S. Polvani

herg1 Gene and HERG1 Protein Are Overexpressed in Colorectal Cancers and Regulate Cell Invasion of Tumor Cells

The acquisition of the capacity to invade surrounding tissues confers a more malignant phenotype to tumor cells and is necessary for the establishment of metastases. The understanding of the molecular mechanisms underlying cell invasion in human solid tumors such as colorectal cancers could provide not only more sensitive prognostic analyses but also novel molecular targets for cancer therapy. We report in this article that K+ ion channels belonging to the HERG family are important determinants for the acquisition of an invasive phenotype in colorectal cancers. The herg1 gene and HERG1 protein are expressed in many colon cancer cell lines, and the activity of HERG channels modulates colon cancer cell invasiveness. Moreover, the amount of HERG1 protein expressed on the plasma membrane is directly related to the invasive phenotype of colon cancer cells. Finally, both the herg1 gene and HERG1 protein were expressed in a high percentage of primary human colorectal cancers, with the highest incidence occurring in metastatic cancers, whereas no expression could be detected either in normal colonic mucosa or in adenomas.

hERG1 channels are overexpressed in glioblastoma multiforme and modulate VEGF secretion in glioblastoma cell lines

Recent studies have led to considerable advancement in our understanding of the molecular mechanisms that underlie the relentless cell growth and invasiveness of human gliomas. Partial understanding of these mechanisms has (1) improved the classification for gliomas, by identifying prognostic subgroups, and (2) pointed to novel potential therapeutic targets. Some classes of ion channels have turned out to be involved in the pathogenesis and malignancy of gliomas. We studied the expression and properties of K+ channels in primary cultures obtained from surgical specimens: human ether a gò-gò related (hERG)1 voltage-dependent K+ channels, which have been found to be overexpressed in various human cancers, and human ether a gò-gò-like 2 channels, that share many of hERG1s biophysical features. The expression pattern of these two channels was compared to that of the classical inward rectifying K+ channels, IRK, that are widely expressed in astrocytic cells and classically considered a marker of astrocytic differentiation. In our study, hERG1 was found to be specifically overexpressed in high-grade astrocytomas, that is, glioblastoma multiforme (GBM). In addition, we present evidence that, in GBM cell lines, hERG1 channel activity actively contributes to malignancy by promoting vascular endothelial growth factor secretion, thus stimulating the neoangiogenesis typical of high-grade gliomas. Our data provide important confirmation for studies proposing the hERG1 channel as a molecular marker of tumour progression and a possible target for novel anticancer therapies.

PPARγ and Oxidative Stress: Con(β) Catenating NRF2 and FOXO

Peroxisome-proliferator activator receptor γ (PPARγ) is a nuclear receptor of central importance in energy homeostasis and inflammation. Recent experimental pieces of evidence demonstrate that PPARγ is implicated in the oxidative stress response, an imbalance between antithetic prooxidation and antioxidation forces that may lead the cell to apoptotic or necrotic death. In this delicate and intricate game of equilibrium, PPARγ stands out as a central player devoted to the quenching and containment of the damage and to foster cell survival. However, PPARγ does not act alone: indeed the nuclear receptor is at the point of interconnection of various pathways, such as the nuclear factor erythroid 2-related factor 2 (NRF2), Wnt/β-catenin, and forkhead box proteins O (FOXO) pathways. Here we reviewed the role of PPARγ in response to oxidative stress and its interaction with other signaling pathways implicated in this process, an interaction that emerged as a potential new therapeutic target for several oxidative-related diseases.

HERG K+ channels activation during beta(1) integrin-mediated adhesion to fibronectin induces an up-regulation of alpha(v)beta(3) integrin in the preosteoclastic leukemia cell line FLG 29.1

Integrin receptors have been demonstrated to mediate either “inside-to-out” and “outside-to-in” signals, and by this way are capable of regulating many cellular functions, such as cell growth and differentiation, cell migration, and activation. Among the various integrin-centered signaling pathways discovered so far, we demonstrated that the modulation of the electrical potential of the plasma membrane (VREST) is an early integrin-mediated signal, which is related to neurite emission in neuroblastoma cells. This modulation is sustained by the activation of HERG K+ channels, encoded by the ether-à-go-go-related gene (herg). The involvement of integrin-mediated signaling is being discovered in the hemopoietic system: in particular, osteoclasts are generated as well as induced to differentiate by interaction of osteoclast progenitors with the stromal cells, through the involvement of integrin receptors. We studied the effects of cell interaction with the extracellular matrix protein fibronectin (FN) in a human leukemic preosteoclastic cell line (FLG 29.1 cells), which has been demonstrated to express HERG currents. We report here that FLG 29.1 cells indeed adhere to purified FN through integrin receptors, and that this adhesion induces an osteoclast phenotype in these cells, as evidenced by the appearance of tartrate-resistant acid phosphatase, as well as by the increased expression of CD51/αvβ3 integrin and calcitonin receptor. An early activation of HERG current (IHERG), without any increase in herg RNA or modifications of HERG protein was also observed in FN-adhering cells. This activation is apparently sustained by the β1 integrin subunit activation, through the involvement of a pertussis-toxin sensitive Gi protein, and appears to be a determinant signal for the up-regulation of αvβ3 integrin, as well as for the increased expression of calcitonin receptor.

Molecular mechanism of hepatitis B virus-induced hepatocarcinogenesis

Hepatitis B virus (HBV) infection is a global public health problem with approximately 2 billion people that have been exposed to the virus. HBV is a member of a family of small, enveloped DNA viruses called hepadnaviruses, and has a preferential tropism for hepatocytes of mammals and birds. Epidemiological studies have proved a strong correlation between chronic hepatitis B virus infection and the development of hepatocellular carcinoma (HCC). HCC is the fifth most common malignancy with about 700000 new cases each year, and more than 50% of them arise in HBV carriers. A large number of studies describe the way in which HBV can contribute to HCC development. Multiple mechanisms have been proposed, including the accumulation of genetic damage due to immune-mediated hepatic inflammation and the induction of oxidative stress. There is evidence of the direct effects of the viral proteins HBx and HBs on the cell biology. Integration of HBV-DNA into the human genome is considered an early event in the carcinogenic process and can induce, through insertional mutagenesis, the alteration of gene expression and chromosomal instability. HBV has also epigenetic effects through the modification of the genomic methylation status. Furthermore, the virus plays an important role in the regulation of microRNA expression. This review will summarize the many mechanisms involved in HBV-related liver carcinogenesis.

Expression pattern of the ether-a-go-go-related (ERG) family proteins in the adult mouse central nervous system: evidence for coassembly of different subunits.

Voltage‐dependent K+ channels are the main determinants in controlling cellular excitability within the central nervous system. Among voltage‐dependent K+ channels, the ERG subfamily is deeply involved in the control of cellular excitability, both in mammals and in invertebrates. ERG channels are encoded by different genes: the erg1 gene, which can generate two alternative transcripts (erg1a and erg1b), erg2 and erg3. The aim of the present study was to determine the expression pattern and cellular localization of ERG proteins (ERG1, ERG2, and ERG3) in the mouse CNS, differentiating, for the first time, the ERG1A and ERG1B isoforms. To this purpose, novel specific antibodies were raised against the various channel proteins and their specificity and immunoreactivity tested. It emerged that: 1) all the erg genes were indeed translated in neuronal tissue; 2) ERG proteins distribution in the mouse CNS often overlapped, and only in specific areas each ERG protein showed a distinct pattern of expression; and 3) ERG proteins were generally expressed in neuronal soma, but dendritic and/or white matter labeling could be detected in specific areas. The finding that ERG proteins often have an overlapping expression suggests that neuronal ERG currents could be determined, at least in part, by heterotetrameric ERG channels. This suggestion is demonstrated to occur for ERG1A/ERG1B by showing that the two isoforms coassemble in mouse brain. J. Comp. Neurol. 491:157–174, 2005.

Thiazolidinediones Inhibit Hepatocarcinogenesis in Hepatitis B Virus―Transgenic Mice by Peroxisome Proliferator-Activated Receptor γ―Independent Regulation of Nucleophosmin

Antidiabetic thiazolidinediones (TZD) have in vitro antiproliferative effect in epithelial cancers, including hepatocellular carcinoma (HCC). The effective anticancer properties and the underlying molecular mechanisms of these drugs in vivo remain unclear. In addition, the primary biological target of TZD, the ligand‐dependent transcription factor peroxisome proliferator‐activated receptor γ (PPARγ), is up‐regulated in HCC and seems to provide tumor‐promoting responses. The aim of our study was to evaluate whether chronic administration of TZD may affect hepatic carcinogenesis in vivo in relation to PPARγ expression and activity. The effect of TZD oral administration for 26 weeks was tested on tumor formation in PPARγ‐expressing and PPARγ‐deficient mouse models of hepatic carcinogenesis. Proteomic analysis was performed in freshly isolated hepatocytes by differential in gel electrophoresis and mass spectrometry analysis. Identified TZD targets were confirmed in cultured PPARγ‐deficient hepatocytes. TZD administration in hepatitis B virus (HBV)–transgenic mice (TgN[Alb1HBV]44Bri) reduced tumor incidence in the liver, inhibiting hepatocyte proliferation and increasing apoptosis. PPARγ deletion in hepatocytes of HBV‐transgenic mice (Tg[HBV]CreKOγ) did not modify hepatic carcinogenesis but increased the TZD antitumorigenic effect. Proteomic analysis identified nucleophosmin (NPM) as a TZD target in PPARγ‐deficient hepatocytes. TZD inhibited NPM expression at protein and messenger RNA levels and decreased NPM promoter activity. TZD inhibition of NPM was associated with the induction of p53 phosphorylation and p21 expression. Conclusion: These findings suggest that chronic administration of TZD has anticancer activity in the liver via inhibition of NPM expression and indicate that these drugs might be useful for HCC chemoprevention and treatment. HEPATOLOGY 2010

Identification of a Posttranslational Mechanism for the Regulation of hERG1 K+ Channel Expression and hERG1 Current Density in Tumor Cells

ABSTRACT A common feature of tumor cells is the aberrant expression of ion channels on their plasma membrane. The molecular mechanisms regulating ion channel expression in cancer cells are still poorly known. K+ channels that belong to the human ether-a-go-go-related gene 1 (herg1) family are frequently misexpressed in cancer cells compared to their healthy counterparts. We describe here a posttranslational mechanism for the regulation of hERG1 channel surface expression in cancer cells. This mechanism is based on the activity of hERG1 isoforms containing the USO exon. These isoforms (i) are frequently overexpressed in human cancers, (ii) are retained in the endoplasmic reticulum, and (iii) form heterotetramers with different proteins of the hERG family. (iv) The USO-containing heterotetramers are retained intracellularly and undergo ubiquitin-dependent degradation. This process results in decreased hERG1 current (IhERG1) density. We detailed such a mechanism in heterologous systems and confirmed its functioning in tumor cells that endogenously express hERG1 proteins. The silencing of USO-containing hERG1 isoforms induces a higher IhERG1 density in tumors, an effect that apparently regulates neurite outgrowth in neuroblastoma cells and apoptosis in leukemia cells.

erg gene(s) expression during development of the nervous and muscular system of quail embryos

The expression pattern of K(+) currents is the principal regulator of electrical activity during development of the nervous and muscular system. We report here a study showing the expression pattern of HERG K(+) currents-encoding (erg) genes in various nervous and muscular tissues at different stages of quail embryo development.

Peroxisome proliferator activated receptors at the crossroad of obesity, diabetes, and pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the fourth cause of cancer death with an overall survival of 5% at five years. The development of PDAC is characteristically associated to the accumulation of distinctive genetic mutations and is preceded by the exposure to several risk factors. Epidemiology has demonstrated that PDAC risk factors may be non-modifiable risks (sex, age, presence of genetic mutations, ethnicity) and modifiable and co-morbidity factors related to the specific habits and lifestyle. Recently it has become evident that obesity and diabetes are two important modifiable risk factors for PDAC. Obesity and diabetes are complex systemic and intertwined diseases and, over the years, experimental evidence indicate that insulin-resistance, alteration of adipokines, especially leptin and adiponectin, oxidative stress and inflammation may play a role in PDAC. Peroxisome proliferator activated receptor-γ (PPARγ) is a nuclear receptor transcription factor that is implicated in the regulation of metabolism, differentiation and inflammation. PPARγ is a key regulator of adipocytes differentiation, regulates insulin and adipokines production and secretion, may modulate inflammation, and it is implicated in PDAC. PPARγ agonists are used in the treatment of diabetes and oxidative stress-associated diseases and have been evaluated for the treatment of PDAC. PPARγ is at the cross-road of diabetes, obesity, and PDAC and it is an interesting target to pharmacologically prevent PDAC in obese and diabetic patients.