Are There Specific Cancer Stem Cell Markers?

The cancer stem cell (CSC) model states that heterogeneous tumor cell populations are organized in a hierarchical manner, with a small population of CSCs at the apex. These CSCs are capable of self-renewal and giving rise to other cancer cell populations, conceptually analogous to the function of normal adult stem cells present in almost all organs. However, there has been significant controversy regarding the existence and identification of CSCs. We argue that technical differences in experimentation and CSC assays, CSC niche-dependency and plasticity, and CSC heterogeneity itself may explain some of the differences observed.

GREM1 is required to maintain cellular heterogeneity in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) shows pronounced epithelial and mesenchymal cancer cell populations1-4. Cellular heterogeneity in PDAC is an important feature in disease subtype specification3-5, but how distinct PDAC subpopulations interact, and the molecular mechanisms that underlie PDAC cell fate decisions, are incompletely understood. Here we identify the BMP inhibitor GREM16,7 as a key regulator of cellular heterogeneity in pancreatic cancer in human and mouse. Grem1 inactivation in established PDAC in mice resulted in a direct conversion of epithelial into mesenchymal PDAC cells within days, suggesting that persistent GREM1 activity is required to maintain the epithelial PDAC subpopulations. By contrast, Grem1 overexpression caused an almost complete 'epithelialization' of highly mesenchymal PDAC, indicating that high GREM1 activity is sufficient to revert the mesenchymal fate of PDAC cells. Mechanistically, Grem1 was highly expressed in mesenchymal PDAC cells and inhibited the expression of the epithelial-mesenchymal transition transcription factors Snai1 (also known as Snail) and Snai2 (also known as Slug) in the epithelial cell compartment, therefore restricting epithelial-mesenchymal plasticity. Thus, constant suppression of BMP activity is essential to maintain epithelial PDAC cells, indicating that the maintenance of the cellular heterogeneity of pancreatic cancer requires continuous paracrine signalling elicited by a single soluble factor.

METTL3 promotes oxaliplatin resistance of gastric cancer CD133+ stem cells by promoting PARP1 mRNA stability.

Oxaliplatin is the first-line regime for advanced gastric cancer treatment, while its resistance is a major problem that leads to the failure of clinical treatments. Tumor cell heterogeneity has been considered as one of the main causes for drug resistance in cancer. In this study, the mechanism of oxaliplatin resistance was investigated through in vitro human gastric cancer organoids and gastric cancer oxaliplatin-resistant cell lines and in vivo subcutaneous tumorigenicity experiments. The in vitro and in vivo results indicated that CD133+ stem cell-like cells are the main subpopulation and PARP1 is the central gene mediating oxaliplatin resistance in gastric cancer. It was found that PARP1 can effectively repair DNA damage caused by oxaliplatin by means of mediating the opening of base excision repair pathway, leading to the occurrence of drug resistance. The CD133+ stem cells also exhibited upregulated expression of N6-methyladenosine (m6A) mRNA and its writer METTL3 as showed by immunoprecipitation followed by sequencing and transcriptome analysis. METTTL3 enhances the stability of PARP1 by recruiting YTHDF1 to target the 3'-untranslated Region (3'-UTR) of PARP1 mRNA. The CD133+ tumor stem cells can regulate the stability and expression of m6A to PARP1 through METTL3, and thus exerting the PARP1-mediated DNA damage repair ability. Therefore, our study demonstrated that m6A Methyltransferase METTL3 facilitates oxaliplatin resistance in CD133+ gastric cancer stem cells by Promoting PARP1 mRNA stability which increases base excision repair pathway activity.

USP28 deletion and small-molecule inhibition destabilizes c-MYC and elicits regression of squamous cell lung carcinoma.

Lung squamous cell carcinoma (LSCC) is a considerable global health burden, with an incidence of over 600,000 cases per year. Treatment options are limited, and patient's 5-year survival rate is less than 5%. The ubiquitin-specific protease 28 (USP28) has been implicated in tumourigenesis through its stabilization of the oncoproteins c-MYC, c-JUN, and Δp63. Here, we show that genetic inactivation of Usp28-induced regression of established murine LSCC lung tumours. We developed a small molecule that inhibits USP28 activity in the low nanomole range. While displaying cross-reactivity against the closest homologue USP25, this inhibitor showed a high degree of selectivity over other deubiquitinases. USP28 inhibitor treatment resulted in a dramatic decrease in c-MYC, c-JUN, and Δp63 proteins levels and consequently induced substantial regression of autochthonous murine LSCC tumours and human LSCC xenografts, thereby phenocopying the effect observed by genetic deletion. Thus, USP28 may represent a promising therapeutic target for the treatment of squamous cell lung carcinoma.

PARP1 Inhibitor Combined With Oxaliplatin Efficiently Suppresses Oxaliplatin Resistance in Gastric Cancer-Derived Organoids via Homologous Recombination and the Base Excision Repair Pathway.

Oxaliplatin (OXA) resistance in the treatment of different types of cancer is an important and complex problem. The culture of tumor organoids derived from gastric cancer can help us to provide a deeper understanding of the underlying mechanisms that lead to OXA resistance. In this study, our purpose was to understand the mechanisms that lead to OXA resistance, and to provide survival benefits to patients with OXA through targeted combination therapies. Using sequence analysis of OXA-resistant and non-OXA-resistant organoids, we found that PARP1 is an important gene that mediates OXA resistance. Through the patients' follow-up data, it was observed that the expression level of PARP1 was significantly correlated with OXA resistance. This was confirmed by genetic manipulation of PARP1 expression in OXA-resistant organoids used in subcutaneous tumor formation. Results further showed that PARP1 mediated OXA resistance by inhibiting the base excision repair pathway. OXA also inhibited homologous recombination by CDK1 activity and importantly made cancers with normal BRCA1 function sensitive to PARP inhibition. As a result, combination of OXA and Olaparib (PARP-1/2/3 inhibitor), inhibited in vivo and in vitro OXA resistant organoid growth and viability.

JunD, not c-Jun, is the AP-1 transcription factor required for Ras-induced lung cancer.

The AP-1 transcription factor c-Jun is required for Ras-driven tumorigenesis in many tissues and is considered as a classical proto-oncogene. To determine the requirement for c-Jun in a mouse model of K-RasG12D-induced lung adenocarcinoma, we inducibly deleted c-Jun in the adult lung. Surprisingly, we found that inactivation of c-Jun, or mutation of its JNK phosphorylation sites, actually increased lung tumor burden. Mechanistically, we found that protein levels of the Jun family member JunD were increased in the absence of c-Jun. In c-Jun-deficient cells, JunD phosphorylation was increased, and expression of a dominant-active JNKK2-JNK1 transgene further increased lung tumor formation. Strikingly, deletion of JunD completely abolished Ras-driven lung tumorigenesis. This work identifies JunD, not c-Jun, as the crucial substrate of JNK signaling and oncogene required for Ras-induced lung cancer.

High expression of vinculin predicts poor prognosis and distant metastasis and associates with influencing tumor-associated NK cell infiltration and epithelial-mesenchymal transition in gastric cancer.

In the process of epithelial-mesenchymal transition (EMT), epithelial cancer cells transdifferentiate into mesenchymal-like cells with high motility and aggressiveness, resulting in the spread of tumor cells. Immune cells and inflammation in the tumor microenvironment are the driving factors of EMT, but few studies have explored the core targets of the interaction between EMT and tumor immune cells. We analyzed thousands of cases of gastric cancer and gastric tissue specimens of TCGA, CPTAC, GTEx and analyzing QPCR and IHC data of 56 gastric cancer patients in SYSU Gastric Cancer Research Center. It was known that EMT has an important connection with the infiltration of NK cells, and that the expression of vinculin may be the target of the phenomenon. The increased expression of vinculin is closely related to the aggressiveness and distant metastasis of cancer, which affects the survival prognosis of the patient. Moreover, through in vitro experiments under 3D conditions, we found that vinculin, cell invasion and metastasis are clearly linked. VCL can affect EMT and tumor immunity by regulating EPCAM gene expression. The role and mechanism of action of vinculin have been controversial, but this molecule may downregulate EpCAM (epithelial cellular adhesion molecule) and its own role in gastric cancer through DNA methylation, causing NK cells to enrich into tumor cells and kill tumor cells. At the same time, it promotes the occurrence of EMT, which in turn causes tumor metastasis and thus poorer prognosis.

YAP and ß-Catenin Cooperate to Drive Oncogenesis in Basal Breast Cancer.

Targeting cancer stem cells (CSC) can serve as an effective approach toward limiting resistance to therapies. While basal-like (triple-negative) breast cancers encompass cells with CSC features, rational therapies remain poorly established. We show here that the receptor tyrosine kinase Met promotes YAP activity in basal-like breast cancer and find enhanced YAP activity within the CSC population. Interfering with YAP activity delayed basal-like cancer formation, prevented luminal to basal transdifferentiation, and reduced CSC. YAP knockout mammary glands revealed a decrease in ß-catenin target genes, suggesting that YAP is required for nuclear ß-catenin activity. Mechanistically, nuclear YAP interacted with ß-catenin and TEAD4 at gene regulatory elements. Proteomic patient data revealed an upregulation of the YAP signature in basal-like breast cancers. Our findings demonstrate that in basal-like breast cancers, ß-catenin activity is dependent on YAP signaling and controls the CSC program. These findings suggest that targeting the YAP/TEAD4/ß-catenin complex offers a potential therapeutic strategy for eradicating CSCs in basal-like breast cancers. SIGNIFICANCE: These findings show that YAP cooperates with ß-catenin in basal-like breast cancer to regulate CSCs and that targeting this interaction may be a novel CSC therapy for patients with basal-like breast cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/8/2116/F1.large.jpg.

High expression of WTAP leads to poor prognosis of gastric cancer by influencing tumour-associated T lymphocyte infiltration.

BACKGROUND: N6-methyladenosine (m6A) methylation, a well-known modification with new epigenetic functions, has been reported to participate in gastric cancer (GC) tumourigenesis, providing novel insights into the molecular pathogenesis of GC. However, the involvement of Wilms' tumour 1-associated protein (WTAP), a key component of m6A methylation, in GC progression is controversial. Here, we investigated the biological role and underlying mechanism of WTAP in GC. METHODS: We determined WTAP expression using tissue microarrays and The Cancer Genome Atlas (TCGA) data set, which was used to construct co-expression networks by weighted gene co-expression network analysis (WGCNA). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed by Database for Annotation, Visualization and Integrated Discovery (DAVID). CIBERSORT was used to determine WTAP expression in 22 immune cell types. RESULTS: Wilms' tumour 1-associated protein was highly expressed in GC, which indicated a poor prognosis, and WTAP expression served as an independent predictor of GC survival. By WGCNA, GO, KEGG and core gene survival analyses, we found that high WTAP expression correlated with RNA methylation and that low expression correlated with a high T cell-related immune response. CIBERSORT was used to correlate low WTAP expression with T lymphocyte infiltration. CONCLUSION: RNA methylation and lymphocyte infiltration are the main causes of high WTAP expression and poor prognosis, respectively.

Cancer Stem Cells Regulate Cancer-Associated Fibroblasts via Activation of Hedgehog Signaling in Mammary Gland Tumors.

Many tumors display intracellular heterogeneity with subsets of cancer stem cells (CSC) that sustain tumor growth, recurrence, and therapy resistance. Cancer-associated fibroblasts (CAF) have been shown to support and regulate CSC function. Here, we investigate the interactions between CSCs and CAFs in mammary gland tumors driven by combined activation of Wnt/ß-catenin and Hgf/Met signaling in mouse mammary epithelial cells. In this setting, CSCs secrete the Hedgehog ligand SHH, which regulate CAFs via paracrine activation of Hedgehog signaling. CAFs subsequently secrete factors that promote expansion and self-renewal of CSCs. In vivo treatment of tumors with the Hedgehog inhibitor vismodegib reduce CAF and CSC expansion, resulting in an overall delay of tumor formation. Our results identify a novel intracellular signaling module that synergistically regulates CAFs and CSCs. Targeting CAFs with Hedgehog inhibitors may offer a novel therapeutic strategy against breast cancer. Cancer Res; 77(8); 2134-47. ©2017 AACR.

Gab1 and Mapk Signaling Are Essential in the Hair Cycle and Hair Follicle Stem Cell Quiescence.

Gab1 is a scaffold protein that acts downstream of receptor tyrosine kinases. Here, we produced conditional Gab1 mutant mice (by K14- and Krox20-cre) and show that Gab1 mediates crucial signals in the control of both the hair cycle and the self-renewal of hair follicle stem cells. Remarkably, mutant hair follicles do not enter catagen, the destructive phase of the hair cycle. Instead, hair follicle stem cells lose quiescence and become exhausted, and thus no stem cell niches are established in the bulges. Moreover, conditional sustained activation of Mapk signaling by expression of a gain-of-function Mek1(DD) allele (by Krox20-cre) rescues hair cycle deficits and restores quiescence of the stem cells. Our data thus demonstrate an essential role of Gab1 downstream of receptor tyrosine kinases and upstream of Shp2 and Mapk in the regulation of the hair cycle and the self-renewal of hair follicle stem cells.

Shp2 signaling suppresses senescence in PyMT-induced mammary gland cancer in mice.

In this study, we have used techniques from cell biology, biochemistry, and genetics to investigate the role of the tyrosine phosphatase Shp2 in tumor cells of MMTV-PyMT mouse mammary glands. Genetic ablation or pharmacological inhibition of Shp2 induces senescence, as determined by the activation of senescence-associated ß-gal (SA-ß-gal), cyclin-dependent kinase inhibitor 1B (p27), p53, and histone 3 trimethylated lysine 9 (H3K9me3). Senescence induction leads to the inhibition of self-renewal of tumor cells and blockage of tumor formation and growth. A signaling cascade was identified that acts downstream of Shp2 to counter senescence: Src, focal adhesion kinase, and Map kinase inhibit senescence by activating the expression of S-phase kinase-associated protein 2 (Skp2), Aurora kinase A (Aurka), and the Notch ligand Delta-like 1 (Dll1), which block p27 and p53. Remarkably, the expression of Shp2 and of selected target genes predicts human breast cancer outcome. We conclude that therapies, which rely on senescence induction by inhibiting Shp2 or controlling its target gene products, may be useful in blocking breast cancer.

Upregulation of myosin Va by Snail is involved in cancer cell migration and metastasis.

Cell migration, which involves acto-myosin dynamics, cell adhesion, membrane trafficking and signal transduction, is a prerequisite for cancer cell metastasis. Here, we report that an actin-dependent molecular motor, unconventional myosin Va, is involved in this process and implicated in cancer metastasis. The mRNA expression of myosin Va is increased in a number of highly metastatic cancer cell lines and metastatic colorectal cancer tissues. Suppressing the expression of myosin Va by lentivirus-based RNA interference in highly metastatic cancer cells impeded their migration and metastasis capabilities both in vitro and in vivo. In addition, the levels of myosin Va in cancer cell lines are positively correlated with the expression of Snail, a transcriptional repressor that triggers epithelial-mesenchymal transition. Repression or overexpression of Snail in cancer cells caused reduced or elevated levels of myosin Va, respectively. Furthermore, Snail can bind to an E-box of the myosin Va promoter and induce its activity, which indicates that Snail might act as a transcriptional activator. These data demonstrate an essential role of myosin Va in cancer cell migration and metastasis, and suggest a novel target for Snail in its regulation of cancer progression.

A novel thioredoxin reductase inhibitor inhibits cell growth and induces apoptosis in HL-60 and K562 cells.

Human thioredoxin reductase (TrxR) system is associated with cancer cell growth and anti-apoptosis process. Effects of 1,2-[bis(1,2-benzisoselenazolone-3(2H)-ketone)]ethane (BBSKE), a novel TrxR inhibitor, were investigated on human leukemia cell lines HL-60 and K562. BBSKE treatment induced cell growth inhibition and apoptosis in both cell lines. Apoptosis induced by BBSKE is through Bcl-2/Bax and caspase-3 pathways. Ehrlich's ascites carcinoma-bearing mice were used to investigate the anti-tumor effect of BBSKE in vivo. Tumor-bearing mice treated with BBSKE showed an increase of life span with a comparable effect to cyclophosphamide (CTX). These results suggest a potential usage of BBSKE as a therapeutic agent against non-solid tumors.

The mechanism of apoptosis induced by a novel thioredoxin reductase inhibitor in A549 cells: possible involvement of nuclear factor-kappaB-dependent pathway.

1,2-[bis(1,2-benzisoselenazolone-3(2H)-ketone)]ethane (BBSKE, PCT: CN02/00412), a novel thioredoxin reductase inhibitor previously synthesized in our lab, has been demonstrated to inhibit the growth of a variety of human cancer cells and to induce apoptosis. Here we report on the potential molecular mechanism of apoptosis induced by BBSKE in A549 cells. The treatment of BBSKE reduced the protein levels of Bcl-2, Bcl-xL, procaspase-9 and procaspase-3, and caused the release of cytochrome C from the mitochondria to the cytosol in a dose-dependent manner, suggesting the onset of mitochondria-dependent apoptosis. Through electrophoretic mobility shift assay (EMSA), the DNA-binding activity of nuclear factor-kappaB (NF-kappaB) was found to be attenuated after BBSKE treatment, accompanied by the diminution of the immunoprecipitated complex of thioredoxin and NF-kappaB in co-immunoprecipitation experiments. Meanwhile, the ratio of pIkappaB-alpha to IkappaB-alpha and the subcellular localization of p65 between cytoplasm and nucleus were not significantly altered by BBSKE treatment, as demonstrated in western analysis and immunocytochemistry assay. Furthermore, the mRNA levels of the NF-kappaB regulated anti-apoptosis genes Bcl-2, Bcl-xL, cIAP-2 and XIAP were decreased in a dose-dependent manner after BBSKE treatment. All the above observations suggest that BBSKE induce mitochondria-dependent apoptosis in A549 cells probably through suppressing the thioredoxin reductase-thioredoxin-NF-kappaB pathway.

A thioredoxin reductase inhibitor induces growth inhibition and apoptosis in five cultured human carcinoma cell lines.

Human thioredoxin reductase (TrxR) system is associated with cancer cell growth and anti-apoptosis process. Effects of 1, 2-[bis (1,2-Benzisoselenazolone-3 (2H) -ketone)]ethane (BBSKE), a novel TrxR inhibitor, were investigated on A549, HeLa, Bel-7402, BGC823 and KB cell lines. After treated with BBSKE, a good linear correlation coefficient (r>or=0.989) between TrxR activity and cell viability exists in each cell line together with cell growth/proliferation inhibition and apoptosis through Bcl-2/Bax and Caspase-3 pathways. These results suggest that there exists some relationship between TrxR inactivation and growth/proliferation inhibition or apoptosis in the investigated cell lines.