Background: Targeting immune checkpoint proteins has recently gained substantial attention due to the dramatic success of this strategy in clinical trials for some cancers. Inducible T-cell co-stimulator ligand (ICOSLG) is a member of the B7 family of immune regulatory ligands, expression of which in cancer is implicated in disease progression due to regulation of anti-tumor adaptive immunity. Although aberrant ICOSLG expression has been reported in glioma cells, the underlying mechanisms that promote glioblastoma (GBM) progression remain elusive. Methods: Here, we investigated a causal role for ICOSLG in GBM progression by analyzing ICOSLG expression in both human glioma tissues and patient-derived GBM sphere cells (GSCs). We further examined its immune modulatory effects and the underlying molecular mechanisms. Results: Bioinformatics analysis and GBM tissue microarray showed that upregulation of ICOSLG expression was associated with poor prognosis in patients with GBM. ICOSLG expression was upregulated preferentially in mesenchymal GSCs but not in proneural GSCs in a tumor necrosis factor-α-/NF-ĸB-dependent manner. Furthermore, ICOSLG expression by mesenchymal GSCs promoted expansion of T cells that produced interleukin-10. Knockdown of the gene encoding ICOSLG markedly reduced GBM tumor growth in immune competent mice, with a concomitant downregulation of interleukin-10 levels in the tumor microenvironment. Conclusions: Inhibition of the ICOSLG-ICOS axis in GBM may provide a promising immunotherapeutic approach for suppressing a subset of GBM with an elevated mesenchymal signature.

Potassium channels regulate excitability, epithelial ion transport, proliferation, and apoptosis. In pancreatic ducts, K+ channels hyperpolarize the membrane potential and provide the driving force for anion secretion. This review focuses on the molecular candidates of functional K+ channels in pancreatic duct cells, including KCNN4 (KCa3.1), KCNMA1 (KCa1.1), KCNQ1 (Kv7.1), KCNH2 (Kv11.1), KCNH5 (Kv10.2), KCNT1 (KCa4.1), KCNT2 (KCa4.2), and KCNK5 (K2P5.1). We will give an overview of K+ channels with respect to their electrophysiological and pharmacological characteristics and regulation, which we know from other cell types, preferably in epithelia, and, where known, their identification and functions in pancreatic ducts and in adenocarcinoma cells. We conclude by pointing out some outstanding questions and future directions in pancreatic K+ channel research with respect to the physiology of secretion and pancreatic pathologies, including pancreatitis, cystic fibrosis, and cancer, in which the dysregulati...

Potassium channels play a vital role in maintaining the membrane potential and the driving force for anion secretion in epithelia. In pancreatic ducts, which secrete bicarbonate-rich fluid, the identity of K⁺channels has not been extensively investigated. In this study, we investigated the molecular basis of functional K⁺channels in rodent and human pancreatic ducts (Capan-1, PANC-1, and CFPAC-1) using molecular and electrophysiological techniques. RT-PCR analysis revealed mRNAs for KCNQ1, KCNH2, KCNH5, KCNT1, and KCNT2, as well as KCNN4 coding for the following channels: KVLQT1; HERG; EAG2; Slack; Slick; and an intermediate-conductance Ca²⁺-activated K⁺(IK) channel (K_Ca3.1). The following functional studies were focused on the IK channel. 5,6-Dichloro-1-ethyl-1,3-dihydro-2 H-benzimidazole-2-one (DC-EBIO), an activator of IK channel, increased equivalent short-circuit current ( I_sc) in Capan-1 monolayer, consistent with a secretory response. Clotrimazole, a blocker of IK channel, inhibited I_sc. IK channel blockers depolarized the membrane potential of cells in microperfused ducts dissected from rodent pancreas. Cell-attached patch-clamp single-channel recordings revealed IK channels with an average conductance of 80 pS in freshly isolated rodent duct cells. These results indicated that the IK channels may, at least in part, be involved in setting the resting membrane potential. Furthermore, the IK channels are involved in anion and potassium transport in stimulated pancreatic ducts.

Although Ca²⁺-activated K⁺ (K_Ca) channels distinct from maxi-K⁺ channels have been suggested to contribute to muscarinically stimulated K⁺ currents in salivary acinar cells, the molecular nature of the channels is unclear. Using electrophysiological and RT-PCR techniques, we have now investigated the involvement of SK4/IK1-like channels in native K_Cacurrents in bovine parotid acinar (BPA) cells. Ca²⁺-dependent K⁺ efflux from perfused bovine parotid tissues was not inhibited by a maxi-K⁺ channel blocker, tetraethylammonium (TEA). Whole cell recordings from BPA cells showed a TEA-insensitive K_Ca conductance, which was highly permeable to Rb⁺. In inside-out macropatches, TEA-insensitive Rb⁺ currents were activated by Ca²⁺ with half-maximal values of 0.4 μM. 1-Ethyl-2-benzimidazolinone (1-EBIO) increased the Ca²⁺sensitivity of the currents. The calmodulin antagonists trifluoperazine, calmidazolium, and W-7 inhibited the Ca²⁺-activated Rb⁺ currents. In outside-out macropatches, Ca²⁺-activated Rb⁺ currents were inhibited by Ba²⁺, quinine, clotrimazole, and charybdotoxin but not by d-tubocrarine or apamin. RT-PCR analysis showed transcripts of SK4/IK1 in BPA cells. These results collectively suggest that SK4/IK1-like channels mediate the native K_Ca currents in BPA cells.

SK4/IK1 encodes an intermediate conductance, Ca²⁺-activated K⁺ channel and fulfills a variety of physiological functions in excitable and nonexcitable cells. Although recent studies have provided evidence for the presence of SK4/IK1 channels in salivary acinar cells, the regulatory mechanisms and the physiological function of the channel remain unknown in these cells. Using molecular and electrophysiological techniques, we examined whether cytosolic ATP-dependent regulation of native SK4/IK1-like channel activity would involve endogenous cAMP-dependent protein kinase (PKA) in rat submandibular acinar (RSA) cells. Electrophysiological properties of tetraethylammonium (TEA) (10 mM)-insensitive, Ca²⁺-dependent K⁺ currents in macropatches excised from RSA cells matched those of whole cell currents recorded from human embryonic kidney-293 cells heterologously expressing rat SK4/IK1 (rSK4/IK1) cloned from RSA cells. In outside-out macropatches, activity of native SK4/IK1-like channels, defined as a charybdotoxin (100 nM)-blockable current in the presence of TEA (10 mM) in the bathing solution, ran down unless both ATP and Mg²⁺ were present in the pipette solution. The nonhydrolyzable ATP analog AMP-PNP failed to support the channel activity as ATP did. The addition of Rp-cAMPS (10 μM), a PKA inhibitor, to the pipette solution containing ATP/Mg²⁺ induced a rundown of the Ca²⁺-dependent K⁺ currents. Inclusion of cAMP (1 mM) into the pipette solution (1 μM free Ca²⁺) containing ATP/Mg²⁺ caused a gradual increase in the currents, the effect being pronounced for the currents induced by 0.1 μM free Ca²⁺. Forskolin (1 μM), an adenylyl cyclase activator, also increased the currents induced by 0.1 μM free Ca²⁺. In inside-out macropatches, cytosolic ATP/Mg²⁺ increased both the maximum current (proportional to the maximum channel activity) and Ca²⁺ sensitivity of current activation. Collectively, these results suggest that ATP-dependent regulation of native SK4/IK1-like channels, at least in part, is mediated by endogenous PKA in RSA cells.

Background: Proper glycemic control is an important goal of critical care medicine, including perioperative patient care that can influence patients’ prognosis. Insulin secretion from pancreatic β-cells is generally assumed to play a critical role in glycemic control in response to an elevated blood glucose concentration. Many animal and human studies have demonstrated that perioperative drugs, including volatile anesthetics, have an impact on glucose-stimulated insulin secretion (GSIS). However, the effects of the intravenous anesthetic propofol on glucose metabolism and insulin sensitivity are largely unknown at present.Methods: The effect of propofol on insulin secretion under low glucose or high glucose was examined in mouse MIN6 cells, rat INS-1 cells, and mouse pancreatic β-cells/islets. Cellular oxygen or energy metabolism was measured by Extracellular Flux Analyzer. Expression of glucose transporter 2 (GLUT2), potassium channels, and insulin mRNA was assessed byqRT-PCR. Protein expression of voltage-dependent potassium channels (Kv2) was also assessed by immunoblot. Propofol’s effects on potassium channels including stromatoxin-1-sensitive Kv channels and cellular oxygen and energy metabolisms were also examined.Results: We showed that propofol, at clinically relevant doses, facilitates insulin secretion under low glucose conditions and GSIS in MIN6, INS-1 cells, and pancreatic β-cells/islets. Propofol did not affect intracellular ATP or ADP concentrations and cellular oxygen or energy metabolism. The mRNA expression of GLUT2 and channels including the voltage-dependent calcium channels Cav1.2, Kir6.2, and SUR1 subunit of K_ATP, and Kv2 were not affected by glucose or propofol. Finally, we demonstrated that propofol specifically blocks Kv currents in β-cells, resulting in insulin secretion in the presence of glucose.Conclusions: Our data support the hypothesis that glucose induces membrane depolarization at the distal site, leading to K_ATPchannel closure, and that the closure of Kv channels by propofol depolarization in β-cells enhances Ca²⁺entry, leading to insulin secretion. Because its activity is dependent on GSIS, propofol and its derivatives are potential compounds that enhance and initiate β-cell electrical activity.