Potassium channel regulation by ras/raf signal transduction cascade

Yi Huang, Purdue University

Abstract

Ras oncogene is the most commonly found oncogene and has been found in at least 30% of all human cancers. However, the mechanism of ras transformation remains unknown. Proliferative signals received by growth factor receptors at the cell surface are transmitted to the nucleus via ras protein and a series of kinases. Activation of these kinases and subsequent expression of ras responsive genes are key signals for cell proliferation. Constitutive stimulation of proliferative signal transduction pathways causes uncontrolled cell growth and transformation, as with the case of oncogenic ras which exists constantly in a GTP-bound active state. Therefore, understanding of ras function and the mechanism of ras transformation depends on defining the final effector molecules such as ras responsive gene products, and their contribution to cell transformation. Using patch clamp electrophysiology, we found that ras-transformation of murine fibroblast cells selectively induces a unique Ca$\sp{2+}$-activated K$\sp+$ current. The single channel underlying the Ca$\sp{2+}$-activated K$\sp+$ current is Ca$\sp{2+}$-activated, K$\sp+$ selective and inwardly rectifying in symmetric KCl solution. Channel activity is weakly increased with depolarization and is blocked by charybdotoxin (ChTX) or tetraethylammonium (TEA). Induction of the unique Ca$\sp{2+}$-activated K$\sp+$ channel in murine fibroblast cell lines depends on ras. In NIH 3T3 cells, ras induction of K$\sp+$ current is mediated through its immediate downstream target, the raf kinase. The importance of this channel in mitogenic signaling is further indicated by its induction in nontransformed cells by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF), and the ability of K$\sp+$ channel blockers to inhibit cell proliferation. I suggest that this Ca$\sp{2+}$-activated K$\sp+$ channel is one ultimate physiological target of ras mediated signal transduction, and that it may play a role in cell proliferation and ras transformation.

Degree

Ph.D.

Advisors

Rane, Purdue University.

Subject Area

Neurology|Biology

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