflammation-cancer transformation.
Most DEmiRNAs had the same expression trend in the two diseases, which further revealed the similar immune mechanism of the host oral microenvironment against inflammation or cancer, perhaps a common pattern of miRNA dysregulation in pro-inflammatory and pro-cancer responses. Co-DEmiRNAs with the highest degree included hsa-mir-224, hsa-mir-210, hsa-mir-31(overexpressed), and hsa-mir-497, hsa-mir-29c, hsa-mir-486(which were low expressed). They are all broadly involved in inflammation, cancer, and host immune responses.hsa-mir-224 is considered an early diagnostic marker of cancer [
22], and both it and hsa-mir-210 are significantly involved in cancer progression and metastasis [
23]. hsa-mir-31 is an important protective factor of the epithelial barrier [
24] and has also been recognized as a cancer biomarker [
25,
26]. hsa-mir-497 and has-mir-29c suppress various cancers, inhibiting the proliferation and growth of cancer [
27‐
30]. hsa-mir-486 is a migration suppressor of various tumors and plays an important role in regulating epithelial-mesenchymal transition (EMT) [
31,
32].
Our study revealed that dysregulation of associated gene expression mediated by noncoding RNA represented by miRNA might be the key mechanism linking PD to OSCC or other cancers. The genes with the highest degree in the Co-DEmiRNA-Gene network include
ZNF460,
FBN1,
CDK6,
BTG2, and
CBX6, which may be the essential hub genes/mediators between OSCC and PD.
ZNF460 (zinc finger protein 460) is involved in the regulation of multiple cancer processes by JAK2/STAT3 pathway [
39], and its high expression is associated with the proliferation, invasion, and metastasis of colorectal cancer and oral cancer [
39,
40].
FBN1 (fibrinin-1) is a common extracellular matrix encoding gene [
41], and inactivation will affect the integrity of tissues (aortic wall, periodontal membrane, oral epithelial barrier, etc.). It encodes the formation of Oxytalan fibers [
42], a unique component of the periodontal ligament (PDL). Low expression of
FBN1 inhibits TGF-β 1-mediated expression of Periosteum, thereby inhibiting collagen fiber production. In addition,
FBN1 also plays an important role in the Wnt/β-catenin signaling pathway that regulates cancer cell migration [
43].
CDK6 (cyclin-dependent kinase 6), as one of the proto-oncogenes driving tumors, has become a key target of various cancer therapies [
44], and its inhibition can significantly affect tumor cell metabolism and antitumor immunity [
45,
46].
CDK6 also inhibits the proliferation of periodontal ligament cells (PDLCs) by regulating the cell cycle in periodontitis [
47].
BTG2 (B cell translocation gene 2) has long been recognized as a tumor suppressor gene in various cellular processes [
48‐
50], including cell division, DNA repair, transcriptional regulation, and messenger RNA stability. Upregulation of
BTG2 inhibits cancer migration, invasion, EMT and, glycolysis [
51].
CBX6 (chromobox protein 6) accelerates EMT in head and neck squamous cell carcinoma [
52], resulting in cancer progression.
In the Co-DEmiRNA-TF network, transcription factors HIF1A, TP53, E2F1, MYCN, and JUN have the highest degree. HIF1A (hypoxia-induced transcription factor 1α) can promote gingival tissue aging and hypoxia stress [
53], regulate apoptosis of PDLCs [
54] and increase the severity of periodontal inflammation [
55]. Inhibits the expression of PPP1R1B and subsequent degradation of the p53 protein in pancreatic cancer cells [
56]. Loss of HIF1A can also increase cancer cell proliferation, invasion, and metastasis activity [
57]. Transcription factor P53 (tumor protein 53) controls the cell cycle, apoptosis, and cell senescence of periodontal ligament fibroblasts in periodontitis [
58]. It plays an important role as a star transcription factor in oral squamous cell carcinoma [
59]. Its protein level and phosphorylated protein levels are important factors in suppressing cancer. Low levels of p53 are directly related to the incidence and poor prognosis of oral squamous cell carcinoma [
60]. E2F1 (recombinant E2F transcription factor 1) is related to changes in cell metabolism, cell–matrix interaction, and cell cycle [
61], and it plays a crucial role in the NF-κB pathway in infection, inflammation and carcinogenesis [
62], which can inhibit cell proliferation, migration, invasion and EMT processes. MYCN (N-Myc proto-oncogene protein) is a key marker for cell survival and a key transcription factor for maintaining the homeostasis of the periodontal epithelial barrier and inhibiting periodontal inflammation [
63]. Its low expression can promote antiapoptotic resistance and EMT [
64]. MYCN is associated with the Wnt/β-catenin pathway in OSCC tumorigenesis and inhibits epithelial-mesenchymal transformation, migration, and colony formation in OSCC. JUN (JUN proto-oncogene protein, AP-1 transcription factor) is related to immune infiltration [
65], which causes inflammation and cell death through immunosuppression, leading to cancer.
Functional enrichment analysis of Co-DEmiRNA-Gene, Hub genes and TF networks showed that many cancer-related KEGG/Reactome pathways are enriched, supporting previous findings that PD is a significant risk factor for OSCC (Like PI3 K-related signaling pathway and MAPK pathway). Ras protein signal transduction and the functional enrichment of transcription factor binding in GO analysis are very obvious. These play a crucial role in inflammation, immunosuppression, and antitumor immunity [
66‐
69].
In this study, the compounds most closely related to Co-DEmiRNA of the two diseases were also analyzed. 5-fluorouracil(5-FU), Ginsenoside, Rh2, and Formaldehyde are the small molecule compounds with the strongest correlation with Co-DEmiRNA. miRNAs reduce the resistance of oral squamous cell carcinoma cells to 5-fluorouracil [
70]. At the same time, 5-FU also increases the severity and duration of periodontitis and damages tissue repair by reducing cell and blood vessel renewal, leading to more severe periodontal damage [
71]. Ginsenoside Rh2 can control inflammation by regulating the STAT3 signaling pathway and NF-κB signaling pathway to reduce the production of inflammatory factors at mucosal sites [
72,
73]. At the same time, it can also inhibit tumor invasion, migration, and angiogenesis by regulating miRNA or AMPK/mTOR and other signaling pathways [
74,
75], and induce cancer cell apoptosis and protective autophagy[
76]. Formaldehyde is a typical risk factor, which can cause oxidative damage, inflammation, and genotoxicity, and greatly increase the risk of cancer [
77,
78]. Future studies will be necessary to investigate these rich compounds in the context of OSCC and PD association.
This study investigated the epigenetic mechanism linked between OSCC and PD, including multiple aspects, such as DEmiRNA, Co-DEmiRNA, Hub gene, TF, and even related compounds. The main limitation is the lack of further experimental data to validate these candidate key linking mechanisms. The datasets used in this study were from a single database, which may limit the accuracy of the results. Future-related research using diverse composite data is critical and necessary. Another point is that other noncoding RNAs, such as lncRNAs, circRNAs, and sncRNAs, may also play an important role in the pathogenic mechanism of OSCC and PD, which were not investigated in this study. Therefore, future studies may further investigate other noncoding RNAs as linkage mechanisms. Future studies should aim to validate the further link between Co-DEmiRNA Hub genes, TF pathway, and compound, these key parts between OSCC and PD, using clinical studies, in vitro and in vivo experiments, etc. In addition, since this association may be bidirectional, it is necessary to comprehensively study the biological mechanisms involved, which will also provide a basis for us to explain the inflammation-cancer transformation further.
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