Cleaved CD44 intracellular domain supports activation of stemness factors and promotes tumorigenesis of breast cancer

Furin, ADAM, and γ-secretase: Core regulatory targets in the Notch pathway and the therapeutic potential for breast cancer

The activation of the Notch pathway promotes the occurrence and progression of breast cancer. The Notch signal plays different roles in different molecular subtypes of breast cancer. In estrogen receptor-positive (ER+) breast cancer, the Notch pathway regulates the activity of estrogen receptors. In human epidermal growth factor receptor 2-positive (HER2+) breast cancer, crosstalk between Notch and HER2 enhances HER2 signal expression. In triple-negative breast cancer (TNBC), Notch pathway activation is closely linked to tumor invasion and drug resistance. This article offers a comprehensive review of the structural domains, biological functions, and key targets of Notch with a specific focus on the roles of Furin protease, ADAM metalloprotease, and γ-secretase in breast cancer and their potential as therapeutic targets. We discuss the functions and mutual regulatory mechanisms of these proteinases in the Notch pathway as well as other potential targets in the Notch pathway, such as the glycosylation process and key transcription factors. This article also introduces new approaches in the treatment of breast cancer, with a special focus on the molecular characteristics and treatment response differences of different subtypes. We propose that the core regulatory molecules of the Notch pathway may become key targets for development of personalized treatment, which may significantly improve treatment outcomes and prognosis for patients with breast cancer.

Promising therapeutic targets for tumor treatment: Cleaved activation of receptors in the nucleus

A new fate of cell surface receptors, cleaved activation in the nucleus, is summarized. The intracellular domain (ICD) of cell surface receptors, cleaved by enzymes like γ-secretase, translocates to the nucleus to form transcriptional complexes participating in the onset and development of tumors. The fate is clinically significant, as inhibitors of cleavage enzymes have shown effectiveness in treating advanced tumors by reducing tumorigenic ICDs. Additionally, the construction of synthetic receptors also conforms with the fate mechanism. This review details each step of cleaved activation in the nucleus, elucidates tumorigenic mechanisms, explores application in antitumor therapy, and scrutinizes possible limitations.

Are androgen receptor agonists a treatment option in bladder cancer?

Sex-related differences in bladder cancer incidence and progression infer a role for sex hormones and their cognate receptors in this disease. In part due to the oncogenic role of androgen receptor signaling in prostate cancer, the focus of most preclinical and clinical research to-date has been on the potential pro-tumorigenic action of androgens in urothelial cancers. However, clinical studies of androgen receptor antagonism have yielded minimal success. In this review, we explore the tumor suppressor role of androgen receptor in bladder cancer and discuss how it might be harnessed therapeutically.

From mitochondria to tumor suppression: ACAT1's crucial role in gastric cancer

Acetyl CoA acetyltransferase 1 (ACAT1), a mitochondrial enzyme, is mainly involved in the formation and decomposition of ketones, isoleucine, and fatty acids. Previous clinical studies showed that mutations in the ACAT1 gene lead to ketoacidosis, Notably the role of ACAT1 in human cancer' pathogenesis varies depending on cancer type, and its specific role in gastric cancer remains largely unknown. In the current study, we found that the expression of ACAT1 in primary late-stage gastric cancer tumor tissues was significantly lower than in early-stage tumors. This observation was further confirmed in high-grade gastric cancer cell line MKN45. The expression of CD44 and OCT4 was decreased, while CD24 expression was increased by overexpressing ACAT1 in MKN45 gastric cancer cells. Moreover, the ability of gastric cancer cells to form colonies on soft agar was also reduced by ACAT1 overexpression. Likewise, overexpression of ACAT1 inhibited epithelial mesenchymal transition (EMT) in gastric cancer cells evidenced by increased expression of the epithelial marker E-Cadherin, decreased expression of mesenchymal marker vimentin, and decreased expression levels of SNAI 1/3. In addition, ACAT1 overexpression inhibited cell migration and invasion, improved the response to 5-Fluorouracil (5-FU) and etoposide. In contrast, inhibition of ACAT1 activity promoted the proliferation of gastric cancer cells. The xenotransplantation results in nude mice showed that overexpression of ACAT1 in gastric cancer cells inhibited tumor growth in vivo. In addition, the low expression of ACAT1 in gastric cancer was further validated by searching public databases and conducting bioinformatic analyses. Mechanistically, bioinformatic analysis found that the inhibitory effect of ACAT1 in gastric cancer may be related to the Adipocytokine Signaling Pathway, Ppar Signaling Pathway, Propanoate Metabolism and P53 Signaling Pathway. Correlation analysis indicated ACAT1 mRNA expression was correlated with immune infiltrates. Collectively, our data show that ACAT1 induces pronounced inhibitory effects on gastric cancer initiation and development, which may impact future strategies to treat this aggressive cancer.

Toward Characterizing Lymphatic Vasculature in the Mammary Gland During Normal Development and Tumor-Associated Remodeling

Lymphatic vasculature has been shown to promote metastatic spread of breast cancer. Lymphatic vasculature, which is made up of larger collecting vessels and smaller capillaries, has specialized cell junctions that facilitate cell intravasation. Normally, these junctions are designed to collect immune cells and other cellular components for immune surveillance by lymph nodes, but they are also utilized by cancer cells to facilitate metastasis. Although lymphatic development overall in the body has been well-characterized, there has been little focus on how the lymphatic network changes in the mammary gland during stages of remodeling such as pregnancy, lactation, and postpartum involution. In this review, we aim to define the currently known lymphangiogenic factors and lymphatic remodeling events during mammary gland morphogenesis. Furthermore, we juxtapose mammary gland pubertal development and postpartum involution to show similarities of pro-lymphangiogenic signaling as well as other molecular signals for epithelial cell survival that are critical in these morphogenic stages. The similar mechanisms include involvement of M2-polarized macrophages that contribute to matrix remodeling and vasculogenesis; signal transducer and activator of transcription (STAT) survival and proliferation signaling; and cyclooxygenase 2 (COX2)/Prostaglandin E2 (PGE2) signaling to promote ductal and lymphatic expansion. Investigation and characterization of lymphangiogenesis in the normal mammary gland can provide insight to targetable mechanisms for lymphangiogenesis and lymphatic spread of tumor cells in breast cancer.

Cell aggregation activates small GTPase Rac1 and induces CD44 cleavage by maintaining lipid raft integrity

Lipid rafts are highly ordered membrane domains that are enriched in cholesterol and glycosphingolipids and serve as major platforms for signal transduction. Cell detachment from the extracellular matrix (ECM) triggers lipid raft disruption and anoikis, which is a barrier for cancer cells to metastasize. Compared to single circulating tumor cells (CTCs), our recent studies have demonstrated that CD44-mediatd cell aggregation enhances the stemness, survival and metastatic ability of aggregated cells. Here, we investigated whether and how lipid rafts are involved in CD44-mediated cell aggregation. We found that cell detachment, which mimics the condition when tumor cells detach from the ECM to metastasize, induced lipid raft disruption in single cells, but lipid raft integrity was maintained in aggregated cells. We further found that lipid raft integrity in aggregated cells was required for Rac1 activation to prevent anoikis. In addition, CD44 and γ-secretase coexisted at lipid rafts in aggregated cells, which promoted CD44 cleavage and generated CD44 intracellular domain (CD44 ICD) to enhance stemness of aggregated cells. Consequently, lipid raft disruption inhibited Rac1 activation, CD44 ICD generation, and metastasis. Our findings reveal two new pathways regulated by CD44-mediated cell aggregation via maintaining lipid raft integrity. These findings also suggest that targeting cell aggregation-mediated pathways could be a novel therapeutic strategy to prevent CTC cluster-initiated metastasis.

CD44 Intracellular Domain: A Long Tale of a Short Tail

CD44 is a single-chain transmembrane receptor that exists in multiple forms due to alternative mRNA splicing and post-translational modifications. CD44 is the main cell surface receptor of hyaluronan as well as other extracellular matrix molecules, cytokines, and growth factors that play important roles in physiological processes (such as hematopoiesis and lymphocyte homing) and the progression of various diseases, the predominant one being cancer. Currently, CD44 is an established cancer stem cell marker in several tumors, implying a central functional role in tumor biology. The present review aims to highlight the contribution of the CD44 short cytoplasmic tail, which is devoid of any enzymatic activity, in the extraordinary functional diversity of the receptor. The interactions of CD44 with cytoskeletal proteins through specific structural motifs within its intracellular domain drives cytoskeleton rearrangements and affects the distribution of organelles and transport of molecules. Moreover, the CD44 intracellular domain specifically interacts with various cytoplasmic effectors regulating cell-trafficking machinery, signal transduction pathways, the transcriptome, and vital cell metabolic pathways. Understanding the cell type- and context-specificity of these interactions may unravel the high complexity of CD44 functions and lead to novel improved therapeutic interventions.

A Narrative Review on CD44's Role in Glioblastoma Invasion, Proliferation, and Tumor Recurrence

High invasiveness is a characteristic of glioblastoma (GBM), making radical resection almost impossible, and thus, resulting in a tumor with inevitable recurrence. GBM recurrence may be caused by glioma stem-like cells (GSCs) that survive many kinds of therapy. GSCs with high expression levels of CD44 are highly invasive and resistant to radio-chemotherapy. CD44 is a multifunctional molecule that promotes the invasion and proliferation of tumor cells via various signaling pathways. Among these, paired pathways reciprocally activate invasion and proliferation under different hypoxic conditions. Severe hypoxia (0.5-2.5% O2) upregulates hypoxia-inducible factor (HIF)-1α, which then activates target genes, including CD44, TGF-β, and cMET, all of which are related to tumor migration and invasion. In contrast, moderate hypoxia (2.5-5% O2) upregulates HIF-2α, which activates target genes, such as vascular endothelial growth factor (VEGF)/VEGFR2, cMYC, and cyclin D1. All these genes are related to tumor proliferation. Oxygen environments around GBM can change before and after tumor resection. Before resection, the oxygen concentration at the tumor periphery is severely hypoxic. In the reparative stage after resection, the resection cavity shows moderate hypoxia. These observations suggest that upregulated CD44 under severe hypoxia may promote the migration and invasion of tumor cells. Conversely, when tumor resection leads to moderate hypoxia, upregulated HIF-2α activates HIF-2α target genes. The phenotypic transition regulated by CD44, leading to a dichotomy between invasion and proliferation according to hypoxic conditions, may play a crucial role in GBM recurrence.

The critical role of γ-secretase and its inhibitors in cancer and cancer therapeutics

As a multi-substrate transmembrane protease, γ-secretase exists widely in various cells. It controls multiple important cellular activities through substrate cleavage. γ-secretase inhibitors (GSIs) play a role in cancer inhibition by blocking Notch cleavage, and are considered as potential therapeutic strategies for cancer. Currently, GSIs have encouraging performance in preclinical models, yet this success does not translate well in clinical trials. In recent years, a number of breakthrough discoveries have shown us the promise of targeting γ-secretase for the treatment of cancer. Here, we integrate a large amount of data from γ-secretase and its inhibitors and cancer in nearly 30 years, comb and discuss the close connection between γ-secretase and cancer, as well as the potential and problems of current GSIs in cancer treatment. We analyze the possible reasons for the failure performance of current GSIs in clinical trials, and make recommendations for future research areas.

CD44 connects autophagy decline and ageing in the vascular endothelium

The decline of endothelial autophagy is closely related to vascular senescence and disease, although the molecular mechanisms connecting these outcomes in vascular endothelial cells (VECs) remain unclear. Here, we identify a crucial role for CD44, a multifunctional adhesion molecule, in controlling autophagy and ageing in VECs. The CD44 intercellular domain (CD44ICD) negatively regulates autophagy by reducing PIK3R4 and PIK3C3 levels and disrupting STAT3-dependent PtdIns3K complexes. CD44 and its homologue clec-31 are increased in ageing vascular endothelium and Caenorhabditis elegans, respectively, suggesting that an age-dependent increase in CD44 induces autophagy decline and ageing phenotypes. Accordingly, CD44 knockdown ameliorates age-associated phenotypes in VECs. The endothelium-specific CD44ICD knock-in mouse is shorter-lived, with VECs exhibiting obvious premature ageing characteristics associated with decreased basal autophagy. Autophagy activation suppresses the premature ageing of human and mouse VECs overexpressing CD44ICD, function conserved in the CD44 homologue clec-31 in C. elegans. Our work describes a mechanism coordinated by CD44 function bridging autophagy decline and ageing.

Effects of Hyaluronan on Breast Cancer Aggressiveness

The expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) in breast cancer cells is critical for determining tumor aggressiveness and targeting therapies. The presence of such receptors allows for the use of antagonists that effectively reduce breast cancer growth and dissemination. However, the absence of such receptors in triple-negative breast cancer (TNBC) reduces the possibility of targeted therapy, making these tumors very aggressive with a poor outcome. Cancers are not solely composed of tumor cells, but also include several types of infiltrating cells, such as fibroblasts, macrophages, and other immune cells that have critical functions in regulating cancer cell behaviors. In addition to these cells, the extracellular matrix (ECM) has become an important player in many aspects of breast cancer biology, including cell growth, motility, metabolism, and chemoresistance. Hyaluronan (HA) is a key ECM component that promotes cell proliferation and migration in several malignancies. Notably, HA accumulation in the tumor stroma is a negative prognostic factor in breast cancer. HA metabolism depends on the fine balance between HA synthesis by HA synthases and degradation yielded by hyaluronidases. All the different cell types present in the tumor can release HA in the ECM, and in this review, we will describe the role of HA and HA metabolism in different breast cancer subtypes.

The role of tumor microenvironment on cancer stem cell fate in solid tumors

In the last few decades, the role of cancer stem cells in initiating tumors, metastasis, invasion, and resistance to therapies has been recognized as a potential target for tumor therapy. Understanding the mechanisms by which CSCs contribute to cancer progression can help to provide novel therapeutic approaches against solid tumors. In this line, the effects of mechanical forces on CSCs such as epithelial-mesenchymal transition, cellular plasticity, etc., the metabolism pathways of CSCs, players of the tumor microenvironment, and their influence on the regulating of CSCs can lead to cancer progression. This review focused on some of these mechanisms of CSCs, paving the way for a better understanding of their regulatory mechanisms and developing platforms for targeted therapies. While progress has been made in research, more studies will be required in the future to explore more aspects of how CSCs contribute to cancer progression. Video Abstract.

Tissue-specific cancer stem/progenitor cells: Therapeutic implications

Surgical resection, chemotherapy, and radiation are the standard therapeutic modalities for treating cancer. These approaches are intended to target the more mature and rapidly dividing cancer cells. However, they spare the relatively quiescent and intrinsically resistant cancer stem cells (CSCs) subpopulation residing within the tumor tissue. Thus, a temporary eradication is achieved and the tumor bulk tends to revert supported by CSCs' resistant features. Based on their unique expression profile, the identification, isolation, and selective targeting of CSCs hold great promise for challenging treatment failure and reducing the risk of cancer recurrence. Yet, targeting CSCs is limited mainly by the irrelevance of the utilized cancer models. A new era of targeted and personalized anti-cancer therapies has been developed with cancer patient-derived organoids (PDOs) as a tool for establishing pre-clinical tumor models. Herein, we discuss the updated and presently available tissue-specific CSC markers in five highly occurring solid tumors. Additionally, we highlight the advantage and relevance of the three-dimensional PDOs culture model as a platform for modeling cancer, evaluating the efficacy of CSC-based therapeutics, and predicting drug response in cancer patients.

B7H6 silencing increases chemosensitivity to dacarbazine and suppresses cell survival and migration in cutaneous melanoma

Cutaneous melanoma (CM) is a highly metastatic cancer whose incidence rate is heightening worldwide. B7H6, as one of the co-stimulatory ligands of the B7 family, is expressed in malignant cells, involved in tumorigenesis. This study aimed to investigate the significance of B7H6 in CM cell chemosensitivity and metastatic ability. A375 CM cells were transfected with B7H6-siRNA and treated with dacarbazine individually or combined. The MTT assay to estimate half-maximal inhibitory concentration of dacarbazine and cell viability, the apoptotic induction using Annexin V/PI, cell cycle progression via flow cytometry, and wound healing assay for determining the migration ability of cells and assessing the clonogenic potential of A375 cells were executed. Functional analyses were performed to evaluate changes in A375 cells. The results illustrated that B7H6 suppression significantly increased the chemosensitivity of A375 cells to dacarbazine. Apoptosis induction by dacarbazine was enhanced after B7H6 knockdown through modulating Caspase-3, Bax, and Bcl-2 mRNA levels. Western blotting indicated enhancement of cleaved caspase-3 protein expression in treatment groups. A375 cells were arrested at the sub-G1 and S phases when using B7H6-siRNA and dacarbazine. B7H6 suppression combined with dacarbazine restrained cell migration through suppression of matrix metalloproteinase (MMP) expression, including MMP2, MMP3, and MMP9. In addition, the clonogenic ability of A375 cells was decreased by downregulating Sox2, Nanog, and CD44 mRNA levels. A visible decrement in STAT3 protein expression was observed in the combination group. Hence, our findings revealed that B7H6 knockdown with dacarbazine could be a promising treatment approach for cutaneous melanoma.

CD44 in Bone Metastasis Development: A Key Player in the Fate Decisions of the Invading Cells?

A participant in key developmental processes, the adhesion glycoprotein CD44 is also expressed in several types of malignancies and can promote metastasis. In addition, the expression of CD44 isoforms in different types of cancer such as prostate and breast cancers may facilitate bone metastases by enhancing tumorigenicity, osteomimicry, cell migration, homing to bone, and anchorage within the bone specialized domains. Moreover, there is evidence that the CD44-ICD fragments in breast cancer cells may promote the cells' osteolytic nature. Yet the mechanisms by which CD44 and its downstream effectors promote the establishment of these cells within the bone are not fully elucidated. In this review, we summarize the current data on the roles played by CD44 in cancer progression and bone metastasis and the possible effects of its interaction with the different components of the bone marrow milieu.

A recombinant adenovirus vector containing the synNotch receptor gene for the treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is known as the most difficult molecular subtype of breast cancer to treat. Recent studies revealed that cancer stem cells (CSCs) play a critical role in TNBC recurrence and metastasis. In this study, we developed a recombinant replication-deficient adenoviral vector (Ad-CD44-N-HIF-3α4), which contains a gene encoding a synthetic Notch (synNotch) receptor composed of the extracellular domain of CD44 (CD44-ECD) and the hypoxia-inducible factor (HIF)-3α4 connected by the Notch core regulatory region. CD44 is a transmembrane glycoprotein and known as a CSC marker in breast cancer and other malignancies. HIF-3α4 is a dominant-negative regulator of HIF-1α and HIF-2α and inhibits hypoxia-inducing effect. Both CD44 and HIF signals contribute cancer stemness and maintaining CSCs in breast cancer. The CD44-ECD in the synNotch receptor acts as the CD44 decoy receptor, and after a ligand such as a hyaluronic acid binds to the CD44-ECD, HIF-3α4 is released from the Notch core domain. We performed an in vivo study using a mouse xenograft model of MDA-MB-231, a highly invasive TNBC cell, and confirmed the significant antitumor activity of the intratumoral injections of Ad-CD44-N-HIF3α4. Our findings in this study warrant the further development of Ad-CD44-N-HIF3α4 for the treatment of patients with TNBC.

Proteomic profiling and ROC analysis identify CD151 and ELAVL1 as potential therapy response markers for the antiviral drug in resistant TNBC

Triple-negative breast cancer is high heterogeneous, aggressive, and metastatic with poor prognosis. Despite of advances in targeted therapies, TNBC has been reported to cause high morbidity and mortality. A rare subpopulation within the tumor microenvironment organized into a hierarchy of cancer stem cells is responsible for therapy resistance and tumor recurrence. Repurposing of antiviral drugs for cancer treatment is gaining momentum due to reduced cost, labour, and research time, but limited due to lack of prognostic, and predictive markers. The present study investigates proteomic profiling and ROC analysis to identify CD151 and ELAVL1 as potential therapy response markers for the antiviral drug 2-thio-6-azauridine (TAU) in resistant TNBC. The stemness of MDA-MB 231 and MDA-MD 468 adherent cells was enriched by culturing them under non-adherent and non-differentiation conditions. Then, CD151⁺ subpopulation was isolated and characterized for the enrichment of stemness. This study found that CD151 has overexpressed in stemness enriched subpopulations, and also showed CD44 high and CD24 low expression along with stem cell-related transcription factors octamer-binding transcription factor 4 (OCT4) and Sex determining Y-box 2 (SOX2). This study also found that TAU induced significant cytotoxicity and genotoxicity in the CD151⁺TNBC subpopulation and inhibited their proliferation by inducing DNA damage, cell cycle arrest at the G₂M phase, and apoptosis. Further, a proteomic profiling study showed that the expression of CD151 along with ELAVL1, an RNA-binding protein, was significantly reduced with TAU treatment. KM plotter showed correlation of CD151 and ELAVL1 gene expression with a poor prognosis of TNBC. ROC analysis predicted and validated CD151 and ELAVL1 as best therapy response marker for TAU in TNBC. These findings provide new insight into repurposing antiviral drug TAU for treatment of metastatic and drug resistant TNBC.

Hypoxia-circular RNA crosstalk to promote breast cancer

The expression of hypoxia-inducible factors (HIFs), particularly HIF-1, plays a major role in the adaptation of solid tumors to hypoxic conditions. The activation of the HIF pathway results in an expression of genes involved in the promotion of cell growth, proliferation, vascularization, metastasis, and therapeutic resistance. Circular RNA (CircRNA) is considered as a major regulator of gene expression. CircRNAs could regulate the HIF-1 pathway in cancer cells. In addition, they might be regulated by the HIF-1 pathway to promote cancer progression. Therefore, the crosstalk between hypoxia and circRNA might be involved in the pathogenesis of cancers, including breast cancer. In this review, we discussed the function of HIF-related circRNAs in the progression, angiogenesis, metabolic reprogramming, and stemness maintenance of breast cancer. In addition, the correlation between HIF-related circRNAs and clinical features of breast cancer is reviewed.

In silico designing and expression of novel recombinant construct containing the variable part of CD44 extracellular domain for prediagnostic breast cancer

BACKGROUND

CD44, as a tumor-associated marker, can be used to detect stem cells in breast cancer. While CD44 is expressed in normal epithelial cells, carcinoma cells overexpress CD44.

AIMS

In the current study, we designed a recombinant protein that included the variable component of the CD44 (CD44v) extracellular domain to apply in clinical diagnosis of breast cancer.

METHODS

A total of 100 CD44v amino-acid residues were determined, and the structure was examined using bioinformatics tools. The construct was inserted into the PET28a vector and transformed in E. coli BL21(DE3). A nearly 12 kDa fusion protein was obtained by Ni-NTA affinity metal chromatography. Recombinant CD44v was examined by Western blotting, ELISA, and immunohistochemistry (IHC) assays.

RESULTS

The findings revealed that the structure of rCD44v was stable, and its antigenic domain was exposed. The recombinant CD44v was confirmed by western blotting, and the presence of antibodies against recombinant CD44v protein in the patient's serum was detected by the ELISA. Our data demonstrated a link between CD44v serum levels and the prevalence of breast cancer.

CONCLUSION

Assessments of antiCD44v antibodies with rCD44v could be a useful tool for identifying breast cancer in its early stages, which can lead to better outcomes.

Cell aggregation prevents anoikis and induces CD44 cleavage by maintaining lipid raft integrity to promote triple negative breast cancer metastasis

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype, and metastasis is the major cause of cancer morbidity and mortality. Therefore, it is urgent to discover novel therapeutic targets and develop effective treatments for this lethal disease. Circulating tumor cells (CTCs) are considered "seeds of metastasis". Compared to single CTCs, our previous studies have demonstrated that CD44 homophilic interaction mediates CTC aggregation to enhance the stemness, survival and metastatic ability of aggregated cells. Importantly, the presence of CD44+ CTC clusters correlates with a poor prognosis in breast cancer patients. Here, we further investigated the underlying mechanism of how CD44-mediated cell aggregation promotes TNBC metastasis. We found that cell detachment, which mimics the condition when tumor cells detach from the extracellular matrix (ECM) to metastasize, induces lipid raft disruption in single cells, but lipid rafts integrity is maintained in aggregated cells. We further found that lipid rafts integrity in aggregated cells is required for Rac1 activation to prevent anoikis. In addition, CD44 and γ-secretase coexisted at lipid rafts in aggregated cells, which promotes CD44 cleavage and generates CD44 intracellular domain (CD44 ICD) to enhance stemness. Consequently, lipid rafts disruption inhibited Rac1 activation, CD44 ICD generation and metastasis. These data reveal a new mechanism of cell aggregation-mediated TNBC metastasis via maintaining lipid raft integrity after cell detachment. The finding provides a potential therapeutic strategy to prevent CTC cluster-initiated metastasis by disrupting lipid raft integrity and its-mediated downstream pathways.

Sulforaphane suppresses skin squamous cell carcinoma cells proliferation through miR-199a-5p/Sirt1/CD44ICD signaling pathway

BACKGROUND

The present study aimed to explore the impact of sulforaphane on the growth of sSCC cells, and the activation of miR-199a-5p/Sirt1 and CD44ICD signaling pathways.

METHODS

Cell viability, count, apoptosis, and invasion assays were performed in the sSCC cell line (SCC-13) in which miR-199a-5p was over-expressed or under-expressed. The expression levels of miR-199a-5p, Sirt1 and CD44ICD mRNA were measured by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Sulforaphane significantly inhibited the cell growth and invasion of SCC-13 cells, and dramatically induced cell apoptosis. Additionally, sulforaphane also greatly increased miR-199a-5p expression and suppressed Sirt1 and CD44ICD mRNA levels. Moreover, miR-199a-5p overexpression considerably down-regulated the expressions of Sirt1 and CD44ICD mRNA, and promoted the ability of sulforaphane to represses cell growth and invasion, and to induce cell apoptosis. However, miR-199a-5p underexpression has the opposite effects.

CONCLUSIONS

Sulforaphane appears to inhibit sCC progression by impacting its growth and invasion ability, and regulates miR-199a-5p/Sirt1 and CD44ICD signaling pathways, and may be utilized to develop a curative approach for sSCC.

Ethyl Acetate Extract of Colletotrichum gloeosporioides Promotes Cytotoxicity and Apoptosis in Human Breast Cancer Cells

Fungal endophytes are known to be a paragon for producing bioactive compounds with a variety of pharmacological importance. The current study aims to elucidate the molecular alterations induced by the bioactive compounds produced by the fungal endophyte Colletotrichum gloeosporioides in the tumor microenvironment of human breast cancer cells. GC/MS analysis of the ethyl acetate (EA) extract of C. gloeosporioides revealed the presence of bioactive compounds with anticancer activity. The EA extract of C. gloeosporioides exerted potential plasmid DNA protective activity against hydroxyl radicals of Fenton's reagent. The cytotoxic activity further revealed that MDA-MB-231 cells exhibit more sensitivity toward the EA extract of C. gloeosporioides as compared to MCF-7 cells, whereas non-toxic to non-cancerous HEK293T cells. Furthermore, the anticancer activity demonstrated by the EA extract of C. gloeosporioides was studied by assessing nuclear morphometric analysis and induction of apoptosis in MDA-MB-231 and MCF-7 cells. The EA extract of C. gloeosporioides causes the alteration in cellular and nuclear morphologies, chromatin condensation, long-term colony inhibition, and inhibition of cell migration and proliferation ability of MDA-MB-231 and MCF-7 cells. The study also revealed that the EA extract of C. gloeosporioides treated cells undergoes apoptosis by increased production of reactive oxygen species and significant deficit in mitochondrial membrane potential. Our study also showed that the EA extract of C. gloeosporioides causes upregulation of pro-apoptotic (BAX, PARP, CASPASE-8, and FADD), cell cycle arrest (P21), and tumor suppressor (P53) related genes. Additionally, the downregulation of antiapoptotic genes (BCL-2 and SURVIVIN) and increased Caspase-3 activity suggest the induction of apoptosis in the EA extract of C. gloeosporioides treated MDA-MB-231 and MCF-7 cells. Overall, our findings suggest that the bioactive compounds present in the EA extract of C. gloeosporioides promotes apoptosis by altering the genes related to the extrinsic as well as the intrinsic pathway. Further in vivo study in breast cancer models is required to validate the in vitro observations.

Exploring cell surface markers and cell-cell interactions of human breast milk stem cells

Background

Breakthrough studies have shown that pluripotent stem cells are present in human breast milk. The expression of pluripotency markers by breast milk cells is heterogeneous, relating to cellular hierarchy, from early-stage multi-lineage stem cells to fully differentiated mammary epithelial cells, as well as weeks of gestation and days of lactation.

Design and methods

Here, we qualitatively analyze cell marker expression in freshly isolated human breast milk cells, without any manipulation that could influence protein expression. Moreover, we use electron microscopy to investigate cell-cell networks in breast milk for the first time, providing evidence of active intercellular communication between cells expressing different cellular markers.

Results

The immunocytochemistry results of human breast milk cells showed positive staining in all samples for CD44, CD45, CD133, and Ki67 markers. Variable positivity was present with P63, Tβ4 and CK14 markers. No immunostaining was detected for Wt1, nestin, Nanog, OCT4, SOX2, CK5, and CD34 markers. Cells isolated from human breast milk form intercellular connections, which together create a cell-to-cell communication network.

Conclusions

Cells freshly isolated form human breast milk, without particular manipulations, show heterogeneous expression of stemness markers. The studied milk staminal cells show "pluripotency" at different stages of differentiation, and are present as single cells or grouped cells. The adjacent cell interactions are evidenced by electron microscopy, which showed the formation of intercellular connections, numerous contact regions, and thin pseudopods.

FBXL2 promotes E47 protein instability to inhibit breast cancer stemness and paclitaxel resistance

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with a high risk of metastasis and recurrence. Although chemotherapy has greatly improved the clinical outcome of TNBC patients, acquired drug resistance remains a huge challenge for TNBC treatment. Breast cancer stem cells (BCSCs) play a critical role in breast cancer development, metastasis, recurrence, and chemotherapy resistance. Thus, it is of great importance to decipher the underlying molecular mechanism of BCSCs regulation for TNBC drug resistance. In this study, we demonstrate that the F-box protein FBXL2 is a critical negative regulator of BCSCs stemness and that downregulation of FBXL2 plays a causal role in TNBC drug resistance. We show that expression levels of FBXL2 significantly influence CD44^high/CD24^low subpopulation and the mammosphere formation ability of TNBC cells. Ectopic expression of FBXL2 inhibits initiation of TNBC and overcomes paclitaxel resistance in vivo. In addition, activation of FBXL2 by nebivolol, a clinically used small-molecule inhibitor of the beta-1 receptor, markedly overcomes BCSCs-induced paclitaxel resistance. Mechanistically, we show that FBXL2 targets transcriptional factor E47 for polyubiquitin- and proteasome-mediated degradation, resulting in inhibition of BCSC stemness. Clinical analyses indicate that low expression of FBXL2 correlates with high expression of E47 as well as with high stemness features, and is associated with poor clinical outcomes of breast cancer patients. Taken together, these results highlight that the FBXL2-E47 axis plays a critical role in the regulation of BCSC stemness and paclitaxel resistance. Thus, targeting FBXL2 might be a potential therapeutic strategy for drug-resistant TNBC.

CD44 Promotes Breast Cancer Metastasis through AKT-Mediated Downregulation of Nuclear FOXA2

The primary cause of breast cancer mortality is the metastatic invasion of cancerous stem cells (CSC). Cluster of differentiation 44 (CD44) is a well-known CSC marker in various cancers, as well as a key role player in metastasis and relapse of breast cancer. CD44 is a cell-membrane embedded protein, and it interacts with different proteins to regulate cancer cell behavior. Transcription factor forkhead box protein A2 (FOXA2) acts as an important regulator in multiple cancers, including breast cancer. However, the biological significance of CD44-FOXA2 association in breast cancer metastasis remains unclear. Herein, we observed that CD44 expression was higher in metastatic lymph nodes compared to primary tumors using a flow cytometric analysis. CD44 overexpression in breast cancer cell lines significantly promoted cell migration and invasion abilities, whereas the opposite effects occurred upon the knockdown of CD44. The stem cell array analysis revealed that FOXA2 expression was upregulated in CD44 knockdown cells. However, the knockdown of FOXA2 in CD44 knockdown cells reversed the effects on cell migration and invasion. Furthermore, we found that CD44 mediated FOXA2 localization in breast cancer cells through the AKT pathway. Moreover, the immunofluorescence assay demonstrated that AKT inhibitor wortmannin and AKT activator SC79 treatment in breast cancer cells impacted FOXA2 localization. Collectively, this study highlights that CD44 promotes breast cancer metastasis by downregulating nuclear FOXA2.

CD44 In Sarcomas: A Comprehensive Review and Future Perspectives

It is widely accepted that the tumor microenvironment, particularly the extracellular matrix, plays an essential role in the development of tumors through the interaction with specific protein-membrane receptors. One of the most relevant proteins in this context is the transmembrane protein CD44. The role of CD44 in tumor progression, invasion, and metastasis has been well established in many cancers, although a comprehensive review concerning its role in sarcomas has not been published. CD44 is overexpressed in most sarcomas and several in vitro and in vivo experiments have shown a direct effect on tumor progression, dissemination, and drug resistance. Moreover, CD44 has been revealed as a useful marker for prognostic and diagnostic (CD44v6 isoform) in osteosarcoma. Besides, some innovative treatments such as HA-functionalized liposomes therapy have become an excellent CD44-mediated intracellular delivery system for osteosarcoma. Unfortunately, the reduced number of studies deciphering the prognostic/diagnostic value of CD44 in other sarcoma subgroups, neither than osteosarcoma, in addition to the low number of patients involved in those studies, have produced inconclusive results. In this review, we have gone through the information available on the role of CD44 in the development, maintenance, and progression of sarcomas, analyzing their implications at the prognostic, therapeutic, and mechanistic levels. Moreover, we illustrate how research involving the specific role of CD44 in the different sarcoma subgroups could suppose a chance to advance towards a more innovative perspective for novel therapies and future clinical trials.

Hyaluronan network: a driving force in cancer progression

Hyaluronan is one of the most abundant macromolecules of the extracellular matrix and regulates several physiological cell and tissue properties. However, hyaluronan has been shown to accumulate together with its receptors in various cancers. In tumors, accumulation of hyaluronan system components (hyaluronan synthesizing/degrading enzymes and interacting proteins) associates with poor outcomes of the patients. In this article, we review the main roles of hyaluronan in normal physiology and cancer, and further discuss the targeting of hyaluronan system as an applicable therapeutic strategy.

Store-Operated Calcium Entry and Its Implications in Cancer Stem Cells

Tumors are composed by a heterogeneous population of cells. Among them, a sub-population of cells, termed cancer stem cells, exhibit stemness features, such as self-renewal capabilities, disposition to differentiate to a more proliferative state, and chemotherapy resistance, processes that are all mediated by Ca²⁺. Ca²⁺ homeostasis is vital for several physiological processes, and alterations in the patterns of expressions of the proteins and molecules that modulate it have recently become a cancer hallmark. Store-operated Ca²⁺ entry is a major mechanism for Ca²⁺ entry from the extracellular medium in non-excitable cells that leads to increases in the cytosolic Ca²⁺ concentration required for several processes, including cancer stem cell properties. Here, we focus on the participation of STIM, Orai, and TRPC proteins, the store-operated Ca²⁺ entry key components, in cancer stem cell biology and tumorigenesis.

siRNA-induced CD44 knockdown suppresses the proliferation and invasion of colorectal cancer stem cells through inhibiting epithelial-mesenchymal transition

CD44 has shown prognostic values and promising therapeutic potential in multiple human cancers; however, the effects of CD44 silencing on biological behaviors of cancer stem cells (CSCs) have not been fully understood in colorectal cancer. To examine the contribution of siRNA‐induced knockdown of CD44 to the biological features of colorectal CSCs, colorectal CSCs HCT116‐CSCs were generated, and CD44 was knocked down in HCT116‐CSCs using siRNA. The proliferation, migration and invasion of HCT116‐CSCs were measured, and apoptosis and cell‐cycle analyses were performed. The sensitivity of HCT116‐CSCs to oxaliplatin was tested, and xenograft tumor growth assay was performed to examine the role of CD44 in HCT116‐CSCs tumorigenesis in vivo. In addition, the expression of epithelial–mesenchymal transition (EMT) markers E‐cadherin, N‐cadherin and vimentin was quantified. siRNA‐induced knockdown of CD44 was found to inhibit the proliferation, migration and invasion, induce apoptosis, promote cell‐cycle arrest at the G1/G0 phase and increase the sensitivity of HCT116‐CSCs to oxaliplatin in HCT116‐CSCs, and knockdown of CD44 suppressed in vivo tumorigenesis and intrapulmonary metastasis of HCT116‐CSCs. Moreover, silencing CD44 resulted in EMT inhibition. Our findings demonstrate that siRNA‐induced CD44 knockdown suppresses the proliferation, invasion and in vivo tumorigenesis and metastasis of colorectal CSCs by inhibiting EMT.

Castanospermine suppresses CD44 ectodomain cleavage as revealed by transmembrane bioluminescent sensors

Cluster of differentiation 44 (CD44) is a single-pass transmembrane glycoprotein that is a widely distributed cell-surface adhesion molecule. CD44 undergoes ectodomain cleavage by membrane-associated metalloproteinases in breast cancer cells. Cleavage plays a critical role in cancer cell migration by mediating the interaction between CD44 and the extracellular matrix. To explore inhibitors of CD44 ectodomain cleavage, we developed two bioluminescent sensors for the detection of CD44 ectodomain cleavage. The sensors were designed as two-transmembrane proteins with split-luciferase fragments, one of which was cyclized by protein trans-splicing of a DnaE intein. These two sensors emit light by the cyclization or the spontaneous complementation of the luciferase fragments. The luminescence intensities decreased by cleavage of the ectodomain in breast cancer cells. The sensors revealed that castanospermine, an α-glucosidase inhibitor, suppressed the ectodomain cleavage of endogenous CD44 in breast cancer cells. Castanospermine also inhibited breast cancer cell invasion. Thus, the sensors are beneficial tools for evaluating the effects of different inhibitors.

Fraction B From Catfish Epidermal Secretions Kills Pancreatic Cancer Cells, Inhibits CD44 Expression and Stemness, and Alters Cancer Cell Metabolism

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer related death in western countries. The successful treatment of PDAC remains limited. We investigated the effect of Fraction B, which is a fraction purified from catfish (Arius bilineatus, Val.) skin secretions containing proteins and lipids, on PDAC biology both in-vivo and in-vitro. We report here that Fraction B potently suppressed the proliferation of both human and mouse pancreatic cancer cells in vitro and significantly reduced the growth of their relevant xenograft (Panc02) and orthotopic tumors (human Panc-1 cells) (p < 0.05). The Reverse Phase Protein Array (RPPA) data obtained from the tumor tissues derived from orthotopic tumor bearing mice treated with Fraction B showed that Fraction B altered the cancer stem cells related pathways and regulated glucose and glutamine metabolism. The down-regulation of the cancer stem cell marker CD44 expression was further confirmed in Panc-1 cells. CBC and blood chemistry analyses showed no systemic toxicity in Fraction B treated Panc-1 tumor bearing mice compared to that of control group. Our data support that Fraction B is a potential candidate for PDAC treatment.

A non-toxic, reversibly released imaging probe for oral cancer that is derived from natural compounds

CD44 is emerging as an important receptor biomarker for various cancers. Amongst these is oral cancer, where surgical resection remains an essential mode of treatment. Unfortunately, surgery is frequently associated with permanent disfigurement, malnutrition, and functional comorbidities due to the difficultly of tumour removal. Optical imaging agents that can guide tumour tissue identification represent an attractive approach to minimising the impact of surgery. Here, we report the synthesis of a water-soluble fluorescent probe, namely HA-FA-HEG-OE (compound 1), that comprises components originating from natural sources: oleic acid, ferulic acid and hyaluronic acid. Compound 1 was found to be non-toxic, displayed aggregation induced emission and accumulated intracellularly in vesicles in SCC-9 oral squamous cells. The uptake of 1 was fully reversible over time. Internalization of compound 1 occurs through receptor mediated endocytosis; uniquely mediated through the CD44 receptor. Uptake is related to tumorigenic potential, with non-tumorigenic, dysplastic DOK cells and poorly tumorigenic MCF-7 cells showing only low intracellular levels and highlighting the critical role of endocytosis in cancer progression and metastasis. Together, the recognised importance of CD44 as a cancer stem cell marker in oral cancer, and the reversible, non-toxic nature of 1, makes it a promising agent for real time intraoperative imaging.

Emerging role of tumor microenvironment derived exosomes in therapeutic resistance and metastasis through epithelial-to-mesenchymal transition

The tumor microenvironment (TME) constitutes multiple cell types including cancerous and non-cancerous cells. The intercellular communication between these cells through TME derived exosomes may either enhance or suppress the tumorigenic processes. The tumor-derived exosomes could convert an anti-tumor environment into a pro-tumor environment by inducing the differentiation of stromal cells into tumor-associated cells. The exosomes from tumor-associated stromal cells reciprocally trigger epithelial-to-mesenchymal transition (EMT) in tumor cells, which impose therapeutic resistance and metastasis. It is well known that these exosomes contain the signals of EMT, but how these signals execute chemoresistance and metastasis in tumors remains elusive. Understanding the significance and molecular signatures of exosomes transmitting EMT signals would aid in developing appropriate methods of inhibiting them. In this review, we focus on molecular signatures of exosomes that shuttle between cancer cells and their stromal populations in TME to explicate their impact on therapeutic resistance and metastasis through EMT. Especially Wnt signaling is found to be involved in multiple ways of exosomal transport and hence we decipher the biomolecules of Wnt signaling trafficked through exosomes and their potential in serving as therapeutic targets.

Reporters of Cancer Stem Cells as a Tool for Drug Discovery

In view of the importance of cancer stem cells (CSCs) in chemoresistance, metastasis and recurrence, the biology of CSCs were explored in detail. Based on that, several modalities were proposed to target them. In spite of the several clinical trials, a successful CSC-targeting drug is yet to be identified. The number of molecules screened and entered for clinical trial for CSC-targeting is comparatively low, compared to other drugs. The bottle neck is the lack of a high-throughput adaptable screening strategy for CSCs. This review is aimed to identify suitable reporters for CSCs that can be used to identify the heterogeneous CSC populations, including quiescent CSCs, proliferative CSCs, drug resistant CSCs and metastatic CSCs. Analysis of the tumor microenvironment regulating CSCs revealed that the factors in CSC-niche activates effector molecules that function as CSC markers, including pluripotency markers, CD133, ABCG2 and ALDH1A1. Among these factors OCT4, SOX2, NANOG, ABCG2 and ALDH1A1 are ideal for making reporters for CSCs. The pluripotency molecules, like OCT4, SOX2 and NANOG, regulate self-renewal, chemoresistance and metastasis. ABCG2 is a known regulator of drug resistance while ALDH1A1 modulates self-renewal, chemoresistance and metastasis. Considering the heterogeneity of CSCs, including a quiescent population and a proliferative population with metastatic ability, we propose the use of a combination of reporters. A dual reporter consisting of a pluripotency marker and a marker like ALDH1A1 will be useful in screening drugs that target CSCs.

Material properties of disulfide-crosslinked hyaluronic acid hydrogels influence prostate cancer cell growth and metabolism

Cells reside in vivo within three dimensional environments in which they interact with extracellular matrices (ECMs) that play an integral role in maintaining tissue homeostasis and preventing tumour growth. Thus, tissue culture approaches that more faithfully reproduce these interactions with the ECM are needed to study cancer development and progression. Many materials exist for modeling tissue environments, and the effects of differing mechanical, physical, and biochemical properties of such materials on cell behaviour are often intricately coupled and difficult to tease apart. Here, an optimized protocol was developed to generate low reaction volume disulfide-crosslinked hyaluronic acid (HA) hydrogels for use in cell culture applications to relate the properties of ECM materials to cell signalling and behaviour. Mechanically, HA hydrogels are comparable to other soft hydrogel materials such as Matrigel and agarose or to tissues lacking type I collagen and other fibrillar ECM components. The diffusion of soluble materials in these hydrogels is affected by unique mass transfer properties. Specifically, HA hydrogel concentration affects the diffusion of anionic particles above 500 kDa, whereas diffusion of smaller particles appears unimpeded by HA content, likely reflecting hydrogel pore size. The HA hydrogels have a strong exclusion effect that limits the movement of proteins into and out of the material once fully formed. Such mass transfer properties have interesting implications for cell culture, as they ultimately affect access to nutrients and the distribution of signalling molecules, affecting nutrient sensing and metabolic activity. The use of disulfide-crosslinked HA hydrogels for the culture of the model prostate cancer cell lines PC3 and LNCaP reveals correlations of protein activation linked to metabolic flux, which parallel and can thus potentially provide insights into cell survival mechanisms in response to starvation that occurs in cancer cell microenvironments.

TRAF4/6 Is Needed for CD44 Cleavage and Migration via RAC1 Activation

The hyaluronan receptor CD44 can undergo proteolytic cleavage in two steps, leading to the release of its intracellular domain; this domain is translocated to the nucleus, where it affects the transcription of target genes. We report that CD44 cleavage in A549 lung cancer cells and other cells is promoted by transforming growth factor-beta (TGFβ) in a manner that is dependent on ubiquitin ligase tumor necrosis factor receptor-associated factor 4 or 6 (TRAF4 or TRAF6, respectively). Stem-like A549 cells grown in spheres displayed increased TRAF4-dependent expression of CD44 variant isoforms, CD44 cleavage, and hyaluronan synthesis. Mechanistically, TRAF4 activated the small GTPase RAC1. CD44-dependent migration of A549 cells was inhibited by siRNA-mediated knockdown of TRAF4, which was rescued by the transfection of a constitutively active RAC1 mutant. Our findings support the notion that TRAF4/6 mediates pro-tumorigenic effects of CD44, and suggests that inhibitors of CD44 signaling via TRAF4/6 and RAC1 may be beneficial in the treatment of tumor patients.

Reg4 and its downstream transcriptional activator CD44ICD in stage II and III colorectal cancer

Reg4 is highly expressed in gastrointestinal malignancies and acts as a mitogenic and pro-invasive factor. Our recent works suggest that Reg4 binds with CD44 and induces its proteolytic cleavage to release intra-cytoplasmic domain of CD44 (CD44ICD). The goal of this study is to demonstrate clinical significance of the Reg4-CD44/CD44ICD pathway in stage II/III colon cancer and its association with clinical parameters of aggression. We constructed a tissue microarray (TMA) of 93 stage II/III matched colon adenocarcinoma patients, 23 with recurrent disease. The TMA was immunohistochemically stained for Reg4, CD44, and CD44ICD proteins and analyzed to identify associations with tumor characteristics, recurrence and overall survival. The TMA data analysis showed a significant correlation between Reg4 and CD44 (r² = 0.23, P = 0.028), CD44 and CD44ICD (r² = 0.36, p = 0.0004), and Reg4 and CD44ICD (r² = 0.45, p ≤ 0.0001). Reg4 expression was associated with larger tumor size (r² = 0.23, p = 0.026). Although, no association was observed between Reg4, CD44, or CD44ICD expression and disease recurrence, Reg4-positive patients had a median survival of 4 years vs. 7 years for Reg4-negative patients (p = 0.04) in patients who recurred. Inhibition of the Reg4-CD44/CD44ICD pathway may be a future therapeutic target for colon cancer patients.

Unlocking the Secrets of Cancer Stem Cells with γ-Secretase Inhibitors: A Novel Anticancer Strategy

The dysregulation of Notch signaling is associated with a wide variety of different human cancers. Notch signaling activation mostly relies on the activity of the γ-secretase enzyme that cleaves the Notch receptors and releases the active intracellular domain. It is well-documented that γ-secretase inhibitors (GSIs) block the Notch activity, mainly by inhibiting the oncogenic activity of this pathway. To date, several GSIs have been introduced clinically for the treatment of various diseases, such as Alzheimer's disease and various cancers, and their impacts on Notch inhibition have been found to be promising. Therefore, GSIs are of great interest for cancer therapy. The objective of this review is to provide a systematic review of in vitro and in vivo studies for investigating the effect of GSIs on various cancer stem cells (CSCs), mainly by modulation of the Notch signaling pathway. Various scholarly electronic databases were searched and relevant studies published in the English language were collected up to February 2020. Herein, we conclude that GSIs can be potential candidates for CSC-targeting therapy. The outcome of our study also indicates that GSIs in combination with anticancer drugs have a greater inhibitory effect on CSCs.

The Breast Cancer Stem Cells Traits and Drug Resistance

Drug resistance is a major challenge in breast cancer (BC) treatment at present. Accumulating studies indicate that breast cancer stem cells (BCSCs) are responsible for the BC drugs resistance, causing relapse and metastasis in BC patients. Thus, BCSCs elimination could reverse drug resistance and improve drug efficacy to benefit BC patients. Consequently, mastering the knowledge on the proliferation, resistance mechanisms, and separation of BCSCs in BC therapy is extremely helpful for BCSCs-targeted therapeutic strategies. Herein, we summarize the principal BCSCs surface markers and signaling pathways, and list the BCSCs-related drug resistance mechanisms in chemotherapy (CT), endocrine therapy (ET), and targeted therapy (TT), and display therapeutic strategies for targeting BCSCs to reverse drug resistance in BC. Even more importantly, more attention should be paid to studies on BCSC-targeted strategies to overcome the drug resistant dilemma of clinical therapies in the future.

Proteolytic Processing of CD44 and Its Implications in Cancer

CD44 is a transmembrane glycoprotein expressed in several healthy and tumor tissues. Modifications in its structure contribute differently to the activity of this molecule. One modification that has provoked interest is the consecutive cleavage of the CD44 extracellular ectodomain by enzymes that belong mainly to the family of metalloproteases. This process releases biologically active substrates, via alternative splice forms of CD44, that generate CD44v3 or v6 isoforms which participate in the transcriptional regulation of genes and proteins associated to signaling pathways involved in the development of cancer. These include the protooncogene tyrosine-protein kinase Src (c-Src)/signal transducer and activator of transcription 3 (STAT3), the epithelial growth factor receptor, the estrogen receptor, Wnt/βcatenin, or Hippo signaling pathways all of which are associated to cell proliferation, differentiation, or cancer progression. Whereas CD44 still remains as a very useful prognostic cell marker in different pathologies, the main topic is that the generation of CD44 intracellular fragments assists the regulation of transcriptional proteins involved in the cell cycle, cell metabolism, and most importantly, the regulation of some stem cell-associated markers.

Beyond just a tight fortress: contribution of stroma to epithelial-mesenchymal transition in pancreatic cancer

Novel effective treatment is direly needed for patients with pancreatic ductal adenocarcinoma (PDAC). Therapeutics that target the driver mutations, especially the KRAS oncoprotein and its effector cascades, have been ineffective. It is increasing clear that the extensive fibro-inflammatory stroma (or desmoplasia) of PDAC plays an active role in the progression and therapeutic resistance of PDAC. The desmoplastic stroma is composed of dense extracellular matrix (ECM) deposited mainly by the cancer-associated-fibroblasts (CAFs) and infiltrated with various types of immune cells. The dense ECM functions as a physical barrier that limits tumor vasculatures and distribution of therapeutics to PDAC cells. In addition, mounting evidence have demonstrated that both CAFs and ECM promote PDAC cells aggressiveness through multiple mechanisms, particularly engagement of the epithelial-mesenchymal transition (EMT) program. Acquisition of a mesenchymal-like phenotype renders PDAC cells more invasive and resistant to therapy-induced apoptosis. Here, we critically review seminal and recent articles on the signaling mechanisms by which each stromal element promotes EMT in PDAC. We discussed the experimental models that are currently employed and best suited to study EMT in PDAC, which are instrumental in increasing the chance of successful clinical translation.

Cancer Stem Cells with Overexpression of Neuronal Markers Enhance Chemoresistance and Invasion in Retinoblastoma

BACKGROUND

Retinoblastoma is a sight and life-threatening embryonal tumor in children. Though chemotherapy is the main mode of therapy, evolving resistance remains a major obstacle in treatment success. The presence of cancer stem cells (CSC) is frequently reported to be responsible for chemoresistance in multiple tumors.

OBJECTIVE

Our study aims to identify the molecular factors that facilitate the chemoresistance through cancer stem cells in retinoblastoma.

METHODS

We developed etoposide and carboplatin resistant retinoblastoma (Y79) cell lines by stepwise drug increment treatment, validated with MTT and TUNEL assays. Colony forming and invasive ability were studied by soft-agar colony forming and transwell assays, respectively. Similar analysis in non-responsive retinoblastoma tumors were carried out by histopathology. Finally, expression of CSC/neuronal markers and ABC transporters were examined by quantitative PCR and protein expression of neuronal stem cell markers was confirmed by Western blot.

RESULTS

Larger colony size of resistant cells in soft-agar assay provided evidence for increased selfrenewability. Histopathology in non-responsive tumors showed poorly differentiated cells predominantly. Besides, both resistant cell lines and non-responsive tumors showed increased invasion with higher expression of neuronal stem cell markers - SOX2, NANOG, OCT4 and ABC transporters - ABCB1 and ABCC3. Increased self-renewal ability and invasion along with overexpression of stemness markers in resistant cells and tumors provide evidence for stemness driving chemoresistance and invasion in retinoblastoma.

CONCLUSION

We have demonstrated Neuronal stem cell/CSC markers that facilitate the maintenance of cancer stem cells. Developing therapies targeting these factors will help in overcoming resistance and improving retinoblastoma treatment.

Identification of sequence-specific interactions of the CD44-intracellular domain with RUNX2 in the transcription of matrix metalloprotease-9 in human prostate cancer cells

Aim

The Cluster of differentiation 44 (CD44) transmembrane protein is cleaved by γ-secretase, the inhibition of which blocks CD44 cleavage. This study aimed to determine the biological consequence of CD44 cleavage and its potential interaction with Runt-related transcription factor (RUNX2) in a sequence-specific manner in PC3 prostate cancer cells.

Methods

Using full-length and C-terminal deletion constructs of CD44-ICD (D1-D5) expressed as stable green fluorescent protein-fusion proteins in PC3 cells, we located possible RUNX2-binding sequences.

Results

Chromatin immunoprecipitation assays demonstrated that the C-terminal amino acid residues between amino acids 671 and 706 in D1 to D3 constructs were indispensable for sequence-specific binding of RUNX2. This binding was minimal for sequences in the D4 and D5 constructs. Correspondingly, an increase in matrix metalloprotease-9 (MMP-9) expression was observed at the mRNA and protein levels in PC3 cells stably expressing D1-D3 constructs.

Conclusion

These results provide biochemical evidence for the possible sequence-specific CD44-ICD/RUNX2 interaction and its functional relationship to MMP-9 transcription in the promoter region.

Cancer Stem Cells-Origins and Biomarkers: Perspectives for Targeted Personalized Therapies

The use of biomarkers in diagnosis, therapy and prognosis has gained increasing interest over the last decades. In particular, the analysis of biomarkers in cancer patients within the pre- and post-therapeutic period is required to identify several types of cells, which carry a risk for a disease progression and subsequent post-therapeutic relapse. Cancer stem cells (CSCs) are a subpopulation of tumor cells that can drive tumor initiation and can cause relapses. At the time point of tumor initiation, CSCs originate from either differentiated cells or adult tissue resident stem cells. Due to their importance, several biomarkers that characterize CSCs have been identified and correlated to diagnosis, therapy and prognosis. However, CSCs have been shown to display a high plasticity, which changes their phenotypic and functional appearance. Such changes are induced by chemo- and radiotherapeutics as well as senescent tumor cells, which cause alterations in the tumor microenvironment. Induction of senescence causes tumor shrinkage by modulating an anti-tumorigenic environment in which tumor cells undergo growth arrest and immune cells are attracted. Besides these positive effects after therapy, senescence can also have negative effects displayed post-therapeutically. These unfavorable effects can directly promote cancer stemness by increasing CSC plasticity phenotypes, by activating stemness pathways in non-CSCs, as well as by promoting senescence escape and subsequent activation of stemness pathways. At the end, all these effects can lead to tumor relapse and metastasis. This review provides an overview of the most frequently used CSC markers and their implementation as biomarkers by focussing on deadliest solid (lung, stomach, liver, breast and colorectal cancers) and hematological (acute myeloid leukemia, chronic myeloid leukemia) cancers. Furthermore, it gives examples on how the CSC markers might be influenced by therapeutics, such as chemo- and radiotherapy, and the tumor microenvironment. It points out, that it is crucial to identify and monitor residual CSCs, senescent tumor cells, and the pro-tumorigenic senescence-associated secretory phenotype in a therapy follow-up using specific biomarkers. As a future perspective, a targeted immune-mediated strategy using chimeric antigen receptor based approaches for the removal of remaining chemotherapy-resistant cells as well as CSCs in a personalized therapeutic approach are discussed.

A low MW inhibitor of CD44 dimerization for the treatment of glioblastoma

BACKGROUND AND PURPOSE

As a hallmark of glioblastoma multiforme (GBM), CD44 plays a crucial role in promoting glioblastoma stem cell (GSC) stemness phenotypes and multiple drug resistance. The therapeutic potential of CD44 has been validated by the clinical successes of several CD44 inhibitors, including antibodies and hyaluronan-related drugs.

EXPERIMENTAL APPROACH

We used systemsDock software to predict verbascoside as a candidate CD44 inhibitor. Microscale thermophoresis was used to confirm the interaction between CD44 and verbascoside. Four glioblastoma cell lines and a patient-derived glioblastoma cell line were used to test the influences of verbascoside on glioblastoma. CD44-overexpressing and CD44-knockout cell lines were also used. Real-time quantitative PCR and western blot analyses were performed. A xenograft mouse model was used to test verbascoside.

KEY RESULTS

Verbascoside bound to CD44 and suppressed its dimerization. By inhibiting CD44 dimerization, verbascoside decreased the release of the CD44 intracellular domain (CD44ICD) and suppressed the expression of CD44 downstream genes. Verbascoside treatment suppressed the stemness phenotypes of cells with high CD44 expression. In a mouse model of glioma, verbascoside treatment highly reduced the growth of intracranial tumours and inhibited CD44ICD release. Both stem cell marker and mesenchymal GBM subtype marker genes were down-regulated in verbascoside-treated mice.

CONCLUSION AND IMPLICATIONS

Verbascoside suppressed growth of glioblastoma cells by inhibiting CD44 dimerization. Stem cell-like cell properties and tumour cell growth were also suppressed by verbascoside, both in vitro and in vivo. Verbascoside significantly prolonged survival of xenografted mice.

P53-induced MRVI1 mediates carcinogenesis of colorectal cancer

Background: Colorectal cancer (CRC) is one of the most prevalent cancer types worldwide. Despite the advancements in current diagnosis and treatment strategies of CRC, the incidence and mortality rates of CRC have been rising. To explore novel mechanism of CRC, this study focused on the expression pattern and functional mechanism of murine retrovirus integration site 1 (MRVI1) in CRC.Methods: Tumor tissues and adjacent normal tissues were collected from CRC patients, and the expression levels of MRVI1 were determined by RT-PCR and Western blot. MRVI1 knockdown was achieved by shRNA in HCT116 and HT29 cells, followed by CCK-8 assay to detect the cell proliferation, and caspase-3 activity assay combined with nucleosome ELISA assay to detect cell apoptosis. Transwell assay was used to detect cell invasion and luciferase reporter assay was used to validate the activation of the MRVI1 promoter by p53.Results: MRVI1 was downregulated in CRC tissues and several CRC cell lines. Knockdown of MRVI1 enhanced the proliferation and apoptosis, while promoted invasion and stemness of CRC cells. Mechanism study revealed that MRVI1 was transcriptionally activated by p53 at its upstream. In addition, p53-induced inhibition of CRC prognosis depended on MRVI1.Conclusion: MRVI1 inhibited the prognosis of CRC via a mechanism involving p53 activation. MRVI1 could serve as a potential target for clinical diagnosis and treatment of CRC.

Switching Homes: How Cancer Moves to Bone

Bone metastases (BM) are a very common complication of the most prevalent human cancers. BM are extremely painful and may be life-threatening when associated with hypercalcaemia. BM can lead to kidney failure and cardiac arrhythmias and arrest, but why and how do cancer cells decide to "switch homes" and move to bone? In this review, we will present what answers science has provided so far, with focus on the molecular mechanisms and cellular aspects of well-established findings, such as the concept of "vicious cycle" and "osteolytic" vs. "osteosclerotic" bone metastases; as well as on novel concepts, such as cellular dormancy and extracellular vesicles. At the molecular level, we will focus on hypoxia-associated factors and angiogenesis, the Wnt pathway, parathyroid hormone-related peptide (PTHrP) and chemokines. At the supramolecular/cellular level, we will discuss tumour dormancy, id est the mechanisms through which a small contingent of tumour cells coming from the primary site may be kept dormant in the endosteal niche for many years. Finally, we will present a potential role for the multimolecular mediators known as extracellular vesicles in determining bone-tropism and establishing a premetastatic niche by influencing the bone microenvironment.

Hyaluronic acid induction on breast cancer stem cells unfolds subtype specific variations in stemness and epithelial-to-mesenchymal transition

The reoccurrence of breast cancer is a major concern due to presence of cancer stem cells (CSCs). Considering the key role of hyaluronic acid (HA) in modulating the inflammation and cellular migration in cancer, the response of high molecular weight (HMW) and low molecular weight (LMW) HA towards various subtypes of breast cancer and breast cancer stem cells remain elusive. The aim of this study is to determine the effect of exogenous HMW-HA and LMW-HA on stemness of CSCs and epithelial-to-mesenchymal transition which may help in designing HA based therapeutic strategies. LMW-HA induces EMT in MCF-7 more prominently as compared to MDA-MB-231. However, HMW-HA did not show significant changes in the expression of EMT genes. Surprisingly, both HMW-HA and LMW-HA have shown to decrease the expression of EpCAM in MCF-7 cells and decrease the expression of CD44 in MDAMB-231 cells. HA has maintained the native stem cells phenotype of bCSCs isolated from MCF-7 only. The bCSCs isolated form MDAMB-231 showed a decrease in CD44. Luminal subtype has shown to follow Wnt/β-catenin whereas in the basal subtype localization of CD44 from surface to cytosol was observed in response to HA. Our study has demonstrated that bCSCs in luminal and basal cells follow differential intracellular signaling mechanisms in response to HA. This study could significantly influence the therapeutics involving HA in breast cancer.

Cancer stem cells and their unique role in metastatic spread

Cancer stem cells (CSC) possess abilities generally associated with embryonic or adult stem cells, especially self-renewal and differentiation, but also dormancy and cellular plasticity that allow adaption to new environmental circumstances. These abilities are ideal prerequisites for the successful establishment of metastasis. This review highlights the role of CSCs in every step of the metastatic cascade from cancer cell invasion into blood vessels, survival in the blood stream, attachment and extravasation as well as colonization of the host organ and subsequent establishment of distant macrometastasis.

MiR-199a-5p represses the stemness of cutaneous squamous cell carcinoma stem cells by targeting Sirt1 and CD44ICD cleavage signaling

Tumorigenic cancer stem cells (CSCs) exist in various tumors including the cutaneous squamous cell carcinoma (cSCC) as a minor subpopulation and are tightly associated with metastasis and therapeutic resistance. Better understanding of CSCs properties is essential for the novel therapeutic strategy targeted toward these cancers. The cSCC stem cells (cSCCSCs) were enriched from a cSCC cell line A431 by repeated sphere culture, and identified via the expression analysis of stemness marker genes and CD44 proteolysis. MiR-199a-5p was previously reported to be related with the proteolysis modulation of CD44, so the specific regulation mechanisms were verified by overexpression in vitro and in vivo. MiR-199a-5p is under-expressed in cSCCSCs and functions as a tumor suppressive molecule. Overexpression of miR-199a-5p reduced the stemness of cSCCSCs and inhibited cell proliferation. By targeting the deacetylase Sirt1, miR-199a-5p inhibited cellular proteolysis of CD44 and reduced the CD44 intracellular domain (CD44ICD) release and nuclear translocation. Overexpression of CD44ICD reversed the effects of miR-199a-5p overexpression or Sirt1 silencing, and increased the transcriptional expression of stemness genes. Our results revealed that the miR-199a-5p/Sirt1/CD44ICD signaling pathway regulates cSCCSCs progression by affecting its migration ability and tumorigenicity, therefore can be utilized to develop a curative approach for cSCC.Abbreviations: CSCs: cancer stem cells; cSCC cutaneous squamous cell carcinoma; cSCCSCs: cSCC stem cells; CD44ICD: CD44 intracellular domain; HA: hyaluronic acid; HNSCC: hand and neck squamous cell carcinoma; ESCC: esophageal squamous cell carcinoma;MMPs: matrix metalloproteinases; SFM: sphere formation medium; EGF: epidermal growth factor; bFGF: basic fibroblast growth factor; BSA: bovine serum albumin; CCK-8: cell counting kit-8.