Normal cell-cycle progression is a crucial task for every multicellular organism, as it determines body size and shape, tissue renewal and senescence, and is also crucial for reproduction. On the other hand, dysregulation of the cell-cycle progression leading to uncontrolled cell proliferation is the hallmark of cancer. Therefore, it is not surprising that it is a tightly regulated process, with multifaceted and very complex control mechanisms. It is now well established that one of those mechanisms relies on ion channels, and in many cases specifically on potassium channels. Here, we summarize the possible mechanisms underlying the importance of potassium channels in cell-cycle control and briefly review some of the identified channels that illustrate the multiple ways in which this group of proteins can influence cell proliferation and modulate cell-cycle progression.

Voltage-gated channels open paths for ion permeation upon changes in membrane potential, but how voltage changes are coupled to gating is not entirely understood. Two modules can be recognized in voltage-gated potassium channels, one responsible for voltage sensing (transmembrane segments S1 to S4), the other for permeation (S5 and S6). It is generally assumed that the conversion of a conformational change in the voltage sensor into channel gating occurs through the intracellular S4–S5 linker that provides physical continuity between the two regions. Using the pathophysiologically relevant KCNH family, we show that truncated proteins interrupted at, or lacking the S4–S5 linker produce voltage-gated channels in a heterologous model that recapitulate both the voltage-sensing and permeation properties of the complete protein. These observations indicate that voltage sensing by the S4 segment is transduced to the channel gate in the absence of physical continuity between the modules.

A linker that connects the voltage-sensing domain and pore domain in voltage-gated K+ channels is thought to provide coupling during gating, but this view has been challenged in KCNH channels. Tomczak et al. investigate gating in KV10.1 channels with disrupted linkers and reveal multiple mechanisms.

Kv10.1 is a voltage-gated potassium channel relevant for tumor biology, but the underlying mechanism is still unclear. We propose that Kv10.1 plays a role coordinating primary cilium disassembly with cell cycle progression through localized changes of membrane potential at the ciliary base. Most non-dividing cells display a primary cilium, an antenna-like structure important for cell physiology. The cilium is disassembled when the cell divides, which requires an increase of Ca concentration and a redistribution of phospholipids in its basal region, both of which would be facilitated by local hyperpolarization. Cells lacking Kv10.1 show impaired ciliary disassembly and delayed entrance into mitosis. Kv10.1 is predominantly expressed during G2/M, a critical period for ciliary resorption, and localizes to the ciliary base and vesicles associated with the centrosome. This could explain the influence of Kv10.1 in cell proliferation, as well as phenotypic features of patients carrying gain of function mutations in the gene.

Voltage-gating of ion channels is crucial for excitable tissues, such as nerve and muscle. Here we show that a voltage-gated potassium channel retains its voltage-dependency of activation, even when the voltage sensor and the pore domain are expressed as two individual proteins from separate cRNAs in Xenopus laevis oocytes. Not only interrupting the S4-S5 cytoplasmic linker at various positions, but also concomitant deletion of several consecutive amino acids from this region yielded functional channels. Moreover, mutations of the voltage-sensor that shift the conductance-voltage curve in either hyperpolarizing or depolarizing direction cause the same shift when the S4-S5 linker is disrupted. Detailed characterization of how the location of discontinuity affects the voltage and time-dependence of activation and deactivation of the split constructs sheds new light on the coupling between the voltage-sensing module and the channel gate. Our findings indicate that an intact S4-S5 linker is not a sine qua non condition for voltage gating in Kv10.1. In consequence, the idea of direct mechanical coupling between the voltage sensor and the pore mediated by the S4-S5 linker needs to be revised, at least for the KNCH-family channels, which may have a different gating mechanism than Shaker. 2147-Pos Board B284Two KCNQ1 Mutations Associated with Familial Atrial Fibrillation, S140G and V141M, Demonstrate Distinct Voltage Sensor Phenotypes

(Wang et al, 2016). We have now systematically examined conformational dynamics of this region in different ionic conditions using smFRET. Our results show that this region undergoes significant conformational dynamics, between well separated structural states in the absence of K

TheKCNHfamily of potassium channels serves relevant physiological functions in both excitable and non-excitable cells, reflected in the massive consequences of mutations or pharmacological manipulation of their function. This group of channels shares structural homology with other voltage-gated K+channels. Still, the mechanisms of gating in this family show significant differences with respect to the canonical electromechanical coupling in these molecules. In particular, the large intracellular domains ofKCNHchannels play a crucial role in gating that is still only partly understood. UsingKCNH1(KV10.1) as a model, we have characterized the behavior of a series of modified channels that the current models could not explain. With electrophysiological and biochemical methods combined with mathematical modeling, we show that the behavior of the mutants can be explained by the uncovering of an open state that is not detectable in the wild type, is accessed from deep closed states, and reflects an intermediate step along the chain of events leading to channel opening. This allowed us to study gating steps prior to opening, which, for example, explain the mechanism of gating inhibition by Ca2+-Calmodulin, and generate a gating model that describes the characteristic features ofKCNHchannels' gating.