[Abstract unavailable

No abstract

It is widely accepted that alterations to cyclooxygenase-2 (COX-2) expression and the abundance of its enzymatic product prostaglandin E(2) (PGE(2)) have key roles in influencing the development of colorectal cancer. Deregulation of the COX-2/PGE(2) pathway appears to affect colorectal tumorigenesis via a number of distinct mechanisms: promoting tumour maintenance and progression, encouraging metastatic spread, and perhaps even participating in tumour initiation. Here, we review the role of COX-2/PGE(2) signalling in colorectal tumorigenesis and highlight its ability to influence the hallmarks of cancer--attributes defined by Hanahan and Weinberg as being requisite for tumorigenesis. In addition, we consider components of the COX-prostaglandin pathway emerging as important regulators of tumorigenesis; namely, the prostanoid (EP) receptors, 15-hydroxyprostaglandin dehydrogenase and the prostaglandin transporter. Finally, based on recent findings, we propose a model for the cellular adaptation to the hypoxic tumour microenvironment that encompasses the interplay between COX-2, hypoxia-inducible factor 1 and dynamic switches in beta-catenin function that fine-tune signalling networks to meet the ever-changing demands of a tumour.

The Wnt/b-catenin signalling and autophagy pathways each play important roles during development, adult tissue homeostasis and tumorigenesis. Here we identify the Wnt/b-catenin signalling pathway as a negative regulator of both basal and stress-induced autophagy. Manipulation of b-catenin expression levels in vitro and in vivo revealed that b-catenin suppresses autophagosome formation and directly represses p62/SQSTM1 (encoding the autophagy adaptor p62) via TCF4. Furthermore, we show that during nutrient deprivation b-catenin is selectively degraded via the formation of a b-catenin-LC3 complex, attenuating b-catenin/TCF-driven transcription and proliferation to favour adaptation during metabolic stress. Formation of the b-catenin-LC3 complex is mediated by a W/YXXI/L motif and LC3-interacting region (LIR) in b-catenin, which is required for interaction with LC3 and non-proteasomal degradation of b-catenin. Thus, Wnt/b-catenin represses autophagy and p62 expression, while b-catenin is itself targeted for autophagic clearance in autolysosomes upon autophagy induction. These findings reveal a regulatory feedback mechanism that place b-catenin at a key cellular integration point coordinating proliferation with autophagy, with implications for targeting these pathways for cancer therapy.

Wound angiogenesis is an integral part of tissue repair and is impaired in many pathologies of healing. Here, we investigate the cellular interactions between innate immune cells and endothelial cells at wounds that drive neoangiogenic sprouting in real time and in vivo. Our studies in mouse and zebrafish wounds indicate that macrophages are drawn to wound blood vessels soon after injury and are intimately associated throughout the repair process and that macrophage ablation results in impaired neoangiogenesis. Macrophages also positively influence wound angiogenesis by driving resolution of anti‐angiogenic wound neutrophils. Experimental manipulation of the wound environment to specifically alter macrophage activation state dramatically influences subsequent blood vessel sprouting, with premature dampening of tumour necrosis factor‐α expression leading to impaired neoangiogenesis. Complementary human tissue culture studies indicate that inflammatory macrophages associate with endothelial cells and are sufficient to drive vessel sprouting via vascular endothelial growth factor signalling. Subsequently, macrophages also play a role in blood vessel regression during the resolution phase of wound repair, and their absence, or shifted activation state, impairs appropriate vessel clearance.

Deregulation of cell survival pathways and resistance to apoptosis are widely accepted to be fundamental aspects of tumorigenesis. As in many tumours, the aberrant growth and survival of colorectal tumour cells is dependent upon a small number of highly activated signalling pathways, the inhibition of which elicits potent growth inhibitory or apoptotic responses in tumour cells. Accordingly, there is considerable interest in therapeutics that can modulate survival signalling pathways and target cancer cells for death. There is emerging evidence that cannabinoids, especially D 9 -tetrahydrocannabinol (THC), may represent novel anticancer agents, due to their ability to regulate signalling pathways critical for cell growth and survival. Here, we report that CB1 and CB2 cannabinoid receptors are expressed in human colorectal adenoma and carcinoma cells, and show for the first time that THC induces apoptosis in colorectal cancer cells. THC-induced apoptosis was rescued by pharmacological blockade of the CB1, but not CB2, cannabinoid receptor. Importantly, THC treatment resulted in CB1-mediated inhibition of both RAS-MAPK/ERK and PI3K-AKT survival signalling cascades; two key cell survival pathways frequently deregulated in colorectal tumours. The inhibition of ERK and AKT activity by THC was accompanied by activation of the proapoptotic BCL-2 family member BAD. Reduction of BAD protein expression by RNA interference rescued colorectal cancer cells from THC-induced apoptosis. These data suggest an important role for CB1 receptors and BAD in the regulation of apoptosis in colorectal cancer cells. The use of THC, or selective targeting of the CB1 receptor, may represent a novel strategy for colorectal cancer therapy. ' 2007 Wiley-Liss, Inc.

Loss of tumour suppressor gene function can occur as a result of epigenetic silencing of large chromosomal regions, referred to as long-range epigenetic silencing (LRES), and genome-wide analyses have revealed that LRES is present in many cancer types. Here we utilize Illumina Beadchip methylation array analysis to identify LRES across 800 kb of chromosome 5q31 in colorectal adenomas and carcinomas (n ¼ 34) relative to normal colonic epithelial DNA (n ¼ 6). This region encompasses 53 individual protocadherin (PCDH) genes divided among three gene clusters. Hypermethylation within these gene clusters is asynchronous; while most PCDH hypermethylation occurs early, and is apparent in adenomas, PCDHGC3 promoter methylation occurs later in the adenoma-carcinoma transition. PCDHGC3 was hypermethylated in 17/28 carcinomas (60.7%) according to methylation array analysis. Quantitative real-time reverse transcription-polymerase chain reaction showed that PCDHGC3 is the highest expressed PCDH in normal colonic epithelium, and that there was a strong reciprocal relationship between PCDHGC3 methylation and expression in carcinomas (R ¼ À0.84). PCDH LRES patterns are reflected in colorectal tumour cell lines; adenoma cell lines are not methylated at PCDHGC3 and show abundant expression at the mRNA and protein level, while the expression is suppressed in hypermethylated carcinoma cell lines (R ¼ À0.73). Short-interfering RNAmediated reduction of PCDHGC3 led to a decrease of apoptosis in RG/C2 adenoma cells, and overexpression of PCDHGC3 in HCT116 cells resulted in the reduction of colony formation, consistent with tumour suppressor capabilities for PCDHGC3. Further functional analysis showed that PCDHGC3 can suppress Wnt and mammalian target of rapamycin signalling in colorectal cancer cell lines. Taken together, our data suggest that the PCDH LRES is an important tumour suppressor locus in colorectal cancer, and that PCDHGC3 may be a strong marker and driver for the adenoma-carcinoma transition.

LGR5 is a marker of normal and cancer stem cells in various tissues where it functions as a receptor for R-spondins and increases canonical Wnt signalling amplitude. Here we report that LGR5 is also highly expressed in a subset of high grade neuroblastomas. Neuroblastoma is a clinically heterogenous paediatric cancer comprising a high proportion of poor prognosis cases (~40%) which are frequently lethal. Unlike many cancers, Wnt pathway mutations are not apparent in neuroblastoma, although previous microarray analyses have implicated deregulated Wnt signalling in high-risk neuroblastoma. We demonstrate that LGR5 facilitates high Wnt signalling in neuroblastoma cell lines treated with Wnt3a and R-spondins, with SK-N-BE(2)-C, SK-N-NAS and SH-SY5Y cell-lines all displaying strong Wnt induction. These lines represent MYCN-amplified, NRAS and ALK mutant neuroblastoma subtypes respectively. Wnt3a/R-Spondin treatment also promoted nuclear translocation of β-catenin, increased proliferation and activation of Wnt target genes. Strikingly, short-interfering RNA mediated knockdown of LGR5 induces dramatic Wntindependent apoptosis in all three cell-lines, accompanied by greatly diminished phosphorylation of mitogen/extracellular signal-regulated kinases (MEK1/2) and extracellular signal-regulated kinases (ERK1/2), and an increase of BimEL, an apoptosis facilitator downstream of ERK. Akt signalling is also decreased by a Rictor dependent, PDK1-independent mechanism. LGR5 expression is cell cycle regulated and LGR5 depletion triggers G1 cell-cycle arrest, increased p27 and decreased phosphorylated retinoblastoma protein. Our study therefore characterises new cancer-associated pathways regulated by LGR5, and suggest that targeting of LGR5 may be of therapeutic benefit for neuroblastomas with diverse etiologies, as well as other cancers expressing high LGR5.