Desmocollin switching in colorectal cancer

Loss of desmocollin-2 confers a tumorigenic phenotype to colonic epithelial cells through activation of Akt/β-catenin signaling

This study provides evidence that decreased expression of the desmosomal cadherin desmocollin-2 enhances intestinal epithelial cell proliferation and promotes tumor formation via an Akt/β-catenin pathway.

Desmocollin-2 (Dsc2) and desmoglein-2 (Dsg2) are transmembrane cell adhesion proteins of desmosomes. Reduced expression of Dsc2 has been reported in colorectal carcinomas, suggesting that Dsc2 may play a role in the development and/or progression of colorectal cancer. However, no studies have examined the mechanistic contribution of Dsc2 deficiency to tumorigenesis. Here we report that loss of Dsc2 promotes cell proliferation and enables tumor growth in vivo through the activation of Akt/β-catenin signaling. Inhibition of Akt prevented the increase in β-catenin–dependent transcription and proliferation following Dsc2 knockdown and attenuated the in vivo growth of Dsc2-deficient cells. Taken together, our results provide evidence that loss of Dsc2 contributes to the growth of colorectal cancer cells and highlight a novel mechanism by which the desmosomal cadherins regulate β-catenin signaling.

Reduced membranous and ectopic cytoplasmic expression of DSC2 in esophageal squamous cell carcinoma: an independent prognostic factor

Desmocollin 2, a desmosomal component, is a key membrane glycoprotein critically involved in cell-cell adhesion and the maintenance of normal tissue architectures in epithelia. Reports exploring the link of desmocollin expression to cancers are limited. The aim of this study was to investigate the expression of desmocollin 2 in esophageal squamous cell carcinoma and, in particular, to determine the extent to which the patterns of desmocollin 2 expression correlated with the clinical parameters. Desmocollin 2 expression was evaluated in 308 cases of esophageal squamous cell carcinoma using immunohistochemistry. Western blotting and reverse transcriptase polymerase chain reaction were performed to characterize the relative expression levels of desmocollin 2 isoforms. The results indicated that desmocollin 2 expression was reduced significantly in esophageal cancer in both protein and messenger RNA levels and that this reduction was associated with poor survival (P = .011). The expression of desmocollin 2 was prominent in normal esophageal epithelia and highly differentiated esophageal tumors, but was reduced or absent in poorly differentiated tumor specimens. Furthermore, in 74.7% of tumor tissues, desmocollin 2 immunoreactivity displayed an abnormal cytoplasmic localization that was correlated with poor tumor differentiation (P < .001), regional lymph node metastasis (P < .001), pathologic tumor-node-metastasis stages (P < .001), and poor prognosis (P = .048). Multivariate analysis showed that desmocollin 2 expression level was an independent prognostic factor for esophageal squamous cell carcinoma. These data suggest that desmocollin 2 is involved in the transformation and development of esophageal tumors and that desmocollin 2 expression level and intracellular localization may serve as a predictor for patient outcomes.

A molecular study of desmosomes identifies a desmoglein isoform switch in head and neck squamous cell carcinoma

Desmosomes, the intercellular junctions that confer strong adhesion between epithelial cells, are frequently altered in malignancy. However, a comprehensive analysis of these structures has not been carried out in oral neoplasia. Oral squamous cell carcinomas (SCCs) and pre-malignant dysplasia can be sub-classified according to their in vitro replicative lifespan, where the immortal dysplasia (ID) and carcinoma (IC) subsets have p16(ink4a) and p53 dysfunction, telomerase deregulation and genetic instability and the mortal subset (MD and MC) do not. We found that the desmosomal proteins exhibit a distinct expression pattern in oral mucosa when compared with epidermis in vivo. Microarray data from a large panel of lines revealed that the transcript levels of DSG3, DSC2/3, DP, PG and PKP1 were reduced in ID and IC. Interestingly, DSG2 was up-regulated in MC. Reduction of DSG3 and up-regulation of DSG2 were found in two independent microarray datasets. Significantly, we demonstrated that reduction of DSG3 and up-regulation of DSG2 was reversible in vitro by using RNAi-mediated knockdown of DSG2 in IC cells. The remaining desmosomal proteins were largely disrupted or internalized and associated with retraction of keratin intermediate filaments in oral SCC lines. These findings suggest dysfunction and loss of desmosomal components are common events in the immortal class of oral SCC and that these events may precede overt malignancy.

A five-gene signature as a potential predictor of metastasis and survival in colorectal cancer

To understand the molecular mechanisms of metastasis and prognosis of colorectal cancer (CRC), we isolated single cell-derived progenies (SCPs) from SW480 cells in vitro and compared their metastatic potential in an orthotopic CRC tumour model in vivo. Two groups of SCPs with the capability of high and low metastasis, respectively, were obtained. By analysing the gene expression profiles of high (SCP51), low (SCP58) metastatic SCPs, and their parental cell line (SW480/EGFP), we demonstrated that 143 genes were differentially expressed either between SCP51 and SCP58 or between SCP58 and SW480/EGFP. Gene-annotation enrichment analysis of DAVID revealed 80 genes in the top ten clusters of the analysis (gene enrichment score > 1). Of the 80-gene set, 32 genes are potentially involved in metastasis, as revealed by Geneclip. Five putative metastatic genes (LYN, SDCBP, MAP4K4, DKK1, and MID1) were selected for further validations. Immunohistochemical analysis in a cohort of 181 CRC clinical samples showed that the individual expression of LYN, MAP4K4, and MID1, as well as the five-gene signature, was closely correlated with lymph node metastasis in CRC patients. More importantly, the individual expression of LYN, MAP4K4, SDCBP, and MID1, as well as the five-gene signature, was significantly correlated with overall survival in CRC patients. Thus, our five-gene signature may be able to predict metastasis and survival of CRC in the clinic, and opens new perspectives on the biology of CRC.

Involvement of CYR61 and CTGF in the fascin-mediated proliferation and invasiveness of esophageal squamous cell carcinomas cells

Fascin is overexpressed in esophageal squamous cell [corrected] carcinoma (ESCC) and involved in the proliferation and invasiveness of ESCC cells. In this study, we retrospectively examined the expression of fascin in ESCC samples by immunohistochemistry and revealed that overexpression of fascin was related to poor patient survival. RNAi-mediated knockdown of fascin in ESCC cells significantly inhibited cell proliferation and invasiveness, whereas forced expression of fascin in immortalized esophageal epithelial cells accelerated cell proliferation and invasiveness. To explore the underlying mechanism, cDNA microarray was performed to identify the differential gene expression profiles between a fascin-depleted cell line by RNAi and the corresponding control ESCC cells. Results showed that 296 genes were differentially expressed on fascin depletion. In this study, we focused on two down-regulated genes: CYR61 and CTGF. We found that restored expression of either CYR61 or CTGF led to a recovery of the suppression of cellular proliferation and invasiveness induced by down-regulation of fascin expression; the protein level of CYR61 and CTGF were up-regulated in ESCCs and their expression pattern correlated with fascin overexpression. Finally, analysis of signal transduction revealed that fascin affected the expressions of CYR61 and CTGF through transforming growth factor (TGF)-beta pathway. Taken together, we propose that fascin regulates the proliferation and invasiveness of ESCC cells by modulating the expression of CTGF and CYR61 via TGF-beta pathway.

Characterization of de novo synthesized proteins released from human colorectal tumour explants

Tumours release many proteins into their microenvironment. These proteins may enter the blood stream and have value as cancer biomarkers. We examined the range of proteins released by colorectal cancer (CRC) liver metastasis (LM) specimens and normal colon mucosa during 16 h culture as explants in the presence of [35S]-methionine. Proteins released into the conditioned media were isolated and separated by 2-DE and detected by CBB stain and de novo synthesized proteins by autoradiography. The majority of proteins released by CRC LM explants in short-term culture were plasma proteins from tumour interstitial fluid and tissue breakdown products including mitochondrial and nuclear proteins from pre-existing necrotic cells within the tumours. De novo synthesized proteins were present at a lower abundance and included a high proportion of cytoplasmic proteins in addition to classically secreted proteins. Many cytoplasmic proteins were also present in the autoradiograph secretomes of four CRC cell lines examined, despite high cell viability (>97%), suggestive of an alternative release mechanism. The secretome profiles varied significantly between different patients, and also between different cell lines, despite low intra-experimental variation. Quantitative analysis of the autoradiograph secretome profiles prepared from tumour and normal colon mucosa tissues revealed 32 protein spots that were differentially abundant between the normal and cancer tissue secretome, including desmocollin-2 and fibrinogen gamma chain, which were upregulated and downregulated in the CRC LM secretomes, respectively. Further characterization of de novo synthesized proteins released from human tumours may help to discover a novel set of serological markers for CRC.

Wnt/Fz signaling and the cytoskeleton: potential roles in tumorigenesis

Wnt/beta-catenin regulates cellular functions related to tumor initiation and progression, cell proliferation, differentiation, survival, and adhesion. Beta-catenin-independent Wnt pathways have been proposed to regulate cell polarity and migration, including metastasis. In this review, we discuss the possible roles of both beta-catenin-dependent and -independent signaling pathways in tumor progression, with an emphasis on their regulation of Rho-family GTPases, cytoskeletal remodeling, and relationships with cell-cell adhesion and cilia/ciliogenesis.

Repression of the desmocollin 2 gene expression in human colon cancer cells is relieved by the homeodomain transcription factors Cdx1 and Cdx2

Desmosomes are intracellular junctions that provide strong cell-cell adhesion in epithelia and cardiac muscle. Their disruption causes several human diseases and contributes to the epithelial-to-mesenchymal transition observed in cancer. Desmocollin 2 (DSC2) is a cadherin superfamily member and a critical component of desmosomes found in intestinal epithelium. However, the mechanism regulating DSC2 gene expression in intestinal cells is not known. Cdx1 and Cdx2 are homeodomain transcription factors that regulate intestine-specific gene expression. Cdx expression in the past has been associated with the induction of desmosomes. We now show that the DSC2 gene is a transcriptional target for Cdx1 and Cdx2. Colon cancer cell lines retaining Cdx2 expression typically express DSC2. Restoration of Cdx expression in Colo 205 cells induced DSC2 mRNA and protein and the formation of desmosomes. The 5'-flanking region of the DSC2 promoter contains two consensus Cdx-binding sites. Electrophoretic mobility shift assays show that Cdx1 and Cdx2 bind these sites in vitro, and chromatin immunoprecipitation confirmed Cdx2 binding in vivo. DSC2 promoter truncations established that these regions are Cdx responsive. The truncations also identify a region of the promoter in which potent transcriptional repressors act. This repressor activity is relieved by Cdx binding. We conclude that the homeodomain transcription factors Cdx1 and Cdx2 regulate DSC2 gene expression in intestinal epithelia by reversing the actions of a transcriptional repressor. The regulation of desmosomal junctions by Cdx contributes to normal intestinal epithelial columnar morphology and likely antagonizes the epithelial-to-mesenchymal transition necessary for the metastasis of colon cancer cells in humans.

HNF4 alpha orchestrates a set of 14 genes to down-regulate cell proliferation in kidney cells

Abstract Few genes are known to be involved in renal cell carcinoma (RCC) development and progression. The cell-specific transcription factor hepatocyte nuclear factor 4 alpha (HNF4 alpha) is down-regulated in RCC and we have shown that HNF4 alpha inhibits cell proliferation in the embryonic kidney cell line HEK293. To clarify the possible tumor suppressor activity of HNF4 alpha we analyzed the whole human expression profile in HEK293 cells upon HNF4 alpha induction. By comparing induced and uninduced cells, we identified 1411 differentially expressed genes. Using RNA interference, we screened 56 HNF4 alpha-regulated genes for their possible role in mediating inhibition of cell proliferation triggered by HNF4 alpha. We demonstrate that 14 of these regulated genes are able to contribute to the inhibitory effect of HNF4 alpha on cell proliferation, including well-known cancer genes, such as CDKN1A (p21), TGFA, MME (NEP) and ADAMTS1. In addition, the genes SEPP1, THEM2, BPHL, DSC2, ANK3, ALDH6A1, EPHX2, NELL2, EFHD1 and PROS1 are also part of the network of HNF4 alpha target genes that regulate proliferation in HEK293 cells. Therefore, we postulate that HNF4 alpha orchestrates, at least, these 14 genes to regulate cell proliferation in HEK293 cells and that down-regulation of HNF4 alpha could contribute to the progression of kidney cancer.

Broken hearts, woolly hair, and tattered skin: when desmosomal adhesion goes awry

Desmosomal cadherins constitute the adhesive core of desmosomes. Different desmosomal cadherins are differentially expressed in a tissue-specific as well as differentiation-dependent manner. The skin and the heart are two examples of tissues whose vital functions require the ability to endure mechanical stress, and therefore, rely on the integrity of desmosomal adhesion. When this adhesion is compromised via mutations in genes encoding desmosomal cadherins or associated plaque proteins, both tissues can suffer the consequences. Open questions revolve around whether the resulting phenotypes are solely because of physical disruption of cell adhesion or whether these events are coupled with signaling mechanisms that influence many additional cellular processes. In this review, we focus on new developments in desmosomal adhesion with an emphasis on the skin, hair, and heart.

Desmosomes: a role in cancer?

Much evidence now attests to the importance of desmosomes and their constituents in cancer. Alterations in the expression of desmosomal components could contribute to the progression of the disease by modifying intracellular signal transduction pathways and/or by causing reduced cell adhesion. The Wnt/beta-catenin pathway is a potential target because of the involvement of the cytoplasmic desmosomal protein plakoglobin. Loss of desmosomal adhesion is a prerequisite for the epithelial-mesenchymal transition, implicated in the conversion of early stage tumours to invasive cancers.