論文の公開元へInvolvements of Furry in YAP inactivation and 14-3-3 proteins in CEP97 degradation
概要
Cell-cell communication is critical for making multicellular organisms and maintaining their biological functions and homeostasis. Cell-cell communication is regulated by the signal transmission from signal-producing cells to signal-receiving cells. In response to extracellular signals, the signal-receiving cells change their states by intracellular signaling pathways. For example, growth factors interact their receptors present in cell surface and trigger the modulation of gene expression for cell proliferation; adhesion receptors transmit the mechanical and chemical signals from the neighboring cells and extracellular matrix. The complexity of cell-cell communication has been investigated for long decades, but further studies are required for elucidating the molecular mechanisms of cell-cell communication and intracellular signaling systems. In this thesis, I investigated the mechanisms of two signaling processes, the Hippo pathway and the growth-arrest-induced ciliogenesis”.
The organ size in multicellular organisms is well controlled by the balance of cell proliferation, apoptosis, stem cell self-renewal and differentiation. Intracellular and extracellular factors tightly regulate these processes, which are essential for normal embryonic development, organogenesis and tissue homeostasis. The aberrations of these regulation systems cause developmental disorder, tumorigenesis and several human diseases.
The Hippo pathway has been established as a signaling pathway that restricts cell proliferation and organ size. This pathway was firstly identified in Drosophila, and the components of this pathway are evolutionarily conserved from yeast to human. The core components of this pathway in mammalian cells are MST1/2 kinases, SAV, LATS1/2 kinases YAP and TAZ. When the cells sense the growth arrest signals, MST1/2 kinases bind to their adaptor protein SAV and phosphorylate and activate downstream kinases, NDR1/2 and LATS1/2. LATS1/2 kinases directly interact with and phosphorylate transcriptional co-activators, YAP and TAZ, to promote their cytoplasmic retention or degradation, resulting in the inhibition of their interactions with TEAD and TEAD-mediated transcriptional activation and thereby the suppression of cell proliferation. Whereas the crucial role of LATS1/2 kinases in YAP inactivation is well known, several studies have shown that LATS1/2 are occasionally dispensable for YAP phosphorylation and inactivation, suggesting that other protein kinase(s) is involved in YAP inactivation. A recent study demonstrated that NDR1/2 also phosphorylate and inactivate YAP. However, the mechanisms regulating YAP phosphorylation is not fully understood.
In chapter Ⅰ of this thesis, I provide evidence that FRY, a novel YAP-binding protein, is crucial for the regulation of YAP localization and phosphorylation. I also demonstrate that FRY promotes the cytoplasmic sequestration of YAP by two mechanisms, increasing the kinase activity of NDR1/2 and associating with YAP.
Primary cilia are antenna-like structures that protrude from the cell surface and are present in most vertebrate cell types. Numerous ion channels and receptors for various signaling are enriched in primary cilia. Primary cilia are essential for development, such as the formation of brain and limb. The defects in the formation and function of cilia result in serious developmental disorders, called ciliopathies.
Primary cilia consist of microtubule-based axoneme, transition-zone, and basal body derived from the mother centriole. Uponr the growth arrest signaling, primary cilia assemble through series of rapid and well-orchestrated events. CP110 and CEP97 proteins are the key negative-regulators for cilia formation. The CP110 and CEP97 complex normally forms a cap at the distal end of the centrioles to prevent microtubule growth in proliferating cells. Upon serum starvation, the CP110-CEP97 complex is specifically released from the mother centriole. A recent study in my laboratory showed that CEP97 is degraded upon serum starvation by the ubiquitin-proteasome system. This study identified the CUL3-RBX1-KCTD10 complex as the E3 ubiquitin ligase complex required for CEP97 ubiquitination and degradation in quiescent cells. However, the mechanism of CEP97 degradation upon serum starvation remains to be solved.
In chapter Ⅱ of this thesis, I analyzed the KCTD10-binding proteins that are involved in CEP97 ubiquitination during the cilium formation. I show that 14-3-3 proteins interact with KCTD10 and CEP97 and provide evidence that 14-3-3 proteins are involved in CEP97 ubiquitination and its removal from the mother centriole during ciliogenesis.
