Differential regulation of human Eag1 channel expression by serum and epidermal growth factor in lung and breast cancer cells.

Oncogenic ether à-go-go-1 (Eag1) potassium channels are overexpressed in most primary human solid tumors. Low oxygen and nutrient/growth factor concentrations play critical roles in tumorigenesis. However, the mechanisms by which tumor cells survive and proliferate under growth factor-depleted conditions remain elusive. Here, we investigated whether serum-deprived conditions and epidermal growth factor (EGF) regulate Eag1 expression in human lung and breast cancer cells. The human cancer cell lines A549 and MCF-7 (from the lungs and breast, respectively) were obtained from the American Type Culture Collection and cultured following the manufacturer's recommendations. Eag1 gene and protein expression were studied by real-time PCR and immunocytochemistry, respectively. Cell proliferation was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and ERK1/2 phosphorylation was investigated by Western blot. Serum-deprived conditions increased Eag1 mRNA and protein expression in both cell lines. This Eag1 upregulation was prevented by EGF and the ERK1/2 inhibitor U0126 in only lung cancer cells; vascular endothelial growth factor did not prevent Eag1 upregulation. Our results suggest that Eag1 may act as a survival and mitogenic factor under low-serum and nutrient conditions and may be a clinical target during the early stages of tumor development.

Astemizole-based anticancer therapy for hepatocellular carcinoma (HCC), and Eag1 channels as potential early-stage markers of HCC.

Hepatocellular carcinoma (HCC) has very poor prognosis. Astemizole has gained great interest as a potential anticancer drug because it targets several proteins involved in cancer including the Eag1 (ether à-go-go-1) potassium channel that is overexpressed in human HCC. Eag1 channels are regulated by cancer etiological factors and have been proposed as early tumor markers. Here, we found that HepG2 and HuH-7 HCC cells displayed Eag1 messenger RNA (mRNA) and protein expression, determined by real-time RT-PCR and immunochemistry, respectively. Astemizole inhibited human HCC cell proliferation (assessed by metabolic activity assay) and induced apoptosis (studied with flow cytometry) in both cell lines. The subcellular Eag1 protein localization was modified by astemizole in the HepG2 cells. The treatment with astemizole prevented diethylnitrosamine (DEN)-induced rat HCC development in vivo (followed by studying γ-glutamyl transpeptidase (GGT) activity). The Eag1 mRNA and protein levels were increased in most DEN-treated groups but decreased after astemizole treatment. GGT activity was decreased by astemizole. The Eag1 protein was detected in cirrhotic and dysplastic rat livers. Astemizole might have clinical utility for HCC prevention and treatment, and Eag1 channels may be potential early HCC biomarkers. These data provide significant basis to include astemizole in HCC clinical trials.

Anterior and intermediate pituitary tissues express claudin 4 in follicle stellate cells and claudins 2 and 5 in endothelial cells.

Follicle-stellate cells are pituitary non-granular cells that are arranged between secretory cells or organized in follicles with small lumens. Cells from the follicles exhibit the typical phenotype of a transporting epithelium, including apical microvilli with a cilium and tight junctions. Freeze-fracture electron microscopy images show that the tight junctions consist of 5-7 anastomosing strands and that cultured follicle-stellate cells develop a trans-epithelial electrical resistance characteristic of "tight" epithelia. Here, we investigate the molecular composition of the tight junction from follicle stellate cells. We found that the rat anterior pituitary lobe expresses mRNAs for claudins 2, 4 and 5; the proteins of all these claudins are observed in the anterior lobe, whereas the intermediate lobe expresses claudins 2 and 5 and the posterior lobe contains only claudin 5. Follicle-stellate cells, identified by their protein marker S100ß, expresses claudin 4 in the apical membrane, in co-localization with dipeptidyl-peptidase and near acetylated ß-tubulin. Claudin 4 partially co-localizes with E-cadherin, indicating that a fraction of the protein is located in the basolateral domain. Follicle-stellate-enriched cell cultures develop patches of polygonal cells expressing claudin 4 and E-cadherin, encircled by extensive monolayers of fusiform cells. Claudin 2 stains specifically blood vessels, identified by claudin 5 and VE-cadherin labels. Thus, follicles in the anterior pituitary consist of "tight" epithelia that can carry out intense vectorial transport, together with a high cation movement in blood vessels, possibly related to the ion requirements of excitable secretory cells for hormone secretion.

Eag1 channels as potential cancer biomarkers.

Cancer is a leading cause of death worldwide. New early tumor markers are needed to treat the disease at curable stages. In addition, new therapeutic targets are required to treat patients not responding to available treatments. Ion channels play major roles in health and disease, including cancer. Actually, several ion channels have been suggested as potential tumor markers and therapeutic targets for different types of malignancies. One of most studied ion channels in cancer is the voltage-gated potassium channel Eag1 (ether à go-go 1), which has a high potential to be used as a cancer biomarker. Eag1 is expressed in most human tumors, in contrast to its restricted distribution in healthy tissues. Several findings suggest Eag1 as a potential early marker for cervical, colon, and breast cancer. In addition, because Eag1 amplification/expression is associated with poor survival in leukemia, colon and ovarian cancer patients, it has also been proposed as a prognosis marker. Moreover, inhibition of either expression or activity of Eag1 leads to reduced proliferation of cancer cells, making Eag1 a potential anticancer target. Using Eag1 in cancer detection programs could help to reduce mortality from this disease.