SH2B1 increases the numbers of IRSp53-induced filopodia

SH2B1 promotes epithelial-mesenchymal transition through the IRS1/β-catenin signaling axis in lung adenocarcinoma

Lung adenocarcinoma (LADC), the most prevalent type of human lung cancer, is characterized by many molecular abnormalities. SH2B1, a member of the SH2‐domain containing family, have recently been shown to act as tumor activators in multiple cancers, including LADC. However, the mechanisms underlying SH2B1 overexpression are not completely understood. Here, we reported that SH2B1 expression levels were significantly upregulated and positively associated with EMT markers and poor patient survival in LADC specimens. Modulation of SH2B1 levels had distinct effects on cell proliferation, cell cycle, migration, invasion, and morphology in A549 and H1299 cells in vitro and in vivo. At the molecular level, overexpression of SH2B1 resulted in the upregulation of the EMT markers, especially induced β‐catenin accumulation and activated β‐catenin signaling to promote LADC cell proliferation and metastasis, while silencing SH2B1 had the opposite effect. Furthermore, ectopic expression of SH2B1 in H1299 cells increased IRS1 expression level. Reduced expression of IRS1 considerably inhibited H1299 cell proliferation, migration, and invasion which were driven by SH2B1 overexpression. Collectively, these results provide unequivocal evidence to establish that SH2B1‐IRS1‐β‐catenin axis is required for promoting EMT, and might prove to be a promising strategy for restraining tumor progression in LADC patients.

Super-resolution imaging for monitoring cytoskeleton dynamics

The cytoskeleton is a key cellular structure that is important in the control of cellular movement, structure, and sensing. To successfully image the individual cytoskeleton components, high resolution and super-resolution fluorescence imaging methods are needed. This review covers the three basic cytoskeletal elements and the relative benefits and drawbacks of fixed versus live cell imaging before moving on to recent studies using high resolution and super-resolution techniques. The techniques covered include the near-diffraction limited imaging methods of confocal microscopy and TIRF microscopy and the super-resolution fluorescence imaging methods of STORM, PALM, and STED.

SH2B1 orchestrates signaling events to filopodium formation during neurite outgrowth

Morphogenesis during development is fundamental to the differentiation of several cell types. As neurite outgrowth marks neuritogenesis, formation of filopodia precede the formation of dendrites and axons. While the structure of filopodia is well-known, the initiation of filopodia during neurite outgrowth is not clear. SH2B1 is known to promote neurite outgrowth of PC12 cells, hippocampal and cortical neurons. As a signaling adaptor protein, SH2B1 interacts with several neurotrophin receptors, and regulates signaling as well as gene expression. Our recent findings suggest that SH2B1 can be recruited to the plasma membrane and F-actin fractions by IRSp53. IRSp53 bends plasma membrane and facilitates actin bundling to set the stage for filopodium formation. We further demonstrate that SH2B1-IRSp53 complexes enhance the formation of filopodia, dendrites and dendritic branches of hippocampal and cortical neurons. While the molecular mechanism underlying filopodium initiation is not clear, we propose that SH2B1-neurotrophin interacting sites may mark the putative sites of filopodium initiation.

IRSp53/BAIAP2 in dendritic spine development, NMDA receptor regulation, and psychiatric disorders

IRSp53 (also known as BAIAP2) is a multi-domain scaffolding and adaptor protein that has been implicated in the regulation of membrane and actin dynamics at subcellular structures, including filopodia and lamellipodia. Accumulating evidence indicates that IRSp53 is an abundant component of the postsynaptic density at excitatory synapses and an important regulator of actin-rich dendritic spines. In addition, IRSp53 has been implicated in diverse psychiatric disorders, including autism spectrum disorders, schizophrenia, and attention deficit/hyperactivity disorder. Mice lacking IRSp53 display enhanced NMDA (N-methyl-d-aspartate) receptor function accompanied by social and cognitive deficits, which are reversed by pharmacological suppression of NMDA receptor function. These results suggest the hypothesis that defective actin/membrane modulation in IRSp53-deficient dendritic spines may lead to social and cognitive deficits through NMDA receptor dysfunction. This article is part of the Special Issue entitled 'Synaptopathy--from Biology to Therapy'.