Interaction between krit1 and malcavernin: Implications for the pathogenesis of cerebral cavernous malformations

OBJECTIVE: Cerebral cavernous malformations (CCM) are a relatively common autosomal dominant disorder leading to the formation of vascular malformations in the nervous system. Mutations in krit1 and malcavernin, the proteins encoded by the genes at the CCM1 and CCM2 loci, respectively, are responsible for the majority of CCMs. Similar to integrin cytoplasmic domain-associated protein-1α, a known krit1 interactor, malcavernin is a phosphotyrosine binding protein. We report here that krit1 also interacts with malcavernin. METHODS: We used two-hybrid analysis, in vivo coimmunoprecipitation, and epitope mapping to explore the interaction between krit1 and malcavernin. Immunocytochemistry was used to study the cellular localization of these proteins. RESULTS: We demonstrate that malcavernin independently binds to two of the three NPXY (asparagine, proline, undetermined/variable amino acid, and tyrosine) motifs in krit1. By immunocytochemistry, malcavernin protein is cytoplasmic at steady state, but shuttles between the nucleus and cytoplasm, despite lacking either a nuclear localization signal or a nuclear export signal in its sequence. CONCLUSION: These data suggest that krit1 interacts with malcavernin through its NPXY motifs and may shuttle it through the nucleus via its nuclear localization signal and nuclear export signals, thereby regulating its cellular function.