Magnetic control of cellular signalling

Cellular functions like migration or division rely on the orchestration of different signaling networks both in time and in the intracellular space. While many tools have been developed over the years to observe these activities within the cell, only a few are able to create local and controlled biochemical activities inside cells. We have designed such a technique, based on magnetic nanoparticles, allowing the activation of signaling networks at the subcellular scale with an unprecedented spatiotemporal resolution. We have shown that local activation of a protein called Rac1 leads to major cytoskeletal rearrangements and changes in the cellular morphology.

HFSP Program Grant holders Maxime Dahan, Yohanns Bellaiche and Jacob Piehler and colleagues
authored on Thu, 25 April 2013

Many cell functions like migration or division rely on the coordinated activity of signalling networks at a subcellular scale. For example, during migration some proteins pushing the cell forward are activated only at the front of the cell within areas in the order of only a few micrometers squared, while the activity of proteins retracting the cell is restricted to the rear. Although the molecular players involved in these processes are known, how their activities are orchestrated in space and time within the cell is still under debate. There is therefore a great need for methods enabling the local perturbations of protein activities within the cell, a task that cannot be achieved by conventional genetic or pharmacological approaches.

We took advantage of recent developments in the field of nanotechnology by using small magnetic nanoparticles (500 nm in diameter), and decorating their surfaces with active signaling proteins. Once inserted inside the cells, the nanoparticles behaved as local signaling platforms, binding partner proteins at their surfaces and locally stimulating intracellular signaling networks. We first used nanoparticles decorated with a protein responsible for polymerization of the actin skeleton at the leading edge of migrating cells: the Rho GTPase cdc42. Since the nanoparticle location was easily imaged, we were able to measure the binding kinetics of a direct effector of cdc42 at the particle's surface (N-WASP) and monitored the formation of thick actin shells around the cdc42 particles, demonstrating that cdc42 is sufficient In Vivo to polymerize the actin cytoskeleton.


 

The next step was to design a magnetic tweezer able to create high forces on the nanoparticles and to displace them into different cellular compartments. With this tool, nanoparticles could be translocated to different locations of the cell within minutes. Using nanoparticles decorated with an activator of Rac1, another Rho-GTPase, we investigated how a local activation of Rac1 mediated by the nanoparticles was processed by the cell as a function of the subcellular location. We demonstrated that these nanoparticles were actively activating Rac1 in their vicinity and found that a local nanoparticle-mediated Rac1 signal was rapidly transduced to actin polymerization only in the protrusive areas of the cell, while no nanoparticle-induced actin polymerization was observed in the other areas of the cell. This result suggests a cooperative action of Rac1 with another partner to polymerize actin in these regions of high membrane activity. Finally, we demonstrated that a local accumulation of nanoparticles activating Rac1 was sufficient to alter the local cellular morphology and to turn a quiescent cellular area into a protrusive region.

Although we applied this new technique to a specific set of proteins known to be major organizers of the cytoskeletons, we emphasize that our new method is quite general and could be applied to any protein whose activity is restricted to subcellular locations. An interesting perspective would be to combine this technique with advanced microfabrication techniques and apply this assay to multiple cells in parallel. Overall, it should enhance our understanding of how local biochemical information is spatially modulated, processed and integrated at the cell scale.

Text by Fred Etoc

Reference

Subcellular control of Rac-GTPase signalling by magnetogenetic manipulation inside living cells. Etoc F, Lisse D, Bellaiche Y, Piehler J, Coppey M, Dahan M. Nat Nanotechnol. 2013 March 8 (3):193-8. doi: 10.1038/nnano.2013.23.

Pubmed link

News and Views (Nature Nanotechnology)