Siah2-GRP78 interaction regulates ROS and provides a proliferative advantage to Helicobacter pylori-infected gastric epithelial cancer cells.

Helicobacter pylori-mediated gastric carcinogenesis involves upregulation of the E3 ubiquitin ligase Siah2 and its phosphorylation-mediated stabilization. This study elucidates a novel mechanism of oxidative stress regulation by phosphorylated Siah2 in H. pylori-infected gastric epithelial cancer cells (GECs). We identify that H. pylori-mediated Siah2 phosphorylation at the 6th serine residue (P-S6-Siah2) enhances proteasomal degradation of the 78-kDa glucose-regulated protein (GRP78) possessing antioxidant functions. S6 phosphorylation stabilizes Siah2 and P-S6-Siah2 potentiates H. pylori-mediated reactive oxygen species (ROS) generation. However, infected S6A phospho-null Siah2-expressing cells have decreased cellular GRP78 level as surprisingly these cells release GRP78 to a higher extent and accumulate significantly higher ROS than the wild type (WT) Siah2 construct-expressing cells. Ectopic expression of GRP78 prevents the loss of mitochondrial membrane potential and cellular ROS accumulation caused by H. pylori. H. pylori-induced mitochondrial damage and mitochondrial membrane potential loss are potentiated in Siah2-overexpressing cells but these effects are further enhanced in S6A-expressing cells. This study also confirms that while phosphorylation-mediated Siah2 stabilization optimally upregulates aggresome accumulation, it suppresses autophagosome formation, thus decreasing the dependency on the latter mechanism in regulating cellular protein abundance. Disruption of the phospho-Siah2-mediated aggresome formation impairs proliferation of infected GECs. Thus, Siah2 phosphorylation has diagnostic and therapeutic significance in H. pylori-mediated gastric cancer (GC).

Imaging dendritic spines: molecular organization and signaling for plasticity.

The structural plasticity of dendritic spines is considered to be essential for various forms of synaptic plasticity and, ultimately, learning and memory. The process is mediated by signaling pathways that promote the reorganization of the actin cytoskeleton and subsynaptic structures, which in turn cause structural and functional changes in dendritic spines. Recent advances in optical technologies have started to reveal the fine molecular structures and dynamic signaling occurring inside spines, providing significant insights into the molecular regulation of spines. Here, we highlight recent studies to resolve the molecular mechanisms underlying the spine actin cytoskeleton and plasticity with high spatiotemporal resolution. Moreover, we discuss new genome editing-based approaches in imaging the molecular structure and plasticity of dendritic spines.