An investigation of the mechanisms of cellular transformation by hERG potassium channels
thesisposted on 30.03.2012, 09:12 by George S. G. Shehatou
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.