ROS in diabetic atria regulate SK2 degradation by Atrogin-1 through the NF-κB signaling pathway.

One of the independent risk factors for atrial fibrillation is diabetes mellitus (DM); however, the underlying mechanisms causing atrial fibrillation in DM are unknown. The underlying mechanism of Atrogin-1-mediated SK2 degradation and associated signaling pathways are unclear. The aim of this study was to elucidate the relationship among reactive oxygen species (ROS), the NF-κB signaling pathway, and Atrogin-1 protein expression in the atrial myocardia of DM mice. We found that SK2 expression was downregulated comitant with increased ROS generation and enhanced NF-κB signaling activation in the atrial cardiomyocytes of DM mice. These observations were mimicked by exogenously applicating H2O2 and by high glucose culture conditions in HL-1 cells. Inhibition of ROS production by diphenyleneiodonium chloride or silencing of NF-κB by siRNA decreased the protein expression of NF-κB and Atrogin-1 and increased that of SK2 in HL-1 cells with high glucose culture. Moreover, chromatin immunoprecipitation assay demonstrated that NF-κB/p65 directly binds to the promoter of the FBXO32 gene (encoding Atrogin-1), regulating the FBXO32 transcription. Finally, we evaluated the therapeutic effects of curcumin, known as a NF-κB inhibitor, on Atrogin-1 and SK2 expression in DM mice and confirmed that oral administration of curcumin for 4 weeks significantly suppressed Atrogin-1 expression and protected SK2 expression against hyperglycemia. In summary, the results from this study indicated that the ROS/NF-κB signaling pathway participates in Atrogin-1-mediated SK2 regulation in the atria of streptozotocin-induced DM mice.

Plasma membrane SK2 channel activity regulates migration and chemosensitivity of high-grade serous ovarian cancer cells.

No data are currently available on the functional role of small conductance Ca2+-activated K+ channels (SKCa) in ovarian cancer. Here, we characterized the role of SK2 (KCa2.2) in ovarian cancer cell migration and chemosensitivity. Using the selective non-cell-permeant SK2 inhibitor Lei-Dab7, we identified functional SK2 channels at the plasma membrane, regulating store-operated Ca2+ entry (SOCE) in both cell lines tested (COV504 and OVCAR3). Silencing KCNN2 with short interfering RNA (siRNA), or blocking SK2 activity with Lei-Dab7, decreased cell migration. The more robust effect of KCNN2 knockdown compared to Lei-Dab7 treatment suggested the involvement of functional intracellular SK2 channels in both cell lines. In cells treated with lysophosphatidic acid (LPA), an ovarian cancer biomarker of progression, SK2 channels are a key player of LPA pro-migratory activity but their role in SOCE is abolished. Concerning chemotherapy, SK2 inhibition increased chemoresistance to Taxol® and low KCNN2 mRNA expression was associated with the worst prognosis for progression-free survival in patients with serous ovarian cancer. The dual roles of SK2 mean that SK2 activators could be used as an adjuvant chemotherapy to potentiate treatment efficacy and SK2 inhibitors could be administrated as monotherapy to limit cancer cell dissemination.

Novel SK channel positive modulators prevent ferroptosis and excitotoxicity in neuronal cells.

Small conductance calcium-activated potassium (SK) channel activity has been proposed to play a role in the pathology of several neurological diseases. Besides regulating plasma membrane excitability, SK channel activation provides neuroprotection against ferroptotic cell death by reducing mitochondrial Ca2+ uptake and reactive oxygen species (ROS). In this study, we employed a multifaceted approach, integrating structure-based and computational techniques, to strategically design and synthesize an innovative class of potent small-molecule SK2 channel modifiers through highly efficient multicomponent reactions (MCRs). The compounds' neuroprotective activity was compared with the well-studied SK positive modulator, CyPPA. Pharmacological SK channel activation by selected compounds confers neuroprotection against ferroptosis at low nanomolar ranges compared to CyPPA, that mediates protection at micromolar concentrations, as shown by an MTT assay, real-time cell impedance measurements and propidium iodide staining (PI). These novel compounds suppress increased mitochondrial ROS and Ca2+ level induced by ferroptosis inducer RSL3. Moreover, axonal degeneration was rescued by these novel SK channel activators in primary mouse neurons and they attenuated glutamate-induced neuronal excitability, as shown via microelectrode array. Meanwhile, functional afterhyperpolarization of the novel SK2 channel modulators was validated by electrophysiological measurements showing more current change induced by the novel modulators than the reference compound, CyPPA. These data support the notion that SK2 channel activation can represent a therapeutic target for brain diseases in which ferroptosis and excitotoxicity contribute to the pathology.

Flooding Tolerance of Rice: Regulatory Pathways and Adaptive Mechanisms.

Rice is a major food crop for more than half of the world's population, while its production is seriously threatened by flooding, a common environmental stress worldwide. Flooding leads to oxygen deficiency, which is a major problem for submerged plants. Over the past three decades, significant progress has been made in understanding rice adaptation and molecular regulatory mechanisms in response to flooding. At the seed germination and seedling establishment stages, the CIPK15-SnRK1A-MYBS1 signaling cascade plays a central role in determining rice submergence tolerance. However, from seedlings to mature plants for harvesting, SUB1A- and SK1/SK2-regulated pathways represent two principal and opposite regulatory mechanisms in rice. In addition, phytohormones, especially gibberellins, induce adaptive responses to flooding throughout the rice growth period. This review summarizes the significant adaptive traits observed in flooded rice varieties and updates the molecular genetics and mechanisms of submergence tolerance in rice.

Involvement of ERK1/2 and JNK Pathways in 17beta-estradiol Induced Kir6.2 and SK2 Upregulation in Rat Osteoblast-like Cells

The functional expression of potassium (K+) channels has electrophysiologically been studied in bone cells from several species, however, their identity and regulation of gene expressions in bone cells are not well known. In the present study, to investigate how K+ channel expressions are regulated by estrogen, we measured changes of transcript levels of various Ca2+-activated (K(Ca)) and ATP-sensitive K+ channels in rat osteoblastic ROS 17/2.8 cells after treatment with estrogen. Application of 17beta-estradiol (E2) for 24 h and 48 h increased mRNA and protein expressions of inwardly rectifying K+ channel (Kir) 6.2 and type 2 small conductance K(Ca) channel (SK2), respectively. Combined treatment of cells with 17beta-E2 and ICI 182,780, a pure antiestrogen, suppressed 17beta-E2-induced alterations of SK2 and Kir6.2 mRNA levels. In addition, treatment of cells with U0126, a specific inhibitor of extracellular receptor kinases (ERK)1/2, and SP600125, a specific inhibitor of c-jun N-terminal kinase (JNK) blocked the enhancing effects of 17beta-E2 on SK2 and Kir6.2 protein expressions. On the other hand, blocking of p38 mitogen-activated protein kinase had no effect. Taken together, these results indicate that 17beta-E2 modulates SK2 and Kir6.2 expressions through the estrogen receptor, involving ERK1/2 and JNK activations.