Silver ions promote blebs growth in U251 glioblastoma cell by activating nonselective cationic currents

Electrophysiological Impact of SARS-CoV-2 Envelope Protein in U251 Human Glioblastoma Cells: Possible Implications in Gliomagenesis?

SARS-CoV-2 is the causative agent of the COVID-19 pandemic, the acute respiratory disease which, so far, has led to over 7 million deaths. There are several symptoms associated with SARS-CoV-2 infections which include neurological and psychiatric disorders, at least in the case of pre-Omicron variants. SARS-CoV-2 infection can also promote the onset of glioblastoma in patients without prior malignancies. In this study, we focused on the Envelope protein codified by the virus genome, which acts as viroporin and that is reported to be central for virus propagation. In particular, we characterized the electrophysiological profile of E-protein transfected U251 and HEK293 cells through the patch-clamp technique and FURA-2 measurements. Specifically, we observed an increase in the voltage-dependent (Kv) and calcium-dependent (KCa) potassium currents in HEK293 and U251 cell lines, respectively. Interestingly, in both cellular models, we observed a depolarization of the mitochondrial membrane potential in accordance with an alteration of U251 cell growth. We, therefore, investigated the transcriptional effect of E protein on the signaling pathways and found several gene alterations associated with apoptosis, cytokines and WNT pathways. The electrophysiological and transcriptional changes observed after E protein expression could explain the impact of SARS-CoV-2 infection on gliomagenesis.

Pharmacological targeting of the mitochondrial calcium-dependent potassium channel KCa3.1 triggers cell death and reduces tumor growth and metastasis in vivo

Ion channels are non-conventional, druggable oncological targets. The intermediate-conductance calcium-dependent potassium channel (K_Ca3.1) is highly expressed in the plasma membrane and in the inner mitochondrial membrane (mitoK_Ca3.1) of various cancer cell lines. The role mitoK_Ca3.1 plays in cancer cells is still undefined. Here we report the synthesis and characterization of two mitochondria-targeted novel derivatives of a high-affinity K_Ca3.1 antagonist, TRAM-34, which retain the ability to block channel activity. The effects of these drugs were tested in melanoma, pancreatic ductal adenocarcinoma and breast cancer lines, as well as in vivo in two orthotopic models. We show that the mitochondria-targeted TRAM-34 derivatives induce release of mitochondrial reactive oxygen species, rapid depolarization of the mitochondrial membrane, fragmentation of the mitochondrial network. They trigger cancer cell death with an EC₅₀ in the µM range, depending on channel expression. In contrast, inhibition of the plasma membrane K_Ca3.1 by membrane-impermeant Maurotoxin is without effect, indicating a specific role of mitoK_Ca3.1 in determining cell fate. At sub-lethal concentrations, pharmacological targeting of mitoK_Ca3.1 significantly reduced cancer cell migration by enhancing production of mitochondrial reactive oxygen species and nuclear factor-κB (NF-κB) activation, and by downregulating expression of Bcl-2 Nineteen kD-Interacting Protein (BNIP-3) and of Rho GTPase CDC-42. This signaling cascade finally leads to cytoskeletal reorganization and impaired migration. Overexpression of BNIP-3 or pharmacological modulation of NF-κB and CDC-42 prevented the migration-reducing effect of mitoTRAM-34. In orthotopic models of melanoma and pancreatic ductal adenocarcinoma, the tumors at sacrifice were 60% smaller in treated versus untreated animals. Metastasis of melanoma cells to lymph nodes was also drastically reduced. No signs of toxicity were observed. In summary, our results identify mitochondrial K_Ca3.1 as an unexpected player in cancer cell migration and show that its pharmacological targeting is efficient against both tumor growth and metastatic spread in vivo.

LY294002 Inhibits Intermediate Conductance Calcium-Activated Potassium (KCa3.1) Current in Human Glioblastoma Cells

Glioblastomas (GBs) are among the most common tumors with high malignancy and invasiveness of the central nervous system. Several alterations in protein kinase and ion channel activity are involved to maintain the malignancy. Among them, phosphatidylinositol 3-kinase (PI3K) activity and intermediate conductance calcium-activated potassium (KCa3.1) current are involved in several aspects of GB biology. By using the electrophysiological approach and noise analysis, we observed that KCa3.1 channel activity is LY294002-sensitive and Wortmannin-resistant in accordance with the involvement of PI3K class IIβ (PI3KC2β). This modulation was observed also during the endogenous activation of KCa3.1 current with histamine. The principal action of PI3KC2β regulation was the reduction of open probability in intracellular free calcium saturating concentration. An explanation based on the “three-gate” model of the KCa3.1 channel by PI3KC2β was proposed. Based on the roles of KCa3.1 and PI3KC2β in GB biology, a therapeutic implication was suggested to prevent chemo- and radioresistance mechanisms.