Feedback Interplay between Phosphoinositides, Rho GTPase and Actin governing cell polarity
We are exploring the interplay between the Rho GTPase regulatory system, the actin cytoskeleton and PI3 kinase in the control of cell polarity. In family-wide screens we have identified novel RhoGEF/RhoGAP proteins that relocalise from the plasma mebrane upon PIP3 phosphoinositide generation or PIP2 phosphoinositide depletion. The systems-level view thereby revealed a yet undescribed positive feedback mechanisms that enables self-sustained exploratory leading-edge polarization. We use optogenetic tools to manipulate the polarity modules PI3 kinase, Rho GTPase and actin to directly infer their signalling interplay that are otherwise masked when inputs are provided at the level of upstream receptors. Furthermore, we use our knowledge to engineer synthetic proteins to rewire a self-organised polarity system and thereby to systematically analyse parameters that control cell front polarisation. This research will elucidate core mechanism for cell polarisation and steering during migration.
Collective control of protrusion-retraction dynamics by focal adhesion-associated Rho GTPase regulators
We investigate the role of focal adhesions as spatially organising platforms that shape Rho signalling patterns (Müller et al NCB 2020). Our aim is to spatiotemporally deconvolute the reciprocal regulation of Rac1/RhoA during FA maturation in order to define functional modules within the FA-associated protein networks. This way, we will dissect individual roles of candidate Rho regulators in the collective control of cell protrusion/retraction cycles and define their potential pathophysiological implications. This work will advance our understanding of cell migration and its interdependency with adhesion and mechanical force.
Single molecule analysis of Rho GTPase membrane dynamics and signalling zone nano-organisation
We analyse at the single molecule level the membrane association kinetics and diffusion behaviour of Rho GTPases. A proof of principle study demonstrates the dynamic nature of these processes. Ongoing work will show how in Rho activity zones the GTPases adopt different diffusional states due to interactions with effector proteins and regulators and reveal new mechanistic insights into the membrane sequestration and release of Rho proteins by RhoGDIs. This work will contribute to a deeper understanding of how Rho GTPases cycle through signalling zones and sample cellular membranes by diffusional exploration.
Endolysosomal targeting of PKA by ARHGAP36
We are continuing to characterise individual RhoGEFs and RhoGAPs with novel clinical implications. Focus is on ARHGAP36 and the question by which mechanism and by which protein machinery it targets PKA into the endolysosomal pathway to mediate tissue-specific control of PKA signalling (Eccles et al Nat Commun 2016).