Identification of KCa3.1 Channel as a Novel Regulator of Oxidative Phosphorylation in a Subset of Pancreatic Carcinoma Cell Lines

Abstract

Pancreatic ductal adenocarcinoma (PDAC) represents the most common form of pancreatic cancer with rising incidence in developing countries and overall 5-year survival rates of less than 5%. The most frequent mutations in PDAC are gain-of-function mutations in KRAS as well as loss-of-function mutations in p53. Both mutations have severe impacts on the metabolism of tumor cells. Many of these metabolic changes are mediated by transporters or channels that regulate the exchange of metabolites and ions between the intracellular compartment and the tumor microenvironment. In the study presented here, our goal was to identify novel transporters or channels that regulate oxidative phosphorylation (OxPhos) in PDAC in order to characterize novel potential drug targets for the treatment of these cancers. We set up a Seahorse Analyzer XF based siRNA screen and identified previously described as well as novel regulators of OxPhos. The siRNA that resulted in the greatest change in cellular oxygen consumption was targeting the KCNN4 gene, which encodes for the Ca2+-sensitive K+ channel KCa3.1. This channel has not previously been reported to regulate OxPhos. Knock-down experiments as well as the use of a small molecule inhibitor confirmed its role in regulating oxygen consumption, ATP production and cellular proliferation. Furthermore, PDAC cell lines sensitive to KCa3.1 inhibition were shown to express the channel protein in the plasma membrane as well as in the mitochondria. These differences in the localization of KCa3.1 channels as well as differences in the regulation of cellular metabolism might offer opportunities for targeted therapy in subsets of PDAC.

KCa3.1 Channels and Glioblastoma: In Vitro Studies

“…In addition to mitogenic signaling, K Ca 3.1 channels in the inner mitochondrial membrane have been proposed to modulate mitochondrial function in colon cancer cells [ 16 , 17 ]. In pancreatic cancer cells, mitochondrial K Ca 3.1 channels have been suggested to regulate oxidative phosphorylation [ 18 ]. Likewise, an adapting function in metabolism has been attributed to plasmalemmal K Ca 3.1 channels.…”

The A818–6 system as an in-vitro model for studying the role of the transportome in pancreatic cancer

“…As formerly described, the epithelial cellular polarity plays an important role in maintaining cellular volume and acid/base transport in pancreatic ductal cells [15], and the involvement of the transportome in PDAC development was also previously reported [17,23,[52][53][54]. Noteworthy, the 3D orientation of HS was previously shown to allow the A818-6 cells to regain relatively normal epithelial polarity which was in turn lost when the HS were disrupted and ML reformed and vice versa [27,29].…”

Pharmacological modulation of mitochondrial ion channels

“…IKCa (also called K Ca 3.1) is expressed in almost all migrating cells and various studies point to its important role in the control of proliferation in human breast cancer, in hepatocellular carcinoma, in chronic lymphocytic leukaemia (B‐CLL) and in lung cancer (for review, see Schwab et al ., ). mtIKCa is functional in HCT116 colon carcinoma and HeLa cells (Sassi et al ., ), is inhibited by TRAM‐34 and clotrimazole (De Marchi et al ., ) and regulates oxidative phosphorylation in pancreatic ductal adenocarcinoma cells (Kovalenko et al ., ). In vitro data suggest that inhibition of IKCa and likely of mtIKCa by membrane‐permeant inhibitors sensitizes melanoma cells to B‐Raf inhibitors, such as vemurafenib, and induces release of mitochondrial ROS (Bauer et al ., ).…”