CEP128 Localizes to the Subdistal Appendages of the Mother Centriole and Regulates TGF-β/BMP Signaling at the Primary Cilium

Abstract

The centrosome is the main microtubule-organizing center in animal cells and comprises a mother and daughter centriole surrounded by pericentriolar material. During formation of primary cilia, the mother centriole transforms into a basal body that templates the ciliary axoneme. Ciliogenesis depends on mother centriole-specific distal appendages, whereas the role of subdistal appendages in ciliary function is unclear. Here, we identify CEP128 as a centriole subdistal appendage protein required for regulating ciliary signaling. Loss of CEP128 did not grossly affect centrosomal or ciliary structure but caused impaired transforming growth factor-β/bone morphogenetic protein (TGF-β/BMP) signaling in zebrafish and at the primary cilium in cultured mammalian cells. This phenotype is likely the result of defective vesicle trafficking at the cilium as ciliary localization of RAB11 was impaired upon loss of CEP128, and quantitative phosphoproteomics revealed that CEP128 loss affects TGF-β1-induced phosphorylation of multiple proteins that regulate cilium-associated vesicle trafficking.

Cep128 associates with Odf2 to form the subdistal appendage of the centriole

“…In this study, we first carried out a database analysis to identify candidates for centriolar appendage components and independently found that Cep128 is localized to the SDA, in accordance with another report (Mazo et al, ; Mönnich et al, ). We then analyzed the topological relationship of fluorescently labeled protein components of SDAs by super‐resolution structured illumination microscopy (SR‐SIM).…”

Primary Cilia as Signaling Hubs in Health and Disease

“…[17] Mass spectrometry successfully revealed novel functions of proteins of primary cilia in regulating TGFβ/bone morphogenic protein signaling [23] and FGF signaling. For example, transcriptome analysis uncovered that TGFβ signaling that is activated at the ciliary pocket, the proximal part of the primary cilium residing in the cytoplasm within an invagination of the plasma membrane, is associated with differentiation into cardiomyocytes.…”

Regulation of ciliary membrane protein trafficking and signalling by kinesin motor proteins

“…Indeed, recent work showed that CEP128 localizes to the SDA of the basal body to control ciliary recruitment of RAB11, and CEP128 loss leads to impaired TGF‐β/BMP signalling at the cilium in mammalian cells and in zebrafish embryos. Consequently, Cep128 morphants displayed defective organ development and other phenotypes indicative of compromised TGF‐β/BMP signalling . Furthermore, TGF‐βRI/II were shown to be targeted to the primary cilium by ARL6 to stimulate SMO in Hedgehog signalling, which is overactivated in metastatic cancer cells due to defects in ceramide‐mediated interaction between TGF‐βRI and SMAD7 that under normal conditions limits ciliary receptor localization .…”

“…). Accumulating evidence has implicated primary cilia, which are nonmotile versions of the organelle found in a single copy on most cell types in our body, in regulation of multiple cellular signalling pathways during development and in the adult, including Hedgehog and G‐protein‐coupled receptor (GPCR) signalling , as well as WNT and planar cell polarity (PCP) , receptor tyrosine kinase (RTK) , Notch , TGF‐β/BMP , Hippo , mTOR and polycystin signalling . The ability of primary cilia to regulate signalling relies on carefully orchestrated trafficking of membrane receptors and other signal transducers into and out of the organelle, both constitutively and in response to specific cellular and environmental stimuli.…”

“…Reproduced from Ref. with permission. (D) Deconvoluted immunofluorescence microscopy image of a ciliated hTERT ‐immortalized human retinal pigment epithelial cell ( hTERT ‐ RPE 1) stained with antibodies against TF marker CEP 164 (magenta) and cilium marker acetylated α‐tubulin (Ac‐tub; red).…”