Pontus Aspenström's projects on GTPases
Rho GTPases in cancer cell migration
The RHO GTPases can be divided into two main categories: the classical RHO GTPases and the atypical RHO GTPases, and a major effort in the group has been to elucidate the functions of the proteins called fast-cycling atypical RHO GTPases.
These proteins have been linked to cancer and it is therefore of great importance to identify their kinetic properties in order to understand how this can influence cancer cell migration, invasion and metastasis. In our research projects we aim to:
- identify novel RHO-regulated pathways
- investigate how RHO GTPases coordinate cytoskeletal organisation and membrane dynamics during cell polarisation and cell migration.
The ultimate goal is to identify proteins and genes that can be targeted with drugs to reduce the increased potency for invasive growth and metastasis of cancer cells.
Cytoskeletal organisation and dynamics; a new diagnostic tool?
Malignant mesothelioma (MM) is a rare but highly aggressive cancer, primarily originating from the pleura and the peritoneum. The cytoskeleton is responsible for upholding normal tissue homeostasis by a tight regulation of cell morphogenesis and cell migration. This homeostasis is lost in cancer, mainly because alterations in cytoskeletal dynamics are leading to an increased migratory and invasive capacity of cancer cells.
The organization of the cytoskeleton is by large an unknown factor in MM, we therefore sought to examine the cytoskeletal dynamics and invasive properties of different MM cell lines originating from patients. We hypothesize that key regulators of cytoskeletal dynamics can serve as markers in the diagnostics of MM. Early diagnosis and new diagnostic tools are urgently needed to effectively treat patients with MM and we believe that our studies can provide such tools that can be further tested on patients.
We have completed a proof of concept study in which we have compared the cytoskeletal organization and migratory behaviour of eight different MM cell lines. We are currently using machine learning approach to increase the precision in our characterization. To this end, a large number of images of MM cell lines representing various stages of MM malignancy have been used to create algorithms that can be used in the image analysis. In the next phase, cells isolated from MM patients will be analysed by the machine learning algorithms and compared with patient material analysed by standard pathological examination.
The role of MIRO GTPases in neurological diseases
The maintenance of normal mitochondrial dynamics is an important factor in cellular homeostasis. Deregulated mitochondrial homeostasis often results in neuropathological conditions, such as Parkinson’s disease.
Mitochondrial transport through the cytoskeleton is done by specialized protein complexes of which Mitochondrial RHO GTPases (MIRO1 and MIRO2) are core components. MIRO’s general structure is characterized by an (N-terminus) GTPase domain, two calcium-sensing EF-hand domains in the middle, and another (C-terminus) GTPase domain and is located in the outer mitochondrial membrane. MIRO acts as a central agent in mitochondrial transport by binding to TRAK, which in turn interacts with Kinesin, forming a motor complex responsible mitochondrial movement. When Ca2+ interacts with the EF-hand domains it disassociates the motor complex from kinesin, and thus arrests mitochondrial transport.
Inactivation of mitochondrial proteins is an important step towards mitochondrial turnover. This is usually initiated by PINK1’s recruitment of PRKN, which ubiquitinates mitochondrial proteins that are then degraded. Ubiquitination of MIRO causes a dissociation of the mitochondria from its transport machinery and arrests mitochondrial. PRKN has been associated with some forms of Parkinson’s disease and is known to dock with MIRO. MIRO has also been shown to affect mitochondrial shape transition in response to Ca2+ stress, the latter of which is involved in pore opening and cell death.
We have recently identified a number of components that could function as modulators of the activity of PRKN. We are currently identifying the molecular mechanisms by which these factors contribute to mitochondrial homeostasis and dynamics in health and disease.