Wnt/beta-catenin signaling suppresses apoptosis in low serum medium and induces morphologic change in rodent fibroblasts

Extirpating the cancer stem cell hydra: Differentiation therapy and Hyperthermia therapy for targeting the cancer stem cell hierarchy

Ever since the discovery of cancer stem cells (CSCs), they have progressively attracted more attention as a therapeutic target. Like the mythical hydra, this subpopulation of cells seems to contribute to cancer immortality, spawning more cells each time that some components of the cancer cell hierarchy are destroyed. Traditional modalities focusing on cancer treatment have emphasized apoptosis as a route to eliminate the tumor burden. A major problem is that cancer cells are often in varying degrees of dedifferentiation contributing to what is known as the CSCs hierarchy and cells which are known to be resistant to conventional therapy. Differentiation therapy is an experimental therapeutic modality aimed at the conversion of malignant phenotype to a more benign one. Hyperthermia therapy (HT) is a modality exploiting the changes induced in cells by the application of heat produced to aid in cancer therapy. While differentiation therapy has been successfully employed in the treatment of acute myeloid leukemia, it has not been hugely successful for other cancer types. Mounting evidence suggests that hyperthermia therapy may greatly augment the effects of differentiation therapy while simultaneously overcoming many of the hard-to-treat facets of recurrent tumors. This review summarizes the progress made so far in integrating hyperthermia therapy with existing modules of differentiation therapy. The focus is on studies related to the successful application of both hyperthermia and differentiation therapy when used alone or in conjunction for hard-to-treat cancer cell niche with emphasis on combined approaches to target the CSCs hierarchy.

Chondroitin sulfate-mediated N-cadherin/β-catenin signaling is associated with basal-like breast cancer cell invasion

Tumor metastasis involves cancer cell invasion across basement membranes and interstitial tissues. The initial invasion step consists of adherence of the tumor cell to the extracellular matrix (ECM), and this binding transduces a variety of signals from the ECM to the tumor cell. Accordingly, it is critical to establish the mechanisms by which extracellular cues influence the intracellular activities that regulate tumor cell invasion. Here, we found that invasion of the basal-like breast cancer cell line BT-549 is enhanced by the ECM component chondroitin sulfates (CSs). CSs interacted with and induced proteolytic cleavage of N-cadherin in the BT-549 cells, yielding a C-terminal intracellular N-cadherin fragment that formed a complex with β-catenin. Of note, the cleavage of N-cadherin increased cytoplasmic and nuclear β-catenin levels; induced the matrix metalloproteinase 9 (MMP9) gene, a target of β-catenin nuclear signaling; and augmented the invasion potential of the cells. We also found that CS-induced N-cadherin proteolysis requires caveolae-mediated endocytosis. An inhibitor of that process, nystatin, blocked both the endocytosis and proteolytic cleavage of N-cadherin induced by CS and also suppressed BT-549 cell invasion. Knock-out of chondroitin 4-O-sulfotransferase-1 (C4ST-1), a key CS biosynthetic enzyme, suppressed activation of the N-cadherin/β-catenin pathway through N-cadherin endocytosis and significantly decreased BT-549 cell invasion. These results suggest that CSs produced by C4ST-1 might be useful therapeutic targets in the management of basal-like breast cancers.

Hypothyroidism reduces mammary tumor progression via Β-catenin-activated intrinsic apoptotic pathway in rats

Experimental hypothyroidism retards mammary carcinogenesis promoting apoptosis of tumor cells. β-catenin plays a critical role in cell adhesion and intracellular signaling pathways conditioning the prognosis of breast cancer. However, the mechanistic connections associated with the expression of β-catenin in thyroid status and breast cancer are not known. Therefore, we studied the relationship between the expression and localization of β-catenin and apoptosis in mammary tumors induced by 7,12-dimethylbenz(a)anthracene (DMBA) in hypothyroid (Hypot) and euthyroid (EUT) rats. Female Sprague Dawley rats were treated with a dose of DMBA (15 mg/rat) at 55 days of age and were then divided into two groups: HypoT (0.01% 6-N-propyl-2-thiouracil in drinking water, n = 54) and EUT (untreated control, n = 43). Latency, incidence and progression of tumors were determined. At sacrifice, tumors were obtained for immunohistological studies and Western Blot. The latency was longer (p < 0.05), the incidence was lower (p < 0.0001) and tumor growth was slower (p < 0.01) in HypoT rats compared to EUT. The expression of Bax, cleaved caspase-9 and caspase-3 was significantly higher in tumors of HypoT than in EUT (p < 0.05) indicating the activation of the intrinsic pathway. In this group, β-catenin was expressed in the plasma membrane and with less intensity, while its expression was nuclear and with greater intensity in the EUT (p < 0.05). Moreover, the expression of survivin was reduced in tumors of HypoT rats (p < 0.05). In conclusion, decreased expression of β-catenin and its normal location in membrane of mammary tumors are associated with augmented apoptosis via activation of the intrinsic pathway in HypoT rats.

Downregulation of dickkopf-1 enhances the proliferation and osteogenic potential of fibroblasts isolated from ankylosing spondylitis patients via the Wnt/β-catenin signaling pathway in vitro

BACKGROUND

Heterotopic ossification of the entheses is one of the most distinctive features in ankylosing spondylitis (AS). Fibroblasts are potential target cells for heterotopic ossification. The Wnt/β-catenin pathway and its inhibitor dickkopf-1 (DKK-1) regulate bone formation. DKK-1 expression in human AS tissues has not been documented.

OBJECTIVE

The purpose of the current study was to investigate the expression of DKK-1 in AS tissues and to elucidate its role in fibroblasts proliferation and osteogenesis in AS.

METHODS

DKK-1 expression was assessed by western blotting, real time-polymerase chain reaction (RT-PCR), and immunohistochemistry analysis of hip synovial tissues obtained from AS and control patients. Fibroblasts were isolated, cultured, and transfected with lentiviral vectors for overexpressing human DKK-1 or an shRNA for silencing DKK-1. MTS [(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl) 2-(4-sulfophenyl)-2H-tetrazolium] and a 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay were used to detect AS fibroblasts proliferation after transfection. The expression levels of β-catenin, phosphorylated β-catenin, c-Myc, cyclin D1, and the osteogenesis markers alkaline phosphatase (ALP), osteocalcin (OCN), and Runt-related transcription factor 2 (Runx2) were then examined by western blot analysis. Alizarin red staining (ARS) was also used to observe biomineralization activity.

RESULTS

DKK-1 was downregulated in hip synovial tissues from AS patients compared to that observed in controls. AS fibroblasts exhibited excessive proliferation, a higher growth rate, and a decreased apoptotic rate. EdU assay demonstrated that DKK-1 suppressed the growth of AS fibroblasts. Downregulation of DKK-1 decreased the phosphorylation of β-catenin and upregulated the expression of β-catenin, c-Myc, cyclin D1, and osteogenesis markers. Overexpression of DKK-1 had the opposite effect, resulting in the inhibition of the Wnt/β-catenin pathway. ARS showed an increase in biomineralization activity after the inhibition of DKK-1.

CONCLUSIONS

AS fibroblasts are characterized by an imbalance between proliferation and apoptosis. DKK-1 may play a role in switching to new bone formation in AS progression.

The relationship between beta-catenin and apoptosis: A cytological and immunocytochemical examination

Disruption of the adhesive role of beta-catenin by caspases has been reported; however, the relationship between the Wnt/beta-catenin signaling pathway and apoptosis remains unclear. Therefore, we aimed to evaluate squamous epithelial cells in cervicovaginal smears by using cytological and immunocytochemical methods to observe changes in the presence and localization of beta-catenin during apoptosis, death receptor-, and mitochondria-mediated apoptosis. We investigated 224 cervicovaginal smears using the Papanicolaou method. Anti-beta-catenin and anti-cleaved caspase 3, 8, and 9 antibodies were used for immunocytochemical staining. Apoptotic cells were negative for beta-catenin. This showed that the Wnt/beta-catenin signaling pathway was inactive in apoptotic cells. However, beta-catenin showed intense positivity in the membrane, cytoplasm, and nucleus of non-apoptotic epithelial cells around these apoptotic cells. Therefore, the Wnt/beta-catenin signaling pathway was active in non-apoptotic epithelial cells, and this activity in non-apoptotic cells may have been induced by apoptotic cells. A highly significant association between the presence of death receptor-mediated apoptosis and the activity of the Wnt/beta-catenin signaling pathway was also found (P<0.001). In conclusion, the Wnt/beta-catenin signaling pathway was found to be inactive in apoptotic cells, but apoptotic cells may induce the Wnt/beta-catenin signaling pathway in non-apoptotic cells to compensate for a decrease in epithelial cells because of apoptosis in order to maintain epithelial tissue integrity.

Wnt5a-induced Wnt1-inducible secreted protein-1 suppresses vascular smooth muscle cell apoptosis induced by oxidative stress

OBJECTIVE

Apoptosis of vascular smooth muscle cells (VSMCs) contributes to thinning and rupture of the atherosclerotic plaque fibrous cap and is thereby associated with myocardial infarction. Wnt protein activation of β-catenin regulates numerous genes that are associated with cell survival. We therefore investigated Wnt/β-catenin survival signaling in VSMCs and assessed the presence of this pathway in human atherosclerotic plaques at various stages of the disease process.

APPROACH AND RESULTS

Wnt5a induced β-catenin/T-cell factor signaling and retarded oxidative stress (H₂O₂)-induced apoptosis in mouse aortic VSMCs. Quantification of mRNA levels revealed a >4-fold (P<0.05; n=9) increase in the expression of the Wnt/β-catenin responsive gene, Wnt1-inducible secreted protein-1 (WISP-1), which was dependent on cAMP response element-binding protein and sustained in the presence of H₂O₂. Exogenous WISP-1 significantly reduced H₂O₂-induced apoptosis by 43% (P<0.05; n=3) and was shown using silencing small interfering RNA, to be important for Wnt5a-dependent survival responses to H₂O₂ (P<0.05; n=3). WISP-1 protein levels were significantly lower (≈50%) in unstable atherosclerosis compared with stable plaques (n=11 and n=14).

CONCLUSIONS

These results indicate for the first time that Wnt5a induces β-catenin survival signaling in VSMCs via WISP-1. The deficiency of the novel survival factor, WISP-1 in intimal VSMCs of unstable coronary plaques, suggests that there is altered Wnt/β-catenin/ T-cell factor signaling with progressive atherosclerosis, and restoration of WISP-1 protein might be an effective stabilization factor for vulnerable atherosclerotic plaques.

Keloid fibroblasts are more sensitive to Wnt3a treatment in terms of elevated cellular growth and fibronectin expression

BACKGROUND

Current evidence suggests the potential role of Wnt signalling in keloids pathogenesis but such literature remains scanty. We hypothesize that Wnt signalling is upregulated in keloid fibroblasts (KFs) and this promotes cellular growth, migration and extracellular matrix (ECM) production in such fibroblasts.

OBJECTIVES

To verify the downregulation of secreted frizzled-related protein 1 (SFRP1), a Wnt inhibitor and test KFs sensitivity to Wnt3a treatment compared to NFs in terms of activation of Wnt/β-catenin, cellular growth, migration and ECM expressions. Next, to investigate if ectopic expression of SFRP1 and treatment of quercetin in KFs can reverse their phenotypes.

METHODS

Quantitative Real-time PCR and western blotting were used to verify SFRP1 expression in NFs and KFs. The fibroblasts were tested with Wnt3a conditioned media and its effects were tested for (1) the cells' sensitivity to direct Wnt signalling via the activation of TCF reporter assay and protein expression of β-catenin, (2) cellular growth, (3) cell migration and (4) expressions of ECM components. Finally KFs were stably transduced with SFRP1 and treated with 2 doses of quercetin.

RESULTS

Lower levels of SFRP1 were confirmed at mRNA and protein levels in KFs which partly explained their sensitivity to Wnt3a treatment in terms of higher Wnt activation, cellular growth and fibronectin expression. Interestingly, Wnt3a did not promote higher cell migration rate and increase in collagen I expression. Ectopic expression of SFRP1 and quercetin treatment was able to mitigate Wnt3a-mediated phenotype of KFs.

CONCLUSIONS

Using SFRP1 or inhibitors of Wnt signalling might be one of the therapeutic solutions to treat keloid scarring.

Influence of human adipose-derived stromal cells on Wnt signaling in organotypic skin culture

BACKGROUND

Human adipose-derived stromal cells (hASCs) produce various cytokines. Also, there is a growing opinion that a large proportion of the useful effects of cell therapy may be attributable to the secretion of cytokines. Several reports suggested beneficial effects of hASCs on skin. These include antioxidant activity, accelerated wound healing, whitening effects, and antiaging. We investigated the effect of hASCs on skin Wnt signaling, which is associated with skin regeneration and differentiation.

METHODS

Pieces of human skin were cocultured with hASCs, and 2 chambered transwell culture plates were used to prevent direct contact between hASCs and skin. In the control group, pieces of skin were cultured without hASCs. Wnt1, Axin2, TCF1, LEF1, and DKK1 mRNA expressions were quantitatively assessed using real-time polymerase chain reaction. The expression levels of β-catenin were compared using Western blot and immunohistochemical analyses.

RESULTS

The Wnt1 and LEF1 mRNA expression of cultured skin was positively influenced by the presence of hASCs in culture medium (P<0.05). The total β-catenin protein level in hASC-cocultured skin was higher than that of the control group. Immunohistochemical staining showed that the β-catenin-stained area of dermis was larger in the hASC-cocultured group than in the control group, and most of the positively stained cells in the dermis were fibroblasts.

CONCLUSIONS

The results of the current study showed that hASCs promoted canonical Wnt signaling in organotypic skin culture through paracrine effects, and the increased Wnt signaling was mainly due to dermal fibroblasts.

Down-regulation of chondroitin 4-O-sulfotransferase-1 by Wnt signaling triggers diffusion of Wnt-3a

During metazoan development, Wnt molecules are secreted from Wnt-producing cells, diffuse to target cells, and determine cell fates; therefore, Wnt secretion is tightly regulated. However, the molecular mechanisms controlling Wnt diffusion are not fully elucidated. The specific chondroitin sulfate (CS) structure synthesized by chondroitin-4-O-sulfotransferase-1 (C4ST-1) binds to Wnt-3a with high affinity (Nadanaka, S., Ishida, M., Ikegami, M., and Kitagawa, H. (2008) J. Biol. Chem. 283, 27333-27343). In this study we tested whether Wnt signaling regulates sulfation patterns of cell-associated CS chains by suppressing expression of C4ST-1 to trigger release of Wnt molecules from Wnt-producing cells. C4ST-1 expression was dramatically reduced in L cells that stably expressed Wnt-3a (L-Wnt-3a cells) and had CS with low affinity for Wnt-3a. Forced expression of C4ST-1 in L-Wnt-3a cells inhibited diffusion of Wnt-3a due to structural alterations in CS chains mediated by C4ST-1. Furthermore, sustained Wnt signaling negatively regulated C4ST-1 expression in a cell-autonomous and non-cell autonomous fashion. These results demonstrated that C4ST-1 is a key downstream target of Wnt signaling that regulates Wnt diffusion from Wnt-producing cells.

Overexpression of Pygopus2 protects HeLa cells from vinblastine-induced apoptosis

Pygopus, a very important component of the Wnt signaling transcriptional complex, has multiple functions in both Wnt-dependent and -independent pathways. Human Pygopus2 (Pygo2) is expressed in many cancers and plays an important role in tumor growth. In the present study, we generated human carcinoma (HeLa) cell lines stably expressing Pygo2, which counteracts vinblastine- induced apoptosis. The anti-apoptotic function was determined by DNA fragmentation, sub-G1 appearance, loss of mitochondrial membrane potential (Deltapsim) and the activation of caspase-9 and caspase-3. In addition, we found that Pygo2 effectively blocks vinblastineinduced c-Jun and AP-1 activation, maintains the anti-apoptotic protein Bcl-2 in an unphosphorylated state, and thus can render cells resistant to apoptosis. However, Pygo2 does not alter the vinblastine-induced cell cycle changes. Here, we describe an anti-apoptotic activity exerted by Pygo2 through blocking activation of the JNK/AP-1 signaling pathway induced by vinblastine.

Stabilized beta-catenin functions through TCF/LEF proteins and the Notch/RBP-Jkappa complex to promote proliferation and suppress differentiation of neural precursor cells

The proliferation and differentiation of neural precursor cells are mutually exclusive during brain development. Despite its importance for precursor cell self renewal, the molecular linkage between these two events has remained unclear. Fibroblast growth factor 2 (FGF2) promotes neural precursor cell proliferation and concurrently inhibits their differentiation, suggesting a cross talk between proliferation and differentiation signaling pathways downstream of the FGF receptor. We demonstrate that FGF2 signaling through phosphatidylinositol 3 kinase activation inactivates glycogen synthase kinase 3beta (GSK3beta) and leads to the accumulation of beta-catenin in a manner different from that in the Wnt canonical pathway. The nuclear accumulated beta-catenin leads to cell proliferation by activating LEF/TCF transcription factors and concurrently inhibits neuronal differentiation by potentiating the Notch1-RBP-Jkappa signaling pathway. beta-Catenin and the Notch1 intracellular domain form a molecular complex with the promoter region of the antineurogenic hes1 gene, allowing its expression. This signaling interplay is especially essential for neural stem cell maintenance, since the misexpression of dominant-active GSK3beta completely inhibits the self renewal of neurosphere-forming stem cells and prompts their neuronal differentiation. Thus, the GSK3beta/beta-catenin signaling axis regulated by FGF and Wnt signals plays a pivotal role in the maintenance of neural stem/precursor cells by linking the cell proliferation to the inhibition of differentiation.

Inhibition of beta-catenin signaling in articular chondrocytes results in articular cartilage destruction

OBJECTIVE

Osteoarthritis is a degenerative joint disease whose molecular mechanism is currently unknown. Wnt/beta-catenin signaling has been demonstrated to play a critical role in the development and function of articular chondrocytes. To determine the role of beta-catenin signaling in articular chondrocyte function, we generated Col2a1-ICAT-transgenic mice to inhibit beta-catenin signaling in chondrocytes.

METHODS

The expression of the ICAT transgene was determined by immunostaining and Western blot analysis. Histologic analyses were performed to determine changes in articular cartilage structure and morphology. Cell apoptosis was determined by TUNEL staining and the immunostaining of cleaved caspase 3 and poly(ADP-ribose) polymerase (PARP) proteins. Expression of Bcl-2, Bcl-x(L), and Bax proteins and caspase 9 and caspase 3/7 activities were examined in primary sternal chondrocytes isolated from 3-day-old neonatal Col2a1-ICAT-transgenic mice and their wild-type littermates and in primary chicken and porcine articular chondrocytes.

RESULTS

Expression of the ICAT transgene was detected in articular chondrocytes of the transgenic mice. Associated with this, age-dependent articular cartilage destruction was observed in Col2a1-ICAT-transgenic mice. A significant increase in cell apoptosis in articular chondrocytes was identified by TUNEL staining and the immunostaining of cleaved caspase 3 and PARP proteins in these transgenic mice. Consistent with this, Bcl-2 and Bcl-x(L) expression were decreased and caspase 9 and caspase 3/7 activity were increased, suggesting that increased cell apoptosis may contribute significantly to the articular cartilage destruction observed in Col2a1-ICAT-transgenic mice.

CONCLUSION

Inhibition of beta-catenin signaling in articular chondrocytes causes increased cell apoptosis and articular cartilage destruction in Col2a1-ICAT- transgenic mice.

Wnt-expressing rat embryonic fibroblasts suppress Apo2L/TRAIL-induced apoptosis of human leukemia cells

Wnt signaling enhances cell proliferation and the maintenance of hematopoietic cells. In contrast, cytotoxic ligand Apo2L/TRAIL induces the apoptosis of various transformed cells. We observed that co-culture of human pre-B leukemia cells KM3 and REH with Wnt1- or Wnt3a-producing rat embryonic fibroblasts efficiently suppressed Apo2L/TRAIL-induced apoptosis of the lymphoid cells. This suppression occurs at the early stages of the Apo2L/TRAIL apoptotic cascade and, interestingly, the activation of the Wnt pathway alone in human leukemia cells is not sufficient for their full anti-apoptotic protection. We hypothesize that a stimulus emanating specifically from Wnt1- or Wnt3a-expressing rat fibroblasts is responsible for the observed resistance to Apo2L/TRAIL. This anti-apoptotic signaling was significantly hampered by the inhibition of the MEK1/ERK1/2 or NFkappaB pathways in KM3 and REH cells. Our results imply that paracrine Wnt-related signals could be important for the survival of pre-B cell-derived malignancies.

Cross-talk between Wnt signaling pathways in human mesenchymal stem cells leads to functional antagonism during osteogenic differentiation

Wnt signaling is involved in developmental processes and in adult stem cell homeostasis. This study analyzes the role(s) of key Wnt signaling mediators in the maintenance and osteogenesis of mesenchymal stem cells (MSCs). We focus specifically on the involvement of low-density lipoprotein-related protein 5 (LRP5), T-cell factor 1 (TCF1), and Frizzled (Fz) receptors, in the presence or absence of exogenous, prototypical canonical (Wnt3a), and non-canonical (Wnt5a) Wnts. In undifferentiated MSCs, LRP5 and TCF1 mediate canonical Wnt signal transduction, leading to increased proliferation, enhanced synergistically by Wnt3a. However, LRP5 overexpression inhibits osteogenic differentiation, further suppressed by Wnt3a. Wnt5a does not affect cell proliferation but enhances osteogenesis of MSCs. Interestingly, Wnt5a inhibits Wnt3a effects on MSCs, while Wnt3a suppresses Wnt5a-mediated enhancement of osteogenesis. Flow cytometry revealed that LRP5 expression elicits differential changes in Fz receptor profiles in undifferentiated versus osteogenic MSCs. Taken together, these results suggest that Wnt signaling crosstalk and functional antagonism with the LRP5 co-receptor are key signaling regulators of MSC maintenance and differentiation.

Genome-wide sequence and functional analysis of early replicating DNA in normal human fibroblasts

BACKGROUND

The replication of mammalian genomic DNA during the S phase is a highly coordinated process that occurs in a programmed manner. Recent studies have begun to elucidate the pattern of replication timing on a genomic scale. Using a combination of experimental and computational techniques, we identified a genome-wide set of the earliest replicating sequences. This was accomplished by first creating a cosmid library containing DNA enriched in sequences that replicate early in the S phase of normal human fibroblasts. Clone ends were then sequenced and aligned to the human genome.

RESULTS

By clustering adjacent or overlapping early replicating clones, we identified 1759 "islands" averaging 100 kb in length, allowing us to perform the most detailed analysis to date of DNA characteristics and genes contained within early replicating DNA. Islands are enriched in open chromatin, transcription related elements, and Alu repetitive elements, with an underrepresentation of LINE elements. In addition, we found a paucity of LTR retroposons, DNA transposon sequences, and an enrichment in all classes of tandem repeats, except for dinucleotides.

CONCLUSION

An analysis of genes associated with islands revealed that nearly half of all genes in the WNT family, and a number of genes in the base excision repair pathway, including four of ten DNA glycosylases, were associated with island sequences. Also, we found an overrepresentation of members of apoptosis-associated genes in very early replicating sequences from both fibroblast and lymphoblastoid cells. These data suggest that there is a temporal pattern of replication for some functionally related genes.

Identification of genes regulated by Wnt/beta-catenin pathway and involved in apoptosis via microarray analysis

BACKGROUND

Wnt/beta-catenin pathway has critical roles in development and oncogenesis. Although significant progress has been made in understanding the downstream signaling cascade of this pathway, little is known regarding Wnt/beta-catenin pathway modification of the cellular apoptosis.

METHODS

To identify potential genes regulated by Wnt/beta-catenin pathway and involved in apoptosis, we used a stably integrated, inducible RNA interference (RNAi) vector to specific inhibit the expression and the transcriptional activity of beta-catenin in HeLa cells. Meanwhile, we designed an oligonucleotide microarray covering 1384 apoptosis-related genes. Using oligonucleotide microarrays, a series of differential expression of genes was identified and further confirmed by RT-PCR.

RESULTS

Stably integrated inducible RNAi vector could effectively suppress beta-catenin expression and the transcriptional activity of beta-catenin/TCF. Meanwhile, depletion of beta-catenin in this manner made the cells more sensitive to apoptosis. 130 genes involved in some important cell-apoptotic pathways, such as PTEN-PI3K-AKT pathway, NF-kappaB pathway and p53 pathway, showed significant alteration in their expression level after the knockdown of beta-catenin.

CONCLUSION

Coupling RNAi knockdown with microarray and RT-PCR analyses proves to be a versatile strategy for identifying genes regulated by Wnt/beta-catenin pathway and for a better understanding the role of this pathway in apoptosis. Some of the identified beta-catenin/TCF directed or indirected target genes may represent excellent targets to limit tumor growth.

Cell-specific Gene Expression in Patients with Usual Interstitial Pneumonia

RATIONALE

Usual interstitial pneumonia (UIP) is characterized by extracellular matrix deposition and the development of pulmonary fibrosis. Fibroblastic foci found in the lung are believed to represent an early stage in the evolution of this disease.

OBJECTIVES

To compare gene expression profiles in different components of lung tissue (fibroblastic foci, adjacent epithelium, and areas of type 2 pneumocyte hyperplasia) from patients with UIP, and contrast these profiles to distal, uninvolved (control) alveolar tissue from patients undergoing lung resection for cancer.

METHODS

Lung resection tissue (UIP, n = 11; controls, n = 11) was snap-frozen for subsequent laser capture microdissection, followed by mRNA extraction, linear amplification, and quantitative real-time polymerase chain reaction.

RESULTS

In patients with UIP, tissue inhibitor of matrix metalloprotease-1 and matrix metalloprotease (MMP)-2 gene expression was up-regulated within the fibroblastic foci compared with the overlying epithelium (p = 0.03, p = 0.02), and to control alveoli (p = 0.001, p = 0.04), respectively. MMP-9 and MMP-7, as well as osteopontin, were up-regulated in fibroblastic foci (p = 0.01, p = 0.08, p = 0.08), the adjacent epithelium (p = 0.001, p = 0.001, p = 0.03), and the hyperplastic type 2 pneumocytes (p = 0.02, p = 0.001, p = 0.08), respectively, compared with control alveoli.

CONCLUSION

Altered gene expression of important profibrotic mediators in the different cellular lung compartments in patients with UIP likely plays an important role in pathogenesis of the deranged extracellular matrix deposition and subsequent fibrosis in this condition.

The paradoxical pro- and anti-apoptotic actions of GSK3 in the intrinsic and extrinsic apoptosis signaling pathways

Few things can be considered to be more important to a cell than its threshold for apoptotic cell death, which can be modulated up or down, but rarely in both directions, by a single enzyme. Therefore, it came as quite a surprise to find that one enzyme, glycogen synthase kinase-3 (GSK3), has the perplexing capacity to either increase or decrease the apoptotic threshold. These apparently paradoxical effects now are known to be due to GSK3 oppositely regulating the two major apoptotic signaling pathways. GSK3 promotes cell death caused by the mitochondrial intrinsic apoptotic pathway, but inhibits the death receptor-mediated extrinsic apoptotic signaling pathway. Intrinsic apoptotic signaling, activated by cell damage, is promoted by GSK3 by facilitation of signals that cause disruption of mitochondria and by regulation of transcription factors that control the expression of anti- or pro-apoptotic proteins. The extrinsic apoptotic pathway entails extracellular ligands stimulating cell-surface death receptors that initiate apoptosis by activating caspase-8, and this early step in extrinsic apoptotic signaling is inhibited by GSK3. Thus, GSK3 modulates key steps in each of the two major pathways of apoptosis, but in opposite directions. Consequently, inhibitors of GSK3 provide protection from intrinsic apoptosis signaling but potentiate extrinsic apoptosis signaling. Studies of this eccentric ability of GSK3 to oppositely influence two types of apoptotic signaling have shed light on important regulatory mechanisms in apoptosis and provide the foundation for designing the rational use of GSK3 inhibitors for therapeutic interventions.

Nuclear beta-catenin correlates with cyclin D1 expression in spindle and pleomorphic sarcomas but not in synovial sarcoma

Nuclear beta-catenin staining in soft tissue sarcomas (STSs) has been shown to correlate with tumor progression as assessed by proliferative activity or poor prognosis. Frequent activation of Wnt signaling pathway has been also shown in synovial sarcoma (SS), suggesting a specific role of this pathway in SS. We examined roles of nuclear beta-catenin staining within soft tissue sarcomas. Immunohistochemical detection of nuclear beta-catenin accumulation correlated with cyclin D1 overexpression in spindle cell and pleomorphic sarcomas (P = .037), and the expression of these proteins evenly distributed throughout each section. In some cases, strong beta-catenin nuclear staining was observed in highly pleomorphic and mitotic cells. Furthermore, tumors with nuclear beta-catenin accumulation showed statistically significant increasing cyclin D1 mRNA expression level compared with those without (P = .023). Cyclin D1 mRNA expression levels were statistically higher in tumors with cyclin D1 overexpression than in tumors without (P = .037), suggesting that cyclin D1 overexpression is due to transcriptional activation. However, these correlations could not be detected in SS. In biphasic SS, beta-catenin nuclear staining was observed in spindle cells, whereas cyclin D1 nuclear staining was seen in glandular areas where beta-catenin kept membranous expression. Mutations in exon 3 of the beta-catenin gene and in the mutation cluster region of adenomatous polyposis coli gene were absent in this series of cases. Thus, cyclin D1 could be considered as one of the targets of the nuclear beta-catenin in spindle cell and pleomorphic sarcomas. A possible association between beta-catenin accumulation and spindle cell morphogenesis may exist in SS.

Viral FLIP enhances Wnt signaling downstream of stabilized beta-catenin, leading to control of cell growth

Death receptor-mediated apoptosis is potently inhibited by viral FLIP (FLICE/caspase 8 inhibitory protein), which is composed of two tandemly repeated death effector domains (DEDs), through reduced activation of procaspase 8. Here, we show that equine herpesvirus 2-encoded viral FLIP E8 enhances Wnt/beta-catenin signaling in a variety of cell lines. E8 was shown to strikingly augment Wnt3a signaling, as shown both in a luciferase assay for T-cell factor/beta-catenin and through induction of endogenous cyclin D1. The effect of E8 was independent of its direct binding activity with DED-containing signaling molecules, including caspase 8 and FADD, in death receptor-mediated apoptosis. E8 enhanced Wnt signaling downstream of stabilized beta-catenin, while a long form of cellular FLIP (c-FLIP(L)) enhanced stabilization of beta-catenin in 293T cells. Consequently, coexpression of E8 and c-FLIP(L) synergistically increased Wnt signaling in 293T cells. Moreover, E8-mediated stimulation of Wnt signaling induced dramatic growth retardation in untransformed cell lines but not in transformed cell lines. Thus, viral FLIP E8 not only inhibits death receptor-mediated apoptosis but also enhances Wnt signaling pathways that are closely related to those of both ontogenesis and oncogenesis.

Tead proteins activate the Foxa2 enhancer in the node in cooperation with a second factor

The cell population and the activity of the organizer change during the course of development. We addressed the mechanism of mouse node development via an analysis of the node/notochord enhancer (NE) of Foxa2. We first identified the core element (CE) of the enhancer, which in multimeric form drives gene expression in the node. The CE was activated in Wnt/β-catenin-treated P19 cells with a time lag, and this activation was dependent on two separate sequence motifs within the CE. These same motifs were also required for enhancer activity in transgenic embryos. We identified the Tead family of transcription factors as binding proteins for the 3′motif. Teads and their co-factor YAP65 activated the CE in P19 cells, and binding of Tead to CE was essential for enhancer activity. Inhibition of Tead activity by repressor-modified Tead compromised NE enhancer activation and notochord development in transgenic mouse embryos. Furthermore, manipulation of Tead activity in zebrafish embryos led to altered expression of foxa2 in the embryonic shield. These results suggest that Tead activates the Foxa2 enhancer core element in the mouse node in cooperation with a second factor that binds to the 5′ element, and that a similar mechanism also operates in the zebrafish shield.

Gene trap screening as an effective approach for identification of Wnt-responsive genes in the mouse embryo

In this study, we examined whether gene trap methodology, which would be available for systematic identification and functional analysis of genes, is effective for screening of Wnt-responsive genes during mouse development. We screened out two individual clones among 794 gene-trapped embryonic stem cell lines by their in vitro response to WNT-3A proteins. One gene was mainly expressed in the ductal epithelium of several developing organs, including the kidney and the salivary glands, and the other gene was expressed in neural crest cells and the telencephalic flexure. The spatial and temporal expression of these two genes coincided well with that of several Wnt genes. Furthermore, the expression of these two genes was significantly decreased in embryos deficient for Wnts or in cultures of embryonic tissues treated with a Wnt signal inhibitor. These results indicate that the gene trap is an effective method for systematic identification of Wnt-responsive genes during embryogenesis.

Expression of Dishevelled-1 in wound healing after acute myocardial infarction: possible involvement in myofibroblast proliferation and migration

One of our previous studies indicated that the expression of beta-catenin, which is the key factor of wnt-frizzled pathway, increased significantly in the ischemic area of the rat heart 7 days after myocardial infarction (MI). Together with the results of other recent studies, we made an assumption that wnt-frizzled pathway may be involved in the controlled cell proliferation and migration during repair processes after MI. To verify this assumption we tried to investigate the expression of another signal transduction molecule called Dishevelled in wnt-frizzled pathway during the wound healing process after MI. The left descending coronary arteries of rats were ligated to induce MI. Immunohistochemistry SABC method and in situ hybridization were performed to detect the expression of Dishevelled-1. The results showed, that one day after MI, Dishevelled-1 mRNA but not protein expression was detected in the cells at the border zone of the infarction area; 4 days after MI the expression of Dishevelled-1 increased exclusively and cytoplasmic Dishevelled-1 was observed not only at the border zone but also in the infarct area; 7 days after MI, it seems that the expression reached its peak, the positive staining even spread into the endothelial and smooth muscle cells of the newly formed and pre-existing blood vessels in the infarction area; after that the Dishevelled-1 expression decreased abruptly and could hardly be detected 28 days after MI. Thus cytoplasmic Dishevelled-1 may be involved in the controlled proliferation and migration of myofibroblasts and vascular endothelial cells, hence play a role during the wound healing process after MI.

Stem cell origin of cancer and differentiation therapy

Our forefathers in pathology, on observing cancer tissue under the microscope in the mid-19th century, noticed the similarity between embryonic tissue and cancer, and suggested that tumors arise from embryo-like cells [Recherches dur le Traitement du Cancer, etc. Paris. (1829); Editoral Archiv fuer pathologische Anatomie und Physiologie und fuer klinische Medizin 8 (1855) 23]. The concept that adult tissues contain embryonic remnants that generally lie dormant, but that could be activated to become cancer was later formalized by Cohnheim [Path. Anat. Physiol. Klin. Med. 40 (1867) 1-79; Virchows Arch. 65 (1875) 64] and Durante [Arch. Memori ed Osservazioni di Chirugia Practica 11 (1874) 217-226], as the "embryonal rest" theory of cancer. An updated version of the embryonal rest theory of cancer is that cancers arise from tissue stem cells in adults. Analysis of the cellular origin of carcinomas of different organs indicates that there is, in each instance, a determined stem cell required for normal tissue renewal that is the most likely cell of origin of carcinomas [Lab. Investig. 70 (1994) 6-22]. In the present review, the nature of normal stem cells (embryonal, germinal and somatic) is presented and their relationships to cancer are further expanded. Cell signaling pathways shared by embryonic cells and cancer cells suggest a possible link between embryonic cells and cancer cells. Wilm's tumors (nephroblastomas) and neuroblastomas are presented as possible tumors of embryonic rests in children. Teratocarcinoma is used as the classic example of the totipotent cancer stem cell which can be influenced by its environment to differentiate into a mature adult cell. The observation that "promotion" of an epidermal cancer may be accomplished months or even years after the initial exposure to carcinogen ("initiation"), implies that the original carcinogenic event occurs in a long-lived epithelial stem cell population. The cellular events during hepatocarcinogenesis illustrate that cancers may arise from cells at various stages of differentiation in the hepatocyte lineage. Examples of genetic mutations in epithelial and hematopoietic cancers show how specific alterations in gene expression may be manifested as maturation arrest of a cell lineage at a specific stage of differentiation. Understanding the signals that control normal development may eventually lead us to insights in treating cancer by inducing its differentiation (differentiation therapy). Retinoid acid (RA) induced differentiation therapy has acquired a therapeutic niche in treatment of acute promyelocytic leukemia and the ability of RA to prevent cancer is currently under examination.

Beta-catenin/Tcf activation partially mimics the transforming activity of Wnt-1 in Rat-1 fibroblasts

We have previously demonstrated that Wnt-1 induction of cytosolic beta-catenin and Tcf/Lef transcriptional activation correlate with enhanced proliferation, survival, and post-confluent growth in Rat-1 fibroblasts. To examine whether beta-catenin mediates the biological responses to Wnt-1 in this context, we characterized Rat-1 clonal cell lines expressing different levels of a mutant, stabilized beta-catenin (beta-cateninS37A). Clonal lines exhibit elevated cytosolic and nuclear beta-cateninS37A and Tcf transcriptional activation, comparable to that elicited by Wnt-1 expression. However, expression of beta-cateninS37A does not promote growth of Rat-1 cells in serum-free conditions and only partially promotes growth post-confluence, when compared to that induced by Wnt-1 expression. As ectopic expression of beta-cateninS37A only partially mimics Wnt-1 effects on Rat-1 cells, we conclude that Wnt-1 signaling elicits biochemical events that act in addition to beta-catenin/Tcf signaling to promote cell growth.

Nemo-like kinase induces apoptosis in DLD-1 human colon cancer cells

Deregulation of Wnt/beta-catenin signaling is thought to play a critical role in human carcinogenesis. Nemo-like kinase (NLK) is an evolutionarily conserved serine/threonine kinase that suppresses beta-catenin/T-cell factor (TCF) complex transcriptional activity through phosphorylation of TCF. Since NLK may be a tumor suppressor as a negative regulator of Wnt/beta-catenin pathway, we established tetracycline-inducible NLK and its kinase-negative mutant expression in DLD-1 human colon cancer cells to analyze the effect of NLK on cell growth and viability. The induction of wild-type NLK in DLD-1 cells caused suppression of cell growth whereas the kinase-negative mutant did not. Flow cytometry indicated that NLK expression increased the number of apoptotic cells but did not induce obvious cell cycle arrest. Apoptosis induction by wild-type NLK was confirmed using TUNEL assays. Our results suggest that overexpression of NLK may have targets other than TCF for induction of apoptosis in human colon carcinoma cells.

Aberrant Wnt/beta-catenin pathway activation in idiopathic pulmonary fibrosis

To investigate the molecular events that may underpin dysfunctional repair processes that characterize idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP), we analyzed the expression patterns of beta-catenin on 20 IPF/UIP lung samples, together with two downstream target genes of Wnt signaling, cyclin-D1, and matrilysin. In 18 of 20 cases of IPF/UIP investigated on serial sections, nuclear beta-catenin immunoreactivity and abnormal levels of cyclin-D1 and matrilysin were demonstrated in proliferative bronchiolar lesions (basal-cell hyperplasia, squamous metaplasia, bronchiolization, honeycombing). The nature of these lesions was precisely defined using specific markers (DeltaN-p63, surfactant-protein-A, cytokeratin-5). Interestingly, nuclear beta-catenin accumulation was also demonstrated in fibroblast foci in most (16 of 20) IPF/UIP samples, often associated with bronchiolar lesions. Similar features were not observed in normal lung and other fibrosing pulmonary diseases (diffuse alveolar damage, organizing pneumonia, nonspecific interstitial pneumonia, desquamative interstitial pneumonia). Sequence analysis performed on DNA extracted from three samples of IPF/UIP did not reveal abnormalities affecting the beta-catenin gene. On the basis of these findings new models for IPF/UIP pathogenesis can be hypothesized, centered on the aberrant activation of Wnt/beta-catenin signaling, with eventual triggering of divergent epithelial regeneration at bronchiolo-alveolar junctions and epithelial-mesenchymal-transitions, leading to severe and irreversible remodeling of the pulmonary tissue.