Serum-activated K and Cl currents underlay U87-MG glioblastoma cell migration

Abstract

Glioblastoma cells in vivo are exposed to a variety of promigratory signals, including undefined serum components that infiltrate into high grade gliomas as result of blood-brain barrier breakdown. Glioblastoma cell migration has been further shown to depend heavily on ion channels activity. We have then investigated the modulatory effects of fetal calf serum (FCS) on ion channels, and their involvement in U87-MG cells migration. Using the perforated patch-clamp technique we have found that, in a subpopulation of cells (42%), FCS induced: (1) an oscillatory activity of TRAM-34 sensitive, intermediate-conductance calcium-activated K (IK(Ca) ) channels, mediated by calcium oscillations previously shown to be induced by FCS in this cell line; (2) a stable activation of a DIDS- and NPPB-sensitive Cl current displaying an outward rectifying instantaneous current-voltage relationship and a slow, voltage-dependent inactivation. By contrast, in another subpopulation of cells (32%) FCS induced a single, transient IK(Ca) current activation, always accompanied by a stable activation of the Cl current. The remaining cells did not respond to FCS. In order to understand whether the FCS-induced ion channel activities are instrumental to promoting cell migration, we tested the effects of TRAM-34 and DIDS on the FCS-induced U87-MG cell migration using transwell migration assays. We found that these inhibitors were able to markedly reduce U87-MG cell migration in the presence of FCS, and that their co-application resulted in an almost complete arrest of migration. It is concluded that the modulation of K and Cl ion fluxes is essential for the FCS-induced glioblastoma cell migration.

Cl − and K + channels and their role in primary brain tumour biology

“…Given the previous evidence, we can theorize that Cl 2 efflux is largely via ClC-3, and K þ efflux via KCa channels, which commonly co-localize and are activated under similar conditions. As mentioned previously, KCa3.1 affects migration after activation by bradykinin, and the same study found colocalization of KCa3.1 and ClC-3 on the invadopodia [38,45] ( figure 3). Furthermore, application of bradykinin activates both channels, and inhibition of either channel decreased migration [38,45].…”

“…As mentioned previously, KCa3.1 affects migration after activation by bradykinin, and the same study found colocalization of KCa3.1 and ClC-3 on the invadopodia [38,45] ( figure 3). Furthermore, application of bradykinin activates both channels, and inhibition of either channel decreased migration [38,45]. Blocking both channels together almost completely inhibits migration in vitro, indicating that both ions are used for migration [38,45].…”

“…Targeting channels that are consistently involved in multiple glioma processes could also be promising. For example, ClC-3 has been implicated in glioma migration and proliferation [12,57], and KCa channels are involved in migration [38,41,42,45] and apoptosis [49,54,56]. Furthermore, interference with ion channel activity may serve as adjuvant to other chemotherapeutic targets; because migration, proliferation and apoptosis are rstb.royalsocietypublishing.org Phil.…”

Ionizing radiation, ion transports, and radioresistance of cancer cells

“…The latter is generated by the loss of Cl − and K + ions along their electrochemical gradients followed by osmotically obliged water fluxes. Involved transporters probably are ClC-3 Cl − channels (Olsen et al, 2003; Cuddapah and Sontheimer, 2010; Lui et al, 2010), Ca 2+ -activated high conductance BK (Ransom and Sontheimer, 2001; Ransom et al, 2002; Sontheimer, 2008) as well as intermediate conductance IK K + channels (Catacuzzeno et al, 2010; Sciaccaluga et al, 2010; Ruggieri et al, 2012) and AQP-1 water channels (Mccoy and Sontheimer, 2007; Mccoy et al, 2010). To a lower extent, K + and Cl − efflux is probably also mediated by KCC1-generated cotransport (Ernest et al, 2005).…”

Role of ion channels in ionizing radiation-induced cell death

“…Inhibition of either of these channels attenuates glioblastoma cell migration or invasion [83,[90][91][92][93][94] confirming their pivotal function in these processes.…”