Characterization of the CD49f+/CD44+/CD24- single-cell derived stem cell population in basal-like DCIS cells

Cancer stem cells: Masters of all traits

Cancer is a heterogeneous disease, which contributes to its rapid progression and therapeutic failure. Besides interpatient tumor heterogeneity, tumors within a single patient can present with a heterogeneous mix of genetically and phenotypically distinct subclones. These unique subclones can significantly impact the traits of cancer. With the plasticity that intratumoral heterogeneity provides, cancers can easily adapt to changes in their microenvironment and therapeutic exposure. Indeed, tumor cells dynamically shift between a more differentiated, rapidly proliferating state with limited tumorigenic potential and a cancer stem cell (CSC)-like state that resembles undifferentiated cellular precursors and is associated with high tumorigenicity. In this context, CSCs are functionally located at the apex of the tumor hierarchy, contributing to the initiation, maintenance, and progression of tumors, as they also represent the subpopulation of tumor cells most resistant to conventional anti-cancer therapies. Although the CSC model is well established, it is constantly evolving and being reshaped by advancing knowledge on the roles of CSCs in different cancer types. Here, we review the current evidence of how CSCs play a pivotal role in providing the many traits of aggressive tumors while simultaneously evading immunosurveillance and anti-cancer therapy in several cancer types. We discuss the key traits and characteristics of CSCs to provide updated insights into CSC biology and highlight its implications for therapeutic development and improved treatment of aggressive cancers.

Cancer stem cells: an insight into the development of metastatic tumors and therapy resistance

The term "cancer stem cells" (CSCs) refers to cancer cells that exhibit traits parallel to normal stem cells, namely the potential to give rise to every type of cell identified in a tumor microenvironment. It has been found that CSCs usually develops from other neoplastic cells or non-cancerous somatic cells by acquiring stemness and malignant characteristics through particular genetic modifications. A trivial number of CSCs, identified in solid and liquid cancer, can give rise to an entire tumor population with aggressive anticancer drug resistance, metastasis, and invasiveness. Besides, cancer stem cells manipulate their intrinsic and extrinsic features, regulate the metabolic pattern of the cell, adjust efflux-influx efficiency, modulate different signaling pathways, block apoptotic signals, and cause genetic and epigenetic alterations to retain their pluripotency and ability of self-renewal. Notably, to keep the cancer stem cells' ability to become malignant cells, mesenchymal stem cells, tumor-associated fibroblasts, immune cells, etc., interact with one another. Furthermore, CSCs are characterized by the expression of particular molecular markers that carry significant diagnostic and prognostic significance. Because of this, scientific research on CSCs is becoming increasingly imperative, intending to understand the traits and behavior of cancer stem cells and create more potent anticancer therapeutics to fight cancer at the CSC level. In this review, we aimed to elucidate the critical role of CSCs in the onset and spread of cancer and the characteristics of CSCs that promote severe resistance to targeted therapy.

Ductal Carcinoma In Situ of Breast: From Molecular Etiology to Therapeutic Management

Ductal carcinoma in situ (DCIS) makes up a majority of noninvasive breast cancer cases. DCIS is a neoplastic proliferation of epithelial cells within the ductal structure of the breast. Currently, there is little known about the progression of DCIS to invasive ductal carcinoma (IDC), or the molecular etiology behind each DCIS lesion or grade. The DCIS lesions can be heterogeneous in morphology, genetics, cellular biology, and clinical behavior, posing challenges to our understanding of the molecular mechanisms by which approximately half of all DCIS lesions progress to an invasive status. New strategies that pinpoint molecular mechanisms are necessary to overcome this gap in understanding, which is a barrier to more targeted therapy. In this review, we will discuss the etiological factors associated with DCIS, as well as the complexity of each nuclear grade lesion. Moreover, we will discuss the possible molecular features that lead to progression of DCIS to IDC. We will highlight current therapeutic management and areas for improvement.

Association of STAT3, PTPRT, TNK2-AS1, LINC-ROR Genes Expression Level with Prostate Cancer and Benign Prostatic Hyperplasia

Background: Prostate cancer (PCa) and benign prostate hyperplasia (BPH) are highly prevalent heterogeneous disorders among men. Since angiogenesis is the key step in cancer progression, the deregulation of genes involved in this process may play a role in cancer development. Objectives: We evaluated the expression level of 4 angiogenesis-related genes including signal transducer and activator of transcription 3 (STAT3), protein tyrosine phosphatase receptor type T (PTPRT), TNK2 antisense RNA 1 (TNK2-AS1), and long intergenic non-protein coding rna-regulator of reprogramming (LINC-ROR) in patients with PCa and BPH. Methods: The expression level of STAT3, PTPRT, TNK2-AS1, and LINC-ROR genes in tumoral and adjacent non-cancerous tissue (ANCT) samples of 50 PCa patients and tissue samples from 50 BPH patients were evaluated, using the real-time PCR method. The statistical analysis was performed to evaluate the association between genes expression and clinicopathological characteristics of patients with PCa. Results: The expression level of STAT3 and LINC-ROR was upregulated in tumoral tissues compared to ANCTs (P < 0.0001 for both). Only the expression level of STAT3 in PCa was higher than in BPH tissues (P = 0.001). The elevated expression of STAT3 was associated with the higher grade group of the tumor (P = 0.03). Also, the high expression level of PTPRT and LINC-ROR genes was associated with a higher stage of cancer in patients with PCa (P = 0.002, P = 0.0001 respectively). The STAT3 gene transcript level had an excellent diagnostic power for discrimination between tumoral tissue and the ANCTs with an area under the curve (AUC) of 0.93. Conclusions: The higher expression of STAT3 and LINC-ROR suggested a role in the pathogenesis of PCa in higher stages. Also, STAT3 expression level could be suggested as a potential biomarker for PCa in combination with PSA level.

LncRNAs and microRNAs as Essential Regulators of Stemness in Breast Cancer Stem Cells

Breast cancer is an aggressive disease with a high incidence in women worldwide. Two decades ago, a controversial hypothesis was proposed that cancer arises from a subpopulation of "tumor initiating cells" or "cancer stem cells-like" (CSC). Today, CSC are defined as small subset of somatic cancer cells within a tumor with self-renewal properties driven by the aberrant expression of genes involved in the maintenance of a stemness-like phenotype. The understanding of the underlying cellular and molecular mechanisms involved in the maintenance of CSC subpopulation are fundamental in the development and persistence of breast cancer. Nowadays, the hypothesis suggests that genetic and epigenetic alterations give rise to breast cancer stem cells (bCSC), which are responsible for self-renewal, tumor growth, chemoresistance, poor prognosis and low survival in patients. However, the prominence of bCSC, as well as the molecular mechanisms that regulates and promotes the malignant phenotypes, are still poorly understood. The role of non-coding RNAs (ncRNAs), such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) acting as oncogenes or tumor suppressor genes has been recently highlighted by a plethora of studies in breast cancer. These ncRNAs positively or negatively impact on different signaling pathways that govern the cancer hallmarks associated with bCSC, making them attractive targets for therapy. In this review, we present a current summary of the studies on the pivotal roles of lncRNAs and microRNAs in the regulation of genes associated to stemness of bCSC.

Breast tumour cell subpopulations with expression of the MYC and OCT4 proteins

The MYC and OCT4 genes are known factors associated with maintaining pluripotency and are linked with a more aggressive course, progression, and resistance to therapy in cancer. Determining the subpopulations of tumour cells expressing the Myc and Oct4 proteins will provide an opportunity to understand which tumour cell subpopulations expressing MYC and OCT4 are associated with metastasis and resistance and which subpopulations can be targeted by anti-MYC and anti-OCT4 therapy. The study included paraffin-embedded tissue from tumours from 27 patients with luminal B breast cancer obtained after neoadjuvant chemotherapy (NACT). Immunofluorescence staining was used to identify subpopulations of tumour cells expressing Myc, Oct4 and Snai2 (Opal™ 7-Color Kit (PerkinElmer, Hopkinton, MA). The following tumour cell subpopulations were identified with the Myc and Oct4 proteins and the Snai2 EMT marker: stem/progenitor tumour cells with/without Myc, Oct4 or Snai2 expression; differentiated tumour cells with/without Myc, Oct4 or Snai2 expression; and other nontumour cells (CK7^-EpCAM^-CD44^+/-Myc^+/-(Oct4, Snai2)^+/-) within the inflammatory infiltrate in the tumour parenchyma and stroma. The circulating tumour cell subpopulations with Oct4 protein expression in the bloodstream were studied by flow cytometry. It was found that in patients with partial regression (PR) in response to NACT, the frequency of tumour stem cells was 3.6-fold increased (p = 0.038) in the non-EMT state (CK7⁺EpCam⁺CD44⁺Snai2^-). In patients with metastases, there was a statistically significant 2.5-fold increase in the frequency of differentiated tumour cells with Myc expression (CK7⁺EpCam⁺CD44^-Myc⁺) and a 2.7-fold increase in the frequency of cells with Oct4 expression (CK7⁺EpCam⁺CD44^-OCT4⁺). In the next stage, the frequencies of subpopulations with expression of the Oct4 protein and signs of EMT among circulating tumour cells (CTCs) were determined. In patients with metastases, the frequency of tumour stem cells in the EMT state (CD326⁺CD44⁺CD24^-CD325⁺) (p = 0.015) was more than fourfold increased, and the frequency of progenitor tumour cells with expression of the Oct4 stem protein (CD326⁺CD44⁺CD24⁺Oct4⁺) (p = 0.016) was almost sixfold higher than that in patients without metastases. Nonstem (differentiated) tumour cells with expression of the stemness proteins Myc and Oct4 were present in the breast tumour. Their content was significantly higher in residual tumours after NACT in patients who subsequently developed metastases compared with that in patients without metastases. Such cells are a new in situ marker of metastasis.

An evolving paradigm of cancer stem cell hierarchies: therapeutic implications

Over a decade of research has confirmed the critical role of cancer stem-like cells (CSCs) in tumor initiation, chemoresistance, and metastasis. Increasingly, CSC hierarchies have begun to be defined with some recurring themes. This includes evidence that these hierarchies are 'flexible,' with both cell state transitions and dedifferentiation events possible. These findings pose therapeutic hurdles and opportunities. Here, we review cancer stem cell hierarchies and their interactions with the tumor microenvironment. We also discuss the current therapeutic approaches designed to target CSC hierarchies and initial clinical trial results for CSC targeting agents. While cancer stem cell targeted therapies are still in their infancy, we are beginning to see encouraging results that suggest a positive outlook for CSC-targeting approaches.

Fibroblasts-dependent invasion of podoplanin-positive cancer stem cells in squamous cell carcinoma

To clear whether podoplanin-positive cancer stem cells in squamous cell carcinoma have higher invasion activity during a fibroblasts-dependent invasion. A collagen gel invasion assay was performed using fluorescent ubiquitination-based cell cycle indicator-labeled A431 cells. The total number and number of invading cells in S/G2/M phase were counted using time-lapse imaging cocultured with fibroblasts. There was no significant difference between the number of invading podoplanin-positive and negative A431 cells when fibroblasts did not exist. On the contrary, the number of invading podoplanin-positive cells was significantly higher when fibroblasts existed. The frequency of cells in S/G2/M phase among invasion was no difference. Knockdown of podoplanin decreased the number of invaded A431 cells significantly when fibroblasts existed. Podoplanin-positive A431 cells display higher invasion activity when fibroblasts exist, suggesting that some biological functions of cancer stem cells might become evident only within the fibrous tumor microenvironment.

Integrin α6 (CD49f), The Microenvironment and Cancer Stem Cells

Cancer is a highly prevalent and potentially terminal disease that affects millions of individuals worldwide. Here, we review the literature exploring the intricacies of stem cells bearing tumorigenic characteristics and collect evidence demonstrating the importance of integrin α6 (ITGA6, also known as CD49f) in cancer stem cell (CSC) activity. ITGA6 is commonly used to identify CSC populations in various tissues and plays an important role sustaining the self-renewal of CSCs by interconnecting them with the tumorigenic microenvironment.

Long Non-Coding RNA in the Pathogenesis of Cancers

The incidence and mortality rate of cancer has been quickly increasing in the past decades. At present, cancer has become the leading cause of death worldwide. Most of the cancers cannot be effectively diagnosed at the early stage. Although there are multiple therapeutic treatments, including surgery, radiotherapy, chemotherapy, and targeted drugs, their effectiveness is still limited. The overall survival rate of malignant cancers is still low. It is necessary to further study the mechanisms for malignant cancers, and explore new biomarkers and targets that are more sensitive and effective for early diagnosis, treatment, and prognosis of cancers than traditional biomarkers and methods. Long non-coding RNAs (lncRNAs) are a class of RNA transcripts with a length greater than 200 nucleotides. Generally, lncRNAs are not capable of encoding proteins or peptides. LncRNAs exert diverse biological functions by regulating gene expressions and functions at transcriptional, translational, and post-translational levels. In the past decade, it has been demonstrated that the dysregulated lncRNA profile is widely involved in the pathogenesis of many diseases, including cancer, metabolic disorders, and cardiovascular diseases. In particular, lncRNAs have been revealed to play an important role in tumor growth and metastasis. Many lncRNAs have been shown to be potential biomarkers and targets for the diagnosis and treatment of cancers. This review aims to briefly discuss the latest findings regarding the roles and mechanisms of some important lncRNAs in the pathogenesis of certain malignant cancers, including lung, breast, liver, and colorectal cancers, as well as hematological malignancies and neuroblastoma.

Sulforaphane Suppresses the Growth of Triple-negative Breast Cancer Stem-like Cells In vitro and In vivo

Triple-negative breast cancer (TNBC) represents the poorest prognosis among all of breast cancer subtypes with no currently available effective therapy. In this study, we hypothesized that sulforaphane, a dietary component abundant in broccoli and its sprouts, can inhibit malignant cell proliferation and tumor sphere formation of cancer stem-like cells (CSC) in TNBC. CSC population was isolated using FACS analysis with the combined stem cell surface markers, CD44⁺/CD24^-/CD49f⁺ The effect of sulforaphane on a stem-related embryonic oncogene CRIPTO-1/TDGF1 (CR1) was evaluated via ELISA. In vivo, BalbC/nude mice were supplemented with sulforaphane before and after TNBC cell inoculation (daily intraperitoneal injection of 50 mg sulforaphane/kg for 5 and 3 weeks, respectively), and the effects of sulforaphane during mammary tumor initiation and growth were accessed with NanoString gene analysis. We found that sulforaphane can inhibit cell proliferation and mammosphere formation of CSCs in TNBC. Further analysis of gene expression in these TNBC tumor cells revealed that sulforaphane significantly decreases the expression of cancer-specific CR1, CRIPTO-3/TDGF1P3 (CR3, a homologue of CR1), and various stem cell markers including Nanog, aldehyde dehydrogenase 1A1 (ALDH1A1), Wnt3, and Notch4. Our results suggest that sulforaphane may control the malignant proliferation of CSCs in TNBC via Cripto-mediated pathway by either suppressing its expression and/or by inhibiting Cripto/Alk4 protein complex formation. Thus, the use of sulforaphane for chemoprevention of TNBC is plausible and warrants further clinical evaluation.

Unraveling the journey of cancer stem cells from origin to metastasis

Cancer biology research over recent decades has given ample evidence for the existence of self-renewing and drug-resistant populations within heterogeneous tumors, widely recognized as cancer stem cells (CSCs). However, a lack of clear understanding about the origin, existence, maintenance, and metastatic roles of CSCs limit efforts towards the development of CSC-targeted therapy. In this review, we describe novel avenues of current CSC biology. In addition to cell fusion and horizontal gene transfer, CSCs are originated by mutations in somatic or differentiated cancer cells, resulting in de-differentiation and reprogramming. Recent studies also provided evidence for the existence of distinct or heterogeneous CSC populations within a single heterogeneous tumor. Our analysis of the literature also opens the doors for a novel hypothesis that CSC populations with specific phenotypes, metabolic profiles, and clonogenic potential metastasize to specific organs.

BRCA1 haploinsufficiency cell-autonomously activates RANKL expression and generates denosumab-responsive breast cancer-initiating cells

Denosumab, a monoclonal antibody to the receptor activator of nuclear factor-κB ligand (RANKL), might be a novel preventative therapy for BRCA1-mutation carriers at high risk of developing breast cancer. Beyond its well-recognized bone-targeted activity impeding osteoclastogenesis, denosumab has been proposed to interfere with the cross-talk between RANKL-producing sensor cells and cancer-initiating RANK+ responder cells that reside within premalignant tissues of BRCA1-mutation carriers. We herein tested the alternative but not mutually exclusive hypothesis that BRCA1 deficiency might cell-autonomously activate RANKL expression to generate cellular states with cancer stem cell (CSC)-like properties. Using isogenic pairs of normal-like human breast epithelial cells in which the inactivation of a single BRCA1 allele results in genomic instability, we assessed the impact of BRCA1 haploinsufficiency on the expression status of RANK and RANKL. RANK expression remained unaltered but RANKL was dramatically up-regulated in BRCA1mut/+ haploinsufficient cells relative to isogenic BRCA1+/+ parental cells. Neutralizing RANKL with denosumab significantly abrogated the ability of BRCA1 haploinsufficient cells to survive and proliferate as floating microtumors or "mammospheres" under non-adherent/non-differentiating conditions, an accepted surrogate of the relative proportion and survival of CSCs. Intriguingly, CSC-like states driven by epithelial-to-mesenchymal transition or HER2 overexpression traits responded to some extent to denosumab. We propose that breast epithelium-specific mono-allelic inactivation of BRCA1 might suffice to cell-autonomously generate RANKL-addicted, denosumab-responsive CSC-like states. The convergent addiction to a hyperactive RANKL/RANK axis of CSC-like states from genetically diverse breast cancer subtypes might inaugurate a new era of cancer prevention and treatment based on denosumab as a CSC-targeted agent.

Tumor-associated myoepithelial cells promote the invasive progression of ductal carcinoma in situ through activation of TGFβ signaling

The normal myoepithelium has a tumor-suppressing nature and inhibits the progression of ductal carcinoma in situ (DCIS) into invasive ductal carcinoma (IDC). Conversely, a growing number of studies have shown that tumor-associated myoepithelial cells have a tumor-promoting effect. Moreover, the exact role of tumor-associated myoepithelial cells in the DCIS-to-IDC development remains undefined. To address this, we explored the role of tumor-associated myoepithelial cells in the DCIS-to-IDC progression. We developed a direct coculture system to study the cell-cell interactions between DCIS cells and tumor-associated myoepithelial cells. Coculture studies indicated that tumor-associated myoepithelial cells promoted the invasive progression of a DCIS cell model in vitro, and mechanistic studies revealed that the interaction with DCIS cells stimulated tumor-associated myoepithelial cells to secrete TGFβ1, which subsequently contributed to activating the TGFβ/Smads pathway in DCIS cells. We noted that activation of the TGFβ signaling pathway promoted the epithelial-mesenchymal transition, basal-like phenotypes, stemness, and invasiveness of DCIS cells. Importantly, xenograft studies further demonstrated that tumor-associated myoepithelial cells enhanced the DCIS-to-IDC progression in vivo Furthermore, we found that TGFβ-mediated induction of oncogenic miR-10b-5p expression and down-regulation of RB1CC1, a miR-10b-5p-targeted tumor-suppressor gene, contributed to the invasive progression of DCIS. Our findings provide the first experimental evidence to directly support the paradigm that altered DCIS-associated myoepithelial cells promote the invasive progression of DCIS into IDC via TGFβ signaling activation.

A High-Fat Diet Promotes Mammary Gland Myofibroblast Differentiation through MicroRNA 140 Downregulation

Human breast adipose tissue is a heterogeneous cell population consisting of mature white adipocytes, multipotent mesenchymal stem cells, committed progenitor cells, fibroblasts, endothelial cells, and immune cells. Dependent on external stimulation, adipose-derived stem cells differentiate along diverse lineages into adipocytes, chondrocytes, osteoblasts, fibroblasts, and myofibroblasts. It is currently not fully understood how a high-fat diet reprograms adipose-derived stem cells into myofibroblasts. In our study, we used mouse models of a regular diet and of high-fat-diet-induced obesity to investigate the role of dietary fat on myofibroblast differentiation in the mammary stromal microenvironment. We found that a high-fat diet promotes myofibroblast differentiation by decreasing microRNA 140 (miR-140) expression in mammary adipose tissue through a novel negative-feedback loop. Increased transforming growth factor β1 (TGF-β1) in mammary adipose tissue in obese mice activates SMAD3 signaling, causing phospho-SMAD3 to bind to the miR-140 locus and inhibit miR-140 transcription. This prevents miR-140 from targeting SMAD3 for degradation, resulting in amplified TGF-β1/SMAD3 signaling and miR-140 downregulation-dependent myofibroblast differentiation. Using tissue and coculture models, we found that myofibroblasts and the fibrotic microenvironment created by myofibroblasts impact the stemness and proliferation of normal ductal epithelial cells and early-stage breast cancer invasion and stemness.

Dysregulation of the BRCA1/long non-coding RNA NEAT1 signaling axis contributes to breast tumorigenesis

Dysregulation of long non-codng RNA (lncRNA) expression has been found to contribute to tumorigenesis. However, the roles of lncRNAs in BRCA1-related breast cancer remain largely unknown. In this study, we delineate the role of the novel BRCA1/lncRNA NEAT1 signaling axis in breast tumorigenesis. BRCA1 inhibits NEAT1 expression potentially through binding to its genomic binding site upstream of the NEAT1 gene. BRCA1 deficiency in human normal/cancerous breast cells and mouse mammary glands leads to NEAT1 overexpression. Our studies show that NEAT1 upregulation resulting from BRCA1 deficiency stimulates in vitro and in vivo breast tumorigenicity. We have further identified molecular mediators downstream of the BRCA1/NEAT1 axis. NEAT1 epigenetically silences miR-129-5p expression by promoting the DNA methylation of the CpG island in the miR-129 gene. Silencing of miR-129-5p expression by NEAT1 results in upregulation of WNT4 expression, a target of miR-129-5p, which leads to activation of oncogenic WNT signaling. Our functional studies indicate that this NEAT1/miR-129-5p/WNT4 axis contributes to the tumorigenic effects of BRCA1 deficiency. Finally our in silico expression correlation analysis suggests the existence of the BRCA1/NEAT1/miR-129-5p axis in breast cancer. Our findings, taken together, suggest that the dysregulation of the BRCA1/NEAT1/miR-129-5p/WNT4 signaling axis is involved in promoting breast tumorigenesis.