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Event: 2044

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Decrease, Smoothend relocation and activation

Short name

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Decrease, SMO relocation

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Biological Context

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Level of Biological Organization
Cellular

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place. For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable. For individual/population events, the organ context is not applicable. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Cell term
cell

Organ term

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor). Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Process	Object	Action
protein localization to cilium	smoothened	decreased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help

AOP Name	Role of event in AOP	Point of Contact	Author Status	OECD Status
Antagonism SMO leads to OFC	KeyEvent	Jacob Reynolds (send email)	Under development: Not open for comment. Do not cite	Under Development

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help

Term	Scientific Term	Evidence	Link
Vertebrates	Vertebrates		NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help

Life stage	Evidence
Embryo

Sex Applicability

An indication of the the relevant sex for this KE. More help

Term	Evidence
Unspecific

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

The Smoothened (SMO) receptor is Class F G protein coupled receptor involved in signal transduction of the Sonic Hedgehog (SHH) pathway. It includes distinct functional groups including ligand binding pockets, cysteine rich domain (CRD), transmembrane helix (TM), extracellular loop (ECL), intracellular loop (ICL), and a carboxyl-terminal tail (C-term tail) (Arensdorf, Marada et al. 2016). SMO signaling is dependent upon its relocation to a subcellular location. This relocation occurs in the primary cilium (PC) in vertebrates (Huangfu and Anderson 2005). Relocation of SMO to the PC typically occurs within ~20 minutes of agonist stimulation (Arensdorf, Marada et al. 2016).

In the absence of SHH ligand, the Patched (PTCH) receptor suppresses the activation of SMO. When HH ligand binds to PTCH, suppression on SMO is released and SMO can relocate, accumulate, and signal to intracellular effectors (Denef, Neubüser et al. 2000, Rohatgi and Scott 2007). It has been shown that SMO localization to the tip of the primary cilia is essential for the SHH signaling cascade in vertebrates (Corbit, Aanstad et al. 2005, Rohatgi, Milenkovic et al. 2007, Rohatgi, Milenkovic et al. 2009). This relocation then leads to signaling to effectors resulting in the activation of the GLI transcription factors and the subsequent induction of HH target gene expression (Alexandre, Jacinto et al. 1996, Von Ohlen and Hooper 1997). The exact mechanism through which PTCH and SMO interact is not known.

While we know that entry to the cilia is tightly controlled, the exact mechanism of SMO ciliary trafficking is not fully understood. The PC is separated from the plasma membrane by the ciliary pockets and the transition zone which function together to regulate the movement of lipids and proteins in and out of the organelle (Goetz, Ocbina et al. 2009, Rohatgi and Snell 2010). The SHH receptor PTCH contains a ciliary localization sequence in its’ carboxy tail. Localization of PTCH to the PC is essential for inhibition of SMO as deletion of the CLS in PTCH prevents PTCH localization as well as inhibition of SMO (Kim, Hsia et al. 2015) (53). SMO also contains a CLS, but only accumulates in the PC upon ligand binding (Corbit, Aanstad et al. 2005). The entry of SMO into the PC is thought to occur either laterally through the ciliary pockets or internally via recycling endosomes (Milenkovic, Scott et al. 2009). Once inside the PC, SMO can diffuse freely, however it will usually accumulate in specific locations depending upon its’ activation state. Inactive SMO will accumulate more at the base of the PC while active SMO will accumulate in the tip of the PC (Milenkovic, Weiss et al. 2015).

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

Fluorescent proteins can be used tag SMO, cilia and the plasma membrane to determine if SMO has relocated to the cilia (Filipova, Diaz Garcia et al. 2020).
Fluorescent binding assay can be used to verify if a compound binds to SMO (Chen, Taipale et al. 2002).
Cell lines can be engineered to express Myc-tagged SMO. This gives a user friendly readout of SMO activation. (Corbit, Aanstad et al. 2005).

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided). More help

Sex- SMO and cilia are present in both male and females and differences in gene expression has not been demonstrated.
Life stages- The Hedgehog pathway is a major pathway in embryonic development.
Taxonomic-SMO relocation to the tip of primary cilia occurs in vertebrates Huangfu and Anderson 2005)

References

List of the literature that was cited for this KE description. More help

Alexandre, C., A. Jacinto and P. W. Ingham (1996). "Transcriptional activation of hedgehog target genes in Drosophila is mediated directly by the cubitus interruptus protein, a member of the GLI family of zinc finger DNA-binding proteins." Genes Dev 10(16): 2003-2013.

Arensdorf, A. M., S. Marada and S. K. Ogden (2016). "Smoothened Regulation: A Tale of Two Signals." Trends Pharmacol Sci 37(1): 62-72.

Chen, J. K., J. Taipale, M. K. Cooper and P. A. Beachy (2002). "Inhibition of Hedgehog signaling by direct binding of cyclopamine to Smoothened." Genes Dev 16(21): 2743-2748.

Corbit, K. C., P. Aanstad, V. Singla, A. R. Norman, D. Y. R. Stainier and J. F. Reiter (2005). "Vertebrate Smoothened functions at the primary cilium." Nature 437(7061): 1018-1021.

Denef, N., D. Neubüser, L. Perez and S. M. Cohen (2000). "Hedgehog induces opposite changes in turnover and subcellular localization of patched and smoothened." Cell 102(4): 521-531.

Filipova, A., D. Diaz Garcia, J. Dvorak, S. Filip, M. Jelicova and Z. Sinkorova (2020). "Simple Detection of Primary Cilia by Immunofluorescence." J Vis Exp(159).

Goetz, S. C., P. J. Ocbina and K. V. Anderson (2009). "The primary cilium as a Hedgehog signal transduction machine." Methods Cell Biol 94: 199-222.

Huangfu, D. and K. V. Anderson (2005). "Cilia and Hedgehog responsiveness in the mouse." Proc Natl Acad Sci U S A 102(32): 11325-11330.

Kim, J., E. Y. Hsia, A. Brigui, A. Plessis, P. A. Beachy and X. Zheng (2015). "The role of ciliary trafficking in Hedgehog receptor signaling." Sci Signal 8(379): ra55.

Milenkovic, L., M. P. Scott and R. Rohatgi (2009). "Lateral transport of Smoothened from the plasma membrane to the membrane of the cilium." J Cell Biol 187(3): 365-374.

Milenkovic, L., L. E. Weiss, J. Yoon, T. L. Roth, Y. S. Su, S. J. Sahl, M. P. Scott and W. E. Moerner (2015). "Single-molecule imaging of Hedgehog pathway protein Smoothened in primary cilia reveals binding events regulated by Patched1." Proc Natl Acad Sci U S A 112(27): 8320-8325.

Rohatgi, R., L. Milenkovic, R. B. Corcoran and M. P. Scott (2009). "Hedgehog signal transduction by Smoothened: pharmacologic evidence for a 2-step activation process." Proc Natl Acad Sci U S A 106(9): 3196-3201.

Rohatgi, R., L. Milenkovic and M. P. Scott (2007). "Patched1 regulates hedgehog signaling at the primary cilium." Science 317(5836): 372-376.

Rohatgi, R. and M. P. Scott (2007). "Patching the gaps in Hedgehog signalling." Nat Cell Biol 9(9): 1005-1009.

Rohatgi, R. and W. J. Snell (2010). "The ciliary membrane." Curr Opin Cell Biol 22(4): 541-546.

Von Ohlen, T. and J. E. Hooper (1997). "Hedgehog signaling regulates transcription through Gli/Ci binding sites in the wingless enhancer." Mech Dev 68(1-2): 149-156.