Krit1 meets partners in distinct subcellular compartments through its “FERM” domain

The Krit1 gene has been associated with Cerebral Cavernous Malformation (CCM), an autosomal dominant disease affecting cerebral microvasculature. This gene encodes for a protein of 736 aa containing an NPXY motif, which mediates the interaction with ICAP1α (Integrin Cytoplasmic domain Associated Protein 1α), three ankyrin repeats, involved in protein-protein interactions, and a FERM domain, which is typical of proteins involved in the connection between the cytoskeleton and the plasma membrane. Although the presence of these domains suggests that KRIT1 may behave as a scaffold protein and play a role in integrin signalling, the biological functions of this protein are poorly understood so far. By fluorescence microscopy analysis, we found that KRIT1 can localize both in the nucleus, in the cytosol and at the plasma membrane. Moreover, using several deletion mutants, we identified the regions of the protein that are important for its subcellular localization: in particular, we found that the FERM domain is important for the nuclear localization, as mutant forms of KRIT1 lacking distinct portions of the FERM domain are excluded from the nucleus. In the attempt to better understand KRIT1 functions, we performed a search for new molecular interactors using an yeast two hybrid approach. By screening a murine embryonic cDNA library using the C-terminus region of KRIT1, containing the FERM domain, as a bait, we identified KRIT1 interactors that localize either in the nucleus, in the cytoplasm or at the plasma membrane. The characterization of the functional significance of these molecular interactions is underway and should help elucidating the biological functions of KRIT1 as well as the molecular mechanisms of CCM pathogenesis.