Loss of primary cilia is a key feature of von Hippel-Lindau tumor suppressor (VHL)-associated pathology. Although VHL-deficiency predisposes cells to precipitous cilia disassembly in response to growth factor cues, it does not affect ciliogenesis. Here, using a siRNA-based screen to find genes that are essential for ciliogenesis only in the presence of the VHL tumor suppressor gene product pVHL, we identify ubiquitin-specific protease (USP)8. The pVHLdependency of USP8 for ciliogenesis is directly linked to its function as a HIF1a deubiquitinating enzyme. By counteracting pVHL-mediated ubiquitination of HIF1a, USP8 maintains a basal expression of HIF1a and HIF transcriptional output in normoxia, including the repression of Rabaptin5, which is essential for endosome trafficking-mediated ciliogenesis.

The generation of novel genes and proteins throughout evolution has been proposed to occur as a result of whole genome and gene duplications, exon shuffling, and retrotransposition events. The analysis of such genes might thus shed light into the functional complexity associated with highly evolved species. One such case is represented by TBC1D3, a primatespecific gene, harboring a TBC domain. Because TBC domains encode Rab-specific GAP activities, TBC-containing proteins are predicted to play a major role in endocytosis and intracellular traffic. Here, we show that the TBC1D3 gene originated late in evolution, likely through a duplication of the RNTRE locus, and underwent gene amplification during primate speciation. Despite possessing a TBC domain, TBC1D3 is apparently devoid of Rab-GAP activity. However, TBC1D3 regulates the optimal rate of epidermal growth factor-mediated macropinocytosis by participating in a novel pathway involving ARF6 and RAB5. In addition, TBC1D3 binds and colocalize to GGA3, an ARF6-effector, in an ARF6-dependent manner, and synergize with it in promoting macropinocytosis, suggesting that the two proteins act together in this process. Accordingly, GGA3 siRNA-mediated ablation impaired TBC1D3-induced macropinocytosis. We thus uncover a novel signaling pathway that appeared after primate speciation. Within this pathway, a TBC1D3:GGA3 complex contributes to optimal propagation of signals, ultimately facilitating the macropinocytic process. INTRODUCTIONGene duplication, exon shuffling, and retrotransposition events played crucial roles during vertebrate evolution (Long, 2001;McLysaght et al., 2002;Brosius, 2003). About 5% of the human genome is composed of duplicated segments that emerged during the past 35 million years of primate evolution, resulting in the generation of novel protein functions (Courseaux and Nahon, 2001;Taylor and Raes, 2004).One of the cellular processes, whose regulation has became more and more complex and tightly regulated during evolution is endocytosis. Endocytosis serves to maintain cellular and organismal homeostasis by mediating the uptake of fluids, solutes, and signaling molecules and their receptors. Multiple mechanisms of endocytosis operate within a single cell (Conner and Schmid, 2003). Among them, two major categories are phagocytosis and pinocytosis, which mediate the uptake of particles or of fluid, respectively (Conner and Schmid, 2003).Pinocytosis encompasses a variety of different membraneentry routes and is invariably characterized by the relatively small size (50 -150 nm) of the internalized particles. Large volumes of fluid are, instead, engulfed by extension, folding, and closure of plasma membranes (PM) through a process termed macropinocytosis (Swanson and Watts, 1995). Macropinocytosis displays many similarities to phagocytosis; the biochemical and cellular components of these endocytic mechanisms have been best characterized in hematopoietic cells, in processes such as phagocytosis by macrophages in response to Fc receptor stimulation, or ma...

The evolutionarily conserved Hippo inhibitory pathway plays critical roles in tissue homeostasis and organ size control, while mutations affecting certain core components contribute to tumorigenesis. Here we demonstrate that proliferation of Hippo pathway mutant human tumor cells exhibiting high constitutive TEAD transcriptional activity was markedly inhibited by dominant negative TEAD4, which did not inhibit the growth of Hippo wild-type cells with low levels of regulatable TEAD-mediated transcription. The tankyrase inhibitor, XAV939, identified in a screen for inhibitors of TEAD transcriptional activity, phenocopied these effects independently of its other known functions by stabilizing angiomotin and sequestering YAP in the cytosol. We also identified one intrinsically XAV939 resistant Hippo mutant tumor line exhibiting lower and less durable angiomotin stabilization. Thus, angiomotin stabilization provides a new mechanism for targeting tumors with mutations in Hippo pathway core components as well as a biomarker for sensitivity to such therapy.

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Epithelial invagination is a central feature of embryonic morphogenesis in animals. Here, we show that RhoA mutant lens placode cells are both longer and less apically constricted than control cells, causing reduced epithelial curvature and reduced invagination. By contrast, Rac1 mutant lens placode cells are shorter and more apically restricted than controls, resulting in increased epithelial curvature and precocious closure of the lens vesicle. Quantification of RhoA and Rac1‐dependent pathway markers over the apical‐basal axis of lens pit cells showed that in RhoA mutant epithelial cells, there was a Rac1 pathway gain‐of‐function and vice versa. These findings suggest that mutual antagonism produces balanced activities of RhoA‐generated apical constriction and Rac1‐dependent cell elongation that controls cell shape and thus the curvature of invaginating epithelium. Previous studies have shown that contractile lens‐specific filopodia, under Cdc42 control, tether to the optic cup during lens placode invagination. Here, we examine the efficacy of lens filopodia in transmitting forces to co‐ordinate lens and retinal shape. Our observations suggest contractile and protrusive forces exerted by lens filopodia aid in shaping the underlying retina, and therefore bring us closer to understanding the important process of tissue co‐ordination for organ functionality.