Receptor tyrosine kinase EphA2 is regulated by p53-family proteins and induces apoptosis

Loss of EphA2 receptor tyrosine kinase reduces ApcMin/+ tumorigenesis

The Eph receptor A2 (EphA2) is overexpressed in a range of human epithelial cancers, a phenotype that is associated with cancer cell proliferation, progression and angiogenesis. Mouse models of mammary neoplasia have confirmed the role of EphA2 as mice carrying a knockout allele of EphA2 were resistant to breast cancer, a phenotype that was associated with interactions between EphA2 and ErbB2. We investigated in vivo the role of EphA2 in GI cancer. To determine whether EphA2 influences intestinal tumorigenesis, we used qRT-PCR to examine the mRNA expression levels of EphA2 in tumors from the small intestine and colon of Apc(Min/+) mice. We found that EphA2 was significantly up-regulated in tumors from both regions when compared with normal control tissues. We then evaluated the spatial expression patterns of EphA2 protein using immunohistochemistry in both the small intestine and colon and found that in normal tissues EphA2 was robustly expressed in highly differentiated cells, such as cells of the villi, but that EphA2 expression was largely absent from the stem cell niche and proliferative zones of intestinal crypts. In contrast, in tumors EphA2 was broadly expressed. Finally, we created a strain of Apc(Min/+) mice carrying a genetic knockout of the EphA2 gene. These mice developed significantly fewer and smaller tumors in both the small and large intestine. Overall, our results indicate that EphA2 plays an oncogenic role in the mammalian intestine suggesting that strategies to target EphA2 activity may offer new therapeutic modalities for colorectal cancer.

The EphA2 receptor and ephrinA1 ligand in solid tumors: function and therapeutic targeting

The Eph receptor tyrosine kinases and ephrin ligands have been studied extensively for their roles in developmental processes. In recent years, Eph receptors and ephrins have been found to be integral players in cancer formation and progression. Among these are EphA2 and ephrinA1, which are involved in the development and maintenance of many different types of solid tumors. The function of EphA2 and ephrinA1 in tumorigenesis and tumor progression is complex and seems to be dependent on cell type and microenvironment. These variables affect the expression of the EphA2 and ephrinA1 proteins, the pathways through which they induce signaling, and the functional consequences of that signaling on the behavior of tumor cells and tumor-associated cells. This review will specifically focus on the roles that EphA2 and ephrinA1 play in the different cell types that contribute to the malignancy of solid tumors, with emphasis on the opportunities for therapeutic targeting.

EphrinB3 is an anti-apoptotic ligand that inhibits the dependence receptor functions of EphA4 receptors during adult neurogenesis

Eph receptors have been implicated in regulating a diverse array of cellular functions in the developing nervous system. Recently, Eph receptors have been shown to promote cell death in adult germinal zones; however, their mechanisms of action remain ill-defined. In this study, we demonstrate that EphA4 is a new member of the dependence receptors family, which can initiate cell death in the absence of its ligand ephrinB3. Upon removal of its ligand, EphA4 triggers cell death that is dependent on caspase activation as caspase inhibitors prevent cell death. EphA4 itself is cleaved by caspase-3-like caspase in the intracellular domain at position D773/774, which is necessary for cell death initiation as mutation of the cleavage site abolishes apoptosis. In the adult subventricular zone, abolishing ephrinB3 results in increased cell death, while the absence of EphA4 results in excessive numbers of neuroblasts. Furthermore, infusion of soluble ephrinB3 into the lateral ventricle reduced cell death, and together these results support a dependence role for EphA4 in adult neurogenesis.

Comparative 3'UTR analysis allows identification of regulatory clusters that drive Eph/ephrin expression in cancer cell lines

Eph receptors are the largest family of receptor tyrosine kinases. Together with their ligands, the ephrins, they fulfill multiple biological functions. Aberrant expression of Ephs/ephrins leading to increased Eph receptor to ephrin ligand ratios is a critical factor in tumorigenesis, indicating that tight regulation of Eph and ephrin expression is essential for normal cell behavior. The 3'-untranslated regions (3'UTRs) of transcripts play an important yet widely underappreciated role in the control of protein expression. Based on the assumption that paralogues of large gene families might exhibit a conserved organization of regulatory elements in their 3'UTRs we applied a novel bioinformatics/molecular biology approach to the 3'UTR sequences of Eph/ephrin transcripts. We identified clusters of motifs consisting of cytoplasmic polyadenylation elements (CPEs), AU-rich elements (AREs) and HuR binding sites. These clusters bind multiple RNA-stabilizing and destabilizing factors, including HuR. Surprisingly, despite its widely accepted role as an mRNA-stabilizing protein, we further show that binding of HuR to these clusters actually destabilizes Eph/ephrin transcripts in tumor cell lines. Consequently, knockdown of HuR greatly modulates expression of multiple Ephs/ephrins at both the mRNA and protein levels. Together our studies suggest that overexpression of HuR as found in many progressive tumors could be causative for disarranged Eph receptor to ephrin ligand ratios leading to a higher degree of tissue invasiveness.

Expressions of EphA2 and EphrinA-1 in early squamous cell cervical carcinomas and their relation to prognosis

By using immunohistochemistry we investigated the expression of EphA2 and EphrinA-1 in 217 early squamous cell cervical carcinomas and examine their prognostic relevance. For EphA2 expression, 21 tumors (10%) showed negative, 108 (50%) weak positive, 69 (32%) moderate positive and 19 (9%) strong positive, whereas for EphrinA-1 expression, 33 tumors (15%) showed negative, 91 (42%) weak positive, 67 (31%) moderate positive and 26 (12%) strong positive. In univariate analysis high expression (strong staining) of EphrinA-1 was associated with poor disease-free (P = 0.033) and disease-specific (P = 0.039) survival. However, in the multivariate analyses neither EphrinA-1 nor EphA2 was significantly associated to survival. The increased levels of EphA2 and EphrinA-1 in a relative high number of early stage squamous cell carcinomas suggested that these two proteins may play an important role in the development of a subset of early cervical cancers. However, EphA2 and EphrinA-1 were not independently associated with clinical outcome.

The receptor tyrosine kinase EphA2 promotes mammary adenocarcinoma tumorigenesis and metastatic progression in mice by amplifying ErbB2 signaling

Overexpression of the receptor tyrosine kinase EPH receptor A2 (EphA2) is commonly observed in aggressive breast cancer and correlates with a poor prognosis. However, while EphA2 has been reported to enhance tumorigenesis, proliferation, and MAPK activation in several model systems, other studies suggest that EphA2 activation diminishes these processes and inhibits the activity of MAPK upon ligand stimulation. In this study, we eliminated EphA2 expression in 2 transgenic mouse models of mammary carcinoma. EphA2 deficiency impaired tumor initiation and metastatic progression in mice overexpressing ErbB2 (also known as Neu) in the mammary epithelium (MMTV-Neu mice), but not in mice overexpressing the polyomavirus middle T antigen in mammary epithelium (MMTV-PyV-mT mice). Histologic and ex vivo analyses of MMTV-Neu mouse mammary epithelium indicated that EphA2 enhanced tumor proliferation and motility. Biochemical analyses revealed that EphA2 formed a complex with ErbB2 in human and murine breast carcinoma cells, resulting in enhanced activation of Ras-MAPK signaling and RhoA GTPase. Additionally, MMTV-Neu, but not MMTV-PyV-mT, tumors were sensitive to therapeutic inhibition of EphA2. These data suggest that EphA2 cooperates with ErbB2 to promote tumor progression in mice and may provide a novel therapeutic target for ErbB2-dependent tumors in humans. Moreover, EphA2 function in tumor progression appeared to depend on oncogene context, an important consideration for the application of therapies targeting EphA2.

EphA2 is an essential mediator of UV radiation-induced apoptosis

One of the physiologic consequences of excessive UV radiation (UVR) exposure is apoptosis. This critical response serves to eliminate genetically injured cells and arises, in part, from activation of DNA damage and p53 signaling. Other contributory pathways, however, likely exist but have not been fully characterized. In a recent global screen of UVR response genes in melanocytes, we identified the receptor tyrosine kinase EPHA2. Using a combination of genetic and pharmacologic approaches, we set out to investigate the upstream regulation of EphA2 by UVR and the functional consequences of this effect. We found that the UVR-associated increase in EphA2 occurs in melanocytes, keratinocytes, and fibroblasts from both human and murine sources. More specifically, UVR effectively up-regulated EphA2 individually in p53-null, p63-null, and p73-null murine embryonic fibroblasts (MEF), suggesting that the p53 family of transcription factors is not essential for the observed effect. However, inhibition of mitogen-activated protein kinase (MAPK) signaling by U0126 and PD98059 significantly reduced the UVR response whereas overexpression of oncogenic NRAS led to an increase in EphA2. These results confirm that UVR induces EphA2 by a p53-independent, but MAPK-dependent, mechanism. In response to UV irradiation, Epha2(-/-) MEFs were highly resistant to UVR-mediated cytotoxicity and apoptosis whereas introduction of EphA2 into both wild-type and p53-null MEFs led to activation of an apoptotic program that can be blocked by caspase-8 inhibition. These functional findings suggest that EphA2 is in fact an essential p53-independent, caspase-8-dependent proapoptotic factor induced by UVR.

Identification and characterization of a novel gene differentially expressed in zebrafish cross-subfamily cloned embryos

Background

Cross-species nuclear transfer has been shown to be a potent approach to retain the genetic viability of a certain species near extinction. However, most embryos produced by cross-species nuclear transfer were compromised because that they were unable to develop to later stages. Gene expression analysis of cross-species cloned embryos will yield new insights into the regulatory mechanisms involved in cross-species nuclear transfer and embryonic development.

Results

A novel gene, K31, was identified as an up-regulated gene in fish cross-subfamily cloned embryos using SSH approach and RACE method. K31 complete cDNA sequence is 1106 base pairs (bp) in length, with a 342 bp open reading frame (ORF) encoding a putative protein of 113 amino acids (aa). Comparative analysis revealed no homologous known gene in zebrafish and other species database. K31 protein contains a putative transmembrane helix and five putative phosphorylation sites but without a signal peptide. Expression pattern analysis by real time RT-PCR and whole-mount in situ hybridization (WISH) shows that it has the characteristics of constitutively expressed gene. Sub-cellular localization assay shows that K31 protein can not penetrate the nuclei. Interestingly, over-expression of K31 gene can cause lethality in the epithelioma papulosum cyprinid (EPC) cells in cell culture, which gave hint to the inefficient reprogramming events occurred in cloned embryos.

Conclusion

Taken together, our findings indicated that K31 gene is a novel gene differentially expressed in fish cross-subfamily cloned embryos and over-expression of K31 gene can cause lethality of cultured fish cells. To our knowledge, this is the first report on the determination of novel genes involved in nucleo-cytoplasmic interaction of fish cross-subfamily cloned embryos.

Fibronectin type I repeat is a nonactivating ligand for EphA1 and inhibits ATF3-dependent angiogenesis

ATF3 stimulated promoter activity of EphA1 by 3.4-fold in ATF3-dependent angiogenesis in vitro. Although tyrosine kinase activation of EphA1 was dispensable, binding of EphA1 to fibronectin through its type I repeat played an essential role in the angiogenesis. Recombinant proteins containing fibronectin 10th to 12th type I repeat (I 10-12) but not I 12 could inhibit the angiogenesis in vitro by competitively targeting EphA1 with the full-length fibronectin. However, I 12 acquired a higher affinity toward EphA2 with K(d) 18 nm and inhibited vascular endothelial growth factor-dependent angiogenic invasion in a Matrigel plug assay.

EphrinB1-EphB signaling regulates thymocyte-epithelium interactions involved in functional T cell development

The Eph and ephrin families are involved in numerous developmental processes. Recently, an increasing body of evidence has related these families with some aspects of T cell development. In the present study, we show that the addition of either EphB2-Fc or ephrinB1-Fc fusion proteins to fetal thymus organ cultures established from 17-day-old fetal mice decreases the numbers of both double-positive (CD4(+)CD8(+)) and single-positive (both CD4(+)CD8(-) and CD4(-)CD8(+)) thymocytes, in correlation with increased apoptosis. By using reaggregate thymus organ cultures formed by fetal thymic epithelial cells (TEC) and CD4(+)CD8(+) thymocytes, we have also demonstrated that ephrinB1-Fc proteins are able to disorganize the three-dimensional epithelial network that in vivo supports the T cell maturation, and to alter the thymocyte interactions. In addition, in an in vitro model, Eph/ephrinB-Fc treatment also decreases the formation of cell conjugates by CD4(+)CD8(+) thymocytes and TEC as well as the TCR-dependent signaling between both cell types. Finally, immobilized EphB2-Fc and ephrinB1-Fc modulate the anti-CD3 antibody-induced apoptosis of CD4(+)CD8(+) thymocytes in a process dependent on concentration. These results therefore support a role for Eph/ephrinB in the processes of development and selection of thymocytes as well as in the establishment of the three-dimensional organization of TEC.

Inhibition of tumor angiogenesis by p53: a new role for the guardian of the genome

The p53 tumor suppressor protein has long been recognized as the central factor protecting humans from cancer. It has been famously dubbed "the guardian of the genome" due to its ability to respond to genotoxic stress, such as DNA damage and other stress signals, and to protect the genome by inducing a variety of biological responses including DNA repair, cell cycle arrest, and apoptosis. However, the tumor suppressive effects of p53 go far beyond its roles in mediating these three processes. There is growing evidence that p53 also exerts its effects on multiple aspects of tumor formation, including suppression of metastasis and, as summarized in this review, inhibition of new blood vessel development (angiogenesis). The p53 protein has been shown to limit angiogenesis by at least three mechanisms: (1) interfering with central regulators of hypoxia that mediate angiogenesis, (2) inhibiting production of proangiogenic factors, and (3) directly increasing the production of endogenous angiogenesis inhibitors. The combination of these effects allows p53 to efficiently shut down the angiogenic potential of cancer cells. Inactivation of p53, which occurs in approximately half of all tumors, reverses these effects; as a consequence, tumors carrying p53 mutations appear more vascularized and are often more aggressive and correlate with poor prognosis for treatment. Thus, the loss of functional p53 during tumorigenesis likely represents an essential step in the switch to an angiogenic phenotype that is displayed by aggressive tumors.

Gene expression pattern in apoptotic QGY-7703 cells induced by homoharringtonine

AIM

To classify the genes responsible for apoptosis in QGY-7703 cells induced by homoharringtonine (HHT).

METHODS

Apoptosis in QGY-7703 cells induced by HHT was demonstrated by DNA fragmentation and morphological observation. cDNA microarray technology was used to detect gene transcription, and the result of microarrays for genes was confirmed by RT-PCR.

RESULTS

Seventy-eight individual mRNA were identified and their transcription levels changed significantly. Those genes, of which 68% were upregulated and 32% were downregulated, were partially related to apoptosis. They were mostly oncogenes, tumor suppressors, enzymes, and kinases.

CONCLUSION

HHT is a potential drug in the treatment of liver cancer. TGF-beta, TNF, FAS, p38MAPK, and p53 apoptosis signaling pathways were activated during apoptosis in QGY-7703 cells. Such inducible genes may play important roles in apoptosis and deserve to be further studied.

Activation of the EGFR gene target EphA2 inhibits epidermal growth factor-induced cancer cell motility

EphA2 overexpression has been reported in many cancers and is believed to play an important role in tumor metastasis and angiogenesis. We show that the activated epidermal growth factor receptor (EGFR) and the cancer-specific constitutively active EGFR type III deletion mutant (EGFRvIII) induce the expression of EphA2 in mammalian cell lines, including the human cancer cell lines A431 and HN5. The regulation is partially dependent on downstream activation of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase and is a direct effect on the EphA2 promoter. Furthermore, EGFR and EphA2 both localize to the plasma membrane and EphA2 coimmunoprecipitates with activated EGFR and EGFRvIII. Ligand activation of EphA2 and EphA2 knockdown by small interfering RNA inhibit EGF-induced cell motility of EGFR-overexpressing human cancer cells, indicating a functional role of EphA2 in EGFR-expressing cancer cells.

A novel mechanism for p53 to regulate its target gene ECK in signaling apoptosis

Transcription factor p53 regulates its target genes through binding to DNA consensus sequence and activating the promoters of its downstream genes. The conventional p53 consensus binding sequence was defined as two copies of the 10-bp motif 5'-PuPuPuC(A/T)(T/A)GPyPyPy-3' with a spacer of 0 to 13 bp, which exists in the regulatory regions of some p53 target genes. However, there is no such p53 consensus sequence in the promoters of a number of p53-responsive genes, suggesting that there might be other mechanisms whereby p53 transactivates the promoters of its target genes. We report here that p53 uses a novel binding mechanism to regulate the transcription of epithelial cell kinase (ECK), a receptor protein-tyrosine kinase implicated in signal transduction. We show that p53 binds to a 10-bp perfect palindromic decanucleotide (GTGACGTCAC) in the ECK promoter, activates the ECK promoter, and increases the transcription of ECK. This palindrome is required for p53-mediated transactivation of the ECK promoter. ECK is highly responsive to oxidative damage that leads to cell death. Ectopic expression of ECK causes spontaneous apoptosis in breast cancer cells. We found that ectopic expression of a mutant ECK fails to induce apoptosis in cancer cells. Our findings show that p53 is a transcriptional regulator of ECK in mediating apoptosis. The discovery of the novel p53-binding motif in the promoter may lead to the identification of a new class of p53 target genes.

Inhibition of EphA7 up-regulation after spinal cord injury reduces apoptosis and promotes locomotor recovery

Functional impairment after spinal cord injury (SCI) is partially attributed to neuronal cell death, with further degeneration caused by the accompanying apoptosis of myelin-forming oligodendrocytes. The Eph receptor protein tyrosine kinase family and its cognate ligands, the ephrins, have been identified to be involved in axonal outgrowth, synapse formation, and target recognition, mainly mediated by repulsive activity. Recent reports suggest that ephrin/Eph signaling might also play a role as a physiological trigger for apoptosis during embryonic development. Here, we investigated the expression profile of EphA7, after SCI, by using a combination of quantitative real-time PCR (QRT-PCR) and immunohistochemical techniques. QRT-PCR analysis showed an increase in the expression of full-length EphA7 at 7 days postinjury (DPI). Receptor immunoreactivity was shown mostly in astrocytes of the white matter at the injury epicenter. In control animals, EphA7 expression was observed predominantly in motor neurons of the ventral gray matter, although some immunoreactivity was seen in white matter. Furthermore, blocking the expression of EphA7 after SCI using antisense oligonucleotides resulted in significant acceleration of hindlimb locomotor recovery at 1 week. This was a transient effect; by 2 weeks postinjury, treated animals were not different from controls. Antisense treatment also produced a return of nerve conduction, with shorter latencies than in control treated animals after transcranial magnetic stimulation. We identified EphA7 receptors as putative regulators of apoptosis in the acute phase after SCI. These results suggest a functional role for EphA7 receptors in the early stages of SCI pathophysiology.

The role of FoxC1 in earlyXenopus development

FoxC1 is an important transcription factor in vertebrate development since its mutation in humans results in Axenfeld-Rieger syndrome. In the mouse, disturbance of its function causes congenital hydrocephalus and abnormalities in the development of various mesodermal derivatives. In this report, we provide one mechanistic basis for the requirement for FoxC1 in vertebrate development. We find that, in Xenopus laevis embryos, FoxC1 expression is regulated by the maternal T-box transcription factor VegT, via the nodal sub-family of TGFbeta signaling transducers. We show that at the late neurula to early tailbud stage, FoxC1 depletion causes the down-regulation of adhesion molecules, EP and E cadherin, as well as members of the Ephrin/EphR signaling families in the mesoderm germ layer resulting in the loss of adhesion and apoptosis of mesodermal cells.

Expression of EphA2 and EphrinA-1 in vulvar carcinomas and its relation to prognosis

AIMS

To examine the expression of EphA2 and EphrinA-1 in vulvar squamous cell carcinomas and investigate their prognostic relevance.

METHODS

Tumours from 224 patients with vulvar squamous cell carcinomas were investigated for expression of EphA2 and EphrinA-1 using single and double immunostaining methods.

RESULTS

High expression (strong/moderate staining intensity) of EphA2 and EphrinA-1 was observed in 114 (51%) and 126 (56%) vulvar carcinomas, respectively. In the three cases tested using the double immunostaining method, colocalisation of EphA2 and EphrinA-1 proteins was identified in the same neoplastic cells. High EphA2 expression was significantly correlated to high expression of EphrinA-1 (p<0.01) and cyclin A (p<0.01), large tumour size (p = 0.03), deep invasion (p<0.01) and higher FIGO stage (p = 0.05). A correlation between high EphrinA-1 expression and high levels of cyclin A (p<0.01) and p21 (p<0.01), deep invasion (p<0.01) and higher FIGO stage (p = 0.01) was also seen. In univariate analysis, high expression of EphrinA-1 was associated with poor survival (p = 0.03). However, in the multivariate analysis neither EphrinA-1 nor EphA2 were significantly correlated to survival.

CONCLUSIONS

EphA2 and EphrinA-1 were overexpressed in 51% and 56% of the vulvar squamous cell carcinomas, respectively, and high levels of EphA2 and EphrinA-1 proteins were associated with deep tumour invasion and high FIGO stage. However, EphA2 and EphrinA-1 were not independently associated with clinical outcome in vulvar carcinomas.

The EphB4 receptor suppresses breast cancer cell tumorigenicity through an Abl–Crk pathway

Recent evidence supports a role for EphB receptor tyrosine kinases as tumour suppressors in colorectal and prostate cancer. However, it is unclear how these receptors inhibit cancer cell tumorigenicity - an activity that is highly unusual for a family of receptor tyrosine kinases. Here, we report that the EphB4 receptor can behave as a tumour suppressor in a mouse xenograft model of breast cancer when stimulated by its ligand, ephrin-B2. In breast cancer cells, EphB4 activates an antioncogenic pathway involving Abl family tyrosine kinases and the Crk adaptor protein. This Abl-Crk pathway inhibits breast cancer cell viability and proliferation in addition to motility and invasion, and also downregulates the pro-invasive matrix metalloprotease, MMP-2. Consistent with these effects, EphB4 and the Abl-Crk pathway are constitutively active in non-transformed mammary epithelial cells. These findings identify a novel Eph receptor signalling pathway with tumour-suppressor activity and predict that therapeutic intervention to activate EphB4 signalling will inhibit tumour progression.

Upregulation of EphA2 during in vivo and in vitro renal ischemia-reperfusion injury: role of Src kinases

Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury in both native kidneys and renal allografts. Disruption of the actin cytoskeleton is a key event with multiple repercussions on cell adhesion and function during IRI. However, receptors involved in regulating cytoskeletal repair following injury have not been identified. In an in vivo model of renal IRI, we used multiprobe RNase protection assay to examine the expression of Eph receptor tyrosine kinases, key regulators of actin dynamics in embryonic development. We found that one receptor in particular, EphA2, was strongly upregulated in the kidney following IRI. Ephrins, the cell-bound ligands of Eph receptors, were also strongly expressed. In cultured renal tubular cells, diverse injurious stimuli mimicking IRI also resulted in upregulation of EphA2 protein expression. Upregulation of EphA2 was inhibited by the Src kinase inhibitor PP2. Conversely, overexpression of Src kinases strongly enhanced the expression of endogenous EphA2 as well as the activity of a human EphA2 promoter construct. Activation of the Erk pathway was necessary, but not sufficient for full induction of EphA2 upreglation by Src kinases. Stimulation of renal tubular epithelial cells with the EphA2 ligand ephrin-A1 caused tyrosine phosphorylation of endogenous EphA2, paxillin, and an unidentified approximately 65-kDa protein and resulted in increased cortical F-actin staining. In summary, under in vitro conditions mimicking IRI, EphA2 expression is strongly upregulated through a Src kinase-dependent pathway. Interactions between upregulated EphA2 and its ephrin ligands may provide critical cell contact-dependent, bidirectional cues for cytoskeletal repair in renal IRI.

EphrinB3 regulates cell proliferation and survival in adult neurogenesis

Interactions between ephrins and their receptors have been implicated in many processes during central nervous system development. In the adult, ephrins and Eph receptors have been implicated in controlling cell proliferation and neuroblast migration, although there is no direct evidence for the role of ephrinB3 in these functions. In addition, activation of Eph receptors has been shown to regulate transduction pathways important in cell cycle control as well as cell death. We show that ephrinB3 contributes to the control of cell proliferation and survival in the adult subventricular zone (SVZ). EphrinB3(-/-) mice exhibit a significant increase in dividing cells along the lateral ventricle, and altered expression of proteins involved in cell cycle regulation. Gain-of-function approach by infusing soluble ephrinB3-Fc molecules in ephrinB3(-/-) can suppress cell proliferation to wild type levels. At the same time, ephrinB3 also regulates cell survival as greater numbers of cells die in the SVZ of ephrinB3(-/-) mice. Together, our results suggest that ephrinB3 negatively regulates cell cycle progression and cell apoptosis in the adult subventricular zone.

p63 and epithelial biology

The transcription factor p63 is a homologue of the tumor suppressor p53. Unlike p53, which is dispensable for normal development, p63 is critical for the development of stratified epithelial tissues such as epidermis, breast, and prostate. p63 encodes multiple protein isoforms with both transactivating and transcriptional repressor activities that can regulate a wide spectrum of target genes. p63 is also implicated in tumor formation and progression in stratified epithelia, with evidence for both tumor suppressive and oncogenic properties. This review will examine current data and hypotheses regarding the role of p63 in the development, maintenance, and tumorigenesis of stratified epithelium.

TAp63alpha induces AP-2gamma as an early event in epidermal morphogenesis

Epidermal morphogenesis begins with the commitment of the single-layered surface ectoderm to initiate a stratification program, a process that requires the expression of the transcription factor TAp63alpha. To determine the molecular mechanism by which TAp63alpha induces genes associated with the commitment to stratification, such as K14, we have used a combination of in vitro and in vivo approaches. Our initial gene expression profiling studies suggested that TAp63alpha could regulate one or more AP-2 genes, which have been implicated in development and maintenance of the epidermis. We now demonstrate that TAp63alpha directly induces AP-2gamma expression in embryonic epidermis, when commitment to stratification occurs. Furthermore, we show that, in the absence of AP-2gamma, TAp63alpha fails to induce K14 expression in vitro. Our data identify AP-2gamma as the first in vivo target gene of TAp63alpha, and provide novel insights into the molecular mechanisms associated with early events in epidermal morphogenesis.

p53, apoptosis and axon-guidance molecules

The p53 tumor-suppressor gene regulates apoptosis through the transcriptional activation of its target genes. The expression of the axon-guidance molecule UNC5B (also designated p53RDL1), which is a receptor for netrin-1, is directly regulated by p53. In the absence of netrin-1, UNC5B mediates p53-dependent apoptosis. Conversely, in the presence of netrin-1, p53-induced apoptosis is inhibited through the signaling pathway activated by the interaction between netrin-1 and UNC5B. A number of other molecules that are involved in axon guidance are inactivated in human cancers and are also regulated by p53. These findings suggest a close link between axon-guidance molecules and tumorigenesis.

Unique Gene Expression Profile Based on Pathologic Response in Epithelial Ovarian Cancer

Purpose

We investigated whether tumor tissue obtained at diagnosis expresses a specific gene profile that is predictive of findings at second-look surgery in patients with epithelial ovarian cancer (EOC).

Patients and Methods

Tumor tissue obtained at the time of diagnosis was profiled with oligonucleotide microarrays. Class prediction analysis was performed in a training set of 24 patients who had undergone a second-look procedure. The resultant predictive signature was then tested on an independent validation set comprised of 36 patients.

Results

A 93-gene signature referred to as the Chemotherapy Response Profile (CRP) was identified through its association with pathologic complete response. When applied to a separate validation set, the CRP distinguished between patients with unfavorable versus favorable overall survival (median 41 months v not yet reached, respectively, log-rank P = .007), with a median follow-up of 52 months. The signature maintained independent prognostic value in multivariate analysis, controlling for other known prognostic factors such as age, stage, grade, and debulking status. There was no genetic overlap between the CRP and our previously described Ovarian Cancer Prognostic Profile (OCPP), which demonstrated similar prognostic value. The combination of the CRP and OCPP yielded better prognostic discrimination then either profile alone. Genes present in the CRP include BAX, a proapoptotic protein previously associated with chemotherapy response in ovarian cancer.

Conclusion

Identification of a gene expression profile based on pathologic response in EOC provides independent prognostic information and offers potential insights into the mechanism of drug resistance. Efforts to identify a more tailored profile using selected genes from both the CRP and OCPP are underway.

A microarray study of MPP+-treated PC12 Cells: Mechanisms of toxicity (MOT) analysis using bioinformatics tools

Background

This paper describes a microarray study including data quality control, data analysis and the analysis of the mechanism of toxicity (MOT) induced by 1-methyl-4-phenylpyridinium (MPP⁺) in a rat adrenal pheochromocytoma cell line (PC12 cells) using bioinformatics tools. MPP⁺ depletes dopamine content and elicits cell death in PC12 cells. However, the mechanism of MPP⁺-induced neurotoxicity is still unclear.

Results

In this study, Agilent rat oligo 22K microarrays were used to examine alterations in gene expression of PC12 cells after 500 μM MPP⁺ treatment. Relative gene expression of control and treated cells represented by spot intensities on the array chips was analyzed using bioinformatics tools. Raw data from each array were input into the NCTR ArrayTrack database, and normalized using a Lowess normalization method. Data quality was monitored in ArrayTrack. The means of the averaged log ratio of the paired samples were used to identify the fold changes of gene expression in PC12 cells after MPP⁺ treatment. Our data showed that 106 genes and ESTs (Expressed Sequence Tags) were changed 2-fold and above with MPP⁺ treatment; among these, 75 genes had gene symbols and 59 genes had known functions according to the Agilent gene Refguide and ArrayTrack-linked gene library. The mechanism of MPP⁺-induced toxicity in PC12 cells was analyzed based on their genes functions, biological process, pathways and previous published literatures.

Conclusion

Multiple pathways were suggested to be involved in the mechanism of MPP⁺-induced toxicity, including oxidative stress, DNA and protein damage, cell cycling arrest, and apoptosis.

Ephrin-B2 is differentially expressed in the intestinal epithelium in Crohn’s disease and contributes to accelerated epithelial wound healing in vitro

AIM: Eph receptor tyrosine kinases and their membrane bound receptor-like ligands, the ephrins, represent a bi-directional cell-cell contact signaling system that directs epithelial movements in development. The meaning of this system in the adult human gut is unknown. We investigated the Eph/ephrin mRNA expression in the intestinal epithelium of healthy controls and patients with inflammatory bowel disease (IBD).

METHODS: mRNA expression profiles of all Eph/ephrin family members in normal small intestine and colon were established by real-time RT-PCR. In addition, differential expression in IBD was investigated by cDNA array technology, and validated by both real-time RT-PCR and immunohistochemistry. Potential effects of enhanced EphB/ephrin-B signaling were analyzed in an in vitro IEC-6 cell scratch wound model.

RESULTS: Human adult intestinal mucosa exhibits a complex pattern of Eph receptors and ephrins. Beside the known prominent co-expression of EphA2 and ephrinA1, we found abundantly co-expressed EphB2 and ephrin-B1/2. Interestingly, cDNA array data, validated by real-time PCR and immunohistochemistry, showed upregulation of ephrin-B2 in both perilesional and lesional intestinal epithelial cells of IBD patients, suggesting a role in epithelial homeostasis. Stimulation of ephrin-B signaling in ephrin-B1/2 expressing rat IEC-6-cells with recombinant EphB1-Fc resulted in a significant dose-dependent acceleration of wound closure. Furthermore, fluorescence microscopy showed that EphB1-Fc induced coordinated migration of wound edge cells is associated with enhanced formation of lamellipodial protrusions into the wound, increased actin stress fiber assembly and production of laminin at the wound edge.

CONCLUSION: EphB/ephrin-B signaling might represent a novel protective mechanism that promotes intestinal epithelial wound healing, with potential impact on epithelial restitution in IBD.

Genomic analysis of rodent pulmonary tissue following bis-(2-chloroethyl) sulfide exposure

Bis-(2-chloroethyl) sulfide (sulfur mustard, SM) is a carcinogenic alkylating agent that has been utilized as a chemical warfare agent. To understand the mechanism of SM-induced lung injury, we analyzed global changes in gene expression in a rat lung SM exposure model. Rats were injected in the femoral vein with liquid SM, which circulates directly to the pulmonary vein and then to the lung. Rats were exposed to 1, 3, or 6 mg/kg of SM, and lungs were harvested at 0.5, 1, 3, 6, and 24 h postinjection. Three biological replicates were used for each time point and dose tested. RNA was extracted from the lungs and used as the starting material for the probing of replicate oligonucleotide microarrays. The gene expression data were analyzed using principal component analysis and two-way analysis of variance to identify the genes most significantly changed across time and dose. These genes were ranked by p value and categorized based on molecular function and biological process. Computer-based data mining algorithms revealed several biological processes affected by SM exposure, including protein catabolism, apoptosis, and glycolysis. Several genes that are significantly upregulated in a dose-dependent fashion have been reported as p53 responsive genes, suggesting that cell cycle regulation and p53 activation are involved in the response to SM exposure in the lung. Thus, SM exposure induces transcriptional changes that reveal the cellular response to this potent alkylating agent.

Analysis of gene expression changes in a cellular model of Parkinson disease

We employed Serial Analysis of Gene Expression to identify transcriptional changes in a cellular model of Parkinson Disease (PD). The model consisted of neuronally differentiated PC12 cells compared before and after 8 hours' exposure to 6-hydroxydopamine. Approximately 1200 transcripts were significantly induced by 6-OHDA and approximately 500 of these are currently matched to known genes. Here, we categorize the regulated genes according to known functional activities and discuss their potential roles in neuron death and survival and in PD. We find induction of multiple death-associated genes as well as many with the capacity for neuroprotection. This suggests that survival or death of individual neurons in PD may reflect an integrated response to both protective and destructive gene changes. Our findings identify a number of regulated genes as candidates for involvement in PD and therefore as potential targets for therapeutic intervention. Such intervention may include both inhibiting the induction/activity of death-promoting genes and enhancing those with neuroprotective activity.

Ephrin signalling controls brain size by regulating apoptosis of neural progenitors

Mechanisms controlling brain size include the regulation of neural progenitor cell proliferation, differentiation, survival and migration. Here we show that ephrin-A/EphA receptor signalling plays a key role in controlling the size of the mouse cerebral cortex by regulating cortical progenitor cell apoptosis. In vivo gain of EphA receptor function, achieved through ectopic expression of ephrin-A5 in early cortical progenitors expressing EphA7, caused a transient wave of neural progenitor cell apoptosis, resulting in premature depletion of progenitors and a subsequent dramatic decrease in cortical size. In vitro treatment with soluble ephrin-A ligands similarly induced the rapid death of cultured dissociated cortical progenitors in a caspase-3-dependent manner, thereby confirming a direct effect of ephrin/Eph signalling on apoptotic cascades. Conversely, in vivo loss of EphA function, achieved through EphA7 gene disruption, caused a reduction in apoptosis occurring normally in forebrain neural progenitors, resulting in an increase in cortical size and, in extreme cases, exencephalic forebrain overgrowth. Together, these results identify ephrin/Eph signalling as a physiological trigger for apoptosis that can alter brain size and shape by regulating the number of neural progenitors.

Decreased tumorigenic potential of EphA2-overexpressing breast cancer cells following treatment with adenoviral vectors that express EphrinA1

The EphA2 receptor tyrosine kinase is frequently overexpressed in invasive breast cancer cells. Moreover, these malignant cells have unstable cell-cell contacts, which preclude EphA2 from interacting with its ligand, EphrinA1, which is anchored to the membrane of adjacent cells. This defect is important because ligand binding causes EphA2 to transmit signals that negatively regulate tumor cell growth and survival, whereas the absence of ligand binding favors these same behaviors. In our present study, human adenoviral type 5 (HAd) vectors were engineered to express secreted-forms of EphrinA1. These vectors were used to infect MDA-MB-231 human breast cancer cells, or MCF-10A human breast epithelial cells providing matched controls. Infection with HAd-EphrinA1-Fc (HAd vector expressing extracellular domain of human EphrinA1 attached to Fc portion of human IgG1 heavy chain) caused increased EphA2 activation and turnover and consequently decreased tumor cell viability in soft agar assays. Consistent with this observation, infection of MDA-MB-231 cells with HAd-EphrinA1-Fc prevented tumor formation in xenograft models. Furthermore, therapeutic modeling via intratumoral inoculation revealed that HAd-EphrinA1-Fc significantly inhibited subsequent tumor growth as compared to matched controls. These results suggest that targeting of EphA2 with adenoviral vectors may have therapeutic value.

The role of ephrins and Eph receptors in cancer

Eph receptors are the largest receptor tyrosine kinase family of transmembrane proteins with an extracellular domain capable of recognizing signals from the cells' environment and influencing cell-cell interaction and cell migration. Ephrins are the ligands to Eph receptors and stimulate bi-directional signaling of the Eph/ephrin axis. Eph receptor and ephrin overexpression can result in tumorigenesis as related to tumor growth and survival and is associated with angiogenesis and metastasis in many types of human cancer. Recent data suggest that Eph/ephrin signaling could play an important role in the development of novel inhibition strategies and cancer treatments to potentially target this receptor tyrosine kinase and/or its ligand. A deeper understanding of the molecular basis for normal versus defective cell-cell interaction through the Eph/ephrin axis will enable the potential development of novel cancer treatments. This review emphasizes the biology of Eph/ephrin as well as the potential for novel targeted therapy through this pathway.

Recent developments in the regulation of the angiogenic switch by cellular stress factors in tumors

Angiogenesis in tumors is controlled by the so-called 'angiogenic switch' which allows the passage from low invasive and poorly vascularized tumors to highly invasive and angiogenic tumors. A number of cellular stress factors such as hypoxia, nutrient deprivation or inducers of reactive oxygen species (ROS) are important stimuli of angiogenic signalling. The HIF system plays a significant role in several of these effects and the molecular mechanisms of its regulation have recently been characterized. In addition, HIF-independent mechanisms have been described which involved number of other molecules and transcription factors such as nuclear factor-(kappa)B (NF-(kappa)B) and p53. p53 is an important intracellular mediator of the stress response and is now also recognized as a modifier of the angiogenic response. p53 may interact with the HIF system but may also have direct effects on angiogenesis regulators or interfere with translation mechanisms of angiogenesis factors.

EphA2 expression is associated with aggressive features in ovarian carcinoma

PURPOSE

EphA2 (epithelial cell kinase) is a transmembrane receptor tyrosine kinase that has been implicated in oncogenesis. There are no published data regarding the role of EphA2 in ovarian carcinoma, which is the focus of the present study.

EXPERIMENTAL DESIGN

Nontransformed (HIO-180) and ovarian cancer (EG, 222, SKOV3, and A2780-PAR) cell lines were evaluated for EphA2 by Western blot analysis. Five benign ovarian masses, 10 ovarian tumors of low malignant potential, and 79 invasive ovarian carcinomas were also evaluated for EphA2 expression by immunohistochemistry. All samples were scored in a blinded fashion. Univariate and multivariate analyses were used to determine significant associations between EphA2 expression and clinicopathological variables.

RESULTS

By Western blot analysis, EG, 222, and SKOV3 cell lines overexpressed EphA2, whereas A2780-PAR and HIO-180 had low to absent EphA2 expression. All of the benign tumors had low or absent EphA2 expression. Among the invasive ovarian carcinomas examined (mean age of patients was 59.2 years), 60 (75.9%) tumors overexpressed EphA2 and the other 19 tumors had negative or minimal EphA2 expression. There was no association of EphA2 overexpression with ascites, likelihood of nodal positivity, pathological subtype, and optimum surgical cytoreduction (residual tumor <1 cm). However, EphA2 overexpression was significantly associated with higher tumor grade (P = 0.02) and advanced stage of disease (P = 0.001). The median survival for patients with tumor EphA2 overexpression was significantly shorter (median, 3.1 years; P = 0.004); the median survival for patients with low or absent EphA2 tumor expression was at least 12 years and has not yet been reached. In multivariate analysis using the Cox proportional hazards model, only volume of residual disease (P < 0.04) and EphA2 overexpression (P < 0.01) were significant and independent predictors of survival.

CONCLUSIONS

EphA2 overexpression is predictive of aggressive ovarian cancer behavior and may be an important therapeutic target.

EphA2: expression in the renal medulla and regulation by hypertonicity and urea stress in vitro and in vivo

EphA2, a member of the large family of Eph receptor tyrosine kinases, is highly expressed in epithelial tissue and has been implicated in cell-cell and cell-matrix interactions, as well as cell growth and survival. Expression of EphA2 mRNA and protein was markedly upregulated by both hypertonic stress and by elevated urea concentrations in cells derived from the murine inner medullary collecting duct. This upregulation likely required transactivation of the epidermal growth factor (EGF) receptor tyrosine kinase and metalloproteinase-dependent ectodomain cleavage of an EGF receptor ligand, based on pharmacological inhibitor studies. A human EphA2 promoter fragment spanning nucleotides -4030 to +21 relative to the putative EphA2 transcriptional start site was responsive to tonicity but insensitive to urea. A promoter fragment spanning -1890 to +128 recapitulated both tonicity- and urea-dependent upregulation of expression, consistent with transcriptional activation. Neither the bona fide p53 response element at approximately -1.5 kb nor a pair of putative TonE elements at approximately -3 kb conferred the tonicity responsiveness. EphA2 mRNA and protein were expressed at low levels in rat renal cortex but at high levels in the collecting ducts of the renal medulla and papilla. Water deprivation in rats increased EphA2 expression in renal papilla, whereas dietary supplementation with 20% urea increased EphA2 expression in outer medulla. These data indicate that transcription and expression of the EphA2 receptor tyrosine kinase are regulated by tonicity and urea in vitro and suggest that this phenomenon is also operative in vivo. Renal medullary EphA2 expression may represent an adaptive response to medullary hypertonicity or urea exposure.

The role of p63 in development and differentiation of the epidermis

Expression of p63, a transcription factor that is transcribed into six isoforms, is required for proper development of stratified epithelia, such as the epidermis. In the absence of p63, epithelia remain single-layered. The molecular role of p63 in development and differentiation of stratified epithelia, however, remains controversial. Based on recent studies, we now believe that p63 has a dual role and is essential for development as well as maintenance of the epidermis. During embryogenesis, p63 may be the molecular switch required for initiation of epithelial stratification. This is based on our recent data demonstrating that ectopic expression of a p63 isoform in single-layered epithelia results in the induction of a stratification program. Furthermore, in the mature epidermis, p63 may maintain the proliferative potential of basal keratinocytes. This is suggested by the observation that p63 is primarily expressed in the basal compartment of the epidermis, that p63 expression induces hyperproliferation, and that its expression needs to be downregulated for terminal differentiation to take place. In this review, we discuss recent evidence supporting this dual role for p63 and place it in the context of our increasing knowledge of epidermal development and differentiation.

Genes involved in stem cell fate decisions and commitment to differentiation play a role in skin disease

Multipotent stem cells residing in the bulge region of the hair follicle give rise to cells of different fates including those forming hair follicles, interfollicular epidermis, and associated glands. Stem cell fate determination is regulated by genes involved in both proliferation and differentiation, which are tightly regulated processes. Understanding the molecular mechanisms by which proliferation and differentiation are regulated will provide useful insight into treating human diseases caused by the deregulation of these processes. Two genes involved in regulating proliferation and differentiation are c-Myc and p63, both of which have been found to be deregulated/mutated in several human diseases. Accelerating proliferation leads to neoplastic human diseases and deregulated c-Myc has been implicated in a variety of cancers. Evidence indicates that c-Myc also diverts stem cells to an epidermal and sebaceous gland fate at the expense of the hair follicle fate. Therefore, deregulation of c-Myc has the potential to not only accelerate tumorigenesis, but also influence skin tumor phenotype. In addition, the inhibition of differentiation may also predispose to the development of skin cancer. Recent evidence suggests that the transcription factor p63, is not only responsible for the initiation of an epithelial stratification program during development, but also the maintenance of the proliferative potential of basal keratinocytes in mature epidermis. Mutations in the p63 gene have been shown to cause ectodermal dysplasias and deregulated expression of p63 has been observed in squamous cell carcinomas. In this review, we will discuss recent data implicating a role for both c-Myc and p63 in human skin diseases.

Cell protection, resistance and invasiveness of two malignant mesotheliomas as assessed by 10K-microarray

Malignant pleural mesothelioma (MPM) is an aggressive serosal tumor, strongly associated with former exposure to asbestos fibers and for which there is currently no effective treatment available. In human, MPM is characterized by a high local invasiveness, poor prognosis and therapeutic outcomes. In order to assess molecular changes that specify this phenotype, we performed a global gene expression profiling of human MPM. Using a 10,000-element microarray, we analyzed mRNA relative gene expression levels by comparing a mesothelioma cell line to either a pleural cell line or tumor specimens. To analyze these gene expression data, we used various bioinformatics softwares. Hierarchical clustering methods were used to group genes and samples with similar expression in an unsupervised mode. Genes of known function were further sorted by enzyme, function and pathway clusters using a supervised software (IncyteGenomics). Taken together, these data defined a molecular fingerprint of human MPM with more than 700 up- or down-regulated genes related to several traits of the malignant phenotype, specially associated with MPM invasiveness, protection and resistance to anticancer defenses. This portrait is meaningful in disease classification and management, and relevant in finding new specific markers of MPM. These molecular markers should improve the accuracy of mesothelioma diagnosis, prognosis and therapy.

More than just innate immunity: comparative analysis of Chlamydophila pneumoniae and Chlamydia trachomatis effects on host-cell gene regulation

Chlamydophila pneumoniae and Chlamydia trachomatis cause infections of the respiratory or urogenital tract. In addition, both species have been associated with atherosclerosis or reactive arthritis respectively. For these intracellular pathogens the interaction with their host-cells is of particular importance. To get insight into this relationship, we conducted a comparative analysis of the host-cell gene regulation of human epithelial cells during infection with Chlamydia. In a screening of HeLa cells by Affymetrix-microchips, numerous regulated host-genes were identified. A detailed expression profile was obtained for 14 genes by real-time RT-PCR - comparing C. pneumoniae, C. trachomatis and intracellular S. typhimurium. The transcriptional responses induced by C. pneumoniae were similar (but usually smaller) compared to C. trachomatis, some were absent. UV-inactivated bacteria induced no differential gene expression suggesting that pathomechanisms other than those associated with innate immunity play here an important role. The expression pattern induced by Salmonella differed substantially. These genus- or group-specific transcriptional response patterns elicited by viable intracellular pathogens may considerably contribute to the different pathologies encountered in the clinic.

EphA2: a determinant of malignant cellular behavior and a potential therapeutic target in pancreatic adenocarcinoma

The EphA2 receptor tyrosine kinase is overexpressed in a variety of human cancers. We sought to characterize the role of EphA2 in pancreatic adenocarcinoma and, using RNA interference (RNAi) mediated by small interfering RNA (siRNA), we determined the effects of suppressing EphA2 expression in vitro and in vivo. EphA2 expression in PANC1, MIAPaCa2, BxPC3 and Capan2 cells was assessed by Northern and Western blot. We artificially overexpressed EphA2 by transient transfection and suppressed EphA2 expression using RNAi. Cellular invasiveness was quantified by modified Boyden chamber assay. Anoikis was induced by anchorage-independent polyHEMA culture and caspase 3 activity was quantified fluorometrically. Focal adhesion kinase (FAK) phosphorylation was assessed by immunoprecipitation. EphA2 siRNA treatment was assessed in a nude mouse xenograft model. Pancreatic adenocarcinoma cells differentially express EphA2. Inherent and induced EphA2 overexpression is associated with increased cellular invasiveness and anoikis resistance. EphA2 siRNA suppresses EphA2 expression, cellular invasiveness, anoikis resistance and FAK phosphorylation in vitro and retards tumor growth and inhibits metastasis in vivo. EphA2 is both a determinant of malignant cellular behavior and a potential therapeutic target in pancreatic adenocarcinoma.

Aquaporin 3 colocates with phospholipase d2 in caveolin-rich membrane microdomains and is downregulated upon keratinocyte differentiation

Aquaporin 3 is a channel that transports both water and glycerol. Aquaporin 3-deficient mice exhibit skin defects, including decreased glycerol content and impairment of water holding capacity, barrier recovery, and wound healing. Whether aquaporin 3 and its glycerol transporting capacity are involved in regulating keratinocyte function, we have previously shown that phospholipase D2 can metabolize phospholipids in the presence of glycerol to yield phosphatidylglycerol. We hypothesized that aquaporin 3 is involved in the regulation of keratinocyte function by a mechanism involving the interaction between aquaporin 3 and phospholipase D. Using sucrose gradient centrifugation, immunoprecipitation analysis, and confocal microscopy, we found that aquaporin 3 and phospholipase D2 colocalized in caveolin-rich membrane microdomains. In addition, aquaporin 3 expression was downregulated at the transcriptional level and glycerol uptake was reduced upon primary mouse keratinocytes to differentiation in response to an elevated extracellular calcium concentration or 1,25-dihydroxyvitamin D3. Our results suggest that aquaporin 3 and phospholipase D2 form a signaling module in lipid rafts, where aquaporin 3 transports glycerol to phospholipase D2 for the synthesis of phosphatidylglycerol. Phosphatidylglycerol, as a bioactive lipid, could potentially mediate the effects of the aquaporin 3-phospholipase D2 signaling module, with aquaporin 3 as a modulatory unit, in the regulation of keratinocyte function.

p73 can suppress the proliferation of cells that express mutant p53

Mutation of the p53 tumor suppressor gene is the most common genetic alteration in human cancer. p73, a member of the p53 family, has been found to exhibit activity similar to that of p53, including the ability to induce growth arrest and apoptosis. p53 and p73 have a high percentage of similarity at several domains, including the DNA binding domain. This domain in p53 is the location of missense mutations in many human cancers. Mutant p53, which cannot suppress cell proliferation, has been found to have a dominant-negative activity that inactivates wild-type p53. To determine the effects of mutant p53 on wild-type p73, we have established cell lines expressing both mutant p53 and wild-type p73 in a dual-inducible system. This system expresses mutant p53 in a tetracycline-repressible system and p73beta in an ecdysone-inducible system in a p53-null lung carcinoma parental cell line. We have found that wild-type p73beta, in the presence of mutant p53, retains the ability to transactivate p21 and suppresses cell growth through induction of both cell cycle arrest and apoptosis. In addition, in cell lines expressing wild-type p53 and wild-type p73beta, we have found that these proteins cooperate to additively transactivate p21 and suppress cell proliferation.

Mapping of candidate region for chordoma development to 1p36.13 by LOH analysis

Various cytogenetic and molecular findings indicate 1p36 loss as a consistent change in sporadic and inherited chordoma, a rare embryogenetic neoplasm arising from notochord remnants. We studied 27 sporadic chordomas by means of loss of heterozygosity (LOH) of 31 microsatellites localized to the 1p36.32-36.11 region, and restricted the minimal LOH interval shared by 85% of the tumours to 1p36.13. We also used RT-PCR analysis to investigate the role of the candidate genes CASP9, EPH2A, PAX7, DAN and DVL1, which were selected on the basis of the physical mapping of the LOH region and their plausible oncosuppressor function. RT-PCR analysis showed the presence of DAN and PAX7 transcript fragments of the expected size in all of 8 chordoma samples, whereas the CASP9-specific fragment was observed in only 3 and EPH2A was absent in one. Smaller than expected DVL1 transcripts were found in 4 tumours as well as in their normal counterpart (nucleus pulposus), which also showed a typically sized transcript. Sequencing revealed the skipping of 3 exons in the smallest DVL1 fragment, thus leading to a frameshift and predicting a truncated DVL1 gene product. Our study of the largest cohort of chordoma patients recruited so far indicates a common molecular lesion at 1p36.13, and suggests that the CASP9, EPH2A and DVL1 genes may play an onco-suppressing role and be involved in the development of chordoma.

Tumorigenesis and the angiogenic switch

It has become evident that we cannot understand tumour growth without considering components of the stromal microenvironment, such as the vasculature. At the same time, the tumour phenotype determines the nature of the tumour vasculature. Much research is now devoted to determining the impact of angiogenesis on tumour development and progression, and the reciprocal influences of tumour products on the microvasculature. A more detailed understanding of the complex parameters that govern the interactions between the tumour and vascular compartments will help to improve anti-angiogenic strategies-- not only for cancer treatment, but also for preventing recurrence.

The activation domains, the proline-rich domain, and the C-terminal basic domain in p53 are necessary for acetylation of histones on the proximal p21 promoter and interaction with p300/CREB-binding protein

The p53 transcription factor contains two separate tandem activation domains (AD1 and AD2), a proline-rich domain (PRD), and a C-terminal basic domain (BD). Previously, we have shown that these domains are necessary for transcriptional activity. To further characterize the role of these domains in transactivation, we analyzed the regulation of p21, a well characterized p53 target gene, by various p53 mutants deficient in one or more of these domains. We found that the induction of endogenous p21 is compromised by AD1-deficient p53 (p53(AD1(-))), AD2-deficient p53 (p53(AD2(-))), both AD1- and AD2-deficient p53 (p53(AD1(-)AD2(-))), p53(deltaPRD), which lacks PRD, and p53(deltaBD), which lacks BD. However, p53(AD2(-)), p53(deltaPRD), and p53(deltaBD) are still capable of activating exogenous p21 promoter to an extent comparable with that by wild-type p53. Thus, we performed chromatin immunoprecipitation assay to measure the DNA binding ability of various p53 mutants in vivo. We found that like wild-type p53, these p53 mutants are capable of binding to the p53 response elements in the p21 promoter. In contrast, we found that the extent of acetylated histones on the p21 promoter, especially the proximal promoter, and the amount of interaction with p300/CREB-binding protein, which contain histone acetyltransferase activity, directly correlate with the activity of p53 to induce endogenous p21. Furthermore, we showed that down-regulation of p300/CBP by short interference RNA markedly decreases the ability of p53 to induce endogenous p21. These data lead us to hypothesize that when p53 binds to the responsive element(s) of a target gene, its ability to interact with histone acetyltransferase-containing proteins and subsequently the acetylation of histones bound to the proximal promoter dictate the induction level of a target gene.

Overexpression and functional alterations of the EphA2 tyrosine kinase in cancer

Cancer is a disease of aberrant signal transduction. The expression and function of intracellular signaling pathways are frequently subverted as cells progress towards a metastatic phenotype. In particular, tyrosine kinases initiate powerful signals that govern many different aspects of cell behavior. In Recent studies have demonstrated that the EphA2 receptor tyrosine kinase is frequently overexpressed and functionally altered in aggressive tumor cells, and that these changes promote metastatic character. Herein, we provide an overview of our current understanding of EphA2, with emphasis upon the differential regulation of EphA2 expression and function. We also show that differential EphA2 expression and function may provide a unique opportunity for selective therapeutic targeting of EphA2 in metastatic disease.

An ephrin mimetic peptide that selectively targets the EphA2 receptor

Eph receptor tyrosine kinases represent promising disease targets because they are differentially expressed in pathologic versus normal tissues. The EphA2 receptor is up-regulated in transformed cells and tumor vasculature where it likely contributes to cancer pathogenesis. To exploit EphA2 as a therapeutic target, we used phage display to identify two related peptides that bind selectively to EphA2 with high affinity (submicromolar K(D) values). The peptides target the ligand-binding domain of EphA2 and compete with ephrin ligands for binding. Remarkably, one of the peptides has ephrin-like activity in that it stimulates EphA2 tyrosine phosphorylation and signaling. Furthermore, this peptide can deliver phage particles to endothelial and tumor cells expressing EphA2. In contrast, peptides corresponding to receptor-interacting portions of ephrin ligands bind weakly and promiscuously to many Eph receptors. Bioactive ephrin mimetic peptides could be used to selectively deliver agents to Eph receptor-expressing tissues and modify Eph signaling in therapies for cancer, pathological angiogenesis, and nerve regeneration.

Epidermal differentiation: transgenic/knockout mouse models reveal genes involved in stem cell fate decisions and commitment to differentiation

Epidermal development and differentiation are similar processes and therefore the study of one is likely to provide insight into the other. The signaling cascades required for epidermal differentiation are largely unknown. Recent evidence, however, has implicated two proteins, p63 and c-Myc, in different stages of epidermal development and differentiation. p63 was shown to be required for embryonic epidermal development. Mice lacking p63 do not develop stratified epithelia and appendages suggesting a role for p63 in the commitment to squamous epithelial lineages. Subsequent stem cell fate decisions are required to form the different structures of stratified epithelia including hair follicles, sebaceous glands, and epidermis. Several genes of the Wnt signaling pathway have been implicated in this process, including c-Myc, a downstream target of the Wnt pathway. Interestingly, targeted overexpression of c-Myc in the basal layer of the epidermis results in an increase in sebaceous gland size and number at the expense of hair follicles. This suggests that c-Myc promotes differentiation of epidermal stem cells into sebaceous glands. In this review, we discuss transgenic/knockout mouse models that have provided evidence linking c-Myc and p63 to different stages of epidermal development and differentiation.

The ferredoxin reductase gene is regulated by the p53 family and sensitizes cells to oxidative stress-induced apoptosis

The p53 tumor suppressor protein, a transcription factor, induces cell cycle arrest and apoptosis via the upregulation of downstream target genes. Ferredoxin Reductase (protein, FR; gene, FDXR) transfers electron from NADPH to cytochrome P450 via ferredoxin in mitochondria. Here, we identified FDXR as a target gene of the p53 family, that is, p53, p63, and p73. We found that FDXR can be induced by DNA damage in cells in a p53-dependent manner and by a mutated form of p53 that is competent in inducing apoptosis. In addition, we identified a p53 response element located within the FDXR promoter that is responsive to wild-type p53, p63alpha, p63gamma, p73alpha, and p73beta. Furthermore, we showed that p53, p63alpha and p73alpha directly bind to the p53 response element in vivo and promote the accessibility of the FDXR promoter by increasing the acetylation of histones H3 and H4. To determine the role of FR in p53 tumor suppression, we generated cell lines that express FR using a tetracycline-regulated promoter. We found that over-expression of FR in lung H1299, breast MCF7, and colorectal HCT116 carcinoma cells have no effect on cell proliferation. However, we showed that FR increases the sensibility of H1299 and HCT116 cells to 5-fluorouracil-, doxorubicin- and H(2)O(2)- mediated apoptosis. Our data support a model of feed-forward loop for p53 activity, that is, various cellular stresses, including reactive oxygen species (ROS), activate p53, which induces the expression of FDXR; and the FDXR gene product, FR, in turn sensitizes cells to ROS-mediated apoptosis.

Estrogen and Myc negatively regulate expression of the EphA2 tyrosine kinase

Estrogen receptor and c-Myc are frequently overexpressed during breast cancer progression but are downregulated in many aggressive forms of the disease. High levels of the EphA2 tyrosine kinase are consistently found in the most aggressive breast cancer cells, and EphA2 overexpression can increase metastatic potential. We demonstrate, herein, that estrogen and Myc negatively regulate EphA2 expression in mammary epithelial cells. These data reveal EphA2 as a downstream target of estrogen and Myc and suggest a mechanism by which estrogen and Myc may regulate breast cancer.