Current and future perspectives on the regulation and functions of miR-545 in cancer development

Micro ribonucleic acids (miRNAs) are a highly conserved class of single-stranded non-coding RNAs. Within the miR-545/374a cluster, miR-545 resides in the intron of the long non-coding RNA (lncRNA) FTX on Xq13.2. The precursor form, pre-miR-545, is cleaved to generate two mature miRNAs, miR-545-3p and miR-545-5p. Remarkably, these two miRNAs exhibit distinct aberrant expression patterns in different cancers; however, their expression in colorectal cancer remains controversial. Notably, miR-545-3p is affected by 15 circular RNAs (circRNAs) and 10 long non-coding RNAs (lncRNAs), and it targets 27 protein-coding genes (PCGs) that participate in the regulation of four signaling pathways. In contrast, miR-545-5p is regulated by one circRNA and five lncRNAs, it targets six PCGs and contributes to the regulation of one signaling pathway. Both miR-545-3p and miR-545-5p affect crucial cellular behaviors, including cell cycle, proliferation, apoptosis, epithelial-mesenchymal transition, invasion, and migration. Although low miR-545-3p expression is associated with poor prognosis in three cancer types, studies on miR-545-5p are yet to be reported. miR-545-3p operates within a diverse range of regulatory networks, thereby augmenting the efficacy of cancer chemotherapy, radiotherapy, and immunotherapy. Conversely, miR-545-5p enhances immunotherapy efficacy by inhibiting T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) expression. In summary, miR-545 holds immense potential as a cancer biomarker and therapeutic target. The aberrant expression and regulatory mechanisms of miR-545 in cancer warrant further investigation.


Introduction
Micro ribonucleic acids (miRNAs) are endogenous single-stranded non-coding RNAs that are approximately 22 nucleotides long and are highly conserved in evolution. 1They weaken or eliminate the function of downstream protein-coding genes (PCGs) by binding to the 3 0 -untranslated regions (3 0 -UTR) of target gene mRNA and play a role in post-transcriptional regulation. 2 The competing endogenous RNA (ceRNA) regulatory network connects long non-coding RNAs (lncRNAs), circular RNAs (circRNAs), miRNAs, and PCGs.miRNAs regulate cancer progression by participating in the ceRNA regulatory axis and affecting downstream PCG expression and signaling pathway activation. 3iR-545 is located at Xq13.2, within intron 1 of the lncRNA FTX (FTX Transcript, XIST Regulator), and it has been associated with cancers in multiple systems, including the nervous, 4,5 respiratory, 6,7 digestive 8 and motor 9 systems.miR-545 is intricately involved in an extensive ceRNA regulatory network, and it is competitively repressed by 15 circRNAs and 12 lncRNAs.It plays a crucial role in regulating multiple signaling pathways, including the catenin, 10 phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT), 8,11 cell cycle, [12][13][14] and p38 pathways. 15Via its participation in these pathways, miR-545 exerts control over critical cellular processes, such as cell cycle progression, proliferation, apoptosis, epithelial-mesenchymal transition (EMT), invasion, and migration.
This study examines miR-545 dysregulation in various human cancers and summarized the genes and pathways involved in its regulation and their roles in vivo and in vitro.Our work also provides a systematic summary of the association between miR-545 and patient prognosis as well as the relationship of miR-545 with various therapeutic approaches.Finally, we discuss the current research progress and limitations of miR-545 to provide directions for future translational medicine research.

miR-545 expression dysregulation in human cancers
Pre-miR-545 is processed into two mature miRNA products: miR-545-3p and miR-545-5p.Both of these miRNAs are expressed in various human cell types.Research has shown that both miR-545-3p and miR-545-5p levels are abnormal in 14 different cancer types Supplementary Table 1.Specifically, miR-545-3p levels were lower than normal in 11 cancers and higher than normal in two cancers.In contrast, miR-545-5p levels were lower than normal in seven types of cancer.
As shown in Supplementary Table 2 and Supplementary Figure 1, based on miRNA data from The Cancer Genome Atlas (TCGA) database, we explored the abnormal expression of miR-545 in over 30 types of cancer and paracancerous tissues and its association with the host gene FTX.Our results showed that pre-miR-545 expression was markedly negatively correlated with FTX in three tumor types: kidney chromophobe (KICH), mesothelioma (MESO), and uterine carcinosarcoma (UCS).miR-545-3p expression was upregulated in uterine corpus endometrial carcinoma (UCEC) and markedly negatively correlated with FTX in three tumor types: MESO, rectum adenocarcinoma (READ), and thymoma (THYM).miR-545-5p expression was upregulated in four tumors, head and neck squamous cell carcinoma, lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC), and UCEC, and substantially negatively correlated with FTX in four tumors: colon adenocarcinoma (COAD), KICH, LUAD, and prostate adenocarcinoma (PRAD) (see Supplementary Material for details).
Conflicting results have been reported regarding the expression patterns of miR-545-3p in colorectal cancer (CRC).Several studies utilizing quantitative reverse transcription polymerase chain reaction (RT-qPCR) have demonstrated that miR-545-3p expression is reduced in both CRC cell lines and tissues compared to that in normal colonic epithelium and non-tumor tissues, respectively. 11,16,17However, another study using microarray profiling found that miR-545-3p expression was higher in the serum exosomes of CRC patients than that in healthy individuals. 18The inconsistencies in miR-545-3p expression patterns in CRC may be attributed to differences in cancer tissues or measurement methods used in different studies.
In summary, variations exist in the expression of miR-545 across different contexts, and its discrepant expression in experimental data compared to that in the TCGA database has been debated.This disparity could potentially be attributed to the limited number of normal control samples in the TCGA database, leading to an imbalanced sample size in the cancer group.For instance, TCGA included 218 CESC tumor samples but only two control samples.Additionally, the reduced number of reads matching the gene in certain chips or algorithms may result from the lower accuracy of transcriptome expression results for low-expression genes as well as the short fragments and lower abundance of miR-545.Consequently, this can contribute to false results.Moreover, errors in measurement outcomes can stem from the biological properties of miR-NAs.For instance, if miR-545 expression undergoes subtle changes in the early stages of cancer but either remains relatively stable during cancer progression or is subject to passive regulation by other genes within the gene regulatory network, it can lead to abnormal fluctuations in its expression levels.Therefore, further studies with larger sample sizes and diverse sample types are necessary to gain a more comprehensive understanding of the aberrant expression patterns of miR-545-3p and miR-545-5p in cancer.

miR-545 and its host gene FTX
FTX is a well-studied lncRNA that plays a crucial role in X chromosome inactivation.Located upstream of the XIST gene in the X chromosome inactivation center (XIC), FTX can enhance XIST expression and trigger X chromosome inactivation. 19Additionally, FTX interacted with DExH-box helicase 9 (DHX9) and endoribonuclease dicer (DICER) to positively regulate both A-to-I RNA editing and miRNA expression. 11iR-374b/421 and miR-545/374a clusters are located within the FTX intron.20 Both FTX and miR-545-3p are upregulated and exhibit tumor-promoting functions in CRC.11 However, FTX suppressed miR-545-5p expression in monocytes from patients with liver cirrhosis.21 These findings suggest that regulation of miR-545-3p/5p expression by the lncRNA FTX may be tissue-specific and dependent on the host FTX transcript.
We analyzed TCGA data and found that pre-miR-545 was substantially negatively correlated with FTX in three tumor types (KICH, MESO, and UCS) but was substantially positively correlated with FTX in skin cutaneous melanoma.miR-545-5p expression was substantially negatively correlated with FTX levels in COAD, KICH, LUAD, and PRAD.miR-545-3p was substantially negatively correlated with FTX levels in the MESO, READ, and THYM groups.Additionally, the expression levels of pre-mir-374a, pre-mir-374b, pre-miR-374c, pre-mir-421, and pre-mir-545 in the miR-374b/421 and miR-545/374a clusters were strongly positively correlated Supplementary Material.This suggests that the regulation of the expression of miR-545 and that of its neighboring genes is related and may be tissue-specific.
As the host gene of miR-545, FTX is located on the X chromosome, it is worth paying attention to sex differences in its expression changes.TCGA data showed that sex differences in miR-545 expression were not significant in most cancers, as only four (pheochromocytoma and paraganglioma, thyroid carcinoma [THCA], MESO, and READ) showed significant differences (see Supplementary Material for details).Previous studies have not considered the sex of the cell line source.More in-depth research is needed to verify whether sex-related differences exist in the regulation of miR-545 expression.

miR-545 and its competing endogenous ribonucleic acids (ceRNAs)
CeRNAs competitively bind to miRNA, weakening its inhibitory effect on target mRNA and regulating cellular activities at the posttranscriptional level. 22As shown in Supplementary Table 3 and Figure 1, the ceRNA regulatory network of miR-545 involves circRNAs and lncRNAs that play regulatory roles in cell biology.

miR-545 regulates cell behaviors
Because miRNAs and their target gene sequences may not be fully complementary, miRNAs have a wide range of regulatory functions that affect cancer progression by regulating various biological behaviors. 49As shown in Supplementary Table 4 and Figure 2, multiple ceRNA/ miR-545/PCG axes can regulate cell cycle, proliferation, apoptosis, EMT, invasion, and migration.

miR-545 regulates the cell cycle
The cell cycle is closely related to cell proliferation and requires appropriate mitotic signals and an appropriate environment for normal cell proliferation. 50miR-545 can inhibit cell cycle progression by targeting four target genes (CCND1, CCND2, CDK4, and CBLL1), and it promotes cell cycle progression by targeting RIG-I.miR-545-3p induces G 0 /G 1 phase arrest in cancer cell lines by targeting CCND1 and CDK4 in LC, 14 CBLL1 in non-small cell lung cancer (NSCLC), 7 and LAMC2 in OSCC. 39In CRC, miR-545-3p arrests the cell cycle at the G 1 phase by targeting CDK4. 12miR-545-5p targets CCND2 44 in NPC, causing G 0 /G 1 phase arrest in the cell line.

miR-545 regulates cell proliferation
The degree of cell proliferation is a key indicator of the pathways and mechanisms governing cell survival and death. 51Disruptions in the inhibitory pathways associated with proliferation can result in abnormal cell growth, a hallmark of malignancy. 50As shown in Supplementary Table 4, miR-545-3p inhibits cell proliferation by targeting 18 PCGs.In GBM/LGG and HCC cells, miR-545-3p promotes cancer cell proliferation by targeting LUZP1 4 and SMAD7, 28 respectively.miR-545-3p targets multiple genes and regulates tumor growth in xenograft animals.For example, it promotes tumor growth via four targets in LC (CCND1 14 and CDK4 14 ) and OC (PLK1 52 and KDM4B 52 ) but inhibits tumor growth in HCC via two targets (RIG-I 8 and MT1M 53 ).Additionally, miR-545-5p promotes tumor growth in animal models of NSCLC and SaOS by targeting c-Met 45 and DIMT1, 9 respectively.
The miR-545-3p/RIG-I axis inhibits the proliferation of OSCC (HSC4) 54 and PDAC (HEK293, PANC1, and SW1990) 55 cell lines while promoting the proliferation CRC DLD-1/HCT116 11 cell lines.In CRC xenografts using LOVO cells in BALB/c nude mice, miR-545-3p promotes tumor growth 17 but inhibits it in HT29/HCT116 cells. 18The impact of miR-545-3p on cell proliferation differs between various cancers owing to variations in gene regulatory networks.Further research is required to elucidate the underlying mechanisms.

miR-545 regulates apoptosis
Apoptosis is a type of programmed cell death that can be initiated by intracellular or extracellular signals, which plays a crucial role in antitumor processes. 56miR-545-3p and miR-545-5p promote apoptosis by targeting ten and two genes, respectively.Additionally, miR-545-3p inhibits apoptosis by downregulating MT1M expression.

miR-545 regulates epithelial-mesenchymal transition
EMT is a key process in tumor metastasis that enables tumor cells to invade blood or lymphatic vessels and generate circulating tumor cells. 58,59miR-545-3p inhibits EMT in NSCLC and CRC cells by targeting CBLL1 7 and MYO6, 16 which suppress the neural-like transformation of E-cadherin and vimentin expression.MiR-545-5p inhibits EMT in NPC cells by targeting CCND2, which prevents the reduction of E-cadherin and the replacement of the cytokeratin cytoskeleton with vimentin. 44dditionally, miR-545-5p downregulates biliverdin reductase by targeting c-Met, thereby inhibiting EMT in NSCLC cells. 45

miR-545 regulates ferroptosis
Ferroptosis is a type of programmed cell death that differs from apoptosis.It occurs because of iron-dependent lipid peroxidation, and it is independent of caspase and RIPK1 activities.Ferroptosis plays a significant role in tumor suppression. 62he xc À transport system is an amino acid antiporter that facilitates GSH synthesis and maintains redox homeostasis. 63SLC7A11 is a membrane-localized light-chain subunit that forms an xc À transport system with the heavy-chain subunit SLC3A2. 64SLC7A11 overexpression can lead to tumorigenesis and ferroptosis resistance. 65n THCA, miR-545-3p targets SLC7A11 to promote ferroptosis in FTC133 and TPC-1 cells.In CRC, miR-545-3p targets transferrin (TF) to render HT-29 or HCT-116 cell-based xenograft mouse models resistant to the ferroptosis inducer erastin.This inhibits abnormal ferroptosis signaling and promotes cancer progression. 18

Wnt/β-catenin signaling pathway
The Wnt/β-catenin pathway is crucial for stem cells. 66Abnormal activation of this pathway promotes tumor stem cell renewal, proliferation, and differentiation. 67ZEB2 is a transcription factor that functions alone or in combination with other proteins. 68In NSCLC, miR-545-3p inhibits ZEB2 expression and reduces free β-catenin protein levels in the cytoplasm.This prevents β-catenin from entering the nucleus and blocks the Wnt/β-catenin pathway.Consequently, cancer cell proliferation, invasion, and metastasis are inhibited. 10,69

PI3K/AKT signaling pathway
The PI3K/AKT pathway regulates cell phenotypes, such as proliferation, invasion, autophagy, and senescence.It is often abnormally activated in human cancers. 70,71RIG-I is an innate immune sensor that acts as a tumor suppressor. 72miR-545-3p targets and inhibits RIG-I expression in CRC and HCC.This activates the PI3K/AKT pathway and promotes cell proliferation. 11However, miR-545-3p inhibits cancer progression by targeting RIG-I in PDAC and OSCC. 54,55WBP2 is an oncoprotein that promotes AKT phosphorylation. 73miR-545-3p targets and inhibits WBP2 expression in TNBC.This inhibits PI3K/AKT pathway activation and slows cancer progression. 33

Mitogen-activated protein kinase signaling pathway
The mitogen-activated protein kinase (MAPK) pathway is important for cancer development and is frequently activated in various cancers. 74NK 75 and p38 76 signals are key components of this pathway that affect cell proliferation, differentiation, and migration.PRKCA encodes PKCα, which promotes p38 phosphorylation and activates the p38 pathway via MKK3/6. 77,78In NSCLC, miR-545-3p inhibits p38 pathway activation by targeting PRKCA. 15It also inhibits cancer cell invasion and promotes apoptosis.PPA1 encodes an inorganic pyrophosphatase dysregulated in several cancers. 79PPA1 activates the JNK pathway and promotes NSCLC progression in a TP53-dependent manner. 80In OC, miR-545-3p suppresses tumor malignancy by targeting PPA1 to inhibit JNK pathway activation. 32

Cellular tumor antigen p53 signaling pathway
TP53 is a crucial tumor suppressor gene that encodes p53.This protein is deleted or mutated in more than half of all cancers. 81,82p53 regulates cell cycle arrest and apoptosis. 83,84MDM2 is an E3 ubiquitin ligase and a major antagonist of p53. 85It cooperates with MDMX to ubiquitinate p53, leading to its degradation and nuclear export.This inhibits p53 transcriptional activity. 86In CRC, miR-545-5p inhibits MDM2 expression, increases p53 transcriptional activity, and inhibits tumor growth. 48

Cell cycle regulation pathway
The cell cycle in cancer metabolism is complex, and its dysregulation is a key feature of cancer progression. 87The cell cycle pathway regulates cell proliferation and affects cancer progression.This is an important target in cancer therapy. 88Various cyclin/CDK complexes play crucial roles in regulating the cell cycle pathway. 89,90The CCND1/CDK4 complex phosphorylates RB1 and promotes E2F transcriptional activity.This promotes the G1/S transition of cells. 91,92The cell cycle is regulated by upstream pathways, such as PI3K/AKT 93 and p53 signaling. 94In CRC and TNBC, miR-545-3p targets CDK4 to inhibit E2F transcriptional activity and causes G1 arrest in cancer cells. 12,13In LC, miR-545-3p inhibits cancer cell proliferation by targeting CCND1 and CDK4. 14

miR-545 has prognostic value in cancer
As shown in Table 1, abnormal expression of miR-545 is substantially associated with the prognosis and clinicopathological features of cancer patients.Thus, it can serve as a biomarker for cancer prognosis.In NSCLC, PDAC, and OC, the low miR-545 expression indicates poor OS, progression-free survival (PFS), and DFS.
In NSCLC, low miR-545-3p expression is associated with more severe lymph node metastasis and a higher tumor stage.This predicts a shorter OS. 10 In PDAC, patients with low miR-545-3p expression have poor OS and DFS. 55In OC, low miR-545-3p expression is associated with poor OS and PFS.It is also strongly associated with a higher pTNM stage and stronger platinum drug resistance. 52,95urrent research on the clinical value of miR-545 is limited, and it has mostly focused on miR-545-3p.Further studies with larger sample sizes are required to understand the association between miR-545 expression and the prognosis of cancer patients.The potential differences between miR-545-3p and miR-545-5p expression in association with patient prognosis need to be determined.

miR-545 and cancer therapy
miRNAs can influence cancer therapy by participating in extensive regulatory networks. 96miR-545 mediates the effects of chemical factors, such as formononetin, 13 and physical factors, such as ionizing radiation, 97 on cancer cells.It can target downstream factors, such as YAP1, HK2, PFKFB3, KU70, and C-C motif chemokine ligand 22 (CCL22), to inhibit cell resistance to chemotherapy and radiotherapy.MiR-545 can also promote resistance to chemotherapy and radiotherapy via MT1M.Additionally, miR-545 enhances immune cell proliferation and infiltration by inhibiting downstream factors, such as TIM-3 and CCL22.

miR-545 and chemotherapy
Chemotherapy is a supplementary treatment for advanced cancers that prevents tumor cell growth. 98Figure 4A shows that formononetin indirectly increases miR-545 levels and improves cell sensitivity to four chemotherapeutic drugs (adriamycin, docetaxel DTX, paclitaxel, and cisplatin DDP).By targeting YAP1, miR-545 increases cell sensitivity to DTX.Targeting HT1M and PPA1 increases cell resistance and sensitivity to DDP.Targeting PFKFB3 increases cell sensitivity to 5-fluorouracil (5-FU).
Formononetin is a 7-hydroxyisoflavone with a methoxy group that can be found in red clovers and the Chinese herb Astragalus membraneceus. 99It can regulate cell death and cell cycle processes, and it shows promise in preventing and treating cancer. 100Formononetin inhibits the growth, invasion, and movement of two TNBC cell lines (MDA-MB-231 and BT-549) by decreasing AFAP1-AS1 expression, increasing miR-545-3p levels, and improving sensitivity to the four drugs mentioned above. 13TX is a chemotherapeutic drug in the taxane family commonly used to treat NSCLC patients. 101In NSCLC, DTX-resistant NCI-H1299 and A549 cell lines exhibit lower miR-545-3p expression levels than non-resistant NCI-H1299 and A549 cell lines. 26High miR-545-3p expression in the circ _0014130/miR-545-3p/YAP1 axis reduces DTX resistance in two NSCLC cell lines (NCI-H1299 and A549). 26DP is a stable platinum coordination compound at normal temperature and pressure that can be used as a standard treatment for ESCC. 102n ESCC, miR-545-3p is a part of the LINC00261/miR-545-3p/MT1M axis that increases DDP resistance in two ESCC cell lines (TE-1 and ESCC109). 43n OC, miR-545-3p involvement in the Circ_0067934/miR-545/PPA1 pathway reduces DDP resistance in the A2780/DDP cell line. 32n addition, 5-FU, a naturally occurring uracil analog, 103 is often used as a nanoagent to treat different types of cancers, including CRC and breast cancer. 104Highly expressed miR-545-3p participated in the Circ_SAMD4A/miR-545/PFKFB3 axis in two CRC cell lines (SW480/5-FU and HCT-116/5-FU) and inhibited 5-FU resistance. 29

miR-545 and immunotherapy
Cancer cells can evade or suppress the immune system by altering their antigens 107 and modifying the tumor microenvironment. 108,109mmunotherapy is a novel cancer treatment that induces antitumor immune responses. 110As shown in Figure 5, miR-545 enhances antitumor immunity by reducing TIM-3 and CCL22 levels.
TIM-3 is an immune checkpoint that negatively regulates immunity in various cancers (CRC, CxCa, and GC) and leukemia stem cells. 111o-expression of PD-1 reduces the effectiveness of tumor immunotherapy and promotes tumor growth. 112,113In OSCC, miR-545-5p reduces TIM-3 expression to enhance immunity and inhibit tumor growth. 47 large number of regulatory T cells can suppress immunity and worsen cancer prognosis. 114CCL22 increases regulatory T cell (Treg) infiltration in tumors and promotes tumor growth. 115In Lewis lung carcinoma, miR-545-3p recruits CD4 þ CD25 þ regulatory T cells via CCL22 to inhibit tumor growth. 106
Further research is needed to understand the interactions between miR-545 and these PCG-targeted drugs to develop new combination therapies for clinical use.

Discussion
MiR-545, located on chromosome Xq13.2,has two mature forms: miR-545-3p and miR-545-5p.Extensive evidence has demonstrated the dysregulation of miR-545 expression in various cancers, making it a promising cancer biomarker.The distinct expression patterns of miR-545 in different tumor types may be attributed to its participation in diverse regulatory networks and varying roles in different cancer contexts.However, comprehensive studies outlining the regulatory landscape of miR-545 in different cancers are lacking.Thus, it is imperative to map the regulatory mechanisms of miR-545 in diverse tumor types in future studies.Although dysregulated miR-545 expression in most tumors has been extensively explored, its differential expression in CRC remains controversial.This discrepancy may stem from factors such as cellular and tissue sample heterogeneity or differences in detection methods.Furthermore, findings from pancancer analyses using large databases, such as TCGA, do not align with experimental data consistently.This discrepancy could be attributed to factors such as the data volume within the database, the differential analysis algorithms employed, or the inherent heterogeneity of the experimental samples.To address these challenges, future research endeavors could increase the sample size and diversity and reduce error rates by integrating data from additional databases, such as the Gene Expression Omnibus (GEO), for joint analysis.Moreover, the expression level of miR-545 could be precisely measured using advanced chips or sequencing technologies.Concurrently, expanding the repertoire of verified cell lines and increasing their numbers would contribute to obtaining more robust and convincing results.Notably, there are discrepancies in the expression patterns of miR-545-3p and miR-545-5p, possibly stemming from insufficient data on certain tumor types in existing studies.Hence, future investigations should focus on elucidating the differential expression of miR-545 in diverse tumor subtypes, stages, clinical features, and prognoses.Leveraging multi-source data and employing multilevel analysis methods would enable a comprehensive assessment of the potential diagnostic value of miR-545 in various tumors.MiR-545 is located within intron 1 of the lncRNA FTX.Analysis of the TCGA database revealed a significant correlation between miR-545 and FTX, as well as other miRNA clusters in certain tumors.However, this correlation was not significant in most TCGA tumors, and FTX CpG island methylation levels did not substantially influence miR-545 expression.This discrepancy may be attributed to missing data in the database.To elucidate the role and mechanisms of the lncRNA FTX and miR-545, along with their adjacent genes, in tumorigenesis, future research could enhance data availability by integrating databases or incorporating self-owned samples.Additionally, comprehensive analyses integrating genomics, transcriptomics, proteomics, metabolomics, and other data can be employed to investigate the multifaceted functions of miR-545 at various levels.Network analysis, systems biology, machine learning, and other methodologies can be applied to construct regulatory networks and functional modules associated with the lncRNA FTX and miR-545.Subsequently, a series of molecular biology experiments should be conducted to further investigate the mechanisms of their interaction.In recent years, sex disparities in tumorigenesis and disease progression have attracted increasing attention.Studies have indicated that fat accumulation or distribution exhibits varying effects on colorectal, esophageal, and liver cancers depending on sex. 117Therefore, it is crucial to consider the unique chromosomal locations of FTX and miR-545, as well as their potential sex-specific implications in tumor diagnosis and treatment.Nevertheless, TCGA results only revealed sex differences in miR-545 expression in a few tumor types, and the current study did not focus on cell line selection based on sex.Future investigations should collect gene expression profiles from patient tissues of different sexes and incorporate clinical data from male and female cancer patients for comprehensive statistical analysis.Furthermore, the expression levels and biological functions of miR-545 were validated using in vitro-cultured cancer cell lines and animal models encompassing both males and females.
miR-545 is competitively inhibited by 15 circRNAs and 12 lncRNAs, actively participating in five tumor-associated pathways that regulate key tumor cell behaviors affecting tumor progression, including cell cycle, proliferation, apoptosis, EMT, invasion, and migration.Although the initial discovery of the miR-545 regulatory network in tumors is promising, most mechanisms identified thus far involve single ceRNA axes, highlighting the need for more systematic and comprehensive network-based studies.Additionally, given the intricate mechanism of action of miRNAs, research on miR-545 should not solely focus on the inhibition of protein translation at the post-transcriptional level but also explore the mechanisms underlying the induction of target RNA degradation.To address these challenges, future studies should integrate bioinformatic analysis with in vivo and in vitro experiments to explore the regulatory network involving miR-545 and its associated molecules more comprehensively.This will help to elucidate their potential as therapeutic targets, thereby establishing a foundation for the development of more precise and targeted therapeutic strategies.
The extensive differential expression patterns and regulatory mechanisms of miR-545 highlight its potential clinical applications.This review revealed a significant correlation between abnormal miR-545 expression and the prognostic and clinicopathological features of various tumors.However, considering the ambiguity surrounding miR-545 expression, its reliability as a stable biomarker warrants further investigation.Future studies should collect extensive clinical data, conduct cohort analyses, and perform validation studies to assess the potential of miR-545 as a reliable biomarker, either alone or in combination with other genes.Moreover, although miR-545 has been implicated in interactions with multiple tumor treatments, such as chemotherapy, radiotherapy, and immunotherapy, via at least 10 downstream factors, research on its interactions with common treatments remains limited.For instance, the role of miR-545 in cancer immunity, including its relationship with immune checkpoints and immune cell functions, requires further exploration.Future studies should expand their scope to include a variety of treatments and drugs and monitor changes in miR-545 expression pre-and post-treatment to gain a better understanding of its involvement in chemotherapy and radiotherapy resistance.RNA therapy offers advantages, such as high therapeutic efficacy, low drug toxicity, strong specificity, and broad applicability. 118Given the involvement of miRNAs in diverse regulatory networks and their close association with normal physiological processes and cancer development, therapeutic strategies targeting miRNAs hold significant promise, and several miRNA-based therapeutic approaches already exist.For instance, rMMN nanomedicines loaded with miR-30a-5p upregulated miR-30a-5p levels both in vitro and in vivo, thereby suppressing the malignant phenotype of ocular melanoma by targeting the transcription factor E2F7. 119 Numerous therapeutic approaches targeting miRNAs and miRNA mimics have been used in clinical research. 120Future research should elucidate the regulatory modes of miR-545, develop appropriate drug delivery vehicles and methods, and ultimately achieve the clinical translation of miR-545 with high efficiency and low side effects.
MiR-545 exhibits differential expression patterns across various tumors and plays a pivotal role in intricate regulatory networks that influence tumor initiation and progression.In the future, we anticipate increased research emphasis on miR-545 and its target interactions, aiming to unravel its molecular mechanisms, therapeutic potential, and diagnostic value.Such investigations will provide valuable insights into the clinical applications of miR-545 in cancer and establish a robust theoretical foundation for subsequent advancements in clinical diagnosis and treatment.Given its potential as a promising diagnostic and therapeutic molecule, miR-545 warrants further comprehensive investigation and in-depth studies.

Conclusions
This review systematically examines miR-545 and its dysregulated expression in cancer cells.It summarizes the regulatory role and molecular mechanisms of miR-545 in cancer and its relationship with patient prognosis and drug treatments.This review highlights the potential of miR-545 as a biomarker and therapeutic target for human cancers and identifies gaps in the current research to guide future studies.MiR-545 is an important regulatory molecule with potential practical applications in clinical cancer treatment.