Down regulation of CSL activity inhibits cell proliferation in prostate and breast cancer cells

Systematic analysis of the effects of genetic variants on chromatin accessibility to decipher functional variants in non-coding regions

Genome-wide association study (GWAS) has identified thousands of single nucleotide polymorphisms (SNPs) associated with complex diseases and traits. However, deciphering the functions of these SNPs still faces challenges. Recent studies have shown that SNPs could alter chromatin accessibility and result in differences in tumor susceptibility between individuals. Therefore, systematically analyzing the effects of SNPs on chromatin accessibility could help decipher the functions of SNPs, especially those in non-coding regions. Using data from The Cancer Genome Atlas (TCGA), chromatin accessibility quantitative trait locus (caQTL) analysis was conducted to estimate the associations between genetic variants and chromatin accessibility. We analyzed caQTLs in 23 human cancer types and identified 9,478 caQTLs in breast carcinoma (BRCA). In BRCA, these caQTLs tend to alter the binding affinity of transcription factors, and open chromatin regions regulated by these caQTLs are enriched in regulatory elements. By integrating with eQTL data, we identified 141 caQTLs showing a strong signal for colocalization with eQTLs. We also identified 173 caQTLs in genome-wide association studies (GWAS) loci and inferred several possible target genes of these caQTLs. By performing survival analysis, we found that ~10% caQTLs potentially influence the prognosis of patients. To facilitate access to relevant data, we developed a user-friendly data portal, BCaQTL (http://gong_lab.hzau.edu.cn/caqtl_database), for data searching and downloading. Our work may facilitate fine-map regulatory mechanisms underlying risk loci of cancer and discover the biomarkers or therapeutic targets for cancer prognosis. The BCaQTL database will be an important resource for genetic and epigenetic studies.

Colon cancer cells secreted CXCL11 via RBP-Jκ to facilitated tumour-associated macrophage-induced cancer metastasis

Metastasis is the main cause of colon cancer‐related deaths. RBP‐Jκ is involved in colon cancer development, but its function in colon cancer metastasis is still unclear. Tumour‐associated macrophages are the main cell components in tumour microenvironments. Here, we aimed to determine the function of RBP‐Jκ in colon cancer metastasis and its underlying mechanisms for modulating interactions between colon cancer cell and tumour‐associated macrophages. Through bioinformation analysis, we found that RBP‐Jκ was overexpressed in colon cancer tissues and associated with advanced colon cancer phenotypes, macrophage infiltration and shorter survival overall as confirmed by our patients’ data. And our patients’ data show that RBP‐Jκ expression and tumour‐associated macrophages infiltration are associated with colon cancer metastasis and are independent prognostic factors for colon cancer patients. Tumour‐associated macrophages induced colon cancer cell migration, invasion and epithelial‐mesenchymal transition through secreting TGF‐β1. Colon cancer cells with high RBP‐Jκ expression induced the expression of TGF‐β1 in tumour‐associated macrophages by secreting CXCL11. Our research revealed that colon cancer cells secreted CXCL11 via overexpression of RBP‐Jκ to enhance the expression of TGF‐β1 in tumour‐associated macrophages to further promote metastasis of colon cancer cells.

Elevated RBP-Jκ and CXCL11 Expression in Colon Cancer is Associated with an Unfavorable Clinical Outcome

Introduction

This study aims at exploring the expression and significance of recombination signal-binding protein for immunoglobulin kappa J region (RBP-Jκ) and C-X-C motif chemokine 11 (CXCL11) in human colon cancer tissues.

Methods

The RBP-Jκ and CXCL11 expression levels were assessed by immunohistochemistry and quantitative real-time polymerase chain reaction (qRT-PCR) in patients with colon cancer, and their prognostic significance was evaluated.

Results

Through analyzing 342 samples of colon cancer patients treated at our institution, increased expression of RBP-Jκ and CXCL11 was found in human colon cancer specimens compared with matched paratumorous normal specimens (P<0.001). A positive correlation was found between RBP-Jκ expression and CXCL11 expression (P<0.001). High RBP-Jκ expression was significantly associated with poorly differentiated tumors (P=0.005), invasion beyond propria muscularis (P=0.025), lymph node metastases (P=0.005), distant metastasis (P<0.001), advanced tumor-node-metastasis (TNM) stage (P=0.004), and a shorter overall survival (P<0.001). An increase in CXCL11 protein expression was associated with poorly differentiated tumors (P=0.015), invasion beyond propria muscularis (P=0.029), lymph node metastases (P=0.031), distant metastasis (P=0.045), advanced TNM stage (P=0.026), and a shorter overall survival of patients (P<0.001). In multivariate Cox regression analysis, RBP-Jκ protein expression (P=0.036), CXCL11 protein expression (P=0.001), differentiation (P<0.001), depth of invasion (P=0.009), distant metastasis (P<0.001), and TNM stage (P<0.001) were independent prognostic indicators of colon cancer.

Conclusion

High expression of RBP-Jκ is closely associated with high CXCL11 expression, which represents a risk factor for the poor overall survival of colon cancer patients.

Identification of PTPRR and JAG1 as key genes in castration-resistant prostate cancer by integrated bioinformatics methods. J Zhejiang Univ Sci B 2021;21:246-255. [PMID: 32133801 DOI: 10.1631/jzus.b1900329]

To identify novel genes in castration-resistant prostate cancer (CRPC), we downloaded three microarray datasets containing CRPC and primary prostate cancer in Gene Expression Omnibus (GEO). R packages affy and limma were performed to identify differentially expressed genes (DEGs) between primary prostate cancer and CRPC. After that, we performed functional enrichment analysis including gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway. In addition, protein-protein interaction (PPI) analysis was used to search for hub genes. Finally, to validate the significance of these genes, we performed survival analysis. As a result, we identified 53 upregulated genes and 58 downregulated genes that changed in at least two datasets. Functional enrichment analysis showed significant changes in the positive regulation of osteoblast differentiation pathway and aldosterone-regulated sodium reabsorption pathway. PPI network identified hub genes like cortactin-binding protein 2 (CTTNBP2), Rho family guanosine triphosphatase (GTPase) 3 (RND3), protein tyrosine phosphatase receptor-type R (PTPRR), Jagged1 (JAG1), and lumican (LUM). Based on PPI network analysis and functional enrichment analysis, we identified two genes (PTPRR and JAG1) as key genes. Further survival analysis indicated a relationship between high expression of the two genes and poor prognosis of prostate cancer. In conclusion, PTPRR and JAG1 are key genes in the CRPC, which may serve as promising biomarkers of diagnosis and prognosis of CRPC.

Notch Signaling in Breast Cancer: A Role in Drug Resistance

Breast cancer is a heterogeneous disease that can be subdivided into unique molecular subtypes based on protein expression of the Estrogen Receptor, Progesterone Receptor, and/or the Human Epidermal Growth Factor Receptor 2. Therapeutic approaches are designed to inhibit these overexpressed receptors either by endocrine therapy, targeted therapies, or combinations with cytotoxic chemotherapy. However, a significant percentage of breast cancers are inherently resistant or acquire resistance to therapies, and mechanisms that promote resistance remain poorly understood. Notch signaling is an evolutionarily conserved signaling pathway that regulates cell fate, including survival and self-renewal of stem cells, proliferation, or differentiation. Deregulation of Notch signaling promotes resistance to targeted or cytotoxic therapies by enriching of a small population of resistant cells, referred to as breast cancer stem cells, within the bulk tumor; enhancing stem-like features during the process of de-differentiation of tumor cells; or promoting epithelial to mesenchymal transition. Preclinical studies have shown that targeting the Notch pathway can prevent or reverse resistance through reduction or elimination of breast cancer stem cells. However, Notch inhibitors have yet to be clinically approved for the treatment of breast cancer, mainly due to dose-limiting gastrointestinal toxicity. In this review, we discuss potential mechanisms of Notch-mediated resistance in breast cancer cells and breast cancer stem cells, and various methods of targeting Notch through γ-secretase inhibitors, Notch signaling biologics, or transcriptional inhibitors. We also discuss future plans for identification of novel Notch-targeted therapies, in order to reduce toxicity and improve outcomes for women with resistant breast cancer.

Multiplex profiling identifies clinically relevant signalling proteins in an isogenic prostate cancer model of radioresistance

The exact biological mechanism governing the radioresistant phenotype of prostate tumours at a high risk of recurrence despite the delivery of advanced radiotherapy protocols remains unclear. This study analysed the protein expression profiles of a previously generated isogenic 22Rv1 prostate cancer model of radioresistance using DigiWest multiplex protein profiling for a selection of 90 signalling proteins. Comparative analysis of the profiles identified a substantial change in the expression of 43 proteins. Differential PARP-1, AR, p53, Notch-3 and YB-1 protein levels were independently validated using Western Blotting. Pharmacological targeting of these proteins was associated with a mild but significant radiosensitisation effect at 4Gy. This study supports the clinical relevance of isogenic in vitro models of radioresistance and clarifies the molecular radiation response of prostate cancer cells.

The Role of Notch Signaling and Leptin-Notch Crosstalk in Pancreatic Cancer

There is accumulating evidence that deregulated Notch signaling affects cancer development, and specifically pancreatic cancer (PC) progression. Notch canonical and non-canonical signaling has diverse impact on PC. Moreover, the actions of RBP-Jk (nuclear partner of activated Notch) independent of Notch signaling pathway seem to affect differently cancer progression. Recent data show that in PC and other cancer types the adipokine leptin can modulate Notch/RBP-Jk signaling, thereby, linking the pandemic obesity with cancer and chemoresistance. The potential pivotal role of leptin on PC, and its connection with Notch signaling and chemoresistance are still not completely understood. In this review, we will describe the most important aspects of Notch-RBP-Jk signaling in PC. Further, we will discuss on studies related to RBP-Jk-independent Notch and Notch-independent RPB-Jk signaling. We will also discuss on the novel crosstalk between leptin and Notch in PC and its implications in chemoresistance. The effects of leptin-Notch/RBP-Jk signaling on cancer cell proliferation, apoptosis, and drug resistance require more investigation. Data from these investigations could help to open unexplored ways to improve PC treatment success that has shown little progress for many years.

Notch-effector CSL promotes squamous cell carcinoma by repressing histone demethylase KDM6B

Notch 1/2 genes play tumor-suppressing functions in squamous cell carcinoma (SCC), a very common malignancy in skin and internal organs. In contrast with Notch, we show that the transcription factor CSL (also known as RBP-Jκ), a key effector of canonical Notch signaling endowed with intrinsic transcription-repressive functions, plays a tumor-promoting function in SCC development. Expression of this gene decreased in upper epidermal layers and human keratinocytes (HKCs) undergoing differentiation, while it increased in premalignant and malignant SCC lesions from skin, head/neck, and lung. Increased CSL levels enhanced the proliferative potential of HKCs and SCC cells, while silencing of CSL induced growth arrest and apoptosis. In vivo, SCC cells with increased CSL levels gave rise to rapidly expanding tumors, while cells with silenced CSL formed smaller and more differentiated tumors with enhanced inflammatory infiltrate. Global transcriptomic analysis of HKCs and SCC cells with silenced CSL revealed major modulation of apoptotic, cell-cycle, and proinflammatory genes. We also show that the histone demethylase KDM6B is a direct CSL-negative target, with inverse roles of CSL in HKC and SCC proliferative capacity, tumorigenesis, and tumor-associated inflammatory reaction. CSL/KDM6B protein expression could be used as a biomarker of SCC development and indicator of cancer treatment.

Activation of Notch pathway is linked with epithelial-mesenchymal transition in prostate cancer cells

Notch signaling has been reported to play an essential role in tumorigenesis. Several studies have suggested that Notch receptors could be oncoproteins or tumor suppressors in different types of human cancers. Emerging evidence has suggested that Notch pathway regulates cell growth, apoptosis, cell cycle, and metastasis. In the current study, we explore whether Notch-1 could regulate the cell invasion and migration as well as EMT (epithelial-mesenchymal transition) in prostate cancer cells. We found that overexpression of Notch-1 enhanced cell migration and invasion in PC-3 cells. However, downregulation of Notch-1 retarded cell migration and invasion in prostate cancer cells. Importantly, we observed that overexpression of Notch-1 led to EMT in PC-3 cells. Notably, we found that EMT-type cells are associated with EMT markers change and cancer stem cell phenotype. Taken together, we concluded that downregulation of Notch-1 could be a promising approach for inhibition of invasion in prostate cancer cells, which could be useful for the treatment of metastatic prostate cancer.

Inhibition of Notch pathway arrests PTEN-deficient advanced prostate cancer by triggering p27-driven cellular senescence

Activation of NOTCH signalling is associated with advanced prostate cancer and treatment resistance in prostate cancer patients. However, the mechanism that drives NOTCH activation in prostate cancer remains still elusive. Moreover, preclinical evidence of the therapeutic efficacy of NOTCH inhibitors in prostate cancer is lacking. Here, we provide evidence that PTEN loss in prostate tumours upregulates the expression of ADAM17, thereby activating NOTCH signalling. Using prostate conditional inactivation of both Pten and Notch1 along with preclinical trials carried out in Pten-null prostate conditional mouse models, we demonstrate that Pten-deficient prostate tumours are addicted to the NOTCH signalling. Importantly, we find that pharmacological inhibition of γ-secretase promotes growth arrest in both Pten-null and Pten/Trp53-null prostate tumours by triggering cellular senescence. Altogether, our findings describe a novel pro-tumorigenic network that links PTEN loss to ADAM17 and NOTCH signalling, thus providing the rational for the use of γ-secretase inhibitors in advanced prostate cancer patients.

Notch signalling is involved in prostate cancer progression and therapeutic resistance. Here, the authors show that loss of PTEN in prostate cancer models results in increased Notch1 cleavage and activation through CUX1-mediated transactivation of ADAM17.

Jagged1 upregulation in prostate epithelial cells promotes formation of reactive stroma in the Pten null mouse model for prostate cancer

The role of Notch signaling in prostate cancer has not been defined definitively. Several large scale tissue microarray studies have revealed that the expression of some Notch signaling components including the Jagged1 ligand are upregulated in advanced human prostate cancer specimens. Jagged1 expressed by tumor cells may activate Notch signaling in both adjacent tumor cells and cells in tumor microenvironment. However, it remains undetermined whether increased Jagged1 expression reflects a cause for or a consequence of tumor progression in vivo. To address this question, we generated a novel R26-LSL-JAG1 mouse model that enables spatiotemporal Jagged1 expression. Prostate specific upregulation of Jagged1 neither interferes with prostate epithelial homeostasis nor significantly accelerates tumor initiation or progression in the prostate-specific Pten deletion mouse model for prostate cancer. However, Jagged1 upregulation results in increased inflammatory foci in tumors and incidence of intracystic adenocarcinoma. In addition, Jagged1 overexpression upregulates Tgfβ signaling in prostate stromal cells and promotes progression of a reactive stromal microenvironment in the Pten null prostate cancer model. Collectively, Jagged1 overexpression does not significantly accelerate prostate cancer initiation and progression in the context of loss-of-function of Pten, but alters tumor histopathology and microenvironment. Our study also highlights an understudied role of Notch signaling in regulating prostatic stromal homeostasis.

Notch promotes tumor metastasis in a prostate-specific Pten-null mouse model

Although Notch signaling is deregulated in prostate cancer, the role of this pathway in disease development and progression is not fully understood. Here, we analyzed 2 human prostate cancer data sets and found that higher Notch signaling correlates with increased metastatic potential and worse disease survival rates. We used the Pten-null mouse prostate cancer model to investigate the function of Notch signaling in the initiation and progression of prostate cancer. Disruption of the transcription factor RBPJ in Pten-null mice revealed that endogenous canonical Notch signaling is not required for disease initiation and progression. However, augmentation of Notch activity in this model promoted both proliferation and apoptosis of prostate epithelial cells, which collectively reduced the primary tumor burden. The increase in cellular apoptosis was linked to DNA damage-induced p53 activation. Despite a reduced primary tumor burden, Notch activation in Pten-null mice promoted epithelial-mesenchymal transition and FOXC2-dependent tumor metastases but did not confer resistance to androgen deprivation. Notch activation also resulted in transformation of seminal vesicle epithelial cells in Pten-null mice. Our study highlights a multifaceted role for Notch signaling in distinct aspects of prostate cancer biology and supports Notch as a potential therapeutic target for metastatic prostate cancer.

Hypoxia regulates Notch-3 mRNA and receptor activation in prostate cancer cells

The Notch-3 receptor is a recognized key regulator of vascular responses and is increasingly associated with tumorigenesis. Hypoxia-inducible factors activate specific signaling pathways such as Notch in a number of cellular models. This study aimed to evaluate the regulation of Notch-3 by hypoxia in prostate cancer cells. Notch-3 gene and protein expression was established in a panel of aerobic and hypoxic prostate cell lines in vitro, the CWR22 xenograft model and RNA extracted from low grade (Gleason score < = 6); high grade (Gleason score > = 7); non-hypoxic (low HIF, low VEGF); hypoxic (high HIF, high VEGF) patient FFPE specimens. NOTCH-3 was upregulated in PC3 (3-fold), 22Rv1 (4.1-fold) and DU145 (3.8-fold) but downregulated in LnCaP (12-fold) compared to the normal cell lines. NOTCH-3 expression was modified following hypoxic exposure in these cells. NOTCH-3 was upregulated (2.2-fold) in higher grade and hypoxic tumors, when compared to benign and aerobic pools. In the CWR22 xenograft model, Notch-3 expression was restored in castrate resistant tumors. Nuclear translocation of the Notch-3 intracellular domain was no longer detected following exposure of cells to hypoxia but not associated with a change in expression of HES-1. Our data further identifies Notch-3 as a potentially key hypoxic-responsive member of the Notch pathway in prostate tumorigenesis.

CSL regulates AKT to mediate androgen independence in prostate cancer progression

BACKGROUND

Aberrant signaling pathways leads to cancer initiation and progression. Both Notch and PI3K/AKT signaling pathways are believed to be involved in prostate cancer. How the interaction between the two pathways contributes to prostate cancer progression to androgen independence is still elusive.

METHODS

Prostate cancer cells were grown in RPMI 1,640 supplemented with 10% heat-inactivated fetal bovine serum (FBS) or 10% charcoal-stripped heat-inactivated fetal bovine serum (FCS), 1% penicillin-streptomycin in 75 cm2 polystyrene flasks, and maintained at 37 °C in a humidified atmosphere with 5% CO2 . Cell proliferation, invasion were performed with cell counting, matrigel assay in vitro. Dual luciferase assays were performed using reporter plasmids with ARE (Androgen Response Element, ARE). RNA interference was applied to gene silence. Tumorigenicity of cancer cells was evaluated by mouse xenograft in vivo.

RESULTS

A subpopulation of casodex resistant prostate cancer cells were identified with an overexpressed androgen receptor (AR) and aggressive phenotypes, characterized with high proliferation, invasion in vitro and enhanced tumorigenesis in vivo. Gene profiling for androgen-dependent LNCaP and androgen-independent LNCaP-CR revealed that both CSL and AKT gave the similar expressional pattern upon casodex treatment. Immunoblot demonstrated that CSL and AKT were dramatically suppressed in androgen dependent LNCaP cells, but slightly inhibited in LNCaP-CR cells as well as other androgen independent prostate cancer cells. Further studies indicated that CSL regulates AKT, and subsequently AR in prostate cancer cells. AKT mediates casodex resistance and androgen independence through regulation of cyclin D1.

CONCLUSION

CSL-AKT-AR axis might play an important role in prostate cancer progression. Targeting CSL depleted the casodex resistant population through inhibition of the AKT, suggesting a more effective therapeutic strategy for abrogating casodex resistance in advanced prostate cancer.

Notch signaling in prostate cancer: refining a therapeutic opportunity

Notch is an evolutionarily conserved signaling pathway that plays a critical role in specifying cell fate and regulating tissue homeostasis and carcinogenesis. Studies using organ cultures and genetically engineered mouse models have demonstrated that Notch signaling regulates prostate development and homeostasis. However, the role of the Notch signaling pathway in prostate cancer remains inconclusive. Many published studies have documented consistent deregulation of major Notch signaling components in human prostate cancer cell lines, mouse models for prostate cancers, and human prostate cancer specimens at both the mRNA and the protein levels. However, functional studies in human cancer cells by modulation of Notch pathway elements suggest both tumor suppressive and oncogenic roles of Notch. These controversies may originate from our inadequate understanding of the regulation of Notch signaling under versatile genetic contexts, and reflect the multifaceted and pleiotropic roles of Notch in regulating different aspects of prostate cancer cell biology, such as proliferation, metastasis, and chemo-resistance. Future comprehensive studies using various mouse models for prostate cancer may help clarify the role of Notch signaling in prostate cancer and provide a solid basis for determining whether and how Notch should be employed as a therapeutic target for prostate cancer.

Notch signaling in the prostate: critical roles during development and in the hallmarks of prostate cancer biology

PURPOSE

This review aims to summarize the evidence that Notch signaling is associated with prostate development, tumorigenesis and prostate tumor progression.

METHODS

Studies in PubMed database were searched using the keywords of Notch signaling, prostate development and prostate cancer. Relevant literatures were identified and summarized.

RESULTS

The Notch pathway plays an important role in determining cell fate, proliferation, differentiation and apoptosis. Recent findings have highlighted the involvement of Notch signaling in prostate development and in the maintenance of adult prostate homeostasis. Aberrant Notch expression in tissues leads to dysregulation of Notch functions and promotes various neoplasms, including prostate cancer. High expression of Notch has been implicated in prostate cancer, and its expression increases with higher cancer grade. However, the precise role of Notch in prostate cancer has yet to be clearly defined. The roles of Notch either as an oncogene or tumor suppressor in prostate cancer hallmarks such as cell proliferation, apoptosis and anoikis, hypoxia, migration and invasion, angiogenesis as well as the correlation with metastasis are therefore discussed.

CONCLUSIONS

Notch signaling is a complicated signaling pathway in modulating prostate development and prostate cancer. Understanding and manipulating Notch signaling could therefore be of potential therapeutic value in combating prostate cancer.

New targeted therapies for breast cancer: A focus on tumor microenvironmental signals and chemoresistant breast cancers

Breast cancer is the most frequent female malignancy worldwide. Current strategies in breast cancer therapy, including classical chemotherapy, hormone therapy, and targeted therapies, are usually associated with chemoresistance and serious adverse effects. Advances in our understanding of changes affecting the interactome in advanced and chemoresistant breast tumors have provided novel therapeutic targets, including, cyclin dependent kinases, mammalian target of rapamycin, Notch, Wnt and Shh. Inhibitors of these molecules recently entered clinical trials in mono- and combination therapy in metastatic and chemo-resistant breast cancers. Anticancer epigenetic drugs, mainly histone deacetylase inhibitors and DNA methyltransferase inhibitors, also entered clinical trials. Because of the complexity and heterogeneity of breast cancer, the future in therapy lies in the application of individualized tailored regimens. Emerging therapeutic targets and the implications for personalized-based therapy development in breast cancer are herein discussed.

NUMB inhibition of NOTCH signalling as a therapeutic target in prostate cancer

Prostate cancer is among the most prevalent life-threatening cancers diagnosed in the male population today. Various methods have been exploited in an attempt to treat this disease but these treatments, alongside preventative tactics, have been insufficient to control mortality rates and have usually resulted in detrimental adverse events. An opportunity to devise more-specific and potentially more-effective approaches for the eradication of prostate tumours can be found by targeting specific biological pathways. NUMB (protein numb homologue), a key regulator of cell fate, represents an attractive, actionable target in prostate cancer. NUMB participates in the observed deregulation of NOTCH (neurogenic locus notch homologue protein) signalling in prostate tumours, and the NUMB-NOTCH interaction regulates cell fate. NUMB has potential both as a target for control of prostate tumorigenesis and as a biomarker for identification of patients with prostate cancer who are likely to benefit from NOTCH inhibition.

Disruption of prostate epithelial differentiation pathways and prostate cancer development

One of the foremost problems in the prostate cancer (PCa) field is the inability to distinguish aggressive from indolent disease, which leads to difficult prognoses and thousands of unnecessary surgeries. This limitation stems from the fact that the mechanisms of tumorigenesis in the prostate are poorly understood. Some genetic alterations are commonly reported in prostate tumors, including upregulation of Myc, fusion of Ets genes to androgen-regulated promoters, and loss of Pten. However, the specific roles of these aberrations in tumor initiation and progression are poorly understood. Likewise, the cell of origin for PCa remains controversial and may be linked to the aggressive potential of the tumor. One important clue is that prostate tumors co-express basal and luminal protein markers that are restricted to their distinct cell types in normal tissue. Prostate epithelium contains layer-specific stem cells as well as rare bipotent cells, which can differentiate into basal or luminal cells. We hypothesize that the primary oncogenic cell of origin is a transient-differentiating bipotent cell. Such a cell must maintain tight temporal and spatial control of differentiation pathways, thus increasing its susceptibility for oncogenic disruption. In support of this hypothesis, many of the pathways known to be involved in prostate differentiation can be linked to genes commonly altered in PCa. In this article, we review what is known about important differentiation pathways (Myc, p38MAPK, Notch, PI3K/Pten) in the prostate and how their misregulation could lead to oncogenesis. Better understanding of normal differentiation will offer new insights into tumor initiation and may help explain the functional significance of common genetic alterations seen in PCa. Additionally, this understanding could lead to new methods for classifying prostate tumors based on their differentiation status and may aid in identifying more aggressive tumors.

Hypoxia, notch signalling, and prostate cancer

The notch signalling pathway is involved in differentiation, proliferation, angiogenesis, vascular remodelling, and apoptosis. Deregulated expression of notch receptors, ligands, and targets is observed in many solid tumours, including prostate cancer. Hypoxia is a common feature of prostate tumours, leading to increased gene instability, reduced treatment response, and increased tumour aggressiveness. The notch signalling pathway is known to regulate vascular cell fate and is responsive to hypoxia-inducible factors. Evidence to date suggests similar, therapeutically exploitable, behaviour of notch-activated and hypoxic prostate cancer cells.

Targeting γ-secretase in breast cancer

γ-secretase complexes are multisubunit protease complexes that perform the intramembrane cleavage of more than 60 type-I transmembrane proteins, including Notch receptors. Since dysregulated Notch signaling has been implicated in the tumorigenesis and progression of breast cancer, small molecule γ-secretase inhibitors (GSIs) are being tested for their therapeutic potential in breast cancer treatment in several clinical trials. Here, the structure of γ-secretase complex and the development of GSIs are briefly reviewed, the roles of Notch and several other γ-secretase substrates in breast cancer are discussed, and the difference between γ-secretase inhibition and Notch inhibition, as well as the side effects associated with GSIs, are described. A better understanding of molecular mechanisms that affect the responsiveness of breast cancer to GSI might help to develop strategies to enhance the antitumor activity and, at the same time, alleviate the side effects of GSI.