CSPP-L Associates with the Desmosome of Polarized Epithelial Cells and Is Required for Normal Spheroid Formation.

Deleterious mutations of the Centrosome/Spindle Pole associated Protein 1 gene, CSPP1, are causative for Joubert-syndrome and Joubert-related developmental disorders. These disorders are defined by a characteristic mal-development of the brain, but frequently involve renal and hepatic cyst formation. CSPP-L, the large protein isoform of CSPP1 localizes to microtubule ends of the mitotic mid-spindle and the ciliary axoneme, and is required for ciliogenesis. We here report the microtubule independent but Desmoplakin dependent localization of CSPP-L to Desmosomes in apical-basal polarized epithelial cells. Importantly, siRNA conferred depletion of CSPP-L or Desmoplakin promoted multi-lumen spheroid formation in 3D-cultures of non-ciliated human colon carcinoma Caco-2 cells. Multi-lumen spheroids of CSPP1 siRNA transfectants showed disrupted apical cell junction localization of the cytoskeleton organizing RhoGEF ECT2. Our results hence identify a novel, non-ciliary role for CSPP-L in epithelial morphogenesis.