Two Patched Protein Subtypes and a Conserved Domain of Group I Proteins That Regulates Turnover

Department of Biochemistry and Biophysics, University of California, San Francisco, California 94158, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 10/2008; 283(45):30964-9. DOI: 10.1074/jbc.M806242200
Source: PubMed


Patched (Ptc) is a 12-cross membrane protein that binds the secreted Hedgehog protein. Its regulation of the Hedgehog signaling
pathway is critical to normal development and to a number of human diseases. This report analyzes features of sequence similarity
and divergence in the Ptc protein family and identifies two subtypes distinguished by novel conserved domains. We used these
results to propose a rational basis for classification. We show that one of the conserved sequence regions in the C-terminal
domain of Ptch1 is responsible, at least in part, for rapid turnover. This sequence is absent in the stable Ptch2 protein.

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    • "The C-terminal tails of Drosophila Ptc and mouse Ptch1 play an important role in determining its membrane distribution and stability, possibly through the highly conserved 'PPXY' motif (Lu et al., 2006; Kawamura et al., 2008), which is recognized by the WW domain frequently found in HECT-domain E3 ligases (Metzger et al., 2012). Mammalian Ptch1 contains an evolutionarily conserved C-terminal 'PPXY' motif and a second one in the third intracellular loop (Figure 1—figure supplement 1), whereas Ptch2 does not and is quite stable (Kawamura et al., 2008). Under a confocal microscope and in transfected murine embryonic fibroblasts (MEFs), Ptch1-GFP was primarily detected in punctate vesicles (Figure 1A), consistent with what was reported in COS and HeLa cells (Incardona et al., 2000; Karpen et al., 2001); a large proportion of these Ptch1-GFP vesicles were likely to be endosomes (see below and in Martin et al., 2001; Incardona et al., 2002). "
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    ABSTRACT: Cell surface reception of Sonic hedgehog (Shh) must ensure that the graded morphogenic signal is interpreted accordingly in neighboring cells to specify tissue patterns during development. Here, we report endocytic sorting signals for the receptor Patched1 (Ptch1), comprising two 'PPXY' motifs, that direct it to degradation in lysosomes. These signals are recognized by two HECT-domain ubiquitin E3 ligases, Smurf1 and Smurf2, which are induced by Shh and become enriched in Caveolin-1 lipid rafts in association with Ptch1. Smurf-mediated endocytic turnover of Ptch1 is essential for its clearance from the primary cilium and pathway activation. Removal of both Smurfs completely abolishes the ability of Shh to sustain the proliferation of postnatal granule cell precursors in the cerebellum. These findings reveal a novel step in the Shh pathway activation as part of the Ptch1 negative feedback loop that precisely controls the signaling output in response to Shh gradient signal.
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    • "Mutation of the cleavage site (D1392N) acts as a dominant negative inhibitor for Ptc1-induced apoptosis. The CTD was suggested to also be a critical regulator of degradation and localization of Ptc1 (Chang et al., 2010; Kawamura et al., 2008; Lu et al., 2006). In addition, it was recently reported that Ptc1 undergoes proteolytic processing at the C-terminus and the soluble CTD translocates to the nucleus and mediates a new form of signal transduction (Kagawa et al., 2011). "
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    ABSTRACT: The notion of noncanonical hedgehog (Hh) signaling in mammals has started to receive support from numerous observations. By noncanonical, we refer to all those cellular and tissue responses to any of the Hh isoforms that are independent of transcriptional changes mediated by the Gli family of transcription factors. In this chapter, we discuss the most recent findings that suggest that Patched1 can regulate cell proliferation and apoptosis independently of Smoothened (Smo) and Gli and the reports that Smo modulates actin cytoskeleton-dependent processes such as fibroblast migration, endothelial cell tubulogenesis, axonal extension, and neurite formation by diverse mechanisms that exclude any involvement of Gli-dependent transcription. We also acknowledge the existence of less stronger evidence of noncanonical signaling in Drosophila.
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    ABSTRACT: Dispatched 1 (Disp1) encodes a twelve transmembrane domain protein that is required for long-range sonic hedgehog (Shh) signaling. Inhibition of Disp1 function, both by RNAi or dominant-negative constructs, prevents secretion and results in the accumulation of Shh in source cells. Measuring the Shh response in neuralized embryoid bodies (EBs) derived from embryonic stem (ES) cells, with or without Disp1 function, demonstrates an additional role for Disp1 in cells transporting Shh. Co-cultures with Shh-expressing cells revealed a significant reduction in the range of the contact-dependent Shh response in Disp1(-/-) neuralized EBs. These observations support a dual role for Disp1, not only in the secretion of Shh from the source cells, but also in the subsequent transport of Shh through tissue.
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