The ubiquitin ligase COP1 is a critical negative regulator of p53.

COP1 (constitutively photomorphogenic 1) is a RING-finger-containing protein that functions to repress plant photomorphogenesis, the light-mediated programme of plant development. Mutants of COP1 are constitutively photomorphogenic, and this has been attributed to their inability to negatively regulate the proteins LAF1 (ref. 1) and HY5 (ref. 2). The role of COP1 in mammalian cells is less well characterized. Here we identify the tumour-suppressor protein p53 as a COP1-interacting protein. COP1 increases p53 turnover by targeting it for degradation by the proteasome in a ubiquitin-dependent fashion, independently of MDM2 or Pirh2, which are known to interact with and negatively regulate p53. Moreover, COP1 serves as an E3 ubiquitin ligase for p53 in vitro and in vivo, and inhibits p53-dependent transcription and apoptosis. Depletion of COP1 by short interfering RNA (siRNA) stabilizes p53 and arrests cells in the G1 phase of the cell cycle. Furthermore, we identify COP1 as a p53-inducible gene, and show that the depletion of COP1 and MDM2 by siRNA cooperatively sensitizes U2-OS cells to ionizing-radiation-induced cell death. Overall, these results indicate that COP1 is a critical negative regulator of p53 and represents a new pathway for maintaining p53 at low levels in unstressed cells.

Loss of the serine/threonine kinase fused results in postnatal growth defects and lethality due to progressive hydrocephalus.

The Drosophila Fused (Fu) kinase is an integral component of the Hedgehog (Hh) pathway that helps promote Hh-dependent gene transcription. Vertebrate homologues of Fu function in the Hh pathway in vitro, suggesting that Fu is evolutionarily conserved. We have generated fused (stk36) knockout mice to address the in vivo function of the mouse Fu (mFu) homologue. fused knockouts develop normally, being born in Mendelian ratios, but fail to thrive within 2 weeks, displaying profound growth retardation with communicating hydrocephalus and early mortality. The fused gene is expressed highly in ependymal cells and the choroid plexus, tissues involved in the production and circulation of cerebral spinal fluid (CSF), suggesting that loss of mFu disrupts CSF homeostasis. Similarly, fused is highly expressed in the nasal epithelium, where fused knockouts display bilateral suppurative rhinitis. No obvious defects were observed in the development of organs where Hh signaling is required (limbs, face, bones, etc.). Specification of neuronal cell fates by Hh in the neural tube was normal in fused knockouts, and induction of Hh target genes in numerous tissues is not affected by the loss of mFu. Furthermore, stimulation of fused knockout cerebellar granule cells to proliferate with Sonic Hh revealed no defect in Hh signal transmission. These results show that the mFu homologue is not required for Hh signaling during embryonic development but is required for proper postnatal development, possibly by regulating the CSF homeostasis or ciliary function.

Myodegeneration in EDA-A2 transgenic mice is prevented by XEDAR deficiency.

EDA-A1 and EDA-A2 are members of the tumor necrosis factor family of ligands. The products of alternative splicing of the ectodysplasin (EDA) gene, EDA-A1 and EDA-A2 differ by an insertion of two amino acids and bind to distinct receptors. The longer isoform, EDA-A1, binds to EDAR and plays an important role in sweat gland, hair, and tooth development; mutations in EDA, EDAR, or the downstream adaptor EDARADD cause hypohidrotic ectodermal dysplasia. EDA-A2 engages the receptor XEDAR, but its role in the whole organism is less clear. We have generated XEDAR-deficient mice by gene targeting and transgenic mice expressing secreted forms of EDA-A1 or EDA-A2 downstream of the skeletal muscle-specific myosin light-chain 2 or skin-specific keratin 5 promoter. Mice lacking XEDAR were indistinguishable from their wild-type littermates, but EDA-A2 transgenic mice exhibited multifocal myodegeneration. This phenotype was not observed in the absence of XEDAR. Skeletal muscle in EDA-A1 transgenic mice was unaffected, but their sebaceous glands were hypertrophied and hyperplastic, consistent with a role for EDA-A1 in the development of these structures. These data indicate that XEDAR-transduced signals are dispensable for development of ectoderm-derived organs but might play a role in skeletal muscle homeostasis.

Tumor-driven paracrine platelet-derived growth factor receptor alpha signaling is a key determinant of stromal cell recruitment in a model of human lung carcinoma.

Activated fibroblasts are thought to play important roles in the progression of many solid tumors, but little is known about the mechanisms responsible for the recruitment of fibroblasts in tumors. Using several methods, we identified platelet-derived growth factor A (PDGFA) as the major fibroblast chemoattractant and mitogen from conditioned medium generated by the Calu-6 lung carcinoma cell line. In addition, we showed that Calu-6 tumors express significant levels of PDGFC, and that the levels of expression of these two PDGFRalpha ligands correlate strongly with the degree of stromal fibroblast infiltration into the tumor mass. The most intense expression of PDGFRalpha was observed in fibroblasts in the tumor outer rim. We subsequently showed that disrupting PDGFRalpha-mediated signaling results in significant inhibition of tumor growth in vivo. Furthermore, analysis of a compendium of microarray data revealed significant expression of PDGFA, PDGFC, and PDGFRalpha in human lung tumors. We propose that therapies targeting this stromal cell type may be effective in treating certain types of solid tumors.

Quantitative in situ hybridization of tissue microarrays.

Tissue microarrays enable the rapid histological localization of gene expression in hundreds of archival samples by in situ hybridization. However, the scoring of tissue microarray data may be influenced by intra- and inter-observer variations, and categorizing continuous variables risks discarding potentially meaningful information. Quantitation imposes a greater degree of objectivity, is more reproducible than subjective discriminations, and facilitates the communication and clarity of definitions. Phosphorimaging has been successfully used to quantitate the hybridization signal intensity from arrayed tissues. The process is rapid and has a wide dynamic range, surpassing the densitometric analysis of autoradiograms. This paper presents a detailed method for quantitative isotopic in situ hybridization on formalin-fixed paraffin-embedded tissue microarrays. In addition, the method includes a protocol for the development of synthetic agarose cores to control for the specificity and sensitivity of hybridization.

EphB2 is a prognostic factor in colorectal cancer.

A receptor tyrosine kinase for ephrin ligands, EphB2 is expressed in colorectal cancer and has been proposed as a target for immunoconjugate therapy. The aim of this study was to perform a detailed histologic analysis of EphB2 expression in normal and neoplastic colorectal tissues. In addition, we sought to evaluate EphB2 expression as a prognostic factor in colorectal cancer. Expression of EphB2 was examined in normal colon (n = 28), colorectal cell lines (n = 20), colorectal adenomas (n = 148), primary cancers (n = 28), and metastases (n = 39) using immunohistochemistry. In addition, a series of primary cancers and matched normal (n = 342) with outcome data were profiled in tissue microarrays. The intensity of EphB2 expression was assessed in the entire series by immunohistochemistry, and in a subset by in situ hybridization. Overall survival and recurrence-free survival were correlated with EphB2 protein expression in retrospective subset analyses. Epithelial EphB2 expression was shown at all stages of colorectal tumorigenesis, including the base of all normal crypts, 77% of adenomas, 82% of primary cancers, and 64% of metastases. Although homogeneous expression was observed in adenomas, the pattern of staining was focal (mean 25%) in most malignant lesions. Patients whose tumor stained 2+ for EphB2 expression (versus 0/1+) exhibited significantly prolonged overall survival: mean duration of survival, 2,514 versus 1,044 days; hazard ratio, 0.45; 95% confidence interval, 0.18 to 0.95 (P = 0.035). In summary, EphB2 is expressed in normal crypts, colorectal adenomas, primary cancers, and metastases. High levels of EphB2 expression are associated with a longer mean duration of survival in colorectal cancer.

COP1, the negative regulator of p53, is overexpressed in breast and ovarian adenocarcinomas.

The tumor suppressor protein p53 plays a central role in protecting normal cells from undergoing transformation. Thus, it is fitting that cancer cells selectively dampen the p53 response to gain a selective growth advantage. In fact, the p53 gene is the most commonly mutated tumor suppressor gene in human cancers, and if the gene is not mutated, then other components of the p53 pathways are skewed to dampen the p53 response to stress. We recently identified COP1 as a novel and critical negative regulator of p53. COP1 is a RING finger-containing protein that targets p53 for degradation to the proteasome and is necessary for p53 turnover in normal and cancer cells. However, the association between COP1 and cancer remains to be determined. We performed expression analysis of COP1 in ovarian and breast cancer tissue microarrays. COP1 is significantly overexpressed in 81% (25 of 32) of breast and 44% (76 of 171) of ovarian adenocarcinoma as assessed by in situ hybridization and immunohistochemistry. Overexpression of COP1 correlated with a striking decrease in steady state p53 protein levels and attenuation of the downstream target gene, p21, in cancers that retain a wild-type p53 gene status. Overall, these results suggest that overexpression of COP1 contributes to the accelerated degradation of p53 protein in cancers and attenuates the tumor suppressor function of p53.

Secreted sulfatases Sulf1 and Sulf2 have overlapping yet essential roles in mouse neonatal survival.

BACKGROUND: Heparan sulfate proteoglycans (HSPGs) use highly sulfated polysaccharide side-chains to interact with several key growth factors and morphogens, thereby regulating their accessibility and biological activity. Various sulfotransferases and sulfatases with differing specificities control the pattern of HSPG sulfation, which is functionally critical. Among these enzymes in the mouse are two secreted 6-O-endosulfatases, Sulf1 and Sulf2, which modify HSPGs in the extracellular matrix and on the cell surface. The roles of Sulf1 and Sulf2 during normal development are not well understood. METHODS/RESULTS: To investigate the importance of Sulf1 and Sulf2 for embryonic development, we generated mice genetically deficient in these genes and assessed the phenotypes of the resulting secreted sulfatase-deficient mice. Surprisingly, despite the established crucial role of HSPG interactions during development, neither Sulf1- nor Sulf2-deficient mice showed significant developmental flaws. In contrast, mice deficient in both Sulf1and Sulf2 exhibited highly penetrant neonatal lethality. Loss of viability was associated with multiple, although subtle, developmental defects, including skeletal and renal abnormalities. CONCLUSIONS: These results show that Sulf1 and Sulf2 play overlapping yet critical roles in mouse development and are redundant and essential for neonatal survival.

Impact of vascular endothelial growth factor-A expression, thrombospondin-2 expression, and microvessel density on the treatment effect of bevacizumab in metastatic colorectal cancer.

PURPOSE: Bevacizumab is a monoclonal antibody to vascular endothelial growth factor-A (VEGF). In the pivotal trial in metastatic colorectal cancer (mCRC), addition of bevacizumab to first-line irinotecan, fluorouracil, and leucovorin (IFL) significantly prolonged median survival. The aim of these retrospective subset analyses was to evaluate VEGF, thrombospondin-2 (THBS-2), and microvessel density (MVD) as prognostic factors and/or predictors of benefit from bevacizumab. PATIENTS AND METHODS: In the pivotal trial, 813 patients with untreated mCRC were randomly assigned to receive IFL plus bevacizumab or placebo. Of 312 tissue samples collected (285 primaries, 27 metastases), outcome data were available for 278 (153 bevacizumab, 125 placebo). Epithelial and stromal VEGF expression were assessed by in situ hybridization (ISH) and immunohistochemistry on tissue microarrays and whole sections. Stromal THBS-2 expression was examined by ISH on tissue microarrays. MVD was quantified by Chalkley count. Overall survival was associated with these variables in retrospective subset analyses. RESULTS: In all subgroups, estimated hazard ratios (HRs) for risk of death were < 1 for bevacizumab-treated patients regardless of the level of VEGF or THBS-2 expression or MVD. Patients with a high THBS-2 score showed a nonsignificant improvement in survival following bevacizumab treatment (HR = 0.11; 95% CI, 0.02 to 0.51) compared to patients with a low score (HR = 0.65; 95% CI, 0.41 to 1.02); interaction analysis P = .22. VEGF or THBS-2 expression and MVD were not significant prognostic factors. CONCLUSION: These exploratory analyses suggest that in patients with mCRC addition of bevacizumab to IFL improves survival regardless of the level of VEGF or THBS-2 expression, or MVD.

Cutting edge: novel human dendritic cell- and monocyte-attracting chemokine-like protein identified by fold recognition methods.

Chemokines play an important role in the immune system by regulating cell trafficking in homeostasis and inflammation. In this study, we report the identification and characterization of a novel cytokine-like protein, DMC (dendritic cell and monocyte chemokine-like protein), which attracts dendritic cells and monocytes. The key to the identification of this putative new chemokine was the application of threading techniques to its uncharacterized sequence. Based on our studies, DMC is predicted to have an IL-8-like chemokine fold and to be structurally and functionally related to CXCL8 and CXCL14. Consistent with our predictions, DMC induces migration of monocytes and immature dendritic cells. Expression studies show that DMC is constitutively expressed in lung, suggesting a potential role for DMC in recruiting monocytes and dendritic cells from blood into lung parenchyma.

Plasmalemmal vesicle-associated protein (PLVAP) is expressed by tumour endothelium and is upregulated by vascular endothelial growth factor-A (VEGF).

Vascular endothelial growth factor-A (VEGF) is an important regulator of vascular permeability. In preclinical studies, VEGF induces endothelial fenestrations in pre-existing and neo-vasculature, while inhibition of VEGF leads to a reduction in endothelial fenestrations. Recently, vascular regression in response to VEGF inhibition has been shown to correlate with the presence of endothelial fenestrations. Plasmalemmal vesicle-associated protein (PLVAP) is believed to be a component of diaphragmed endothelial fenestrations, but a direct relationship with VEGF signalling has not been established. The aim of this study was to characterize the expression pattern of PLVAP and investigate whether PLVAP is a transcriptional target of VEGF signal transduction. The expression pattern of PLVAP was characterized in normal and neoplastic human tissues by in situ hybridization and/or immunohistochemistry. The role of VEGF signal transduction in the regulation of PLVAP expression was investigated in vitro using receptor-selective engineered forms of VEGF, a neutralizing monoclonal antibody against VEGF, and inhibitors of downstream signalling pathways. PLVAP mRNA and protein were widely expressed in the endothelium of normal and neoplastic tissues. In cultured endothelial cells, VEGF signalling through receptor 2 stimulated expression of PLVAP total RNA and protein. This induction could be blocked with an anti-VEGF monoclonal antibody and by inhibitors of phosphatidylinositol 3-kinase (LY294002) or p38 mitogen-activated protein kinase (SB203580), but not by PD98059, a mitogen-activated protein/extracellular signal-regulated kinase 1 inhibitor. These data show that PLVAP is more widely expressed in the vasculature of normal tissues than previously thought and that it is expressed in the vasculature of most human tumours. We suggest that PLVAP is a downstream target of VEGF signalling. This work solidifies the association between VEGF and the appearance and maintenance of fenestrations by providing a potential mechanistic link.

WISP-1 is an osteoblastic regulator expressed during skeletal development and fracture repair.

Wnt-1-induced secreted protein 1 (WISP-1) is a member of the CCN (connective tissue growth factor, Cyr61, NOV) family of growth factors. Experimental evidence suggests that CCN family members are involved in skeletogenesis and bone healing. To investigate the role of WISP-1 in osteogenic processes, we characterized its tissue and cellular expression and evaluated its activity in osteoblastic and chondrocytic cell culture models. During embryonic development, WISP-1 expression was restricted to osteoblasts and to osteoblastic progenitor cells of the perichondral mesenchyme. In vitro, we showed that WISP-1 expression in differentiating osteoblasts promotes BMP-2-induced osteoblastic differentiation. Using in situ and cell binding analysis, we demonstrated WISP-1 interaction with perichondral mesenchyme and undifferentiated chondrocytes. We evaluated the effect of WISP-1 on chondrocytes by generating stably transfected mouse chondrocytic cell lines. In these cells, WISP-1 increased proliferation and saturation density but repressed chondrocytic differentiation. Because of the similarity between skeletogenesis and bone healing, we also analyzed WISP-1 spatiotemporal expression in a fracture repair model. We found that WISP-1 expression recapitulates the pattern observed during skeletal development. Our data demonstrate that WISP-1 is an osteogenic potentiating factor promoting mesenchymal cell proliferation and osteoblastic differentiation while repressing chondrocytic differentiation. Therefore, we propose that WISP-1 plays an important regulatory role during bone development and fracture repair.

A mouse model of hepatocellular carcinoma: ectopic expression of fibroblast growth factor 19 in skeletal muscle of transgenic mice.

Most mouse models of hepatocellular carcinoma have expressed growth factors and oncogenes under the control of a liver-specific promoter. In contrast, we describe here the formation of liver tumors in transgenic mice overexpressing human fibroblast growth factor 19 (FGF19) in skeletal muscle. FGF19 transgenic mice had elevated hepatic alpha-fetoprotein mRNA as early as 2 months of age, and hepatocellular carcinomas were evident by 10 months of age. Increased proliferation of pericentral hepatocytes was demonstrated by 5-bromo-2'-deoxyuridine incorporation in the FGF19 transgenic mice before tumor formation and in nontransgenic mice injected with recombinant FGF19 protein. Areas of small cell dysplasia were initially evident pericentrally, and dysplastic/neoplastic foci throughout the hepatic lobule were glutamine synthetase-positive, suggestive of a pericentral origin. Consistent with chronic activation of the Wingless/Wnt pathway, 44% of the hepatocellular tumors from FGF19 transgenic mice had nuclear staining for beta-catenin. Sequencing of the tumor DNA encoding beta-catenin revealed point mutations that resulted in amino acid substitutions. These findings suggest a previously unknown role for FGF19 in hepatocellular carcinomas.

GEPIS--quantitative gene expression profiling in normal and cancer tissues.

MOTIVATION: Expression profiling in diverse tissues is fundamental to understanding gene function as well as therapeutic target identification. The vast collection of expressed sequence tags (ESTs) and the associated tissue source information provides an attractive opportunity for studying gene expression. RESULTS: To facilitate EST-based expression analysis, we developed GEPIS (gene expression profiling in silico), a tool that integrates EST and tissue source information to compute gene expression patterns in a large panel of normal and tumor samples. We found EST-based expression patterns to be consistent with published papers as well as our own experimental results. We also built a GEPIS Regional Atlas that depicts expression characteristics of all genes in a selected genomic region. This program can be adapted for large-scale screening for genes with desirable expression patterns, as illustrated by our large-scale mining for tissue- and tumor-specific genes. AVAILABILITY: The email server version of the GEPIS application is freely available at http://share.gene.com/share/gepis. An interactive version of GEPIS will soon be freely available at http://www.cgl.ucsf.edu/Research/genentech/gepis/. The source code, modules, data and gene lists can be downloaded at http://share.gene.com/share/gepis.