Induction of mutual stabilization and retardation of tumor growth by coexpression of plakoglobin and E-cadherin in mouse skin spindle carcinoma cells

Human papillomavirus 16 E5 modulates the expression of host microRNAs

Human papillomavirus (HPV) infection is a prerequisite of developing cervical cancer, approximately half of which are associated with HPV type 16. HPV 16 encodes three oncogenes, E5, E6, and E7, of which E5 is the least studied so far. Its roles in regulating replication and pathogenesis of HPV are not fully understood. Here we utilize high-throughput screening to coordinately investigate the effect of E5 on the expression of host protein-coding and microRNA genes. MicroRNAs form a class of 22nt long noncoding RNAs with regulatory activity. Among the altered cellular microRNAs we focus on the alteration in the expression of miR-146a, miR-203 and miR-324-5p and their target genes in a time interval of 96 hours of E5 induction. Our results indicate that HPV infection and subsequent transformation take place through complex regulatory patterns of gene expression in the host cells, part of which are regulated by the E5 protein.

E-cadherin modulates Wnt-dependent transcription in colorectal cancer cells but does not alter Wnt-independent gene expression in fibroblasts

E-cadherin mediates homophilic adhesion of epithelial cells and is a major determinant of epithelial differentiation during embryonic development and tumor progression. At cell junctions, E-cadherin associates with beta-catenin, which also functions as a transcriptional co-activator of the canonical Wnt signaling pathway by interacting with TCF transcription factors. Here, we have analyzed whether E-cadherin plays a role in the control of gene expression in Wnt-dependent and -independent cellular systems. In DLD-1 colorectal cancer cells, which show constitutive activation of Wnt signaling and exhibit E-cadherin-based cell contacts, the siRNA-mediated knock-down of E-cadherin led to the disturbance of cell junctions, translocation of beta-catenin to the nucleus and an enhancement of beta-catenin/TCF-dependent reporter activity. In L929 fibroblasts, which are deficient in Wnt signaling and E-cadherin-mediated cell adhesion, ectopic expression of E-cadherin induced the stabilization of beta-catenin at the cell junctions and caused marked alterations in cellular morphology and phenotype. However, E-cadherin did not significantly change the transcriptional program of these cells as revealed by DNA microarray analysis. Our data indicate that E-cadherin may modulate Wnt-dependent gene expression by regulating the availability of beta-catenin but has a surprisingly small impact on gene expression in the absence of Wnt signaling.

Drebrin, an Actin-Binding, Cell-Type Characteristic Protein: Induction and Localization in Epithelial Skin Tumors and Cultured Keratinocytes

Isoform E2 of drebrin, an actin-binding protein originally identified in neuronal cells, has recently been identified in diverse non-neuronal cells, mostly in association with cell processes and intercellular junctions. Here, we report on the presence of drebrin in normal human skin, epithelial skin cancers, and cultured keratinocytes. Keratinocytes of normal epidermis contain almost no drebrin but the protein is readily seen in hair follicles. By immunohistochemistry and immunoblot, basal cell carcinomas (BCC) are rich in drebrin, and confocal laser scanning and immunoelectron microscopy show accumulation at adhering junctions, in co-localization with actin and partially with plaque proteins. In squamous cell carcinomas, keratoacanthomas, and in epidermal precancers, drebrin is heterogeneously distributed, appearing as mosaics. Primary keratinocyte cultures contain significant amounts of drebrin enriched at adhering junctions. When epithelium-derived cells devoid of drebrin are transfected with drebrin-enhanced green fluorescent protein, constructs accumulate in the cell periphery, and immunoprecipitation shows complexes with actin. During epidermal growth factor induced formation of cell processes, drebrin retains this junction association, as observed by live cell microscopy. Our results suggest novel functions of drebrin such as an involvement in cell-cell adhesion and tumorigenesis and a potential value in diagnosis of BCC.

Snail and E47 repressors of E-cadherin induce distinct invasive and angiogenic properties in vivo

The transcription factors Snail and E47 are direct repressors of E-cadherin, with both inducing a full epithelial-mesenchymal transition and invasive behaviour in vitro when expressed in the prototypic epithelial MDCK cell line. The role of these repressors in the invasive process and in other tumorigenic properties is, nevertheless, still poorly understood. However, organotypic cultures and in vivo transplantation assays indicate that cells expressing MDCK-Snail and MDCK-E47 exhibit significant differences. MDCK-Snail cells have a higher infiltrative potential than MDCK-E47 cells. Interestingly, both cell types induce angiogenesis of the host stromal tissue in transplantation assays, but this property is greatly enhanced in transplants of MDCK-E47 cells. Xenografted tumours induced in nude mice also show signs of strong angiogenic potential, again markedly increased in tumours induced by MDCK-E47 which exhibit a higher vessel density and proliferation rate than those induced by MDCK-Snail cells. These results suggest differential roles for Snail and E47 E-cadherin repressors in tumour progression where Snail is implicated in promoting the initial invasion and E47 plays an active role in tumour cell growth by promoting angiogenesis.

Tumor progression: Small GTPases and loss of cell-cell adhesion

Tumor progression involves the transition from normal to malignant cells, through a series of cumulative alterations. During this process, invasive and migratory properties are acquired, enabling cells to metastasize (reach and grow in tissues far from their origin). Numerous cellular changes take place during epithelial malignancy, and disruption of E-cadherin based cell-cell adhesion is a major event. The small Rho GTPases (Rho, Rac and Cdc42) have been implicated in multiple steps during cellular transformation, including alterations on the adhesion status of the tumor cells. This review focuses on recent in vivo evidence that implicates RhoGTPases in epithelial tumor progression. In addition, we discuss different hypotheses to explain disruption of cadherin-mediated cell-cell adhesion, directly or indirectly, through activation of Rho GTPases. Understanding the molecular mechanism of how cadherin adhesion and RhoGTPases interplay in normal cells and how this balance is altered during cellular transformation will provide clues as to how to interfere with tumor progression.

TCDD-dependent downregulation of gamma-catenin in rat liver epithelial cells (WB-F344)

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is the most potent tumor promoter ever tested in rodents. Although it is known that most of the effects of TCDD are mediated by binding to the aryl hydrocarbon receptor (AHR), the mechanisms leading to tumor promotion still remain to be elucidated. Loss of contact-inhibition is a characteristic hallmark in tumorigenesis. In WB-F344 cells, TCDD induces a release from contact-inhibition manifested by a 2- to 3-fold increase in DNA-synthesis and the emergence of foci when TCDD (1 nM) is given to confluent cells. We focussed our interest on potential cell membrane proteins mediating contact-inhibition in WB-F344 cells, namely E-cadherin, alpha,- beta,- and gamma-catenin (plakoglobin). Using indirect immunofluorescence, E-cadherin, alpha-, beta- and gamma-catenin were detected at cell adhesion sites in untreated, confluent cells. After TCDD-exposure, gamma-catenin was exclusively localized in the cytoplasm whereas localization of E-cadherin, alpha- and beta-catenin remained unaffected. Cytoplasmic gamma-catenin could be extracted by Triton X-100 treatment, demonstrating that gamma-catenin was no longer bound to the actin cytoskeleton. Western blot analysis showed downregulation of gamma-catenin protein levels. This effect was not blocked by pre-incubation with the selective proteasome inhibitor MG-132, indicating that proteolytical degradation of gamma-catenin by the proteasome system was not increased by TCDD. Because mRNA-levels of gamma-catenin were markedly diminished after TCDD-exposure, we conclude that transcriptional downregulation or destabilization of the mRNA contributes to the decrease in gamma-catenin protein levels in response to TCDD. Because gamma-catenin is considered to be a tumor suppressor, our findings might give more insight into the tumor promoting actions of TCDD.

Abnormal immunoreactivity of the E-cadherin/catenin (alpha-, beta-, and gamma-) complex in premalignant and malignant non-melanocytic skin tumours

E-cadherin/catenin (alpha-, beta-, and gamma-) complex plays a critical role in the control of epithelial differentiation. The aim of this study was to examine the immunoreactivity of E-cadherin and alpha-, beta-, and gamma-catenins in premalignant and malignant non-melanocytic skin tumours (NMST) and to correlate their expression with the grade of tumour differentiation, as assessed by the established histopathological criteria and by the Ki-67 index. Benign NMSTs were also studied. To investigate any possible influence of immunosuppression in the expression of E-cadherin and catenins, the study compared tumours obtained from renal transplant recipients (RTRs) and immunocompetent patients. Immunoperoxidase staining of E-cadherin and alpha-, beta-, and gamma-catenins was performed in 42 squamous cell carcinomas (SCCs) (26 from RTRs and 16 from non-RTRs), 30 lesions of Bowen's disease (11 from RTRs and 19 from non-RTRs), 11 atypical squamoproliferative lesions from RTRs, 19 actinic keratoses (9 from RTRs and 10 from non-RTRs), and 20 viral warts from RTRs. The findings of this study were as follows. Firstly, the probability of abnormal expression of E-cadherin and alpha-, beta-, and gamma-catenins increased from benign to premalignant and malignant NMSTs (p<0.001 for all). Secondly, there was agreement in abnormal expression between most of the molecules measured in malignant and premalignant NMSTs (p<0.05). Thirdly, in SCC, abnormal expression of E-cadherin and catenins was more frequent in lesions with a high (>40%) Ki-67 index than in those with a low Ki-67 index (<40%) (p=0.003). However, only the abnormal expression of gamma-catenin increased with the grade of SCC differentiation (p=0.008). Fourthly, abnormal expression of gamma-catenin predicted a high proliferation index (Ki-67 index 40%) in NMSTs (p<0.01, OR=6.19). Finally, there was no difference in the abnormal expression of E-cadherin and catenins between NMSTs from immunosuppressed and immunocompetent patients. Thus, abnormal expression of the E-cadherin/catenin complex was quite common in SCC and Bowen's disease and also in a proportion of intraepithelial dysplastic lesions, such as atypical squamoproliferative lesions and actinic keratosis, suggesting that these changes may be early indicators of the neoplastic process. Abnormal expression of gamma-catenin was the sole predictor of high proliferation in NMST and was also correlated with the tumour grade, suggesting a possible important role for gamma-catenin in tumourigenesis.

Ectopic expression of PA2.26 antigen in epidermal keratinocytes leads to destabilization of adherens junctions and malignant progression

PA2.26 antigen is a small mucin-type transmembrane glycoprotein induced in mouse epidermal keratinocytes during carcinogenesis. It is located at plasma membrane projections, such as microvilli and ruffles, where it interacts with the actin cytoskeleton. Previous studies revealed that ectopic expression of PA2.26 in epidermal MCA3D keratinocytes induces cell surface extensions and increased motility. Here, we show that PA2.26-expressing MCA3D (3D2.26) cell transfectants undergo a phenotypic conversion linked to the acquisition of malignant characteristics. The 3D2.26 cells down-regulate basal keratin K14 and up-regulate vimentin and keratin K8 expression. Immunofluorescence analysis in 3D2.26 cell cultures showed loss of cortical actin filaments and destabilization of adherens junctions mediated by E- and P-cadherin, although both cadherin mRNAs were expressed in the transfectants. When the cadherin protein levels were analyzed in Western blots, no P-cadherin protein or smaller polypeptide E-cadherin forms were detected, suggesting that E- and P-cadherin synthesized in 3D2.26 cells was unstable and proteolytically degraded. Transplantation of 3D2.26 cells into athymic nude mice induced tumors, whereas MCA3D cells and control (3DN) transfectants were not tumorigenic after 72 days postinjection. The phenotype of the tumors was undifferentiated, with mixed regions exhibiting a glandular differentiation pattern in which the presence of numerous surface microvilli was observed at the ultrastructural level. Interestingly, PA2.26 antigen was highly expressed in these microvillous cell surfaces. Tumor cells were vimentin- and K8-positive and showed an aberrant pattern of E-cadherin protein expression in which large cytoplasmic aggregates were found close to the nucleus. Infiltration of tumor cells into lymphatic vessels and the presence of frequent regional lymph node metastases were also observed in the tumors. These results indicate that expression of PA2.26 antigen in premalignant keratinocytes induces a fully transformed and metastatic phenotype, and they suggest an involvement of PA2.26 in malignant progression.

The transcription factor snail controls epithelial-mesenchymal transitions by repressing E-cadherin expression

The Snail family of transcription factors has previously been implicated in the differentiation of epithelial cells into mesenchymal cells (epithelial-mesenchymal transitions) during embryonic development. Epithelial-mesenchymal transitions are also determinants of the progression of carcinomas, occurring concomitantly with the cellular acquisition of migratory properties following downregulation of expression of the adhesion protein E-cadherin. Here we show that mouse Snail is a strong repressor of transcription of the E-cadherin gene. Epithelial cells that ectopically express Snail adopt a fibroblastoid phenotype and acquire tumorigenic and invasive properties. Endogenous Snail protein is present in invasive mouse and human carcinoma cell lines and tumours in which E-cadherin expression has been lost. Therefore, the same molecules are used to trigger epithelial-mesenchymal transitions during embryonic development and in tumour progression. Snail may thus be considered as a marker for malignancy, opening up new avenues for the design of specific anti-invasive drugs.

Three-dimensional spheroid cultures of human prostate cancer cell lines

BACKGROUND

Many of the available human prostate cancer (PC) cell lines have lost androgen sensitivity and no longer secrete prostate-specific proteins after serial culturing in cell monolayers. Three-dimensional spheroid cultures have been found to better mimic the in vivo phenotypes of several nonprostatic cell lines.

METHODS

We analyzed seven PC cell lines to determine if spheroid culturing results in greater sensitivity to androgens and 1alpha,25(OH)(2) vitamin D(3) (1,25(OH)(2) D(3)) with regards to their growth, differentiation, and apoptotic potential.

RESULTS

Only PC-3 cells showed greater sensitivity to the growth-inhibitory effects of 1, 25(OH)(2) D(3), while ALVA-31 showed a diminished response. The regulation of prostate-specific antigen and prostate-specific acid phosphatase remained unchanged. However, these studies provided several unique findings not observed in cell monolayers. First, three basic spheroid morphologies were observed with varying degrees of intercellular adhesions. Secondly, the cell lines that formed the tightest spheroids consistently grew at the slowest rates, regardless of their growth rate in monolayers. Lastly, 1,25(OH)(2) D(3) treatment of ALVA-31 and PPC-1 spheroids greatly reduced intercellular adhesions, and rendered ALVA-31 spheroids resistant to apoptotic induction by Fas ligand expressed via a recombinant adenoviral construct.

CONCLUSIONS

Our results suggest that spheroid cultures of human PC cells may provide unique insights regarding cell adhesion and apoptotic potential that are diminished or absent in monolayer cultures.