Cdc42 and RhoA reveal different spatio-temporal dynamics upon local stimulation with Semaphorin-3A

Lung cancer cell-intrinsic IL-15 promotes cell migration and sensitizes murine lung tumors to anti-PD-L1 therapy

BACKGROUND

IL-15 plays a vital role in enhancing NK cell- and T-cell-mediated antitumor immune responses; however, the direct effect of IL-15 on tumor cells has not been fully elucidated. Herein, we investigated the effect of IL-15 on lung adenocarcinoma cells.

METHODS

Silencing and overexpression techniques were used to modify endogenous IL-15 expression in tumor cells. Transwell assays were used to assess tumor cell migration and invasion; a live-cell analysis system was used to evaluate cell motility; cellular morphological changes were quantified by confocal fluorescence microscopy; the molecular mechanisms underlying the effect of IL-15 on tumor cells were analyzed by western blotting; and RhoA and Cdc42 activities were evaluated by a pulldown assay. NCG and C57BL/6 mouse models were used to evaluate the functions of IL-15 in vivo.

RESULTS

Cancer cell-intrinsic IL-15 promoted cell motility and migration in vitro and metastasis in vivo via activation of the AKT-mTORC1 pathway; however, exogenous IL-15 inhibited cell motility and migration via suppression of the RhoA-MLC2 axis. Mechanistic analysis revealed that both the intracellular and extracellular IL-15-mediated effects required the expression of IL-15Rα by tumor cells. Detailed analyses revealed that the IL-2/IL-15Rβ and IL-2Rγ chains were undetected in the complex formed by intracellular IL-15 and IL-15Rα. However, when exogenous IL-15 engaged tumor cells, a complex containing the IL-15Rα, IL-2/IL-15Rβ, and IL-2Rγ chains was formed, indicating that the differential actions of intracellular and extracellular IL-15 on tumor cells might be caused by their distinctive modes of IL-15 receptor engagement. Using a Lewis lung carcinoma (LLC) metastasis model, we showed that although IL-15 overexpression facilitated the lung metastasis of LLC cells, IL-15-overexpressing LLC tumors were more sensitive to anti-PD-L1 therapy than were IL-15-wild-type LLC tumors via an enhanced antitumor immune response, as evidenced by their increased CD8+ T-cell infiltration compared to that of their counterparts.

CONCLUSIONS

Cancer cell-intrinsic IL-15 and exogenous IL-15 differentially regulate cell motility and migration. Thus, cancer cell-intrinsic IL-15 acts as a double-edged sword in tumor progression. Additionally, high levels of IL-15 expressed by tumor cells might improve the responsiveness of tumors to immunotherapies.

Using Biosensors to Study Organoids, Spheroids and Organs-on-a-Chip: A Mechanobiology Perspective

The increasing popularity of 3D cell culture models is being driven by the demand for more in vivo-like conditions with which to study the biochemistry and biomechanics of numerous biological processes in health and disease. Spheroids and organoids are 3D culture platforms that self-assemble and regenerate from stem cells, tissue progenitor cells or cell lines, and that show great potential for studying tissue development and regeneration. Organ-on-a-chip approaches can be used to achieve spatiotemporal control over the biochemical and biomechanical signals that promote tissue growth and differentiation. These 3D model systems can be engineered to serve as disease models and used for drug screens. While culture methods have been developed to support these 3D structures, challenges remain to completely recapitulate the cell-cell and cell-matrix biomechanical interactions occurring in vivo. Understanding how forces influence the functions of cells in these 3D systems will require precise tools to measure such forces, as well as a better understanding of the mechanobiology of cell-cell and cell-matrix interactions. Biosensors will prove powerful for measuring forces in both of these contexts, thereby leading to a better understanding of how mechanical forces influence biological systems at the cellular and tissue levels. Here, we discussed how biosensors and mechanobiological research can be coupled to develop accurate, physiologically relevant 3D tissue models to study tissue development, function, malfunction in disease, and avenues for disease intervention.

Neuronal actin cytoskeleton gain of function in the human brain

BACKGROUND

While advancements in imaging techniques have led to major strides in deciphering the human brain, successful interventions are elusive and represent some of the most persistent translational gaps in medicine. Human restricted CHRFAM7A has been associated with neuropsychiatric disorders.

METHODS

The physiological role of CHRFAM7A in human brain is explored using multiomics approach on 600 post mortem human brain tissue samples. The emerging pathways and mechanistic hypotheses are tested and validated in an isogenic hiPSC model of CHRFAM7A knock-in medial ganglionic eminence progenitors and neurons.

FINDINGS

CHRFAM7A is identified as a modulator of intracellular calcium dynamics and an upstream regulator of Rac1. Rac1 activation re-designs the actin cytoskeleton leading to dynamic actin driven remodeling of membrane protrusion and a switch from filopodia to lamellipodia. The reinforced cytoskeleton leads to an advantage to tolerate stiffer mechanical properties of the extracellular environment.

INTERPRETATION

CHRFAM7A modifies the actin cytoskeleton to a more dynamic and stiffness resistant state in an α7nAChR dependent manner. CHRFAM7A may facilitate neuronal adaptation to changes in the brain environment in physiological and pathological conditions contributing to risk or recovery. Understanding how CHRFAM7A affects human brain requires human studies in the areas of memory formation and erasure, cognitive reserve, and neuronal plasticity.

FUNDING

This work is supported in part by the Community Foundation for Greater Buffalo (Kinga Szigeti). Also, in part by the International Society for Neurochemistry (ISN) and The Company of Biologists (Nicolas Rosas). ROSMAP is supported by NIA grants P30AG10161, P30AG72975, R01AG15819, R01AG17917. U01AG46152, and U01AG61356.

Manipulating oligodendrocyte intrinsic regeneration mechanism to promote remyelination

In demyelinated lesions, astrocytes, activated microglia and infiltrating macrophages secrete several factors regulating oligodendrocyte precursor cells' behaviour. What appears to be the initiation of an intrinsic mechanism of myelin repair is only leading to partial recovery and inefficient remyelination, a process worsening over the course of the disease. This failure is largely due to the concomitant accumulation of inhibitory cues in and around the lesion sites opposing to growth promoting factors. Here starts a complex game of interactions between the signalling pathways controlling oligodendrocytes migration or differentiation. Receptors of positive or negative cues are modulating Ras, PI3K or RhoGTPases pathways acting on oligodendrocyte cytoskeleton remodelling. From the description of this intricate signalling network, this review addresses the extent to which the modulation of the global response to inhibitory cues may pave the route towards novel therapeutic approaches for myelin repair.

miR-30b Promotes spinal cord sensory function recovery via the Sema3A/NRP-1/PlexinA1/RhoA/ROCK Pathway

Spinal cord injury (SCI) induces both motor and sensory dysfunctions. We wondered whether miR-30b could promote primary sensory neuron (PSN) axon growth in inhibitory microenvironment. The neurite growth was promoted by miR-30b agomir and inhibited by antagomir. MiR-30b targeted and degraded sema3A mRNA. MiR-30b regulated the formation of sema3A-NRP-1-PlexinA1 complex via targeting sema3A. The neurite length was induced by the miR-30b agomir, and the application of sema3A protein could reverse the effect of agomir. GTP-RhoA and ROCK expression were down-regulated by miR-30b. Neurite outgrowth that inhibited by sema3A and the miR-30b antagomir was increased by Y-27632. Agomir promoted neurite growth in NogoA inhibitory conditions, which indicated miR-30b could both enhance neuronal intrinsic regenerative ability and promote neurite growth against inhibitory microenvironment via Sema3A/NRP-1/PlexinA1/RhoA/ROCK axis. The agomir could also regulate Sema3A/NRP-1/PlexinA1/RhoA/ROCK axis in vivo and restore spinal cord sensory conductive function. In conclusion, miR-30b could be a novel target for sensation recovery after SCI.

Actin dynamics in cell migration

Cell migration is an essential process, both in unicellular organisms such as amoeba and as individual or collective motility in highly developed multicellular organisms like mammals. It is controlled by a variety of activities combining protrusive and contractile forces, normally generated by actin filaments. Here, we summarize actin filament assembly and turnover processes, and how respective biochemical activities translate into different protrusion types engaged in migration. These actin-based plasma membrane protrusions include actin-related protein 2/3 complex-dependent structures such as lamellipodia and membrane ruffles, filopodia as well as plasma membrane blebs. We also address observed antagonisms between these protrusion types, and propose a model - also inspired by previous literature - in which a complex balance between specific Rho GTPase signaling pathways dictates the protrusion mechanism employed by cells. Furthermore, we revisit published work regarding the fascinating antagonism between Rac and Rho GTPases, and how this intricate signaling network can define cell behavior and modes of migration. Finally, we discuss how the assembly of actin filament networks can feed back onto their regulators, as exemplified for the lamellipodial factor WAVE regulatory complex, tightly controlling accumulation of this complex at specific subcellular locations as well as its turnover.

In vivo topology converts competition for cell-matrix adhesion into directional migration

When migrating in vivo, cells are exposed to numerous conflicting signals: chemokines, repellents, extracellular matrix, growth factors. The roles of several of these molecules have been studied individually in vitro or in vivo, but we have yet to understand how cells integrate them. To start addressing this question, we used the cephalic neural crest as a model system and looked at the roles of its best examples of positive and negative signals: stromal-cell derived factor 1 (Sdf1/Cxcl12) and class3-Semaphorins. Here we show that Sdf1 and Sema3A antagonistically control cell-matrix adhesion via opposite effects on Rac1 activity at the single cell level. Directional migration at the population level emerges as a result of global Semaphorin-dependent confinement and broad activation of adhesion by Sdf1 in the context of a biased Fibronectin distribution. These results indicate that uneven in vivo topology renders the need for precise distribution of secreted signals mostly dispensable.

Migrating cells encounter multiple signals such as extracellular matrix (ECM) and chemokinetic factors but how these integrate in vivo is unclear. Here, the authors report that overall control of cell-ECM adhesion by Sema3A and Sdf1 can be converted into directional migration by a biased ECM network.

Combining FRET and optical tweezers to study RhoGTPases spatio-temporal dynamics upon local stimulation

Local stimulation with optical tweezers has been used to mimic natural stimuli that occur in biological processes such as cell migration or differentiation. Carriers (beads and lipid vesicles) with sizes down to 30 nm can be manipulated with a high spatial and temporal resolution: they are positioned with a sub-micrometric precision on a specific cell compartment and the beginning of the stimulation can be triggered with millisecond precision. RhoGTPases are a Ras-related family of proteins that regulate many different functions including cell polarity, microtubule dynamics and membrane transport pathways. Here we combine local stimulation with FRET microscopy to study RhoGTPases spatial and temporal activation following guidance cue local stimulation. We used two different vectors for local delivery: silica micro-beads and micro-sized lipid vesicles. The experimental methods associated with neuronal growth cone local stimulation are discussed in detail, as well as the analysis methods. Here we present a protocol that enables to study neuronal growth cone cytoskeleton rearrangements in response to a gradient of molecules in a way that better mimics physiological conditions, and it can be similarly applied to each secreted molecule involved in cell signaling.