An investigation of the mechanisms of cellular transformation by hERG potassium channels

Human ether-à-go-go-related gene 1 (hERG1) potassium channels are expressed in a variety of tumour cells and expression of hERG1 K+ channels in normal cells can induce a transformed phenotype. The transformative potential of hERG1 appears to be extracellular matrix-dependent. hERG1-expressing NIH-3T3 cells maintained a normal cell morphology when plated on collagen-1 and cell migration speeds were not different to those measured for empty vector-transfected NIH-3T3 cells (NIH-VC). However, hERG1-expressing NIH-3T3 cells displayed a transformed morphology and enhanced cell migration speeds when plated on laminin-1 or fibronectin, and this was associated with a reduction in vinculin protein cell content and cytoskeletal rearrangements. I have provided evidence to indicate that the ion flux through the hERG1 pore and its cell-surface localization is important for its oncogenic potential. Unlike for wild-type hERG1, stable expression of a non-conducting G628S hERG1, or a trafficking-deficient A561V hERG1 mutant did not induce a transformed phenotype in NIH-3T3 cells. Pentamidine, a compound which inhibits hERG1 trafficking to the cell-surface, inhibited fibronectin-dependent migration of wild-type hERG1-expressing cells. Although dofetilide, which blocks the ion conductance of hERG1, did not alter the transformative effect of wild-type hERG1 expression in cell grown on fibronectin, chronic application of this hERG1 inhibitor at a therapeutically-relevant concentration (100 nM) did cause a near-complete reversion of hERG1-expressing cells to a normal cell phenotype within 14 days. NIH-3T3 cells transiently transfected with a plasmid encoding both hERG1 and hERG1b exhibited increases in cell proliferation relative to cells expressing either isoform alone, suggesting a potential role for the hERG1b isoform in regulating hERG1 pro-oncogenic effects. In summary, the transforming potential of hERG1 expression appears to be dependent on hERG1 trafficking to the cell-surface and its ion channel functionality. Chronic administration of hERG1-blockers may be able to impair oncogenic progression in hERG1-expressing tumours

An investigation of the mechanisms of cellular transformation by hERG potassium channels

Human ether-à-go-go-related gene 1 (hERG1) potassium channels are expressed in a variety of tumour cells and expression of hERG1 K+ channels in normal cells can induce a transformed phenotype. The transformative potential of hERG1 appears to be extracellular matrix-dependent. hERG1-expressing NIH-3T3 cells maintained a normal cell morphology when plated on collagen-1 and cell migration speeds were not different to those measured for empty vector-transfected NIH-3T3 cells (NIH-VC). However, hERG1-expressing NIH-3T3 cells displayed a transformed morphology and enhanced cell migration speeds when plated on laminin-1 or fibronectin, and this was associated with a reduction in vinculin protein cell content and cytoskeletal rearrangements. I have provided evidence to indicate that the ion flux through the hERG1 pore and its cell-surface localization is important for its oncogenic potential. Unlike for wild-type hERG1, stable expression of a non-conducting G628S hERG1, or a trafficking-deficient A561V hERG1 mutant did not induce a transformed phenotype in NIH-3T3 cells. Pentamidine, a compound which inhibits hERG1 trafficking to the cell-surface, inhibited fibronectin-dependent migration of wild-type hERG1-expressing cells. Although dofetilide, which blocks the ion conductance of hERG1, did not alter the transformative effect of wild-type hERG1 expression in cell grown on fibronectin, chronic application of this hERG1 inhibitor at a therapeutically-relevant concentration (100 nM) did cause a near-complete reversion of hERG1-expressing cells to a normal cell phenotype within 14 days. NIH-3T3 cells transiently transfected with a plasmid encoding both hERG1 and hERG1b exhibited increases in cell proliferation relative to cells expressing either isoform alone, suggesting a potential role for the hERG1b isoform in regulating hERG1 pro-oncogenic effects. In summary, the transforming potential of hERG1 expression appears to be dependent on hERG1 trafficking to the cell-surface and its ion channel functionality. Chronic administration of hERG1-blockers may be able to impair oncogenic progression in hERG1-expressing tumours.EThOS - Electronic Theses Online ServiceScholarhip - Mansoura UniversityEgyptGBUnited Kingdo

Long-term channel block is required to inhibit cellular transformation by human ether-à-go-go-related gene (hERG1) potassium channels

Both human ether-à-go-go-related gene (hERG1) and the closely related human ether-à-go-go (hEAG1) channel are aberrantly expressed in a large proportion of human cancers. In the present study, we demonstrate that transfection of hERG1 into mouse fibroblasts is sufficient to induce many features characteristic of malignant transformation. An important finding of this work is that this transformation could be reversed by chronic incubation (for 2-3 weeks) with the hERG channel blocker dofetilide (100 nM), whereas more acute applications (for 1-2 days) were ineffective. The hERG1 expression resulted in a profound loss of cell contact inhibition, multiple layers of overgrowing cells, and high saturation densities. Cells also changed from fibroblast-like to a more spindle-shaped morphology, which was associated with a smaller cell size, a dramatic increase in cell polarization, a reduction in the number of actin stress fibers, and less punctate labeling of focal adhesions. Analysis of single-cell migration and scratch-wound closure clearly demonstrated that hERG1-expressing cells migrated more rapidly than vector-transfected control cells. In contrast to previous studies on hEAG1, there were no increases in rates of proliferation, or loss of growth factor dependency; however, hERG1-expressing cells were capable of substrate-independent growth. Allogeneic transplantation of hERG1-expressing cells into nude mice resulted in an increased incidence of tumors. In contrast to hEAG1, the mechanism of cellular transformation is dependent on ion conduction. Trafficking-deficient and conduction-deficient hERG1 mutants also prevented cellular transformation. These results provide evidence that hERG1 expression is sufficient to induce cellular transformation by a mechanism distinct from hEAG1. The most important conclusion of this study is that selective hERG1 channel blockers have therapeutic potential in the treatment of hERG1-expressing cancers