Maintenance of retinal stem cells by Abcg2 is regulated by notch signaling

Phytochemical intervention in BCRP-driven cancer drug resistance: A comprehensive review

Drug resistance (DR) remains a significant challenge in cancer treatment, accounting for over 90 % of cancer-related deaths. Multidrug resistance (MDR) complicates chemotherapy by enabling cancer cells to evade therapeutic agents. This review focuses on the role of ATP-binding cassette (ABC) transporters, particularly the breast cancer resistance protein (BCRP), in mediating drug resistance. BCRP functions as a drug efflux pump, actively transporting chemotherapeutic agents out of cancer cells, thereby reducing their efficacy. The regulation of BCRP is influenced by various signaling pathways, including PI3K/AKT, MAPK/ERK, NF-κB, and Wnt/β-catenin, all of which collectively enhance its expression and contribute to the MDR phenotype. Recent studies have highlighted the potential of phytochemical-based strategies to reverse drug resistance by inhibiting these transporters. Compounds such as tetrandrine and resveratrol have shown promise in sensitizing drug-resistant cancer cells. Understanding the complex interplay between BCRP regulation and these signaling pathways is essential for the development of effective therapeutic strategies to counteract cancer. Targeting multiple pathways or employing combination therapies may offer new avenues to overcome MDR and improve treatment outcomes for cancer patients.

Canonical and noncanonical NOTCH signaling in the nongenetic resistance of cancer: distinct and concerted control

Therapeutic resistance in cancer is responsible for numerous cancer deaths in clinical practice. While target mutations are well recognized as the basis of genetic resistance to targeted therapy, nontarget mutation resistance (or nongenetic resistance) remains poorly characterized. Despite its complex and unintegrated mechanisms in the literature, nongenetic resistance is considered from our perspective to be a collective response of innate or acquired resistant subpopulations in heterogeneous tumors to therapy. These subpopulations, e.g., cancer stem-like cells, cancer cells with epithelial-to-mesenchymal transition, and drug-tolerant persisters, are protected by their resistance traits at cellular and molecular levels. This review summarizes recent advances in the research on resistant populations and their resistance traits. NOTCH signaling, as a central regulator of nongenetic resistance, is discussed with a special focus on its canonical maintenance of resistant cancer cells and noncanonical regulation of their resistance traits. This novel view of canonical and noncanonical NOTCH signaling pathways is translated into our proposal of reshaping therapeutic strategies targeting NOTCH signaling in resistant cancer cells. We hope that this review will lead researchers to study the canonical and noncanonical arms of NOTCH signaling as an integrated resistant mechanism, thus promoting the development of innovative therapeutic strategies.

Cancer stem cells: advances in knowledge and implications for cancer therapy

Cancer stem cells (CSCs), a small subset of cells in tumors that are characterized by self-renewal and continuous proliferation, lead to tumorigenesis, metastasis, and maintain tumor heterogeneity. Cancer continues to be a significant global disease burden. In the past, surgery, radiotherapy, and chemotherapy were the main cancer treatments. The technology of cancer treatments continues to develop and advance, and the emergence of targeted therapy, and immunotherapy provides more options for patients to a certain extent. However, the limitations of efficacy and treatment resistance are still inevitable. Our review begins with a brief introduction of the historical discoveries, original hypotheses, and pathways that regulate CSCs, such as WNT/β-Catenin, hedgehog, Notch, NF-κB, JAK/STAT, TGF-β, PI3K/AKT, PPAR pathway, and their crosstalk. We focus on the role of CSCs in various therapeutic outcomes and resistance, including how the treatments affect the content of CSCs and the alteration of related molecules, CSCs-mediated therapeutic resistance, and the clinical value of targeting CSCs in patients with refractory, progressed or advanced tumors. In summary, CSCs affect therapeutic efficacy, and the treatment method of targeting CSCs is still difficult to determine. Clarifying regulatory mechanisms and targeting biomarkers of CSCs is currently the mainstream idea.

Progress of Cancer Stem Cells in Retinoblastoma

The theory of cancer stem cells is a breakthrough discovery that offers exciting possibilities for comprehending the biological behavior of tumors. More and more evidence suggests that retinoblastoma cancer stem cells promote tumor growth and are likely to be the origin of tumor formation, drug resistance, recurrence, and metastasis. At present, some progress has been made in the verification, biological behavior, and drug resistance mechanism of retinoblastoma cancer stem cells. This article aims to review the relevant research and explore future development direction.

OGG1 competitive inhibitors show important off-target effects by directly inhibiting efflux pumps and disturbing mitotic progression

One of the most abundant DNA lesions induced by Reactive oxygen species (ROS) is 8-oxoG, a highly mutagenic lesion that compromises genetic instability when not efficiently repaired. 8-oxoG is specifically recognized by the DNA-glycosylase OGG1 that excises the base and initiates the Base Excision Repair pathway (BER). Furthermore, OGG1 has not only a major role in DNA repair but it is also involved in transcriptional regulation. Cancer cells are particularly exposed to ROS, thus challenging their capacity to process oxidative DNA damage has been proposed as a promising therapeutic strategy for cancer treatment. Two competitive inhibitors of OGG1 (OGG1i) have been identified, TH5487 and SU0268, which bind to the OGG1 catalytic pocket preventing its fixation to the DNA. Early studies with these inhibitors show an enhanced cellular sensitivity to cytotoxic drugs and a reduction in the inflammatory response. Our study uncovers two unreported off-targets effects of these OGG1i that are independent of OGG1. In vitro and in cellulo approaches have unveiled that OGG1i TH5487 and SU0268, despite an unrelated molecular structure, are able to inhibit some members of the ABC family transporters, in particular ABC B1 (MDR1) and ABC G2 (BCRP). The inhibition of these efflux pumps by OGG1 inhibitors results in a higher intra-cellular accumulation of various fluorescent probes and drugs, and largely contributes to the enhanced cytotoxicity observed when the inhibitors are combined with cytotoxic agents. Furthermore, we found that SU0268 has an OGG1-independent anti-mitotic activity-by interfering with metaphase completion-resulting in a high cellular toxicity. These two off-target activities are observed at concentrations of OGG1i that are normally used for in vivo studies. It is thus critical to consider these previously unreported non-specific effects when interpreting studies using TH5487 and SU0268 in the context of OGG1 inhibition. Additionally, our work highlights the persistent need for new specific inhibitors of the enzymatic activity of OGG1.

Cell trajectory modeling identifies a primitive trophoblast state defined by BCAM enrichment

In early placental development, progenitor cytotrophoblasts (CTB) differentiate along one of two cellular trajectories: the villous or extravillous pathways. CTB committed to the villous pathway fuse with neighboring CTB to form the outer multinucleated syncytiotrophoblast (SCT), whereas CTB committed to the extravillous pathway differentiate into invasive extravillous trophoblasts (EVT). Unfortunately, little is known about the processes controlling human CTB progenitor maintenance and differentiation. To address this, we established a single cell RNA sequencing (scRNA-seq) dataset from first trimester placentas to identify cell states important in trophoblast progenitor establishment, renewal and differentiation. Multiple distinct trophoblast states were identified, representing progenitor CTB, column CTB, SCT precursors and EVT. Lineage trajectory analysis identified a progenitor origin that was reproduced in human trophoblast stem cell organoids. Heightened expression of basal cell adhesion molecule (BCAM) defined this primitive state, where BCAM enrichment or gene silencing resulted in enhanced or diminished organoid growth, respectively. Together, this work describes at high-resolution trophoblast heterogeneity within the first trimester, resolves gene networks within human CTB progenitors and identifies BCAM as a primitive progenitor marker and possible regulator.

A microfluidic platform enables comprehensive gene expression profiling of mouse retinal stem cells

Loss of photoreceptors due to retinal degeneration is a major cause of untreatable visual impairment and blindness. Cell replacement therapy, using retinal stem cell (RSC)-derived photoreceptors, holds promise for reconstituting damaged cell populations in the retina. One major obstacle preventing translation to the clinic is the lack of validated markers or strategies to prospectively identify these rare cells in the retina and subsequently enrich them. Here, we introduce a microfluidic platform that combines nickel micromagnets, herringbone structures, and a design enabling varying flow velocities among three compartments to facilitate a highly efficient enrichment of RSCs. In addition, we developed an affinity enrichment strategy based on cell-surface markers that was utilized to isolate RSCs from the adult ciliary epithelium. We showed that targeting a panel of three cell surface markers simultaneously facilitates the enrichment of RSCs to 1 : 3 relative to unsorted cells. Combining the microfluidic platform with single-cell whole-transcriptome profiling, we successfully identified four differentially expressed cell surface markers that can be targeted simultaneously to yield an unprecedented 1 : 2 enrichment of RSCs relative to unsorted cells. We also identified transcription factors (TFs) that play functional roles in maintenance, quiescence, and proliferation of RSCs. This level of analysis for the first time identified a spectrum of molecular and functional properties of RSCs.

Multidrug efflux transporter ABCG2: expression and regulation

The adenosine triphosphate (ATP)-binding cassette efflux transporter G2 (ABCG2) was originally discovered in a multidrug-resistant breast cancer cell line. Studies in the past have expanded the understanding of its role in physiology, disease pathology and drug resistance. With a widely distributed expression across different cell types, ABCG2 plays a central role in ATP-dependent efflux of a vast range of endogenous and exogenous molecules, thereby maintaining cellular homeostasis and providing tissue protection against xenobiotic insults. However, ABCG2 expression is subjected to alterations under various pathophysiological conditions such as inflammation, infection, tissue injury, disease pathology and in response to xenobiotics and endobiotics. These changes may interfere with the bioavailability of therapeutic substrate drugs conferring drug resistance and in certain cases worsen the pathophysiological state aggravating its severity. Considering the crucial role of ABCG2 in normal physiology, therapeutic interventions directly targeting the transporter function may produce serious side effects. Therefore, modulation of transporter regulation instead of inhibiting the transporter itself will allow subtle changes in ABCG2 activity. This requires a thorough comprehension of diverse factors and complex signaling pathways (Kinases, Wnt/β-catenin, Sonic hedgehog) operating at multiple regulatory levels dictating ABCG2 expression and activity. This review features a background on the physiological role of transporter, factors that modulate ABCG2 levels and highlights various signaling pathways, molecular mechanisms and genetic polymorphisms in ABCG2 regulation. This understanding will aid in identifying potential molecular targets for therapeutic interventions to overcome ABCG2-mediated multidrug resistance (MDR) and to manage ABCG2-related pathophysiology.

ATP-binding cassette (ABC) transporters in cancer: A review of recent updates

The ATP-binding cassette (ABC) transporter superfamily is one of the largest membrane protein families existing in wide spectrum of organisms from prokaryotes to human. ABC transporters are also known as efflux pumps because they mediate the cross-membrane transportation of various endo- and xenobiotic molecules energized by ATP hydrolysis. Therefore, ABC transporters have been considered closely to multidrug resistance (MDR) in cancer, where the efflux of structurally distinct chemotherapeutic drugs causes reduced itherapeutic efficacy. Besides, ABC transporters also play other critical biological roles in cancer such as signal transduction. During the past decades, extensive efforts have been made in understanding the structure-function relationship, transportation profile of ABC transporters, as well as the possibility to overcome MDR via targeting these transporters. In this review, we discuss the most recent knowledge regarding ABC transporters and cancer drug resistance in order to provide insights for the development of more effective therapies.

Overexpressing microRNA-34a overcomes ABCG2-mediated drug resistance to 5-FU in side population cells from colon cancer via suppressing DLL1

Colon cancer side population (SP) cells are a small subset of cancer cells that have cancer stemness capacity and enhanced drug resistance. ABCG2 is a multidrug resistance-related protein in SP cells and has been demonstrated to be regulated by Notch signalling pathway. Recently, microRNAs are reported to play a critical role in SP cell fate. However, their role in ABCG2-mediated drug resistance in colon cancer SP cells remains unclear. In the current study, the different expressions of miR-552, miR-611, miR-34a and miR-5000-3p were compared within SP and non-SP cells, which were separated from human colon cancer cell lines (SW480 and LoVo). We found that miR-34a was significantly down-regulated in SP cells and that overexpressing miR-34a overcame drug resistance to 5-fluorouracil (5-FU). The luciferase reporter assay indicated that miR-34a negatively regulated DLL1, a ligand of Notch signalling pathway, via binding with 3'-untranslated region of its messenger RNA. In addition, overexpressing miR-34a overcame ABCG2-mediated resistance to 5-FU via DLL1/Notch pathway in vitro, and suppressed tumour growth under 5-FU treatment in vivo. In conclusion, our findings suggest that miR-34a acts as a tumour suppressor via enhancing chemosensitivity to 5-FU in SP cells, which provides a novel therapeutic target in chemotherapy-resistant colon cancer.

Cancer and Alzheimer's disease inverse relationship: an age-associated diverging derailment of shared pathways

Several epidemiological studies show an inverse association between cancer and Alzheimer's disease (AD). It is debated whether this association is the consequence of biological mechanisms shared by both these conditions or may be related to the pharmacological treatments carried out on the patients. The latter hypothesis, however, is not sustained by the available evidence. Hence, the focus of this review is to analyze common biological mechanisms for both cancer and AD and to build up a biological theory useful to explain the inverse correlation between AD and cancer. The review proposes a hypothesis, according to which several molecular players, prominently PIN1 and p53, have been investigated and considered involved in complex molecular interactions putatively associated with the inverse correlation. On the other hand, p53 involvement in both diseases seems to be a consequence of the aberrant activation of other proteins. Instead, PIN1 may be identified as a novel key regulator at the crossroad between cancer and AD. PIN1 is a peptidyl-prolyl cis-trans isomerase that catalyzes the cis-trans isomerization, thus regulating the conformation of different protein substrates after phosphorylation and modulating protein function. In particular, trans-conformations of Amyloid Precursor Protein (APP) and tau are functional and "healthy", while cis-conformations, triggered after phosphorylation, are pathogenic. As an example, PIN1 accelerates APP cis-to-trans isomerization thus favoring the non-amyloidogenic pathway, while, in the absence of PIN1, APP is processed through the amyloidogenic pathway, thus predisposing to neurodegeneration. Furthermore, a link between PIN1 and tau regulation has been found, since when PIN1 function is inhibited, tau is hyperphosphorylated. Data from brain specimens of subjects affected by mild cognitive impairment and AD have revealed a very low PIN1 expression. Moreover, polymorphisms in PIN1 promoter correlated with an increased PIN1 expression are associated with a delay of sporadic AD age of onset, while a polymorphism related to a reduced PIN1 expression is associated with a decreased risk of multiple cancers. In the case of dementias, in particular of Alzheimer's disease, new biological markers and targets based on the discussed players can be developed based on a theoretical approach relying on different grounds compared to the past. An unbiased expansion of the rationale and of the targets may help to achieve in the field of neurodegenerative dementias similar advances to those attained in the case of cancer treatment.

The Antitumor Natural Compound Falcarindiol Disrupts Neural Stem Cell Homeostasis by Suppressing Notch Pathway

Neural stem cells (NSCs) are undifferentiated, multi-potent cells that can give rise to functional neurons and glial cells. The disruption in NSC homeostasis and/or the impaired neurogenesis lead to diverse neurological diseases, including depression, dementia, and neurodegenerative disorders. Falcarindiol (FAD) is a polyacetylene found in many plants, and FAD shows the cytotoxicity against breast cancers and colon cancers. However, there is no research on the consequence of FAD treatment in normal stem cells. Here, we suggest that FAD has anticancer roles against glioblastoma cells by inducing the differentiation of glioblastoma stem-like cells, as well as activating apoptosis pathway in glioblastoma cells. On the other hand, we also show that FAD has detrimental effects by disrupting the maintenance of normal NSCs and altering the balance between self-renewal and differentiation of NSCs.

A role for ABCG2 beyond drug transport: Regulation of autophagy

The ABC drug transporters, including ABCG2, are well known for their ability to efflux a wide spectrum of chemotherapeutic agents, thereby conferring a multidrug-resistant phenotype. However, studies over the past several years suggest that the ABC transporters may play additional role(s) in cell survival in the face of stress inducers that are not ABCG2 substrates (i.e., nutrient deprivation, ionizing radiation, rapamycin). The mechanism by which this occurs is largely unknown. In the present study, using several cancer cell lines and their ABCG2-overexpressing sublines, we show that cells overexpressing ABCG2 were more resistant to these stressors. This resistance was associated with an elevated level of autophagy flux, as measured by a higher rate of SQSTM1/p62 degradation and greater accumulation of LC3-II when compared to parental cells. Knockdown of ABCG2 reduced autophagic activity in resistant cells to a level similar to that observed in parental cells, confirming that the enhanced autophagy was ABCG2-dependent. Moreover, using cell viability, apoptosis, and clonogenic assays, we demonstrated that the ABCG2-expressing cells were more resistant to amino acid starvation and radiation-induced cell death. Importantly, knockdown of the critical autophagy factors ATG5 and ATG7 greatly reduced cell survival, verifying that enhanced autophagy was critical for this effect. Taken together, these data indicate that autophagy induced by various stressors is enhanced/accelerated in the presence of ABCG2, resulting in delayed cell death and enhanced cell survival. This defines a new role for this transporter, one with potential clinical significance.

Cultivation and characterization of pterygium as an ex vivo study model for disease and therapy

PURPOSE

Development of ex vivo model to study pathogenesis, inflammation and treatment modalities for pterygium.

METHODS

Pterygium obtained from surgery was cultivated (3 months). Gravitational attachment method using viscoelastic facilitated adherence of graft and outgrowing cells. Medium contained serum as the only growth supplement with no use of scaffolds. Surface profiling of the multi-layered cells for hematopoietic- and mesenchymal stem cell markers was performed. Examination of cells by immunohistochemistry using pluripotency, oxidative stress, stemness, migration and proliferation, epithelial and secretory markers was performed. The effect of anti-proliferative agent Mitomycin C upon secretion of pro-inflammatory cytokines IL-6 and IL-8 was assessed.

RESULTS

Cells showed high expression of migration- (CXCR4), secretory- (MUC1, MUC4) and oxidative damage- (8-OHdG) markers, and low expression of hypoxia- (HIF-1α) and proliferation- (Ki-67) markers. Moderate and low expression of the pluripotency markers (Vimentin and ΔNp63) was present, respectively, while the putative markers of stemness (Sox2, Oct4, ABCG-2) and epithelial cell markers- (CK19, CK8-18) were weak. The surface marker profile of the outgrowing cells revealed high expression of the hematopoietic marker CD47, mesenchymal markers CD90 and CD73, minor or less positivity for the hematopoietic marker CD34, mesenchymal marker CD105, progenitor marker CD117 and attachment protein markers while low levels of IL-6 and IL-8 secretion ex vivo, were inhibited upon Mitomycin C treatment.

CONCLUSION

Ex vivo tissue engineered pterygium consists of a mixture of cells of different lineage origin, suitable for use as a disease model for studying pathogenesis ex vivo, while opening possibilities for new treatment and prevention modalities.

Expression and function of ABCG2 and XIAP in glioblastomas

Despite multimodal treatment that includes surgery, radiation and chemotherapy, virtually all glioblastomas (GBM) recur, indicating that these interventions are insufficient to eradicate all malignant cells. To identify potential new therapeutic targets in GBMs, we examined the expression and function of proteins that are associated with therapy resistance and cancer cell survival. We measured the expression of eight such proteins in 50 GBM samples by immunohistochemistry and analyzed patient survival. We report that GBM patients with high expression of ABCG2 (also called BCRP) or XIAP at the protein level had worse survival than those with low expression. The adjusted hazard ratio for ABCG2 was 2.35 and for XIAP was 2.65. Since glioma stem cells (GSCs) have been shown to be more resistant than bulk tumor cells to anti-cancer therapies and to express high levels of these proteins, we also sought to determine if ABCG2 and XIAP have functional roles in GSCs. We used small molecule inhibitors to treat patient-derived GBM tumorspheres in vitro and observed that inhibitors of ABCG2, Ko143 and fumitremorgin, significantly reduced self-renewal. These results suggest that ABCG2 and XIAP proteins may be useful indicators of patient survival and that inhibition of ABCG2 may be a promising therapeutic strategy in GBMs.

NOTCH1 Signaling Regulates Self-Renewal and Platinum Chemoresistance of Cancer Stem-like Cells in Human Non-Small Cell Lung Cancer

Cancer stem-like cells (CSC) are thought to drive tumor initiation, metastasis, relapse, and therapeutic resistance, but their specific pathogenic characters in many cancers, including non-small cell lung cancer (NSCLC), have yet to be well defined. Here, we develop findings that the growth factor HGF promotes CSC sphere formation in NSCLC cell populations. In patient-derived sphere-forming assays (PD-SFA) with HGF, CD49f and CD104 were defined as novel markers of lung CSC (LCSC). In particular, we isolated a subpopulation of CD166⁺CD49f^hiCD104^-Lin^- LCSC present in all human specimens of NSCLC examined, regardless of their histologic subtypes or genetic driver mutations. This specific cell population was tumorigenic and capable of self-renewal, giving rise to tumor spheres in vitro and orthotopic lung tumors in immune-compromised mice. Mechanistic investigations established that NOTCH1 was preferentially expressed in this cell subpopulation and required for self-renewal via the transcription factor HES1. Through a distinct HES1-independent pathway, NOTCH1 also protected LCSCs from cisplatin-induced cell death. Notably, treatment with a γ-secretase inhibitor that blunts NOTCH1 function ablated self-renewing LCSC activity and restored platinum sensitivity in vitro and in vivo Overall, our results define the pathogenic characters of a cancer stem-like subpopulation in lung cancer, the targeting of which may relieve platinum resistance in this disease. Cancer Res; 77(11); 3082-91. ©2017 AACR.

ABCG2-overexpressing H460/MX20 cell xenografts in athymic nude mice maintained original biochemical and cytological characteristics

H460/MX20 are derived from large cell lung cancer H460 cell line and then transformed into ABCG2-overexpressing cells by mitoxantrone’s induction, which are widely used in study of multidrug resistance (MDR) in vitro. To establish and spread the model of H460/MX20 cell xenografts, we investigated whether cell biological characteristics and the MDR phenotype were maintained in vivo model. Our results demonstrated that the cell proliferation, cell cycle, and ABCG2 expression level in xH460/MX20 cells isolated from H460/MX20 cell xenografts were similar to H460/MX20 cells in vitro. Importantly, xH460/MX20 cells exhibited high levels of resistance to ABCG2 substrates such as mitoxantrone and topotecan as H460/MX20 cells did. Furthermore, lapatinib, the inhibitor of ABCG2, potently reversed mitoxantrone- and topotecan-resistance of xH460/MX20 cells. Taken together, these results suggest that H460/MX20 cell xenografts in athymic nude mice still retain their original cytological characteristics and MDR phenotype. Thus, the H460/MX20 cell xenografts model could serve as a sound model in vivo for study on reversal MDR.

Role of miR-223/paired box 6 signaling in temozolomide chemoresistance in glioblastoma multiforme cells

Glioblastoma (GBM) is the predominant and most fatal type of brain tumor in adults. The prognosis of GBM remains poor despite advances in surgery, chemotherapy and radiotherapy. It is common that patients with GBM exhibit innate or acquired resistance to temozolomide (TMZ), a standard chemotherapeutic agent for GBM, and a previous report demonstrated that miRNA‑233 (miR‑223) promotes the growth and invasion of GBM cells by targeting tumor suppressor paired box 6 (PAX6). The present study explored the effect of TMZ on miR‑223/PAX6 signaling in addition to the effect of miR‑223/PAX6 signaling on TMZ chemoresistance in human GBM cells. Luciferase reporter assays confirmed that miR‑223 directly targets PAX6 through binding to its 3'‑untranslated region. TMZ reduced the expression level of miR‑223 in a concentration‑dependent manner in U251 and U118 GBM cells, which led to increased expression of PAX6. miR‑223 and/or PAX6 were overexpressed and knocked down in U251 and U118 cells, and the half maximal inhibitory concentration (IC50) of TMZ and cell proliferation under TMZ treatment were used as measures of TMZ chemoresistance. The results demonstrated that overexpression of miR-223 in GBM cells markedly decreased TMZ-induced inhibition of cell proliferation and increased TMZ IC50, which could be abolished by overexpression of PAX6. On the other hand, knocking down miR‑223 in GBM cells with antagomir significantly enhanced the inhibitory effect of TMZ on GBM cell proliferation and decreased the TMZ IC50, which could be abolished by knockdown of PAX6. In conclusion, the present study demonstrated that TMZ inhibits GBM cell proliferation by inhibiting the expression of miR‑223, which leads to increased expression of tumor suppressor PAX6. Overexpression of miR‑223 increases TMZ chemoresistance, while inhibition of miR‑223 with antagomir markedly decreases TMZ chemoresistance in GBM cells. The present study provided novel insight into the molecular mechanisms underlying the pharmacological effects, in addition to the chemoresistance, of TMZ for GBM.

The Efflux Transporter ABCG2 Maintains Prostate Stem Cells

Prostate stem cells (PSC) are characterized by their intrinsic resistance to androgen deprivation therapy (ADT), possibly due to the lack of androgen receptor (AR) expression. PSCs resistance to ADT and PSC expansion in castration resistant prostate cancer (CRPC) has sparked great interest in using differentiation therapy as an adjuvant to ADT. Understanding the mechanisms, by which PSCs maintain their undifferentiated phenotype, thus has important implications in differentiation therapy. In the prostate, the ATP binding cassette sub-family G member 2 (ABCG2) transporters, which enrich for AR-positive, ADT-resistant PSCs, play an important role in regulating the intracellular androgen levels by effluxing androgens. We hypothesized that the ABCG2-mediated androgen efflux is responsible for maintaining PSCs in an undifferentiated state. Using the HPr-1-AR (nontumorigenic) and CWR-R1 (tumorigenic) prostate cell lines, it was demonstrated that inhibiting the ABCG2-mediated androgen efflux, with Ko143 (ABCG2 inhibitor), increased the nuclear AR expression due to elevated intracellular androgen levels. Increased nuclear translocation of AR is followed by increased expression of AR regulated genes, a delayed cell growth response, and increased luminal differentiation. Furthermore, Ko143 reduced tumor growth rates in mice implanted with ABCG2-expressing CWR-R1 cells. In addition, Ko143-treated mice had more differentiated tumors as evidenced by an increased percentage of CK8⁺/AR⁺ luminal cells and decreased percentage of ABCG2-expressing cells. Thus, inhibiting ABCG2-mediated androgen efflux forces the PSCs to undergo an AR-modulated differentiation to an ADT-sensitive luminal phenotype.

IMPLICATIONS

This study identifies the mechanism by which the prostate stem cell marker, ABCG2, plays a role in prostate stem cell maintenance and provides a rationale for targeting ABCG2 for differentiation therapy in prostate cancer. Mol Cancer Res; 15(2); 128-40. ©2016 AACR.

Ovarian Cancer Chemoresistance Relies on the Stem Cell Reprogramming Factor PBX1

The evolution of chemoresistance is a fundamental characteristic of cancer that ultimately hampers its clinical management. However, it may be possible to improve patient outcomes significantly by a better understanding of resistance mechanisms, which cancers rely upon during the evolution to an untreatable state. Here we report an essential role of the stem cell reprogramming factor, PBX1, in mediating chemoresistance in ovarian carcinomas. In the clinical setting, high levels of PBX1 expression correlated with shorter survival in post-chemotherapy ovarian cancer patients. In tumor cells with low endogenous levels of PBX1, its enforced expression promoted cancer stem cell-like phenotypes, including most notably an increase in resistance to platinum-based therapy used most commonly for treating this disease. Conversely, silencing PBX1 in platinum-resistant cells that overexpressed PBX1 sensitized them to platinum treatment and reduced their stem-like properties. An analysis of published genome-wide chromatin immunoprecipitation data indicated that PBX1 binds directly to promoters of genes involved in stem cell maintenance and the response to tissue injury. We confirmed direct regulation of one of these genes, STAT3, demonstrating that the PBX1 binding motif at its promoter acted to positively regulate STAT3 transcription. We further demonstrated that a STAT3/JAK2 inhibitor could potently sensitize platinum-resistant cells to carboplatin and suppress their growth in vivo Our findings offer a mechanistic rationale to target the PBX1/STAT3 axis to antagonize a key mechanism of chemoresistance in ovarian cancers and possibly other human cancers. Cancer Res; 76(21); 6351-61. ©2016 AACR.

The evolving landscape of prostate cancer stem cell: Therapeutic implications and future challenges

Prostate cancer (PCa) is the most common cause of malignancy in males and the second leading cause of cancer mortality in United States. Current treatments for PCa include surgery, radiotherapy, and androgen-deprivation therapy. Eventually, PCa relapses to an advanced castration-resistant PCa (CRPC) that becomes a systematic disease and incurable. Therefore, identifying cellular components and molecular mechanisms that drive aggressive PCa at early stage is critical for disease prognosis and therapeutic intervention. One potential strategy for aggressive PCa is to target cancer stem cells (CSCs) that are identified by several unique characteristics such as immortal, self-renewal, and pluripotency. Also, CSC is believed to be a major factor contributing to resistance to radiotherapy and conventional chemotherapies. Moreover, CSCs are thought to be the critical cause of metastasis, tumor recurrence and cancer-related death of multiple cancer types, including PCa. In this review, we discuss recent progress made in understanding prostate cancer stem cells (PCSCs). We focus on the therapeutic strategies aimed at targeting specific surface markers of CSCs, the key signaling pathways in the maintenance of self-renewal capacity of CSCs, ATP-binding cassette (ABC) transporters that mediate the drug-resistance of CSCs, dysregulated microRNAs expression profiles in CSCs, and immunotherapeutic strategies developed against PCSCs surface markers.

ABCG2 regulates self-renewal and stem cell marker expression but not tumorigenicity or radiation resistance of glioma cells

Glioma cells with stem cell traits are thought to be responsible for tumor maintenance and therapeutic failure. Such cells can be enriched based on their inherent drug efflux capability mediated by the ABC transporter ABCG2 using the side population assay, and their characteristics include increased self-renewal, high stem cell marker expression and high tumorigenic capacity in vivo. Here, we show that ABCG2 can actively drive expression of stem cell markers and self-renewal in glioma cells. Stem cell markers and self-renewal was enriched in cells with high ABCG2 activity, and could be specifically inhibited by pharmacological and genetic ABCG2 inhibition. Importantly, despite regulating these key characteristics of stem-like tumor cells, ABCG2 activity did not affect radiation resistance or tumorigenicity in vivo. ABCG2 effects were Notch-independent and mediated by diverse mechanisms including the transcription factor Mef. Our data demonstrate that characteristics of tumor stem cells are separable, and highlight ABCG2 as a potential driver of glioma stemness.

Function of Integrin-Linked Kinase in Modulating the Stemness of IL-6-Abundant Breast Cancer Cells by Regulating γ-Secretase-Mediated Notch1 Activation in Caveolae

Interleukin-6 (IL-6) and Notch signaling are important regulators of breast cancer stem cells (CSCs), which drive the malignant phenotype through self-renewal, differentiation, and development of therapeutic resistance. We investigated the role of integrin-linked kinase (ILK) in regulating IL-6–driven Notch1 activation and the ability to target breast CSCs through ILK inhibition. Ectopic expression/short hairpin RNA-mediated knockdown of ILK, pharmacological inhibition of ILK with the small molecule T315, Western blot analysis, immunofluorescence, and luciferase reporter assays were used to evaluate the regulation of IL-6–driven Notch1 activation by ILK in IL-6–producing triple-negative breast cancer cell lines (MDA-MB-231, SUM-159) and in MCF-7 and MCF-7^IL-6 cells. The effects of ILK on γ-secretase complex assembly and cellular localization were determined by immunofluorescence, Western blots of membrane fractions, and immunoprecipitation. In vivo effects of T315-induced ILK inhibition on CSCs in SUM-159 xenograft models were assessed by mammosphere assays, flow cytometry, and tumorigenicity assays. Results show that the genetic knockdown or pharmacological inhibition of ILK suppressed Notch1 activation and the abundance of the γ-secretase components presenilin-1, nicastrin, and presenilin enhancer 2 at the posttranscriptional level via inhibition of caveolin-1-dependent membrane assembly of the γ-secretase complex. Accordingly, knockdown of ILK inhibited breast CSC-like properties in vitro and the breast CSC subpopulation in vivo in xenograft tumor models. Based on these findings, we propose a novel function of ILK in regulating γ-secretase–mediated Notch1 activation, which suggests the targeting of ILK as a therapeutic approach to suppress IL-6–induced breast CSCs.

Cervical Cancer Stem Cells Selectively Overexpress HPV Oncoprotein E6 that Controls Stemness and Self-Renewal through Upregulation of HES1

PURPOSE

Perturbation of keratinocyte differentiation by E6/E7 oncoproteins of high-risk human papillomaviruses that drive oncogenic transformation of cells in squamocolumnar junction of the uterine cervix may confer "stem-cell like" characteristics. However, the crosstalk between E6/E7 and stem cell signaling during cervical carcinogenesis is not well understood. We therefore examined the role of viral oncoproteins in stem cell signaling and maintenance of stemness in cervical cancer.

EXPERIMENTAL DESIGN

Isolation and enrichment of cervical cancer stem-like cells (CaCxSLCs) was done from cervical primary tumors and cancer cell lines by novel sequential gating using a set of functional and phenotypic markers (ABCG2, CD49f, CD71, CD133) in defined conditioned media for assessing sphere formation and expression of self-renewal and stemness markers by FACS, confocal microscopy, and qRT-PCR. Differential expression level and DNA-binding activity of Notch1 and its downstream targets in CaCxSLCs as well as silencing of HPVE6/Hes1 by siRNA was evaluated by gel retardation assay, FACS, immunoblotting, and qRT-PCR followed by in silico and in vivo xenograft analysis.

RESULTS

CaCxSLCs showed spheroid-forming ability, expressed self-renewal and stemness markers Oct4, Sox2, Nanog, Lrig1, and CD133, and selectively overexpressed E6 and HES1 transcripts in both cervical primary tumors and cancer cell lines. The enriched CaCxSLCs were highly tumorigenic and did recapitulate primary tumor histology in nude mice. siRNA silencing of HPVE6 or Hes1 abolished sphere formation, downregulated AP-1-STAT3 signaling, and induced redifferentiation.

CONCLUSIONS

Our findings suggest the possible mechanism by which HPVE6 potentially regulate and maintain stem-like cancer cells through Hes1. Clin Cancer Res; 22(16); 4170-84. ©2016 AACR.

Long-Term Cultures of Human Cornea Limbal Explants Form 3D Structures Ex Vivo - Implications for Tissue Engineering and Clinical Applications

Long-term cultures of cornea limbal epithelial stem cells (LESCs) were developed and characterized for future tissue engineering and clinical applications. The limbal tissue explants were cultivated and expanded for more than 3 months in medium containing serum as the only growth supplement and without use of scaffolds. Viable 3D cell outgrowth from the explants was observed within 4 weeks of cultivation. The outgrowing cells were examined by immunofluorescent staining for putative markers of stemness (ABCG2, CK15, CK19 and Vimentin), proliferation (p63α, Ki-67), limbal basal epithelial cells (CK8/18) and differentiated cornea epithelial cells (CK3 and CK12). Morphological and immunostaining analyses revealed that long-term culturing can form stratified 3D tissue layers with a clear extracellular matrix deposition and organization (collagen I, IV and V). The LESCs showed robust expression of p63α, ABCG2, and their surface marker fingerprint (CD117/c-kit, CXCR4, CD146/MCAM, CD166/ALCAM) changed over time compared to short-term LESC cultures. Overall, we provide a model for generating stem cell-rich, long-standing 3D cultures from LESCs which can be used for further research purposes and clinical transplantation.

Endometrial side population cells: potential adult stem/progenitor cells in endometrium

Uterine endometrium is one of the most important organs for species preservation. However, the physiology of human endometrium remains poorly understood, because the human endometrium undergoes rapid and large changes during each menstrual cycle and it is very difficult to investigate human endometrium as one organ. This remarkable regenerative capacity of human endometrium strongly suggests the existence of adult stem cells, and physiology of endometrium cannot be explained without adult stem cells. Therefore, investigating endometrial stem/progenitor cells should lead to a breakthrough in understanding the normal endometrial physiology and the pathophysiology of endometrial neoplastic disorders, such as endometriosis and endometrial cancer. Several cell populations have been discovered as putative endometrial stem/progenitor cells. Emerging evidence reveals that the endometrial side population (SP) is one of the potential endometrial stem/progenitor populations. Of all the endometrial stem/progenitor cell candidates, the endometrial SP (ESP) is best investigated in vitro and in vivo, and has the largest number of references. In this review, we provide an overview of the accumulating evidence for the ESP cells, both directly from human endometria and from cultured endometrial cells. Furthermore, SP cells are compared to other potential stem/progenitor cells, and we discuss their stem cell properties. We also discuss the difficulties and unsolved issues in endometrial stem cell biology.

Downregulation of ABCG2 protein inhibits migration and invasion in U251 glioma stem cells

ABCG2 is a member of the ATP-binding cassette transporter family, which has been detected in a wide variety of human aggressive tumors, including glioma stem cells (GSCs), glioma tissues of higher grades, and implanted glioma xenografts. Previous research has implied that ABCG2 might be associated closely with invasion and spread in tumors. However, the specific roles and mechanisms of ABCG2 in regulating the migration and invasion of GSCs remain unclear. In this study, we aimed to identify the effects and mechanisms of ABCG2 on invasion by GSCs. Our results showed that downregulation of ABCG2 protein significantly inhibited the migration and invasion potentials of U251 GSCs. Further research on the underlying mechanism showed that the effects of ABCG2 downregulation on inhibiting the migration and invasion of U251 GSCs were through significantly decreasing the activity of matrix metalloproteinase-9, but not the expression of matrix metalloproteinase-9 protein. These findings show that ABCG2 plays an important role in regulating the migration and invasion of GSC, and represents a potential novel therapeutic agent to target the progression of GSCs.

Prolyl-isomerase Pin1 controls normal and cancer stem cells of the breast

Mammary epithelial stem cells are fundamental to maintain tissue integrity. Cancer stem cells (CSCs) are implicated in both treatment resistance and disease relapse, and the molecular bases of their malignant properties are still poorly understood. Here we show that both normal stem cells and CSCs of the breast are controlled by the prolyl-isomerase Pin1. Mechanistically, following interaction with Pin1, Notch1 and Notch4, key regulators of cell fate, escape from proteasomal degradation by their major ubiquitin-ligase Fbxw7α. Functionally, we show that Fbxw7α acts as an essential negative regulator of breast CSCs' expansion by restraining Notch activity, but the establishment of a Notch/Pin1 active circuitry opposes this effect, thus promoting breast CSCs self-renewal, tumor growth and metastasis in vivo. In human breast cancers, despite Fbxw7α expression, high levels of Pin1 sustain Notch signaling, which correlates with poor prognosis. Suppression of Pin1 holds promise in reverting aggressive phenotypes, through CSC exhaustion as well as recovered drug sensitivity carrying relevant implications for therapy of breast cancers.

ABCG2 is not able to catalyze glutathione efflux and does not contribute to GSH-dependent collateral sensitivity

ABCG2 is a key human ATP-binding cassette (ABC) transporter mediating cancer cell chemoresistance. In the case of ABCC1, another multidrug transporter, earlier findings documented that certain modulators greatly increase ABCC1-mediated glutathione (GSH) efflux and, upon depletion of intracellular GSH, induce "collateral sensitivity" leading to the apoptosis of multidrug resistant cells. Recently, it has been suggested that ABCG2 may mediate an active GSH transport. In order to explore if ABCG2-overexpressing cells may be similarly targeted, we first looked for the effects of ABCG2 expression on cellular GSH levels, and for an ABCG2-dependent GSH transport in HEK293 and MCF7 cells. We found that, while ABCG2 overexpression altered intracellular GSH levels in these transfected or drug-selected cells, ABCG2 inhibitors or transport modulators did not influence GSH efflux. We then performed direct measurements of drug-stimulated ATPase activity and (3)H-GSH transport in inside-out membrane vesicles of human ABC transporter-overexpressing Sf9 insect cells. Our results indicate that ABCG2-ATPase is not modulated by GSH and, in contrast to ABCC1, ABCG2 does not catalyze any significant GSH transport. Our data suggest no direct interaction between the ABCG2 transporter and GSH, although a long-term modulation of cellular GSH by ABCG2 cannot be excluded.

Functional and molecular characterization of ex vivo cultured epiretinal membrane cells from human proliferative diabetic retinopathy

Characterization of the cell surface marker phenotype of ex vivo cultured cells growing out of human fibrovascular epiretinal membranes (fvERMs) from proliferative diabetic retinopathy (PDR) can give insight into their function in immunity, angiogenesis, and retinal detachment. FvERMs from uneventful vitrectomies due to PDR were cultured adherently ex vivo. Surface marker analysis, release of immunity- and angiogenesis-pathway-related factors upon TNF α activation and measurement of the intracellular calcium dynamics upon mechano-stimulation using fluorescent dye Fura-2 were all performed. FvERMs formed proliferating cell monolayers when cultured ex vivo, which were negative for endothelial cell markers (CD31, VEGFR2), partially positive for hematopoietic- (CD34, CD47) and mesenchymal stem cell markers (CD73, CD90/Thy-1, and PDGFR β ), and negative for CD105. CD146/MCAM and CD166/ALCAM, previously unreported in cells from fvERMs, were also expressed. Secretion of 11 angiogenesis-related factors (DPPIV/CD26, EG-VEGF/PK1, ET-1, IGFBP-2 and 3, IL-8/CXCL8, MCP-1/CCL2, MMP-9, PTX3/TSG-14, Serpin E1/PAI-1, Serpin F1/PEDF, TIMP-1, and TSP-1) were detected upon TNF α activation of fvERM cells. Mechano-stimulation of these cells induced intracellular calcium propagation representing functional viability and role of these cells in tractional retinal detachment, thus serving as a model for studying tractional forces present in fvERMs in PDR ex vivo.

ShRNA targeting Notch1 sensitizes breast cancer stem cell to paclitaxel

Breast cancer is currently the most lethal gynecologic malignancy in many countries, and paclitaxel is a cornerstone in the treatment of this malignancy. Unfortunately, the efficacy of paclitaxel is limited due to the development of drug resistance. Evidence has suggested that cancer stem cells (CSCs) are involved in resistance to various forms of therapies, including chemotherapy. However, the interaction between paclitaxel resistance and CSCs and its underlying mechanisms have not been previously explored. In this study, we confirmed that paclitaxel enriched breast CSCs (CD44+/CD24-) in a dose-dependent manner in MCF-7 human breast cancer cell line. We then demonstrated that Notch1 was overexpressed in breast CSCs isolated from paclitaxel-treated MCF-7 cells compared to non-CSCs. The short hairpin RNA (shRNA) mediated knock-down of Notch1 inhibited MCF-7 cell proliferation and induced cell apoptosis. The anti-apoptosis protein NF-κB was decreased significantly when treated with shRNA-Notch1, and this effect was sharply improved by combination with paclitaxel. Paclitaxel decreased CD44+/CD24- cell population in MCF-7 cells and reduced the size and number of primary mammospheres after down-regulating the Notch1. Furthermore, shRNA-Notch1 inhibited the growth of tumor xenografts in nude mice noticeably. RT-PCR and Western blotting analysis showed that the expressions of ALDH1, NICD, Hes-1 and the drug transporter ABCG2 were decreased both in vitro and in vivo. These results suggest that Notch1 might play a critical role in the resistance to paclitaxel, and targeting Notch1 may have important clinical applications in cancer therapy.

Characterization of a new murine retinal cell line (MU-PH1) with glial, progenitor and photoreceptor characteristics

Unlike fish and amphibians, mammals do not regenerate retinal neurons throughout life. However, neurogenic potential may be conserved in adult mammal retina and it is necessary to identify the factors that regulate retinal progenitor cells (RPC) proliferative capacity to scope their therapeutic potential. Müller cells can be progenitors for retinal neuronal cells and can play an essential role in the restoration of visual function after retinal injury. Some members of the Toll-like receptor (TLR) family, TLR2, TLR3 and TLR4, are related to progenitor cells proliferation. Müller cells are important in retinal regeneration and stable cell lines are useful for the study of retinal stem cell biology. Our purpose was to obtain a Müller-derived cell line with progenitor characteristics and potential interest in regeneration processes. We obtained and characterized a murine Müller-derived cell line (MU-PH1), which proliferates indefinitely in vitro. Our results show that (i) MU-PH1 cells expresses the Müller cell markers Vimentin, S-100, glutamine synthetase and the progenitor and stem cell markers Nestin, Abcg2, Ascl1, α-tubulin and β-III-tubulin, whereas lacks the expression of CRALBP, GFAP, Chx10, Pax6 and Notch1 markers; (ii) MU-PH1 cell line stably express the photoreceptor markers recoverin, transducin, rhodopsin, blue and red/green opsins and also melanopsin; (iii) the presence of opsins was confirmed by the recording of intracellular free calcium levels during light stimulation; (iv) MU-PH1 cell line also expresses the melatonin MT1 and MT2 receptors; (v) MU-PH1 cells express TLR1, 2, 4 and 6 mRNA; (vi) MU-PH1 express TLR2 at cell surface level; (vii) Candida albicans increases TLR2 and TLR6 mRNA expression; (viii) C. albicans or TLR selective agonists (Pam(3)CysSK(4), LPS) did not elicit morphological changes nor TNF-α secretion; (ix) C. albicans and Pam(3)CysSK(4) augmented MU-PH1 neurospheres formation in a statistically significant manner. Our results indicate that MU-PH1 cell line could be of great interest both as a photoreceptor model and in retinal regeneration approaches and that TLR2 may also play a role in retinal cell proliferation.

Genome-wide analysis of N1ICD/RBPJ targets in vivo reveals direct transcriptional regulation of Wnt, SHH, and hippo pathway effectors by Notch1

The Notch pathway plays a pivotal role in regulating cell fate decisions in many stem cell systems. However, the full repertoire of Notch target genes in vivo and the mechanisms through which this pathway activity is integrated with other signaling pathways are largely unknown. Here, we report a transgenic mouse in which the activation of the Notch pathway massively expands the neural stem cell (NSC) pool in a cell context-dependent manner. Using this in vivo system, we identify direct targets of RBPJ/N1ICD in cortical NSCs at a genome-wide level through combined ChIP-Seq and transcriptome analyses. Through a highly conservative analysis of these datasets, we identified 98 genes that are directly regulated by N1ICD/RPBJ in vivo. These include many transcription factors that are known to be critical for NSC self-renewal (Sox2, Pax6, Tlx, and Id4) and the transcriptional effectors of the Wnt, SHH, and Hippo pathways, TCF4, Gli2, Gli3, Yap1, and Tead2. Since little is known about the function of the Hippo-Yap pathway in NSCs, we analyzed Yap1 expression and function in NSCs. We show that Yap1 expression is restricted to the stem cell compartment in the developing forebrain and that its expression is sufficient to rescue Notch pathway inhibition in NSC self-renewal assays. Together, results of this study reveal a previously underappreciated complexity and breadth of Notch1 targets in vivo and show direct interaction between Notch and Hippo-Yap pathways in NSCs.

Cardiac side population cells: moving toward the center stage in cardiac regeneration

Over the past decade, extensive work in animal models and humans has identified the presence of adult cardiac progenitor cells, capable of cardiomyogenic differentiation and likely contributors to cardiomyocyte turnover during normal development and disease. Among cardiac progenitor cells, there is a distinct subpopulation, termed "side population" (SP) progenitor cells, identified by their unique ability to efflux DNA binding dyes through an ATP-binding cassette transporter. This review highlights the literature on the isolation, characterization, and functional relevance of cardiac SP cells. We review the initial discovery of cardiac SP cells in adult myocardium as well as their capacity for functional cardiomyogenic differentiation and role in cardiac regeneration after myocardial injury. Finally, we discuss recent advances in understanding the molecular regulators of cardiac SP cell proliferation and differentiation, as well as likely future areas of investigation required to realize the goal of effective cardiac regeneration.

Retinoic acid-dependent signaling pathways and lineage events in the developing mouse spinal cord

Studies in avian models have demonstrated an involvement of retinoid signaling in early neural tube patterning. The roles of this signaling pathway at later stages of spinal cord development are only partly characterized. Here we use Raldh2-null mouse mutants rescued from early embryonic lethality to study the consequences of lack of endogenous retinoic acid (RA) in the differentiating spinal cord. Mid-gestation RA deficiency produces prominent structural and molecular deficiencies in dorsal regions of the spinal cord. While targets of Wnt signaling in the dorsal neuronal lineage are unaltered, reductions in Fibroblast Growth Factor (FGF) and Notch signaling are clearly observed. We further provide evidence that endogenous RA is capable of driving stem cell differentiation. Raldh2 deficiency results in a decreased number of spinal cord derived neurospheres, which exhibit a reduced differentiation potential. Raldh2-null neurospheres have a decreased number of cells expressing the neuronal marker β-III-tubulin, while the nestin-positive cell population is increased. Hence, in vivo retinoid deficiency impaired neural stem cell growth. We propose that RA has separable functions in the developing spinal cord to (i) maintain high levels of FGF and Notch signaling and (ii) drive stem cell differentiation, thus restricting both the numbers and the pluripotent character of neural stem cells.

Standard of care therapy for malignant glioma and its effect on tumor and stromal cells

Glioblastoma is the most common and deadly of the primary central nervous system tumors. Recent advances in molecular characterization have subdivided these tumors into at least three main groups. In addition, these tumors are cellularly complex with multiple stromal cell types contributing to the biology of the tumor and treatment response. Because essentially all glioma patients are treated with radiation, various chemotherapies and steroids, the tumor that finally kills them has been modified by these treatments. Most of the investigation of the effects of therapy on these tumors has focused on the glioma cells per se. However, despite the importance of the stromal cells in these tumors, little has been done to understand the effects of treatment on stromal cells and their contribution to disease. Understanding how current standard therapy affects the biology of the tumor and the tumor stroma may provide insight into the mechanisms that are important to the inhibition of tumor growth as well as the biology of recurrent tumors.

Evaluation of 309 environmental chemicals using a mouse embryonic stem cell adherent cell differentiation and cytotoxicity assay

The vast landscape of environmental chemicals has motivated the need for alternative methods to traditional whole-animal bioassays in toxicity testing. Embryonic stem (ES) cells provide an in vitro model of embryonic development and an alternative method for assessing developmental toxicity. Here, we evaluated 309 environmental chemicals, mostly food-use pesticides, from the ToxCast™ chemical library using a mouse ES cell platform. ES cells were cultured in the absence of pluripotency factors to promote spontaneous differentiation and in the presence of DMSO-solubilized chemicals at different concentrations to test the effects of exposure on differentiation and cytotoxicity. Cardiomyocyte differentiation (α,β myosin heavy chain; MYH6/MYH7) and cytotoxicity (DRAQ5™/Sapphire700™) were measured by In-Cell Western™ analysis. Half-maximal activity concentration (AC₅₀) values for differentiation and cytotoxicity endpoints were determined, with 18% of the chemical library showing significant activity on either endpoint. Mining these effects against the ToxCast Phase I assays (∼500) revealed significant associations for a subset of chemicals (26) that perturbed transcription-based activities and impaired ES cell differentiation. Increased transcriptional activity of several critical developmental genes including BMPR2, PAX6 and OCT1 were strongly associated with decreased ES cell differentiation. Multiple genes involved in reactive oxygen species signaling pathways (NRF2, ABCG2, GSTA2, HIF1A) were strongly associated with decreased ES cell differentiation as well. A multivariate model built from these data revealed alterations in ABCG2 transporter was a strong predictor of impaired ES cell differentiation. Taken together, these results provide an initial characterization of metabolic and regulatory pathways by which some environmental chemicals may act to disrupt ES cell growth and differentiation.

Notch in the vertebrate nervous system: an old dog with new tricks

The Notch pathway is prominent among those known to regulate neural development in vertebrates. Notch receptor activation can inhibit neurogenesis, maintain neural progenitor character, and in some contexts promote gliogenesis and drive binary fate choices. Recently, a wave of exciting studies has emerged, which has both solidified previously held assertions and expanded our understanding of Notch function during neurogenesis and in the adult brain. These studies have examined pathway regulators and interactions, as well as pathway dynamics, with respect to both gene expression and cell-cell signaling. Here, focusing primarily on vertebrates, we review the current literature on Notch signaling in the nervous system, and highlight numerous recent studies that have generated interesting and unexpected advances.

Molecular pathogenesis of malignant glial tumors

Malignant glial tumors are the most aggressive and difficult to treat neoplasms arising in the brain. More than 22,000 people in the United States are diagnosed with a malignant glioma annually, and most will die within the first two years from diagnosis. Traditionally, gliomas have been categorized based solely on tumor histological features. However, expression studies have found that molecular signatures can be used to categorize these tumors into subclasses that more effectively predict patient outcome. The heterogeneity between tumors as well as within individual tumors makes understanding the molecular aspects of tumorigenesis extremely important. Several genetically engineered mouse models (GEMMs) of glioma have been developed that recapitulate the molecular alterations observed in the human disease. GEMMs of glioma have allowed researchers to more closely study the role of cancer stem cells (CSC) in gliomagenesis as well as the relevance of signaling within the CSC microenvironment. Knowledge of the underlying molecular signatures of malignant glial tumors coupled with the existence of a variety of human disease-relevant GEMMs of this tumor type provide researchers and clinicians with valuable resources for the discovery of new drug targets.

Notch and Wnt signaling mediated rod photoreceptor regeneration by Müller cells in adult mammalian retina

BACKGROUND

Evidence emerging from a variety of approaches used in different species suggests that Müller cell function may extend beyond its role of maintaining retinal homeostasis to that of progenitors in the adult retina. Enriched Müller cells in vitro or those that re-enter cell cycle in response to neurotoxin-damage to retina in vivo display multipotential and self-renewing capacities, the cardinal features of stem cells.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrate that Notch and Wnt signaling activate Müller cells through their canonical pathways and that a rare subset of activated Müller cells differentiates along rod photoreceptor lineage in the outer nuclear layer. The differentiation of activated Müller cells along photoreceptor lineage is confirmed by multiple approaches that included Hoechst dye efflux analysis, genetic analysis using retina from Nrl-GFP mice, and lineage tracing using GS-GFP lentivirus in wild type and rd mice in vitro and S334ter rats in vivo. Examination of S334ter rats for head-neck tracking of visual stimuli, a behavioral measure of light perception, demonstrates a significant improvement in light perception in animals treated to activate Müller cells. The number of activated Müller cells with rod photoreceptor phenotype in treated animals correlates with the improvement in their light perception.

CONCLUSION/SIGNIFICANCE

In summary, our results provide a proof of principle for non-neurotoxin-mediated activation of Müller cells through Notch and Wnt signaling toward the regeneration of rod photoreceptors.

Targeting brain cancer: advances in the molecular pathology of malignant glioma and medulloblastoma

Malignant brain tumours continue to be the cause of a disproportionate level of morbidity and mortality across a wide range of individuals. The most common variants in the adult and paediatric populations - malignant glioma and medulloblastoma, respectively - have been the subject of increasingly intensive research over the past two decades that has led to considerable advances in the understanding of their basic biology and pathogenesis. This Review summarizes these developments in the context of the evolving notion of molecular pathology and discusses the implications that this work has on the design of new treatment regimens.

Direct and coordinate regulation of ATP-binding cassette transporter genes by Myc factors generates specific transcription signatures that significantly affect the chemoresistance phenotype of cancer cells

Increased expression of specific ATP-binding cassette (ABC) transporters is known to mediate the efflux of chemotherapeutic agents from cancer cells. Therefore, establishing how ABC transporter genes are controlled at their transcription level may help provide insight into the role of these multifaceted transporters in the malignant phenotype. We have investigated ABC transporter gene expression in a large neuroblastoma data set of 251 tumor samples. Clustering analysis demonstrated a strong association between differential ABC gene expression patterns in tumor samples and amplification of the MYCN oncogene, suggesting a correlation with MYCN function. Using expression profiling and chromatin immunoprecipitation studies, we show that MYCN oncoprotein coordinately regulates transcription of specific ABC transporter genes, by acting as either an activator or a repressor. Finally, we extend these notions to c-MYC showing that it can also regulate the same set of ABC transporter genes in other tumor cells through similar dynamics. Overall our findings provide insight into MYC-driven molecular mechanisms that contribute to coordinate transcriptional regulation of a large set of ABC transporter genes, thus affecting global drug efflux.