CLIP2: a novel functional player in AQP5 trafficking dynamics and implications for Sjögren's disease.

BACKGROUND: Sjögren's disease (SjD) is an autoimmune condition affecting exocrine glands, resulting in decreased saliva and tear production. Aquaporin 5 (AQP5) is a transmembrane water channel playing a central role in water transport. In SjD, deregulation of AQP5 expression, trafficking and interactions with various proteins contribute to the underlying disease mechanisms. METHODS: Co-immunoprecipitation followed by mass spectrometry, proximity ligation assay, microscale thermophoresis and in-silico modelling were carried out to investigate protein-protein interaction. CRISPR/Cas9-mediated knockout was performed in a salivary gland cell line stably transfected with AQP5. Protein colocalization and AQP5 trafficking were studied by immunofluorescence. Autoantibodies were quantified by ELISA. RESULTS: We identified CAP-Gly Domain Containing Linker Protein 2 (CLIP2) as a novel AQP5-interacting partner. Structural modeling of the AQP5-CLIP2 interaction revealed that the interaction is similar to other CAP-Gly domain complexes. Functional investigations indicated CLIP2 significantly influences AQP5 trafficking to the plasma membrane. Furthermore, interactions of CLIP2 with other AQP5 partners reveal the possible formation of multiprotein complexes in salivary glands. In SjD patients, alterations in these complexes and the presence of autoantibodies against AQP5, CLIP2, and other AQP5-interacting partners such as Ezrin and prolactin-inducible protein (PIP) may also contribute to disease pathogenesis. CONCLUSION: Our study identifies CLIP2 as a novel player in the AQP5 interactome and sheds light on its crucial role in AQP5 trafficking. In SjD, the alterations in AQP5-CLIP2 interactions and the presence of autoantibodies against both proteins highlighted their potential as targets for future therapeutic interventions in SjD.