Cancer Stem-like Cells Act via Distinct Signaling Pathways in Promoting Late Stages of Malignant Progression

Understanding the autophagic functions in cancer stem cell maintenance and therapy resistance

Complex tumour ecosystem comprising tumour cells and its associated tumour microenvironment (TME) constantly influence the tumoural behaviour and ultimately impact therapy failure, disease progression, recurrence and poor overall survival of patients. Crosstalk between tumour cells and TME amplifies the complexity by creating metabolic changes such as hypoxic environment and nutrient fluctuations. These changes in TME initiate stem cell-like programmes in cancer cells, contribute to tumoural heterogeneity and increase tumour robustness. Recent studies demonstrate the multifaceted role of autophagy in promoting fibroblast production, stemness, cancer cell survival during longer periods of dormancy, eventual growth of metastatic disease and disease resistance. Recent ongoing studies examine autophagy/mitophagy as a powerful survival strategy in response to environmental stress including nutrient deprivation, hypoxia and environmental stress in TME. It prevents irreversible senescence, promotes dormant stem-like state, induces epithelial-mesenchymal transition and increases migratory and invasive potential of tumour cells. The present review discusses various theories and mechanisms behind the autophagy-dependent induction of cancer stem cell (CSC) phenotype. Given the role of autophagic functions in CSC aggressiveness and therapeutic resistance, various mechanisms and studies based on suppressing cellular plasticity by blocking autophagy as a powerful therapeutic strategy to kill tumour cells are discussed.

IGF1R signaling induces epithelial-mesenchymal plasticity via ITGAV in cutaneous carcinoma

BACKGROUND

Early cutaneous squamous cell carcinomas (cSCCs) generally show epithelial differentiation features and good prognosis, whereas advanced cSCCs present mesenchymal traits associated with tumor relapse, metastasis, and poor survival. Currently, the mechanisms involved in cSCC progression are unclear, and the established markers are suboptimal for accurately predicting the clinical course of the disease.

METHODS

Using a mouse model of cSCC progression, expression microarray analysis, immunofluorescence and flow cytometry assays, we have identified a prognostic biomarker of tumor relapse, which has been evaluated in a cohort of cSCC patient samples. Phosphoproteomic analysis have revealed signaling pathways induced in epithelial plastic cancer cells that promote epithelial-mesenchymal plasticity (EMP) and tumor progression. These pathways have been validated by genetic and pharmacological inhibition assays.

RESULTS

We show that the emergence of epithelial cancer cells expressing integrin αV (ITGAV) promotes cSCC progression to a mesenchymal state. Consistently, ITGAV expression allows the identification of patients at risk of cSCC relapse above the currently employed clinical histopathological parameters. We also demonstrate that activation of insulin-like growth factor-1 receptor (IGF1R) pathway in epithelial cancer cells is necessary to induce EMP and mesenchymal state acquisition in response to tumor microenvironment-derived factors, while promoting ITGAV expression. Likewise, ITGAV knockdown in epithelial plastic cancer cells also blocks EMP acquisition, generating epithelial tumors.

CONCLUSIONS

Our results demonstrate that ITGAV is a prognostic biomarker of relapse in cSCCs that would allow improved patient stratification. ITGAV also collaborates with IGF1R to induce EMP in epithelial cancer cells and promotes cSCC progression, revealing a potential therapeutic strategy to block the generation of advanced mesenchymal cSCCs.

Cancer cell plasticity defines response to immunotherapy in cutaneous squamous cell carcinoma

Immune checkpoint blockade (ICB) approaches have changed the therapeutic landscape for many tumor types. However, half of cutaneous squamous cell carcinoma (cSCC) patients remain unresponsive or develop resistance. Here, we show that, during cSCC progression in male mice, cancer cells acquire epithelial/mesenchymal plasticity and change their immune checkpoint (IC) ligand profile according to their features, dictating the IC pathways involved in immune evasion. Epithelial cancer cells, through the PD-1/PD-L1 pathway, and mesenchymal cancer cells, through the CTLA-4/CD80 and TIGIT/CD155 pathways, differentially block antitumor immune responses and determine the response to ICB therapies. Accordingly, the anti-PD-L1/TIGIT combination is the most effective strategy for blocking the growth of cSCCs that contain both epithelial and mesenchymal cancer cells. The expression of E-cadherin/Vimentin/CD80/CD155 proteins in cSCC, HNSCC and melanoma patient samples predicts response to anti-PD-1/PD-L1 therapy. Collectively, our findings indicate that the selection of ICB therapies should take into account the epithelial/mesenchymal features of cancer cells.

Lymph Vessels Associate with Cancer Stem Cells from Initiation to Malignant Stages of Squamous Cell Carcinoma

Tumor-associated lymph vessels and lymph node involvement are critical staging criteria in several cancers. In skin squamous cell carcinoma, lymph vessels play a role in cancer development and metastatic spread. However, their relationship with the cancer stem cell niche at early tumor stages remains unclear. To address this gap, we studied the lymph vessel localization at the cancer stem cell niche and observed an association from benign skin lesions to malignant stages of skin squamous cell carcinoma. By co-culturing lymphatic endothelial cells with cancer cell lines representing the initiation and promotion stages, and conducting RNA profiling, we observed a reciprocal induction of cell adhesion, immunity regulation, and vessel remodeling genes, suggesting dynamic interactions between lymphatic and cancer cells. Additionally, imaging analyses of the cultured cells revealed the establishment of heterotypic contacts between cancer cells and lymph endothelial cells, potentially contributing to the observed distribution and maintenance at the cancer stem cell niche, inducing downstream cellular responses. Our data provide evidence for an association of lymph vessels from the early stages of skin squamous cell carcinoma development, opening new avenues for better comprehending their involvement in cancer progression.

miR-22 promotes stem cell traits via activating Wnt/β-catenin signaling in cutaneous squamous cell carcinoma

Emerging evidence suggests that the cancer stem cells (CSCs) are key culprits of cancer metastasis and drug resistance. Understanding mechanisms regulating the critical oncogenic pathways and CSCs function could reveal new diagnostic and therapeutic strategies. We now report that miR-22, a miRNA critical for hair follicle stem/progenitor cell differentiation, promotes tumor initiation, progression, and metastasis by maintaining Wnt/β-catenin signaling and CSCs function. Mechanistically, we find that miR-22 facilitates β-catenin stabilization through directly repressing citrullinase PAD2. Moreover, miR-22 also relieves DKK1-mediated repression of Wnt/β-catenin signaling by targeting a FosB-DDK1 transcriptional axis. miR-22 knockout mice showed attenuated Wnt/β-catenin activity and Lgr5+ CSCs penetrance, resulting in reduced occurrence, progression, and metastasis of chemically induced cutaneous squamous cell carcinoma (cSCC). Clinically, miR-22 is abundantly expressed in human cSCC. Its expression is even further elevated in the CSCs proportion, which negatively correlates with PAD2 and FosB expression. Inhibition of miR-22 markedly suppressed cSCC progression and increased chemotherapy sensitivity in vitro and in xenograft mice. Together, our results revealed a novel miR-22-WNT-CSCs regulatory mechanism in cSCC and highlight the important clinical application prospects of miR-22, a common target molecule for Wnt/β-catenin signaling and CSCs, for patient stratification and therapeutic intervention.

Epithelial Plasticity, Autophagy and Metastasis: Potential Modifiers of the Crosstalk to Overcome Therapeutic Resistance

Epithelial-to-mesenchymal transition (EMT) initiates malignant transformation of cancer cells and is responsible for the generation of heterogenic subsets of cancer stem cells (CSCs). Signals in the form of environmental cues and paracrine factors within tumor microenvironment (TME) niche, support the possibility of generation of pool of CSCs with two distinct functional transition states. Cyclic CSCs with predominant epithelial phenotype, self-renew and differentiate into mature cancer cells. Subsets of autophagic/ non-cyclic CSCs with predominant mesenchymal phenotype have capacity to invade, metastasize, resist to apoptosis, escape immunosurveillance, survive chemotherapies and are majorly responsible for cancer mortality. Differences in phenotypic plasticity may form the basis of differential impact of therapeutic outcomes on heterogeneous subpopulations of CSCs. Activation of autophagy is responsible for the recycling of damaged organelles and protein aggregates, regulates EMT, confers the survival advantage to neoplastic cells to anti-cancer therapies, significantly affects the invasive potential of cancer cells and supports their metastatic dissemination in a tissue and tumor stage dependent manner. Therapy resistance is the primary obstacle in the complete ablation of tumor cells. Combinational treatments based on targeting autophagic CSCs and inhibiting EMT regulators may represent potential anticancer strategies for the prevention of cancer invasion, metastatic spread and disease relapse.

FGFR Inhibition Overcomes Resistance to EGFR-targeted Therapy in Epithelial-like Cutaneous Carcinoma

PURPOSE

Recurrent and/or metastatic unresectable cutaneous squamous cell carcinomas (cSCCs) are treated with chemotherapy or radiotherapy, but have poor clinical responses. A limited response (up to 45% of cases) to EGFR-targeted therapies was observed in clinical trials with patients with advanced and metastatic cSCC. Here, we analyze the molecular traits underlying the response to EGFR inhibitors, and the mechanisms responsible for cSCC resistance to EGFR-targeted therapy.

EXPERIMENTAL DESIGN

We generated primary cell cultures and patient cSCC-derived xenografts (cSCC-PDXs) that recapitulate the histopathologic and molecular features of patient tumors. Response to gefitinib treatment was tested and gefitinib-resistant (GefR) cSCC-PDXs were developed. RNA sequence analysis was performed in matched untreated and GefR cSCC-PDXs to determine the mechanisms driving gefitinib resistance.

RESULTS

cSCCs conserving epithelial traits exhibited strong activation of EGFR signaling, which promoted tumor cell proliferation, in contrast to mesenchymal-like cSCCs. Gefitinib treatment strongly blocked epithelial-like cSCC-PDX growth in the absence of EGFR and RAS mutations, whereas tumors carrying the E545K PIK3CA-activating mutation were resistant to treatment. A subset of initially responding tumors acquired resistance after long-term treatment, which was induced by the bypass from EGFR to FGFR signaling to allow tumor cell proliferation and survival upon gefitinib treatment. Pharmacologic inhibition of FGFR signaling overcame resistance to EGFR inhibitor, even in PIK3CA-mutated tumors.

CONCLUSIONS

EGFR-targeted therapy may be appropriate for treating many epithelial-like cSCCs without PIK3CA-activating mutations. Combined EGFR- and FGFR-targeted therapy may be used to treat cSCCs that show intrinsic or acquired resistance to EGFR inhibitors.

Role of Flavonoids in the Prevention of AhR-Dependent Resistance During Treatment with BRAF Inhibitors

BRAF and MEK inhibitors (BRAFi and MEKi) are the standard of care for the treatment of metastatic melanoma in patients with BRAF^V600E mutations, greatly improving progression-free survival. However, the acquisition of resistance to BRAFi and MEKi remains a difficult clinical challenge, with limited therapeutic options available for these patients. Here, we investigated the therapeutic potential of natural flavonoids as specific AhR (Aryl hydrocarbon Receptor) transcription factor antagonists in combination with BRAFi. Experimental Design: Experiments were performed in vitro and in vivo with various human melanoma cell lines (mutated for BRAF^V600E) sensitive or resistant to BRAFi. We evaluated the role of various flavonoids on cell sensitivity to BRAFi and their ability to counteract resistance and the invasive phenotype of melanoma. Results: Flavonoids were highly effective in potentiating BRAFi therapy in human melanoma cell lines by increasing sensitivity and delaying the pool of resistant cells that arise during treatment. As AhR antagonists, flavonoids counteracted a gene expression program associated with the acquisition of resistance and phenotype switching that leads to an invasive and EMT-like phenotype. Conclusions: The use of natural flavonoids opens new therapeutic opportunities for the treatment of patients with BRAF-resistant disease.

Sox2: A Regulatory Factor in Tumorigenesis and Metastasis

The transcription factor Sox2 plays an important role in various phases of embryonic development, including cell fate and differentiation. These key regulatory functions are facilitated by binding to specific DNA sequences in combination with partner proteins to exert their effects. Recently, overexpression and gene amplification of Sox2 has been associated with tumor aggression and metastasis in various cancer types, including breast, prostate, lung, ovarian and colon cancer. All the different roles for Sox2 involve complicated regulatory networks consisting of protein-protein and protein-nucleic acid interactions. Their involvement in the EMT modulation is possibly enabled by Wnt/ β-catenin and other signaling pathways. There are number of in vivo models which show Sox2 association with increased cancer aggressiveness, resistance to chemo-radiation therapy and decreased survival rate suggesting Sox2 as a therapeutic target. This review will focus on the different roles for Sox2 in metastasis and tumorigenesis. We will also review the mechanism of action underlying the cooperative Sox2- DNA/partner factors binding where Sox2 can be potentially explored for a therapeutic opportunity to treat cancers.

The transcription factor LEF1 promotes tumorigenicity and activates the TGF-β signaling pathway in esophageal squamous cell carcinoma

Background

Esophageal squamous cell carcinoma (ESCC) is the most difficult subtype of esophageal cancer to treat due to the paucity of effective targeted therapy. ESCC is believed to arise from cancer stem cells (CSCs) that contribute to metastasis and chemoresistance. Despite advances in diagnosis and treatment, the prognosis of ESCC patients remains poor.

Methods

In this study, we applied western blot, quantitative real-time polymerase chain reaction (qRT-PCR), immunohistochemistry, RNA-Seq analysis, luciferase reporter assay, Chip-qPCR, bioinformatics analysis, and a series of functional assays to show the potential role of LEF1 in regulating esophageal CSCs.

Results

We found that the overexpression of LEF1 was associated with aberrant clinicopathological characteristics and the poor prognosis of ESCC patients. In addition, the elevated expression of LEF1 and OV6 was significantly associated with aberrant clinicopathological features, and poor patient prognosis. Moreover, the overexpression of LEF1 was observed in esophageal CSCs purified by the magnetic sorting of adherent and spheroidal ESCC cells. The increased level of LEF1 in CSCs facilitated the expression of CSC markers, stem cell-like properties, resistance to chemotherapy, and tumorigenicity and increased the percentage of CSCs in ESCC samples. Conversely, the knockdown of LEF1 significantly diminished the self-renewal properties of ESCC. We showed that LEF1 played an important mechanical role in activating the TGF-β signaling pathway by directly binding to the ID1 gene promoter. A positive association between LEF1 and ID1 expression was also observed in clinical ESCC samples.

Conclusion

Our results indicate that the overexpression of LEF1 promotes a CSC-like phenotype in and the tumorigenicity of ESCC by activating the TGF-β signaling pathway. The inhibition of LEF1 might therefore be a novel therapeutic target to inactivate CSCs and inhibit tumor progression.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1296-7) contains supplementary material, which is available to authorized users.

PDGFR-induced autocrine SDF-1 signaling in cancer cells promotes metastasis in advanced skin carcinoma

Advanced and undifferentiated skin squamous cell carcinomas (SCCs) exhibit aggressive growth and enhanced metastasis capability, which is associated in mice with an expansion of the cancer stem-like cell (CSC) population and with changes in the regulatory mechanisms that control the proliferation and invasion of these cells. Indeed, autocrine activation of PDGFRα induces CSC invasion and promotes distant metastasis in advanced SCCs. However, the mechanisms involved in this process were unclear. Here, we show that CSCs of mouse advanced SCCs (L-CSCs) express CXCR4 and CXCR7, both receptors of SDF-1. PDGFRα signaling induces SDF-1 expression and secretion, and the autocrine activation of this pathway in L-CSCs. Autocrine SDF-1/CXCR4 signaling induces L-CSC proliferation and survival, and mediates PDGFRα-induced invasion, promoting in vivo lung metastasis. Validation of these findings in patient samples of skin SCCs shows a strong correlation between the expression of SDF1, PDGFRA, and PDGFRB, which is upregulated, along CXCR4 in tumor cells of advanced SCCs. Furthermore, PDGFR regulates SDF-1 expression and inhibition of SDF-1/CXCR4 and PDGFR pathways blocks distant metastasis of human PD/S-SCCs. Our results indicate that functional crosstalk between PDGFR/SDF-1 signaling regulates tumor cell invasion and metastasis in human and mouse advanced SCCs, and suggest that CXCR4 and/or PDGFR inhibitors could be used to block metastasis of these aggressive tumors.

Cancer stem cells and fibroblast niche cross talk in an in-vitro oral dysplasia model

Understanding the cellular interactions during oral carcinogenesis has the potential to identify novel prognostic and therapeutic targets. This study aimed at investigating the cancer stem cell (CSC)-fibroblast niche interactions using in-vitro dysplastic cell line models developed from different stages of 4NQO-induced oral carcinogenic mice model. The spontaneously transformed epithelial cells (DysMSCTR6, 14 and 16) were developed from three time points (mild/moderate/severe), while two fibroblast cell lines (FibroMSCTR12, 16) were developed from moderate and severe dysplastic tissue. The epithelial (Epcam+/Ck+) and the fibroblast cell lines (Vimentin+/α-SMA+/Ck-) were authenticated and assessment of cells representing progressive grades of dysplastic severity indicated a significant increase in dysplastic marker profile (P < 0.05). Evaluation of the CSC characteristics showed that an increase in expression of Cd133, Cd44, Aldh1a1, Notch1, and Sox2 was accompanied by an increase in migratory (P > 0.05) and colony formation capacity (P > 0.005). Targeting Notch1 (GSI inhibitor PZ0187; 30 μM), showed a significant reduction in cell proliferation capacity (P < 0.05) and in the dysplastic marker profile. Further, Notch1 inhibition resulted in down regulation of Cd133 and Aldh1a 1 (P < 0.05) and a complete abrogation of colony formation ability (P < 0.0001). The effect of niche interactions evaluated using FibroMSCTR12-conditioned media studies, revealed an enrichment of ALDH1A1+ cells (P < 0.05), induction of spheroid formation ability (P < 0.0001) and increased proliferation capacity (3.7 fold; P < 0.005). Although PZ0187 reduced cell viability by ∼40%, was unable to abrogate the conditioned-media induced increase in proliferation capacity completely. This study reports a Notch-1 dependent enrichment of CSC properties during dysplastic progression and a Notch-1 independent dysplastic cell-fibroblast interaction during oral carcinogenesis.

Effects of multi and selective targeted tyrosine kinase inhibitors on function and signaling of different bladder cancer cells

BACKGROUND

Signaling of receptor tyrosine kinases (RTK) is dysregulated in various malignancies including bladder cancer. RTKs trigger pro-proliferative, anti-apoptotic and metastatic signaling pathways. Here, we assessed the effects of a selective tyrosine kinase inhibitor (TKI) (BGJ398) targeting fibroblast growth factor receptor (FGFR) and a pan-TKI (TKI258) targeting (FGFR), platelet derived growth factor receptor (PDGFR) and vascular endothelial growth factor receptor (VEGFR) in bladder cancer cells.

METHODS

Levels of mRNA transcripts were measured in nine human cell lines by quantitative RT-PCR. Cell function was assessed for viability, colony formation, migration, apoptosis and proliferation. Protein mediators of signal transduction were measured by Western-blot.

RESULTS

mRNA transcripts encoding RTK-related components, transcription factors, epithelial and mesenchymal transition (EMT) markers as well as cell cycle and apoptotic factors were determined in the cell lines. Principal component analysis ordered one epithelial-like cell cluster (5637, BFTC-905, MGHU4, RT112) and one mesenchymal-like cell cluster (T24, UMUC3, HU456, TCC-SUP). Cell response scores towards TKI258 and BGJ398 treatment were heterogeneous between cell lines and correlated with certain transcript levels. Analysis of signal transduction pathways revealed inhibition of fibroblast growth factor receptor (FGFR) signaling and induction of cell cycle dependent kinase (CDKN1A, p21) in epithelial-like cells differing in this regard from responses to mesenchymal-like cells that exhibited inhibition of mitogen-activated protein kinase (MAPK).

CONCLUSION

RTK and EMT related transcript analysis separate bladder cancer cells in two clusters. Functional responses towards TKI258 and BGJ398 treatment of bladder Fcancer cells were heterogeneous with deviating effects on signaling and possibly different therapeutic outcome.

Cancer cell plasticity: Impact on tumor progression and therapy response

Most tumors exhibit intra-tumor heterogeneity, which is associated with disease progression and an impaired response to therapy. Cancer cell plasticity has been proposed as being an important mechanism that, along with genetic and epigenetic alterations, promotes cancer cell diversity and contributes to intra-tumor heterogeneity. Plasticity endows cancer cells with the capacity to shift dynamically between a differentiated state, with limited tumorigenic potential, and an undifferentiated or cancer stem-like cell (CSC) state, which is responsible for long-term tumor growth. In addition, it confers the ability to transit into distinct CSC states with different competence to invade, disseminate and seed metastasis. Cancer cell plasticity has been linked to the epithelial-to-mesenchymal transition program and relies not only on cell-autonomous mechanisms, but also on signals provided by the tumor microenvironment and/or induced in response to therapy. We provide an overview of the dynamic transition for cancer cell states, the mechanisms governing cell plasticity and their impact on tumor progression, metastasis and therapy response. Understanding the mechanisms involved in cancer cell plasticity will provide insights for establishing new therapeutic interventions.

Stage-dependent therapeutic efficacy in PI3K/mTOR-driven squamous cell carcinoma of the skin

Cutaneous squamous cell carcinoma (SCC) is a recurrent cancer that is prevalent in predisposed subjects such as immunosuppressed patients and patients being treated for other malignancies. Model systems to trial therapies at different stages of SCC development are lacking, therefore precluding efficient therapeutic interventions. Here, we have disrupted the expression of the tumor suppressor GRHL3 to induce loss of PTEN and activation of the PI3K/mTOR signaling pathway in mice and human skin, promoting aggressive SCC development. We then examined the potential for targeting PI3K/mTOR and an oncogenic driver miR-21, alone and in combination, for the prevention and treatment of SCC during the initiation, promotion/progression and establishment stages. Treatment with PI3K/mTOR inhibitors completely prevented tumor initiation, and these inhibitors significantly delayed the course of papilloma progression to malignancy. However, established SCC did not undergo any growth regression, indicating that this therapy is ineffective in established cancers. Mechanistically, the resistant SCCs displayed increased miR-21 expression in mice and humans where antagonists of miR-21 rescued expression levels of GRHL3/PTEN, but the combination of miR-21 antagonism with PI3K/mTOR inhibition resulted in acquired SCC resistance in part via c-MYC and OCT-4 upregulation. In conclusion, our data provide molecular evidence for the efficacy of targeting oncogenic drivers of SCC during the initiation and promotion stages and indicate that combination therapy may induce an aggressive phenotype when applied in the establishment stage.

Characterization and functional analysis of a slow-cycling subpopulation in colorectal cancer enriched by cell cycle inducer combined chemotherapy

The concept of cancer stem cells has been proposed in various malignancies including colorectal cancer. Recent studies show direct evidence for quiescence slow-cycling cells playing a role in cancer stem cells. There exists an urgent need to isolate and better characterize these slow-cycling cells. In this study, we developed a new model to enrich slow-cycling tumor cells using cell-cycle inducer combined with cell cycle-dependent chemotherapy in vitro and in vivo. Our results show that Short-term exposure of colorectal cancer cells to chemotherapy combined with cell-cycle inducer enriches for a cell-cycle quiescent tumor cell population. Specifically, these slow-cycling tumor cells exhibit increased chemotherapy resistance in vitro and tumorigenicity in vivo. Notably, these cells are stem-cell like and participate in metastatic dormancy. Further exploration indicates that slow-cycling colorectal cancer cells in our model are less sensitive to cytokine-induced-killer cell mediated cytotoxic killing in vivo and in vitro. Collectively, our cell cycle inducer combined chemotherapy exposure model enriches for a slow-cycling, dormant, chemo-resistant tumor cell sub-population that are resistant to cytokine induced killer cell based immunotherapy. Studying unique signaling pathways in dormant tumor cells enriched by cell cycle inducer combined chemotherapy treatment is expected to identify novel therapeutic targets for preventing tumor recurrence.

Is Ep-CAM Expression a Diagnostic and Prognostic Biomarker for Colorectal Cancer? A Systematic Meta-Analysis

Background

Cancer stem cell (CSC) epithelial cell adhesion molecule (Ep-CAM) is frequently expressed in colorectal cancer (CRC). However, the clinical significance of Ep-CAM expression in CRC is not clear. This study evaluated whether Ep-CAM provided valuable insight as a molecular biomarker for CRC diagnosis and prognosis and the potential of Ep-CAM as a novel therapeutic target in CRC.

Methods

Publications were selected online using electronic databases. The pooled odds ratios (ORs) or hazard ratios (HRs) with their 95% confidence intervals (95% CIs), and the combined sensitivity, specificity, and area under the curve (AUC) were calculated and summarized.

Results

Eleven eligible articles published in English involving 4561 cases were analyzed in this study. Ep-CAM expression was significantly higher in CRC compared with normal controls, and its overexpression was negatively linked to tumor differentiation, tumor stage, vascular invasion, depth of tumor invasion, lymph node metastasis, distant metastasis, and tumor budding in CRC patients. The loss of Ep-CAM expression positively correlated with these characteristics. Multivariate analysis of loss of Ep-CAM expression correlated with a poor prognosis in disease-free survival (DFS), disease-specific survival (DSS), and overall survival (OS). The pooled sensitivity, specificity and AUC values of Ep-CAM expression in patients with CRC vs. normal controls were 0.93, 0.90, and 0.94, respectively.

Conclusions

The present findings suggest that Ep-CAM expression may be associated with CRC carcinogenesis, while the loss of Ep-CAM expression is correlated with the progression, metastasis, and poor prognosis of CRC. Ep-CAM expression may be a useful biomarker for the clinical diagnosis of CRC.

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Cancer stem cell (CSC) epithelial cell adhesion molecule (Ep-CAM) expression may correlate with CRC tumorigenesis.

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Frequent overexpression of Ep-CAM was a favorable factor for CRC progression and metastasis.

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Loss of Ep-CAM expression correlated with the progression, metastasis, and poor prognosis of patients with CRC.

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Ep-CAM expression may be a potential marker for the detection of CRC.

Ep-CAM expression was reported in CRC, but no clear direction for the diagnostic and prognostic effects of Ep-CAM expression was documented in patients with CRC. We performed a systematic meta-analysis of the existing evidence to determine the clinical significance of Ep-CAM expression in CRC. The findings indicated that Ep-CAM expression was associated with CRC risk. Frequent overexpression of Ep-CAM correlated with a decreased risk of CRC progression and metastasis, and loss of Ep-CAM expression played an important role in CRC progression, metastasis and prognosis. The detection of Ep-CAM expression may be a promising biomarker in diagnosing CRC.

Clinicopathological, prognostic and predictive value of CD166 expression in colorectal cancer: a meta-analysis

CD166 has been identified as an important cancer stem cell (CSC) marker in colorectal cancer (CRC). The purpose of our study was to investigate the relationship between CD166 expression and clinical features and to examine the role of CD166 expression on the survival of patients with CRC. A total of 15 studies with 3,332 cases were identified in this meta-analysis. The pooled OR indicated that CD166 expression was significantly higher in CRC than in colonic adenomas or normal colonic mucosa (OR = 3.48, P = 0.002 and OR = 55.13, P = 0.017, respectively). CD166 expression was found to be negatively correlated with vascular invasion (OR = 0.75, P = 0.017), but it was not associated with gender, tumor location, lymph node status, distant metastasis, clinical stage, T classification or tumor differentiation. Meanwhile, CD166 expression was not associated with the prognosis of overall survival (OS) (HR = 1.20, 95% CI = 0.45-3.22, P = 0.72) in multivariate regression analysis. One study reported that CD166 expression may be a predictor of survival in stage II CRC patients using multivariate logistic regression analysis (OS: OR = 9.97, P = 0.035; disease-specific survival: OR = 29.02, P = 0.011). Our findings suggest that CD166 expression may be correlated with CRC carcinogenesis and a decreased risk of vascular invasion, and it may become a predictive biomarker of survival for stage II CRC patients, but additional studies with large sample sizes are essential to validate the prognostic and predictive values of CD166 expression.

Loss of Dnmt3a and Dnmt3b does not affect epidermal homeostasis but promotes squamous transformation through PPAR-γ

The DNA methyltransferase Dnmt3a suppresses tumorigenesis in models of leukemia and lung cancer. Conversely, deregulation of Dnmt3b is thought to generally promote tumorigenesis. However, the role of Dnmt3a and Dnmt3b in many types of cancer remains undefined. Here, we show that Dnmt3a and Dnmt3b are dispensable for homeostasis of the murine epidermis. However, loss of Dnmt3a-but not Dnmt3b-increases the number of carcinogen-induced squamous tumors, without affecting tumor progression. Only upon combined deletion of Dnmt3a and Dnmt3b, squamous carcinomas become more aggressive and metastatic. Mechanistically, Dnmt3a promotes the expression of epidermal differentiation genes by interacting with their enhancers and inhibits the expression of lipid metabolism genes, including PPAR-γ, by directly methylating their promoters. Importantly, inhibition of PPAR-γ partially prevents the increase in tumorigenesis upon deletion of Dnmt3a. Altogether, we demonstrate that Dnmt3a and Dnmt3b protect the epidermis from tumorigenesis and that squamous carcinomas are sensitive to inhibition of PPAR-γ.

The role of autophagy in the cross-talk between epithelial-mesenchymal transitioned tumor cells and cancer stem-like cells

Epithelial-mesenchymal transition (EMT) and cancer stem-like cells (CSC) are becoming highly relevant targets in anticancer drug discovery. A large body of evidence suggests that epithelial-mesenchymal transitioned tumor cells (EMT tumor cells) and CSCs have similar functions. There is also an overlap regarding the stimuli that can induce the generation of EMT tumor cells and CSCs. Moreover, direct evidence has been brought that EMT can give rise to CSCs. It is unclear however, whether EMT tumor cells should be considered CSCs or if they have to undergo further changes. In this article we summarize available evidence suggesting that, indeed, additional programs must be engaged and we propose that macroautophagy (hereafter, autophagy) represents a key trait distinguishing CSCs from EMT tumor cells. Thus, CSCs have often been reported to be in an autophagic state and blockade of autophagy inhibits CSCs. On the other hand, there is ample evidence showing that EMT and autophagy are distinct events. CSCs, however, represent, by themselves, a heterogeneous population. Thus, CSCs have been distinguished in predominantly non-cycling and cycling CSCs, the latter representing CSCs that self-renew and replenish the pool of differentiated tumor cells. We now suggest that the non-cycling CSC subpopulation is in an autophagic state. We propose also two models to explain the relationship between EMT tumor cells and these two major CSC subpopulations: a branching model in which EMT tumor cells can give rise to cycling or non-cycling CSCs, respectively, and a hierarchical model in which EMT tumor cells are first induced to become autophagic CSCs and, subsequently, cycling CSCs. Finally, we address the therapeutic consequences of these insights.

Cancer Stem Cells in Squamous Cell Carcinoma

Cancer stem cells (CSCs) are found in many cancer types, including squamous cell carcinoma (SCC). CSCs initiate cancer formation and are linked to metastasis and resistance to therapies. Studies have revealed that several distinct CSC populations coexist in SCC and that tumor initiation and metastatic potential of these populations can be uncoupled. Therefore, it is critical to understand CSC biology to develop novel CSC-targeted therapies for patients with SCC with poor prognoses. This review compares the properties of CSCs in SCC with normal stem cells in the skin, summarizes current advances and characteristics of CSCs, and considers the challenges for CSC-targeted treatment of SCC.