Lipid rafts, KCa/ClCa/Ca2+ channel complexes and EGFR signaling: Novel targets to reduce tumor development by lipids?

Membrane lipid rafts are distinct plasma membrane nanodomains that are enriched with cholesterol, sphingolipids and gangliosides, with occasional presence of saturated fatty acids and phospholipids containing saturated acyl chains. It is well known that they organize receptors (such as Epithelial Growth Factor Receptor), ion channels and their downstream acting molecules to regulate intracellular signaling pathways. Among them are Ca2+ signaling pathways, which are modified in tumor cells and inhibited upon membrane raft disruption. In addition to protein components, lipids from rafts also contribute to the organization and function of Ca2+ signaling microdomains. This article aims to focus on the lipid raft KCa/ClCa/Ca2+ channel complexes that regulate Ca2+ and EGFR signaling in cancer cells, and discusses the potential modification of these complexes by lipids as a novel therapeutic approach in tumor development. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

SK4 oncochannels regulate calcium entry and promote cell migration in KRAS-mutated colorectal cancer.

BACKGROUND: Colorectal cancer (CRC) metastases are the main cause of CRC mortality. Intracellular Ca2+ regulates cell migration and invasion, key factors for metastases. Ca2+ also activates Ca2+-dependent potassium channels which in turn affect Ca2+ driving force. We have previously reported that the expression of the Ca2+ activated potassium channel KCNN4 (SK4) is higher in CRC primary tumors compared to normal tissues. Here, we aimed to investigate the role of SK4 in the physiology of CRC. RESULTS: SK4 protein expression is enhanced in CRC tissues compared to normal colon tissues, with a higher level of KCNN4 in CRC patients with KRAS mutations. At the cellular level, we found that SK4 regulates the membrane potential of HCT116 cells. We also found that its inhibition reduced store operated Ca2+ entry (SOCE) and constitutive Ca2+ entry (CCE), while reducing cell migration. We also found that the activity of SK4 is linked to resistance pathways such as KRAS mutation and the expression of NRF2 and HIF-1α. In addition, the pharmacological inhibition of SK4 reduced intracellular reactive oxygen species (ROS) production, NRF2 expression and HIF1α stabilization. CONCLUSION: Our results suggest that SK4 contributes to colorectal cancer cell migration and invasion by modulating both Ca2+ entry and ROS regulation. Therefore, SK4 could be a potential target to reduce metastasis in KRAS-mutated CRC.

Synthetic alkyl-ether-lipid promotes TRPV2 channel trafficking trough PI3K/Akt-girdin axis in cancer cells and increases mammary tumour volume.

The Transient Receptor Potential Vanilloid type 2 (TRPV2) channel is highly selective for Ca2+ and can be activated by lipids, such as LysoPhosphatidylCholine (LPC). LPC analogues, such as the synthetic alkyl-ether-lipid edelfosine or the endogenous alkyl-ether-lipid Platelet Activating Factor (PAF), modulates ion channels in cancer cells. This opens the way to develop alkyl-ether-lipids for the modulation of TRPV2 in cancer. Here, we investigated the role of 2-Acetamido-2-Deoxy-l-O-Hexadecyl-rac-Glycero-3-PhosphatidylCholine (AD-HGPC), a new alkyl-ether-lipid (LPC analogue), on TRPV2 trafficking and its impact on Ca2+ -dependent cell migration. The effect of AD-HGPC on the TRPV2 channel and tumour process was further investigated using calcium imaging and an in vivo mouse model. Using molecular and pharmacological approaches, we dissected the mechanism implicated in alkyl-ether-lipids sensitive TRPV2 trafficking. We found that TRPV2 promotes constitutive Ca2+ entry, leading to migration of highly metastatic breast cancer cell lines through the PI3K/Akt-Girdin axis. AD-HGPC addresses the functional TRPV2 channel in the plasma membrane through Golgi stimulation and PI3K/Akt/Rac-dependent cytoskeletal reorganization, leading to constitutive Ca2+ entry and breast cancer cell migration (without affecting the development of metastasis), in a mouse model. We describe, for the first time, the biological role of a new alkyl-ether-lipid on TRPV2 channel trafficking in breast cancer cells and highlight the potential modulation of TRPV2 by alkyl-ether-lipids as a novel avenue for research in the treatment of metastatic cancer.

Ca2+ protein alpha 1D of CaV1.3 regulates intracellular calcium concentration and migration of colon cancer cells through a non-canonical activity.

It is generally accepted that voltage-gated Ca2+ channels, CaV, regulate Ca2+ homeostasis in excitable cells following plasma membrane depolarization. Here, we show that the Ca2+ protein α1D of CaV1.3 channel is overexpressed in colorectal cancer biopsies compared to normal tissues. Gene silencing experiments targeting α1D reduced the migration and the basal cytosolic Ca2+ concentration of HCT116 colon cancer cell line and modified the cytosolic Ca2+ oscillations induced by the sodium/calcium exchanger NCX1/3 working in its reverse mode. Interestingly, NCX1/3 regulated membrane potential of HCT116 cells only when α1D was silenced, and blocking NCX1/3 increased cytosolic Ca2+ concentration and cell migration. However, membrane depolarization did not induce an increase in intracellular Ca2+. Patch-clamp experiments clearly showed that the inward Ca2+ current was absent. Finally, flow cytometry and immunofluorescence studies showed that α1D protein was localized at the plasma membrane, in cytosol and cell nuclei. Altogether, we uncover a novel signaling pathway showing that α1D is involved in the regulation of Ca2+ homeostasis and cell migration by a mechanism independent of its plasma membrane canonical function but that involved plasma membrane Na+/Ca2+ exchanger.

New Disaccharide-Based Ether Lipids as SK3 Ion Channel Inhibitors.

The SK3 potassium channel is involved in the development of bone metastasis and in the settlement of cancer cells in Ca(2+) -rich environments. Ohmline, which is a lactose-based glycero-ether lipid, is a lead compound that decreases SK3 channel activity and consequently limits the migration of SK3-expressing cells. Herein we report the synthesis of three new ohmline analogues in which the connection of the disaccharide moieties (1→6 versus 1→4) and the stereochemistry of the glycosyl linkage was studied. Compound 2 [3-(hexadecyloxy)-2-methoxypropyl-6-O-α-d-glucopyranosyl-ß-d-galactopyranoside], which possesses an α-glucopyranosyl-(1→6)-ß-galactopyranosyl moiety, was found to decrease SK3 current amplitude (70 % inhibition at 10 µm), displace SK3 protein outside caveolae, and decrease constitutive Ca(2+) entry (50 % inhibition at 300 nm) and SK3-dependent cell migration (30 % at 300 nm) at a level close to that of the benchmark compound ohmline. Compound 2, which decreases the activity of SK3 channel (but not SK2 channel), is a new drug candidate to reduce cancer cell migration and to prevent bone metastasis.