CD24 induces expression of the oncomir miR-21 via Src, and CD24 and Src are both post-transcriptionally downregulated by the tumor suppressor miR-34a

Hsa-miR-21-5p and Hsa-miR-145-5p Expression: From Normal Tissue to Malignant Changes-Context-Dependent Correlation with Estrogen- and Hypoxia-Vascularization-Related Pathways Genes: A Pilot Study

Ovarian cancer (OC) is a severe gynecological malignancy with a high mortality rate among women worldwide. It is often diagnosed at advanced stages due to the lack of effective screening methods. This study investigated the expression patterns of microRNAs (miRNAs) hsa-miR-21-5p and hsa-miR-145-5p as potential OC prognostic and diagnostic biomarkers and their correlation with estrogen-dependent (ESR1 & 2, PELP1 and c-SRC) and hypoxia-neovascularization-induced (HIF1A, EPAS1, and VEGFA) pathway genes. Tissue samples obtained from twenty patients with confirmed ovarian cancer and twenty controls were analyzed using quantitative polymerase chain reaction (qPCR) to examine miRNA and mRNA levels. The qPCR analysis revealed significantly higher hsa-miR-21-5p and lower hsa-miR-145-5p expression in OC tissues than controls. Moreover, a significant trend was observed in hsa-miR-21-5p and hsa-miR-145-5p expression levels across normal, non-cancerous changes and malignant ovarian tissues. The hsa-miR-21-5p showed better diagnostic potential than hsa-miR-145-5p. We also observed inconsistent correlations in hsa-miR-21-5p and hsa-mir-145-5p and estrogen-related and hypoxia-neovascularization-dependent genes in ovarian cancer across all groups. This suggests that the relationship between these miRNAs and the selected genes is context-specific. Our findings suggest that hsa-miR-21-5p and hsa-miR-145-5p expression levels may be prognostic or diagnostic markers for ovarian cancer patients.

Neutrophil extracellular traps impede cancer metastatic seeding via protease-activated receptor 2-mediated downregulation of phagocytic checkpoint CD24

BACKGROUND

Phagocytic clearance by macrophages represents a critical immune surveillance mechanism in cancer liver metastasis. Neutrophils, the most abundant immune cells encountered by cancer cells in circulation, play key roles in metastasis through neutrophil extracellular traps (NETs). Although NETs promote macrophage phagocytosis during infection, whether they regulate phagocytosis during cancer metastasis is unknown. The present study aimed to explore the roles of NETs in regulating macrophage phagocytosis during the seeding process of liver metastasis and the mechanisms underlying the roles.

METHODS

A lipopolysaccharide-induced NET model was applied to study the role of NETs on colorectal cancer (CRC) liver metastasis. The neutrophils isolated from human peripheral blood were stimulated with PMA to release NETs, which were collected and added to the cultures of different CRC cell lines for in vitro studies. Macrophage phagocytosis was assessed with flow cytometry in vitro and in vivo. RNA-seq and microRNA array analyses were performed to identify key pathways regulated by NETs and downstream key molecules. The macrophage phenotypes were evaluated using immunohistochemistry, flow cytometry, and cytokine and chemokine arrays.

RESULTS

NETs promote macrophage phagocytosis both in vitro and in vivo. Neutrophil elastase (NE), which was able to inactivate the canonical signal of protease-activated receptor 2 (PAR2), downregulated the phagocytotic checkpoint CD24. Notably, PAR2 deficiency imitated the effect of NETs on phagocytosis and CD24. Mechanistic studies indicated that inhibiting PAR2 expression upregulated miR-34a and miR-146a and downregulated CD24 in cancer cells. In addition, PAR2 depletion enhanced the recruitment and M1 polarization of macrophages by upregulating CSF-1 and CXCL1. The correlation of NETs/NE and CD24 was corroborated using human CRC specimens. Furthermore, PAR2 blockade combined with an anti-EGFR antibody (cetuximab (CTX)) synergistically enhanced the phagocytic ability of macrophages and suppressed liver metastasis in vivo.

CONCLUSIONS

NET-derived elastase inactivated PAR2 canonical signaling and promoted phagocytosis by downregulating CD24, which functions as a phagocytotic checkpoint in CRC liver metastasis. Thus, PAR2 inhibitors combined with CTX may serve as a novel therapeutic strategy against advanced CRC.

The role of MiRNA-34 family in different signaling pathways and its therapeutic options

MiRNAs are short non-coding RNA molecules that have been shown to affect a vast number of genes at the post-transcriptional level, hence regulating several signaling pathways. Because the miRNA-34 family regulates a number of different signaling pathways, including those linked to cancer, the immune system, metabolism, cellular structure, and neurological disorders, it has garnered a great deal of attention from researchers. Members of the miRNA-34 family have been shown to inhibit tumors in a variety of cancer types. This family is also important for obesity, the cardiovascular system, and glycolysis. It's interesting to note that the miRNA-34 family is known to play a role in major depressive disorder, schizophrenia, Parkinson's disease (PD), adverse childhood experiences or trauma, regulation of stress responses, Alzheimer's disease (AD), and stress-related psychatric conditions. In this review, the expected targets of the miRNA-34 family are presented alongside the well-established targets identified by pathway analysis. Furthermore, the therapeutic potential of this miRNA family will be discussed.

MET overexpression in ovarian cancer via CD24-induced downregulation of miR-181a: A signalling for cellular quiescence-like state and chemoresistance in ovarian CSCs

Increased expression of CD24 and MET, markers for cancer stem-like cells (CSCs), are each associated with ovarian cancer severity. However, whether CD24 and MET are co-expressed in ovarian CSCs and, if so, how they are related to CSC phenotype manifestation remains unknown. Our immunohistochemistry analysis showed that the co-expression of CD24 and MET was associated with poorer patient survival in ovarian cancer than those without. In addition, analyses using KM plotter and ROC plotter presented that the overexpression of CD24 or MET in ovarian cancer patients was associated with resistance to platinum-based chemotherapy. In our miRNA transcriptome and putative target genes analyses, miR-181a was downregulated in CD24-high ovarian cancer cells compared to CD24-low and predicted to bind to CD24 and MET 3'UTRs. In OV90 and SK-OV-3 cells, CD24 downregulated miR-181a expression by Src-mediated YY1 activation, leading to increased expression of MET. And, CD24 or MET knockdown or miR-181a overexpression inhibited the manifestation of CSC phenotypes, cellular quiescence-like state and chemoresistance, in OV90 and SK-OV-3 cells: increased colony formation, decreased G0/G1 phase cell population and increased sensitivity to Cisplatin and Carboplatin. Our findings suggest that CD24-miR-181a-MET may consist of a signalling route for ovarian CSCs, therefore being a combinatory set of markers and therapeutic targets for ovarian CSCs.

CD24 induced cellular quiescence-like state and chemoresistance in ovarian cancer cells via miR-130a/301a-dependent CDK19 downregulation

Cancer stem-like cell (CSC) is thought to be responsible for ovarian cancer recurrence. CD24 serves as a CSC marker for ovarian cancer and regulates the expression of miRNAs, which are regulators of CSC phenotypes. Therefore, CD24-regulated miRNAs may play roles in manifesting the CSC phenotypes in ovarian cancer cells. Our miRNA transcriptome analysis showed that 94 miRNAs were up or down-regulated in a CD24-high clone from an ovarian cancer patient compared to a CD24-low one. The CD24-dependent expression trend of the top 7 upregulated miRNAs (miR-199a-3p, 34c, 199a-5p, 130a, 301a, 214, 34b*) was confirmed in other 8 clones (4 clones for each group). CD24 overexpression upregulated the expression of miR-199a-3p, 34c, 199a-5p, 130a, 301a, 214, and 34b* in TOV112D (CD24-low) cells compared to the control, while CD24 knockdown downregulated the expression of miR-199a-3p, 199a-5p, 130a, 301a, and 34b* in OV90 (CD24-high) cells. miR-130a and 301a targeted CDK19, which induced a cellular quiescence-like state (increased G0/G1 phase cell population, decreased cell proliferation, decreased colony formation, and decreased RNA synthesis) and resistance to platinum-based chemotherapeutic agents. CD24 regulated the expression of miR-130a and 301a via STAT4 and YY1 phosphorylation mediated by Src and FAK. miR-130a and 301a were positively correlated in expression with CD24 in ovarian cancer patient tissues and negatively correlated with CDK19. Our results showed that CD24 expression may induce a cellular quiescence-like state and resistance to platinum-based chemotherapeutic agents in ovarian cancer via miR-130a and 301a upregulation. CD24-miR-130a/301a-CDK19 signaling axis could be a prognostic marker for or a potential therapeutic target against ovarian cancer recurrence.

The biological roles of CD24 in ovarian cancer: old story, but new tales

CD24 is a glycosylphosphatidylinositol linked molecular which expressed in diverse malignant tumor cells, particular in ovarian carcinoma cells and ovarian carcinoma stem cells. The CD24 expression is associated with increased metastatic potential and poor prognosis of malignancies. CD24 on the surface of tumor cells could interact with Siglec-10 on the surface of immune cells, to mediate the immune escape of tumor cells. Nowadays, CD24 has been identified as a promising focus for targeting therapy of ovarian cancer. However, the roles of CD24 in tumorigenesis, metastasis, and immune escape are still not clearly demonstrated systematically. In this review, we i) summarized the existing studies on CD24 in diverse cancers including ovarian cancer, ii) illustrated the role of CD24-siglec10 signaling pathway in immune escape, iii) reviewed the existing immunotherapeutic strategies (targeting the CD24 to restore the phagocytic effect of Siglec-10 expressing immune cells) based on the above mechanisms and evaluated the priorities in the future research. These results might provide support for guiding the CD24 immunotherapy as the intervention upon solid tumors.

Emerging phagocytosis checkpoints in cancer immunotherapy

Cancer immunotherapy, mainly including immune checkpoints-targeted therapy and the adoptive transfer of engineered immune cells, has revolutionized the oncology landscape as it utilizes patients' own immune systems in combating the cancer cells. Cancer cells escape immune surveillance by hijacking the corresponding inhibitory pathways via overexpressing checkpoint genes. Phagocytosis checkpoints, such as CD47, CD24, MHC-I, PD-L1, STC-1 and GD2, have emerged as essential checkpoints for cancer immunotherapy by functioning as "don't eat me" signals or interacting with "eat me" signals to suppress immune responses. Phagocytosis checkpoints link innate immunity and adaptive immunity in cancer immunotherapy. Genetic ablation of these phagocytosis checkpoints, as well as blockade of their signaling pathways, robustly augments phagocytosis and reduces tumor size. Among all phagocytosis checkpoints, CD47 is the most thoroughly studied and has emerged as a rising star among targets for cancer treatment. CD47-targeting antibodies and inhibitors have been investigated in various preclinical and clinical trials. However, anemia and thrombocytopenia appear to be formidable challenges since CD47 is ubiquitously expressed on erythrocytes. Here, we review the reported phagocytosis checkpoints by discussing their mechanisms and functions in cancer immunotherapy, highlight clinical progress in targeting these checkpoints and discuss challenges and potential solutions to smooth the way for combination immunotherapeutic strategies that involve both innate and adaptive immune responses.

The signal transducer CD24 suppresses the germ cell program and promotes an ectodermal rather than mesodermal cell fate in embryonal carcinomas

Testicular germ cell tumors (GCTs) are stratified into seminomas and nonseminomas. Seminomas share many histological and molecular features with primordial germ cells, whereas the nonseminoma stem cell population-embryonal carcinoma (EC)-is pluripotent and thus able to differentiate into cells of all three germ layers (teratomas). Furthermore, ECs are capable of differentiating into extra-embryonic lineages (yolk sac tumors, choriocarcinomas). In this study, we deciphered the molecular and (epi)genetic mechanisms regulating expression of CD24, a highly glycosylated signaling molecule upregulated in many cancers. CD24 is overexpressed in ECs compared with other GCT entities and can be associated with an undifferentiated pluripotent cell fate. We demonstrate that CD24 can be transactivated by the pluripotency factor SOX2, which binds in proximity to the CD24 promoter. In GCTs, CD24 expression is controlled by epigenetic mechanisms, that is, histone acetylation, since CD24 can be induced by the application histone deacetylase inhibitors. Vice versa, CD24 expression is downregulated upon inhibition of histone methyltransferases, E3 ubiquitin ligases, or bromodomain (BRD) proteins. Additionally, three-dimensional (3D) co-cultivation of EC cells with microenvironmental cells, such as fibroblasts, and endothelial or immune cells, reduced CD24 expression, suggesting that crosstalk with the somatic microenvironment influences CD24 expression. In a CRISPR/Cas9 deficiency model, we demonstrate that CD24 fulfills a bivalent role in differentiation via regulation of homeobox, and phospho- and glycoproteins; that is, it is involved in suppressing the germ cell/spermatogenesis program and mesodermal/endodermal differentiation, while poising the cells for ectodermal differentiation. Finally, blocking CD24 by a monoclonal antibody enhanced sensitivity toward cisplatin in EC cells, including cisplatin-resistant subclones, highlighting CD24 as a putative target in combination with cisplatin.

MSX2 represses tumor stem cell phenotypes within oral squamous cell carcinomas via SOX2 degradation

Oral squamous cell carcinoma (OSCC) is the sixth malignancy in the world with high incidence. The MSX2 (muscle segment homeobox 2)-Sry-related high-mobility box 2 (SOX2) signaling pathway plays a significant role in maintaining cancer stem cells, which are the origin of malignancy, leading to unfavorable outcomes in several carcinomas. This study aims to elucidate the mechanisms through which the MSX2-SOX2 pathway controls the cancer stem cell-like characterization in OSCC. The results showed that MSX2 was remarkably downregulated in OSCC and that the MSX2 expression level was related to unfavorable outcomes in patients with OSCC. Meanwhile, the MSX2 expression level was lower in the CD44+/CD24- population than in the other populations of OSCC cells. The OSCC2 cells exhibited decreased percentage of CD44+/CD24- cells, owing to MSX2 overexpression but increased owing to MSX2 knockdown. Moreover, a negative correlation was observed between MSX2 expression and is SOX2 transcriptional levels in different populations within the OSCC cell lines. Regarding the loss and gain of function, cancer stem cell phenotypes such as tumor globular formation, CD44+ subpopulation cells, and stem cell-associated gene expression were enhanced by MSX2 knockdown in OSCC CD44+/CD24- cells but decreased by MSX2 overexpression in other OSCC populations. However, these events were counteracted by the co-knockdown or SOX2 overexpression. Cells with MSX2 overexpression or knockdown formed smaller or bigger cancers in vivo, thereby showing a lower or a higher tumor incidence, respectively. Thus, our results confirm that MSX2 has a tumor suppression effect on the cancer stem cell phenotypes of OSCC and indicate that the MSX2-SOX2 signaling pathway could be a useful target for OSCC treatment.

MiRNA-146a/AKT/β-Catenin Activation Regulates Cancer Stem Cell Phenotype in Oral Squamous Cell Carcinoma by Targeting CD24

CD44^highCD24^low population has been previously reported as cancer stem cells (CSCs) in Oral Squamous Cell Carcinoma (OSCC). Increasing evidence suggests potential involvement of microRNA (miRNA) network in modulation of CSC properties. MiRNAs have thus emerged as crucial players in tumor development and maintenance. However, their role in maintenance of OSCC stem cells remains unclear. Here we report an elevated expression of miR-146a in the CD44^highCD24^low population within OSCC cells and primary HNSCC tumors. Moreover, over-expression of miR-146a results in enhanced stemness phenotype by augmenting the CD44^highCD24^low population. We demonstrate that miR-146a stabilizes β-catenin with concomitant loss of E-cadherin and CD24. Interestingly, CD24 is identified as a novel functional target of miR-146a and ectopic expression of CD24 abrogates miR-146a driven potential CSC phenotype. Mechanistic analysis reveals that higher CD24 levels inhibit AKT phosphorylation leading to β-catenin degradation. Using stably expressing miR-146a/CD24 OSCC cell lines, we also validate that the miR-146a/CD24/AKT loop significantly alters tumorigenic ability in vivo. Furthermore, we confirmed that β-catenin trans-activates miR-146a, thereby forming a positive feedback loop contributing to stem cell maintenance. Collectively, our study demonstrates that miR-146a regulates CSCs in OSCC through CD24-AKT-β-catenin axis.

Small in Size, but Large in Action: microRNAs as Potential Modulators of PTEN in Breast and Lung Cancers

MicroRNAs (miRNAs) are well-known regulators of biological mechanisms with a small size of 19–24 nucleotides and a single-stranded structure. miRNA dysregulation occurs in cancer progression. miRNAs can function as tumor-suppressing or tumor-promoting factors in cancer via regulating molecular pathways. Breast and lung cancers are two malignant thoracic tumors in which the abnormal expression of miRNAs plays a significant role in their development. Phosphatase and tensin homolog (PTEN) is a tumor-suppressor factor that is capable of suppressing the growth, viability, and metastasis of cancer cells via downregulating phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling. PTEN downregulation occurs in lung and breast cancers to promote PI3K/Akt expression, leading to uncontrolled proliferation, metastasis, and their resistance to chemotherapy and radiotherapy. miRNAs as upstream mediators of PTEN can dually induce/inhibit PTEN signaling in affecting the malignant behavior of lung and breast cancer cells. Furthermore, long non-coding RNAs and circular RNAs can regulate the miRNA/PTEN axis in lung and breast cancer cells. It seems that anti-tumor compounds such as baicalein, propofol, and curcumin can induce PTEN upregulation by affecting miRNAs in suppressing breast and lung cancer progression. These topics are discussed in the current review with a focus on molecular pathways.

SIRT1-Mediated Expression of CD24 and Epigenetic Suppression of Novel Tumor Suppressor miR-1185-1 Increases Colorectal Cancer Stemness

NAD-dependent deacetylase sirtuin-1 (SIRT1) is a class III histone deacetylase that positively regulates cancer-related pathways such as proliferation and stress resistance. SIRT1 has been shown to promote progression of colorectal cancer and is associated with cancer stemness, yet the precise mechanism between colorectal cancer stemness and SIRT1 remains to be further clarified. Here we report that SIRT1 signaling regulates colorectal cancer stemness by enhancing expression of CD24, a colorectal cancer stemness promoter. A novel miRNA, miR-1185-1, suppressed the expression of CD24 by targeting its 3'UTR (untranslated region) and could be inhibited by SIRT1 via histone deacetylation. Targeting SIRT1 by RNAi led to elevated H3 lysine 9 acetylation on the promoter region of miR-1185-1, which increased expression of miR-1185-1 and further repressed CD24 translation and colorectal cancer stemness. In a mouse xenograft model, overexpression of miR-1185-1 in colorectal cancer cells substantially reduced tumor growth. In addition, expression of miR-1185-1 was downregulated in human colorectal cancer tissues, whereas expression of CD24 was increased. In conclusion, this study not only demonstrates the essential roles of a SIRT1-miR-1185-1-CD24 axis in both colorectal cancer stemness properties and tumorigenesis but provides a potential therapeutic target for colorectal cancer treatment. SIGNIFICANCE: A novel tumor suppressor miR-1185-1 is involved in molecular regulation of CD24- and SIRT1-related cancer stemness networks, marking it a potential therapeutic target in colorectal cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/23/5257/F1.large.jpg.

Molecular Mechanism of Tumor Cell Immune Escape Mediated by CD24/Siglec-10

Tumor immune escape is an important part of tumorigenesis and development. Tumor cells can develop a variety of immunosuppressive mechanisms to combat tumor immunity. Exploring tumor cells that escape immune surveillance through the molecular mechanism of related immunosuppression in-depth is helpful to develop the treatment strategies of targeted tumor immune escape. The latest studies show that CD24 on the surface of tumor cells interacts with Siglec-10 on the surface of immune cells to promote the immune escape of tumor cells. It is necessary to comment on the molecular mechanism of inhibiting the activation of immune cells through the interaction between CD24 on tumor cells and Siglec-10 on immune cells, and a treatment strategy of tumors through targeting CD24 on the surface of tumor cells or Siglec-10 on immune cells.

miR-21: a promising biomarker for the early detection of colon cancer

Purpose

The aim of this study was to compare the expression of miR-21 gene in stages II-IV of formalin-fixed paraffin-embedded (FFPE) tissue in patients with colon cancer and introduce miR-21 as a potential molecular marker for detection of colon cancer in the early stages.

Introduction

Currently, identification of key molecules involved in the pathogenesis of cancer is one of the areas under consideration. miRNAs, are small RNAs which have been identified in many cancers. In this study, we investigated the expression of miR-21 in three pathologic stages in patients with colon cancer in the north of Iran.

Patients and methods

A total of 40 FFPE samples were obtained from patients with stages II, III, and IV from hospitals in Mazandaran and Golestan provinces. After extraction of RNA, treatment with DNase I and cDNA synthesis was performed and miR-21 expression was assessed by qPCR. Then, the data were analyzed using statistical software R (3.4.3).

Results

The expression of miR-21 in stage II was significantly different from stage IV. However, no significant difference was observed between the other stages. In stage II, the level of miR-21 expression was higher in men than women. Moreover, in the second pathological stage, miR-21 expression was reduced in patients with adjacent lymphoid tissue engagement. In addition, the expression of miR-21 in grade I was significantly higher than grade II.

Conclusion

The results of this study suggest that miR-21 can be a diagnostic marker for early stages of colon cancer, especially in men. It can also be considered as a good candidate for targeted treatment of colon cancer in the early stages of the disease. Furthermore, for the first time, we suggested that miR-21 can be a good molecular marker for classification of the stages of colon cancer.

Overview upon miR-21 in lung cancer: focus on NSCLC

Considering the high mortality rate encountered in lung cancer, there is a strong need to explore new biomarkers for early diagnosis and also improved therapeutic targets to overcome this issue. The implementation of microRNAs as important regulators in cancer and other pathologies expanded the possibilities of lung cancer management and not only. MiR-21 represents an intensively studied microRNA in many types of cancer, including non-small cell lung cancer (NSCLC). Its role as an oncogene is underlined in multiple studies reporting the upregulated expression of this sequence in patients diagnosed with this malignancy; moreover, several studies associated this increased expression of miR-21 with a worse outcome within NSCLC patients. The same pattern is supported by the data existent in the Cancer Genome Atlas (TCGA). The carcinogenic advantage generated by miR-21 in NSCLC resides in the target genes involved in multiple pathways such as cell growth and proliferation, angiogenesis, invasion and metastasis, but also chemo- and radioresistance. Therapeutic modulation of miR-21 by use of antisense sequences entrapped in different delivery systems has shown promising results in impairment of NSCLC. Hereby, we review the mechanisms of action of miR-21 in cancer and the associated changes upon tumor cells together a focused perspective on NSCLC signaling, prognosis and therapy.

MicroRNA-34 family in breast cancer: from research to therapeutic potential

MicroRNA (miRNA)-34 family (miR-34s), including miR-34a/b/c, is the most well studied non-coding RNAs that regulate gene expression post-transcriptionally. The miR-34s mediates the tumor suppressor function of p53 in the pathogenesis of breast cancer by targeting different oncogenes. This review focuses on the anti-oncogenic regulation of the miR-34s, emphasizing the major signaling pathways that are involved in the modulation of miR-34s in breast cancer. Moreover, it highlights how epigenetic modification by the p53/miR-34s axis regulates the proliferation, invasiveness, chemoresistance, and sternness of breast cancer. A better understanding of the molecular mechanisms of miR-34s will open new opportunities for the development of novel therapeutic strategies and define a new approach in identifying potential biomarkers for early diagnosis of breast cancer.

microRNA Regulation in Estrogen Receptor-Positive Breast Cancer and Endocrine Therapy

As de novo and acquired resistance to standard first line endocrine therapies is a growing clinical challenge for estrogen receptor-positive (ER⁺) breast cancer patients, understanding the mechanisms of resistance is critical to develop novel therapeutic strategies to prevent therapeutic resistance and improve patient outcomes. The widespread post-transcriptional regulatory role that microRNAs (miRNAs) can have on various oncogenic pathways has been well-documented. In particular, several miRNAs are reported to suppress ERα expression via direct binding with the 3’ UTR of ESR1 mRNA, which can confer resistance to estrogen/ERα-targeted therapies. In turn, estrogen/ERα activation can modulate miRNA expression, which may contribute to ER⁺ breast carcinogenesis. Given the reported oncogenic and tumor suppressor functions of miRNAs in ER⁺ breast cancer, the targeted regulation of specific miRNAs is emerging as a promising strategy to treat ER⁺ breast cancer and significantly improve patient responsiveness to endocrine therapies. In this review, we highlight the major miRNA-ER regulatory mechanisms in context with ER⁺ breast carcinogenesis, as well as the critical miRNAs that contribute to endocrine therapy resistance or sensitivity. Collectively, this comprehensive review of the current literature sheds light on the clinical applications and challenges associated with miRNA regulatory mechanisms and novel miRNA targets that may have translational value as potential therapeutics for the treatment of ER⁺ breast cancer.

STAT5 induces miR-21 expression in cutaneous T cell lymphoma

In cutaneous T cell lymphomas (CTCL), miR-21 is aberrantly expressed in skin and peripheral blood and displays anti-apoptotic properties in malignant T cells. It is, however, unclear exactly which cells express miR-21 and what mechanisms regulate miR-21. Here, we demonstrate miR-21 expression in situ in both malignant and reactive lymphocytes as well as stromal cells. qRT-PCR analysis of 47 patients with mycosis fungoides (MF) and Sezary Syndrome (SS) confirmed an increased miR-21 expression that correlated with progressive disease. In cultured malignant T cells miR-21 expression was inhibited by Tofacitinib (CP-690550), a clinical-grade JAK3 inhibitor. Chromatin immunoprecipitation (ChIP) analysis showed direct binding of STAT5 to the miR-21 promoter. Cytokine starvation ex vivo triggered a decrease in miR-21 expression, whereas IL-2 induced an increased miR-21 expression in primary SS T cells and cultured cytokine-dependent SS cells (SeAx). siRNA-mediated depletion of STAT5 inhibited constitutive- and IL-2-induced miR-21 expression in cytokine-independent and dependent T cell lines, respectively. IL-15 and IL-2 were more potent than IL-21 in inducing miR-21 expression in the cytokine-dependent T cells. In conclusion, we provide first evidence that miR-21 is expressed in situ in CTCL skin lesions, induced by IL-2 and IL-15 cytokines, and is regulated by STAT5 in malignant T cells. Thus, our data provide novel evidence for a pathological role of IL-2Rg cytokines in promoting expression of the oncogenic miR-21 in CTCL.

MicroRNAs in the etiology of colorectal cancer: pathways and clinical implications

MicroRNAs (miRNAs) are small single-stranded RNAs that repress mRNA translation and trigger mRNA degradation. Of the ∼1900 miRNA-encoding genes present in the human genome, ∼250 miRNAs are reported to have changes in abundance or altered functions in colorectal cancer. Thousands of studies have documented aberrant miRNA levels in colorectal cancer, with some miRNAs reported to actively regulate tumorigenesis. A recurrent phenomenon with miRNAs is their frequent participation in feedback loops, which probably serve to reinforce or magnify biological outcomes to manifest a particular cellular phenotype. Here, we review the roles of oncogenic miRNAs (oncomiRs), tumor suppressive miRNAs (anti-oncomiRs) and miRNA regulators in colorectal cancer. Given their stability in patient-derived samples and ease of detection with standard and novel techniques, we also discuss the potential use of miRNAs as biomarkers in the diagnosis of colorectal cancer and as prognostic indicators of this disease. MiRNAs also represent attractive candidates for targeted therapies because their function can be manipulated through the use of synthetic antagonists and miRNA mimics.

Summary: This Review provides an overview of some important microRNAs and their roles in colorectal cancer.

The epigenetically-regulated miR-34a targeting c-SRC suppresses RAF/MEK/ERK signaling pathway in K-562 cells

Previous reports show that miR-34a suppressed K-562 cell proliferation and contributed to megakaryocytic differentiation of K-562 cells. Here, we reported that miR-34a, a tumor suppressor gene, is down-regulated in the K-562 cells and chronic myeloid leukemia (CML) patients due to aberrant DNA hypermethylation. c-SRC is a target of miR-34a. Restoring miR-34a expression resulted in down-regulation of c-SRC and phosphorylated (Tyr416) c-SRC protein in K-562 cells, which consequently triggered suppression of the RAF/MEK/ERK signaling pathway to decrease cell proliferation.

Self-renewal molecular mechanisms of colorectal cancer stem cells

Colorectal cancer stem cells (CCSCs) represent a small fraction of the colorectal cancer cell population that possess self-renewal and multi-lineage differentiation potential and drive tumorigenicity. Self-renewal is essential for the malignant biological behaviors of colorectal cancer stem cells. While the self-renewal molecular mechanisms of colorectal cancer stem cells are not yet fully understood, the aberrant activation of signaling pathways, such as Wnt, Notch, transforming growth factor-β (TGF-β)/bone morphogenetic protein (BMP) and Hedgehog-Gli (HH-GLI), specific roles mediated by cell surface markers and micro-environmental factors are involved in the regulation of self-renewal. The elucidation of the molecular mechanisms behind self-renewal may lead to the development of novel targeted interventions for the treatment of colorectal cancer.

CD24 Is Not Required for Tumor Initiation and Growth in Murine Breast and Prostate Cancer Models

CD24 is a small, heavily glycosylated, GPI-linked membrane protein, whose expression has been associated with the tumorigenesis and progression of several types of cancer. Here, we studied the expression of CD24 in tumors of MMTV-PyMT, Apc^1572/T+ and TRAMP genetic mouse models that spontaneously develop mammary or prostate carcinoma, respectively. We found that CD24 is expressed during tumor development in all three models. In MMTV-PyMT and Apc^1572T/+ breast tumors, CD24 was strongly but heterogeneously expressed during early tumorigenesis, but decreased in more advanced stages, and accordingly was increased in poorly differentiated lesions compared with well differentiated lesions. In prostate tumors developing in TRAMP mice, CD24 expression was strong within hyperplastic lesions in comparison with non-hyperplastic regions, and heterogeneous CD24 expression was maintained in advanced prostate carcinomas. To investigate whether CD24 plays a functional role in tumorigenesis in these models, we crossed CD24 deficient mice with MMTV-PyMT, Apc^1572T/+ and TRAMP mice, and assessed the influence of CD24 deficiency on tumor onset and tumor burden. We found that mice negative or positive for CD24 did not significantly differ in terms of tumor initiation and burden in the genetic tumor models tested, with the exception of Apc^1572T/+ mice, in which lack of CD24 reduced the mammary tumor burden slightly but significantly. Together, our data suggest that while CD24 is distinctively expressed during the early development of murine mammary and prostate tumors, it is not essential for the formation of tumors developing in MMTV-PyMT, Apc^1572T/+ and TRAMP mice.

CD24 associates with EGFR and supports EGF/EGFR signaling via RhoA in gastric cancer cells

Background

CD24, a mucin-like membrane glycoprotein, plays a critical role in carcinogenesis, but its role in human gastric cancer and the underlying mechanism remains undefined.

Methods

The contents of CD24 and epidermal growth factor receptor (EGFR) in gastric cancer cells (SGC-7901 and BGC-823) and non-malignant gastric epithelial cells (GES-1) were evaluated by Western blotting assay. Cellular EGFR staining was examined by immunofluorescence assay. Cell migration rate was measured by wound healing assay. The effects of depletion/overexperssion of CD24 on EGFR expression and activation of EGF/EGFR singaling pathways were evaluated by immunofluorescence, qPCR, Western blotting and flow cytometry techniques. RhoA activity was assessed by pulldown assay. CD24 and EGFR expression patterns in human gastric tumor samples were also investigated by immunohistochemistry staining.

Results

CD24 was overexpressed in human gastric cancer cells. Ectopic expression of CD24 in gastric epithelial cells augmented the expression of EGFR, while knockdown of CD24 in gastric cancer cells decreased the level of EGFR and cell migration velocity. To further explore the mechanisms, we investigated the effect of CD24 expression on EGF/EGFR signaling. We noticed that this effect of CD24 on EGFR expression was dependent on promoting EGFR internalization and degradation. Lower ERK and Akt phosphorylations in response to EGF stimulation were observed in CD24-depleted cells. In addition, we noticed that the effect of CD24 on EGFR stability was mediated by RhoA activity in SGC-7901 gastric cancer cells. Analysis of gastric cancer specimens revealed a positive correlation between CD24 and EGFR levels and an association between CD24 expression and worse prognosis.

Conclusion

Thus, these findings suggest for the first time that CD24 regulates EGFR signaling by inhibiting EGFR internalization and degradation in a RhoA-dependent manner in gastric cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0787-y) contains supplementary material, which is available to authorized users.

miR-34a Silences c-SRC to Attenuate Tumor Growth in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype with no clinically proven biologically targeted treatment options. The molecular heterogeneity of TNBC and lack of high frequency driver mutations other than TP53 have hindered the development of new and effective therapies that significantly improve patient outcomes. miRNAs, global regulators of survival and proliferation pathways important in tumor development and maintenance, are becoming promising therapeutic agents. We performed miRNA-profiling studies in different TNBC subtypes to identify miRNAs that significantly contribute to disease progression. We found that miR-34a was lost in TNBC, specifically within mesenchymal and mesenchymal stem cell-like subtypes, whereas expression of miR-34a targets was significantly enriched. Furthermore, restoration of miR-34a in cell lines representing these subtypes inhibited proliferation and invasion, activated senescence, and promoted sensitivity to dasatinib by targeting the proto-oncogene c-SRC. Notably, SRC depletion in TNBC cell lines phenocopied the effects of miR-34a reintroduction, whereas SRC overexpression rescued the antitumorigenic properties mediated by miR-34a. miR-34a levels also increased when cells were treated with c-SRC inhibitors, suggesting a negative feedback exists between miR-34a and c-SRC. Moreover, miR-34a administration significantly delayed tumor growth of subcutaneously and orthotopically implanted tumors in nude mice, and was accompanied by c-SRC downregulation. Finally, we found that miR-34a and SRC levels were inversely correlated in human tumor specimens. Together, our results demonstrate that miR-34a exerts potent antitumorigenic effects in vitro and in vivo and suggests that miR-34a replacement therapy, which is currently being tested in human clinical trials, represents a promising therapeutic strategy for TNBC.

Repression of CD24 surface protein expression by oncogenic Ras is relieved by inhibition of Raf but not MEK or PI3K

CD24 is a dynamically regulated cell surface protein. High expression of CD24 leads to progression of lung, prostrate, colon, and pancreatic cancers, among others. In contrast, low expression of CD24 leads to cell proliferation and metastasis of breast cancer stem cells (BCSCs). Activating mutations in Ras are found in 30% of all human cancers. Oncogenic Ras constitutively stimulates the Raf, PI3K, and Ral GDS signaling pathways, leading to cellular transformation. Previous studies have shown that expression of oncogenic Ras in breast cancer cells generates CD24⁻ cells from CD24⁺ cells. However, the molecular mechanisms involved in the generation of CD24⁻ cells were not determined. Here, we demonstrate that oncogenic Ras (RasV12) expression suppresses CD24 mRNA, protein, and promoter levels when expressed in NIH/3T3 cells. Furthermore, activation of only the Raf pathway was sufficient to downregulate CD24 mRNA and protein expression to levels similar to those seen in with RasV12 expression. In contrast, activation of the PI3K pathway downregulated mRNA expression with a partial effect on protein expression whereas activation of the RalGDS pathway only partially affected protein expression. Surprisingly, inhibition of MEK with U0126 only partially restored CD24 mRNA expression but not surface protein expression. In contrast, inhibition of Raf with sorafenib did not restore CD24 mRNA expression but significantly increased the proportion of RasV12 cells expressing CD24. Therefore, the Raf pathway is the major repressor of CD24 mRNA and protein expression, with PI3K also able to substantially inhibit CD24 expression. Moreover, these data indicate that the levels of CD24 mRNA and surface protein are independently regulated. Although inhibition of Raf by sorafenib only partially restored CD24 expression, sorafenib should still be considered as a potential therapeutic strategy to alter CD24 expression in CD24⁻ cells, such as BCSCs.

Correction: CD24 Induces Expression of the Oncomir miR-21 via Src, and CD24 and Src Are Both Post-Transcriptionally Downregulated by the Tumor Suppressor miR-34a

[This corrects the article DOI: 10.1371/journal.pone.0059563.].

microRNAs and Colorectal Cancer

Colorectal cancer (CRC) is one of the most common types of human cancer with high cancer-related morbidity and mortality rates. The development and clinical validation of novel therapeutic avenues have improved the clinical outcome, but metastatic CRC still remains an incurable disease in most cases. The interest in discovering novel pathophysiological drivers in CRC is intensively ongoing and the search for novel biomarkers for early diagnosis, for patient's stratification for prognostic purposes or for predicting treatment response are warranted. microRNAs are small RNA molecules that regulate the expression of larger messenger RNA species by different mechanisms with the final consequence to provide a fine tuning tool for global gene expression patterns. First discovered in worms, around 15 years ago it became clear that microRNAs are also existing in humans and that they are widely involved in human carcinogenesis. Within the last years, tremendous progress in the understanding of microRNAs and their role in CRC carcinogenesis has been developed. In this book chapter, several examples of previously identified microRNAs and how they influence colorectal carcinogenesis will be discussed. The information starting at the underlying molecular mechanisms towards clinical applications will be depicted and an overview what great potential these small molecules might carry in future colorectal cancer medicine, will be discussed.

MicroRNAs in colorectal cancer: small molecules with big functions

Colorectal cancer (CRC) is the third most lethal malignancy, with pathogenesis intricately dependent upon microRNAs (miRNAs). miRNAs are short, non-protein coding RNAs, targeting the 3'-untranslated regions (3'-UTR) of certain mRNAs. They usually serve as tumor suppressors or oncogenes, and participate in tumor phenotype maintenance. Therefore, miRNAs consequently regulate CRC carcinogenesis and other biological functions, including apoptosis, development, angiogenesis, migration, and proliferation. Due to its differential expression and distinct stability, miRNAs are regarded as molecular biomarkers (for diagnosis/prognosis) and therapeutic targets for CRC. Recently, a remarkable number of miRNAs have been discovered with implications via incompletely understood mechanisms in CRC. As further study of relevant miRNAs continues, it is hopeful that novel miRNA-based therapeutic strategies may be available for CRC patients in the future.

Impact of the mitogen-activated protein kinase pathway on the subproteome of detergent-resistant microdomains of colon carcinoma cells

Lipid rafts play a key role in the regulation of fundamentally important cellular processes, including cell proliferation, differentiation, and survival. The composition of such detergent-resistant microdomains (DRMs) is altered under pathologic conditions, including cancer. Although DRMs have been analyzed in colorectal carcinoma little information exists about their composition upon treatment with targeted drugs. Hence, a quantitative proteomic profiling approach was performed to define alterations within the DRM fraction of colorectal carcinoma cells upon treatment with the drug U0126, an inhibitor of the mitogen-activated protein kinase pathway. Comparative expression profilings resulted in the identification of 300 proteins, which could partially be linked to key oncogenic signaling pathways and tumor-related cellular features, such as cell proliferation, adhesion, motility, invasion, and apoptosis resistance. Most of these proteins were downregulated upon inhibitor treatment. In addition, quantitative proteomic profilings of cholesterol-depleted versus intact lipid rafts were performed to define, which U0126-regulated target structures represent bona fide raft proteins. Selected differentially abundant raft proteins were validated at the mRNA and/or protein level using U0126- or Trametinib-treated cells. The presented data provide insights into the molecular mechanisms associated with the response to the treatment with MEK inhibitors and might also lead to novel candidates for therapeutic interventions.

Mir-34: a new weapon against cancer?

The microRNA(miRNA)-34a is a key regulator of tumor suppression. It controls the expression of a plethora of target proteins involved in cell cycle, differentiation and apoptosis, and antagonizes processes that are necessary for basic cancer cell viability as well as cancer stemness, metastasis, and chemoresistance. In this review, we focus on the molecular mechanisms of miR-34a-mediated tumor suppression, giving emphasis on the main miR-34a targets, as well as on the principal regulators involved in the modulation of this miRNA. Moreover, we shed light on the miR-34a role in modulating responsiveness to chemotherapy and on the phytonutrients-mediated regulation of miR-34a expression and activity in cancer cells. Given the broad anti-oncogenic activity of miR-34a, we also discuss the substantial benefits of a new therapeutic concept based on nanotechnology delivery of miRNA mimics. In fact, the replacement of oncosuppressor miRNAs provides an effective strategy against tumor heterogeneity and the selective RNA-based delivery systems seems to be an excellent platform for a safe and effective targeting of the tumor.

Cancer stem cells in colorectal cancer from pathogenesis to therapy: Controversies and perspectives

Colorectal cancer remains one of the most common and lethal malignancies worldwide despite the use of various therapeutic strategies. A better understanding of the mechanisms responsible for tumor initiation and progression is essential for the development of novel, more powerful therapies. The traditional, so-called “stochastic model” of tumor development, which assumes that each cancer cell is tumorigenic, has been deeply challenged during the past decade by the identification of cancer stem cells (CSCs), a biologically distinct subset of cells within the bulk of tumor mass. This discovery led to the development of the hierarchical model of tumorigenesis which assumes that only CSCs have the ability to initiate tumor growth, both at primary and metastatic sites. This model implies that the elimination of all CSCs is fundamental to eradicate tumors and that failure to do so might be responsible for the occurrence of relapses and/or metastases frequently observed in the clinical management of colorectal cancer patients. Identification and isolation of CSCs is essential for a better understanding of their role in the tumorigenetic process and for the development of CSC-specific therapies. Several methods have been used for this purpose and many efforts have been focused on the identification of specific CSC-surface markers. This review provides an overview of the proposed roles of CSC in human colorectal tumorigenesis focusing on the most important molecules identified as CSC-specific markers in colorectal cancer and on the potential strategies for the development of CSC-targeted therapy.

Construction and analysis of regulatory genetic networks in cervical cancer based on involved microRNAs, target genes, transcription factors and host genes

Over recent years, genes and microRNA (miRNA/miR) have been considered as key biological factors in human carcinogenesis. During cancer development, genes may act as multiple identities, including target genes of miRNA, transcription factors and host genes. The present study concentrated on the regulatory networks consisting of the biological factors involved in cervical cancer in order to investigate their features and affect on this specific pathology. Numerous raw data was collected and organized into purposeful structures, and adaptive procedures were defined for application to the prepared data. The networks were therefore built with the factors as basic components according to their interacting associations. The networks were constructed at three levels of interdependency, including a differentially-expressed network, a related network and a global network. Comparisons and analyses were made at a systematic level rather than from an isolated gene or miRNA. Critical hubs were extracted in the core networks and notable features were discussed, including self-adaption feedback regulation. The present study expounds the pathogenesis from a novel point of view and is proposed to provide inspiration for further investigation and therapy.

Advances in understanding the relationship between CD24 and colorectal cancer

Colorectal cancer (CRC) is the third cause of cancer-related morbidity and mortality in America. In China and other Asian countries, an increasingly westernized diet has led to a high incidence of CRC. There is currently an urgent demand for the discovery of novel biomarkers for CRC prognostic evaluation and molecular targeted therapies. CD24 is a mucin-like glycoprotein that is highly expressed on the surface of CRC cells. It may play a significant role in the multistep process of CRC carcinogenesis, invasion and metastasis and is correlated with therapeutic resistance and poor prognosis of CRC. As one of surface markers for potential cancer stem cells (CSCs), CD24 may be used as an ideal target for curative CRC therapy. In this review, we summarize the role of CD24 in CRC initiation, progression and metastasis. Moreover, we discuss the vital part of CD24 in CSC identification, isolation and complete CRC eradication.