Suicidal chemotaxis in bacteria

Bacteria commonly live in communities on surfaces where steep gradients of antibiotics and other chemical compounds routinely occur. While many species of bacteria can move on surfaces, we know surprisingly little about how such antibiotic gradients affect cell motility. Here we study the behaviour of the opportunistic pathogen Pseudomonas aeruginosa in stable spatial gradients of a range of antibiotics by tracking thousands of cells in microfluidic devices as they form biofilms. Unexpectedly, these experiments reveal that individual bacteria use pili-based ('twitching') motility to actively navigate towards regions with higher antibiotic concentrations. Our analyses suggest that this biased migration is driven, at least in part, by a direct response to the antibiotics. Migrating cells can reach antibiotic concentrations hundreds of times higher than their minimum inhibitory concentration in a few hours and remain highly motile. However, isolating these cells - using fluid-walled microfluidic devices that can be reconfigured in situ - suggests that these bacteria are terminal and not able to reproduce. In spite of moving towards their death, we show that migrating cells are capable of entering a suicidal program to release bacteriocins that are used to kill other bacteria. Our work suggests that bacteria respond to antibiotics as if they come from a competing colony growing in the neighbourhood, inducing them to invade and attack. As a result, clinical antibiotics have the potential to serve as a bait that lures bacteria to their death.

Leaving the damage behind

A mechanism by which migrating cells shed defective mitochondria is identified.

Multiple roles of syndecan-4 during myoblast migration

Background and purpose: Cell migration is one of the cornerstones of regeneration processes, as it is necessary for wound healing, and also required for embryonic development, immune system activation, or tumor metastasis formation. Skeletal muscle has a special, advanced dynamism that allows it to adapt to various impacts and recover successfully after an injury, exercise, or muscle disease. Satellite stem cells are activated by local damage during muscle regeneration, and after asymmetric division, myoblasts (i.e., activated satellite cells) migrate to the site of injury, differentiate, and fuse to form muscle fibers. Migration of the cells requires cellular polarization, the creation of leading and trailing edges, as well as the proper orientation and positioning of organelles inside the cell. Efficient migration also requires the presence of an asymmetrical front-to-rear calcium (Ca2+) gradient to regulate focal adhesion assembly and actomyosin contractility. The transmembrane proteoglycan syndecan-4 (SDC4), which is one of the cell surface markers of resting and activated satellite stem cells, is involved in the formation of focal adhesions. Furthermore, SDC4 plays a variety of roles in signal transduction processes, including controlling the function of the small GTPase Rac1 by binding to and inhibiting the activity of T-lymphoma invasion and metastasis-1 (Tiam1), a guanine nucleotide exchange factor for Rac1 (Ras-related C3 botulinum toxin substrate 1) GTPase. Cell migration also requires Rac1-mediated actin remodeling. SDC4 knockout mice are unable to regenerate damaged muscle; however, its underlying precise mechanism is unclear; therefore, our aim was to analyze the role of SDC4 in myoblast migration. Experimental approaches: To achieve SDC4 knockdown, C2C12 murine myoblast cells were transfected stably with plasmids expressing short hairpin RNAs (shRNAs) specific for mouse SDC4 (shSDC4#1 and shSDC4#2) or a scrambled target sequence. To study cell migration, time-lapse images were captured at 37 °C and 5% CO2 using a high-content imaging system for single-cell tracking or wound scratch assay was performed. To evaluate the movement of the single cells, the cell nuclei were tracked with ImageJ and CellTracker software. Super-resolution direct stochastic optical reconstruction microscopy (dSTORM) measurements were performed for the nanoscale analysis of the lamellipodial actin network of the migrating cells. To study the intracellular Ca2+ level, Fluo-4 and Fura Red indicators were applied. Immunofluorescence cytochemistry was performed to analyze the distribution of SDC4, Tiam1, centrosomes, FAK (focal adhesion kinase) or GM130 (anti- Golgi matrix protein of 130 kDa) followed by wide-field fluorescence or confocal microscopy. Image analysis was performed with ImageJ. Rac1 was inhibited by NSC23766 treatment during the measurements (50 µM). Key results: Silencing of SDC4 disrupts the correct polarization of migrating mammalian myoblasts. SDC4 knockdown completely abolished the intracellular Ca2+ gradient, abrogated centrosome reorientation, and thus decreased cell motility, demonstrating the role of SDC4 in cell polarity. Additionally, SDC4 exhibited a polarized distribution during migration. SDC4 knockdown cells exhibited decreases in the total movement distance during migration, maximum and vectorial distances from the starting point, as well as average and maximum cell speeds. Analysis of the dSTORM images of SDC4 knockdown cells revealed nanoscale changes in the actin cytoskeletal architecture, such as decreases in the numbers of branches and individual branch lengths in the lamellipodia of the migrating cells. The Rac1 inhibitor NSC23766 did not restore the migration capacity of SDC4 silenced cells; in fact, it reduced it further. SDC4 knockdown decreased the directional persistence of migration, abrogated the polarized, asymmetric distribution of Tiam1, and reduced the total Tiam1 level of the cells. Conclusion: According to our results, SDC4 affects the migration of C2C12 myoblasts and modulates cell polarity by influencing centrosome positioning, intracellular Ca2+ and Tiam1 distribution. These findings may promote greater understanding the essential role of SDC4 in the embryonic development and postnatal regeneration of skeletal muscle. Given the ubiquitous expression and crucial role of SDC4 in cell migration, we conclude that our findings can facilitate understanding the general role of SDC4 during cell migration.

Store Operated Calcium Entry in Cell Migration and Cancer Metastasis

Ca2+ signaling is ubiquitous in eukaryotic cells and modulates many cellular events including cell migration. Directional cell migration requires the polarization of both signaling and structural elements. This polarization is reflected in various Ca2+ signaling pathways that impinge on cell movement. In particular, store-operated Ca2+ entry (SOCE) plays important roles in regulating cell movement at both the front and rear of migrating cells. SOCE represents a predominant Ca2+ influx pathway in non-excitable cells, which are the primary migrating cells in multicellular organisms. In this review, we summarize the role of Ca2+ signaling in cell migration with a focus on SOCE and its diverse functions in migrating cells and cancer metastasis. SOCE has been implicated in regulating focal adhesion turnover in a polarized fashion and the mechanisms involved are beginning to be elucidated. However, SOCE is also involved is other aspects of cell migration with a less well-defined mechanistic understanding. Therefore, much remains to be learned regarding the role and regulation of SOCE in migrating cells.

Mechanistic of Rac and Cdc42 synchronization at the cell edge by ARHGAP39-dependent signaling nodules and the impact on protrusion dynamics

Compartmentalization of GTPase regulators into signaling nodules dictates the GTPase pathways selected. Rac and Cdc42 are synchronized at the cell edge for effective protrusion in motile cells but how their activity is coordinated remains elusive. Here, we discovered that ARHGAP39, a Rac and Cdc42 GTPase-activating protein, sequentially interacts with WAVE and mDia2 to control Rac/lamellipodia and Cdc42/filopodia protrusions, respectively. Mechanistically, ARHGAP39 binds to WAVE and, upon phosphorylation by Src kinase, inactivates Rac to promote Cdc42-induced filopodia formation. With our optimized FRET biosensor, we detected active Cdc42 at the filopodia tips that controls filopodia extension. ARHGAP39 is transported to filopodia tips by Myosin-X where it binds mDia2 and inactivates Cdc42 leading to filopodia retraction. Failure in lamellipodia to filopodia switch by defective ARHGAP39 impairs cell invasion and metastasis. Our study reveals that compartmentalization of ARHGAP39 within Rac/Cdc42 signaling nodules orchestrates the synchronization of lamellipodia/filopodia crosstalk and highlights the intricate regulation of leading edge dynamics in migrating cells.

Toosendanin Affects the Occurrence and Development of Prostate Carcinoma Cells DU145 by Regulating Forkhead Box C2-Antisense RNA 1

Prostate carcinoma is a common malignant tumor of the male genitourinary system. Toosendanin can inhibit the biological behavior of a variety of malignant tumor cells (such as ovarian carcinoma, lung carcinoma, and breast carcinoma, etc.), but its effect on the malignant behavior of prostate carcinoma cells and its mechanism are not yet understood. Therefore, this article discusses the influence of toosendanin on the multiplication, apoptosis, migration, and invasion of prostate carcinoma cells and its possible mechanism. Different doses (0.125, 0.25, 0.5 ^M) of toosendanin can reduce the cell viability, number of colonies, number of migrating cells, number of invasive cells, and Bcl-2 protein and FOXC2-AS1 levels of prostate carcinoma cells, as well as increase the apoptosis rate and Bax protein level. Overexpression of FOXC2-AS1 can increase the cell viability, number of colonies formed, number of migrating cells, number of invasive cells, and Bcl-2 protein expression, as well as reduce the rate of apoptosis and Bax protein level after toosendanin treatment of prostate carcinoma cells. It was demonstrated that toosendanin may inhibit the multiplication, migration, and invasion of prostate carcinoma cells and promote its apoptosis by down-regulating FOXC2-AS1 expression.